KBS-3H Design, Production and Initial State of the Compartment and Drift Plugs POSIVA February Posiva Oy

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1 POSIVA KBS-3H Design, Production and Initial State of the Compartment and Drift Plugs Posiva Oy February 2018 POSIVA OY Olkiluoto FI EURAJOKI, FINLAND Phone (02) (nat.), ( ) (int.) Fax (02) (nat.), ( ) (int.)

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3 POSIVA KBS-3H Design, Production and Initial State of the Compartment and Drift Plugs Posiva Oy February 2018 This work has been carried out under KBS-3H System Design project co-funded by Posiva and SKB. POSIVA OY Olkiluoto FI EURAJOKI, FINLAND Phone (02) (nat.), ( ) (int.) Fax (02) (nat.), ( ) (int.)

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5 Posiva Oy Olkiluoto FI EURAJOKI, FINLAND Puh (31) - Int. Tel (31) Raportin tunnus - Report code POSIVA Julkaisuaika - Date February 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy Nimeke Title KBS-3H -DESIGN, PRODUCTION AND INITIAL STATE OF THE COMPARTMENT AND DRIFT PLUG Tiivistelmä Abstract The compartment plug is used to section off the drift into two compartments, approximately 150 m long with the purpose to improve the performance of the other barriers by keeping installed components in place, thereby contributing to favorable conditions in the drift and facilitating artificial watering and air evacuation (DAWE) operations. The drift plug is installed close to the mouth of the deposition drift to plug the drift. The purpose is to engineering barrier components in place and to avoid significant water flows out of the drift, which could give rise to buffer erosion and to facilitate DAWE operations. The compartment plug and the drift plug consists of following three main components, fastening ring, collar and cap. The collar is also provided with three lead-through pipes to allow the water filling pipes and air evacuation. Based on the long-term performance, titanium has been selected for the plugs. Verification of the mechanical integrity of the plugs under applicable loading conditions were made by modelling and various calculations. The plug components are manufactured from titanium plates through conventional cutting and welding processes. Manufacturing of titanium plugs has not been carried out so far but performed manufacturing of carbon steel plugs has verified that it is possible to manufacture plugs within specified tolerances. The plug components and welds are inspected to ensure conformity to the specifications of the reference design. The initial state of the plugs is defined as the state at which the plugs are finally installed in the repository. Avainsanat - Keywords Compartment plug, drift plug, final disposal, KBS-3H, drift, initial state ISBN ISSN ISBN ISSN Sivumäärä Number of pages Kieli Language 68 English

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7 Posiva Oy Olkiluoto FI EURAJOKI, FINLAND Puh (31) - Int. Tel (31) Raportin tunnus - Report code POSIVA Julkaisuaika - Date February 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy NIMEKE TITLE KBS-3H OSASTOTULPAN JA PÄÄTYTULPAN SUUNNITTELU, TUOTANTO JA ALKUTILA Tiivistelmä Abstract Osastotulppa jakaa loppusijoitusreiän kahteen n.150 m pituiseen osastoon ja tulpan tarkoituksena on parantaa muiden päästöesteiden toimintakykyä pitämällä asennetut reikäkomponentit paikoillaan, mikä edesauttaa suotuisten olosuhteiden saavuttamista loppusijoitusreiässä. Osastotulppa mahdollistaa osaston keinotekoisen kastelun ja ilmastuksen (DAWE) suunnitelmien mukaisesti. Lähelle loppusijoitusreiän alkupäätä asennettava päätytulppa sulkee loppusijoitusreiän. Päätytulpan tarkoituksena on myös pitää tekniset päästöesteet paikoillaan ja estää veden virtaus loppusijoitusreiästä, mikä voisi johtaa puskurin eroosioon. Lisäksi päätytulppa mahdollistaa osaston keinotekoisen kastelun ja ilmastuksen (DAWE) suunnitelmien mukaisesti. Osasto- ja päätytulppa koostuvat seuraavista kolmesta komponentista: kiinnitysrenkaasta, renkaaseen kiinnitetystä kauluksesta ja kaulukseen kiinnitetystä kannesta. Kaulukseen on tehty kolme läpivientiä vesiputkia varten ja yksi ilmastusputkea varten. Tulppamateriaaliksi on valittu titaani sen pitkäaikaistoimintakyvyn perusteella. Tulppien mekaaninen eheys soveltuvissa kuormitusolosuhteissa on verifioitu mallintamisella ja erilaisilla laskelmilla. Tulppakomponentit valsmistetaan titaanilevystä konventionaalisia leikkaus- ja hitsausprosesseja käyttämällä. Titaanista tulppaa ei ole vielä valmistettu, mutta projektissa toistaiseksi valmistetut hiiliterästulpat ovat osoittaneet, että määriteltyjen toleranssien mukaisten tulppien valmistaminen on mahdollista. Tulppakomponentit ja hitsaukset tarkistetaan niiden ja referenssisuunnitelmalle annettujen spesifikaatioiden välisten yhdenmukaisuuksien varmistamiseksi. Tulppien alkutila määritellään tilaksi, jossa ne ovat loppusijoitustilassa asennuksen jälkeen. Avainsanat - Keywords Osastotulppa, päätytulppa, loppusijoitus, KBS-3H-menetelmä, sijoitusreikä, alkutila ISBN ISSN ISBN ISSN Sivumäärä Number of pages Kieli Language 68 Englanti

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9 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ PREFACE INTRODUCTION General basis... 8 This report... 8 The design of the plugs... 9 The production of the plugs Purpose, objectives and limitations Purpose Objectives Limitations Interfaces to other KBS-3H reports and aspects The report for the long-term safety analysis The design basis report Operational safety The repository production report Structure and content Overview Design basis Reference design Conformity of the reference design to the design basis Manufacturing of the plugs Installation Initial state of the plugs DESIGN BASIS FOR THE PLUG General basis Identification and documentation of design basis Definition, purpose and basic design of the plugs Barrier functions and design considerations Functions and properties of the plug in the KBS 3H repository and repository facility Design considerations Design basis for the plug Design basis related to the properties of the plugs in the KBS-3H repository Design basis from the engineered barriers Design basis related to the production and operation Design basis imposed by the plugs Deposition drifts REFERENCE DESIGN OF THE PLUGS Description of the reference design... 25

10 2 Fastening ring Collar Cap Air evacuation and wetting pipes (and lead-through) Modification proposals Manufacturing aspects of plugs Fastening Ring Collar Material properties Low ph-concrete Plug data CONFORMITY OF THE REFERENCE PLUG TO THE DESIGN PREMISES Conditions for the analyses of mechanical loads Codes and standards Partial Factors Load conditions Modelling and calculations Compartment plug Drift plug Test of mechanical strength Pipe removal Plug material Watertight seal MANUFACTURING OF THE PLUG Overview Design basis for the production of the plug Manufacturing of the plugs Key stages in the production of the plug Preassembly of components Manufacturing inspection and documentation INSTALLATION AND TRANSPORTATION/HANDLING Transportation of the plug components Installation of plug Preparation of drift Closure of compartment/drift INITIAL STATE OF THE PLUG Initial state of the plugs and conformity to the reference design Initial State Material properties Dimensions Watertight seal SUMMARY Design basis for the plugs Reference design of the plugs and conformity to design basis The production and installation of the plugs Initial state of the plugs... 62

11 3 9 REFERENCES APPENDIX A - GLOSSARY OF ABBREVIATIONS AND SPECIALISED TERMS USED... 67

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13 5 PREFACE The KBS-3V production line reports (produced by Posiva and SKB, respectively) have formed the basis for the organization s respective license applications for the construction, possession and operation of the KBS-3H repository. 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; the underground openings. The latter four production lines are reported in new 3H-specific production reports. The former four are expected to only deviate slightly from their 3V counterparts and are thus left without further adaptation and any significant differences are accounted for in a new 3H-specific repository production report which also presents the common basis for the production line 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 for KBS-3H, 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 further harmonize the Posiva and SKB requirements. The preparation of the above-mentioned set of reports has been led and coordinated by Anders Winberg (Conterra AB) with support from Antti Öhberg (Saanio & Riekkola Oy). This report has been authored by Bo Halvarsson (Vattenfall AB) and Peter Sandberg (Vattenfall AB). The KBS-3H design has been developed jointly by SKB and Posiva since This report has been prepared within the project phase KBS-3H - System Design

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15 7 1 INTRODUCTION KBS-3H is a variant of the KBS-3 method and an alternative to the KBS-3V reference design. KBS-3H is based on horizontal emplacement of several canisters in a series in long deposition drifts whereas KBS-3V calls for vertical emplacement of the canister in individual depositions holes within a deposition tunnel, see Figure 1-1. Horizontal emplacement has been studied jointly with Posiva in parallel with the development of the KBS-3V reference design since the late 90 s and the current reference design as well as the reference methods are presented in KBS-3H complementary studies report (SKB 2012). The design basis in this report in essence is those given for KBS-3V and they are supplemented with method specific premises/ basis. This has established the reference case for the KBS-3H method as well as the current status in developing design and methods. In Posiva s terminology design basis refers to the current and future environmentally induced loads and interactions that are taken into account in the design of the disposal system, and, ultimately, to the requirements that the planned disposal system must fulfil in order to achieve the objectives set for safety (i.e. the design premises). In SKB terminology the design premises are used as input to the production reports, which present the reference design analysed in the long-term safety assessment SR-Site. The design premises correspond to the design requirements and system specifications in Posiva s terminology. Design basis is used when referring to the design premise in the following text and in the Summary. In Posiva s terminology the system design premises comprise the objectives set for the whole system, limitations set by the environment, technology and knowledge and existing operating environment (regulations, responsibilities, organisations and resources). These form the starting point for the definition of the design basis of disposal operations. Design basis (in line with this report) is published in (Posiva 2016a). Figure 1-1. Schematic drawing of the KBS-3V reference design (left) and KBS-3H (right)

16 8 1.1 General basis This report This report presents the reference design, production and initial state of the plugs in deposition drifts in a KBS 3H repository for spent nuclear fuel. It is included in a set of reports presenting how the KBS 3H repository is designed, produced and inspected. The set of reports is denominated production reports. The production reports and their short names used as references within the set are illustrated in Figure 1-2. The reports within the set referred to in this report and their full names are presented in Table 1-1. The KBS-3H design has been developed jointly by SKB and Posiva since This report has been prepared within the project phase KBS-3H - System Design This report is part of the safety report for the KBS 3H repository and repository facility. It is based on the results and review of the most recent long-term safety assessment and the current knowledge, technology and results from research and development. The reference design of the plugs and the reference methods to produce the plugs presented in this report constitutes a solution that is technically feasible. It is, however, foreseen that the design basis, the design as well as the presented methods for production, test and inspection will be further developed and optimized before the actual construction of the KBS-3 repository facility commences. In this context, it should be mentioned that there are alternative designs that conform to the design basis as well as alternative ways to produce the reference design. In addition, the safety assessments as well as future safety assessments may result in up-dated design basis. The ambition is to continuously develop and improve both the design and production. Repository production report Spent fuel report Canister production report Supercontainer production report Buffer and filling component production report Plug production report Closure production report Underground openings construction report Figure 1-2. Reports included in the set of reports describing how the KBS-3H repository is designed, produced, tested and inspected. The 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 have produced their respective non-generic reports). Repository production report includes some information from other production reports (spent fuel, canister, closure) if there are differences between 3V and 3H.

17 9 Table 1-1. The reports within the set of production reports referred to in this report. Full title Design and production of the KBS-3 repository Design, construction and initial state of the underground openings Design production report and initial state of the buffer Short name used within the Production reports 3H Repository production report 3H Underground openings construction report Buffer and filling components production report Title in reference lists Posiva 2016d Design and production of the KBS-3H repository. Posiva Oy, Posiva Posiva 2016c KBS-3H Design, Construction and Initial State of the underground openings. Posiva Oy, Posiva Posiva 2016b KBS-3H Design, production and initial state of the buffer and filling components. Posiva Oy, Posiva The design of the plugs The presented designs, see Section 2.1.2, of the plugs (compartment plug and drift plug) in the horizontal deposition drifts presume a repository based on the KBS 3H reference design, the DAWE design alternative, with horizontal deposition of supercontainers as further described in the 3H Repository production report (Posiva 2016d). The production of the plugs The KBS 3H system and its facilities etc. are presented in the 3H Repository production report and illustrated in Figure 1-3. The presented handling and installation of the plugs are included in the deposition works in the KBS 3H repository facility. They are based on the filling sequence presented in the 3H Repository production report.

18 10 Figure 1-3. Overview of the activities in the technical barriers and underground openings. 1.2 Purpose, objectives and limitations Purpose The purpose of this report is to describe how the plugs in deposition drifts are designed, produced and inspected in a manner related to its importance for the safety of the KBS 3H repository. The report shall provide the information on the design, production and initial state of the plug in deposition drifts required for the long-term safety report as well as the information on how to produce and inspect it as required for the analysis of operational safety. With this report Posiva and SKB intend to present the design basis for the plugs in horizontal deposition drifts and demonstrate how it can be designed, produced and inspected to conform to the stated design basis. The report shall present the reference design and production methods and summarize the research and development efforts that supports that the plugs can be produced in conformity to the design basis. Objectives Based on the above purpose the objectives of this report are to present: the design basis/requirements for the plugs, the reference design of the plugs,

19 11 the conformity of the reference design to the design basis, the planned production, the initial state of the plugs, i.e. the expected result of the production comprising as built data on the properties taken credit for as contributing to, or affecting, the barrier functions and safety. Limitations This report includes present design basis for the plugs related to the long-term safety of the KBS 3H repository. The presented reference designs must conform to this design basis and consequently they have in most cases determined the design. Design basis related to other aspects than safety and radiation protection are only included if they have determined the design of the plug or the methods to produce them. The current report presents SKB s and Posiva s reference design and methods. Alternative designs and planned developments of the design and methods are only briefly mentioned in this report. This report also includes the design considerations taken with respect to the application of best available technique with regard to safety and radiation protection. It includes the related design basis for the design and development of methods to produce them. Motivations of the presented reference design and methods as the best available technique are reported elsewhere. 1.3 Interfaces to other KBS-3H reports and aspects The role of the production reports in the safety report is presented in the 3H Repository production report. A summary of the interfaces to other reports included in the safety report is given below. The report for the long-term safety analysis By providing a basic understanding of the repository performance over different timeperiods and by the identification of scenarios that can be shown to be especially important from the standpoint of risk the long-term safety assessment provides feedback to the design of the engineered barriers and underground openings. The methodology used for deriving design basis from the long-term safety assessment is introduced in the 3H Repository production report. The design basis report A thorough description as well as the resulting design basis are given in the report Design basis (Posiva 2016a) for a KBS-3H repository, hereinafter referred to as Design basis for long-term safety. These design bases constitute a basic input to the design of the plugs.

20 12 (SKB 2012) is the report presenting the current main reference design as well as the reference methods. The design bases in essence are those given for KBS-3V and they are supplemented with method specific design basis. This has established the reference case for the KBS-3H method as well as the current status in developing design and methods. Operational safety No specific operational safety report has been prepared during this project phase. The current report, however, provides information to the operational safety report on the design of the plugs and the technical systems used to construct and inspect them as well as instructions on where and when inspections shall be performed. The repository production report The 3H Repository production report presents the context of the set of Production reports and their role within the safety report. It also includes definitions of some central concepts of importance for the understanding of the Production reports. The 3H Repository production report sets out the laws and regulations and demands from the nuclear power plant owners applicable for the design of a final repository for spent nuclear fuel. In addition, it describes the safety functions of a KBS-3H repository and how safety is provided by the barriers and their barrier functions. The report describes how design basis are derived from laws and regulations, owner demands and the iterative processes of design and safety assessment and design and technique development respectively. The starting point for the design basis presented in this report is the barrier functions and design considerations introduced in the 3H Repository production report. The design and production of the different engineered barriers and underground openings are interrelated. An overview of the design and production interfaces is provided in the 3H Repository production report. The design basis imposed by the plugs on the design and production of the other engineered barriers and underground openings are presented in this report. The design basis are repeated and verified in the production reports for the engineered barriers and underground openings on which the plugs impose design basis. 1.4 Structure and content Overview The general flow of information in the current Plug production report can be described as follows: design basis; reference design; conformity of the reference design to the design basis;

21 13 production; installation; and initial state. The listed bullets are further described in the following sections. In addition, the context of the report is presented in this chapter and in Appendix A abbreviations and branch terms used in this report are explained. Design basis The design basis set out the information required for the design. The design basis for the plugs in horizontal deposition drifts are presented in Chapter 2 of this report. The chapter is initiated with the definition of the plugs, its purpose and basic design. After that follows a presentation of the barrier functions the plugs shall provide to contribute to the safety of the final repository, including considerations that shall be made in the design with respect to the application of a well-established and reliable technique. Finally, the detailed design basis for the plugs is given. They state the properties the reference design shall have to maintain the functions and to conform to the design considerations. Reference design The descriptions of the reference design comprise the plug material and components of the installed plug which are presented in Chapter 3. The reference design is specified by a set of variables denominated design parameters. The design parameters shall be inspected in the production and acceptable values for them are given for the reference designs. The design basis and considerations that have determined the design parameters are also presented. Conformity of the reference design to the design basis An important part of this report is the analyses verifying the conformity of the reference design to the design basis. The conformity to each of the design basis, given as feedback from the long-term safety assessment as well as the design basis related to technical feasibility, production and operation, is analyzed and relevant conclusions are drawn. The conformity of the reference plug to the design basis is presented in Chapter 4. Manufacturing of the plugs The presentation of the production of the plugs is initiated by an overview comprising: requirements on the production and design basis for the development of methods to produce, test and inspect the plugs, illustration of the main parts and different stages of the production, short descriptions of the reference methods for production, test and inspection,

22 14 overview of the design parameters and the corresponding parameters measured in the production to inspect them, and at which stage of the production the design parameters are determined, affected and inspected. After that follows descriptions of each stage in the production of the plugs and how the design parameters are affected, tested and inspected within each stage. The current experiences and results from each main part of the production are summarized. An overview of the key issues to be considered in the production of the plugs is provided in Chapter 5. Installation Installation of the plugs within the KBS-3H system is provided in Chapter 6. The chapter also describes the inspections that shall be performed in the different stages of the assembly, transports, handling, storage and deposition. Initial state of the plugs In Chapter 7, the initial state chapter for the plugs, the expected values of the design parameters, and other parameters required for the assessment of the long-term safety, at the initial state are presented. The expected values are based on the current understanding and experiences from the production trials (manufacturing and installation), and they are discussed and justified in relation to the currently available results presented in the production chapter (Chapter 5).

23 15 2 DESIGN BASIS FOR THE PLUG 2.1 General basis In this chapter the design basis for the plugs are presented. They comprise the functions and properties the plugs shall sustain in the KBS 3H repository and the premises for their design. The required functions and design basis are written in italics. Identification and documentation of design basis The methodology to derive, review and document design basis is presented in the 3H Repository production report (Posiva 2016d) and is detailed for KBS-3H in (Posiva 2016a). The design basis is based on: international treaties, national laws and regulations, the functions of the KBS 3H repository, the safety assessment, technical feasibility, the planned production. The 3H Repository production report includes a presentation of the laws and regulations applicable for the design of a final repository for spent nuclear fuel. Based on the treaties, laws and regulations SKB has substantiated functions and considerations as a specification of the KBS 3H repository, and as guidelines for the design of its engineered barriers and underground openings. In the 3H Repository production report the functions and properties the plugs shall sustain in order to contribute to the functions of the KBS 3H repository are presented. The 3H Repository production report also presents the design considerations to be applied in the design work. The design basis related to the functions of the plug in the KBS 3H repository is based on the results from the latest performed long-term safety assessment and some subsequent analyses. This design basis for the plug is presented in Section 2.3 in this report. Design basis related to technical feasibility refer to the properties the plugs shall have to fit, and work, together with the engineered barriers and other parts of the final repository during the production. The general approach to substantiate this kind of design basis and the interfaces to the engineered barriers and other parts in the production is presented in the 3H Repository production report for the plugs. Finally, design basis related to the operation of the KBS- 3H repository facility and the production of the plug are presented in Section in this report for the plug. Definition, purpose and basic design of the plugs The compartment plug is used to section the drift into two compartments, each approximately 150 m long.

24 16 The purpose of the compartment plug is to support the performance of the other barriers by keeping the drift components in place, and thereby to contribute to favorable conditions in the drift and to facilitate the artificial watering and air evacuation (DAWE) operations. The drift plug is the component installed close to the mouth of the deposition drift to plug the drift, finishing the operations in that particular drift. The purpose of the drift plug is to avoid significant water flows out of the drift, which could give rise to piping and erosion of the installed buffer or filling components. It also keeps the drift components in place prior to the backfilling and saturation of the adjacent underground openings and to facilitate the artificial watering and air evacuation (DAWE) operations. The location of the compartment plug and the drift plug in the KBS-3H deposition drift are illustrated in Figure 2-1. The plugs consist of three metallic component types; the fastening ring which is cast into a pre-prepared rock notch, the collar, which is attached to the fastening ring and finally the cap, see Figure 2-2. The plugs are also provided with bushings in the collar for the watering and air evacuation pipes and an opening in the cap for pellet filling behind the plug forming a part of the transition zone described in the Buffer and filling components production report (Posiva 2016b). Drift plug ~150 m ~300 m Figure 2-1. Illustration of the KBS-3H deposition drift and location of the compartment and drift plug Figure 2-2. Illustration of the plug

25 Barrier functions and design considerations In this section the barrier functions of the plugs and design considerations for plugs are presented. They are based on the functions of the final repository presented in Section in the 3H Repository production report and have been divided into: functions and properties the plug shall sustain (Section 2.2.1), issues that shall be considered when developing a plug design and methods for its manufacturing, preparation, installation, test and inspection (Section 2.2.2). Functions and properties of the plug in the KBS 3H repository and repository facility In order for the barrier system of the final repository to withstand conditions, events and processes that may impact its functions the following functions are required for the two types of plugs: Compartment plug the compartment plug shall keep the drift components in the closed compartment in place, the plug shall provide an adequate drift seal that prevents flow through the plug and the rock/plug interface, to avoid loss of buffer and filler materials during the operational phase, the plug shall be capable of supporting full hydrostatic pressure at repository depth during the operational phase. Drift plug the drift plug shall keep the drift components in place, the drift plug shall be sufficiently tight to avoid loss of buffer and filling component materials through erosion from the deposition drift, the drift plug shall withstand full hydrostatic pressure at repository depth plus the swelling pressure of the buffer and filling components in the deposition drift for as long as the adjacent central tunnels are not backfilled and saturated, the drift plug shall withstand spatial variations in pressure acting on the plug surface. In the long-term perspective in the final repository, in order for the repository to maintain the multi-barrier principle, the plugs must: Support the safety functions and performance of the other engineered system components and the host rock. These functions and properties shall be secured and maintained during different periods of the lifetime of the plugs, see further description in Section 2.3.

26 18 Design considerations This section presents the design considerations that shall be regarded in the design of the plugs and in the development of methods to manufacture, install, test and inspect it and its components. The design considerations mainly affect the development of methods. A determined reference design together with the design considerations, form the basis for the detailed design basis for the development of methods to manufacture, install, test and inspect the plugs, as presented in Section The barrier system of the final repository shall withstand failures and conditions, events and processes that may adversely impact their functions. Hence, the following shall be considered in the development of the plug concept. The design and methods for preparation, installation, test and inspection shall be based on well-tried or tested technique. The plug design shall be such that the collar and the cap can be installed within 24 hours after that the drift section has been filled. The plug components shall be designed so that the welds do not carry any load, thus only function as a seal. The plug collar shall be provided with penetrations (lead-throughs) for the water filling and air evacuation pipes that will be installed in the drift. The collar shall be provided with a drain pipe in the low point to allow water to be drained from drift before final sealing and the artificial water filling. The plug cap shall be provided with a filling pipe for bentonite pellets. The fastening ring shall be prepared with grouting tubes to enable for silica sol grouting in case of leakage at the boundary between the fastening ring and the concrete casting and/or between the concrete casting and the rock. In order for the construction, manufacturing, installation and non-destructive tests of the barriers of the final repository to be reliable, the following shall be considered. plugs with specified properties shall be possible to prepare and install with high reliability. The properties of the plugs shall be possible to test and inspect relative to specified acceptance criteria. A reliable production is also required with respect to Posiva s and SKB s shared objective to achieve high quality and cost-effectiveness. Regarding cost-effectiveness, the following shall be considered. The design of the plugs and methods for preparation, installation, test and inspection shall be cost-effective. plug assembly and installation shall be possible to perform in the prescribed rate. Further, environmental impact such as noise and vibrations, emissions to air and water and consumption of material and energy shall be considered in the design. Methods to

27 19 prepare and install the plugs must also conform to regulations for occupational safety. Design basis related to these aspects can generally be met in alternative ways for plug designs that conform to the safety and radiation protection design basis. Together with design basis related to efficiency and flexibility they are of importance for the design of technical systems and equipment used in the production of the plugs. 2.3 Design basis for the plug In this section the design basis for the plug are given. They constitute a specification for the design of the plug. The design basis comprises the properties and parameters to be designed and premises for the design such as quantitative information on features, performance, events, loads, stresses, combinations of loads and stresses and other information, e.g. regarding environment or adjacent systems, which form the necessary basis for the design. The design basis is based on the functions and properties presented in Section and the design considerations presented in Section The design basis given as feedback from the long-term safety analyses is compiled in (Posiva 2016a). Initial state properties of the as built repository in the production line reports is a starting point for the safety analysis. The design basis given as feedback from the technical development are based on the reference designs of the other parts of the KBS 3H repository and the construction, deposition and backfill sequence presented in Section in the 3H Repository production report. Design basis related to the properties of the plugs in the KBS-3H repository In the final repository during the post closure phase the plug must not significantly impair the barrier function of the engineered barriers or rock. The design basis related to the properties of the plug in the KBS-3H repository are compiled in Table 2-1.

28 20 Table 2-1. Design basis for the plugs related to its properties in the repository during the post closure phase. Design consideration Required property Design basis The plug must not significantly impair the functios of the engineered barriers or rock. Volumes and compressibility of the plug (all parts) plug material (all parts) Concrete (casting/grouting of fastening ring) The decrease in the volume must not cause loss in buffer/filling component density that significantly reduce its barrier functions. The plugs shall be made of materials that, by interaction, do not affect the properties of the buffer or filling components and their ability to meet the performance target for the buffer or filling components, or, if this is not possible the region affected by this interaction should be shown to extend only a limited distance into the buffer or filling components. Low ph concrete shall be used. The leachates from the concrete must have a ph 11. Design basis from the engineered barriers In this section design basis imposed by the engineered barriers on the plugs are given. Buffer and filling components The compartment plugs in deposition drifts are important for the properties and function of the buffer and filling components. The compartment plug shall provide a physical restraint to material transport and keep the compartment buffer and filling components in place during the operational phase before the drift has finally been sealed and closed. The design basis related to the functions the compartment plug shall maintain during the operational phase is presented in Table 2-2. The drift plugs in deposition drifts are important for the properties and function of the buffer and filling components. The drift plug shall provide a physical restraint to material transport and keep the buffer and filling components in the deposition drift for as long as the adjacent central/main tunnels are not backfilled and saturated. The design basis related to the functions the drift plug shall be maintained during the sealing phase are presented in Table 2-3. When the main/central tunnel is filled, it will provide a counter pressure for backfill expansion/swelling, and when it is saturated there is no longer a flow introduced potential for material

29 21 Table 2-2. Design basis related to the functions of the compartment plugs shall maintain during the operational phase Function or property The compartment plug shall resist the full hydrostatic pressure at repository depth. The compartment plug shall limit water flow during the installation phase. The compartment plug shall be durable and maintain its functions in the environment expected in the repository facility and repository until the drift is sealed. Property and design parameters to be designed The strength of the compartment plug. Material quality and amount. The watertightness of the plug Compartment plug deformation properties. Bond between fastening ring and the rock (water conductive features must not be developed) Compartment plug design working life Design basis 5 MPa water pressure The amount of water accepted to pass the plug. The accepted water volume will depend on the acceptable transport of buffer material out from the compartment during the installation phase. The displacement of the compartment plug that can be accepted with respect to the decrease in buffer density. See design premise for limitation of water flow. The design working life is at least 100 years.

30 22 Table 2-3. Design basis related to the functions the drift plugs shall maintain during the operational phase Function or property The drift plug shall resist the hydrostatic pressure at repository depth and the swelling pressure of the buffer filling components adjacent to central/main tunnels that are not backfilled and saturated. The drift plug shall limit water flow from the drift untill the adjacent main/central tunnel is filled and saturated. The drift plug shall be durable and maintain its functions in the environment expected in the repository facility and repository until the closure in the main/central tunnel is saturated. Property and design parameters to be designed The strength of the drift plug. Material quality and amount. Maximum applied swelling pressure. Length of transition zone. The watertightness of the plug The watertightness of the drift plug Properties of the interfaces between rock / grouting / concrete Drift plug deformation properties. Bond between fastening ring and the rock (water conductive features must not develop) The drift plug design working life. Drainage pipes design working life. Design basis The sum of the hydrostatic water pressure at repository depth and the swelling pressure from the buffer and filling components. Corresponds to a hydrostatic pressure of 5 MPa and a swelling pressure of approx. 2 MPa resulting from buffer and filling components. Dimensioning load of the drift plug. The amount of water accepted to pass the drift plug. The accepted water volume will depend on the acceptable transport of buffer material out from the deposition drift during this phase and remains to be quantified. The displacement of the drift plug that can be accepted with respect to the decrease in buffer density. See design premise for limitation of water flow. The design working life is at least 100 years. transport across the drift plug and out from the deposition drift. The drift plug has then fulfilled its sealing functions. Design basis related to the production and operation In this section the design basis related to the production of the plug are given. In Table 2-4 design basis for the plug related to its construction are given while the design basis for the construction and construction methods are presented in Section

31 23 Table 2-4. Design basis related to the installation of the plug Design consideration Required property Design basis plugs with specified properties shall be possible to prepare and install with high reliability and rate. The plug shall not be exposed to high water pressures until grouting has gained sufficient strength. The plug design shall be such that the collar and the cap can be installed within 24 hours after that the drift section has been filled. Time until the plug is exposed for load will be sufficiently long to allow the grouting to gain sufficient strenght 2.4 Design basis imposed by the plugs. In this section the design basis imposed by the plugs on the engineered barriers and the underground openings in order to achieve a technically feasible design and reliable production are presented. The plugs provide design basis for the deposition drifts. The latter are further discussed and verified in the 3H Underground openings construction report (Posiva 2016c). Deposition drifts The design basis imposed by the plug on the underground openings is presented in Table 2-5. Table 2-5. Design basis imposed by the plug on the design of deposition drifts. Required property Inflow/seepage of water to the part of the deposition drift where the plug shall be installed must be limited since excessive water inflow during construction of the plug may impair the properties of the finished plug. No fractures areallowed at the plug location. A notch for foundation of the plug shall be prepared in the rock. Anchoring for structures for the installation of the plug shall be prepared in the rock. The strenght and properties of the rock in the area of the recess for the plug shall be sufficient to resist the load transmitted from the plug without fracturing. Design basis Accepted inflow rate for the whole drift is about 10 l/min. Geometry of the reference plug. Geometry and loads according to the reference design of the plug. The forces transmitted from the plug to the rock.

32 24

33 25 3 REFERENCE DESIGN OF THE PLUGS 3.1 Description of the reference design As mentioned in Section 2.2 the compartment plugs are used to hydraulically separate and seal off sections in the deposition drift and they also enable the water filling procedures of DAWE. The function and the reference design of the drift plug is similar to the compartment plug but is used to seal the outer end of the deposition drift to avoid significant water flows out of the drift, which could give rise to piping and erosion of the buffer, either through the plug itself, or through the adjacent rock. The drift plug also enables the water filling procedures of DAWE. The requirements for the drift plug are considerably stricter than those for the compartment plug, both regarding the pressure tolerances and durability over time. This is because the compartment plug has a function only during the installation phase, whereas the drift plug must withstand the full hydrostatic pressure and the swelling pressure, and be sufficiently tight to form a part of the system as long as the adjacent central tunnels are not backfilled and saturated. The compartment plug and the drift plug consists of following three main components: Fastening ring Collar (with bushings/lead-throughs for watering and air evacuation pipes) Cap (with connection for pellet filling) The present reference design originates from the prototype of the compartment plug that was developed during 2009 and 2010 with the objective to verify the ability to divide a KBS-3H drift into hydrologically separated compartments. The prototype was tested in the 15 metre long drift, DA1622A01, at the -220 metre level at Äspö HRL (SKB 2012). The compartment plug used for the tests was made of carbon steel (grade S355). The tests were successful and it was shown that the design fulfilled the set-up test criteria. The compartment plug prototype design was subsequently used as a plug to seal the MPT drift which also included lead-throughs/bushings for artificial watering and air evacuation pipes (SKB 2012). The drift plug has not been manufactured, nor tested. However, a preliminary FEM calculation has been performed for the drift plug based on a modified version of the compartment plug using titanium to show that the design has potential to be a viable solution that can fulfil high requirements when the deposition process is completed. Detailed design drawings have not yet been developed for the compartment or the drift plug in titanium. This will be done at a later stage. The plug reference design is therefore not necessarily optimised and the design may at a later stage be changed provided that it can be demonstrated that the new design conforms to the design basis. Some modification proposals to the reference design are presented in Section 3.2. The fastening ring is a V-shaped ring that is cast into an excavated rock notch using low-ph concrete. The collar is attached to the fastening ring by welding and the cap is attached to the collar also by welding. The compartment plug and the drift plug are both designed so that the welds do not carry any load, thus only function as a seal. The

34 26 overall principle of the plugs is shown in Figure 3-1. Figure 3-2 shows the watering and air evacuation pipes located in the lower part of the plug. Figure 3-1. Section view of the compartment plug Figure 3-2. Watering and air evacuation pipes To allow installation of the fastening rings and the collar they are divided in four sections that are fixed together in the deposition drift, see Figure 3-3. The main dimensions are shown in Figure 3-4.

35 27 Figure 3-3. Exploded 3D view of the compartment plug. Left, from inside. Right, from outside. Notch approx. Ф2350 Ф2250 Ф1850 Ф1440 Ф Figure 3-4. Section view of the plug showing the main dimensions in mm. Fastening ring The fastening ring is a V-shaped ring, see Figure 3-5, placed in the notch that is cut out in the rock surrounding the deposition drift. The annular space between the notch and the fastening ring shall be grouted using low-ph concrete. The installation of the fastening ring will be performed before commencing filling of the drift. The fastening ring is not allowed to protrude outside the rock surface of the drift because this would

36 28 interfere with the subsequent deposition activities that will take place after installation of the fastening ring. The fastening ring shall be rigid and form stable enough to ensure good fitting when the collar is installed. As mentioned in Section 3.1, to allow installation of the fastening ring, the ring is divided into four sections that are fixed together in the deposition drift. The ring sections are provided with set screws such that the position in the notch can be adjusted and fixed. Special consideration shall be made regarding bonding between the ring surface and the concrete. The bottom of the fastening ring is provided with openings to allow for connection of grout injection hoses and for air evacuation at the top. The fastening ring casting arrangement is shown in Figure 3-6. To make it possible running over the fastening ring with the deposition machine is, after installation, a bridge arrangement is placed at the bottom of the fastening ring, see Figure 3-7. After the deposition has been completed the bridge is removed to allow for installation of the collar. Figure 3-5. Fastening ring of the compartment plug Figure 3-6. Fastening ring, section view of the casting arrangement.

37 29 Figure 3-7. Fastening ring bridge arrangement to allow the deposition machine to run in the drift Collar The collar is a ring that is V-shaped on the outer edge to fit to the inside of the fastening ring, see Figure 3-8. The collar will transfer the load from the cap to the rock via the fastening ring and the grouting. As in the case of the fastening ring, the collar must be divided in four sections to allow installation of the collar in the deposition drift. The collar is also provided with a ring to which the cap will be mounted. After that the sections have been fixed together the collar will be welded to the fastening ring see Figure 3-9. The collar is also provided with three lead-throughs to allow the water filling pipes and one penetration for the air evacuation pipes, see also section Figure 3-8. Collar of the compartment plug

38 30 Rock Weld Weld Figure 3-9. Section view showing weld locations fastening ring/collar Cap The cap has the shape of a dome and is attached to the collar by welding. The shape of the cap is chosen so that the stress in the cap is distributed as evenly as possible. The cap is provided with a filling pipe (DN100) for bentonite pellets provided with a flange on the outside. The pellets will be introduced after that the cap has been installed. The filling pipe is plugged by a blind flange bolted in place after filling. Air evacuation and wetting pipes (and lead-through) In the reference design alternative the empty annular space in the slot between the deposition drift wall and the supercontainer, distance block and filling components inside a sealed compartment will be artificially filled with water. Water filling will be done by pumping water through the plug via the watering pipes. The pipes are extending approximately two metres into the drift. During the water filling, air will be compressed and accumulated at the end of the drift compartment due to its slightly upward inclination. This trapped air needs to be evacuated through a pipe (maximum length 150 m). The three water filling pipes extend behind the pellet filling section underneath the transition block, see Figure In the compartment end the air evacuation pipe is extended with a short bottom pipe to the highest point of the drift, this ensures complete water filling, see Figure Water is pumped in through the three pipes with a flow rate of about 25 l/min per pipe for approximately 8 hours and after the water starts to come out of the air evacuation pipe all the valves are closed.

39 31 Air evacuation Pipe Watering Pipe Figure Watering and air evacuation pipes Main components of the water filling system with short pipes through the compartment plug (similar design for the drift plug). The three short water filling pipes lead the water past the pellet filling section underneath the transition block. The lead-throughs in the collar are provided with sealing and with closing valves in which the watering and air evacuation pipes are running through, see Figure The watering and air evacuation pipe dimensions are ϕ33.7x2 mm. The watering and air evacuation pipes are provided with valves at the end. After finalized filling the valves are closed and the pipes are retracted out from the compartment and removed. The watering pipes are short (<3 metres) and can be removed as one piece. When removing/retracting the pipes the pipe is pulled out until the end of the pipe is near the sealing, after which the lead through valve is closed and the pipe can be fully removed. The air evacuation pipe is up to 150 metres long and is therefore divided in sections of approximately 5 metres. The pipe is connected to the rock wall with clips, the clips will be left in the drift after removal of the pipe. The pipe sections are provided with treads. The far end of the pipe is provide with a check valve, see Figure 3-12 and Figure 3-13 that closes when the pipe is retracted from its fixed position to prevent water running out from the compartment when the pipe is removed. The housing for the check valve and the pipe leading up to the top of the drift is left inside the deposition drift after removal of the pipe. After that the pipes have been removed the valve and the adapter fitted to the leadthrough are removed and the lead-through is sealed with a seal plug. The plug is welded to the lead-through. The plugging is illustrated in Figure Installation of the seal plug will be done without releasing water out from the compartment.

40 32 End towards collar Valve Sealing Watering/Air evacuation Pipe Water connection Valve Figure Lead-through arrangement showing the adapter towards the collar, leadthrough valve, sealing arrangement and the watering/air evacuation pipe with valve. Part of pipe that is left inside the drift Check valve housing that is left inside the drift Figure Schematic location of the air evacuation pipe at the rear end of the drift. The circular 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.

41 33 Connection for pipe leading to top of drift Housing part that will be left in the drift Check valve fixed to end of the air evacuation pipe Figure Check valve that is fixed to the end of the air evacuation pipe. Figure Illustration showing the principle of sealing the lead-trough pipes with a welded plug.

42 Modification proposals Manufacturing aspects of plugs As mentioned in Section 3.1 the design is complicated since it includes a large number of welds. It is proposed to investigate if it is possible to make design simplifications and/or to use alternative manufacturing methods. It is however difficult to make any major changes to the general concept that has been demonstrated functional in situ. Due to the complicated design and many welds, casting techniques could be one way of overcoming troublesome fabrication sequences. Some parts of the drift plug such as the fastening ring and the collar should be evaluated whether there is a possibility of manufacturing these parts from titanium casting. Fastening Ring It is proposed to redesign/improve the bounding capability and to make the ring stiffer. A new design is shown in Figure 3-15 where horizontal plates provided with stiffeners are added at the top of the V to improve the bounding to the grout near the weld area. The plate at the bottom of the V has also been extended to improve the bounding capability and together with the other stiffeners extend the potential leak path between the fastening ring and the grouting. It is also proposed to install a guide channel at the bottom of the V for an injection tube. The guide channel will allow for installation of the injection hose during assembly of the fastening ring segments. The guide channel will ensure for a correct positioning of the injection tube. The guide channel can be made of a half pipe or a u-bar provided with holes/slots welded to the ring segments. The side towards the grouting shall be covered with a fiber cloth (geotextile) to prevent the grouting to enter the guide channel during installation. With the new proposed design which creates an extended leak path it might however not be necessary with post grouting. The guide channel can in this case be eliminated. Decision can be made after tests.

43 35 Guide channel for grouting hose Plate extended Grouting Rock Fastening ring New plate with stiffeners Figure Section view showing new proposed fastening ring. Set screw Set screw Figure Section view of the fastening ring showing set screws. Set screws (studs) for fixation/positioning of the fastening ring can be arranged as shown in Figure 3-16 below. After installation, the screws shall be cut flush with the fastening ring plate.

44 36 Collar Figure 3-17 shows a section view with the new reference design for the collar which will make it much easier to access the weld locations. This will improve the conditions for using automated welding equipment and will also improve accessibility for NDT examination of the welds. The proposed design will also reduce the overall weight. The shape will also make the installation of the lead-through for the water filling and air evacuation pipes easier. The lead-through and a new drain pipe in the low point are illustrated in Figure The drain pipe can in principle be identical with the leadthrough pipes. It is assumed that the proposed design can be used for the collar of both the compartment plug and the drift plug and that only plate thickness, especially for the cap, and number of stiffeners in the collar will vary. The proposed collar design and its feasibility are presently based on experience and engineering judgment. This must of course be verified by new calculations during detailed design. Figure 3-19 shows sectional views of the installation. Grouting Rock Fastening ring New weld location Collar Cap New weld location Collar stiffener Figure Section view showing new proposed fastening ring (in red) and collar (in blue) design

45 37 Lead-throughs Drain pipe Figure Section view showing an illustration of the plug from the outside. Leadthroughs and drain pipe are shown in green. Figure Section view from side 3.3 Material properties Based on the long-term performance aspects titanium has been selected for the plugs. The plugs shall be manufactured in Titanium Grade 3 or Grade 12 (ASTM). Titanium Grade 3 and 12 have similar mechanical properties and either one can be chosen depending on availability. Mechanical properties of Titanium Grade 3 and 12 are shown in Table 3-1 and the corresponding chemical compositions are shown in Table 3-2.

46 38 Table 3-1. Material properties of Titanium Grade 3 and Grade 12 Density ρ [kg/m3] Tensile strength Yield σy [MPa] Tensile strength Ultimate σuts [MPa] Grade Grade min 345 (typical 480) min 483 (typical 620) Table 3-2. Chemical compositions Titanium Grade 3 and Grade 12 Content (%) Ti N C H Fe O Mo Ni Grade 3 bal Grade 12 bal Low ph-concrete The grouting around the fastening ring shall be made with low ph-concrete to avoid negative impact on the barriers. A low ph-concrete (ph< 11) is a concrete where 40 wt- % of the binder is replaced with silica fume. The concrete is determined so that it will have the strength and tightness required to conform to the design basis. Concrete recipe has however not been developed yet for this application. 3.5 Plug data Table 3-3 presents estimates of the weight of the different plug components when manufactured in titanium and also the corresponding estimated grouting volumes. The estimated weight of the drift plug is based on the assumption that the swelling pressure will be maximum 5 MPa. Table 3-3. Estimated weight of compartment plug and drift plug components when manufactured in titanium and the corresponding grouting volumes Fastening ring Collar Cap Total weight Grouting [kg] [kg] [kg] [kg] [m 3 ] Compartment plug Drift plug

47 39 4 CONFORMITY OF THE REFERENCE PLUG TO THE DESIGN PREMISES This chapter summarizes the performed analyses and measures taken to verify that the reference plugs conform to the design basis, as described in Chapter Conditions for the analyses of mechanical loads Verification analyses have been carried out based on the reference design described in Sections 3.1 and 3.2 and any deviations from this are given in conjunction with the specific load case. Codes and standards The compartment plug and the drift plug shall be designed in accordance with European Steel Code EC3. Partial Factors The following partial factors according to EC3 are proposed: Safety Class partial factor γγ dd = 0.83 (Safety class 1) Material Property partial factor γγ MM = 1.0 Hydrostatic Load partial factor γγ QQ,h = 1.0 (dddddd tttt nnnnnnnnnnnn oooo llllllll) Swelling Pressure partial factor γγ QQ,ss = 1.35 Load conditions Compartment plug The compartment plug shall be watertight and be able to withstand a hydrostatic pressure of 5 MPa representing the pressure of a 500 m water column. The swelling pressure of the bentonite shall not be added. It has been assumed that by the time the swelling pressure has developed, the drift will be filled and sealed. Drift plug The drift plug shall be watertight and shall be able to withstand a hydrostatic pressure of 5 MPa and a uniform swelling pressure of X 1 MPa resulting from buffer and filling components. In addition, as a hypothesis the cap shall be able to withstand uneven swelling pressure acting on one third of the cap and is proposed to vary up to 50 % of the maximum swelling pressure. The uneven swelling pressure is assumed to be caused by e.g. uneven wetting and swelling during homogenisation/saturation. 1 Maximum swelling pressure to be determined. According to calculations the maximum swelling pressure that can act on the plug is about 1.4 MPa (Posiva 2016b).

48 Modelling and calculations Compartment plug Strength calculations of the compartment plug were performed using the Algor software ( which is a Finite Element (FEM) program. Either 6 or 8 node brick elements and either linear or nonlinear material models have been used in the calculations. Loads and coefficients The calculations were performed with the data listed in Table 4-1 and Table 4-2. Table 4-1. Design data used for the calculation of the compartment plug. Design Data Pressure 5 MPa Load safety factor 1.35 Material safety factor 1.1 Material steel S355 (yield limit 355 MPa) Grout elastic modulus 35.5 GPa Rock elastic modulus 50 GPa Steel elastic modulus 205 GPa Poisson s coefficient 0.3 (0.15 for the grout) Table 4-2. Geometry of the compartment plug. Geometry Diameter of the dome membrane (cap) Height of dome membrane (cap) Thickness of dome membrane (cap) Collar main plates thickness Thickness of the grout layer Thickness of the rock layer 1650 mm 400 mm 16 mm 20 mm 40 mm 60 mm Model geometry and restraints of the dome The dome element mesh includes a quarter of the dome (axi-symmetry). The perimeter of the dome is considered to be rigidly fixed. Symmetry boundary condition is applied on the other boundaries. The shape for the dome was chosen from candidate by obtaining a shape with which the maximum peak stress value is lowest. The chosen shape for the dome is derived by trial and error and it is shown in Figure 4-1.

49 41 Figure 4-1. Geometrical shape of the compartment plug dome. Results The von Mises stress distribution and displacements of the dome are shown in Figure 4-2. Figure 4-2. Left, von Mises stress distribution. Right, Displacements of the dome membrane of the compartment plug. As can be seen in Figure 4-2, the highest stresses occur at the centre of the dome. Some stress concentration can be seen at the perimeter of the dome, where there is a fixed boundary condition. The von Mises stresses are below the calculation strength fd = 323 MPa (355/1.1), and hence the stresses are on an acceptable level. Maximum displacement at the centre of the dome is 1.4 mm with a load safety factor of 1.35 and thereby the displacement with the nominal load of 5 MPa is approx. 1 mm.

50 42 Evaluation of the complete structure In the model of the complete structure, the dome is supported by a collar through coneshaped flanges. Forces from the collar are transmitted by contact surfaces to the fastening ring and thereafter to the casting and rock. The model of the whole structure includes all steel parts, rock, and the concrete cast between the rock and the steel. The model geometry is shown in Figure 4-3. Figure 4-3. Model geometry for the whole compartment plug structure including concrete cast and rock. In Figure 4-3, each different part is represented by a different colour. A contact surface allowing parallel movement of the parts in respect to each other is defined between parts. Between the concrete casting (grey) and the rock (brown) adhesion is assumed, therefore a fixed contact between the surfaces is defined. Symmetrical boundary conditions are applied on the cut planes of the model. A fixed boundary condition is applied on the outer surface of the rock. Results The resulting displacements of the structure are shown in Figure 4-4. The load safety factor 1.35 is included in the values. The displacements outside the dome are of a magnitude of tenths of millimetres.

51 43 Figure 4-4. Calculated displacement (mm) for the whole structure for the compartment plug. Von Mises stresses are shown in Figure 4-5. Outside the dome, which is covered by the distinct element model, the highest stresses appear in the stiffening ribs. The stress level (maximum stress 230 MPa) is, however, well below the calculation strength of the steel. Figure 4-5. von Mises stress distribution (MPa) for the whole structure for the compartment plug. Compression stresses in the concrete cast and the rock are shown in Figure 4-6. Stress peaks can be seen at the intersection points of the collar profile and stiffening ribs. The maximum stresses in the concrete are in general 100 MPa. Stress peaks are somewhat higher than that, but the area where stresses above 100 MPa occur is negligible. The

52 44 compression is evening out rapidly in the concrete cast. In the rock, at the bottom of the groove, highest compression stress values are approximately 32 MPa. Figure 4-6. Left, minimum principal stress in concrete cast. Right, minimum principal stress in rock for the compartment plug. Drift plug A FEM-analysis has been carried out on the drift plug-design, and its input parameters are summarised in Table 4-3 and Table 4-4. Geometry.

53 45 Table 4-3. Design data used for the calculation for the drift plug. Design Data Hydrostatic pressure 5 MPa Swelling pressure 10 MPa 2 Hetrogeneous pressure 2 MPa Load safety factor 1.35 Material safety factor 1.1 Material Titanium Grade 12 (ASTM) Material yield limit 380 MPa Modulus of elasticity, tensile 105 GPa Modulus of elasticity, compressive 110 GPa Poisson s coefficient 0.37 Modulus of elasticity, grout 35.5 GPa Modulus of elasticity, rock 50 GPa Steel elastic modulus 205 GPa Poisson s coefficient 0.3 (0.15 for the grout) Table 4-4. Geometry of the drift plug. Geometry Diameter of the dome membrane Height of dome membrane Thickness of dome membrane Collar main plates thickness Thickness of the grout layer Thickness of the rock layer 1,650 mm 400 mm 32 mm 20 mm 40 mm 50 mm The analysis, see Figure 4-7, shows that the stresses on the cap are below the acceptance level. According to analysis the drift plug will withstand a load of 22 MPa before failure of the components is expected, which indicates that it will withstand the design loading of 15 MPa with a high degree of confidence. The maximum stress in the grouting layer is calculated to be 84 MPa, which is acting on a very limited area. The average stress is 48 MPa. Concrete strength depends on the mixture used, but tests in the laboratory done so far on low-ph concrete samples indicate a strength of approximately 88 MPa. The highest compressional stress in the rock is 44 MPa. In addition to the stresses from the plug, stresses from other sources exist after deposition, i.e. in situ rock stresses, and 2 This was an assumption made at the time of this calculation.

54 46 excavation (drift, V-notch) induced stresses as well as thermally induced stresses. Calculations of these were not performed within the scope of the initial work but will be carried out in the upcoming project phase in order to fully describe the plug-rock interactions and strengths. This will possibly require optimisation of the geometry of the notch and will enable calculations of the required minimum distance between the plug and the entrance to the drift. Figure 4-7. Result of complete structure of the drift plug. Conclusions It can be concluded that the analysed design for the drift plug has potential to be a viable solution that can fulfil the high requirements when the deposition process is completed. It is however to be noted that the present analysis is conservative with regards to the swelling pressure. The final design for the drift plug will probably not differ very much from that of the compartment plug other than the thickness of the dome to withstand the swelling pressure. 4.3 Test of mechanical strength The mechanical strength of the compartment plug was checked during the test installation that was done during the winter 2008/2009 at the 220 m level at the Äspö HRL where it was in full scale demonstrated that the compartment plug can withstand a hydrostatic pressure of 5 MPa (SKB 2012).