KBS-3H Design, Production and Initial State of Buffer and Filling Components POSIVA January Posiva Oy

POSIVA 2016-06 KBS-3H Design, Production and Initial State of Buffer and Filling Components Posiva Oy January 2018 POSIVA OY Olkiluoto FI-27160 EURAJOKI, FINLAND Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.) Fax (02) 8372 3809 (nat.), (+358-2-) 8372 3809 (int.)

POSIVA 2016-06 KBS-3H Design, Production and Initial State of Buffer and Filling Components Posiva Oy January 2018 This work has been carried out under KBS-3H System Design project co-funded by Posiva and SKB. POSIVA OY Olkiluoto FI-27160 EURAJOKI, FINLAND Phone (02) 8372 31 (nat.), (+358-2-) 8372 31 (int.) Fax (02) 8372 3809 (nat.), (+358-2-) 8372 3809 (int.)

ISBN: 978-951-652-253-4 ISSN: 2343-4740

Posiva Oy Olkiluoto FI-27160 EURAJOKI, FINLAND Puh. 02-8372 (31) - Int. Tel. +358 2 8372 (31) Raportin tunnus - Report code POSIVA 2016-06 Julkaisuaika - Date January 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy Nimeke Title KBS-3H DESIGN, PRODUCTION AND INITIAL STATE OF BUFFER AND FILLING COMPONENTS Tiivistelmä Abstract This report is one in a set of KBS-3H specific Production reports, presenting how the KBS-3H repository is to be designed, produced and inspected. The set of reports will form the basis for the safety reports for the KBS-3H repository and repository facility. In the repository, the buffer is the component that surrounds the canister and fills the void spaces between the canister and the rock. The purpose of the buffer is to protect the canister from detrimental thermal, hydraulic, mechanical and chemical, including microbiological (THMC) processes that could compromise the safety function of complete containment, and further to maintain favourable conditions for the canister and slow down the transport of radionuclides in the event the canister is breached and starts to leak. In practice this means that the main component of the buffer material shall consist of natural swelling clays and further that the amounts of substances in the buffer that could adversely affect the canister, filling components or bedrock shall be limited. In order to fulfil the performance targets the saturated buffer density shall be 1,950-2,050 kg/m 3. The current buffer design consists of at least three main components: solid disk blocks and ring shaped blocks around the canister embedded in a supercontainer and distance blocks separating the supercontainers in the deposition drift. The reference material of the buffer and filling components is high-grade sodium bentonite with a montmorillonite content between 75-90%. The alternative material is a high-grade calcium bentonite, although any other swelling clay material may be considered in the future, if it meets the requirements set for the buffer. The production chain of the buffer and filling components starts with the excavation of materials, manufacturing and installation of the solid ring and disk blocks inside the supercontainer, and ends with the installation of supercontainer, distance and filling blocks and pellets in conjunction with plugs and subsequent inspection of the installed components. The buffer and filling component blocks are manufactured using the isostatic compression method and the pellets with the roller compaction method. The blocks are installed using the deposition machine. Quality control is a vital part of every phase of the manufacturing and installation. In the future, both the quality control system and the complete manufacturing and installation process will be further developed and tested before operational production begins. Alternative buffer materials will also still be studied. The description of the initial state includes a range of densities and other properties both for buffer components and the buffer as a whole. However, based on calculations it can be stated that the average saturated buffer density will be between the limits set for the saturated density of the buffer for almost all possible combinations of acceptable deposition drift dimensions and densities and geometries of buffer blocks, filling blocks and pellets used here. This statement is valid both for the deposition drift as a whole and for all cross sections along the deposition drift. Avainsanat - Keywords Clay, deposition, distance block, drift, final disposal, supercontainer ISBN ISSN ISBN 978-951-652-253-4 ISSN 2343-4740 Sivumäärä Number of pages Kieli Language 170 English

Posiva Oy Olkiluoto FI-27160 EURAJOKI, FINLAND Puh. 02-8372 (31) - Int. Tel. +358 2 8372 (31) Raportin tunnus - Report code POSIVA 2016-06 Julkaisuaika - Date January 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy Nimeke Title KBS-3H PUSKURIN JA TÄYTTÖKOMPONENTTIEN SUUNNITTELU, TUOTANTO JA ALKUTILA Tiivistelmä Abstract Käytetyn ydinpolttoaineen loppusijoitus perustuu KBS-3 menetelmään. Vaakaratkaisu KBS-3H ja pystyratkaisu KBS-3V edustavat KBS-3 menetelmän kahta vaihtoehtoista ratkaisua. KBS-3Hvaihtoehdossa kapselit sijoitetaan 100-300 m pitkiin ja loivasti yläkätisiin loppusijoitusreikiin. Loppusijoitussyvyys on 400-450 m. KBS-3V-ratkaisussa puolestaan kapselit loppusijoitetaan yksittäisiin pystyreikiin, jotka porataan loppusijoitustunnelin lattiatason alapuolelle. Molemmissa vaihtoehdoissa kapselietäisyydet keskipisteistä laskettuina ovat samat. Loppusijoituslaitoksen rakentamisen kannalta KBS-3H- ja KBS-3V-ratkaisut ovat hyvin samankaltaisia keskenään lukuun ottamatta loppusijoitustunneleita (3V) ja loppusijoitusreikiä (3H), joissa ilmenevät suurimmat eroavaisuudet. 3H-ratkaisussa loppusijoitustunnelia ei tarvita lainkaan, mikä heijastuu tarvittavassa täyttömateriaalin tilavuudessa. Ratkaisuvaihtoehtoihin liittyvät kapselien loppusijoitustekniikat poikkeavat myös suuresti toisistaan. Vaakaratkaisussa kapselit pakataan asennuspakkauksiin, jotka koostuvat itse kapselista ja sen ympärille asennettavasta puskuribentoniittikerroksesta sekä rei itetystä titaanivalmisteisesta suojasylinteristä. Pystyratkaisussa osa puskuribentoniitista lasketaan pystyreikään ennen kapselin asentamista, ja osa sen jälkeen. KBS-3H-puskuri ja -täyttökomponentit ovat puristettuja lohkoja ja pellettejä, jotka koostuvat bentoniitista, jonka smektiittipitoisuus on 75-90%. Puskurin ja täyttökomponenttien tuotantoketju koostuu raaka-aineen louhinnasta ja prosessoinnista, toimituserän hyväksymisprosessista ja toimittamisesta, raaka-aineen ja valmiiden komponenttien kuljetuksesta ja varastoinnista eri vaiheissa ja komponenttien valmistuksesta ja asentamisesta. Laadunvalvonta on osa ketjun jokaista vaihetta. Avainsanat - Keywords Asennuspakkaus, loppusijoitus, KBS-3H-menetelmä, sijoitusreikä, välitulppa ISBN ISSN ISBN 978-951-652-253-4 ISSN 2343-4740 Sivumäärä Number of pages Kieli Language 170 Englanti

1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ PREFACE... 5 1 INTRODUCTION... 7 1.1 General... 7 1.2 Purpose and objectives... 8 1.3 Structure and content of report... 9 1.4 Limitations... 11 1.5 Interfaces with other production line reports... 11 2 DESIGN BASIS... 13 2.1 Design basis related to the safety functions in the KBS-3 repository... 13 2.2 General of design basis... 13 2.3 Buffer... 13 2.3.1 Performance targets for the buffer... 14 2.3.2 Design requirements for the buffer... 16 2.3.3 Design specifications for the buffer... 17 2.4 Filling blocks... 25 2.4.1 Performance targets for the filling blocks... 27 2.4.2 Design requirements for the filling blocks... 28 2.4.3 Design specifications for the filling blocks... 30 2.5 Transition zones for compartment plugs... 31 2.5.1 Performance targets for the transition zones for compartment plugs.. 31 2.5.2 Design requirements for the transition zones for compartment plugs... 32 2.5.3 Design specifications for the transition zones for compartment plugs... 33 2.6 Transition zones for drift plugs... 34 2.6.1 Performance targets for the transition zones for drift plugs... 34 2.6.2 Design requirements for the transition zones for drift plugs... 35 2.6.3 Design specification for the transition zones for drift plugs... 36 2.7 Boundary conditions... 36 3 DESIGN OF BUFFER AND FILLING COMPONENTS... 39 3.1 KBS-3H general design... 39 3.1.1 Preparations in a drift prior to installation of the components... 41 3.1.2 Plugs... 41 3.1.3 Wetting and air evacuation... 41 3.1.4 Pipe removal and sealing a compartment... 43 3.2 Differences between Posiva and SKB implementation... 43 3.3 Design of Buffer components... 43 3.3.1 General... 43 3.3.2 Buffer blocks in the supercontainer... 44 3.3.3 Distance blocks... 47 3.3.4 Verification analysis of the final buffer density... 49 3.3.5 The effect of gaps on the final buffer density... 50

2 3.3.6 Concluding remarks... 51 3.4 Design of filling components... 51 3.4.1 General... 51 3.4.2 Filling in position of inflows... 52 3.4.3 Filling components on the sealed side of the compartment and drift plugs and outside compartment plug... 56 3.4.4 Filling at drift end and pilot hole... 59 3.4.5 Filling of pilot hole... 60 3.4.6 Conclusions... 62 3.5 Buffer and filling component materials... 62 3.5.1 The reference material used for buffer and filling components... 62 4 CONFORMITY OF REFERENCE DESIGN WITH DESIGN BASIS... 69 4.1 Distance block... 69 4.2 Supercontainer... 70 4.3 Transition zone... 73 4.4 Innermost drift section... 75 4.5 Calculations using the @RISK code... 76 4.6 Thermal behaviour of bentonite buffer... 79 4.7 Maintaining swelling pressure, hydraulic conductivity and shear strength... 85 4.8 Design basis from other barriers, production and operation... 90 4.8.1 Deposition of canister... 90 4.8.2 Compactibility of the bentonite material... 90 4.8.3 Installation of buffer and filling components... 90 4.9 Summary of results and conclusions... 91 4.9.1 Material composition... 91 4.9.2 Initially installed mass and density at saturation... 91 4.9.3 Dimensions... 92 4.9.4 Thermal properties... 92 4.9.5 Maintaining swelling pressure, hydraulic conductivity and shear strength... 93 5 PRODUCTION OF THE BUFFER AND FILLING COMPONENTS... 95 5.1 Overview... 95 5.1.1 Requirements for the production of the buffer and filling components... 95 5.1.2 Production line for the buffer and filling material... 96 5.1.3 Reference methods for manufacturing and installation... 98 5.1.4 Reference strategy and methods for test and inspection... 98 5.1.5 Design parameters and production inspection schemes... 98 5.3 Excavation and delivery... 105 5.2.1 Procurement of buffer and filling components material - purchase. 105 5.2.2 Excavation and pre-processing... 106 5.2.3 Shipment... 108 5.2.4 Material delivery and intermediate storage in the harbour... 108 5.2.5 Transport to storage at the production plant... 110 5.2.6 Methods for testing and inspection... 111 5.2.7 Experiences and results... 112 5.3 Manufacturing of blocks and pellets... 112 5.3.1 Conditioning of the bentonite... 112 5.3.2 Compression of blocks... 115 5.3.3 Machining of blocks... 117 5.3.4 Pressing of pellets... 118

3 5.3.5 Methods for testing and inspection... 119 5.4 Transport and storage of bentonite blocks and pellets... 120 5.4.1 Transport in the repository site and intermediate storage at ground level... 120 5.4.2 Transport to and storage at the repository level... 122 5.5 Handling and installation... 122 5.5.1 Installation of supercontainer, distance blocks and filling components... 122 5.5.2 Methods for testing and inspection of weight,... 124 6 INITIAL STATE OF THE BUFFER AND FILLING COMPONENTS... 127 6.1 Initial state and conformity to the reference design... 127 6.1.1 Initial state... 127 6.1.2 Material composition... 133 6.1.3 Blocks and pellets... 134 6.1.4 Installed buffer density... 135 6.1.5 Buffer geometry... 136 6.2 Conformity to design basis long-term safety at the initial state... 136 6.2.1 Material composition... 136 6.2.2 Installed density... 136 6.2.3 Buffer geometry... 137 6.2.4 Buffer thermal properties... 137 6.2.5 Maintaining swelling pressure, hydraulic conductivity and shear strength... 137 7 SUMMARY AND CONCLUSIONS... 139 8 REFERENCES... 143 APPENDIX 1: KEY DEFINITIONS AND ABBREVIATIONS... 149 APPENDIX 2: DIMENSIONING OF TRANSITION ZONE... 153 APPENDIX 3: PROPOSED QUANTITY OF TESTS FOR THE BENTONITE RAW MATERIAL TO BE USED FOR BUFFER (MODIFIED FROM AHONEN ET AL. 2008)... 163 APPENDIX 4: METHODS FOR TESTING AND INSPECTION OF MATERIAL COMPOSITION... 165 APPENDIX 5: TEST METHODS TO ASSURE THE QUALITY OF BENTONITE (MODIFIED FROM AHONEN ET AL. 2008)... 169

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5 PREFACE The existing KBS-3V production line reports are largely applicable to KBS-3H production line reports. In order to provide a conform description this report follows the structure and uses common text from the corresponding SKB s and Posiva s KBS-3V production line reports. The KBS-3V production line reports (produced by Posiva and SKB, respectively) have formed the basis for the organizations respective licence applications. For the construction of the KBS-3H repository SKB and Posiva have defined a set of production lines: the spent nuclear fuel; the canister; the closure; the backfill; the buffer and filling components; the supercontainer; the plugs; and the underground openings. The latter four production lines are reported in separate KBS-3H specific Production reports. The former four are expected to deviate only slightly from their 3V counterparts and are incorporated in a Repository production report which also presents the common basis for the reports. This set of reports addresses primarily applicable design basis (according to the Posiva VAHA system), reference design, conformity of the reference design to the applicable design basis, production and the initial state, i.e. the results of the production. Comparison with the SKB design premises is provided in dedicated tables setting forth the differences between the two organizations and repository sites. In parallel with this process an overarching process is underway that is expected to harmonize the Posiva and SKB requirements. The work for this report has been ordered by Magnus Kronberg from SKB and has been supervised by Anders Winberg of Conterra AB who has also taken part in coordination, follow-up and preliminary review of the report as well as producing some of the information concerning the content. The work is based on to the similar KBS-3V Buffer Production Line 2012 report written by Markku Juvankoski (VTT). The report has been factually reviewed by Jukka-Pekka Salo of Posiva Oy and Lennart Börgesson of Clay Technology AB. The KBS-3H design has been developed jointly by SKB and Posiva since 2002. This report has been prepared within the project phase KBS-3H - System Design 2011-2016.

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7 1 INTRODUCTION 1.1 General This report describes the design, production and initial state of the buffer and filling components of the KBS-3H disposal system. KBS-3H is an alternative design of KBS-3 methdod, the reference design being KBS-3V. The description is focused on the engineered barriers, mainly the system consisting of buffer, filling components and plugs in the deposition drifts. The disposal canister, other underground openings and the closure are similar as in KBS-3V variant, and presented in other documentation. Posiva Oy's spent nuclear fuel disposal is based on the KBS-3 method and on the characteristics of the Olkiluoto site. The KBS-3H disposal system is composed of several subsystems: supercontainers, plugs, underground openings (disposal facility) and buffer and filling components (Figure 1-1). The spent nuclear fuel elements are disposed in copper-iron canisters, surrounded by bentonite buffer emplaced in a cylindrical perforated metallic shell, the assembly is named supercontainer. OL-1 and 2 type canisters are used as the reference in this document. Buffer in the form of distance blocks are placed between the supercontainers and those drift sections that are not suitable for emplacement of supercontainers are filled with filling components. After all canisters have been disposed in the horizontal KBS-3H disposal compartment, the deposition drift will be closed with a compartment plug. After all, supercontainers have been emplaced in the outer compartment, the drift is plugged with a drift plug. After all deposition drifts in a deposition panel have been plugged, the central tunnels and other openings in the panel will be backfilled and plugged, i.e. closed. The KBS-3 disposal system and its subsystems feature safety functions determined by taking into account the regulatory requirements, operational safety and efficiency, environmental aspects and quality assurance. From the safety functions, performance requirements for each subsystem have been defined. These form the design basis of each subsystem. The performance requirements and design requirements derived from them have been compiled in (Posiva 2016a). Figure 1-1. Overview of a typical KBS-3H deposition drift. The deposition drift and its main components. The deposition drift is excavated from the niche with a slight inclination upwards enabling drainage during installation (based on Posiva 2013a).

8 The production line reports describe the design, production and initial state of each subsystem of the disposal system including the underground openings and the engineered barriers, i.e. the supercontainer (disposal canister, supercontainer shell and associated buffer), the filling components adjacent to the supercontainer, and the plug of the deposition drifts. Backfill of the other openings (transport tunnels and main/central tunnels) is covered by the KBS-3V production line reports and are briefly described in the 3H Repository production report (Posiva 2016b). The design specifications of each subsystem and for the various phases of the production are presented in the respective production line report. The production line report addresses how the given subsystem has been designed to meet the design requirements. The production of the subsystem comprises the purchase and handling of raw materials, the manufacturing of the subsystem components, the transportation and storage of the components prior to the installation, the installation and the quality assurance measures throughout the production process. As a final outcome of the design and production, the initial state of the emplaced subsystem is described. The initial state of each subsystem serves as input information for the performance assessment of the subsystem and for the safety assessment of the whole disposal system. The design of the subsystem and the associated production phases, that are performed in the disposal facility or at the disposal site act as input information for facility design. The Production line reports provide information on how to produce, handle and inspect the engineered barriers and underground openings within the facilities of the KBS-3H system, c.f. Figures 1-2 and 1-3. The 3V Canister production reports (SKB 2010c and Raiko et al. 2012) and the Spent fuel reports (SKB 2010a and Raiko et al. 2012) and Closure production reports (SKB 2010d and 2010e, Keto et al. 2012 and Sievänen et al. 2012) are judged to be basically the same for KBS-3H as for KBS-3V and hence adapted reports are not produced for KBS-3H. The KBS-3H design has been developed jointly by SKB and Posiva since 2002. This report has been prepared within the project phase KBS-3H - System Design 2011-2016. 1.2 Purpose and objectives The purpose of this report is to present performance targets, design requirements and specifications, design, the whole production chain, quality control and quality assurance measures in each step of production, initial state and fulfillment of requirements. The performance targets and design requirements have been derived from design basis presented in (Posiva 2016a). The objectives of the report are to: - Describe design basis (performance targets, design requirements and specifications) used as basis of the buffer and filling component design. - Present the design of the filling components. - Persent the design of the drift system and buffer components.

9 - Describe the whole buffer and filling component production chain, together with quality assurance and quality control measures in each step of the operation. - Describe the initial state of the filling components and buffer right after its installation. The description of the initial state includes variations in the properties and the information is used to evaluate the fulfillment of the design requirements and specifications in the initial state. 1.3 Structure and content of report This report is one component of the documentation shown in Figure 1-2 and is part of the large entity of work shown in Figure 1-3. The report summarises the design basis, reference design, manufacturing and assembly of the filling components and buffer in the deposition drift. Operation of the deposition drift, supercontainer and plugs are handled in other production line reports. As a summary of the design and implementation, the initial state of the filling components and plug are determined as well as conformity to the design basis. The design basis regarding performance targets and design requirements presented in this report are described and rationalised in the design basis report (Posiva 2016a). The performance targets, design requirements and design specifications are presented in this report. The acquisition of buffer and filling component raw materials, principles of quality assurance and control as well as handling and storage of the raw materials are described in this report. Figure 1-2. Reports included in the set of reports describing how the KBS-3H repository is designed, produced, tested and inspected. The dashlined Spent fuel, Canister and Closure Production reports are essentially the same for KBS-3H and for KBS-3V and hence adapted reports are not produced for KBS-3H (SKB and Posiva Oy have produced their respective KBS-3V reports).

10 Figure 1-3. Overview of the activities related to technical barriers and underground openings (Figure from Posiva 2016e). The scope of this this report covers the following topics: - General background and introduction, c.f. Chapter 1 - Design basis and requirements, c.f. Chapter 2 - Design of buffer and filling components, c.f. Chapter 3 - Conformity of reference design with design basis, c.f. Chapter 5 - Production of buffer and filling components, c.f. Chapter 5, including: - Manufacturing of buffer blocks and rings (for the supercontainer), c.f. Section 5.3 - Manufacturing of distance blocks, c.f. Section 5.3 - Manufacturing of filling components, c.f. Section 5.3 - The delivery chain for the material for filling components and buffer blocks is described in Section 5.2. - Storage and transportation of buffer and filling components, c.f. Section 5.4 - Equipment for emplacement involves the deposition maschine described in (Posiva 2016d). - Set-up of equipment, c.f. Section 5.5 - Initial state of the buffer and filling components, c.f. Chapter 6

11 1.4 Limitations The requirements that are described in this report are mainly limited to the system and design requirements established for long-term safety. Operational requirements presented in this report are preliminary. The report describes the design and implementation in the way it is planned today. The design and various phases of implementation are still under development and they may change prior to the application for an operation licence. The future plans and planned development and testing work will be described in Posiva (2015). 1.5 Interfaces with other production line reports This report has been compiled using the relevant information from the KBS-3V Backfill production line reports (SKB 2010d and Keto et al. 2013) and other construction, supercontainer and plug related KBS-3H production line reports (Posiva 2016d, Posiva 2016e and Posiva 2016f).

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13 2 DESIGN BASIS 2.1 Design basis related to the safety functions in the KBS-3 repository The KBS-3H design basis has been presented in detail in Posiva (2016a). General features of the design basis, more comprehensive information of Posiva Oy s requirements management system VAHA, and Laws and Decrees regulating the long-term safety of disposal can be found on the Posiva (2016b) and the details are given in Posiva (2016a). 2.2 General of design basis Posiva (2016a) covers all requirements presented for Posiva Oy s requirements management system VAHA, modified for KBS-3H. The evaluation of whether these requirements for the barriers have been fulfilled is the goal of KBS-3H Safety Evaluation (Posiva 2016c), the latter which assumes that the components of the system have been manufactured and installed as designed, i.e. the KBS-3H system meets its design requirements. The requirements at the highest levels in VAHA are of a general nature and the requirements become more detailed at the subsystem and design requirement levels (Levels 3 and 4). The structuring in the current report follows the same principles. The VAHA requirements are presented in italics, and then the rationale for each requirement is provided. The subsystem requirements (Level 3) and the design requirements (Level 4) are discussed in the subsequent sections with the aim of giving justification for the requirements based on the extensive research which has been conducted during the development of the KBS-3 method, and for the KBS-3H design variant in particular. The fulfilment of these requirements during the assessment period will be discussed in Posiva (2016c). 2.3 Buffer The safety functions of the buffer are to contribute to mechanical, geochemical and hydrogeological conditions that are predictable and favourable to the canister, and to protect canisters from external processes that could compromise the safety function of complete containment of the spent nuclear fuel and associated radionuclides, and to limit and retard radionuclide releases in the event of canister failure. The buffer in the KBS- 3H distance blocks has the further safety function of hydraulically and thermally separate the supercontainers from each other. The general structure of the buffer requirements is presented in Figure 2-1. The requirements can be divided into two categories: requirements related to the performance of the buffer, and requirements related to support to other disposal system components. The performance requirements can be further divided into requirements related to chemical protection, mechanical protection, limitation of mass flows in the near field, and heat transfer, which is needed for EBS compatibility.

14 VAHA Level 3 VAHA Level 4 Figure 2-1. General structure of the buffer requirements (Posiva 2016a). 2.3.1 Performance targets for the buffer The performance targets (VAHA Level 3) are given in the KBS-3H Design Basis report (Posiva 2016a). Definition Buffer is the component that: Surrounds the canister and fills the void spaces between the canister and the supercontainer shell, and later fills any void spaces between the canister and the drift wall, It is also installed as distance blocks on either side of each supercontainer. - The purpose of the buffer is to protect the canister from detrimental thermal, hydraulic, mechanical and chemical, including microbiological (THMC) processes that could compromise the safety function of complete containment, to maintain favourable conditions for the canister and to slow down the transport of radionuclides if the canister starts leaking (L3-BUF-2H).

15 Performance Limitation of amounts of substances harmful to other components - The amount of substances in the buffer that could adversely affect the canister, filling components, compartment plugs and drift plugs or host rock shall be limited (L3-BUF-21H). Swelling capacity - The buffer shall have a sufficient swelling capacity (L3- BUF-31H). Preservation of required properties in repository conditions - The buffer shall fulfil the requirements listed below over hundreds of thousands of years in the expected repository conditions (L3-BUF-4H). Heat transfer - The buffer shall transfer the heat from the canister efficiently enough to keep the buffer temperature < 100 C (L3-BUF-6). Gas transfer - The buffer shall allow gases to pass through it without causing damage to the repository system (L3-BUF-19). Chemical protection - The buffer shall limit microbial activity (L3-BUF-8). Mitigation of rock shear impact on canister - The buffer shall mitigate the impact of rock shear on the canister (L3-BUF-10). Limitation of mass flows from and onto the canister and and - The buffer shall be impermeable enough to limit the transport of radionuclides from the canisters into the bedrock (L3-BUF-12). - The buffer shall be impermeable enough to limit the transport of corroding substances from the rock onto the canister surface (L3-BUF-13). - The buffer shall limit the transport of radiocolloids to the rock (L3-BUF-14).

16 Support to other system components Support to deposition drift - The buffer shall provide support to the deposition drift walls to mitigate potential effects of rock damage (L3-BUF-16H). Keeping the canister in position - The buffer shall prevent significant displacement of the canister, so that the canister remains in the correct position and orientation in the drift (L3-BUF- 17H). Hydraulic separation of supercontainers - The distance blocks shall limit the transport along the drift to be diffusion dominated, effectively separating the supercontainers hydraulically from each other and from any nearby filling components (L3-BUF-32H). 2.3.2 Design requirements for the buffer Definition - The main component of the buffer material shall consist of natural swelling clays (L4-BUF-2). Performance Self-sealing - The buffer shall be designed to be self-sealing after initial installation and selfhealing after any hydraulic and mechanical disturbances (L4-BUF-16). Chemical protection and - The buffer shall be so designed that the possibility of corrosion of a canister by sulphide and other corrodants, including microbially-induced processes, will be limited (L4-BUF-5). - The buffer material shall be selected so as to limit the contents of harmful substances (organics, oxidising compounds, sulphur and nitrogen compounds) and microbial activity (L4-BUF-19). Mechanical protection - The buffer shall be so designed that it will mitigate the mechanical impact of the postulated rock shear displacements on the canister to the level that the canister integrity is preserved (L4-BUF-7).

17 Limitation of mass fluxes to and from canister and and - The buffer shall be designed in such a way as to make diffusion the dominant transport mechanism for solutes (L4-BUF-9). - The buffer material must be selected in a way that favours the retardation of the transport of radionuclides by sorption (e.g. cation exchange) at the clay and other mineral surfaces (L4-BUF-10). - The buffer shall have sufficiently fine pore structure so that transport of radiocolloids formed within or around the canister is limited (L4-BUF-18). Heat transfer - The gap between the canister and buffer and between the supercontainer shell and rock shall be made as narrow as possible without compromising the future performance of the buffer (L4-BUF-21H). Support to other system components Contact between buffer and host rock - The buffer shall provide a contact with the host rock after artificial wetting (L4- BUF-12H). Limitation of buffer axial movement - The buffer components shall be designed so that they will not move axially in the deposition drift in a way that impairs long-term safety (L4-BUF-31H). Limitation of temperature - The distance blocks shall be long enough to limit the temperatures to an acceptable level (L4-BUF-32H). 2.3.3 Design specifications for the buffer The Design specifications for the buffer are presented in Table 2-1 and discussed below. Definitions - L5-BUF-2 The buffer material is MX-80 type bentonite, containing mainly mineral Montmorillonite. The selection of MX-80 type bentonite is based on its good swelling properties and low hydraulic conductivity at the design density and at the prevailing and expected site conditions (see Section 4.7). Also the alternative material Ibeco RWC has these good

18 properties (see Section 4.7), although the swelling pressure and shear strength is higher for Ibeco RWC. Both materials also have a low content of impurities (SKB 2009, p. 20). - L5-BUF-3H The thickness of bentonite buffer between the cylindrical surface of supercontainer and canister shall be 341 mm before wetting. - L5-BUF-5H The thickness of bentonite buffer between the end plates of canister and the supercontainer shall be 350 mm after saturation. The thickness of buffer material along the canister shall be thick enough to protect the canisters from rock movements. It shall also be thick enough to provide for retention and retardation of radionuclides. However, it shall be so thin that it facilitates the transfer of heat from the canister so that maximum temperature limits are not exceeded. (SKB 2000, p. 113). Table 2-1. VAHA Level 5 design specifications for KBS-3H - Bufferuffer (largelybased on Juvankoski et al. (2012), c.f. Appendix 1 therein). ID Design specifications - Buffer Reference L5-BUF-1 1 Definitions L5-BUF-2 The buffer material is MX-80 type bentonite, containing mainly mineral Montmorillonite. L5-BUF-3H The thickness of bentonite buffer between the cylindrical surface of supercontainer and canister shall be 341 mm before wetting. L5-BUF-5H The thickness of bentonite buffer between the end plates of canister and the supercontainer shall be 350 mm after saturation. L5-BUF-6 2 Material specifications L5-BUF-7 The montmorillonite content of the dry buffer material shall be 75-90% by weight L5-BUF-8H The water content of the buffer material shall be at least 11 wt% in the buffer inside the supercontainer and at least 15 wt% in the distance blocks Anttila et al. (2008) Posiva (2013) Posiva (2013) Posiva (2013) Posiva (2012b) Table 4-1; Börgesson et al (2016). Posiva (2013) L5-BUF-9H The target density of buffer at saturation shall be 2,000 kg/m 3 with tolerances defined. L5-BUF-10 The total sulphur content shall be less than 1 wt%, with sulphides Posiva (2013) making, at most, half of this. L5-BUF-11 The organics content in the bentonite shall be lower than 1 wt% Posiva (2013) L5-BUF-12 L5-BUF-20H L5-BUF-21H 3 Support of other system components The thickness of saturated bentonite between supercontainers is as specified below depending on the canister type: - LO1 2: 3,013 mm - OL1 2: 3,613 mm - OL3 4: 4,741 mm. The thickness of saturated bentonite adjacent to first and last supercontainer in the compartment is as specified in L5-BUF-20H. Kirkkomäki and Rönnqvist (2011) Posiva (2013) In SKB (2006a, p. 22) it is stated that an increased buffer thickness will reduce the damage on the canister due to rock shear, but given the high shear stiffness of highly compacted bentonite, the effect is marginal. An increased buffer thickness will also increase the

19 overall buffer mass, which would make the buffer more resistant to alteration and massloss processes (i.e. a smaller fraction of the total mass will be altered or lost). Still, it is not an unambiguous advantage since an increased thickness also would decrease the heat transfer capacity. An increased diameter would also increase the diffusional distance between the canister and the rock. Furthermore, in SKB (2006b, p. 22) it is stated based on the results from SR-Can that a thicker buffer would only improve the situation marginally in colloid formation/erosion cases of glacial melt water. The time required to create advective conditions in the buffer would increase with the increased buffer mass loss required to create such conditions, but this time is overshadowed by the considerably longer time required to corrode the canister to the extent that a failure occurs. It is thus concluded in SKB (2006b and in SKB 2011, p. 808) that an increased buffer thickness would not improve the situation markedly. The tolerances for the buffer thickness around the canister are selected based on calculations that the allowed saturated density interval is achieved in almost all deposition holes (Juvankoski 2013). It is also taken into account that the swelling pressure remains in practice in the interval of 2-15 MPa (Juvankoski 2013) while the montmorillonite content of the bentonite remains in the specified range. The technical plans will be further revised and optimised taking into account the latest advances made in technology and research. Material specifications - L5-BUF-7 The montmorillonite content of the dry buffer material shall be 75-90% by weight. One of the most important properties of bentonite to be used as a buffer material is its swelling ability. The swelling ability is strongly dependent on the montmorillonite content of the bentonite. Karnland (2010, p. 25) has used the montmorillonite content and the water content at full saturation in his swelling pressure studies and in developing the equations for swelling pressure. The limits set for the bentonite montmorillonite content (Juvankoski 2013) are mainly based on the fact that the swelling pressure of the buffer is limited to the level used in dimensioning of the canister (15 MPa; Raiko 2012). Karnland s equations (Equations 5-9 through 5-13, Karnland 2010, p. 26) are used in defining these limits. The buffer density interval stated later is based on a montmorillonite content of 75-90% for the dry material. The specified densities are not valid outside this range. High grade commercial bentonite normally contains more than 75% montmorillonite by weight for the dry material. (Karnland et al. 2009) Since the bentonite buffer is a natural material, a mineralogical variation with respect to accessory minerals must be accepted (see Table 3-14 in Section 3.5.1). None of the present accessory minerals in the bentonites studied in SR-Can have any identified importance for the function, as long as the montmorillonite content is above 75% as stated above (Karnland et al. 2009). No quantitative criteria for other accessory minerals than

20 sulphide, total sulphur and organic carbon in the bentonite are defined in SR-Site too (SKB 2011, p. 185). - L5-BUF-8H : The water content of the buffer material shall be at least 11 wt% in the buffer inside the supercontainer and at least 15 wt% in the distance blocks 15 wt.-%. The selection of the minimum water content is based on the desired thermal conductivity of bentonite and density, which both affect the thermal conductivity. In thermal dimensioning of the repository the thermal conductivity used for the bentonite buffer is 1.0 W/m/K (Ikonen 2009 and Ikonen and Raiko 2012, Table 1 and Table 3). This in line with other results, since according to Equation 2 in Kahr and Müller-von Moos (1982) (also presented as Equation 2-1 in Börgesson et al. (1994) and Eqn. 4-1 in Pusch (2003), respectively). (NB. the sign of the first terms of the two latter referenced equations should be corrected to being negative, as originally formulated by Kahr and Müller-von Moos (1982)). This in line with other results, since according to Equation 2 in Kahr and Müllervon Moos (1982) the thermal conductivity of a bentonite block with a water content of 15 % and a nominal block bulk density is 1.05 W/m/K. For drier buffer material, the thermal conductivity will be less and the canister temperatures higher. According to Table 5-16 in Åkesson et al. (2010a, p. 148) the thermal conductivity of the block is higher, about 1.17-1.25 W/m/K for disk blocks and for ring shaped blocks if the water content would be 15 %. The chosen water content for the blocks and pellets is now 17 % based on the behaviour in moist air (see Sections 5.3 and 11.2.1 in Juvankoski 2013). Lower 11% water content is required in the buffer blocks inside the supercontainer to enable manufacturing of these high density blocks. High density blocks tend to crack more easily, however, inside supercontainer this is acceptable because the blocks are supported by the supercontainer shell which provides sufficient structural integrity in situations where the low water content may result cracking. - L5-BUF-9H : The target density of buffer at saturation shall be 2000 kg/m 3 with tolerances defined in (Posiva 2013). In Crawford and Wilmot (1998, p. 69) it is stated that the desired swelling capacity and low hydraulic conductivity of the bentonite buffer will be obtained in the brackish and saline groundwaters at Hästholmen and Olkiluoto by ensuring that the density of the compacted bentonite is sufficiently high, around 2,000 kg/m 3 at saturation. In Chapter 4 in this report it has been shown that the already former used tolerances for the saturated density of the buffer, ±50 kg/m 3, are valid and that the saturated density of the buffer are almost in all situations between 1,950 and 2,050 kg/m 3. In the reference design, the upper limit may be exceeded locally if the maximum allowable densities of blocks coincide with the minimum gap width. Several factors assume minimum densities for the buffer. These are for example: - Preventing significant advective transport in the buffer - Preventing colloid-facilitated radionuclide transport - Preventing canister displacemnent

21 - Ensuring tightness and self-sealing and - Preventing significant microbial activity. The maximum density for the buffer is defined by the need to ensure protection of the canister against rock shear (see Section 8.2 in Juvankoski 2013). - The buffer shall limit microbial activity (L3-BUF-8). It is the last point in the previous list that sets the largest requirement to the minimum saturated density for the buffer. Bacteria are not expected to be able to thrive in the specified high density of the buffer. Microbial activity decreases with increasing density. However, it is difficult to formulate a strict criterion on buffer density. The demanded saturated density limit stated in literature varies and is in the level of 1,800 and 1,900 kg/m 3. The first figure is stated in the SR-Can safety assessment; the clay density limit for microbial sulphide production was set at 1,800 kg/m 3 (SKB 2006a, p. 16; SKB 2011, p. 824). The second figure is based on the swelling pressure according to which the sulphate-reducing bacteria cannot survive in bentonite if the bentonite is compacted to a density corresponding to a swelling pressure of 2 MPa (SKB 2006a, p. 186; SKB 2009, p. 21). With an additional margin to account for losses due to piping and erosion, this leads to the requirement that the saturated density must exceed 1,950 kg/m 3. The swelling pressure is always over 2 MPa in all of the calculation sets at up to 70 g/l NaCl groundwater concentrations presented in Juvankoski (2013), if this 1,950 kg/m 3 is regarded as the lower density limit. In SKB (2011, p. 255) it is stated that to prevent additional microbes from intruding, a buffer density much less than the reference density (between 1,950 and 2,050 kg/m 3 ) is sufficient. - The buffer shall be impermeable enough to limit the transport of radionuclides from the canisters into the bedrock (L3-BUF-12). - The buffer shall be impermeable enough to limit the transport of corroding substance from the rock onto the canister surface (L3-BUF-13). - The buffer shall limit the transport of radiocolloids to the rock (L3-BUF-14). - The buffer shall be designed in such a way as to make diffusion the dominant transport mechanism for solutes (L4-BUF-9). These first three requirements are related to similar processes and arise from the safety functions of the buffer, which are to contribute to mechanical, geochemical and hydrogeological conditions that are predictable and favourable to the canister, and to protect canisters from processes that could compromise the safety function of complete containment of the spent nuclear fuel and associated radionuclides; and to limit and retard radionuclide releases in the event of canister failure (Posiva 2016a). If the buffer has sufficiently low permeability, transport of corrosive agents and radionuclides will take place mainly by aqueous diffusion, which is a slow process. The diffusive transport of fuel colloids through highly compacted bentonite is assumed to be negligible, due to the tortuosity and small size of the bentonite pores. Experiments

22 with 1 nm gold colloids show that the microstructure of a bentonite with a dry density of 1,000 kg/m 3 effectively filters gold colloids. This corresponds to a saturated clay density of about 1,640 kg/m 3. Even at these densities, colloids will diffuse through the bentonite, but the transport capacity is limited. The judgement is that the colloid transport in the buffer can be neglected if the density at saturation exceeds 1,650 kg/m 3 (SKB 2009, p 21). The performance target addressing the flow conditions is fulfilled when the hydraulic conductivity is less than 10-12 m/s. If the buffer density falls within the target range given in (Juvankoski 2013), then the performance target on hydraulic conductivity is also expected to be upheld given the expected evolution of groundwater salinity at repository depth and assuming no cracking of the buffer, due, for example, to mineralogical alteration or freezing. Hydraulic conductivities between 10-13 and 10-14 m/s have been measured in saturated bentonite in saline conditions at dry densities above about 1,450 kg/m 3 (see Figure 2-3, p. 48 of SKB 2006b) or saturated density above about 1,900 kg/m 3 (Figure 4-22), which show hydraulic conductivities as a function of densities for bentonite exposed to NaCl solutions ranging from 0.0 M to 3.0 M (or 0 to 180 g/l). Under these conditions, mass transport is clearly diffusion-dominated. In the Performance Assessment report (Posiva 2016c), it is stated that even if the dry density is 1,000-1,400 kg/m 3 the conditions are largely non-advective, but the risk of advective conditions increases when the dry density decreases towards 1,000 kg/m 3. - The buffer shall be designed to be self-sealing after initial installation and selfhealing after any hydraulic and mechanical disturbances (L4-BUF-16). After installation the buffer is self-sealing because of the swelling of bentonite. The selfhealing is however dependent of the amount of bentonite in the buffer. Buffer mass may be lost due to e.g. piping and erosion during the water saturation phase. The contact between the buffer and the host rock, and in the gap between the buffer and canister, are not initially tight along the length of the deposition drift due to spaces needed for installation. The swelling of the buffer during saturation shall be sufficient to self-seal the gaps to prevent preferential flow paths from forming (Posiva 2016a). Hydraulic disturbances, e.g. increased groundwater flow due to increased hydraulic gradients during the repository operating period or caused by an ice sheet, may also result in local mass loss (Miller and Marcos 2007). A hydraulic conductivity of 10 12 m/s and a swelling pressure of 1 MPa are regarded to be sufficient to rule out advection in the buffer. These values have some safety margins. The minimum swelling pressure needed to ensure that the self-sealing ability is maintained and no channels or pipes will be formed is presumed to be about 100 kpa. (SKB 2006a, p. 282). When the worst expected salinity conditions at Olkiluoto (TDS 70 g/l) are taken into account, this means a minimum dry density of about 1,200 kg/m 3 or a saturated density of 1,768 kg/m 3 (based on Karnland s equation (5-9) (Karnland 2010, p. 26) and parameters for MX-80Ca (Karnland 2010, p. 26) because calcium converted material has lower swelling pressure at lower densities; and equations (8) and (9) in Hedin (2004, p. 30). If the mass loss is not taken into account, the swelling pressure is always over 2 MPa (see Section 9.5.2 and 9.6 in Juvankoski 2013).

23 According to the Performance Assessment report (Posiva 2016c), it is estimated for swelling properties that the swelling pressure up to the order of several MPa is maintained when the dry density remains >1,500 kg/m 3. If the dry density of 1,500 kg/m 3 is set as a limit, it means that, on average, 91-95 kg of mass could be lost per 1 m 3 of buffer material. - The buffer shall provide support to the deposition drift walls to mitigate potential effects of rock damage. (L3-BUF-16H). A contact between the buffer and host rock is needed for several reasons: the deposition drift walls need support during the period of high temperature during the first decades after repository closure in order to mitigate the effects of rock spalling. Also, during the saturation phase and later if hydraulic conditions change during changes in isostatic pressure, groundwater flow may be enhanced and cause piping and erosion in the buffer, thus flow paths are formed (Posiva 2015). The host rock may start spalling when the temperature increases after the supercontainer has been placed in the deposition drift and the drift has been closed (Hakala et al. 2008), possibly forming flow paths along the deposition drift. If spalling occurs, the buffer s self-sealing and self-healing capability due to swelling should be able to mitigate the effects of spalling damage. The outer gap between host rock and both the supercontainer and distance block is not filled after emplacement. This does not give support at the beginning to the rock wall and prevents rock pieces from falling. When wetting takes place the support increases. A radial swelling pressure from tens to few hundred kpa can be achieved already in a month or two if there is enough water available based on results in Posiva (2013). According to the analysis of Hakala et al. (2008), an active bentonite swelling pressure of 1.0 MPa seems to effectively limit the depth of spalling and induced displacements. Also in-situ observations at the URL in Canada and at Äspö Hard Rock Laboratory in Sweden have shown that quite low confinement, of the order of 0.1-0.25 MPa, can mitigate stress failure (Hakala et al. 2008, p. 52). - The buffer shall prevent significant displacement of the canister, so that the canister remains in the correct position and orientation in the drift (L3-BUF- 17H). The buffer's main role is to reduce the potential negative interactions between the canister and the host rock including the groundwater. If the buffer density is too low, allowing it to deform under the weight of the canister and thus allowing the canister either to sink or to tilt, the buffer's safety functions would no longer be effective. There is also one requirement for the buffer that is fulfilled if the saturated density of the buffer is low enough: - The buffer shall mitigate the impact of rock shear on the canister (L3-BUF-10).

24 Rock shear movements are possible when the stresses in bedrock are released. The buffer acts as a damper between the host rock and canister, which reduces the effect of a rock shear substantially. However, at the high density the stiffness and the shear strength of the buffer are rather high. The stiffness is also a function of the rate of shear and the shear strength, increasing with increased shear rate, which means that there may be substantial damage on the canister at very high shear rates. (SKB 2006a, p. 323). The subsystem requirements for host rock state that the probability of a rock shear displacement larger than 5 cm shall be low (L3-ROC-23). It also states that the location of the deposition holes shall be selected so as to minimize the likelihood of rock shear movements large enough to break the canister. The system must be designed to withstand this load. The design of the buffer shall be such that it can mitigate the consequences for the canister. To perform this function, the swelling pressure of the buffer must be kept under a specific limit. The ability of the buffer to perform as a damper is based on the research done by SKB. SKB has worked with this issue over the past 30 years in characterising material behaviour, developing material models, and performing numerical modelling simulations (Read 2011, p. 60). In Read (2011), a review is given of relevant literature from SKB, covering laboratory testing of bentonite clay buffer material, scaled analogue tests, and the development of related material models to simulate rock shear effects. In this reference, a testing programme is also proposed for various new tests. According to SKB (2009, p. 15) the design basis (design premises) for the canister is: The copper corrosion barrier should remain intact after a 5 cm shear movement at a velocity of 1 m/s for buffer material properties of a 2,050 kg/m 3 calcium bentonite, for all locations and angles of the shearing fracture in the deposition hole, and for temperatures down to 0 C. The insert should maintain its pressurebearing properties to isostatic loads. This requirement can be expressed as the maximum buffer density. The condition set out for the canister withstanding shear load, requires that the saturated buffer density is less than 2,050 kg/m 3. (SKB 2009, p. 22; SKB 2011, p. 434). In summarising the points addressed above, it can be stated that the initially deposited buffer mass should be such that it corresponds to a saturated buffer density in the volume initially filled with buffer that is: - Higher than 1,950 kg/m 3, i.e. sufficiently high to ensure a swelling pressure of 2 MPa with margin for possible loss of material and - Less than 2,050 kg/m 3 to prevent too high shear impact on the canister. If the saturated density remains in this range, the long-term requirements, the most important of which are the hydraulic conductivity, the swelling pressure and the elasticity, are likely to be met in all parts of the buffer, also after the initial swelling and expansion in the buffer pore water composition, which evolves in response to transient changes in

25 the groundwater. This variation has been taken into account in establishing the target range for the density. - L5-BUF-10 The total sulphur content shall be less than 1 wt.-%, with sulphides making, at most, half of this. - L5-BUF-11 The organics content in the bentonite shall be lower than 1 wt.-%. From a safety assessment point of view, the content of harmful accessory minerals has to be sufficiently low. The buffer material should not contain canister corroding agents. Only sulphur (sulphate and sulphide) and organic carbon are considered possibly harmful in the present reference bentonites. Special criteria will therefore be used for these substances both with respect to accepted contents and to analysing methods. Similar treatment will be used in case of other potentially harmful substances in the bentonite. The content of organic carbon should be less than 1 wt.-%. The sulphide content should not exceed 0.5 wt.-% of the total mass, corresponding to approximately 1% of pyrite. Furthermore, there is also reason to put a limit on the sulphate content, since sulphate could be reduced to sulphide. A limit of 1 wt.-% of the total sulphur content should be applied (Karnland et al. 2009). The organic content of the bentonite may also contribute to canister corrosion, e.g., as energy sources for microbes. If microbial activity would be possible active microbes can produce gas if organic carbon is available for metabolism (SKB 2006a, p. 127). Support of other components and - L5-BUF-20H The thickness of saturated bentonite between supercontainers is as specified below depending on the canister type: LO1 2: 3,013 mm, OL1 2: 3,613 mm and OL3 4: 4,741 mm. - L5-BUF-21H The thickness of saturated bentonite adjacent to first and last supercontainer in the compartment is as specified in L5-BUF-20H. The distance between the last supercontainer in the compartment and the deposition drift bottom or compartment plug and the distance between the first supercontainer and the compartment or drift plug is filled with a distance block The main reason is to get same thickness of buffer as between supercontainers so that the transport resistance would be equal. In addition, there are other filling components such as transition zones next to plugs adjacent to these distance blocks. 2.4 Filling blocks The filling components consist of several parts shown in Figure 2-2. The filling blocks discussed in this section include the filling in inflow position, see Section 3.4.2. The filling components related to plugs are discussed in Sections 2.5 and 2.6. Filling at the

26 drift end and filling of the pilot hole end are not considered to be part of the engineered barrier system and are not discussed in this report. The safety functions of the filling blocks are to separate possible transmissive fractures intersecting the drift from the canisters and buffer, to contribute to favourable and predictable mechanical, geochemical and hydrogeological conditions for the buffer and canisters and to limit and retard radionuclide releases in the possible event of canister failure. The general structure of the filling block requirements is presented in Figure 2-3. The requirements can be divided into two categories: requirements related to the performance of the filling blocks, and requirements related to support to other system components. Figure 2-2. KBS-3H drift design with different filling components (Posiva 2012b, Fig. 4-9): a) Filling on the sealed side of the drift plug (and compartment plug), b) Filling blocks in position of inflows, c) Filling on the drift entrance side of the compartment plug, d) Filling at drift bottom end (far end of the drift) and e) Filling of pilot hole. VAHA Level 3 VAHA Level 4 Figure 2-3. General structure of the filling block requirements (Posiva 2016a). The filling block requirements are not discussed in detail in this report. The rationale for the requirements, the loads to be taken into account and the related requirements will be given in (Posiva 2016a). It should be noted that since this component is not present in a KBS-3V repository, all its requirements are new compared with the VAHA for KBS-3V.

27 2.4.1 Performance targets for the filling blocks The performance targets (VAHA Level 3) are given in the Design Basis report (Posiva 2016a). Definition of Filling blocks (at inflow locations) - Filling blocks are the components used in drift sections where relatively high initial groundwater inflows render the sections unsuitable for supercontainer and distance block emplacement. - The purpose of the filling blocks is (i) to fill void spaces in the drift, contributing to its mechanical stability, and to confine the buffer as it takes up water, such that the buffer s saturated density remains within the design specifications, (ii) to protect the buffer from the effects of transient water flows, e.g. piping and erosion, that may occur during the operational period for a drift and the following period leading to saturation, and (iii) to separate the canisters and buffer from larger and more transmissive geological features that may detrimentally affect the canisters and buffer in the longer term and provide preferential pathways for radionuclide transport in the event of canister failure (L3-FIL-3H). Performance Preservation of required properties in repository conditions - The filling blocks shall fulfil the performance targets listed below over hundreds of thousands of years in the expected repository conditions (L3-FIL-5H). Sufficiently low compressibility - The filling blocks shall have a sufficiently low compressibility (L3-FIL-6H). Swelling capacity - The filling blocks shall have a sufficient but not excessive swelling capacity (L3- FIL-7H). Limitation of advective flow - The filling blocks shall limit the advective flow and mass transfer along the drift (L3-FIL-8H). Chemical protection - The chemical composition of the filling blocks shall not have an unfavourable effect on the performance of the other barriers (L3-FIL-9H). Gas pressure - The filling blocks shall prevent the build-up of excessive gas pressure in adjoining drift sections to avoid damage to the other barriers (L3-FIL-10H).

28 Prevention of microbial activity - The filling blocks shall limit microbial activity that might lead to unfavourable chemical conditions in the adjacent buffer or at the canister surface (L3-FIL- 11H). Prevention of formation of colloids - The filling blocks shall limit the formation and transport of colloids (L3-FIL- 12H). Support to other system components Support to deposition drift - The filling blocks shall provide support to the deposition drift walls to mitigate potential effects of rock damage (L3-FIL-14H). Compatibility with other barriers - The filling blocks shall be compatible with other engineered barriers and the host rock (L3-FIL-15H). Keeping the buffer and canister in place - The filling blocks shall contribute to keeping the buffer and canister in place (L3- FIL-16H). 2.4.2 Design requirements for the filling blocks Definition - The main component of the filling block material shall consist of natural swelling clays (L4-FIL-3H). Performance Self-sealing - The filling blocks shall be designed to be self-sealing after initial installation and self-healing after any hydraulic and mechanical disturbances (L4-FIL-5H). Hydraulic properties Avoidance of erosion - The filling blocks shall be designed to be erosion-resistant (L4-FIL-7H).

29 Limitation of advective flow - The filling blocks shall be designed in such a way that they limit the advective flow and mass transfer so that diffusion remains the dominant transport mechanism for solutes (L4-FIL-8H). Retardation of radionuclide transport - The filling block material must be selected in a way that favours the retardation of the transport of radionuclides by sorption (e.g. cation exchange) at the clay and other mineral surfaces (L4-FIL-9H). Mechanical properties Good contact with the host rock - The filling blocks shall be so designed that they have a good contact with the host rock (L4-FIL-11H). Low compressibility - The filling blocks shall be so designed that they have a sufficiently low compressibility (L4-FIL-12H). Chemical properties Limitation of harmful substances - The filling block materials shall be selected so as to limit the contents of harmful substances (organics, oxidising compounds, sulphur and nitrogen compounds) and microbial activity (L4-FIL-14H). Limitation of colloid formation - The filling blocks shall have such a chemical composition that colloids are not formed at the filling block/rock interface (L4-FIL-15H). Support to other system components Ability to stay in place - The filling blocks shall be designed so that they remain in place in the drift (L4- FIL-17H). Gas transfer - The filling blocks shall be designed to allow gases to pass through without causing damage to the repository system (L4-FIL-18H). Compatibility with other barriers - The filling blocks shall be designed so that they are compatible with other engineered barriers and the host rock (L4-FIL-19H).

30 2.4.3 Design specifications for the filling blocks The Design specifications for the filling blocks are presented in Table 2-2. The material selection and performance is based on the same principles as for buffer. The use of same material and diameter for filling blocks and adjoining distance blocks eliminates the possible chemical and physical interactions between these components. Same material specifications and diameter also simplifies the manufacturing and operation. The dimensioning of the blocks is discussed in Section 3.4.2. Table 2-2. VAHA Level 5 design specifications for KBS-3H - Filling blocks. ID Design Specifications Filling components Reference L5-FIL-1H 1 Filling Blocks L5-FIL-2H 1.1 Definitions L5-FIL-3H L5-FIL-4H L5-FIL-5H The material used in filling is MX-80 type bentonite, containing mainly mineral Montmorillonite. 1.2 Performance The montmorillonite content of the dry filling material material shall be 75-90% by weight Anttila et al. (2008) Posiva (2013) L5-FIL-6H The target density of filling material at saturation shall be 2,000 Posiva (2013) kg/m 3 with tolerances defined in Posiva 2013. L5-FIL-7H The total sulphur content shall be less than 1 wt%, with sulphides Posiva (2013) making, at most, half of this. L5-FIL-8H The organics content in the bentonite shall be lower than 1 wt% Posiva (2013) L5-FIL-9H 1.3 Support of other system components L5-FIL-10H The diameter of filling block is the same as for distance blocks. Kirkkomäki and Rönnqvist (2011) L5-FIL-11H The length of filling block is such that the shortest distance from the leaking fracture to the Supercontainer is 3 m if the initial flow is 0.1-0.5 l/min. L5-FIL-12H The length of filling block is such that the shortest distance from the leaking fracture to the Supercontainer is 5 m if the initial flow is 0.5-1.0 l/min. L5-FIL-13H The length of filling block is such that the shortest distance from the leaking fracture to the Supercontainer is 6 m if the initial flow is larger than 1.0 l/min. L5-FIL-14H The filling block between Distance Blocks shall provide a good contact with the host rock soon after wetting. Posiva (2013) Posiva (2013) Posiva (2013) Posiva (2013)

31 2.5 Transition zones for compartment plugs The transition zones discussed in this chapter refer to the filling used on both sides of a compartment plug shown in Figure 3-15 and 3-16. Both such transition zones consist of a transition block and pellet filling. The safety functions of the transition zones for compartment plugs are to contribute to favourable and predictable mechanical and hydrogeological conditions for the buffer and adjoining filling components. 2.5.1 Performance targets for the transition zones for compartment plugs Definition - For installation reasons, transition zones are required on both sides of a compartment plug to separate it from distance blocks. A transition zone consists of a transition block and bentonite pellets. - The purpose of the transition zone on the sealed side of the compartment plug is to fill the empty drift section that remains next to the plug after it has been mounted, and thus to support the performance of the adjacent distance block. The purpose of the transition zone on the drift entrance side of the compartment plug is to function as backfilling material and thus to support the performance of adjacent drift components (L3-TRA-3H). Performance Fulfilment of requirements for hundreds of thousands of years - The transition zone for a compartment plug shall fulfil its performance targets over hundreds of thousands of years in the expected repository conditions (L3- TRA-5H). Protection of distance blocks - The transition zone shall support the functions of the distance blocks (L3-TRA- 6H). Limitation of advective flow - The transition zone shall limit advective flow and mass transfer in the drift (L3- TRA-7H).

32 Support to other system components Support to deposition drift - The transition zones for a compartment plug shall provide support to the deposition drift walls to mitigate potential effects of rock damage (L3-TRA-9H). Compatibility with other barriers - The transition zones for a compartment plug shall be compatible with other engineered barriers and the host rock (L3-TRA-10H). 2.5.2 Design requirements for the transition zones for compartment plugs Definition - The main component of the transition zone material in the transition zones related to a compartment plug shall consist of natural swelling clays (L4-TRA-3H). Performance Protection of distance blocks - The length of the transition zone shall be dimensioned so that its density in the part next to the adjacent distance block is the same as the designed distance block density (L4-TRA-5H). Sealing of potential pathways - The transition zone shall be so designed that its hydraulic conductivity is low enough to limit advective flow and mass transfer in the drift (L4-TRA-6H). Respect distance to flowing fracture - The transition zone length shall be designed so that in case of intersection of the transition zone by a transmissive feature, the respect distance between the feature and the supercontainer will be the same as presented for filling blocks (L4-TRA- 7H). Retardation of radionuclide transport - The transition zone material must be selected in a way that favours the retardation of the transport of radionuclides by sorption (e.g. cation exchange) at the clay and other mineral surfaces (L4-TRA-8H).

33 Support to other system components Compatibility with other barriers - The transition zones for a compartment plug shall be designed so that they are compatible with other engineered barriers and the host rock (L4-TRA-10H). 2.5.3 Design specifications for the transition zones for compartment plugs The Design specifications for the transition zones for compartment plugs are presented in Table 2-3. Table 2-3. VAHA Level 5 design specifications for KBS-3H Transition zones for compartment plugs. ID L5-TRA-1H L5-TRA-2H Design Specifications Transition zones for compartment plugs 2 Transition zone for compartment plugs 2.1 Definitions L5-TRA-3H The material used in filling is MX-80 type bentonite, containing mainly mineral Montmorillonite. L5-TRA-4H L5-TRA-5H 2.2 Performance The Montmorillonite content of the transition block material shall be 75-90% by weight Reference Anttila et al. (2008) Posiva (2013) L5-TRA-6H The target dry density of transition block material shall be 1712 This report kg/m 3 before wetting. L5-TRA-7H The target dry density of pellet filling shall be 1,000 kg/m 3. This report L5-TRA-8H The total sulphur content shall be less than 1 wt%, with sulphides Posiva (2013) making, at most, half of this. L5-TRA-9H The organics content in the bentonite shall be lower than 1 wt% Posiva (2013) L5-TRA-10H 2.3 Support of other system components L5-TRA-11H The diameter of transition block is the same as the distance block. Posiva (2013) L5-TRA-12H L5-TRA-13H The thickness of the transition block adjacent to the distance block is 6,310 mm before wetting. The thickness of the pellet filling adjacent to the compartment plug is 1,300 mm before wetting. This report This report The material selection and performance is based on the same principles as for buffer and filling blocks. The use of same material and diameter for transition blocks and adjoining filling or distance blocks eliminates the possible chemical and physical interactions between these components. The same material specifications and diameter also simplifies the manufacturing and operation. The dimensioning of the blocks is discussed in Section 3.4.3.

34 2.6 Transition zones for drift plugs The transition zones discussed in this chapter refer to the filling used on the sealed side of a drift plug shown in Figure 3-15. Such a transition zone consists of a transition block and pellet filling. The safety functions of the transition zones for drift plugs are to contribute to favourable and predictable mechanical, geochemical and hydrogeological conditions for the buffer and canisters and to limit and retard radionuclide releases in the possible event of canister failure. 2.6.1 Performance targets for the transition zones for drift plugs Definition - A transition zone (consisting of a transition block and bentonite pellets) will be installed between a drift plug (close to the mouth of the deposition drift) and the first distance block in the drift. - The purpose of the transition zone for the drift plug is to fill the empty drift section next to the plug that is needed for mounting the plug in a way that supports the performance of the adjacent distance block (L3-TRA-13). Performance Fulfilment of requirements for hundreds of thousands of years - The transition zone for a drift plug shall fulfil its performance targets over hundreds of thousands of years in the expected repository conditions (L3-TRA- 15H). Protection of distance blocks - The transition zone shall support the functions of the distance blocks (L3-TRA- 16H). Limitation of advective flow - The transition zone shall limit advective flow and mass transfer in the drift (L3- TRA-17H). Support to other system components Support to deposition drift - The transition zones for a drift plug shall provide support to the deposition drift walls to mitigate potential effects of rock damage (L3-TRA-19H).

35 Compatibility with other barriers - The transition zone for a drift plug shall be compatible with other engineered barriers and the host rock (L3-TRA-20H). 2.6.2 Design requirements for the transition zones for drift plugs Definition - The main component of the transition zone material in the transition zone related to a drift plug shall consist of natural swelling clays (L4-TRA-13H). Performance Protection of distance blocks - The length of the transition zone shall be dimensioned so that its density in the part next to the adjacent distance block is the same as the designed distance block density L4-TRA-15H). Limitation of advective flow - The transition zone shall be so designed that its hydraulic conductivity is low enough to limit advective flow and mass transfer in the drift (L4-TRA-16H). Respect distance to flowing fracture - The transition zone length shall be designed so that in case of intersection of the transition zone by a transmissive feature, the respect distance between the feature and the supercontainer will be the same as presented for filling blocks (L4-TRA- 17H). Retardation of radionuclide transport - The transition zone material must be selected in a way that favours the retardation of the transport of radionuclides by sorption (e.g. cation exchange) at the clay and other mineral surfaces (L4-TRA-18H). Support to other system components Compatibility with other barriers - The transition zone for a drift plug shall be designed so that it is compatible with other engineered barriers and the host rock (L4-TRA-20H).

36 2.6.3 Design specification for the transition zones for drift plugs The design specifications for transition zones for drift plugs are presented in Table 2-4. The material selection and performance is based on the same principles as for buffer and filling blocks. The use of same material and diameter for transition blocks and adjoining filling or distance blocks eliminates the possible chemical and physical interactions between these components. The same material specifications and diameter also simplifies the manufacturing and operation. The dimensioning of the blocks is discussed in Sections 3.4.3 and 3.4.4. Table 2-4. VAHA Level 5 design specifications for KBS-3H - Transition zones for drift plugs. ID Design specifications - Transition zones for drift plugs Reference L5-TRA-14H L5-TRA-15H 3 Transition zone for drift plugs 3.1 Definitions L5-TRA-16H The material used in filling is MX-80 type bentonite, containing mainly mineral Montmorillonite. L5-TRA-17H L5-TRA-18H 3.2 Performance The Montmorillonite content of the transition block material shall be 75-90% by weight Anttila et al. (2008) Posiva (2013) L5-TRA-19H The target dry density of transition block material shall be 1,712 This report kg/m 3 before wetting. L5-TRA-20H The target dry density of pellet filling shall be 1,000 kg/m 3. This report L5-TRA-21H The total sulphur content shall be less than 1 wt%, with sulphides Posiva (2013) making, at most, half of this. L5-TRA-22H The organics content in the bentonite shall be lower than 1 wt% Posiva (2013) L5-TRA-23H 3.3 Support of other system components L5-TRA-24H The diameter of transition block is the same as the distance block. Posiva (2013) L5-TRA-25H L5-TRA-26H The thickness of transition block adjacent to the distance block is 6310 mm before wetting. The thickness of the pellet filling adjacent to the compartment plug is 1,300 mm before wetting. This report This report 2.7 Boundary conditions The boundary conditions of the buffer and filling component system are related to many properties including groundwater inflow, groundwater chemistry, compartment plug, drift plug and properties of deposition drift. In addition, the buffer blocks must be manufactured and installed inside the supercontainer properly, which sets inter-related requirements between supercontainer shell and buffer blocks. The requirements that are related to groundwater inflows, drift quality and plugs are presented in the Posiva (2016e), Posiva (2016f) and some of the design requirements related to buffer and filling components in Posiva (2016d) and supercontainer sections being:

37 - Limitation of inflow to deposition drifts, - Straightness of deposition drifts, - Quality of drift wall, - Limitation of inflow to supercontainer sections, - Avoidance of shear fractures, - Avoidance of brittle deformation zones. The requirements that are related to both compartment and drift plugs are presented in Posiva (2016c), some of the design requirements related to buffer and filling components: - Keeping the drift components in place, - Ability to withstand pressure, - The plug shall be dimensioned to withstand the full hydrostatic pressure at repository depth after artificial wetting of both adjoining compartments, - Ability to withstand pressure and pressure heterogeneity, - Sufficient tightness to avoid loss of eroded material.

38

39 3 DESIGN OF BUFFER AND FILLING COMPONENTS 3.1 KBS-3H general design The KBS-3H design has originally been presented in Anttila et al. (2008). Complementary development work has been presented in Posiva (2013). The description of the design presented here is based on these two documents. In addition, the development carried out in the Multi Purpose Test (MPT) at Äspö (SKB 2013) has been taken into account. The KBS-3H design is based on horizontal emplacement of several spent fuel canisters in a drift whereas the KBS-3V design calls for vertical emplacement of the canisters in individual deposition tunnel, see Figure 3-1. According to Posiva Oy s current plans, the repository is to be located at the depth of -420 m below sea level at Olkiluoto. These conditions serve as the basis for the reference design presented in this report. The dimensions of the different components vary depending on the canister type, with different designs for fuel elements from the Boiling Water Reactor (BWR) the Pressurized Water Reactor (PWR) and European Pressurized Water Reactor (EPR). The access to the deposition areas and general design of the deposition areas are different for the SKB and Posiva Oy KBS-3 repositories, partly due to different regulations in Sweden and Finland and partly due to that optimisation led to different results, however, these differences are not particular to KBS-3H alone. Figure 3-1. Principles of the SKB s KBS-3V and KBS-3H repository designs (left) and supercontainer (right). In the KBS-3H design variant, multiple canisters containing spent fuel are emplaced at a depth of about 400-500 m in bedrock in parallel 1,850 mm diameter, 100-300 m long, near horizontal deposition drifts, see Figures 1-1 and 3-1. The drifts are divided into two approximately 150 m long compartments, assuming a typical longest drift length of 300 m, to facilitate manual watering of the drift and simultaneous air evacuation in addition to ease the operation and reduce possible operational risks through the use of compartment plugs and drift plugs. The canister and buffer are placed in a perforated titanium shell and the entire assembly, supercontainer, is emplaced in the horizontal drift.

40 In a compartment the supercontainers are separated by cylindrical distance blocks made of compacted bentonite to manage the heat and to seal off each canister position from the next, and to prevent the transport of water and bentonite along the drift. The two compartments are separated by a compartment plug. The outermost compartment is sealed by a drift plug, which is similar to the compartment plug in design (Posiva 2016c, c.f. Figure 3-1 therein). According to the KBS-3H design, about 23-35 pre-fabricated supercontainers depending on the type of spent fuel will be deposited in each drift. Filling components are placed in positions which cannot be used for supercontainers or distance blocks based on positioning. Filling blocks are used in the drift sections where inflow is equal to or exceeds 0.1 l/min per supercontainer section including half of a distance block on both sides of the supercontainer and where supercontainers and distance blocks therefore cannot be emplaced. Transition blocks together with bentonite pellets, forming a transition zone are installed adjacent to the plugs. All components excluding the pellet filling sections are radially centered in the drift so that the average gap width between the distance blocks and the drift wall is 42.5 mm (gap at the top 33.1 mm and at bottom 51.8 mm). The annular gap around the supercontainers is slightly larger than this. The average gap is 44.5 mm (gap at the top 37.6 mm and at the bottom 51.4 mm). The drift components (supercontainers, distance blocks and filling components) will be deposited using a deposition machine, which is described in more details in Posiva (2013, c.f. Section 9.4). Use of Mega-packer post grouting for groundwater control is expected to reduce inflow into the drifts, thereby preventing possible bentonite erosion caused by leakages occurring during the operational phase. The drainage of the compartment during deposition is achieved by the upward inclination of the drift, water will therefore self- drain along the drift floor out of the drift until the compartment or drift plug is installed. Spray or drip shields, i.e. thin titanium sheets, will be mounted in positions of water spraying or dripping, this done in order to protect the buffer against mechanical erosion allowing the leakage water to flow freely down the drift walls to the floor. In the previous KBS-3H project phase, between 2004-2007, two drifts were constructed at the -220 level at Äspö HRL one 15 meters long drift and one 95 meters long drift. During the 2004-2007 project phase the drifts were used for testing, among other issues, grouting with the mega-packer. The drifts have also been used during the project phase 2008 2010; the longer drift has been used for testing the deposition technique and deposition equipment while the shorter drift has been used for testing of the compartment plug. The longer drift is being used in the fullscale Multi Purpose Test test at Äspö, where a combination of several components, including a supercontainer and distance blocks are tested at full-scale in the drift.

41 3.1.1 Preparations in a drift prior to installation of the components The plugs (compartment plug and drift plug) will be installed in sound rock with no or a few fractures in drift sections that are determined prior to installation of the components. The criteria for positioning the plugs will be addressed later in the project. For the installation of the plugs notches will be excavated in the drift (see Posiva 2016f) and fastening rings casted in the notches as a preparatory measure before installation phase. The fastening rings must allow unperturbed emplacement activity in the drift during installation phase, see Posiva (2016e) for details. The artificial water filling and air evacuation procedure requires that the long air evacuation pipe is installed in the drift before emplacement of drift components can be initiated. Installation of the air evacuation pipe is described in more details in Section 3.1.3. 3.1.2 Plugs After installation of the drift components is finished the compartment will be sealed with a plug (compartment plug or drift plug). Mounting of the plug includes installation of the collar on the fastening ring that was already casted in the notch in an earlier phase. Additionally, threading the air pipe through the collar lead through tube with a valve and pushing the wetting pipes with valves through the collar lead-in tubes will be done. Next the cap of the plug (including the pellet filling hole) will be installed on the collar. The section between the compartment plug and the transition block will be filled by bentonite pellets through the pellet filling hole in the cap, see Figure 3-2. The filling hole will be plugged with a blind flange fitted by bolts after filling. 3.1.3 Wetting and air evacuation The empty void space in the annular slot (average 44.5 mm between the supercontainers and rock wall and 42.5 mm between distance blocks/filling blocks and rock wall) between the deposition drift wall and the drift components inside a sealed compartment will be artificially filled with water. This guarantees the initial swelling of the buffer, i.e. the distance blocks and the buffer inside the supercontainers, the development of counter pressure against drift surface and that the canisters are fixed in place and axial displacement and significant buffer erosion can be avoided. The volume of the annular gap for a 150 m long drift compartment is approximately 40 m 3. The water filling is made rapidly and in order to accelerate the swelling of buffer and filling components simultaneously in the compartment. The inflow into the drift will eventually slow down as the pressure inside the drift increases (pressure gradient will be even in the drift and in the adjacent rock mass), this is achieved within hours. Water filling will be done by pumping fresh water through the plug with short (approximately 2 m) wetting pipes (Figure 3-2). During the water filling air will be compressed and accumulated at the end of the drift compartment due to its slightly upward inclination and this trapped air needs to be evacuated through a pipe (maximum length 150 m) to allow complete filling with water. For water filling and air evacuation purposes the plug collar is equipped with four identical lead-ins with valves, three for the

42 water pipes and one for the air evacuation pipe (Figure 3-3). The three short water filling pipes extend behind the pellet filling section underneath the transition block, see Figure 3-2. Figure 3-2. Main components for water filling system with short pipes through compartment plug (similar design in drift plug). The three short water filling pipes lead the water past the pellet filling section underneath the transition block (Posiva 2013). Figure 3-3. The air evacuation pipe at the rear end of the drift and the bottom filling and buffer blocks in the model of MPT tests at Äspö. The short pipe in the rear part of the drift (compartment) that is turned upwards to the roof is needed because the air is accumulated in the upper part of the inclined drift. The pipe is fixed on the drift surface with attachments shown in the figure. The three tie-rods (not part of the final design) that keep the 0.5 m thick block slices together are also shown. The feet are also seen under the block.

43 Water is pumped in through the three pipes with a flow rate of about 25 l/min per one pipe for c. 8 hours and when the water starts to exit from the air evacuation pipe all the valves are closed. 3.1.4 Pipe removal and sealing a compartment Water filling and the subsequent pipe removal were identified as potential weaknesses of the design in the previous project phase and focus was put on developing and studying water filling methods that would minimise the risk involved in removal of long pipes. Water filling using shorter pipes was proven feasible in performed erosion tests during the recent project phase, thereby providing advantages both from technical performance (less preparative work, shorter water filling time etc.) and long-term safety point of view, because the risk of foreign materials left in the drift due to a failure in the removal is much smaller. After the water filling and air evacuation have taken place the pipes will be removed from the compartment as required due to long-term safety. The pipe removal of the long air evacuation pipe and the short water filling pipes will take place directly after water filling and air evacuation phases. When removing the long air evacuation pipe the coupling will allow it to be released from the short pipe, which will be left in the drift. The winch/pulling system for removing the air evacuation pipe is set up at the deposition niche and the procedure will depend on the location of the plug (compartment plug or drift plug). In case of compartment plug located approximately at the midpoint of the drift, the pipe can be pulled out in one piece to the first half of the drift and then split to 6 m long pieces. In the case of drift plug the pipe is pulled out as long sections as allowed by the space (niche and central tunnel) available, probably as 24 to 30 m long parts. After the pipe is totally removed the ball valve of the lead-in tube is closed. The ball valve is replaced by a plug by screwing in the pipe lead-in tube. 3.2 Differences between Posiva and SKB implementation The main differences between Posiva and SKB implementation of KBS-3H are presented in (Posiva 2016b, Section 1.6). There are differences in underground openings, rock engineering, canisters and supercontainers which are discussed in the relevanr production line reports. The differences relevant to buffer and filling components are: - The buffer blocks inside the supercontainer have differences because of the differences in canisters (see Section 3.3.2) - The distance blocks have different lengths (Section 3.3.3) 3.3 Design of Buffer components 3.3.1 General The buffer components include blocks inside the supercontainer and the distance blocks placed between supercontainers. The dimensions of distance blocks and buffer segments

44 in supercontainers are different for Swedish and Finnish repository designs and depend on the canister length, canister spacing, drift spacing and thermal conductivity of bedrock. It is assumed that the buffer components are manufactured by isostatic compaction technique. The design of buffer components presented below is based on (Börgesson et al. 2016). 3.3.2 Buffer blocks in the supercontainer The buffer is composed of different types of bentonite sections with different dimensions, dry densities and water contents (Börgesson et al 2016). Section I corresponds to ringshaped blocks, Section II to solid cylindrical blocks at both ends inside a supercontainer and section III to solid cylindrical distance blocks between supercontainers. The reference designs of the blocks are presented in Tables 3-3 and 3-4, and Figures 3-4 and 3-5. The densities are given as dry densities. Posiva reference design of canister has an integral flat bottom instead of a welded bottom in the SKB design, which affects the details of adjoining buffer. The supercontainer (Figure 3-4) consists of the following components, c.f. details in (Posiva 2016d): - Spent Fuel Canister (Copper Canister), - Bentonite buffer, - Perforated titanium Shell. The geometry affects the dimensions of the buffer blocks inside the supercontainer. The shell is a perforated cylinder with solid end plates provided with five pairs of feet. The perforation has impact on the saturation and swelling of buffer inside the supercontainer shell as well as the penetration through the perforation during swelling. The feet are located under the joints between the bentonite blocks. The thickness of the perforated shell and solid end plates shall be 6 mm. The shell is perforated to a degree of approximately 61-62% depending of type of SF canister. The perforation consists of holes with a diameter of 100 mm. The hole pattern is shown in Figure 3-6. The shell is in total provided with 49 holes radially and 37, 47, 48 or 52 holes lengthwise depending of type of SF canister see Table 3-1. Figure 3-4. The buffer components in the KBS-3H supercontainer consists of bentonite rings and bentonite end blocks. The shell around the buffer is perforated, but the end plates are solid (Posiva 2016a).

45 a) TOP BLOCK 798 1740 828 350 73 1740 350 350 83 b) BOTTOM BLOCK c) BOTTOM BLOCK FLAT 1740 d) RING 1058 1740 Figure 3-5. Schematic drawing of the blocks inside the supercontainer. a) Top block, b) Bottom block, c) Bottom block flat and d) Ring block. See Figure 3-4 for the whole setup. Details are presented in Posiva (2016d).

46 Lengthwise Radially Figure 3-6. Hole pattern in the supercontainer shell (Posiva 2016d). Table 3-1. Shell thickness, holes and perforation degree (Posiva 2016d). Thickness [mm] Holes radially [mm] Holes lenghtwise [mm] SKB PWR 6 49 48 62 SKB BWR 6 49 48 62 Posiva BWR 6 49 47 61 Posiva VVER 6 49 37 61 Posiva EPR 6 49 52 62 Perforation degree [%] The dimensions of the supercontainer shell with tolerances for the different canisters without end plates and feet are presented in Posiva (2016d). The total length of the shell is determined by the sum of the length of the buffer blocks and rings plus the thickness of the end plates. Dimensions with tolerances and weight of the end plate are presented in Posiva (2016d). The feet shall be 100 mm wide and approximately 560 mm long. The feet are provided with holes that are matching the hole pattern of the shell to allow the bentonite to swell out evenly around the supercontainer. The supercontainer is provided with pair of feet placed close to the joints between the buffer blocks/rings. The dimensions of the canisters, supercontainers, an estimation of the total weight and distance block length are presented in Tables 3-2, 3-3 and 3-4.

47 Table 3-2. The length of the Posiva canisters, supercontainers, distance blocks and supercontainer sections per canister type. NB. the term supercontainer section refers to a section of the drift that covers one supercontainer and half a distance block on both sides of the supercontainer. OL1-2 are the references canisters in this document. Parameter/canister type BWR (OL1 2) VVER-40 (LO1 2) PWR (EPR) (OL3 4) Canister length (mm) 4,752 3,552 5,223 Supercontainer length (mm) 5,387 4,187 5,859 Distance block length (mm) 3,613 3,013 4,741 Supercontainer section length (mm) 9,000 7,200 10,600 Table 3-3. Dry densities and water contents of reference buffer blocks inside the supercontainer (Börgesson et al 2016). Design parameter Nominal design Accepted variation Solid blocks inside the supercontainer Dry density [kg/m 3 ] 1,753 ± 20 Water content [wt.-%] 17 ± 1 Ring shaped blocks inside the supercontainer Dry density [kg/m 3 ] 1,885 ± 20 Water content [wt.-%] 11 ± 1 Table 3-4. Dimensions and tolerances of reference buffer blocks inside the supercontainer (Börgesson et al 2016). Buffer component Outer diameter [mm] Inner diameter [mm] Length [mm] Top Block 1,740 +1 /-2 798 +0 /-2 350 +1 /-1 1,836 Bottom block, bottom with recess 1,740 +1 /-2 828 +0 /-2 350 +1 /-1 1,830 Bottom block, flat bottom 1,740 +1 /-2-350 +1 /-1 1,741 Ring, SKB PWR/BWR 1,740 +1 /-2 1,058 +1 /-2 1,211 +1 /-1 3,722 Ring, Posiva BWR 1,740 +1 /-2 1,058 +1 /-2 1,190 +1 /-1 3,658 Ring, Posiva VVER 1,740 +1 /-2 1,058 +1 /-2 890 +1 /-1 2,736 Ring, Posiva EPR 1,740 +1 /-2 1,058 +1 /-2 1,308 +1 /-1 4,021 Approx. weight [kg] 3.3.3 Distance blocks The distance blocks are placed between the installed supercontainers in a drift. The reference design of the blocks is presented in Table 3-5 and Figure 3-7. The densities are given as dry densities. The water content of the distance blocks is higher than in the supercontainer blocks in order to prevent humidity induced cracking during operation. The length of each distance block section is determined by the modelled temperature and varies dependending on the thermal properties; type of canister, bedrock properties and the layout. The Finnish reference distance block lengths are illustrated in Figure 3-8 and Table 3-6 presents a summary of four different canister spacings and corresponding distance block lengths for Swedish spent fuel canisters. If there is a filling component between supercontainers (see Figure 3-1) the distance block is split to two equal parts on both sides of the filling component.

48 The distance blocks are standing on feet made of titanium, centralized in the deposition tunnels. With this design, inflowing water from the rock can flow free on the tunnel floor during the installation without direct contact with the bentonite. The feet will also be used during the installation for temporary resting of the stepwise movements of blocks. One pair of feet will be attached to each distance block. The two feet are connected to each other via a perforated thin sheet. The feet are attached to the distance blocks by using bolts that are screwed in threaded holes in the bentonite blocks. Table 3-5 Reference buffer block outside the supercontainer (distance blocks). Design parameter Nominal design Accepted variation Solid blocks outside the supercontainer (distance blocks) Dry density [kg/m 3 ] 1,712 ± 20 Water content [wt.-%] 21 ± 1 Dimensions [mm] Height: 500 ± 1 500 1765 Figure 3-7. Schematic drawing of the distance blocks between the supercontainers (distance blocks) and feet design, 1 = distance block, 2 = perforated sheet connecting the feet, 3 = one foot. The width of the perforated sheet is 175 mm.

49 Figure 3-8. Different distance block alternatives for Finnish spent fuel canisters. Table 3-6. A summary of four different canister spacings and corresponding distance block lengths for Swedish spent fuel canisters with respect to deposition drift spacing and thermal conductivity of bedrock. Deposition drift spacing (m) Canister spacing (m) Thermal conductivity (W/mK) Distance block length (m) 30 8.6 2.9 3.04 30 7.2 3.57 1.64 40 7.9 2.9 2.34 40 6.5 3.57 6.5 3.3.4 Verification analysis of the final buffer density The nominal values of the parameters yield a final target buffer density of about 2,000 kg/m 3 after saturation, which is the target density with the allowed density range of 1,950-2,050 kg/m 3. The following parameters have been varied in order to evaluate the sensitivity of the final average buffer density: 1. The section of the buffer. The ring shaped blocks (Section I of the buffer) are placed around the canister in the supercontainer while the solid blocks (Section II of the buffer) are placed at the end sections of the supercontainer. Distance blocks (Section III of the buffer) are positioned outside each supercontainer separating the installed supercontainers. 2. The diameter of the deposition drift can vary between 1,850 1,855 mm. 3. The dry density of the blocks can vary about ±20 kg/m 3 from the nominal values. 4. The type of supercontainer shell titanium being the reference material. 5. The volume of the corroded supercontainer shell (constant/twice to triple for the shell made of steel, copper and titanium) for titanium, due to the very low corrosion rate (1 nm/yr), it will take a very long time to attain the volume increase.

50 The supercontainer perforated titanium shell, selected as the reference design, has an outer diameter of 1,761 mm and an inner diameter of 1,749 mm (i.e. thickness of 6 mm). Corrosion of supercontainer shell causes expansion. The evaluation of effect of corrosion expansion on buffer density is made with the assumption that no axial swelling of the buffer occurs. The figures show that the risk of getting a lower buffer density than 1950 kg/m 3 at saturation is not high since extreme values are required of the diameter of the drift. Results for a supercontainer shell made of titanium (supercontainer shell outer diameter 4 mm smaller than with steel shell) are summarized in Table 3-7. 3.3.5 The effect of gaps on the final buffer density The canister (diameter 1,050 mm) length for BWR (Posiva s reference canister) is 4752 mm, for VVER it is 3552 mm and for EPR it is 5223 mm. In Posiva s case the canister spacings are the same in 3V and in 3H. The length of the supercontainer and the distance block length summed up is equal to canister spacing. The supercontainer lengths are 5387 mm for BWR, 4187 mm for VVER and 5859 mm for EPR type canisters. According to reference design of KBS-3H the nominal gap between the canister and the solid blocks is 8 mm. This design presumes that the axial gap inside the supercontainer is located at one side only because of the assembly procedure. Assuming that this gap will vanish during the saturation phase, it is possible to calculate an average density of the buffer in the section between the canister lid and the supercontainer lid, using a dry density of the solid blocks of 1,753 kg/m 3 and corresponding dry density for the ring shaped blocks of 1,885 kg/m 3. The buffer density at saturation calculated at these conditions will be about 1,985 kg/m 3. This density is above the lowest acceptable density at saturation of 1,950 kg/m 3 (Posiva 2013, p.65). The calculations made assume that no swelling in axial direction occurs. With respect to the density of buffer in the gap between supercontainer shell and drift surface it is uncertain what the final density in the gap will be, however preliminary simplified modelling and small scale tests (1:10) (Kristensson et al. 2016) indicate that the density in the gap is sufficiently high. The issue is being investigated in homogenization studies and will be reported later. Table 3-7. Data extracted from the analyses of the buffer density. The calculations are made for a supercontainer shell made of titanium with the assumption of constant volume of the corroded supercontainer. The numbers marked green in the table are nominal, representing the installed system. Diameter of drift [m] Dry density of block [kg/m 3 ] Section 1.850 1,885 Section I 2,000 1.850 1,905 Section I 2,024 1.855 1,865 Section I 1,981 1.850 1,753 Section II 1,998 1.850 1,773 Section II 2,019 1.855 1,733 Section II 1,981 Buffer density at saturation [kg/m 3 ]

51 3.3.6 Concluding remarks The results to estimate system density are based on the data for the drift, the supercontainer and the buffer blocks presented in this report. The following conclusions can be made from the calculations: - The calculations of the buffer density at the three investigated sections assuming nominal values of the density and dimensions of the blocks, nominal dimensions of the drift, the supercontainer shell with constant volume and no axial swelling will give a final buffer density of about 2,000 kg/m 3 at saturation. - A lower initial block density than the defined nominal value will result in a buffer density at saturation of less than 2,000 kg/m 3. The lowest saturated density, about 1,981 kg/m 3, was calculated for the case of blocks with an initial density 20 kg/m 3 lower than the nominal both for the distance blocks (Section III) and for the solid blocks inside the supercontainer (Section II) for the case of a supercontainer shell made of titanium. Furthermore, it is assumed that the drift has the maximum allowed diameter of 1,855 mm. - The calculations made for a supercontainer shell made of titanium produce a buffer density at saturation between 1,981 2,024 kg/m 3. - An axial swelling of the buffer with nominal values of the buffer and the drift will lead to a saturated buffer density of less than 2,000 kg/m 3. A simplified calculation of the buffer density when taking into account an axial swelling yields a final buffer saturated density of 1,985 kg/m 3 at one of the two end sections. This design presumes that the axial gap inside the supercontainer is located at one side only because of the assembly procedure. - The design at this stage has not addressed the design of the feet under distance blocks. In summary, for all the cases examined for supercontainer installation in deposition drifts according to the design presented in (Posiva 2016d), the equilibrated, water-saturated density of the buffer are within the allowed range of 1,950 2,050 kg/m 3. This should ensure that this type of installation also meets the thermal, hydraulic and mechanical requirements. 3.4 Design of filling components 3.4.1 General As presented earlier the updated KBS-3H drift design includes five filling components, which are illustrated in Figure 3-9. The design inside the compartment and drift plug are basically the same and five different components have been designed. a) Filling components on the sealed side of the compartment and drift plugs consisting of transition blocks and pellets filling b) Filling in position of inflows. c) Filling on entrance side of compartment plug consisting of transition block and pellets filling. d) Filling at drift end.

52 e) Filling of the remainder of the pilot hole The design of filling components and especially transient zone is based on the internal friction of the filling material and therefore permanent density gradients will remain along the drift in filling components. This assumption is commonly used in evaluation of buffer performance and is presently being studied in homogenization research in order to provide more evidence as to its validity (Kristensson et al. 2016). The design of filling components presented below is based on (Börgesson et al. 2016). 3.4.2 Filling in position of inflows In the current KBS-3H design, filling blocks will be placed in drift positions intersected by fractures giving initial inflows to the drift above 0.1 l/min per supecontainer section (i.e.supercontainer length + half of a distance block length on both sides of the supercontainer (Figure 3-10). Such drift sections are currently excluded as locations for supercontainer or distance block emplacement. Figure 3-9. KBS-3H drift design with different filling components. Distance blocks, which are part of buffer, are presented in grey color. Figure 3-10. KBS-3H drift, showing the position of a filling block between split distance blocks and two supercontainers, see Figure 3-1 and Section 3.3.3. Note that the inclination of fracture has an effect on the length of filling block. The distance from fracture to supercontainer end plate is represented by parameter L. (i.e. respect distance).

53 Dimensioning The dimensioning of filling blocks is based on following principles: - There is half of distance block on both sides of the filling block, see Figure 3.12. This conforms to a situation where there is an inflow of exactly 0.099 l/min (less than the limit 0.1 l/min used to reject it for emplacement of supercontainer) and a normal distance block is positioned between supercontainers in this section (see Posiva 2013). - The length of filling block depends on: a) Inclination of fracture, see Figure 3-11 and 3-12, b) Length of distance blocks and c) inflow rate. This is based on the principle that the length of filling block sets the transport length (and resistance) from canister embedded in the supercontainer to the nearest transmissive feature. The larger the inflow, the larger the required transport length. Note that the design is consequently based on virgin inflows before any possible sealing operations. - It is assumed that the filling blocks are composed of 50 cm thick bentonite block slices based on the present production technique used for buffer (mainly press and mould). This, however, can be adjusted and optimised if needed. - The filling blocks are made of the same material and have the same diameter as the distance blocks in order to simplify the manufacturing and to avoid introduction of new materials and interrelated processes in the system. The erosion resistance of different alternative materials is being studied and the results may affect the design later. The length of the filling block has been established as a function of the initial inflow from the fracture by using the principles presented above. Scoping calculations have given tentative estimates for the respect distance (L in Figure 3-10) needed to water-conductive fractures with specific inflows ranging from 0.1-0.5 l/min, 0.5-1 l/min and >1 l/min, with upper limit of 10 l/min. These tentative criteria are set on the basis that the release rate of C-14 emanating from a failed canister to the fracture should be such that Finnish regulatory geo-bio flux constraints are satisfied by a significant margin. The approach is presented in Posiva (2013) and the resulting respect distances are presented in Table 3-8 below. Design It should be noted that the respect distances in Table 3-8 include half a distance block section on each side of the supercontainer (see Figure 3-10). The filling block lengths corresponding to the selected distance block lengths and the above mentioned respect distances are presented below in Figures 3-12 through 3-14. The design of filling block is similar to distance blocks. The reference design of the blocks is presented in Table 3-9. The densities are given as dry densities.

54 Table 3-8. Respect distances (L in Figure 3-10) with respect to inflow rates (note that uppermost limit for inflows in the drift based on operation of deposition equipment is 10 l/min, which is mainly based on the functionality of present deposition machine, however, there is also risk that the buffer and filling blocks can get wet during transportation using deposition machine based on Posiva 2013). Initial inflow range [litres min -1 ] Respect distance L [m] 0.1-0.5 3 0.5-1 5 > 1 6 The respect distance is measured from the closest point where the fracture plane intersects the drift wall to the supercontainer, see Figure 3-10. This applies to both sides of the filling block. The lengths of the filling blocks have their minimum values in each inflow range category, when the fracture plane runs perpendicularly to the drift with the inclination of 90 degrees. In these cases, the length of the filling block is increased based on the length of the fracture plane between the two closest points with the specified respect distance to the next supercontainer. This length of the fracture plane is projected to the drift axis. The important parameter here is the angle between the fracture plane and the drift axis. Other parameters which affect the length of a filling block are the length of the distance block and the inflow rate into the supercontainer section. As 50% of the distance block length is included in the respect distance this will conclude that the increase in the length of the distance block will shorten the length of the filling block with the same amount. The length of filling blocks with respect to the intersection angle of water leaking fracture is shown in Figure 3-11.

55 25,00 Length of Filling Block 20,00 15,00 10,00 5,00 Groundwater inflow ranges 0.1-0.5 l/min 0.5-1.0 l/min Over 1 l/min 0,00 10 20 30 40 50 60 70 80 90 Angle between Drift axis and fracture (deg.) Figure 3-11. The length of a filling block as function of the angle (see Figure 3-12) between drift axis and the fracture plane in three different inflow range categories, with specific respect distances. The length of the distance block that has been used in this case is 3.013 m. Figure 3-12. Filling block for positions where inflow is 0.1-0.5 l/min.

56 Figure 3-13. Filling block for positions where inflow is 0.5-1.0 l/min. Figure 3-14. Filling block for positions where inflow is larger than 1.0 l/min. Table 3-9. Reference buffer blocks (distance blocks) used for filling and transition blocks. Design parameter Nominal design Accepted variation Dry density [kg/m 3 ] 1,712 ±20 Water content [wt.-%] 21 ±1 Dimensions [mm] Height: 500 Outer diameter: 1,765 ±1 3.4.3 Filling components on the sealed side of the compartment and drift plugs and outside compartment plug The design for filling components adjacent to the drift plug and for the sealed side of compartment plug is identical and therefore presented in this section. In addition, the design outside the compartment plug is based on same principle and dimensions and is therefore also presented in this section. The schematic principle of filling adjacent to drift plug and for filling components for the sealed side of compartment plug are shown in Figure 3-15 and for compartment plug in Figure 3-16. The key requirements and factors specific to the drift plug and the compartment plug affecting the design of filling components are similar with the exception that the compartment plug is exposed to hydrostatic pressure only and not exposed to significant swelling pressure of buffer and adjoining filling components as the drift plug. This difference is not assessed as having impact on the design of these filling components. The preliminary requirements and prerequisites based on Posiva (2013) can be summarized as:

57 - The drift plug must withstand 5.0 MPa hydrostatic pressure plus the swelling pressure of the bentonite inside the drift. The assumed 5.0 MPa swelling pressure is considered conservative and there is indication from buffer studies ((Kristensson et al. 2016)) that the real pressure could be closer to 2 MPa. The loading from the filling components should be as evenly distributed as possible to reduce force heterogeneity on the plug. - In case of the compartment plug it must withstand hydrostatic pressure only and low swelling pressure in the order of a few tens of kpa s. - The drift and compartment plug shall be tight assuming the largest allowed water leakage past the plug specified as 0.1 l/min (tentative requirement). The compartment plug was tested in full-scale at the Äspö HRL (Posiva 2013, Section 4.7). The leakage during the test was initially at approximately 0.05 l/min and after a couple of days it was reduced to 0.002 l/min. Therefore, it is likely that the leakage rate past the plug will be significantly lower than the tentative requirement. The structures of the drift and compartment plug are similar and therefore the results apply to both. - It shall not under its working time or afterwards affect fulfilment of requirements of the neighbouring distance block section. Especially the density of adjacent distance block must not be affected. - The function of the drift plug is needed for a long time, whereas function of compartment plug is needed for only a relatively short time (order of weeks until drift plug is in place). - It has been found feasible to use bentonite pellets (in addition to obtaining proper density distribution) to fill empty volumes adjacent to the plugs in order to enhance sealing of possible leakages through microfractures. - In order to be able to build the plug an empty space of 1.3 m length is needed inside the plug in order to mount the cap of the plug. The length used in this section was measured from the crown of the cap, see Figures 3-15 and 3-16. To obtain symmetrical swelling on both sides of the plug, the same 1.3 m distance is used on boths sides of the plug for pellet filled section. - The plug includes lead throughs that allow for artificial water filling of the unfilled space inside the plug and there is a small lid in the plug for filling of bentonite pellets behind the plug. The design is based on the following principles: - The empty volume on the sealed side of the plugs is filled with pellets resulting in lower density. - A section of highly compacted blocks called transition block is placed between the pellet filling sections and the adjacent distance blocks. As filling components absorb water and swell, there will be a transition zone from the drift plug to distance block with a density gradient. The transition blocks can be composed of several smaller blocks in similar way as distance blocks. The compaction method is based on isostatic compaction and the dimensions of blocks will be optiomized later based on that. Dimensioning The design of the transition zone is based on the requirement that the distance block adjacent to a transition block section is unaffected by the swelling in the transition zone

58 (containing transition blocks and pellets, see Figure 3-15) and the associated compression of the pellet filling. Since the pellet filling has much lower density than the transition blocks there will evidently develop a transition of density between the distance block and the plug where the density gradually increases towards the closest distance block. Figure 3-15. Design of filling adjacent to the drift plug (the same design applies for the compartment plug). Figure 3-16. Schematic drawing of the filling components adjacent to a compartment plug. The same design is used for filling components for the sealed side of compartment plug as for filling adjacent to the drift plug. NB. the accounting of the pellet filling and the transition block is not made with a unified relative length scale. The required length of the transition zone is determined by the density gradient caused by the swelling of the transition blocks into the pellet filling. The length of the zone is dimensioned so that the density of the swelled and homogenized transition zone in contact with the distance block will be the same as the density of the distance block, leading to that no axial swelling of the distance block takes place. Due to mainly friction between the bentonite and the rock surface the density reduction of the transient block will be limited spatially and can be estimated in a simplified way with equations that are derived from force equilibrium in the axial direction.

59 The compartment and drift plug lead-throughs were not included in the analysis since they were assessed to be negligible to the design. Only the filling between the plug and the distance block were studied. The dimensions of the transition zone and the expected swelling pressure acting on the plug were resolved. The dimensions of the transition zone can be calculated either numerically using Finite Element Method or analytically in a simplified way. The analytical solution has been used at this stage, and the results are shown in Table 3-10. The principle of calculations is presented in (Åkesson et al. 2010a and 2010b) and (Posiva 2013). The required length of the transition zone and the resulting swelling pressure on the plug are dependent on the friction angle as seen in Table 3-10. The friction angle for swelling pressures between 1 and 10 MPa is estimated to be about φ=5º based on (Åkesson et al. 2010b), and assuming that the friction angle between bentonite and a smooth plane surface of rock is about 50 % lower than internal friction in bentonite (Börgesson et al. 1995). Design Transition block length of 6.31 m (see Figure 3-16) is used in the design based on Table 3-10. The material properties in the design are as follows: - Dry density of the pellet filling ρdp=1,000 kg/m 3, - Dry density of the transition blocks ρdb=1,712 kg/m 3, - Dry density of the transition block section (over drift diameter 1.85 m) ρdt=1,558 kg/m 3, - Water content of the transition block 21wt.-%, - Average calculated dry density of the transition zone (both blocks and pellets over the length of transition zone 7.61 m) ρ =1,464 kg/m 3. The design of highly compacted bentonite used in the transition blocks is presented above in Table 3-9 and in Figure 3-16. Table 3-10. Length of Transition block, transition zone and resulting swelling pressure on plug with respect to friction angle. Friction angle φ Total length of transition zone LT Length of transition block L Swelling pressure on the plug 5º 7.61 m 6.31 m 1,413 kpa 10º 5.67 m 4.37 m 771 kpa 20º 3.74 m 2.44 m 315 kpa 30º 2.98 m 1.68 m 146 kpa 3.4.4 Filling at drift end and pilot hole A filling component is emplaced in the KBS-3H deposition drift end between the drift face and the adjacent distance block, see Figure 3-17. The motivation for placing a filling component is based on concentrated rock stresses around the corners of the drift end. Therefore, the rock adjacent to the drift face might be more vulnerable to smaller scale

60 disturbances and opening of fracturing. If there are small deviations in the drift lengths these can also be compensated by adjustments made by using filling components. The filling component between the drift face and the adjacent distance block is integrated into the distance block design so that it can be installed in one package. The filling component between the drift face and the distance block is merely to compensate the gap at drift face and function as additional buffer against drift face. Dimensioning The same type of compacted bentonite blocks similar to distance blocks are used for the filling next to the drift face as for previously presented filling components. The dimensioning is based on compensating the open volume in the gaps by adding compacted bentonite so that the required final average density will be the same as for distance blocks. Design The design is presented in Figure 3-17 and the dimensions in Table 3-11. The shape of the innermost surface of the filling component is modified to conform to the rock surface. Only one 0.5 m long filling component with the same properties as a distance block is placed at the drift bottom. 3.4.5 Filling of pilot hole The remaining pilot hole beyond the end of drift is filled to avoid possible open cavities that might reduce the density of buffer and other filling components. Another objective is to seal the pilot hole to prevent possible groundwater flow between drift system and host rock. The remaining pilot hole is filled with cylindrical highly compacted bentonite blocks with a length of 0.5 m. The length will be optimized later based e.g. on the selection between the uniaxial and isostatic compaction techniques and efficiency. The latter one assumed as the reference method in this report.. The compacted bentonite is of the same type as used for filling blocks (and distance blocks). The hole will not be perfectly straight, so a small curvature is expected and to compensate that, several shorter blocks are used for filling instead only one long one. The curvature and technique to compensate that depends on the length of the remaining pilot hole. The diameter of pilot hole is 152 mm and the diameter of the blocks, 132 mm. The objective is to reach final saturated density of buffer which is in the range of the filling blocks. The design is presented in Figure 3-17 and the dimensions in Table 3-12.

61 Figure 3-17. Air evacuation pipe and filling component at the drift bottom as implemented in The Multi Purpose Test (MPT) (SKB 2013). Table 3-11. Dimensions and properties of filling component at the drift bottom. Drift bottom end filling component properties Lenght 0.50 m Diameter of blocks 1.765 m Initial dry density of blocks 1,712 kg/m 3 Table 3-12. Dimensions and properties of pilot hole filling component. Pilot hole filling specifications Pilot hole length 2,000 mm Pilot hole diameter 152 mm Diameter of blocks 132 mm Length of a single block 500 mm Initial dry density of block 1,712 kg/m 3

62 3.4.6 Conclusions The following conclusions can be made from the design of filling components: - The main function of the filling components is to support the buffer components by exerting sufficient swelling pressure so that the there will not occur displacement or deformation that would exceed the requirements. The present design is based on establishing equal swelling pressure exerted from filling components as generated from the buffer components. Therefore, the density of the components will be as designed about 2,000 kg/m 3 at saturation. - The design of filling components is based on the internal friction of the filling material and therefore permanent density gradients will remain in filling components. This assumption is commonly used in evaluation of buffer performance and is presently being studied in homogenization research in order to provide more evidence as to its validity. - The dimensioning of filling components adjacent to drift and compartment plugs is based on mathematical calculations and include uncertainties such as the friction angle to be used for the calculations and assumptions that hysteresis has no significant influence on the swelling. The calculations were based on the assumption that high density bentonite filling can maintain density and swelling pressure difference for long periods of time, which is related to homogenization of bentonite. 3.5 Buffer and filling component materials 3.5.1 The reference material used for buffer and filling components The same material is used in the compacted blocks in supercontainers, in distance blocks, and in transition blocks, as well as in pellets. Only density, water content and dimensions may differ between different types of components. The reference buffer material used is bentonite clay with the material requirements specified in Table 3-13. Examples of commercially available bentonites with this material composition are MX-80 and Ibeco RWC (Deponit CA-N), which were analysed in SR-Can. Table 3-13. Reference buffer material used also in filling components (SKB 2012). Design parameter Nominal design [wt.-%] Accepted variation [wt.-%] Montmorillonite content 80-85 75-90 Sulphide content < 0.5 < 0.5 Total sulphur content (including < 1 < 1 the sulphide) Organic carbon < 1 < 1

63 Material composition Examples of the reference buffer material (Table 3-13), commercial bentonite clay, are high grade sodium bentonite from Wyoming (MX-80) and high grade calcium bentonite from Milos (Ibeco RWC, also often called Deponit CaN). These materials are analysed for example in SR-Can (SKB 2004, p. 48; SKB 2006b, p. 14) and in Ahonen et al. (2008, p. 58), Kumpulainen and Kiviranta (2010, 2011), Kiviranta and Kumpulainen (2011), and Kiviranta et al. (2016). High grade sodium bentonite from Wyoming is the reference material for both the buffer blocks and the pellets. MX-80 is the commercial name of a Wyoming sodium bentonite with a montmorillonite content above 75 %. It is, however, acceptable that as long as any other bentonite type containing montmorillonite above 75 % fulfils the performance targets of the buffer, the alternative bentonite can be considered as a suitable candidate in the future. The capability of the buffer to maintain the stated safety functions (see Sections 2.3 through 2.6) will depend on its swelling pressure, hydraulic conductivity, stiffness and content of substances that may be harmful for the other barriers. According to the design basis the montmorillonite content in the buffer material must be sufficient for the buffer to provide the required performance in the disposal system. In the design basis the montmorillonite content, the amount of organic carbon, the sulphide and the total sulphur content are used to specify the bentonite clay. A high content of swelling mineral will result in a high swelling pressure and stiffness. At a density relevant for the buffer performance, this is expected to give various bentonites similar properties regarding swelling pressure, hydraulic conductivity and to some extent stiffness. The swelling properties and stiffness are also dependent on the magnitude and the position of the layer charge and on the type of charge compensating cation. In the repository the cation may be exchanged. However, the swelling pressure, hydraulic conductivity and stiffness must be preserved at the required level. Apart from montmorillonite, bentonite clays contain accessory minerals. Typical accessory minerals may be other clays, feldspars, quartz, cristobalite, gypsum, carbonates and pyrite. Pyrite contains sulphur as sulphide, which may cause canister corrosion. Bentonite clays may also contain organic carbon that may impact the radionuclide transport. A bentonite with a high content of accessory minerals with high solubility (e.g. halite) would be unsuitable for the KBS-3 application. However, such minerals have not been found in the investigated bentonites in significant amounts. Most of the identified accessory minerals can generally be considered as inert. The amount of organic carbon, the sulphide and total sulphur are chosen to specify the quality of the bentonite clay since these substances may impact the radionuclide transport or cause canister corrosion. A high amount of iron might favour bentonite transformation and to some extent affect the swelling pressure of the buffer and its hydraulic and radionuclide retention properties (SKB 2010b). High grade commercial bentonites generally fulfil the requirements for the content of montmorillonite, organic carbon, sulphides and total sulphur specified in the design

64 specifications. For the contents of montmorillonite, organic carbon, sulphides and total sulphur, see for example Kiviranta and Kumpulainen (2011), Kumpulainen and Kiviranta (2010), Kiviranta et al. (2016) and Karnland et al. (2006). The content of montmorillonite, organic carbon, sulphides and total sulphur shall be quantified and their conformity with the reference design at the initial state shall be confirmed. In addition to these substances, the dominant cation and the cation exchange capacity (CEC) are important material parameters. The dominant cation, CEC and content of accessory minerals will vary between different bentonites, which can be seen in Table 3-14 where the mineral content in MX-80 and Ibeco RWC is specified. These material parameters are measured to control the quality of the purchased material. Table 3-14. Typical composition and characteristics of reference bentonites (Kiviranta et al. 2016). Mineralogical composition (in wt.%) determined with Siroquant except for the smectite and illite contents which were adjusted after Siroquant analysis based on chemical composition of purified clay fraction assuming all potassium was bound to illite. Values in parenthesis for selected minerals are calculated from chemical compositions, assuming that all sulphatic sulphur is bound to gypsum, all sulphidic sulphur to pyrite, all Ti to anatase or rutile, and all inorganic carbon to calcite (except for Friedland clay in which all inorganic carbon was assumed to be bound in siderite). See also (Kumpulainen and Kiviranta 2010, Kiviranta and Kumpulainen 2011). Wy-- BT0012** * Wy-- BT0013** * Wy-- BT0014** * Wy-- BT0017** * Wy-- BT0020** * Wy-- BT0020-3*** Wy-- BT0027 Wy BT0029 Smectite 83.3 81.1 78.1 83.3 83.1 86.0 82.0 88.0 Illite 0.8 1.2 1.1 0.8 0.2 0.3 0.5 0.5 Muscovite 3.4 2.7 Quartz 3.9 3.5 4.9 2.9 3.8 3.2 3.1 5.5 Cristobalite tr 0.5 tr tr 0.1 0.3 0.7 0.7 Plagioclase 6.4 8.3 8.4 7.4 5.5 2.5 6.2 2.2 Calcite tr (1.0) 0.6 (1.1) 1.3 (1.6) 0.3 (1.0) 0.2 (0.8) 0.8 (0.9) 0.3 (1.0) 0.9 (1.5) Dolomite 0.3 Ankerite 0.5 K-feldspar 2.2 1.9 3.6 1.8 2.1 0.9 3.2 0.7 Biotite tr tr tr tr Zircon tr tr tr tr Apatite tr tr tr Hematite tr tr 0.1 0.1 Lepidocrocite 0.2 Pyrite 0.7 (0.2) 0.5 (0.2) 0.7 (0.1) 0.5 (0.1) 1.5 (0.1) 1.0 (0.1) 1.8 (0.1) (0.1) Anatase 0.1 (0.2) (0.2) 0.1 (0.2) 0.0 (0.2) Rutile 0.9 (0.2) 0.6 (0.2) 0.5 (0.2) 1.6 (0.2) Gypsum 1.6 (1.0) 1.7 (1.2) 1.5 (1.1) 1.4 (1.1) (1.1) 1.7 (1.0) 1.7 (1.3) 1.3 (0.9) Pyroxene tr

65 Mi- NaA- BT0016 *,** Mi-- BT0019 *,** Mi- NaA- BT0023 Mi- NaA- BT0024 Fr-- BT0007 *,** Fr-- BT0009 xx- BT0001 xx- BT0002 xx- BT0003 xx- BT0004 Smectite 79.3 76.3 80.6 82.0 30.0 + 26.7 + 89.8 99.3 94.0 93.1 Illite 5.6 8.0 2.7 2.4 15.1 + 16.3 + 1.4 0.7 0.5 0.4 Kaolin 2.5 0.2 0.6 12.5 10.1 Vermiculite 3.1 Muscovite 7.4 9.2 Quartz 0.2 tr 1.1 1.3 27.4 31.6 3.7 tr 0.4 0.3 Cristobalite 0.8 0.7 0.7 0.6 Tridymite/Opal tr Plagioclase 3.4 9.0 6.0 4.8 1.4 3.5 4.7 Calcite 3.9 0.6 3.7 3.3 (8.9) (0.9) (7.4) (12.0) (0.1) (0.5) (0.1) (0.1) Dolomite 0.5 0.4 1.6 Siderite 2.4 0.3 (4.6) (0.5) K-feldspar 2.7 2.4 1.0 0.4 3.0 Biotite tr tr Chlorite tr Zircon tr Hematite 0.4 tr 0.4 0.8 0.1 Goethite tr Pyrite 1.2 1.3 1.4 1.1 (<0.04) (<0.04) (0.3) (1.1) (0.6) (0.6) (0.04) (<0.04) (<0.04) (<0.04) Magnetite 1.5 0.8 Anatase Rutile 0.2 (0.7) 0.2 (0.8) Gypsum (0.6) (0.4) Soda (hydrated) 2.4 0.6 (0.9) 1.8 (3.2) 0.4 (0.6) 1.2 (1.4) 1.1 (1.0) (0.7) (1.0) (0.3) (0.4) (0.1) (0.1) Notices: Phases observed with XRD or optical microscopy but not given quantified values were considered to be present only as traces (tr). * Smectite/illite contents were not adjusted because the information on purified clay fraction composition was not available. ** Measured with previous method (different equipment) described in Kiviranta and Kumpulainen (2011). *** XRD measurements were performed at Helsinki University. + Within interstratified illite-smectite. 1.6 (2.1) 2.0 (0.8) (0.4) 0.9 (1.8) 1.0 (1.9) Material ready for compression The water content of the reference processed bentonite material used for the compression of the end blocks, transition blocks, distance blocks and for the pellets is 17 %. For the ring shaped blocks the acceptable variation of the water content is ±1 %. Figure 3-18 presents the nominal granular distribution of the material and the acceptable upper (Max) and lower limits (Min) for the grading.

66 The production of the buffer and filling components shall be reliable and the raw material has to be in such a form that it allows compaction. Furthermore, the blocks shall be homogeneous and free from cracks and damages. The density and homogeneity of the produced blocks and pellets will depend on the grain size distribution and water content of the material to be compacted and on the compression pressure. To achieve high reliability in the production, the grain size distribution and water content must be specified. The specification will depend on the chosen bentonite material. The specifications of water content (17 %) and grain size distribution in Figure 3-18 are valid for MX-80. The grain size distribution is based on the laboratory test done by Ritola and Pyy (2011). Blocks and pellets Basic properties for the buffer blocks, pellets (reference design) and qualification are presented in Table 3-15. The densities are given as bulk densities since it is the bulk densities that are going to be inspected in the production. To determine the final saturated density of an initially unsaturated material the water content, grain density and porosity must be known. For a saturated material, the density of the dry material and porosity can be calculated if the water content is known. The saturated densities specified in the reference design are based on a grain density around 2,750 kg/m 3. This is the grain density of many bentonite clays. A different grain density requires an adjustment of the density of the buffer blocks. The grain density of MX-80 (and also Ibeco RWC) is between 2,750-2,780 kg/m 3 in different NaCl solutions (Karnland 2010, p. 20). 100 90 Passing percentage, % 80 70 60 50 40 30 20 10 0 0.01 0.1 1 10 Grain size, mm Average Max Min Figure 3-18. Nominal grain size distribution of MX-80 used in blocks and the allowed distribution limits.

67 Table 3-15. Preliminary buffer blocks and pellets for the reference design and methods to define them. Design parameter Design value Allowed Qualification deviation End blocks Water content of solid blocks 17 wt.-% ± 1%-unit See Ahonen et al. 2008, App. 3:11 Bulk density of solid blocks 2,051 kg/m 3 ± 23 kg/m 3 Weight and volume measurement Solid block outer diameter 1,740 mm +1/-1 mm Measurement Solid block height 350 mm +1/-1 mm Measurement Parallelism block bottom / top < 1 mm / Measurement 1,750 mm Ring blocks Water content of ring blocks 11 wt.-% ± 1%-unit see Ahonen et al. 2008, App. 3:11 Bulk density of ring blocks 2,092 kg/m 3 ± 22 kg/m 3 Weight and volume measurement Ring block outer diameter 1,740 mm +1/-2 mm Measurement Hole diameter in ring blocks 1,058 mm +1/-2 mm Measurement Ring block height 890-1,308 mm +1/-1 mm Measurement Pellets Bulk density separate pellets 2,050 kg/m 3 ± 80 kg/m 3 Measurement 2) Dimensions 11x11x5 mm 1) - - Bulk density of pellet filling 1,210 kg/m 3 ± 50 kg/m 3 Weight and volume measurement Water content of pellet filling 21% ± 1%-unit see Ahonen et al. (2008, App. 3:11) Distance blocks, transition blocks and filling blocks Bulk density 2,047 kg/m 3 Weight and volume measurement Water content 21% see Ahonen et al. 2008, App. 3:11 Diameter 1,765 mm ± 1 mm Measurement Length varies Measurement 1) Estimated dimensions for roller compacted pillow shape pellets 2) Volume measurement in paraffin oil or wax The dimensions and the shape of the pellets shall be such that they can be installed in the required open space in a reliable way. The dimensions need to be specified and inspected for the production but regarding the installed density it is sufficient to specify the bulk density of loose filling. The dimensions and density of individual pellets may be altered as long as they can be administrated into the gap and yield the required bulk density of loose filling. No compaction or vibration of the poured filling is used, since using compaction can result in the density being too high (Kivikoski and Marjavaara 2011).

68

69 4 CONFORMITY OF REFERENCE DESIGN WITH DESIGN BASIS The objective of this chapter is to verify the reference design of the buffer for OL1-2 type canister, i.e., that the densities and dimensions conform to the design basis and the initially installed buffer mass corresponds to a saturated density between 1,950 kg/m 3 and 2,050 kg/m 3. The buffer and filling components (distance block, supercontainer, transition zone etc.) are discussed individually in the following sections. @RISK calculations (@Risk - manual 2000) for each component are presented in Section 4.5. 4.1 Distance block Distance blocks are positioned between the supercontainers in the deposition drift. The nominal values and acceptable variations for the parameters related to a distance block section in the drift are presented in Table 4-1. The saturated density for distance block section was calculated varying the drift diameter and the distance block dry density. Calculated saturated densities are presented in Figure 4-1. Table 4-1. Parameters and their acceptable variation related to distance block section used in analysis. Parameter Nominal value Acceptable variation Drift diameter 1,850 mm +5/-0 mm Block diameter 1,765 mm * Block length 3,613 mm * Block dry density 1,712 kg/m 3 ± 20 kg/m 3 Block water content 21 wt.-% * Density of solids 2,750 kg/m 3 * *) No data on variation is available. Distance blocks Density at saturation (kg/m3) 2060 2040 2020 2000 1980 1960 2003 1998 1992 1986 1980 1975 1940 1,84 1,845 1,85 1,855 1,86 1,865 Diameter drift (m) Block dry density: 1732 kg/m3 Block dry density: 1712 kg/m3 Block dry density: 1692 kg/m3 Figure 4-1. Saturated density in distance block section with varying drift diameter and distance block dry density.

70 The figure shows that with nominal drift diameter (1.85 m) and nominal distance block dry density (1,712 kg/m 3 ) the saturated density of the buffer is 1,992 kg/m 3. With the nominal drift diameter and highest allowed dry density the saturated density is 2,003 kg/m 3, which is lower than the upper limit 2,050 kg/m 3. With the largest allowed drift diameter and lowest allowed dry density, the saturated density is 1,975 kg/m 3, which is larger than the lower limit 1,950 kg/m 3. 4.2 Supercontainer Supercontainer is a perforated titanium shell containing the canister and buffer components surrounding the canister. The perforation allows buffer to swell from within the supercontainer into the drift outside the supercontainer. A schematic drawing of a supercontainer is presented in Figure 4-2. Supercontainer data is based on information presented in Posiva (2016d) where additional information can be found. The nominal values and acceptable variations for each component in supercontainer section are presented in Table 4-2. Figure 4-2. Supercontainer unit. The measures are opened up in Table 4-2.

71 Table 4-2. Nominal values and acceptable variations for components in supercontainer section, c.f. details Posiva (2016d). Parameter Measure (in Nominal value Acceptable variation Figure 4-2) Drift diameter 1,850 mm + 5/- 0 mm Ring block dry density 1,885 kg/m 3 ± 20 kg/m 3 End block dry density 1,753 kg/m 3 ± 20 kg/m 3 Density of solids 2,750 kg/m 3 * Shell perforation 62% * Tot length SC l1 5,387 mm ± 6 mm Tot length canister l2 4,752 mm + 3.25/- 2.75 mm Length buffer ring l3 1,190 mm ± 1 mm Thickness buffer top block l4 350 mm ± 1 mm Thickness buffer bottom block l5 350 mm ± 1 mm Recess buffer top block l6 85 mm ± 1 mm Thickness top end plate t1 6 mm * Thickness bottom end plate t2 6 mm * Diameter canister d3 1,050 mm ± 1.2 mm Inner diameter buffer rings d4 1,058 mm ± 1.2 mm Diameter buffer rings and blocks d5 1,740 mm +1/- 2 mm Inner diameter SC d6 1,749 mm + 0/- 2 mm Diameter SC d7 1,761 mm + 0/- 2 mm Inner diameter of recess buffer d8 798 mm + 0/- 2 mm top block Diameter top recess canister d9 821 mm + 0/- 0.5 mm Axial gap canister/buffer top block g1 8 mm + 16.45/- 0.95 mm (recess) Axial gap canister/buffer top block g2 8 mm + 14.75/- 0.75 mm Radial gap canister/buffer top g4 11.5 mm + 12.5/- 11.25 mm block (recess) Radial gap canister/buffer rings g6 4 mm + 5.1/- 2.9 mm Radial gap buffer/sc g7 4.5 mm + 5.5/ -3 mm *) No data on variation is available. The saturated density of buffer in a drift with supercontainer was calculated by varying the dry densities of ring blocks and end blocks and the drift diameter. The calculations were performed with a constant titanium shell volume and also with the volume of titanium shell tripled (fully corroded case). The end plates of supercontainer were assumed to be solid. The calculation results are presented in Figures 4-3 and 4-4. Figure 4-3 shows the results calculated with the nominal drift diameter while Figure 4-4 shows the results calculated with the maximum drift diameter. More complex calculations varying all the parameters from Table 4-2 were also performed using @RISK program. These results are discussed in Section 4.5.

72 Density at saturation (kg/m3) Supercontainer, drift diameter 1.850 2025 2020 2022 2015 2010 2011 2005 2000 2001 2003 1995 1990 1992 1985 1980 1982 1975 1865 1875 1885 1895 1905 Dry density block (kg/m3) Constant titanium volume The volume of titanium tripled Figure 4-3. The average saturated density of buffer with the nominal drift diameter. Volume of titanium is varied along with the dry density of buffer blocks. The x-axis shows the dry density of ring blocks but the dry density of end blocks (1,753 ± 20 kg/m 3 ) is varied correspondingly. Density at saturation (kg/m3) Supercontainer, drift diameter 1.855 2020 2015 2014 2010 2005 2000 2004 1995 1996 1993 1990 1985 1985 1980 1975 1974 1970 1865 1875 1885 1895 1905 Dry density block (kg/m3) Constant titanium volume The volume of titanium tripled Figure 4-4. The average saturated density of buffer with the maximum drift diameter. Volume of titanium is varied along with the dry density of buffer blocks. The x-axis shows the dry density of ring blocks but the dry density of end blocks (1,753 ± 20 kg/m 3 ) is varied correspondingly. Figure 4-3 shows that nominal dry densities in ring blocks (1,885 kg/m 3 ) and end blocks (1,753 kg/m 3 ) along with constant titanium shell result in a saturated buffer density of 1,992 kg/m 3 when the drift diameter is nominal. When these conditions change to minimum dry density in ring blocks (1,865 kg/m 3 ) and end blocks (1,733 kg/m 3 ) the saturated density is 1,982 kg/m 3, which is higher than the lower limit 1,950 kg/m 3. When

73 these conditions change to maximum dry densities in ring blocks (1,905 kg/m 3 ) and end blocks (1,773 kg/m 3 ) with the volume of titanium shell tripled the saturated density of buffer will be 2,022 kg/m 3, which is lower than the upper limit 2,050 kg/m 3. Figure 4-4 shows that nominal dry densities in ring blocks and end blocks along with constant titanium volume result in a saturated buffer density of 1,985 kg/m 3 when the drift diameter is maximum (1,855 mm). When these conditions change to minimum dry density in ring blocks and end blocks the saturated density is 1,974 kg/m 3, which is higher than the lower limit 1,950 kg/m 3. With maximum dry density for ring blocks and end blocks and the volume of titanium tripled the saturated density for buffer is 2,014 kg/m 3, which is lower than the upper limit 2,050 kg/m 3. 4.3 Transition zone The transition zone is the zone on both sides of the compartment plug or next to the drift plug consisting of a pellet filling section and a transition block similar to distance block, see Section 3.4.3 for details. The transition zones are presented in Figure 3-16. The nominal values and acceptable variations regarding the transition zone are presented in Table 4-3. The shape of the dome shaped cap is not exactly circular so an estimated equivalent circle radius of 1.05 m is used in the calculations. The error is minimal when calculating the cap volume. The saturated densities in transition zones were calculated varying the drift diameter and the transition block dry density. Saturated densities in the transition zones are presented in Figures 4-5 and 4-6. Table 4-3. Nominal values and acceptable variations regarding the transition zone. Parameter Nominal value Acceptable variation Drift diameter 1,850 mm +5/-0 mm Block diameter 1,765 mm * Block length 6,310 mm * Block dry density 1,712 kg/m 3 ± 20 kg/m3 Block water content 21% ± 1% Pellet filling length 1,300 mm * Pellet dry density 1,000 kg/m 3 * Pellet filling water cont. 21% * Cap radius 1.051 m * Cap height 400 mm * Density of solids 2,750 kg/m 3 * *) No data on variation is available.

74 Density at saturation (kg/m3) 1980 1960 1940 1920 1900 Transition zone (convex side) 1948 1938 1928 1943 1933 1923 1880 1,84 1,845 1,85 1,855 1,86 1,865 Diameter drift (m) Block dry density: 1732 kg/m3 Block dry density: 1712 kg/m3 Block dry density: 1692 kg/m3 Figure 4-5. Saturated average density in the transition zone (convex inner side) varying the drift diameter and the transition block dry density. Density at saturation (kg/m3) 2000 1980 1960 1940 1920 Transition zone (concave side) 1950 1940 1930 1945 1936 1926 1900 1,84 1,845 1,85 1,855 1,86 1,865 Diameter drift (m) Block dry density: 1732 kg/m3 Block dry density: 1712 kg/m3 Block dry density: 1692 kg/m3 Figure 4-6. Saturated average density in the transition zone (concave outer side) varying the drift diameter and the transition block dry density. Figure 4-5 shows that with the nominal drift diameter and highest allowed block dry density the average saturated density of the transition zone is 1,948 kg/m 3, which is close to the the lower limit 1,950 kg/m 3 for buffer. All the other cases result in lower saturated density of transient than the lower limit. Figure 4-6 shows that no acceptable configuration results in a saturated density of buffer above the lower limit 1,950 kg/ m 3. The transient zone design is, however, based on having density distribution inside the zone (see Section 3.4.3) and therefore the average density cannot be used to assess the conformity.

75 4.4 Innermost drift section The innermost drift section includes a 500 mm long section of the drift. The length of pilot hole may vary and it is assumed to be 2 m for design purposes with a diameter of 152 mm. The drift section is filled with a 500 mm long distance block and the pilot hole is filled with bentonite blocks with a diameter of 132 mm. The design is presented in Section 3.4.5, c.f. Figure 3-17. An example of what the pilot hole may look like is presented in Figure 4-7. The calculations for the saturated buffer density in drift bottom were performed by varying the drift diameter and the dry density of the bentonite blocks. The saturated density in innermost drift section (bottom) is presented in Figure 4-8. Figure 4-7. The drift bottom of the 95 m drift at the Äspö HRL (220 m level) showing the pilot hole stub (Posiva 2016f). Density at saturation (kg/m3) Drift bottom 2040 2020 2000 1999 1993 1987 1980 1982 1976 1971 1960 1940 1,84 1,845 1,85 1,855 1,86 1,865 Diameter drift (m) Block dry density: 1732 kg/m3 Block dry density: 1712 kg/m3 Block dry density: 1692 kg/m3 Figure 4-8. Saturated average buffer density in drift bottom varying the drift diameter and block dry density.

76 Figure 4-8 shows that with nominal drift diameter and nominal block dry density the saturated density of the buffer is 1,987 kg/m 3. With the nominal drift diameter and highest allowed dry density the saturated density is 1,999 kg/m 3, which is lower than the upper limit 2,050 kg/m 3. With the largest allowed drift diameter and lowest allowed dry density, the saturated density is 1,971 kg/m 3, which is larger than the lower limit 1,950 kg/m 3. 4.5 Calculations using the @RISK code The code @RISK was used to perform a risk analysis for the saturated buffer densities in the different drift sections. Monte Carlo simulation was performed with 45,000 calculations for each drift section. The parameters with acceptable variances were given a triangular distribution where the nominal value is the most probable and the probability reduces when approaching the limits of acceptable variation, see detailed description in (Juvankoski 2013). The distributions for saturated buffer densities are presented in Figures 4-9 through 4-14. Figure 4-9. The distribution of saturated distance block densities. Figure 4-10. The distribution of saturated buffer densities inside supercontainer assuming a constant titanium volume.

77 Figure 4-11. The distribution of saturated buffer densities inside supercontainer assuming a tripled titanium volume. Figure 4-12. The distribution of saturated transition zone densities (convex side of the plug).

78 Figure 4-13. The distribution of saturated transition zone densities (concave side of the plug). Figure 4-14. The distribution of saturated densities at the drift bottom. The transition zones were found to be the only sections in the drift where the saturated density of filling component is at risk to have a value below the lower limit 1,950 kg/m 3. In the simulations, the transition zone on the convex and concave side of the plug had saturated density below 1,950 kg/m 3 in all of the cases. The largest uncertainty in the dimensioning is the friction angle (see Section 3.4.3 for uncertainties), this has also effect on the density distribution both radially to drift axis and along it.

79 4.6 Thermal behaviour of bentonite buffer In this section the impact of the heat transport in the buffer on the total temperature drop between the rock and the canister is investigated. In the design basis, it is stated that the maximum temperature in the buffer shall be less than 100 C, which specifies the highest allowed temperature at the interface between canister and buffer. The temperature in the buffer depends on many parameters like thermal properties of buffer and rock, conditions in the gaps, decay power and interaction of canisters, which can be adjusted by changing deposition drift and canister spacing. The thermal conductivity of the bentonite buffer, which is rather low compared to conductivity of other materials, strongly depends on the saturation rate. Temperatures are determined for three cases: a) at initial condition, b) with artificially wetted outer gap and c) outer gap filled with saturated bentonite and saturated buffer case. The initial condition (case a) means the conditions experienced immediately after disposal. Artificial wetting (case b) takes place after about two weeks after disposal. A fully saturated buffer case (case c) is reached within a few decades. The principal layout of the Posiva Oy repository at Olkiluoto is shown in Figure 4-15 at the depth of 420 m. The analyses were made for the Finnish BWR and PWR fuel canisters of Olkiluoto and Loviisa nuclear power plants. The maximum allowable temperature in a canister shall be limited to the design temperature of +100 o C. Due to uncertainties and natural variation in parameters involved in the thermal analysis the allowable calculated maximum canister/buffer interface temperature (reference temperature) is set to 95 o C rendering a safety margin of 5 o C. The work consists of first the adaptation, checking and verification of the calculation process and then the analyses of the repository. The work is reported in Ikonen and Raiko (2015) which describes the basis for evaluation, thermal properties, details of calculation and results). The primary results of the work are presented here.

80 Figure 4-15. Principal layout of the Olkiluoto repository (Posiva Oy). The temperature of the whole panel is calculated with an analytical model taking into account a great number of canisters. For this an in-house computer code named OSASTO has been developed by VTT (Ikonen and Raiko 2015). The different canister spacings caused by transition blocks around the plugs are taken into consideration. The result is the highest surface temperature of a canister, which is located in the middle of the compartment area. The deposition schedule and order of the canisters are taken into account in the calculation process. Initial condition (Case a) The maximum temperature evolution for BWR, VVER 400 and EPR canister panels is shown in Figure 4-16. The eccentricity effect is taken into account by lowering the canister temperature. First the canister having maximum temperature in the panel is searched and then the temperature evolution for that canister is determined and presented as curves in Figure 4-16. The temperature evolution of the rock surface related to the same canister is also plotted. The time in Figure 4-16 is measured from the time at which the canister having maximum temperature is emplaced. With greater times (over 100 years) the greater difference between the temperature curves of the different canister types is caused by the different decay heat powers. Figure 4-17 presents the temperatures and temperature differences after 15 years when maximum temperature is reached. VVER canister has higher temperature than BWR and EPR canisters. In Figure 4-17 the temperatures and temperature differences are at highest after about 15 years. Large number of canisters on the central areas has nearly same temperature profile as in Figure 4-17. With longer times temperatures and temperature differences decrease due to canister thermal power decrease. Figure 4-18 shows the temperatures and temperature differences when maximum temperature is reached, on the

81 canister surface in the buffer, in the supercontainer and in the rock both in case of a single BWR canister and representing the hottest canister at initial condition. Figure 4-16. KBS-3H maximum temperature evolution of a BWR, VVER and EPR canisters at initial condition (Case a) (Ikonen and Raiko 2015). Figure 4-17. KBS-3H temperature profiles of a BWR, VVER and EPR canisters at initial condition (Case a) (Ikonen and Raiko 2015).

82 Figure 4-18. Temperature profiles of a BWR supercontainer and near-field rock for the initial condition of the hottest canister of the panel and, for comparison only, for a single supercontainer (average air gap) (Ikonen and Raiko 2015). Temperatures with artificially wetted outer gap (Case b) This case is like an initial condition case having the inner air filled gap, but in the outer gap air is replaced by water having an improved thermal conductivity, see (Ikonen and Raiko 2015) for details. The results of calculations are presented in Table 4-4. When compared to initial condition case, the artificially wetted outer gap lowers the canister surface temperature about 4 C. Artificial wetting was not assumed to cause permanent humidity changes in the bentonite buffer. Saturated case (Case c) In the saturated buffer case the air space in the gaps is filled with saturated bentonite, whose thermal conductivity is set to 1.3 W/m/K. The air gap 15 mm on the top end (right) of the canister is also filled with bentonite. The maximum temperature evolution for BWR, VVER and EPR canister panels is presented in Figure 4-19. The time is measured from the time, when the canister having the maximum temperature is emplaced, see details in (Ikonen and Raiko 2015). Figure 4-20 shows the temperature profiles from the moment, when the maximum temperature on the canister surface is reached. Large number of canisters on the central areas has nearly same temperature profile as in Figure 4-20. VVER canister has about 2.0 C higher temperature than BWR and EPR canisters as in the initial condition case. Figure 4-21 shows the maximum temperatures on the canister surface, in the buffer, in the supercontainer and rock in case of a single BWR canister and in saturated buffer conditions. The maximum canister surface temperatures in the whole canister panel are shown in Table 4-4.

83 The time to attain buffer saturation cannot be known precisely beforehand. That is why the maximum canister temperatures can be somewhere between the initial condition case (Figure 4-16) and the saturated buffer case (Figure 4-19). Figure 4-19. Maximum temperature evolution of BWR, VVER and EPR canisters in a saturated buffer (Case c). The time is measured from the moment, when the canister having maximum temperature is emplaced (Ikonen and Raiko 2015). Figure 4-20. Temperature profiles of BWR, VVER and EPR canisters in saturated buffer case (Case c) (Ikonen and Raiko 2015).

84 Figure 4-21. Temperature profiles of a BWR canister in saturated case (Case c) and for the hottest canister in the panel, and for comparison, only for a single canister (Ikonen and Raiko 2015). Table 4-4. KBS-3H maximum temperature for the BWR, VVER and EPR fuel canisters. Drift spacing 25 m (Ikonen and Raiko 2015). Conclusions The results show that acceptable temperatures are not exceeded and give quidance to proper canister spacings. Initial values, related to dimensions with tolerances, are chosen so that temperatures are conservatively overestimated. The temperatures were determined in the initial conditions (Case a), with artificially wetted outer gap (Case b) and in the saturated buffer case (Case c). Artificial wetting was not assumed to cause permanent humidity changes in the bentonite buffer. The maximum temperature on the canister/buffer interface is limited to the design temperature of +100 o C. However, due to uncertainties in parametes governing the analysis of thermal evolution (e.g. variation in rock thermal conductivity) the allowable calculated maximum canister/ buffer interface temperature is set to 95 o C leaving a safety margin of 5 o C. The allowable temperature can be controlled by adjusting the spacing between adjacent canisters, adjacent drifts and the distance between individual panels of the repository and by adjusting the pre-cooling time affecting thermal power of the canisters. In the horizontal disposal the inner air gap is closed underneath the cylinder and heat transfer at the contact area is improved, when compared to corresponding axisymmetric

85 case. The effect of eccentricity was studied by a 2D model in the cross-section of a canister. Sensitivity analyses of the effect of different parameters were made also. Thermal conductivity and capacity of rock, thermal conductivity of bentonite, the emissivity of the copper surface, the gap width on the canister surface, the canister spacing and the precooling time were varied. The result was that for the initial conditions (case a) the temperature on the canister/buffer interface was 2.9 3.7 o C lower than that of the corresponding KBS-3V configuration. Despite the fact that the maximum temperature in KBS-3H is only about 2.9 3.7 C lower than in KBS-3V when using the same canister spacing, the minimum canister spacings in KBS-3H (based on the thermal analysis alone) would be for BWR 8.0 m, for VVER 6.4 m and for EPR 9.1 m, when the allowable temperature is 95 C. 4.7 Maintaining swelling pressure, hydraulic conductivity and shear strength With nominal drift diameter (1.85 m) and nominal distance block dry density (1,712 kg/m 3 ) the saturated density of the buffer is 1,992 kg/m 3. With the nominal drift diameter and highest allowed dry density the saturated density is 2,003 kg/m 3, which is lower than the upper limit 2,050 kg/m 3. With the largest allowed drift diameter and lowest allowed dry density, the saturated density is 1,975 kg/m 3, which is larger than the lower limit 1,950 kg/m 3, see Figure 4-1. Buffer inside supercontainers with nominal dry densities in ring blocks (1,885 kg/m 3 ) and end blocks (1,753 kg/m 3 ) along with constant titanium shell result in a saturated buffer density of 1,992 kg/m 3 when the drift diameter is nominal. When these conditions change to minimum dry density in ring blocks (1,865 kg/m 3 ) and end blocks (1,733 kg/m 3 ) the saturated density is 1,982 kg/m 3, which is higher than the lower limit 1,950 kg/m 3. When these conditions change to maximum dry densities in ring blocks (1,905 kg/m 3 ) and end blocks (1,773 kg/m 3 ) with the volume of titanium shell tripled the saturated density of buffer will be 2,003 kg/m 3, which is lower than the upper limit 2,050 kg/m 3, see Section 4.2. In the design basis, it is stated that the buffer after swelling should uphold the minimum swelling pressure of 1 MPa to rule out advection, and the hydraulic conductivity of the buffer should not exceed 10-12 m/s. In addition, the buffer has to protect the canisters in the event of rock shear movements. It is also stated in the design basis that the sulphatereducing bacteria cannot survive in bentonite if the bentonite is compacted to a density corresponding to a swelling pressure of 2 MPa. With an additional margin to account for losses due to piping and erosion, this leads to the requirement that the saturated density must exceed 1,950 kg/m 3. In the design basis, it is also stated that the buffer material designed or proposed for use in a repository at a given location must be able to fulfil the performance requirements under maximum groundwater salinity. The groundwater salinity (TDS) at the repository level shall, in general, be below 35 g/l but local or temporal variations up to 70 g/l can be allowed (Posiva 2012b; L3-ROC-15). This corresponds to about 1.2 M in NaCl.

86 Furthermore, in the design basis it is stated that if the saturated buffer density is between 1,950-2,050 kg/m 3, the swelling pressure, hydraulic conductivity and shear strength will be maintained. It has been calculated that the density of buffer at saturation inside supercontainer and distance blocks will be between 1,950-2,050 kg/m 3 with almost all combinations of parameter values within the allowable ranges. Karnland et al. (2006) has investigated the relation between saturated density and swelling pressure and the relation between saturated density and hydraulic conductivity for different salt concentrations. The investigations are made for MX-80, which is an example of a buffer material according to the specification for the reference design. The results are presented in Figure 4-22 for MX-80. In Figure 4-23 the same results are presented for Ibeco RWC. The results show that the reference material for the specified density interval maintains the minimum swelling pressure and the maximum hydraulic conductivity with a large margin. The swelling pressure of the bentonite buffer was also evaluated by Juvankoski (2013) according to different relationships presented in literature. Evaluating the swelling pressure according to the equations presented in Hedin (2004, eq. 21, 22, p. 30; parameters A and B from Baumgartner et al. 2008 in Hedin 2004, p. 10), the swelling pressure of the buffer for an average saturated density of 2,010 kg/m 3 is 9.4 MPa for fresh water, 8.8 MPa for water containing NaCl 10 g/l and 5.9 MPa for water containing NaCl 70 g/l. The maximum swelling pressure is 13.3 MPa (saturated density 2,050 kg/m 3 and fresh water) and the minimum swelling pressure is 2.9 MPa (saturated density 1,950 kg/m 3 and salt concentration NaCl 70 g/l). Evaluating the swelling pressure for purified and calcium converted MX-80 material according to the relationship and parameters presented in Karnland 2010 (eqn. 5-9, p. 26), the swelling pressure for an average saturated density of 2,010 kg/m 3 is 12.2 MPa. The maximum value of the swelling pressure is 17.7 MPa (saturated density 2,050 kg/m 3 ) and the minimum pressure is 7.1 MPa (saturated density 1,950 kg/m 3 ). The statistical calculations (see Section 4.5) showed that the average density of buffer will meet the requirements. Shear The design basis, Chapter 2, defines that the buffer shall be designed so that it will mitigate the mechanical impact of the expected rock shear displacement on the canister to the level that the canister integrity will be preserved. The effect of shear has been evaluated in (Juvankoski 2013) and in (Posiva 2013).

87 Figure 4-22. Swelling pressure (left) and hydraulic conductivity (right) in the Wyoming MX-80 reference material (WyR1) versus saturated bentonite density. The legends show the NaCl concentrations in the test solutions in successive contact with the WyR1 test sample (Karnland 2010, p. 24; original reference to Karnland et al. 2006). Figure 4-23. Swelling pressure (left) and hydraulic conductivity (right) in the IBECO RWC material (MiR1) versus saturated bentonite density. The legends show the concentrations in the test solutions in successive contact with the MiR1 test sample (Karnland 2010, p. 24; original reference to Karnland et al. 2006). The measurements were made using NaCl solution.

88 The properties of the buffer that affect the response to a rock shear are the bentonite type, the density which yields a swelling pressure, the shear strength, the stiffness before the maximum shear stress is reached and the shear rate, which also affects the shear strength (Börgesson et al. 2010, p. 3). Description of the modelling presented here is found in (Posiva 2013) and is described in detail by (Börgesson et al. 2010) and the application for the modelling is described by (Hernelind 2010). The most important properties of the bentonite for the rock shear are the stiffness and the shear strength. These properties vary with bentonite type, density and rate of strain. Ca-bentonite has higher shear strength than Na-bentonite and the shear strength increases with increasing density and strain rate. Since it cannot be excluded that the Na-bentonite MX-80 will be ion-exchanged to Ca-bentonite after a long time period, the properties of Ca-bentonite are used in the modelling. The result is a slightly conservative starting point, but the difference between these materials is rather small. Since the acceptable density at saturation of the buffer material is 1,950 kg/m 3 2,050 kg/m 3 the highest density 2,050 kg/m 3 is used in the modelling, again providing a conservative basis for the analysis. The bentonite is modelled as linear elastic combined with von Mises plastic hardening. The plastic hardening curve is made as a function of the strain rate of the material. The reason for the latter relation is that the shear strength of bentonite is rather sensitive to the strain rate. It increases by about 10 % for every magnitude increase in strain rate. Since the rock shear in conjunction with an earthquake is estimated to be 1 m/s the influence is strong and the resulting shear strength will be different in different parts of the buffer. Figure 4-24 shows the material model. The stress-strain relation is plotted at different strain rates. The bentonite buffer is strongly plasticized during the rock shear, which helps to protect the canister. Figure 4-25 shows the plastic strain after 10 cm shear. Figure 4-24. Material model of the bentonite buffer at density of 2,050 kg/m 3 at different strain rates.

89 KBS-3H KBS-3V Figure 4-25. Plastic strain in the entire bentonite buffer after 10 cm rock displacement. See Posiva (2013), Section 5.7.2 for details. The conclusions of the performed modeling of one of the most severe cases of rock shear through KBS-3H are that the difference in consequences of the rock shear between KBS- 3H and KBS-3V repository design variant is insignificant at the same type of shear (Posiva 2013). It has also been concluded that the consequences of the uncertainties regarding the differences between the two alternatives are insignificant. This means that the results and conclusions of the extensive investigations and modeling exercises of a rock shear in KBS-3V can also be used for KBS-3H. The effect of rock shear through a deposition hole in KBS-3V has been extensively investigated for SR-Site and is reported by (Hernelind 2010). The purpose of the work undertaken to address this issue was to model one of the worst cases with respect to stress transfer and to compare the results obtained for the KBS-3H and KBS-3V geometries. The KBS-3V finite element model has been used as the basis for modelling but the geometry is changed for the KBS-3H orientation and the supercontainer has been included. One of the most severe rock shear cases has been modeled for KBS-3H with identical element mesh, material models and modelling technique as was used for KBS-3V. The only substantial difference in these two models is the difference in geometry that exists between the two concepts and the supercontainer that is present in KBS-3H. The comparison shows that the supercontainer shell is so strongly deformed close to the shear plane that it would probably break and that otherwise the difference between the effects of a rock shear in the two concepts is very small for the stresses in the bentonite and negligible for the stresses in the canister. The very small difference in behavior observed seems to favor KBS-3H since in the supercontainer there is an extra 5 cm thickness of bentonite buffer outside the canister, and secondly, the thick bentonite blocks between

90 the consequent supercontainers decrease the load effects of rock shear on the copper lids of the canister. The supercontainer can therefore be assumed to be capable of withstanding a 5 cm rock shear of the type evaluated for the KBS-3V canister according to the supplementary analyses made (Posiva 2013). 4.8 Design basis from other barriers, production and operation 4.8.1 Deposition of canister The installed buffer shall contain a hole large enough for deposition of the canister. The installation with required dimensions is presented in the Supercontainer production report. 4.8.2 Compactibility of the bentonite material When a bentonite product and supplier is selected it shall be verified that it is possible to compact the bentonite from the selected deposit to the required density. Tests in which blocks are pressed from bentonite samples with different grain size distributions and water contents will be performed. It shall be verified that it is possible to compact the bentonite to the required density. It must be verified that raw bentonite can be re-mixed with addition of water to achieve accurate water content while maintaining suitable grain size distribution (mixing can cause particle shape variations which can affect compactibility). The required grain size distribution, water content and pressure must be adapted to the selected bentonite product, i.e. the reference material ready for compression presented in Section 3.5 is only valid for MX-80 and must be revised if another material is selected. Chapter 5 addresses the reference compaction methods, as well as other manufacturing aspects. 4.8.3 Installation of buffer and filling components The installation of buffer and filling components is presented in Posiva (2016d). The same equipment that has been used for supercontainer installation, will be used for distance blocks. The buffer and filling components shall be designed so that installation can be performed with high reliability. Details in the block and pellet design that will impact the reliability of the installation are the water content and the dimensions. Relatively high water content will limit damage caused by exposure to high relative humidity (RH). Isostatically compressed MX-80 blocks and roller compacted pellets with a water content of 17 % used for example in the small-scale buffer tests have been handled, machined, packaged, transported and stored successfully (Kivikoski and Marjavaara 2011, Marjavaara et al. 2013)

91 The blocks must be designed so that they are possible to lift, transport and install with high reliability, preferably by applying well-tried techniques and equipment. The dimensions of the blocks are adapted so that their weight will allow the use of lifting and transport equipment. The dimensions and shape of the pellets must allow that they can be administered in the gaps adjacent to plugs and filled it to the specified bulk density. Tests that verify the water content and dimensions according to the reference design resulting in a reliable production have been performed in laboratory conditions (Kivikoski and Marjavaara 2011, Marjavaara et al. 2013). 4.9 Summary of results and conclusions 4.9.1 Material composition In VAHA the required montmorillonite content and the allowed content of organic carbon, sulphides and total sulphur are stated. The related buffer and filling component property and design parameters determined in the design are: - Buffer and filling component property: material composition, - Design parameters: content of montmorillonite, sulphide, total sulphur and organic carbon. The montmorillonite content shall be sufficient for the buffer material to have capacity to yield the required hydraulic conductivity and swelling pressure and to create an environment where microbes do not survive for a long period. Furthermore, the buffer must not result in stiffness and shear strength exposing the canister to larger stresses than assumed for the dimensioning shear load case. The content of sulphides and total sulphur must not cause significant canister corrosion and the content of organic carbon must not impact radionuclide transport. The contents specified for the reference buffer material conform to the contents specified in VAHA. 4.9.2 Initially installed mass and density at saturation For the specified buffer and filling component material, the initially installed density shall be sufficient for the buffer to maintain its barrier functions, i.e. to limit flow of water; keep the canister in its centred position in the deposition drift; limit microbiological activity; prevent transport of colloids and not significantly impair the barrier functions of the engineered barriers or rock. In the design basis (Chapter 2) it is stated that the saturated buffer density shall be higher than 1,950 kg/m 3, i.e. sufficiently high for example to limit microbiological activity (SKB 2006a, p. 373) and less than 2,050 kg/m 3 to prevent too high of a shear impact on the canister. It is also stated that if the saturated density fulfils these conditions then the design basis for hydraulic conductivity, swelling pressure etc. required to maintain the other barrier functions are also met. The related buffer property and design parameters determined in the design are:

92 - Buffer property: installed density, - Design parameters: the water content (in the material ready for compression) and bulk density of buffer blocks. The installed density will depend on: - The dimensions of the deposition drift, the installed blocks and the canister, and - The densities and water contents of the blocks and the filling components. In Section 4.1 through 4.5 all these parameters, with exception of the dimensions of the canister and the inner gap, have been varied within their acceptable limits and the resulting saturated density has been calculated. The conclusion is that in almost all cases the saturated density of the buffer will lie within the acceptable limits for all acceptable cross sections of the deposition drift and buffer block. The densities of filling components will as well lie within acceptable limits. In case of the filling component transient zone adjacent to plugs the average density falls in certain cases below the limits for buffer. The transient zone design is, however, based on having density distribution inside the zone see Section 3.4.3 and therefore the average density cannot be used to assess the conformity to design basis. 4.9.3 Dimensions The buffer and filling component dimensions used as the reference dimensions are as described in Chapter 3. The related buffer and filling component properties and design parameters determined in the design have been presented in Sections 3.3 and 3.4. The dimensions are regarded as nominal, i.e. to the stated dimensions, where variations that may occur in the production have to be added when evaluating the final dimensions. The supercontainer system enables well controlled and precise centering of canister inside the buffer blocks which remains during installation, therefore ensuring the required buffer thicknesses will remain inside the specified limits. 4.9.4 Thermal properties The buffer and filling component geometry (e.g. void spaces), water content and distances between deposition drifts should be selected such that the temperature in the buffer is <100 C (Posiva 2012a). Also, the distances between canisters are selected to conform to this performance target (Ikonen and Raiko 2015). The increase in temperature will be largest for buffer with low thermal conductivity, i.e. for a dry buffer and an inner gap between the canister and buffer. In the case of saturated buffer, the temperature at the canister surface is at most 76.6 C. The maximum temperature in an artificially wetted outer gap is 89.0 C and the initial condition the

93 maximum temperature is 93.0 C, which ensures that the maximum temperature in the buffer stays well below 100ºC. 4.9.5 Maintaining swelling pressure, hydraulic conductivity and shear strength After swelling the buffer shall uphold the minimum swelling pressure, the allowed hydraulic conductivity and the allowed shear strength in an ambient groundwater salinity of < 70 g/l (TDS) (NaCl 1.2 M). The buffer property to be designed to conform to this requirement (target property for the host rock) is the material composition, i.e. the montmorillonite content and the density. Based on laboratory tests of MX-80, which is an example of a bentonite with a montmorillonite content according to the Juvankoski (2013), it is confirmed that at a saturated density of 1,950 kg/m 3 to 2,050 kg/m 3, the hydraulic conductivity will be less than 10-12 m/s and the swelling pressure will exceed 2 MPa for salt concentrations up to 70 g/l (TDS, 1.2 M, see Section 4.7) as specified in the design basis. The penetration of buffer through the perforated holes in the supercontainer in the gap between rock and supercontainer and subsequent radial density is under research. The shear strength will depend on the density and dominating cation. High densities and the ion change of bentonite (sodium to calcium cations) will result in a stiffer buffer and severe load on the canister. The strength will also depend on the deformation rate. Also based on tests of MX-80, it is confirmed that a buffer with calcium as the dominating cation at a saturated density of 1,950-2,050 kg/m 3 will have the shear strength presumed for the shear load case analysed in SKB (2010b, Section 4.5).

94

95 5 PRODUCTION OF THE BUFFER AND FILLING COMPONENTS The production line of the buffer and filling components is presented in this chapter based on Juvankoski et al. 2012). The production line depicts how the buffer and filling components are produced, installed and inspected, applying the current reference methods. The buffer and filling components consists of the buffer blocks inside the supercontainer, distance blocks and filling components presented in Chapter 3. 5.1 Overview 5.1.1 Requirements for the production of the buffer and filling components The design basis that is used in developing the methods of production, testing and inspection of the buffer and filling components are presented in this section. The overview of the buffer and filling components production process is presented in Figure 5-1. In total, about 4,500 canisters of types LO1-2, OL1-2, OL-3 and OL-4 and corresponding supercontainers are emplaced in deposition drifts. The manufactured buffer and filling components shall lie within the acceptable limits specified for the reference design in Sections 3.3 and 3.4. In addition, the design considerations presented in Chapter 2 shall be kept in mind when developing the methods, i.e. systems and processes for preparation, installation, testing and inspection of the buffer. The methods must also be applicable for the current reference sequence for deposition of the canister, buffer and filling components. The reference sequence for deposition is briefly described in Posiva (2016d) and Posiva (2013). Figure 5-1. Overview of the buffer and filling component production process.

96 5.1.2 Production line for the buffer and filling material The production line of the buffer and filling components is comprised of the following five main parts: - Procurement of material, - Manufacturing, - Storage and transportation of components, - Preparation of the deposition drift, cleaning, installation and inspection, - Emplacement of components including the installation of supercontainers, distance blocks, plugs and filling components. The buffer and filling component production line is presented in Figure 5-2. The subtasks are also presented in this figure. The presented production line is valid for MX-80 type sodium bentonite. The manufacturing of blocks and pellets is material specific and needs to be adapted to the selected material in order to obtain blocks and pellets with the required properties. The buffer and filling component production line begins with the procurement of bentonite material, continues with the manufacturing of buffer and filling components, which is followed by the storage of the components, the preparation of the drift, the installation of the various buffer components into the deposition drift, removal of any temporary elements from the deposition drift and finally completing the filling with plugging the drift. At the end of the buffer and filling component production line, the completed deposition drift is filled to the level where the drift plug starts. The supercontainer (including buffer blocks), distance block and filling block installation procedure is presented in Posiva (2016d). The installation of plugs is presented in Posiva (2016e).

97 Procurement of Material Excavation and pre-processing Material Delivery and Intermediate Storage at the Harbour Transport and Storage at the Production Plant Manufacturing Conditioning of the Bentonite Pressing of the Blocks Machining of the Blocks Manufacturing of the Pellets Protection of the Blocks and Pellets Storage and Transportation of Components Intermediate Storage at Ground Level Transport to Storage at the Repository Level Preparation of the Deposition Drift Cleaning, installation (pipes, fastening rings and collars for plugs) and inspection. Emplacement of supercontainers Emplacement including the Installation of filling components Emplacement of filling components Plugging and water filling of compartment Operation of next compartment Plugging of the Deposition drift Plugging, filling and water filling Figure 5-2. Buffer and Filling component production line. Sub-tasks are also shown.

98 5.1.3 Reference methods for manufacturing and installation The reference methods for manufacturing of blocks and pellets are based on existing techniques used in other industrial fields. These methods are adapted to the disposal needs so that the blocks and pellets, according to the reference design, are possible to manufacture. Conventional techniques are also adapted for the transport, handling and storage of blocks and pellets. The installation of blocks and pellets has been developed and tested in different scales and will later be tested in repository conditions. Installation was tested and demonstrated in MPT project that is part of the KBS-3H project and also part of LucoeX-project. Reports are available from www.lucoex.eu. The buffer blocks are manufactured with the isostatic compression method (Ritola and Pyy 2011), which is Posiva s reference method for block manufacturing. The reference method for manufacturing of pellets is roller compaction of small briquettes (Marjavaara et al. 2013). The selected reference method for installation of the blocks and filling components is descibed in Posiva (2016d). 5.1.4 Reference strategy and methods for test and inspection The purpose of the tests and inspections is to assure that the properties of the materials and components of the buffer and filling components fulfil the requirements set for them. The tests and inspections are performed in every stage of the production line. The type of test and inspection and the number of tests will be defined in the quality plan. These tests are to ensure that only material and components that fulfil the quality requirements are used in production. The methods for testing and inspection are based on existing reliable techniques from other industrial fields. The accuracy of the measurements shall lie within the acceptable variations of the properties to be inspected. Conventional techniques and equipment with sufficient accuracy of measurement are available. 5.1.5 Design parameters and production inspection schemes The design parameters that are used to specify the reference design of the buffer and filling components are described in Chapter 3. These parameters shall, directly or indirectly, be inspected during the production of the buffer and filling components to confirm that the produced buffer and filling components conforms to the reference design. The outcome of the design parameters need to be known for the initial state. The properties required with respect to the long-term safety and the production (Chapter 2), the design parameters and parameters inspected in the production and their relations are accounted for in Tables 5-1 and 5-2.

99 Table 5-1. Required properties and related design parameters and parameters inspected in the production. Required property Design parameter Parameter inspected in the production Material composition Montmorillonite content X-ray diffraction pattern Sulphide content Combustion gases Total sulphur content Combustion gases (including the sulphide) Organic carbon Combustion gases Compaction properties of Grain size distribution Sieving curve material ready for compression Water content Weight before and after drying Density and dimensions of blocks Density and dimensions of pellets Bulk density Dimensions Bulk density of separate pellets Dimensions Bulk density of loose filling Weight and volume by dimensions Height Outer diameter Hole diameter of ring shaped blocks Weight and dimensions of individual pellets Diameter (or thickness and width) and length of separate pellets Weight and volume of loose material Table 5-2. Required properties, related design parameters and parameters inspected in the production. Required property Design parameter Parameter inspected in the production Buffer and filling Bulk density of blocks Weight of the blocks to be installed component density* Bulk density of pellet filling Weight and volume of the pellets to be installed Volume of pellet filled Geometry of the deposition drift volume*** Position of the installed blocks and drift components Installed geometry** Buffer and filling components thickness Volume of pellet filling Diameter / geometry of the hole inside the installed ring blocks**** Geometry of the deposition drift Dimensions of the blocks to be installed Positions of the installed blocks and drift components Geometry of the deposition drift Dimensions of the blocks to be installed Positions of the installed blocks and drift components Dimensions of the blocks to be installed in supercontainer Positions of the installed blocks * Last weight measurement of the blocks is taken during installation by the installation machine ** Geometry of the deposition drift and dimensions of the blocks are measured prior to installation *** Calculated according to scanned hole volume and buffer and filling components block dimension **** Part of supercontainer assembly.

100 To give an overview of the production and how the design parameters are processed and inspected within each stage, production-inspection schemes illustrating the main parts of the production and the stages they include are presented. For each design parameter and stage, the performed processes and inspections are presented. Details about the production processes are given in the text about each stage. The text about each stage also includes an account for the inspections performed within the stage. The methods for testing and inspection are presented separately for each main part of the production. The production inspection scheme for the whole process is presented in Table 5-3. The phases in which the inspection takes place are divided in Table 5-3 into 12 parts that are presented in Figure 5-3. In this table the points of inspection are denoted with a star. The inspected properties, which contain the design parameters, are divided into material composition, compaction properties, density and dimensions of blocks, density and dimension of pellets, installed density and installed geometry. Figure 5-3. Inspection phases in the buffer and filling component production line. Note that Table 5-3 does not include steps related to plugging of deposition drift and compartments because these are part of plug production line.

101 For a more detailed presentation, the inspections in Table 5-3 are denoted with a yellow part and a turquoise part. The yellow part contains phases in which the blocks and pellets are prepared and manufactured and the turquoise part is related to installation phases. The more detailed contents of the yellow part are presented in Table 5-4 containing the material composition, and in Table 5-5 containing the compaction properties and the density and the dimensions of the blocks and the pellets. The more detailed contents of the turquoise part are presented in Table 5-6.

102 Table 5-3. The production inspection scheme for the buffer and filling components production. Checks are denoted with an asterisk (*). Property Design parameter 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Excavatio Material Transport Conditioning Pressing Machining Inter- Transport Preparatio Installatio Installation of n and preprocessin delivery of the of blocks / of blocks to storage mediate to and n of n of distance and inter- at bentonite Pressing storage storage at depositio supercont blocks and g mediate storage production plant of pellets repository n drift 4) level ainer filling components Material Montmorillonite * * * composition Organic carbon * * * Sulphide * * * Total sulphur * * * Swelling index * * * Cation exchange capacity * * * Compaction Grain size distribution * * * * properties Water content * * * * 1 * Density and Bulk density * * dimensions Dimensions * 2 * of blocks Density and Bulk density separate pellets * dimension Dimensions * of pellets Bulk density loose filling * Installed Dimensions * * 3 density Bulk density of blocks * * 3 * * Bulk density of pellet filling * * 3 * Volume of pellet filling * * Installed Position of installed blocks * * geometry volume of pellet filled * * opening Diameter of drift within the installed blocks * 1) After adding water and mixing, before compression 3) After visual inspection of covers if needed 2) Before machining 4) Phase 9 Preparation of the drift does not contain inspections focused directly on the bentonite buffer

103 Table 5-4. Methods for testing and inspection of the material composition in manufacturing of the buffer and filling components, c.f. Figure 5-3. Property Material composition Design parameter 1. Excavation and preprocessing* 2. Material delivery and intermediate storage 3. Transport to storage at production plant Montmorillonite MQC X-ray diffraction X-ray diffraction Organic carbon MQC Heating in furnace Heating in furnace Sulphide MQC Heating in furnace Heating in furnace Total sulphur MQC Heating in furnace Heating in furnace Swelling index MQC Swelling in graduated cylinder Cation exchange MQC Displacing the exchangeable capacity cations * By supplier according to manufacturer quality control (MQC) system Swelling in graduated cylinder Displacing the exchangeable cations Table 5-5. Methods for testing and inspection of the material compaction properties and the density and dimensions of blocks and pellets in manufacturing of the buffer and filling components, c.f. Figure 5-3. Property Compaction properties Density and dimensions of blocks Density and dimension of pellets Design parameter Grain size distribution Water content Bulk density 1. 2. Excavation Material and preprocessing* intermediate delivery and storage 3. Transport to storage at production plant MQC 1 Sieving Sieving Sieving 1 4. 5. Conditioning of blocks / Pressing of the Pressing of bentonite pellets 6. Machining of blocks MQC 2 Drying in oven 3 Drying in oven 4 Drying in oven 5 Drying in oven Weighing and dimensions Dimensions Calliper Machine information** Bulk density of separate pellets Weighing and dimensions *** Calliper Weighing and dimensions Dimensions Bulk density Weighing of of loose defined filling volume * By supplier according to manufacturer quality control (MQC) system ** CNC-machining (computerised numerical control machining) *** Bulk density of separate pellets defined by weighing in paraffin oil 1 After grinding phase, 2 After drying phase, 3 After transportation, 4 After transportation, 5 After mixing phase

104 Table 5-6. Methods for testing and inspection of the installed density and the installed geometry in installation of the buffer and filling components, c.f. Figure 5-3. Property Design parameter 7. Intermediate storage 8. Storage at repository level 9. Preparation of deposition drift 10. Installation of supercontainer 11. Installation of distance blocks and filling components Installed density Dimensions of blocks Dimensions measurement Dimensions measuremen t if required Bulk density of blocks Weighing and visual inspection Visual inspection of and if required weighing Visual inspection and functional test of moisture protection system Block installation machine information Block installation machine information Bulk density of pellet filling Weighing and visual inspection of pellets and big bags Visual inspection of big bags and if required weighing Weighing and volume before installation Width of pellet filled gap Block installation machine information Block installation machine information Installed geometry Position of installed blocks Block installation machine information Block installation machine information Width of pellet filled gap* Block installation machine information Block installation machine information Diameter of drift within the installed blocks Block installation machine information * Based on position of installed blocks and scanned deposition drift dimensions

105 5.3 Excavation and delivery The different phases included, from the acquisition of the bentonite material till it is in the store at the production plant in Olkiluoto is depicted in Figure 5-4. 5.2.1 Procurement of buffer and filling components material - purchase Bentonite is a product used in many industrial and infrastructure applications. Bentonite mats for example have been used in landfills and in groundwater protection structures for over twenty years. Bentonite excavation and handling processes in the bentoniteprocessing industry are well-known and proven technology. MX-80 sodium bentonite from North America has been used in buffer and filling components block manufacturing tests and in material tests. Ibeco RWC calcium bentonite from the Greek island of Milos (Deponit CaN) has been tested as an alternative type of bentonite. These materials are also options for the raw material used for the pellets in the buffer. The final selection of the bentonite is governed by the suitability of the bentonite from the long term safety point of view, the bentonite quality, the reliability of supply and availability that spans a sufficiently long period of time (Posiva 2009). The purchase of bentonite is based on known properties of the material to be ordered. All relevant properties and their variability should be known. The purchase will be carried out according to the process description made for that purpose, as described in Laaksonen (2009a). Decisions about strategies used in purchasing are to be done early in order to ensure that suitable bentonite is available in sufficient quantities and at a reasonable price for years to come. The purchase process shall be done in such a way that it will ensure that all necessary documentation of the product will be delivered with the cargo. This includes also all producers QC-test results of the pre-determined properties. Call for bids from Posiva Offers to Posiva Selection of supplier Delivery agreement between Posiva and the supplier Excavation Stockpiling Processing Sampling and testing Petition of delivery to Posiva Bagging Storage Loading bags to containers Storage in containers Tranport to dock Storage at dock Loading to ship Unloding Sampling and tests Storage at dock Transport to intermediate storage Transport to resellers storage Tranport to intermediate storage at Olkiluoto Material inspections Transport to insde storage Posiva Producer Reseller Production facility Figure 5-4. Phases included to the acquisition of bentonite material.

106 Laaksonen (2009a) has identified and listed some relevant and at that time known producers or resellers of bentonite with corresponding trademarks and quarries. Each listed seller/producer has a quality management system, QMS (typically ISO 9001), and the ability to perform the basic tests. Ordering bentonite with well-specified properties requires an initial agreement between the producer and the customer, using documents with requests for quotation, technical specifications, and submission of the order (Laaksonen 2009a). 5.2.2 Excavation and pre-processing The process In this process stage the montmorillonite, sulphide, total sulphur and organic carbon content are determined. The bentonite can be mixed and the content homogenised during later stages but no active efforts to alter the material composition are allowed after the initial processing stage. The bentonite is excavated from open pits. Exactly how the excavation is performed depends on the deposit. The procedure described in this report is based on Wyoming type bentonite supplied by the American Colloid Company. Before excavation, the surface soil layers are removed and the bentonite deposit is fully exposed. Samples are taken from different parts of the deposit to specify the composition of the clay. The clay is excavated and hauled to a processing plant. At the plant the bentonite is segregated by various quality attributes and put into stockpiles. Quality inspectors supervise the building and use of these stockpiles to ensure that each quality is kept separate and free of contamination. The bentonite is collected from the stockpiles and mixed, grinded and dried so it complies with the specification given in the order. Inspections The inspection scheme in this phase of excavation and delivery is shortly described in Table 5-7. Table 5-7. Inspection scheme for excavation and pre-processing. Checking is denoted with an asterisk (*), see Figure 5-3.. Property Design parameter 1. Excavation and pre-processing Material composition Montmorillonite * Organic carbon * Sulphide * Total sulphur * Swelling index * Cation exchange capacity * Compaction properties Grain size distribution * Water content *

107 The report by Laaksonen (2009a) can be used as an aid in selecting and approving of suppliers. This comprises inspection of the quality assurance measures and systems applied by the supplier as well as laboratory tests of bentonite samples. The tests comprise measurements of material composition as well as investigations of material properties. The bentonite suppliers must have a well-documented quality assurance system. According to Laaksonen (2009a) the producer or the reseller must provide the customer at least the following information in connection with the delivery agreement: - Quality system certificate - Reports of relevant internal and external audits - Process description including quarrying, drying, milling, mixing, stockpiling, shipping, environmental conditions - Method descriptions, uncertainty - List of subcontractors: accredited laboratories, others. Before each delivery the bentonite is inspected by the supplier. The inspections shall comprise the parameters specified by Posiva Oy (Laaksonen 2009a). The specific requirements for the ordered bentonite (sodium bentonite) could include for example: 1. Montmorillonite content (XRD analysis): 75-90% by weight 2. Content of organic carbon < 1% by weight 3. Sulphide content 0.5% by weight 4. Total sulphur content (including the sulphide) 1% by weight 5. Swelling index (ASTM D 5890): 20 ml/2g 6. Grain size distribution (ASTM C958-92 (2000)), see Figure 3-18 7. Water content (ASTM D 2216): 13% by weight For iron content (measurement by XRF-analysis/ICP-AES) there is no given limits. However, the iron content of the bentonite material needs to be known when selecting the supplier of the bentonite. In determining the cation exchange capacity, tests that are more commonly used in Europe are also possible, for example AFNOR NF EN 933, NF P 94-068 or VDG P69. If other tests than ASTM are used the requirements may be expressed in other units. In this context it is presumed that the supplier grinds and screens the bentonite to a desired grain size distribution. The exact amount of tests carried out at the producer s laboratories will be defined in the delivery agreement. Site and laboratory audit visits shall be done to ensure that the process description is valid and that the laboratory is capable of carrying out the necessary tests. Normal acceptance tests (Appendix 3) will be carried out by Posiva Oy upon delivery, for each lot delivered.

108 5.2.3 Shipment The supplier is responsible for the inspection of the cargo space before loading, as well as any necessary cleaning of the cargo space if bentonite is transported in bulk. Bentonite is usually shipped in big bags (flexible intermediate bulk containers, capacity of about 1 ton) in 20 ton containers. The big bags must be water vapour resistant. During transportation the bentonite is not allowed to be in contact with water vapour or liquid water, other liquids or chemicals of any kind. The material is not allowed to freeze or be exposed to temperature < 0ºC during the transport on ship or truck, during storage or during any other phase of the process. Along with the material, a predefined set of documents must be delivered. This documentation contains detailed information about the shipped material and conditions during the shipment for example temperature and moisture monitoring, recorded data. These data will be delivered along with the cargo (Laaksonen 2009b). 5.2.4 Material delivery and intermediate storage in the harbour The process After shipping the bentonite to Finland, unloading of the containers at the harbour is done by workers of the shipping agents. The containers are either stacked up in the storage area of the harbour or sent immediately forward with trucks or train to storage (Laaksonen 2009b). Inspections The inspection scheme in this phase of material delivery and intermediate storage is shortly described in Table 5-8. Sampling is done to ensure that the material is acceptable and corresponds to the specifications stated in the order. Sampling can be done from big bags. Sampling will be carried out according to a predetermined plan. The sampling will be carried out either in the presence of both parties (the supplier/reseller or reseller s representative and the customer) or it will be done by a third party accepted by both parties (Laaksonen 2009b).

109 Table 5-8. Inspection scheme for material delivery and intermediate storage. Checking is denoted with an asterisk (*), see Figure 5-3. Property Design parameter 2. Material delivery and intermediate storage Material composition Montmorillonite * Organic carbon * Sulphide * Total sulphur * Swelling index * Cation exchange capacity * Compaction properties Grain size distribution * Water content * Normal acceptance tests (Appendix 3) will be carried out by Posiva Oy upon delivery for each lot delivered. Typically, the most numerous tests are water content tests. All the tested parameters must lie within predetermined limits to ensure their correct level and homogeneity; otherwise the lot will be rejected from buffer and filling components manufacturing (Laaksonen 2009b). Especially important are the results of tests described in Table 5-4. The need for quality control (QC) and acceptance tests will remain the same whatever the storage alternative will be: Posiva Oy's own or reseller's stock (Laaksonen 2009b). Storage at harbour Because the QC-tests will take time, from 2 to 5 days at least, the question of storage during this intervening time should be considered carefully. To eliminate additional transportation, it might be reasonable to let the lot wait at the harbour during the acceptance tests and decision of approval. The storage conditions must be monitored throughout the storage period and the data collected to be either stored or reported immediately. This need applies to all storing of this material whatever the location (Laaksonen 2009b). Storage at reseller's stock Resellers operating in Finland import bentonite either as a ready product or as raw bentonite. It is stored in cold ( 0º) or even warm warehouses, protected from wind and rain. Bentonite is imported in big bags. The big bags provide a more contamination-free alternative than tank truck transfer. A couple of resellers have their warehouses in southwest Finland. From there the material can be distributed by trucks in big bags. It can be assumed that all resellers can arrange temporary storage for batches up to 500 1000 tons if necessary. A reasonable delivery size of a final product might be around 500 tons per shipment (Laaksonen 2009b).

110 5.2.5 Transport to storage at the production plant The process Transport from port to reseller s stock or to customer The bentonite is transported from the harbour to the reseller s stock or to the customer s premises in big bags where the material is also stored in big bags. This will require a protected (dry, warm) warehouse with the necessary equipment for handling. It may happen that drying would be needed for some reason. It is possible to add a drying unit in the line. It is more practical to purchase material that is slightly too dry rather than too moist, because drying needs space, energy and time. The material is not allowed to freeze during any stage of transport or storage. The conditions must be monitored during the truck transport, at least during winter time from the beginning of October to the end of April (Laaksonen 2009b). Storage at customer site Posiva Oy has a facility reservation at the disposal site for the bentonite block and pellet production plant and the raw material storage. This ensures that the buffer and filling components production will be near by the repository. The bentonite is stored at the production facility in original big bags before the manufacturing starts. The amount of bentonite needed for one deposition drifts (assuming two compartments and total of 30 supercontainers) is about 647 metric tons. The space needed is about 1 m 2 for a big bag of 1 ton, i.e. about 700 m 2 total per one drift in floor level space plus the reservation for handling of the big bags. If the amount of bentonite is stored in containers, the number of 20 ton containers is about 33 in total. The net area demanded by the containers is about 550 m 2 if the containers are stored in one layer. The conditions, temperature and moisture shall be monitored and controlled during the storing. Inspections The inspection scheme in this phase of transport and storage at the production plant is shortly described in Table 5-9. The material composition, montmorillonite content, organic carbon, sulphide and total sulphur of the stored bentonite, its grain size distribution and water content are determined during the storage time.

111 Table 5-9. Inspection scheme for transport to storage at production plant. Checking is denoted with an asterisk (*), see Figure 5-3. Property Design parameter 3. Transport to storage at production plant Material composition Montmorillonite * Organic carbon * Sulphide * Total sulphur * Swelling index * Cation exchange capacity * Compaction properties Grain size distribution * Water content * 5.2.6 Methods for testing and inspection Methods for testing and inspection of material composition are described in Appendix 4. These tests include: - X-ray diffraction montmorillonite content, - Infrared spectroscopy (FTIR), - Optical polarising microscopy, - Determination of organic carbon, iron, sulphide and sulphur, - Inductively coupled plasma atomic emission spectroscopy (ICP-AES), - Cation exchange capacity (CEC), - Methylene Blue test and - Swelling index. Standard procedures or specifically developed guides on how to measure for each method will be clarified in the future. The grain size distribution in bentonite may be classified by dry sieving through a set of nested sieves, but the method is restricted to particle size > 75 µm (Ahonen et al. 2008, Appendix 4, 3:16). The grain size range of 5-100 µm may be studied by micro sieving using ultrasonic vibration. Gravitational settling (sedimentation) can be used in particle size analysis to the size range 2 200 µm. Mineral processors use cyclones and hydrocyclones in classifying small mineral particles. These methods utilise gravity and centrifugal force in gas or fluid stream in separating particles of micrometre scale (Ahonen et al. 2008). Bentonite contains water in different modes. Bulk material may contain loosely bound or even free water depending on the conditions of storage. This water may be removed by drying and storage at room temperature. Interlamellar space of the smectite lattice contains variable amounts of water molecules, which are electrostatically bound and form hydrates with the exchangeable cations. This water H2O- can be removed without breaking the crystal structure by heating at 105ºC, but a relatively long heating time (24 hours) is necessary to get a good result. Gravimetric determination of weight loss is a simple and accurate method for the water analysis.

112 Some test methods to assure the quality of bentonite are presented in Appendix 4 and 5. Examples of some preliminary test information from the producer and the frequency of sampling for the quality control at the procurement phase of the bentonite is presented in Appendix 3. The final methods to be used during operation will be developed later in order to measure the required properties rapidly. 5.2.7 Experiences and results The bentonite acquisition process has been developed in Purchase of bentonite - process description (Laaksonen 2009a) with the aim of producing an example of the purchase order documentation for the bentonite acquisition process. An important detail in the acquisition of bentonite is that uniform standards are employed in the specification of the bentonite material properties, which must be verified in connection with the acquisition. For the quality assurance of the bentonite, it is also important to ensure the traceability of the material. Handling of bentonite Studies have been conducted on the bentonite handling processes and the effect of storing conditions on the properties of bentonite. When the blocks are being manufactured, the single most important handling task is the mixing of moisture with the bentonite. The report (Laaksonen 2009b) was prepared concerning this task. As a result of this study, more information has been obtained on the moisture behaviour of bentonite and on undertaking the transportation of the material in such a manner that possible contamination from foreign materials can be prevented. For the storage of bentonite, it is important to provide information and guidelines on the following themes: - Acceptable humidity and temperature limits for the storage of the raw material, - Package size and intermediate storage, and - Traceability of the material. 5.3 Manufacturing of blocks and pellets 5.3.1 Conditioning of the bentonite The process In the process stage the delivered material is processed to the material specific grain size distribution, if not done before, and the water content is adjusted to a suitable level for pressing blocks and pellets. The grain size distribution and water content of the material ready for compression are finally checked. The conditioning of the material comprises the following activities: 1. Drying to a water content suitable for grinding (not necessarily required), 2. Grinding to a grain size suitable for compression (not necessarily required),

113 3. Storage of ground material (not necessarily required), 4. Wetting of ground material to a water content suitable for compression, including mixing, and 5. Storage of material ready for compression (and to let the water content stabilize). Activities 1, 2 and 3 Drying, grinding and storage If the bentonite needs grinding, the water content measured is used to determine whether the material needs to be dried to a moisture content suitable for grinding. The drying is done in a dryer if needed. Drying is needed if the raw material is too moist due to humid or wet transport conditions or the block manufacturing requires drying of the bentonite. Both alternatives are usually dealing with relatively small material quantities and are typically infrequent. The latter may deal with all the material, if a very high dry density is needed and the producer is not willing to dry the material enough before shipment. It is more practical to purchase slightly too dry material than too moist, because drying needs space, energy and time. After drying, the material is transported to a mill and ground to the required grain size. After the grinding the ground material is transported to a silo where it is stored. Activity 4 Wetting of grinded material to a water content suitable for compression Mixing is done to homogenize the mass and/or moisturise the mass to a certain level. The moisture level chosen is based on eliminating the harmful deformations and failures during the installation and ensuring a sufficient bulk density for the blocks to contain enough bentonite to swell and fill the hole together with the pellets in the gap. The mixing procedure is based on batch type mixing, where several batches are mixed and the bentonite is transported to a silo for a period of establishing moisture homogeneity. From another silo the already normalised bentonite is used for compressing the blocks. If different water contents are used for disk blocks, ring blocks or pellets, a pair of silos is needed for each water content. The number of silos and logistics how to produce the desired final water contents can be implemented in several ways and the final solution is being developed later. Before entering the mixer, the material should go through a unit, breaking any clods that might have formed in the silo or pipelines. After breaking the clods the mass should go through a sieving unit removing any larger particles that might have followed from the silo through the line. Possible techniques are, for example, flat screening and centrifugal screening. Both techniques can be integral parts of the conveyer (Laaksonen 2009b). Mixing produces homogeneous material with respect to particle properties, particle distribution and moisture. If the material is properly handled, no segregation or sorting can happen. The homogeneity of the mixed material can be tested with trial mixings. Mixing is probably always required, even if no water addition is needed. The water content required in the bentonite for the compression of the blocks and the pellets is achieved by adding a fine-mist water spray to the bentonite during mixing.

114 Moisturising may cause clods and these have to be eliminated by using an effective mixing process and removing possible clods from the mass. The target mix design (dry density, water content and their allowed variations) for each material comes from the reference design documentation. The amount of the added water for each batch must be determined and fed with the automatic control unit. Whatever the water adding and mixing methods are, they shall result in homogenous moisture and mixing (Figure 5-5). Activity 5 Storage of material ready for compression After mixing there is a need to let the mass reach the moisture equilibrium. The time needed for this depends on the mixing and water adding procedures and from the initial water content. The wetted bentonite is stored in silos (from 2 to 4 silos, each about ~50 m 3 ). The mixed and moisturised bentonite mass has to be transported from the temporary stock silos to the compression unit. The distance should be short and during the transport no drying of mass or any contamination from dust is allowed to happen. The transportation of material to the compression mould (and to the pellet press) will be done by a screw conveyor. There may be a need to control the average water content of each bentonite batch. This can be done with calibrated automatic sensors or by manual sampling. Manual sampling will take at least 15 minutes to receive the result. For compression of the bentonite blocks the material must be transported and put into the mould so that no segregation of the mass will happen. This requires a special method to supply the material flow to different parts of the buffer and filling components block mould. The homogeneity of the block is a quality issue, which has to be tested and verified before large scale manufacturing. Inspections The inspection scheme in the phase of conditioning before manufacturing is shortly described in Table 5-10. The water content of the delivered raw material is inspected before and after drying to yield a level suitable for grinding, independently from the executer. The water content and grain size distribution of the material ready for compression is finally inspected in connection with the mixing. The water content is inspected before the mixing to determine the amount of water to be added. The amount of water added is measured and finally the water content of the mixed material ready for compression is inspected. Samples are taken from each mixing of material.

115 Figure 5-5. An example of bentonite handling in plant (block compression; principle description, drawing by Jauhetekniikka; modified from Laaksonen 2009b). Table 5-10. Inspection scheme for conditioning of the bentonite. Checking is denoted with an asterisk (*), see Figure 5-3. Property Design parameter 4. Conditioning of the bentonite Compaction properties Grain size distribution * Water content * 1 1) After adding water and mixing, before compression The water content is inspected for each mixed batch transferred to the silo. The number of samples shall be sufficient to determine the average water content. The grain size distributions are inspected for each fifth batch transferred to the silo. The most important aspect of this chain is the accurate determination of mass and moisture. This means that the devices (scales, balances) must have a correct capacity, sensitivity and accuracy. These devices must also be suitable for conditions where they are used. Accurate measurement of quantities requires accurate instruments and data loggers, which will be periodically checked and calibrated. This means not only periodic calibrations made by external organisations but also internal day by day checks with dummy specimens (mass and moisture). The moisturising process will require flow meters to be used to control the added amount of water. These flow meters must also be included in the regular checking and calibration process of the devices (Laaksonen 2009b). 5.3.2 Compression of blocks The process Posiva Oy's reference method for compression of the blocks is the isostatic compression method (Ritola and Pyy 2011). In this stage the bulk density of the blocks is finally determined. The compression process is controlled to yield the specified density. The bulk density of the blocks depends on the

116 grain size distribution and water content of the material to be compressed and on the compression pressure. The conditioned material to be filled in the mould is weighed. The principle of isostatic compression is to encapsulate material that will be compressed in an impermeable and flexible mould. The container is put in a high-pressure vessel and the pressure is increased inside the vessel up to a desired level. Hydrostatic pressure will compress the material in the flexible bag homogenously from all directions thus producing a homogeneous block. The powders to be compacted are encapsulated in a shaped membrane, known as a bag tool, which serves both as a mould for the part and as a barrier against the press liquid. The principle of the press and operation is shown in Figure 5-6 (Laaksonen 2009c). The process employs a chamber filled with liquid which applies hydraulic pressure uniformly on all surfaces of the block being compressed. Wet bag pressing: o o o o o A flexible tool, usually made out of rubber, is filled with the material to be compressed. The filled tool is sealed watertight. The tool is inserted into the pressing chamber which is then filled with the pressing fluid; hence the name wet bag pressing. Pressure is applied for a certain period of time. Then the tool is pulled out and the compressed block removed from the tool. Figure 5-6. Principle of operation of an isostatic compression apparatus (Laaksonen 2009c). (http://www.loomis-gmbh.de/index.pl/isostatic_pressing, 4.12.2008). The bentonite s water content and the compression pressure are the two most important properties determining the characteristics of the compressed blocks. By adjusting these two properties it is possible to produce blocks at a desired density. The commonly used compression pressure in the manufacturing of bentonite blocks is 100 MPa, which compresses bentonite to approximately half its original volume, while doubling its density. The compression process must be well controlled (Ritola and Pyy 2011).