Design and Production of the KBS-3H Repository

Transcription

1 POSIVA Design and Production of the KBS-3H Repository Posiva Oy January 2018 POSIVA OY Olkiluoto FI EURAJOKI, FINLAND Phone (02) (nat.), ( ) (int.) Fax (02) (nat.), ( ) (int.)

2

3 POSIVA Design and Production of the KBS-3H Repository 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 EURAJOKI, FINLAND Phone (02) (nat.), ( ) (int.) Fax (02) (nat.), ( ) (int.)

4 ISBN: ISSN:

5 Posiva Oy Olkiluoto FI EURAJOKI, FINLAND Puh (31) - Int. Tel (31) Raportin tunnus - Report code Posiva Julkaisuaika - Date January 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy Nimeke Title Design and production of the KBS-3H repository Tiivistelmä Abstract This report presents the common basis for a set of reports, denoted the production reports, that presents how the KBS-3H final repository for spent nuclear fuel is designed and constructed. It provides support to a safety evaluation of the KBS-3H final repository and the KBS-3H disposal facility. Following a summary of the KBS-3H design basis and a description of the KBS-3H repository system, an accounting is made of all production lines applicable to KBS-3H, with special emphasis of the KBS-3H-specific production lines; the buffer and filling components, the supercontainer, the plug and the underground openings construction production lines, respectively. Differences between SKB and Posiva implementation of KBS-3H are indicated. Avainsanat - Keywords Design basis, production line, repository system ISBN ISSN ISBN ISSN Sivumäärä Number of pages Kieli Language 96 English

6

7 Posiva Oy Olkiluoto FI EURAJOKI, FINLAND Puh (31) - Int. Tel (31) Raportin tunnus - Report code Posiva Julkaisuaika - Date January 2018 Tekijä(t) Author(s) Posiva Oy Toimeksiantaja(t) Commissioned by Posiva Oy Nimeke Title KBS-3H loppusijoituslaitoksen suunnittelu ja tuotanto Tiivistelmä Abstract Tässä raportissa esitetään yhteinen perusta tuotantolinjaraporttisarjalle, joissa kuvataan, miten KBS-3H -ratkaisussa käytetyn ydinpolttoaineen loppusijoituslaitos suunnitellaan, toteutetaan ja tarkastetaan. Tuotantolinjaraporttisarja tulee muodostamaan perustan KBS-3H turvallisuusraporttien ja loppusijoituslaitoksen yhteenvetoraportin laadinnalle. KBS-3H ratkaisun suunnitteluperusteiden ja loppusijoitusjärjestelmän kuvauksen mukaisesti tässä raportissa on esitetty pääpiirteittäin vaakaratkaisua koskevat tuotantolinjat pääpainon ollessa sille ominaisille tuotantolinjoille; puskuri ja täyttökomponentit, asennuspakkaus, tulpat ja maanalaiset tilat. Organisaatioiden (Posiva ja SKB) väliset erot vaakaratkaisun toteutuksessa tuodaan esille Avainsanat - Keywords Suunnitteluperuste, tuotantolinja, loppusijoitusjärjestelmä ISBN ISSN ISBN ISSN Sivumäärä Number of pages Kieli Language 96 englanti

8

9 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ PREFACE INTRODUCTION General basis The role of this report Central concepts Terminology Differences in terminology between the Posiva and SKB application Purpose, objectives and limitations Purpose and objectives Limitations Structure and content This report The spent fuel report The canister report The engineered barrier production reports The underground openings construction report Main differences between Posiva and SKB implementation of KBS-3H Underground openings design basis Rock engineering Supercontainer design basis SUMMARY OF DESIGN BASIS Introduction The Posiva VAHA system Overview of the SKB RMS system Demands related to the design The spent fuel to be disposed Functions of the KBS-3H repository and design considerations The KBS-3H disposal concept Functions of the KBS-3H repository Design considerations Design basis from safety assessment, design and technology development General approach Design basis related to functions of the KBS-3H repository Design basis from other parts of the repository Design basis related to production and operation Design basis related to the safe operation of the disposal facility THE KBS-3H REPOSITORY SYSTEM The KBS-3H repository and its functions Definitions, purpose and reference design The functions and properties of the KBS-3H repository The engineered barriers and other parts of the KBS-3H repository The spent fuel Definitions Properties of importance for the design and long-term safety of the KBS- 3H repository... 35

10 Types of spent fuel to be deposited The canister Definition and purpose The safety functions of the canister Review of canister design/-s Supercontainer Definition and purpose Requirements on supporting functions Review of supercontainer design The buffer and filling components Definition and purpose The safety functions of the buffer and filling components Review of buffer and filling components design The plugs Different kinds of plugs and their purposes The safety functions of the plugs Review of plug design The closure Definition and purpose The safety functions of the closure Review of closure design Host rock and underground openings Definition and purpose The safety functions of the host rock and the functions of the underground openings Review of underground openings design Design considerations Logistics of the KBS-3H repository system THE KBS-3H PRODUCTION LINES Facilities related to disposal Definition and scope Interim storage, encapsulation and transportation The KBS-3H disposal facility The production and the production lines The production The production lines Design and production line interfaces The spent fuel line Overview Interfaces between the design of the KBS-3H repository and its barriers and the handling of the spent fuel Production line interfaces The canister production line Overview Design interfaces Production line interfaces The buffer and filling components production line Overview of design Design interfaces Production line interfaces The supercontainer production line Overview of design of supercontainer... 68

11 Design interfaces Production line interfaces The production of plugs Overview of plug design Design interfaces Production line interfaces Construction of the underground openings Overview of design of underground openings Design interfaces Production line interfaces Closure production line Overview Design interfaces Production line interfaces REFERENCES... 93

12 4

13 5 PREFACE For the construction of the KBS-3H repository Posiva and SKB have defined a set of production lines: (the spent nuclear fuel), (the canister), the buffer and filling components, the supercontainer, the plugs the underground openings, and (the closure, including backfill of the main/central tunnels). The production lines without parentheses are reported in new separate KBS-3H-specific production reports, and in addition there is an overarching Repository production report (the current report) which presents an overview of the separate production lines and the common basis for these reports. The production lines within parentheses are, with minor exceptions, essentially generic to both the KBS-3V and KBS-3H disposal variants. Overall KBS-3H reference is therefore made to the corresponding KBS-3V reports produced by Posiva and SKB, respectively. Identified differences between KBS-3V and KBS-3H are accounted for in the current report. The set of KBS-3H production line reports addresses design premises/design basis, reference design, conformity of the reference design to design premises/design basis, production and the initial state, i.e. the results of the production. Thus, the reports provide input to any KBS-3H safety assessment concerning the characteristics of the as built KBS-3H repository and to any KBS-3H repository operation concerning the handling of the engineered barriers and construction of underground openings. The report has been compiled by Anders Winberg (Conterra AB) with assistance from Annika Hagros and Antti Ikonen (Saanio and Riekkola Oy), Bo Halvarsson (Vattenfall AB) and Jorma Autio (B+Tech). Acknowledgement is also given to the authorship of the SKB 3V repository production report (SKB 2010a) which provided the overall structure for the current report. 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 phase

14 6

15 7 1 INTRODUCTION 1.1 General basis This report contains the common basis for a set of reports, referred to as the Production reports, presenting how the KBS-3H final repository for spent nuclear fuel is designed and constructed. It provides support to a safety evaluation of the KBS-3H final repository and the KBS-3H disposal facility. The KBS-3H final repository is based on the KBS 3 method developed by Posiva and SKB, c.f. Figure 1-1 and KBS-3H-related details in Figure 4-7. The term KBS-3H repository refers to the final repository and the term KBS-3H disposal facility refers to the facility within which the KBS-3H repository is constructed. During the operational phases the KBS-3H disposal facility will contain areas where canisters are being deposited and buffer and backfill installed as well as areas where construction of new deposition drifts are underway, it will also contain finished parts of the KBS-3H repository where deposition has been completed. When all canisters with spent fuel have been deposited, the KBS-3H disposal facility will be decommissioned and closed. Figure 1-1. The KBS-3 disposal facility (mid) and the KBS-3H repository (right) and the KBS-3V repository (left). The KBS-3H repository is constructed within the KBS-3H disposal facility.

16 8 The establishment of a KBS-3H repository requires that there is a system, the KBS-3 system, comprising the facilities etc, that are needed for the disposal of spent nuclear fuel according to the KBS-3 method. The KBS-3 system consists of a central facility for interim storage and encapsulation of the spent nuclear fuel, a transport system for the transportation of canisters with encapsulated spent nuclear fuel, a KBS3H repository and a KBS-3H disposal facility. SKB and Posiva have already submitted license applications for constructing KBS-3V repositories which are based on vertical deposition. In this latter alternative, the canisters are deposited in vertical holes (c. 8 m long and c m in diameter) lined with bentonite blocks. The vertical deposition holes are drilled in near horizontal deposition tunnels which are subsequently backfilled with clay blocks (where SKB s choice is blocks of Na bentonite) after the disposal has been completed. The KBS-3H repository differs in so much that deposition is made in near horizontal deposition drifts (1.85 m in diameter) into which canisters with spent nuclear fuel are administered by way of prefabricated supercontainers, c m in diameter and typically m long depending of type of SF-canister, made up of a perforated titanium shell containing the canister embedded in bentonite buffer. The space in the deposition drifts between the supercontainers, located and distributed on the basis of applicable design premises/design basis, is filled with bentonite blocks (distance blocks) whereas filling components are administered close to plugs or where criteria related to deposition are not fulfilled. The KBS-3H repository and its engineered barriers and underground openings are produced within the KBS 3 system. Posiva and SKB have jointly defined the following production lines for the construction of the KBS-3H repository (the ones listed within parentheses are assumed covered by existing documents produced for KBS-3V by Posiva and SKB): (the spent nuclear fuel), (the canister), the supercontainer, the buffer and filling components, the plugs, the underground openings, and (the closure, including backfill of main/central tunnels). The production lines comprise all the activities to handle the spent nuclear fuel, to produce and install the engineered barriers and to design and construct the underground openings. The production reports within parentheses are essentially generic to both the KBS-3V and KBS-3H alternatives of the KBS-3 system. Hence these production reports are only covered tentatively in this report for reasons of completeness, highlighting any important differences. Reference is made to the corresponding KBS-3V production reports and any noted differences are indicated.

17 9 1.2 The role of this report The SKB 3V Repository production report (SKB 2010a) was produced ahead of the 3V component PLs and served the purpose of presenting the necessary background, judicial and regulatory framework and introduce and discuss the various design and functional elements of the repository, allowing the component PLs to make reference to the repository production PL. Posiva did not produce a corresponding 3V repository production report, whereas the corresponding individual PLs were produced, see Table 1-1. In the case of KBS-3H the process is somewhat retrograde. The various KBS-3H component PLs as well as the KBS-3H Design basis report (Posiva 2016a) have been developed beforehand and essentially independent of the current KBS-3H Repository Production report. The latter, having being overall produced posterior to the PLs, building largely on the disposition of the SKB 3V repository production report (SKB 2010a), however serving more as an umbrella and overview document of the KBS-3H production, also presenting relationships and references to those production reports which are common to KBS-3V. The individual reports that form the set of production reports and their short names used as references within the set of production reports are illustrated in Figure 1-2 their full names are given in Table 1-1. 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. The set of KBS-3H production reports and their short names. The canister, buffer and filling components, plug and closure (including backfill) production reports are commonly referred to as Engineered barrier production reports.

18 10 Table 1-1. The set of Production line reports and their full and short names. Full title Short name used within the Production reports Reference Design and production of the KBS-3H Repository. SKB : Spent nuclear fuel for disposal in the KBS-3 repository. Posiva : Canister Production Line 2012 Design, production and initial state of the canister. SKB : Design, production and initial state of the canister. Posiva : Canister Production Line 2012 Design, production and initial state of the canister. KBS-3H Design, production and initial state of the KBS-3H buffer and filling components. KBS-3H Design, production and initial state of the supercontainer. KBS-3H Design, production and initial state of the Compartment and Drift Plug. SKB : Design, production and initial state of the backfill and plug in deposition tunnels. SKB : Design, production and initial state of the closure. Posiva : Backfill Production Line 2012 Design, production and initial state of the deposition tunnel backfill and plug. Posiva : Closure Production Line 2012 Design, production and initial state of closure. KBS-3H - Design, Construction and Initial State of the Underground Openings 3H Repository production report (Spent fuel report) (Canister production report ) Buffer and filling components production report Supercontainer production report Plug production report Closure production report 3H Underground openings construction report This report : Posiva 2016f, Posiva Oy SKB (3V) : SKB 2010a SKB : SKB 2010b Posiva : Raiko et al SKB : SKB 2010c Posiva : Raiko et al Posiva 2016b, Posiva Oy Posiva 2016d, Posiva Oy Posiva 2016c, Posiva Oy SKB : SKB 2010d, 2010d Posiva : Sievänen et al. 2012, Keto et al. 2013, Posiva 2016e, Posiva Oy 1.3 Central concepts Terminology In this section, some concepts of importance for the production reports are defined and explained. Concepts are written in bold italics, definitions are written in italics and explanations are written in normal text. The concepts are introduced in alphabetic order. Regarding quality management SKB has decided to apply the vocabulary in the standard /ISO 9000:2005/. Posiva s management system takes into account the

19 11 following standards: SFS-EN ISO 9001:2008, SFS-EN ISO 14001:2004 and OHSAS 18001:fi (2007). barrier: engineered or natural barrier used for achieving long-term safety functions. conformity: fulfilment of a requirement (ISO 9000:2005). design basis: in Posiva s terminology design basis refers to the current and future environment-induced loads and interactions that are taken into account in the design of the repository system, and, ultimately, to the requirements that the planned repository system must fulfil in order to achieve the objectives set for safety and other factors. design premises: in SKB s 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 design specifications in Posiva s terminology. (Technical) Design requirement: requirement that a characteristic of an engineered barrier or underground opening shall fulfill to be approved as a part of the KBS-3 repository (from ( Posiva SKB 2017). design specification: detailed specification to be used in the design, construction and manufacturing. engineered barriers: man-made barriers (see Barrier and EBS). initial state: the state when direct control over a specific part of the system ceases and only limited information can be obtained on the subsequent development of conditions in that part of the system or its near-field. For surface environment, initial state is defined as the present conditions. inspection: conformity evaluation by observation and judgement accompanied, as appropriate, by measurement, testing or gauging (ISO 9000:2005). KBS-3H disposal facility: an entirety comprising the rooms for the disposal of the waste packages and the adjoining underground and above-ground auxiliary facilities. KBS-3H repository : the emplacement rooms for the spent nuclear fuel, consisting of spent nuclear fuel, canister, buffer, filling components, plugs and the related underground openings (deposition drifts). organisation: group of people and facilities with an arrangement of responsibilities, authorities and relationships /ISO 9000:2005/. performance target: a measurable or assessable characteristic of a barrier. The performance target shall include a criterion describing the characteristic which, when met, ensures the performance of a safety function. procedure: specified way to carry out an activity or process /ISO 9000:2005/. process: set of interrelated or interacting activities which transforms inputs to outputs /ISO 9000:2005/. product: result of a process /ISO 9000:2005/. production line: the ordered sequence of stages in the handling of the spent nuclear fuel and production of the engineered barriers. The successive as more information on the

20 12 conditions in the rock becomes available design, site adaptation and construction of underground openings. qualification: investigation and demonstration which shows that a person or a testing, processing or integration process can fulfil its specified tasks /SSMFS 2008:13/. qualification process: process to demonstrate the ability to fulfil specified requirements /ISO 9000:2005/. quality plan: document specifying which procedures and associated resources shall be applied by whom and when to a specific project, product, process or contract /ISO 9000:2005/. record document: document stating results achieved or providing evidence of activities performed /ISO 9000:2005/. reference design: a design that is valid from a defined point in time until further notice. The established reference design shall be used as the precondition for technical development, further design and the analyses of safety, radiation protection and environmental impact. A reference design may be either general or site specific. requirement: a need or expectation that is stated, generally implied or obligatory /ISO 9000:2005/. See design premise above and Chapter 2. safety function: the functions achieved by the characteristics or processes of engineered and natural barriers that are intended to isolate the nuclear waste from the bedrock and the biosphere or to impede the migration of radionuclides Differences in terminology between the Posiva and SKB application 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) and other factors. In SKB s 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 design specifications in Posiva s terminology. Design basis is used when referring to the design premises 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, resources). These form the starting point for the definition of the design basis of disposal operations. Design basis (in line with this report) will be published in (Posiva 2016a).

21 13 It should be noted that although definitions from (SKB Posiva 2016) have been included in Section 1.3.1, it is still open to which extent the same terms will be used within SKB and Posiva, and the KBS-3H Design basis report (Posiva 2016a) uses the Posiva terms, as the report is based on Posiva s VAHA system. Note. In the current report the term design basis (with Posiva s definition and meaning) is used throughout in the remainder of the report. The Posiva-SKB harmonized terms introduced in (SKB Posiva 2016), i.e. safety function, performance target and design specification are used in this document. The exception being that the Level 4 requirements are denoted design requirements instead of technical design requirements, this in order to comply with the KBS-3H Design basis report (Posiva 2016a). 1.4 Purpose, objectives and limitations Purpose and objectives The purpose of the set of KBS-3H production reports is to present how the spent nuclear fuel is handled and how the engineered barriers and underground openings of the KBS- 3H repository are designed, produced and inspected in a manner related to their importance for the safety of the KBS-3H repository. Through the KBS-3H-specific production reports SKB and Posiva intend to present the design specifications for the KBS-3H repository and their sources, and demonstrate how the engineered barriers and underground openings can be designed and produced to conform to the stated design basis. The production reports shall present the current reference designs and production methods and summarise the research and development efforts that support that the KBS-3H repository can be produced in conformity to the design basis. The purpose of the current report the 3H Repository production report is to give an overview of the barriers and barrier functions of the KBS-3H repository and to summarize the overarching design basis applicable to their design. The report shall also provide an overview and summary of the specifics of the KBS-3H system and the associated production lines for the handling of the production of the engineered barriers and construction of the underground openings, and present the main design and production interfaces. The purpose of the Engineered barrier production reports (i.e. for the buffer and filling components, supercontainer and plugs) and the 3H Underground openings construction report is to provide information on design basis, design, production and construction and the resulting initial state as a basis for the KBS-3H safety evaluation. The Engineered barrier production reports and the 3H Underground openings construction report shall also provide information on operational aspects, including handling, deposition and installation of the engineered barriers and construction of the underground openings. The objectives of this report are to present:

22 14 the role of the KBS-3H production reports (also within the KBS-3H safety evaluation), central concepts and their definitions, a summary of the overarching design basis for the KBS-3H repository and its engineered barriers and underground openings, the methodology to derive and manage design specifications, the KBS-3H repository, its barriers and their barrier functions, the KBS-3H system and the handling of the spent fuel and the production of the KBS 3 repository with focus on common aspects and interfaces and dependencies between the production lines, an overview of quality management and safety classification of the engineered barriers, under-ground openings and other parts of the KBS-3H repository and their application within the Production reports, Main aspects of the individual KBS-3H-specific production lines Limitations This report provides a description of the KBS-3H alternative of the KBS-3 system and its facilities. Assessments of its safety, environmental impact, costs etc, are presented in other documents. The respective KBS-3H production reports present in detail how the engineered barriers and underground openings are designed, and produced to conform to the stated design basis. Other aspects of the production, e.g. occupational safety have not been covered during this project phase. The Production reports present one design of the KBS-3H repository and its engineered barriers and underground openings that can be produced in conformity to the KBS-3H design basis (Posiva 2016a). It is foreseen that the presented design, if pursued, will be further developed and improved as a result of additional technology development and safety assessments. The Supercontainer and Buffer and filling components and Plug production reports and the 3H Underground openings construction report together present the design considerations made with respect to the application of best available safety and radiation protection technique and how they have affected the design. Motivations for the described reference design and methods as being the best available are presented separately. The 3H Underground openings construction report contains a general description of how the repository is adapted to a selected site; the Posiva Olkiluoto site. The locations of the other facilities within the KBS-3 system are presented in the KBS-3H Disposal facility description report (Posiva 2016f).

23 Structure and content This report The current report, which is tailored to the SKB 3V repository production report (SKB 2010a), sets the production reports in their context and provides the common basis for the KBS-3H Engineered barrier production reports and the Underground openings construction report. The canister and closure (including backfill of transport and central/main tunnels) production lines for KBS-3H are assumed covered by the corresponding KBS-3V reports, c.f. Table 1-1. The purposes and limitations of the production reports and their role in the KBS-3H safety evaluation are presented in Chapter 1. The latter chapter also contains an overview of the structure and content of the reports and a presentation of some concepts of importance for the reports. In Chapter 2 the substantiation of design basis for the KBS-3 repository is summarized and discussed. The different kinds of design basis related to the different levels of detail in the design and their sources are presented. The treaties, laws and regulations of importance for the design, the spent fuel to be deposited, as well as the approach to substantiate design basis from the results of the safety assessment and technology development are discussed. In Chapter 3 the functions and considerations substantiated based on the treaties, laws and regulations as a specification of the KBS-3 repository, and as guidelines for the design, are presented. The spent fuel to be deposited and its impact on the design are discussed. The purposes, reference designs and barrier functions of the engineered barriers as well as the purpose and functions of the underground openings and plugs are stated. Furthermore, an overview of the logistics and work flow associated with KBS-3H disposal is outlined. In Chapter 4 the facilities of the KBS-3 system and the production lines are presented in brief. The chapter contains a presentation of the facilities their purposes and main activities as well as an overview of the production lines and their interfaces The spent fuel report The Spent fuel report (SKB 2010a, Raiko et al. 2012) comprises a description of the spent fuel to be deposited and the properties of the spent fuel of importance for the design and safety of the KBS-3 repository. It is noted that there is no difference between KBS-3V and KBS-3H in this regard. Consequently, the spent fuel production reports prepared by Posiva and SKB, respectively, are applicable also for the KBS-3H alternative. In the reports, the requirements on the handling of the spent fuel that are related to the design and safety of the KBS-3 repository are stated. The fuel is not produced but handled within the KBS-3 system, and the production line in the respective Spent fuel report comprises a presentation of the handling in accordance with the requirements. Finally, for the initial state the resulting radionuclide inventory and other properties of the encapsulated spent nuclear fuel required for the safety report are presented.

24 The canister report Notable is that there are no major differences between the KBS-3V and KBS-3H canisters since they are physically identical (Raiko et al 2012, Raiko 2013). However, there are some minor differences which are known or are currently being studied. These differences are; The thermo-mechanical loads are different, at least from a theoretical standpoint. There may be differences in the potential for criticality. A study on this topic is currently being carried out by Posiva. Concerning the loads the following has been noted; Thermal analysis carried out by Ikonen and Raiko (2015) studied the impact of the supercontainer in the context of horizontal disposal. The conclusion in brief is that small changes in the structure and orientation of buffer do not influence the cooling negatively. On the contrary, heat transfer (cooling) is improved compared to KBS-3V by the fact that the canister has a tight contact with buffer at the bottom of the drift (resting on the inside of the buffer rings, c.f. Figure 4-11), where also the buffer also has a tight contact with the shell, and by the artificial wetting The engineered barrier production reports The general flow of information in the Engineered barrier production reports (buffer and filling components, supercontainer and plugs) can be described as follows: design basis, reference design, conformity of reference design to design basis, production, initial state, i.e. the results of the production. The barrier functions and design considerations introduced in Chapter 3 of this report are repeated and form the basis for the detailed design basis for each engineered barrier accounted for in the Engineered barrier production reports. The reference designs of the engineered barriers are specified and their basis discussed. The conformity of the reference designs to the design basis is analysed. The presentation of the production starts with the main parts of the production lines presented in Chapter 4 of this report including an introduction to the reference methods applied in the production. This introduction is followed by more detailed descriptions of the individual stages of the production line. The initial state comprises results of the production and the conformity of the produced engineered barriers to their design basis and reference designs The underground openings construction report The design basis for the KBS-3H underground openings are presented in the same way as for the engineered barriers, i.e. starting from the functions and considerations presented in

25 17 Chapter 3 of this report, followed by the more detailed design basis. The presentation of the design basis is followed by a description of the rock engineering and adaptation to site conditions (here specifically to Olkiluoto conditions) including a presentation of the rock engineering methodologies Posiva and SKB intend to apply. The reference designs of the underground openings comprise their site-specific layouts and properties, and their conformity to the design basis. The production part in the underground openings construction report (Posiva 2016e) comprises a presentation of the reference methods to construct and inspect the different underground openings and an overview of possible mitigation measures that may be used to rectify non-conformity to the design basis. As for the engineered barriers, the results of the construction comprise the initial states of the different underground openings and their conformity to their reference designs and design basis. 1.6 Main differences between Posiva and SKB implementation of KBS- 3H The differences between Posiva and SKB application of the KBS-3H disposal alternatives are accounted for in the respective production line reports. In the following, only principal differences are exemplified for reference Underground openings design basis Nominal (centre to centre) horizontal distance from deposition drift to another (drift spacing) is 25 m in Olkiluoto and 30 or 40 m (30 m preferred in terms of utilization) in Forsmark (SKB 2012). The repository shall have sufficient capacity to store 4,500 canisters (Posiva) and 6,000 canisters (SKB) Rock engineering SKB s design differ from that of Posiva in that SKB employs a single main tunnel where as Posiva employs a system with dual central tunnels (20 m nominal rock mass between). In the SKB s concept the deposition drift niche is excavated between the main tunnel and the planned drift whereas in Posiva s case the niche is excavated between the dual tunnels so that the drift starts from the bounding central tunnel Supercontainer design basis The Posiva canisters come in three different lengths (L= 3.552, and m, respectively) with variable supercontainer lengths accordingly, c.f. the supercontainer production report (Posiva 2016d). The SKB canisters however, only come in one length (L= m) which entails that the corresponding supercontainers also come in one size.

26 18

27 19 2 SUMMARY OF DESIGN BASIS 2.1 Introduction The engineered barrier production reports and 3H Underground openings construction report shall contain the design basis for the engineered barriers and underground openings of the KBS-3 repository. The design basis is derived from the following sources: international treaties, Finnish and Swedish laws and regulations, stakeholder demands and agreements, the properties of the spent nuclear fuel, the chosen method for final disposal, the barriers of the final repository and their barrier functions, couplings and interdependencies between them and decisions made in the design, the production and handling of the engineered barriers and the construction of the underground openings, the repository site, the general knowledge about processes that may impact the barrier functions and the safety of the repository, the existing safety assessment and evaluation, primarily the long-term safety but also the operational safety part. There are different kinds of design basis related to the different sources and levels of detail in the design. The most general, highest level, specify the problem to be solved and the basic principles that shall be applied in the design. This top-level design basis is based on laws and regulations, stakeholder demands and decisions and agreements. The next two levels of detail provide high-level specifications of the method and system by which to solve the problem. At these two levels the KBS-3 method and KBS-3H repository and its barriers are specified and their purposes and functions are described. The design basis on these levels are based on the basic principles to be applied, laws and regulations, the properties of the spent nuclear fuel and the chosen method to manage the spent fuel. Finally, the design basis expressing the properties that the different components of the sub-systems, i.e. the barriers and parts of the KBS-3 repository, must have in order to maintain the functions is specified. The design basis specifies the properties to be designed and provide quantitative information on features, events and processes that shall be considered when determining a reference design. The design basis on this level is based on the required functions and feedback from performed safety assessments and technical development. Within the production reports the design basis has been divided

28 20 into: design basis related to the functions in the KBS-3 repository, design basis imposed by other parts of the KBS-3 repository and those related to the production and operation The design basis specifying the issues to be solved by the KBS-3H repository and the functions of the KBS-3H repository and its engineered barriers and underground openings are presented in the KBS-3H Design basis report (Posiva 2016a), whereas this report the 3H Repository production report reviews and summarizes the design specifications and considerations made in deriving the reference designs presented in the KBS-3H engineered barrier production reports (buffer and filling components, supercontainer and plugs) and the 3H underground openings construction report. The KUPP-VAHA 3V process embraces a strive to harmonize Posiva s and SKB s views on technical design requirement applicable to the various barriers of the KBS-3V repository system (SKB Posiva 2016). However, the KBS-3H project during the current project phase has retained the Posiva terminology and associated design basis as presented in the KBS-3H Design basis report (Posiva 2016a), the latter being based on Posiva s VAHA system, see Section The Posiva VAHA system Posiva s requirements management system VAHA is an information system designed in Posiva to manage the requirements related to the geological disposal of spent nuclear fuel. VAHA aims to include all relevant requirements, their origin and rationale with existing solutions to fulfil and verify them, and enables an effective review of compliance and dependencies between separate specifications and requirements. The VAHA database is organized into five levels: - Level 1 consists of the Stakeholder requirements. These are the requirements arising from laws, regulatory requirements, decisions-in-principle and other stakeholder requirements. - Level 2 consist of the System requirements as defined by Posiva on the basis of Posiva s owners requirements and the legal and regulatory requirements listed on Level 1. Level 2 requirements define the EBS components and the functions of the EBS and host rock. - Level 3 consists of the Subsystem requirements which are specific requirements for the canister, buffer, backfill (only in KBS-3V deposition tunnels and main/central tunnels), closure and host rock and underground openings, as well as for filling components, compartment plugs and drift plugs in KBS-3H. The requirements of Level 3 are mostly general and set qualitative requirements (performance targets and target properties) for EBS and host rock performance. - Level 4 Design requirements further clarify and provide more details to the requirements of Level 3. - Level 5 presents the Design specifications. These are the detailed specifications to be used in the design, construction and manufacturing.

29 21 Each requirement has its own ID on the requirements management system VAHA, which is based on the requirement level, system and requirement number. For example, L3-ROC-2 relates to the Level 3 requirement on host rock and underground openings, VAHA requirement 2. In the KBS-3H Design Basis report (Posiva 2016, in prep.), the suffix H is added to the requirement ID whenever a KBS-3H-specific modification has been made to the requirement, or if the requirement is completely new. Requirement tables for Levels 1-4 for KBS-3H are presented in Posiva (2016a, c.f. Appendix A therein). Level 5 requirements (design specifications) are accounted for in the respective KBS- 3H production line reports, to the extent currently being decided upon Overview of the SKB RMS system To manage the different kinds of design basis and their interdependencies, SKB has for the KBS-3V repository developed a requirement management system RMS (SKBDoc ) within which the design basis is reviewed, settled and documented. Within the RMS information such as review status, sources, translation is kept for each design basis. Notably, SKB has so far not devised a particular RMS accounting of the KBS-3H disposal system alternative. 2.2 Demands related to the design The final repository shall conform to the requirements in relevant laws and regulations. Posiva s guiding principles as expressed in VAHA, c.f. Section 2.1.1, or in case of SKB the stakeholder demands expressed in SKB s guiding principles: safety, efficiency and responsiveness shall be considered in the design, see also Section Further, the final repository for spent nuclear fuel shall be adapted to the scopes and time schedules of the Finnish and Swedish nuclear power programmes, respectively. The applicable international treaties, national laws and regulations relevant for the design of a final repository for spent nuclear fuel in Finland and Sweden, respectively, are detailed in the KBS-3H design basis report (Posiva 2016a). This said, references (between slashes / /) are in places given in the following to applicable regulations in conjunction with presentation of the design basis, where full references to judicial and regulatory documentation are provided in (Posiva 2016a). 2.3 The spent fuel to be disposed One property of the spent nuclear fuel, which contributes to the long-term safety and is of essential importance for the KBS-3 method, is the form of the spent nuclear fuel. The bulk of the fuel to be deposited consists of uranium oxide, which has very low solubility in a KBS-3 repository environment. With respect to this the fuel to be deposited in a KBS-3 repository shall be in oxide form or in some other form with similar low solubility

30 22 in the groundwater that may penetrate deposited canisters. This applies both to the KBS- 3V and KBS-3H repository alternatives. The spent nuclear fuel to be finally deposited form an important basis for the design of the final repository. Parameters that will affect the design of the final repository are the radiotoxicity and decay power and the total amount of spent fuel to be deposited. Both these parameters are determined by the radionuclide inventory and will decrease as the radioactive decay proceeds. Also, the dimensions of the fuel assemblies will impact the design. The final repository shall provide protection against the harmful effects of radiation for as long as is necessary with respect to the radiotoxicity of the spent nuclear fuel. The time for the radiotoxicity of the spent fuel to decay to naturally occurring levels is an important input to the design of the KBS-3 repository and its engineered barriers. The requirement that the engineered barriers shall maintain their barrier functions with respect to features, events and processes that can affect their performance has resulted in a maximum allowed temperature in the KBS-3 repository. The maximum allowed temperature will together with the total amount of spent fuel and the number of fuel assemblies in each canister determine the minimum size of the final repository. The temperature in the final repository will depend on the decay power of the spent nuclear fuel, the dimensions and thermal properties of the engineered barriers, the inter-canister spacings, the thermal properties of the host rock and the ambient temperature at the depth level in question. The decay power will decrease with time. Consequently, the time period from when the fuel assemblies are taken out of the nuclear power reactor until they are encapsulated and deposited in the final repository will impact the size of the repository. The fuel parameters of importance for the design of the final repository in Sweden are further discussed in the Spent fuel report, see (SKB 2010b, Section 2.3 therein) and for the Finnish repository, the spent fuel characteristics important to longterm safety have been summarised in (Posiva 2012b, c.f. Chapter 5 therein). 2.4 Functions of the KBS-3H repository and design considerations The KBS-3H disposal concept The long-term safety principles of Posiva s planned repository system (see, e.g. Section 5.1 of Posiva 2012a) have been updated and adapted in order to apply to the KBS-3H design alternative. These principles are part of Level 2 of the VAHA for KBS-3H, c.f. Section The 3H-specific long-term safety principles are (Posiva 2016a): 1. The spent fuel elements shall be disposed of in a repository located deep in the bedrock. The release of radionuclides shall be prevented by employing a multibarrier disposal system consisting of a system of engineered barriers (EBS) and a host rock such that the system effectively isolates the radionuclides from the biosphere. 2. The engineered barrier system of KBS-3H consists of; a) the canister to contain the radionuclides as long as they could cause significant harm to the environment

31 23 b) the buffer, which is initially in the supercontainers (surrounding the canister) and in the distance blocks between the supercontainers, to protect the canisters as long as containment of radionuclides is needed c) the filling components, i.e. the filling blocks to separate possible transmissive fractures from the canisters and buffer, and the transition zones related to the plugs d) the compartment plugs to divide the disposal drift into two compartments, and the drift plugs to keep all components in the drift in place until the adjacent central tunnel is backfilled and saturated e) the closure, i.e. the backfill and sealing structures to decouple the repository from the surface environment. 3. The host rock and depth of the repository shall be selected in such a way as to make it possible for the EBS to fulfil the functions of containment and isolation described above. 4. Should any of the canisters start to leak, the repository system as a whole shall hinder or retard the release of radionuclides to the biosphere to the level specified by the long-term safety criteria. Due to the long-term hazard of the spent nuclear fuel, it has to be isolated from the biosphere over a long period of time. The KBS-3 method provides long-term isolation and containment of spent nuclear fuel by a system of multiple barriers, both engineered and natural, and by ensuring a sufficient depth of disposal (the key safety features of the system in Figure 5-1 of Posiva (2012a)). All of these barriers have their roles in establishing the required long-term safety of the repository system. The biosphere is not given any safety functions; instead it is considered as the object of the protection provided by the repository system Functions of the KBS-3H repository The safety and radiation protection principles introduced in Section 2.2 and the properties of the spent nuclear fuel, mainly its radiotoxicity and its decay with time, constitute the basis for the substantiation of the functions of the KBS-3 repository. The purpose of the final repository is to protect man and the environment from unacceptable radiological impact. In the final report of the KBS (nuclear fuel safety) project Final storage of spent nuclear fuel KBS-3 (SKBF/KBS 1983) which has given the name to the KBS-3 method it is stated that: This can be achieved in two ways. One is to contain the radioactive substances for a sufficiently long period of time to allow the process of decay to reduce activity to acceptable levels. The other is that the radioactive substances are diluted, i.e. released and dispersed so slowly that the maximum concentrations that can reach man are acceptably low. In the current regulations, the term diluted is not used but it is stated that the functions of the barriers of a final repository shall be: to in one or several ways, contribute to contain the radioactive substances or to prevent or retard their dispersion /SSMFS 2008:21 3 /. In a final repository based on the KBS-3 method containment as well as prevention or

32 24 retardation of dispersion of radioactive substances are employed to protect man and the environment from radiation. This approach is common for final repositories developed in many other countries. In addition to the safety and radiation protection principles and the radiotoxicity of the spent nuclear fuel, the host rock and geological conditions are important when determining the functions of a final repository. The functions of the KBS-3H repository and its engineered barriers and underground openings constitute a specification of a KBS-3H repository, and are high level premises for the design of its engineered barriers and underground openings. The functions of a KBS-3H repository and its barriers and other parts are presented in Chapter 3 in this report Design considerations For some design basis, quantitative criteria for the evaluation of the conformity of the design to the design basis are provided. Based on the functions of the final repository quantitative requirements for the design of the engineered barriers and underground openings can be substantiated. In some cases, the functions as such can be verified against quantitative criteria, e.g. for the protection of man and the environment from ionising radiation quantitative dose and/or risk criteria are stated. However, there is also some design requirements for which no absolute quantitative criteria for the conformity of the design can be given. Examples are that the technical solutions shall be well-tried or tested and be cost-effective. In the production reports these design premises are referred to as design considerations. The design considerations are presented in Section 3.9 of this report. They shall be regarded in the design of the engineered barriers and underground openings and in the development and choice of methods to manufacture, install, construct and inspect them. 2.5 Design basis from safety assessment, design and technology development General approach The development of the design basis and design of the KBS-3H repository, with its engineered barriers and underground openings, has been and continues to be an iterative process with several loops of design, technology development and assessment. In addition, for the underground openings the successively developed and more detailed site descriptive model is an important starting point for the development of the design. The high level design basis is in principle expressed in laws and regulations, or based on the properties of the spent nuclear fuel or the chosen method to finally dispose the spent nuclear fuel. These high level design (Level 1) basis for a KBS-3 repository are presented in Chapter 3 in this report. However, the support for lower level design basis (Levels 4 to 5) for the design of the properties, e.g. geometry, material composition and strength, of the engineered barriers and underground openings requires input and feedback from technical development and safety assessments. The properties shall

33 25 provide the required functions and be technically feasible to achieve. A flow chart for the iterative process of substantiation of design basis, design and technology development and safety assessment is given in Figure 2-2. The lower level design basis stating the properties and parameters to be designed and the requirements the design shall fulfil are defined in the KBS-3H Design Basis report (Posiva 2016, in prep.), which includes the Levels 1 4 requirements for a KBS-3H repository to be constructed at Olkiluoto, since that is the reference site in the KBS-3H safety evaluation However, the Production reports are intended to take into account also the repository planned by SKB, and the structure of the Production reports overall follow that used in previous SKB s Production reports (for KBS-3V). There the requirements are divided into design basis: related to the functions in the KBS-3 repository, from other parts of the KBS-3 repository, related to the production and operation. Figure 2-2. The iterative process of substantiation of design basis from design, technology development and safety assessment. Regarding design basis from other parts of the KBS-3H repository, they are stated in the production reports for the part i.e. spent fuel, engineered barrier or underground opening imposing the basis, and repeated and verified in the production line for the part that shall conform to the design basis. In addition to the design basis for the design of the different parts of the KBS-3H repository there are also premises for the development of the methods to produce and construct them. The properties that contribute to the functions and safety of the KBS-3 repository shall be possible to achieve by proven or well-tested technology. The production and operation shall be reliable, cost-effective and carried out at the

34 26 prescribed rate. The detailed premises for the development of methods are presented in the chapters presenting the production and construction in the Engineered barrier production reports and Underground openings construction reports, respectively. The Level 5 requirements (design specifications) are defined in the individual Production reports and they fulfil the Level 1 through 4 requirements defined in the Design Basis report (Posiva 2016a). It is foreseen that the lower level requirements (design specifications) as derived from performed safety assessment, technical development, production and construction will further develop as a result of further assessments, research and development. In the case of SKB, in order to make the development traceable, all types of design basis and also the reference designs should be documented within SKB s requirement management system (RMS) Design basis related to functions of the KBS-3H repository The design basis related to the functions in the KBS-3H repository is based on the results from the assessment of the long-term safety, including those made for KBS-3V by Posiva and SKB. Any design must start from a specification of what shall be achieved and the required functions. The design shall have the capability of sustaining the functions. Whether a specific design results in a final repository that conform to the safety criteria can only be determined through a safety assessment where all parts of the system are evaluated together. In the general recommendations to SSM s regulations concerning safety in connection with the disposal of nuclear material and nuclear waste, SSMFS 2008:21, it is stated that: The safety assessment should also aim at providing a basic understanding of the repository performance on different time-periods and at identifying requirements regarding the performance and design of different repository components. The safety assessment methodology and methods for deriving design basis from the assessment have gradually been developed. In the most recent SKB assessment of longterm safety, SR-Site (SKB 2011), the roles through which the repository components contribute to safety were expressed as safety functions. In Posiva s safety case TURVA (Posiva 2012d), similar safety functions were used and their fulfilment evaluated using more detailed performance targets (requirements for long-term behaviour) and design requirements (for conditions to be verified in the operational phase), see (Posiva 2012a). Furthermore, in the general recommendations to SSM s regulations concerning safety in connection with the disposal of nuclear material and nuclear waste, SSMFS 2008:21, it is stated that Based on scenarios that can be shown to be especially important from the standpoint of risk, a number of design basis cases should be identified. Design basis cases and other design feedback for a KBS-3V repository were presented in a specially dedicated report titled Design premises for a KBS-3V repository based on results from the safety assessment SR-Can and some subsequent analyses (SKB 2009a). This report comprises design premises for the design of the engineered barriers and underground

35 27 openings related to their functions in the KBS-3V repository, but it also constitutes a key reference to the Design basis developed specifically for KBS-3H (Posiva 2016a) and the associated 3H Production reports. Another key reference has been the KBS-3V Design Basis report from the TURVA-2012 safety case (Posiva 2012a). The approach to define requirements from the assessment of the long-term safety and the resulting design basis for KBS-3H is further discussed in Posiva (2016a) and the iteration between requirements, safety assessment and design is discussed in more detail in Hagros et al (2015) Design basis from other parts of the repository Design premises from, or imposed by, other parts concern technical feasibility. Interactions and interdependencies between the different components occurring in the KBS-3H repository after the parts are finally installed in the repository are addressed within the assessment of the long-term safety and expressed in the design basis from the assessment. For KBS-3H, the design basis is given in Posiva (2016, in prep.) and the evolution of the KBS-3H repository will be assessed in the safety evaluation for KBS- 3H (Posiva 2017). In order to be technically feasible, the different parts of the repository must fit, and work, together so that they can acquire the properties needed to provide the required functions. Thus, the reference design of one component may constitute a design basis for another. For example, in order for the buffer in deposition drifts to maintain its functions a sufficiently high density of the buffer material is required. The resulting buffer density depends on the installed material mass and on the deposition drift volume, and also on other properties of the drift and its components (e.g. the plugs and filling components). The reference design of the buffer is thus a design basis for the deposition drifts, the diameter of which needs to remain within the acceptable tolerances in order to allow for a sufficient buffer density. In practice, the designs of the different parts are mutually adapted to achieve a technically feasible and robust solution. An exception is the spent nuclear fuel for which the design cannot be altered. However, requirements on the handling of the spent fuel may be imposed by the other parts of the KBS-3H repository Design basis related to production and operation The properties of importance for the function in the KBS-3H repository shall be possible to achieve and inspect in the production. Further, to achieve a reliable production, loads occurring during handling and transportation shall be considered in the design of the canister, buffer, backfill and closure components. According to the general recommendations to SSM s regulations concerning safety in connection with the disposal of nuclear material and nuclear waste, SSMFS 2008:21: information, such as on manufacturing method and controllability, should be used to substantiate the design basis such as requirements on barrier properties.. STUK

36 28 (YVL D.5, 510) states that the transfer and installation of the disposal canister along with the installation of buffer and backfill materials shall be so performed as to prevent the occurrence of any damage compromising the performance of engineered barrier. The design must be such that the properties can be achieved and inspected in a reliable manner, and the methods for production and inspection may impose premises on the design. The loads occurring during the handling must not significantly impair the properties of importance for the functions in the KBS-3H repository. Consequently, engineered barriers must not be exposed to loads that significantly impair the properties of importance for the functions in the KBS-3H repository. Further, they must be designed to withstand the loads that occur in the normal operation. The handling of the engineered barriers, most significantly of the canister, will impact the operational safety. The substantiation of design basis related to the operation of nuclear facilities is regulated. A summary of how technical design basis for the handling of the engineered barriers are substantiated from the assessment of the operational safety is given in Section Design basis related to the safe operation of the disposal facility The operational safety of the disposal facility refers to technical, organisational and administrative measures to prevent; i) the canister from being damaged in such a way that the containment is breached and radioactive substances dispersed, or ii) the occurrence of radiation doses higher than those accepted for normal operation of the facility. This means that the canister must be tight when it arrives to the disposal facility and remain tight during handling within the facility. As a consequence of this the disposal facility and its technical systems and equipment must be designed so that the canister cannot be exposed to loads and stresses that may result in leaks. The canister in turn must be designed to withstand the loads it may be exposed to, not only during normal operation but also for less likely events that may occur in the facility. The loads occurring during normal operation and less likely events constitute design basis for the canister. To minimise the radiation doses to the personnel within the facility, and also due to the requirements on reliability and operational stability, it is desirable that the canisters and their contents are always fit for deposition and should not need to be retrieved for repair or replacement of the canister. Even if it will not result in canisters not fit for deposition, damages on installed buffer that will necessitate retrieval of deposited canisters from the deposition drifts shall be avoided. According to the general recommendations to SSM s regulations concerning safety in nuclear facilities the safety analysis of the KBS-3 disposal facility should include: a set of events or scenarios which can affect the function of the defense-in-depth system and, thereby, ultimately have a radiological impact on the environment. The events shall be divided into classes based on their expected frequency. The event classes are denominated by the letter H followed by an integer, where a higher number indicates lower frequency of occurrence. Based on the classes design basis events should be identified. STUK s Guide YVL D.5 (Para. A04) states that the scenarios shall be systematically composed to cover any events and factors that may be of relevance to longterm safety and that may arise from:

37 29 a. external factors, such as climate changes, geological processes and events or human actions; b. radiological, mechanical, thermal, hydrological, chemical, biological and radiation-related factors internal to the disposal system; c. quality non-conformances in the barriers; and the combined effects of all the aforementioned factors.

38 30

39 31 3 THE KBS-3H REPOSITORY SYSTEM 3.1 The KBS-3H repository and its functions Definitions, purpose and reference design A KBS-3H repository is a final repository for spent nuclear fuel in which: the spent nuclear fuel is encapsulated in tight, corrosion resistant and load bearing canisters, the canisters are deposited in near horizontal deposition drifts in crystalline rock at a depth of metres, the canisters are pre-emplaced in readymade supercontainers made up by an outer metallic cylindrical perforated shell where the SF-canister is surrounded by a buffer which provides protection to mechanical damage and prevents contact with flowing groundwater, the supercontainers in the deposition drifts are separated by buffer distance blocks and in some instances by filling blocks depending on inflow conditions, the deposition drifts are effectively closed using metallic. A KBS-3H repository comprises the host rock at the repository site, the canisters containing spent nuclear fuel, the supercontainer shell, the buffer, bentonite filling components, plugs and closure structures as well as engineered and residual materials that remain in the repository once the underground openings have been backfilled and closed.

40 32 Figure 3-1. The KBS-3 repository after closure with its natural and engineered barriers and parts without barrier functions for the alternative 3V and 3H concepts. For details regarding layout in the deposition drift of KBS-3H related components, including filling components, see also Figure Spent nuclear fuel from the five licensed Finnish nuclear power reactors presently covered by Posiva responsibility (including wastes produced at the Loviisa power plant from 1996 and onwards and wastes from the Olkiluoto power plant) will be disposed in Posiva s repository The functions and properties of the KBS-3H repository SKB has, based on the treaties, laws and regulations presented in Section 2.2, substantiated the following functions and considerations as a specification of the KBS-3H repository, and as guidelines for the design of its engineered barriers and underground openings. The functions and considerations are high level design basis (level 2 in Figure 2-1) and are written in italics. In line with the multi-barrier principle and radiation protection principles, the KBS-3 repository (irrespective of vertical or horizontal deposition) shall: contain the spent nuclear fuel and isolate it from the biosphere,

41 33 if the containment is breached prevent and retard the dispersion of radioactive substances so that the ionising radiation, if some of the radioactive substances finally reach the environment at the surface, does not cause harm, have a system of passive barriers which, in one or several ways, shall contribute to contain, prevent or retard the dispersion of radioactive substances, either directly, or indirectly by protecting other barriers in the barrier system, provide protection against the harmful effects of radiation for as long as the radiotoxicity of the spent nuclear fuel is significantly higher than the radiotoxicity of naturally occurring uranium ores. Further: Measures taken to facilitate access, surveillance or retrieval of disposed nuclear fuel, or to impede intrusion, shall not be detrimental to the safety of the final repository. In line with the principles stated in the international treaty Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management the following shall be considered in the design of the KBS-3 repository. The barriers of the final repository shall be passive. Consideration shall be given to unintentional intrusion in the design of the final repository so that the repository site after closure of the disposal facility can be utilised without compromising the freedom of action, needs and aspirations of future generations. On completion of deposition, it shall be technically feasible for the final disposal facility to be closed. In line with the defence-in-depth principle and the principle to apply the best available technique the following shall be considered in the design of the KBS-3 repository. The barrier system of the final repository shall be capable of withstanding malfunctions and features, events and processes that could have a detrimental impact on their functions. The construction, manufacturing, deposition, installation and non-destructive testing of the final repository barrier system shall be reliable and operationally stable. Among technically feasible alternative designs, techniques and measures, those alternatives which in the short term best restrict radiation doses to human-beings and which in the long term are judged to offer the best protective capability shall be selected. In line with non-proliferation principles and the Euratom Treaty the final repository facility shall: be well protected and guarded against intrusion and illegal diversion of nuclear material. be accessible for and be provided with necessary means for the inspection of nuclear material.

42 34 This will to some extent affect the design of the final repository. It is important to recognise that it is the demands stated in the laws and regulations that the final repository shall conform to. The functions and considerations stated above constitute guidelines for the design, and are intended as a means to achieve designs that conform to laws and regulations. The treaties, laws and regulations used as the basis for this high-level specification of the KBS-3 repository are described in (SKBdoc ). According to the reactor owners, and SKB s own demands the final repository shall: accommodate all spent nuclear fuel from the currently approved Swedish nuclear power programme, shall have a high level of quality and be cost-effective, be flexible for alternative designs within the KBS-3 method. Further: The final repository shall be constructed and the final repository facility operated for a limited period of time adapted to the operating times of the nuclear power plants. As stated in Section 2.2 the environmental code and the rules of consideration shall be kept in mind in the design of the final repository for spent nuclear fuel. This means that environmental impact such as emissions into water and air, noise and vibrations and impact on groundwater shall be considered in the design and development of methods for construction, manufacturing, installation and inspections. Further, the consumption of raw materials and energy shall be considered and with respect to the overall safety of the final repository as far as possible be limited. In Posiva s case, the corresponding demands have been updated for KBS-3H and reported comprehensively in the Design basis report (Posiva 2016a), which also includes an appendix (Appendix A) summarising all requirements (Levels 1 to 5) in tabular form. Posiva s requirements are, therefore, not repeated here. The KBS-3Hspecific production reports are intended to consider the Posiva repository specifically and highlight differences in the implementation of a corresponding SKB repository. Requirements defined by both organisations are therefore of relevance The engineered barriers and other parts of the KBS-3H repository The functions of the final repository shall be provided by the following barriers and their barrier functions: the canister, the buffer, the filling components, the compartment and drift plugs, the closure (including backfill of main/central tunnels),

43 35 the host rock (the barrier functions of which is optimized by careful adaptation of the underground openings to the thermal, hydrological, mechanical and chemical properties). Notably the KBS-3H buffer is made up of two parts, i.e. the buffer immediately adjacent to the canister which is contained and kept in place by the so-called supercontainer shell made up of a perforated metallic shell, c.f. Figure 3-1. The second type of buffer component is the distance blocks between the supercontainers. The filling components are employed in conjunction with the plugs or where criteria related to deposition are not fulfilled. The functions and properties of the engineered barriers and the underground openings are presented in Sections 3.2 through 3.8. The barrier functions of the engineered barriers and functions of the underground openings constitute specifications of each engineered barrier or part of the repository. They are in similarity with the safety functions of the KBS-3 repository based on the treaties, laws and regulations presented in Section 2.2. In Posiva s case, the key requirements in the laws and regulations are documented at Level 1 of VAHA, which applies to both KBS-3H and KBS-3V (e.g. Posiva 2012a, c.f. Appendix A therein). The treaties, laws and regulations considered when substantiating the specifications are accounted for in (SKBdoc ), which also include references to which of the functions of the KBS-3 repository the different barrier functions contribute to The barrier functions of the engineered barriers and functions of the underground openings form the basis for substantiation of premises for the design and are repeated in the KBS-3H Engineered barrier production reports and the 3H Underground openings construction report. For the spent nuclear fuel, the properties of importance for the safety and design of the final repository are introduced in this report and further discussed in SKB s Spent fuel report, Section 2.3 therein, and in Posiva s Description of the Disposal System report, Chapter 5 (Posiva 2012b). 3.2 The spent fuel Definitions In the KBS-3H Production reports, spent nuclear fuel refers to the fuel to be encapsulated and disposed in the KBS-3H repository. Encapsulated spent fuel is the spent nuclear fuel within the canister ready for deposition in the repository. Gases and liquids in the cavities of the canister and the fuel assemblies are considered as a part of the encapsulated spent fuel Properties of importance for the design and long-term safety of the KBS-3H repository The KBS-3H repository is designed to protect man and the environment from unacceptable radiological impact from the radionuclide inventory in the spent nuclear fuel, in the same way as the KBS-3V repository. The spent fuel is not considered as a

44 36 barrier. Only fuels in oxide form or in some other form with low solubility are accepted for encapsulation and disposal in a KBS-3 repository, see Section 2.3. These kinds of spent nuclear fuel have properties that will contribute to prevent and retard the dispersion of radioactive substances. The properties of the encapsulated spent fuel of importance for the design of the engineered barriers and the layout of the repository and safety of the final KBS-3H repository, are: the enrichment, the burnup, the irradiation and power history, the age from the point in time the fuel assembly was discharged from the nuclear reactor, the dimensions and materials, encapsulated liquids and gases. The enrichment and burnup will affect the propensity for criticality. The fuel assemblies shall be selected for encapsulation, with respect to the design of the canister, so that criticality under no circumstances can occur in the canister. The burnup and age of the spent fuel assemblies will determine the radionuclide inventory and thus the radioactivity of the spent fuel. The radioactivity in turn will determine the decay power, radiation and radiotoxicity of the spent fuel. The decay power in each canister will determine the distances between deposition holes so as not to exceed the maximum allowed temperature in the repository. The radiation at the canister surface must not exceed levels assumed in the assessments of the operational and long-term safety. The radionuclide inventory and the radiotoxicity of the spent fuel constitute important input to the assessments of the operational and long-term safety. The irradiation and power history will, in comparison to the burnup, have a minor impact on the radionuclide inventory of the spent fuel assemblies. However, the power history will impact the part of the radionuclide inventory located at the fuel grain boundaries and in the gaps within the fuel cladding. This part of the inventory will in comparison to the radionuclides embedded in the fuel matrix be released very rapidly if the spent fuel pellets are exposed to vapour or water, hence this is of importance for the assessments of the operational and long-term safety. The dimensions of the spent fuel assemblies must be considered when determining the dimensions of the canister. The content of encapsulated gases and liquids must be limited since they may cause corrosion of the canister. The parameters presented above and the requirements on the handling of the spent fuel assemblies within the facilities of the KBS-3 system they impose are further discussed in the respective Spent fuel reports of SKB (SKB 2010b, c.f. Section 2.3 and Chapter 3 therein) and Posiva (Anttila 2005; Posiva 2012b, c.f. Chapter 5 therein). These reports also contain detailing of the types of spent fuels involved in the various canisters.

45 37 Most of the processes in the spent fuel are not dependent on the repository design alternative (whether KBS-3V or KBS-3H). The orientation of the canister may have some effect on its reactivity and as a response to requests by the regulatory authorities in Finland and Sweden, long-term criticality scenarios will be formulated and analysed in for both KBS-3H and KBS-3V (Posiva 2015, c.f. Section therein) Types of spent fuel to be deposited SKB The spent fuel to be deposited in the final repository mainly consist of fuel assemblies from the Swedish boiling light water reactors BWR assemblies and pressurised light water reactors PWR assemblies. The BWR assemblies constitute the largest number of assemblies as well as the largest amount in tonnes of uranium to be deposited. In addition to the BWR and PWR assemblies there are some miscellaneous fuels to be deposited in the KBS-3 repository. They consist of a limited number of BWR and PWR MOX (mixed oxide fuel) assemblies which result from concluded reprocessing agreements from the early operation of the nuclear power plants. The miscellaneous fuels also comprise spent fuel from the Ågesta reactor and fuel residues from the Studsvik nuclear facility. The spent fuel to be deposited is further discussed in the Spent fuel report (SKB 2010b), c.f. Chapter 2. Posiva In Finland, the spent nuclear fuel produced by the currently operating reactors (OL1 2, LO1 2) the OL3 unit being under construction and the planned OL4 unit will be slightly different depending on the reactor type. The OL1 and OL2 reactors at Olkiluoto are boiling water reactors (BWR), Loviisa LO1 and LO2 are VVER-440 type reactors and OL3, currently under construction, will be a European Pressurised Water Reactor (EPR). The design of the fuel assemblies varies depending on the reactor type. The OL4 reactor type has not been decided yet and in the TURVA-2012 safety case it was assumed to correspond to OL3 (Posiva 2012b, Section 5.1.1). During the course of the KBS-3H Safety Evaluation, the planning of OL4 has been cancelled, but in the safety evaluation the assumed quantity of the fuel is the same as in TURVA-2012, i.e tu. 3.3 The canister Definition and purpose The canister is a container with a tight, corrosion resistant shell of copper and a load bearing iron insert in which spent nuclear fuel is placed for deposition in the final repository. The canister shall contain the spent nuclear fuel and prevent the release of radionuclides into the surroundings. The canister shall also shield radiation and prevent criticality.

46 38 The canister is also a barrier, i.e. a physical confinement of radioactive substances /SSMFS 2008:1/, in the repository during operation and in the long term, and a confinement during transports of the encapsulated spent nuclear fuel. In Raiko et al (2012) a similar definition may be found in Section 2.3.1: The canister is a container with a water- and gas-tight shell and a mechanical load-bearing insert in which the spent nuclear fuel is placed for final disposal in the repository. The canister shall contain the spent fuel and prevent and, in the case of a leak, limit the spread of radioactive substances in to the environment. There are additional definitions and system requirements related to the canister given in Section and the design requirements related to the canister are given in Section of Raiko et al (2012) The safety functions of the canister The KBS-3 repository shall accommodate all spent nuclear fuel from the currently approved Swedish and Finnish nuclear power programme. This means that the canister shall: contain the various types of spent nuclear fuel that results from the currently approved Swedish nuclear power programme. In order for the KBS-3 repository to contain, prevent or retard the dispersion of radioactive substances, the canister shall: contain the spent nuclear fuel and prevent the dispersion of radioactive substances, withstand the mechanical loads that are expected to occur in the final repository, withstand the corrosion loads that are expected to occur in the final repository. In order for the KBS-3 repository to maintain the multi-barrier principle and have several barriers, which individually and together contribute to maintain the barrier functions, the canister shall: not significantly impair the safety functions of the other barriers, prevent criticality. After the canister is sealed, it shall contain the spent nuclear fuel and prevent criticality also in the facilities and the transport system included in the KBS-3 system. Furthermore, with respect to the safe operation of the KBS-3 system it shall be possible to: transport, handle and deposit the canister in a safe way without significantly affecting the properties of importance for the safety functions in the final repository.

47 39 The final repository facility shall be accessible for and be provided with necessary means for the inspection of nuclear material. With respect to this, the following is stated for the design of the canister. In the control of nuclear material, each sealed canister shall represent a reporting unit. The safety function defined for the canister in the Olkiluoto-specific design basis report for KBS-3H (Posiva 2016a) is to: Ensure a prolonged period of containment of the spent nuclear fuel. This safety function rests first and foremost on the mechanical strength of the canister s cast iron insert and the corrosion resistance of the copper surrounding it. The performance targets for the canister are more detailed requirements for the longterm performance of the canister and they are listed in Posiva (2016a, c.f. Appendix A therein) Review of canister design/-s The canister is cylindrical and consists of a tight copper shell and a load bearing insert. Copper has been selected due to its resistance against corrosion in the chemical environment in the KBS-3 repository. Copper cannot provide the mechanical strength required with respect to the mechanical conditions in the final repository and must thus be complemented by a load bearing insert. The ductility of the copper and the related capability to resist strains that may be the result of deformations against the load bearing insert is a prerequisite for the selection of copper as material of the tight shell. The insert shall provide sufficient mechanical strength. Cast iron is currently considered the most favourable material that can provide the strength and be manufactured with high reliability. In addition to the strength the propensity for criticality, i.e. the possibility to distance the fuel assemblies from each other, has been considered in the design of the insert. The long-term behaviour of the canister is not expected to be greatly dependent on its orientation (horizontal or vertical) and a similar canister design as in KBS-3V is, therefore, assumed also for KBS-3H. However, some differences in the expected longterm processes can be related to the mechanical deformation of the cast iron insert and the copper overpack by external loads, which is affected by the relative orientation of the canister in the stress field (Gribi et al. 2008, c.f. Section 3.6 therein). The long-term performance of the canister in KBS-3H is evaluated in the KBS-3H performance assessment (Posiva 2016h). Posiva specifics Posiva s reference design is to use an integral flat bottom instead of a welded bottom as employed in the SKB design, the latter affecting the buffer block design. The wall thickness of the copper shell and lid systems are the same for all Finnish canister types (49 mm). In other respects, however, the geometries of the overpack and insert vary

48 40 between fuel types. The length of the canisters is thus also dependent on the fuel type (whether OL1 2, LO1 2 or OL3). The size and shape of the canisters have been derived based on the space needed for the actual spent nuclear fuel assemblies and on requirements for mechanical strength, radiation shielding and cooling capability. Economic optimisation has also been carried out, which maximises the number of positions for assemblies in the canister and minimises the size (or weight) of the canister, constrained by the performance requirements. The current reference canister design is the result of several stages of optimisation. The number of fuel assemblies is 12 (OL1 2, LO1 2) or 4 (OL3) (Posiva 2012b, c.f. Chapter 6 therein). SKB specifics The radial measures for the copper thickness are the same for the Swedish canisters (SKB 2010c) as those stated for the Finnish canisters above. All canisters shall have the same external dimensions. The reason for this is to facilitate, and thereby make the handling of the canister cost-effective, safe and reliable. Further, BWR and PWR assemblies shall not be mixed in the same canister. As a consequence, there shall be two versions of insert, one adapted to the dimensions of the BWR assemblies and one adapted to the PWR assemblies, further the height of the canister will be determined by the length of the tallest fuel assembly (a BWR assembly). The miscellaneous fuels shall be encapsulated either in BWR or PWR canisters in both cases employing a welded bottom. The number of assemblies shall be twelve in a BWR insert and four in a PWR insert. This is based on an assessment of costs where the decay power of the spent fuel assemblies and its impact on the layout of the final repository and the operational periods of the nuclear power plants as well as of the facilities of the KBS-3 system were considered. Other factors that were considered were the safe handling of the canister, the possible geometrical configuration of the assemblies in the insert and the propensity for criticality. 3.4 Supercontainer The supercontainer is not considered a barrier in its own right and is therefore not discussed in VAHA Levels 2 and 3 of the KBS-3H design basis (Posiva 2016a). However, the supercontainer supports the safety functions of the actual engineered barriers and host rock. It is of particular importance given its close proximity to the canister with surrounding buffer Definition and purpose The supercontainer is the assembly that contains the canister and the bentonite buffer, with an outer perforated metal shell. The purpose of the supercontainer shell is to keep the unit together and allow for practical and safe disposal Requirements on supporting functions The supercontainer shell must not significantly impair the barrier functions. This implies that it shall take the performance requirements for the canister and buffer into

49 41 account. This requirement in mainly related to the chemical properties of the supercontainer shell material. The supercontainer shell thickness shall allow the supercontainer shell to withstand the loads during handling, transportation and installation. The perforation of the supercontainer shell must be such as the buffer can swell and form a tight seal with the drift wall Review of supercontainer design The supercontainer is made up of the perforated cylindrical titanium shell with the buffer components that engulf the canister, c.f. Figure The buffer and filling components Definition and purpose The buffer is clay containing swelling minerals. The buffer surrounds the canister in the supercontainer and fills the space between the supercontainers distributed along the individual deposition drift and the bedrock. The buffer shall prevent flow of water and protect the canister. In case the containment provided by the canister is breached the buffer shall prevent and retard the dispersion of radioactive substances from the canister to the bedrock The safety functions of the buffer and filling components The KBS-3H buffer components consist of the buffer blocks of the supercontainer and the buffer of the distance blocks, c.f. Figure 3-1. In order for the KBS-3H repository to contain, prevent or retard the dispersion of radioactive substances, the buffer: inside the supercontainers and in the distance blocks shall protect the canisters (for as long as containment of radionuclides is needed), of the distance blocks shall prevent flow of water (advective transport) in the deposition drift and provide thermal isolation between the supercontainers, To protect the canister and preserve the containment the buffer also shall: have ability to limit microbial activity. To contribute to prevent or retard the dispersion of radioactive substances the buffer also shall: prevent that colloids are transported through it.

50 42 In order for the KBS-3H repository to maintain the multi-barrier principle and have several barriers which individually and together contribute to maintain the barrier functions the buffer must: not significantly impair the barrier functions of the other barriers. For the final repository to provide protection against harmful effects of radiation as long as required regarding the radiotoxicity of the spent nuclear fuel, and to withstand events and processes that can affect the barrier system the buffer shall: maintain its barrier functions and be long-term durable in the environment expected in the final repository, allow the canister to be deposited without causing damages that significantly impair the barrier functions of the canister or buffer. The latter is also required with respect to the operational safety of the KBS-3H repository facility. The safety functions defined for the buffer in the Olkiluoto-specific design basis report for KBS-3H (Posiva 2016a) are to: Contribute to mechanical, geochemical and hydrogeological conditions that are predictable and favourable to the canister. Protect canisters from external processes that could compromise the safety function of complete containment of the spent fuel and associated radionuclides. Limit and retard radionuclide releases in the event of canister failure. In addition, the buffer in the distance blocks shall Hydraulically and thermally separate the supercontainers from each other. The safety functions defined for the filling components (Posiva 2016a) are to: Contribute to favourable and predictable mechanical, geochemical and hydrogeological conditions for the buffer and canisters. Limit and retard radionuclide releases in the possible event of canister failure. In addition, the filling blocks (at inflow locations) shall Separate possible transmissive fractures intersecting the drift from the canisters and buffer. The performance targets for the buffer and filling components are listed in Posiva (2016a, c.f. Appendix A therein) Review of buffer and filling components design The buffer consists of compacted bentonite clay components to be installed in the supercontainer and as distance blocks between the supercontainers. Bentonite has been

51 43 selected since it has capability to provide the barrier functions stated in Section Bentonite generally describes clay consisting essentially of montmorillonite, regardless of its origin and occurrence. Different kinds of bentonite clays may be selected for the buffer. There are several types of filling components to be used in the deposition drift: Filling blocks, which are used at hydraulically conductive sections that are not suitable for supercontainer or distance block emplacement, Transition zones on both sides of the compartment plug, Transition zone on the sealed side of the drift plug, Minor filling components located near the end of the drift. 3.6 The plugs Different kinds of plugs and their purposes The compartment plug is used to section the drift into two compartments, typically approximately 150 m long (but shorter compartment lengths may apply), with the purpose 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 seal off and close the drift, c.f. Figure 3-1, finishing the operations in that particular drift with the purpose 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 safety functions of the plugs The safety function defined for the compartment and drift plugs in Posiva (2016a) is to: Contribute to favourable and predictable mechanical, geochemical and hydrogeological conditions for the filling components, buffer and canisters by keeping the drift components in place. The performance targets for the compartment and drift plugs are listed in Appendix A of Posiva (2016a). Further to this, in order for the barrier system of the final repository to withstand conditions, events and processes that may impact its functions, the following applies for the two types of plugs:

52 44 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 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 the lifetime of the plugs Review of plug design The compartment plug and the drift plug consists of following three main components; fastening ring (V-shaped ring that is cast into a rock notch using low-ph grouting, collar (attached to the fastening by welding) and cap (attached to the collar by welding). The collar is also provided with three lead-throughs to allow the water filling pipes and one lead-through for the air evacuation pipe. Based on the long-term performance and the aspect of clay interaction, titanium has been selected as the material for the plugs. Studies has shown that titanium is expected to be the most inert material, having the lowest corrosion rate and lowest rate of production of hydrogen and is a stronger material with good mechanical properties and has therefore been selected as the reference material (SKB 2012, c.f. Chapter 7 therein).

53 The closure Definition and purpose The closure includes the sealing structures and materials installed in investigation boreholes, rock caverns, shafts and ramp and tunnels that are not deposition drifts, in order to fill and close them. Notable in this context is that the section between the drift plug and the central/main tunnel belongs to closure. The purpose and function of the closure is to considerably obstruct unintentional intrusion into the final repository and to restrict groundwater flow through the underground openings The safety functions of the closure The safety functions defined for the closure in Posiva (2016a) are to: Prevent the underground openings from compromising the long-term isolation of the repository from the surface environment and normal habitats for humans, plants and animals. Contribute to favourable and predictable geochemical and hydrogeological conditions for the other engineered barriers by preventing the formation of significant water conductive flow paths through the openings. Limit and retard inflow to and release of harmful substances from the repository. The performance targets for the closure are listed in Posiva (2016a, c.f. Appendix A therein). In order for the KBS-3 repository (irrespective of whether vertical or horizontal deposition is employed) to maintain the multi-barrier principle and have several barriers, which individually and together contribute to maintain the barrier functions, the closure shall: prevent that water conductive channels, that may jeopardise the barrier functions of the rock, are formed between the repository and the surface, not significantly impair the barrier functions of other barriers. To maintain the multi-barrier principle, the closure in different underground openings shall have the following barrier functions. The closure in main/central tunnels shall keep the drift plug in place and thus contribute to keeping the drift materials in place. The successive process of closure shall keep the closure in underlying or immediately adjacent/preceding underground openings in place. In the design of the KBS-3 repository, unintentional intrusion shall be considered so that the repository site after closure of the repository facility can be utilised without compromising the freedom of action, needs and aspirations of future generations. From this follows that:

54 46 The closure in the upper part of the ramp, shafts and boreholes shall significantly obstruct unintentional intrusion into the final repository. For the final repository to provide protection against harmful effects of radiation as long as required regarding the radiotoxicity of the spent nuclear fuel and to withstand events and processes that can affect the post-closure performance the closure shall: be long-term durable and maintain its barrier functions in the environment expected in the repository Review of closure design The design of the closure will depend on the underground opening to be closed and the required function of the closure in the particular underground opening. In investigation boreholes and underground openings where flow of water shall be restricted precompacted clay components will be used as closure material. At repository depth, the closure backfill of underground openings will consist largely of clay, but the proportion of clay will likely be reduced when approaching more shallow depths, this in order to limit erosional loss of clay, with an associated increase in the proportion of rock in the closure backfill (see e.g. Sievänen et al. 2012). In the upper part of underground openings connected to the surface, to obstruct intrusion, the closure consists of well fitted blocks of crystalline rock. 3.8 Host rock and underground openings Definition and purpose By definition, the host rock is the rock surrounding the KBS-3H deposition drifts and other excavated rooms that shall provide sufficiently favourable and predictable conditions so that the EBS can fulfil its functions of containment and isolation and ensure that the transport of radionuclides is limited in the case of release. It is required that the host rock shall with high likelihood retain its favourable properties up to at least several hundreds of thousands of years (Posiva 2016a, c.f. Chapter 6 therein). Many parts of the disposal facility (e.g. the access tunnel and shafts) will be identical for both KBS-3V and KBS-3H, c.f. Figure 3-1. The main difference being the KBS-3H deposition drift and the associated deposition niche, some 25 m long, at the mouth the respective drift. Another difference is that the total main/central tunnel length may be greater in the case of KBS-3H, because the maximum length of KBS-3H deposition drifts is only 300 m (as opposed to 350 m for KBS-3V deposition tunnels). Notable in this context is that removal of the air evacuation pipe from up to a 150 m long deposition drift compartments is still considered feasible. The resulting increase in the number of deposition drifts required will consequently increase the total length of central tunnels. For details on the closure (including backfill) of the underground openings other than the deposition drift, c.f. Section

55 47 The underground openings are the cavities constructed in the rock that are required for the sub-surface part of the final KBS-3H repository facility. The underground openings comprise: the actual geometry and location of the cavities, the rock surrounding the openings that is affected by the rock construction works, the engineered materials for sealing and rock reinforcement, and residual materials from performance of activities in the final repository facility which, at deposition, backfilling or closure, remain in and on the rock, that surrounds the openings. The underground openings as such do not contribute to the safety of the KBS-3H repository and do not have any barrier functions. However, the locations of the deposition areas and deposition drifts with respect to the thermal, hydrological, mechanical and chemical properties of the rock are important for the utilization of the rock as a barrier and thus for the safety of the final repository. Furthermore, damage inflicted on the rock surrounding the tunnels (the so-called excavation damaged zone, EDZ), other types of disturbance and engineered and residual materials that remain in the rock may impact on the barrier functions of the rock and/or the engineered barriers, and must therefore be known when assessing the safety of the final repository. In addition, the underground openings shall be designed with respect to the design basis imposed by the design of the supercontainer, buffer components, filling components, plugs and closure The safety functions of the host rock and the functions of the underground openings The safety functions defined for the host rock in Posiva (2016a) are to: Isolate the spent fuel repository from the surface environment and normal habitats for humans, plants and animals and limit the possibility of human intrusion, and isolate from changing conditions at the ground surface. Provide favourable and predictable mechanical, geochemical and hydrogeological conditions for the engineered barriers. Limit the transport and retard the migration of harmful substances that could be released from the repository. The performance targets (target properties) for the host rock are listed in Posiva (2016a, c.f. Appendix A therein). In order for the final repository to contain, prevent or retard the dispersion of radioactive substances, the rock shall provide stable and favourable conditions for the engineered barriers so that their barrier functions can be sustained for as long as necessary bearing in mind the radiotoxicity of the spent nuclear fuel. Should the containment provided by the canister and buffer be breached, the rock will contribute to the safety of the final

56 48 repository by preventing or retarding the dispersion of radioactive substances. In order for the rock to sustain its barrier functions and to maintain the multi-barrier principle, the layout of the underground openings shall be adapted to the conditions at the final repository site so that: thermally favourable conditions are provided and the containment of radioactive substances can be sustained over a long period of time, mechanically stable conditions are provided and the containment of radioactive substances can be sustained over a long period of time, favourable hydrogeologic and transport conditions are provided and the containment, prevention or retardation of dispersion of radioactive substances can be sustained over a long period of time, chemically favourable conditions are provided and the containment, prevention or retardation of dispersion of radioactive substances can be sustained over a long period of time. In order for the KBS-3 repository to maintain the multi-barrier principle and have several barriers which individually and together contribute towards maintaining the barrier functions, the underground openings shall: be designed so that they do not significantly impair the barrier functions of the rock or the engineered barriers. In the design of the KBS-3H repository unintentional intrusion shall be considered so that the final repository site after closure of the repository facility can be utilised without compromising the freedom of action, needs and aspirations of future generations. With respect to this and the fact that the final repository shall isolate the spent fuel from the environment at the surface: the repository depth shall be selected with respect to the human activities which, based on present living habits and technical prerequisites, may occur at the repository site. In order for the KBS-3H repository to be able to accommodate all spent nuclear fuel from the currently approved Swedish or Finnish nuclear power programme the underground openings shall: accommodate the sub-surface part of the final repository facility with the number of approved supercontainer positions that are required in order to deposit all canisters with spent nuclear fuel. In order for the barrier system of the final repository to withstand failures and conditions, events and processes that may impact their functions, the underground openings shall: allow the emplacement of the supercontainers (with canister and buffer), distance blocks, filling components and compartment and drift plugs with the desired barrier functions,

57 49 allow the installation of closure with the desired barrier functions. The latter is also required in order for the barriers of the closed final repository to be passive, and in order for it to be, technically feasible to close and seal the final repository facility after the deposition has been carried out. For the nuclear operation of the final repository facility to be safe, the underground openings shall: be designed so that breakdowns and mishaps in connection with the nuclear operations are prevented. The underground openings shall also be designed so that other activities in the final repository facility can be carried out in a safe way Review of underground openings design KBS-3H is based on horizontal emplacement of several canisters in a series in long deposition drifts. The spent nuclear fuel is introduced in the deposition drift by way of a supercontainer containing bentonite buffer blocks and the copper canister. At the disposal area, the super-containers, distance blocks and filling components are installed from deposition niches into the drifts. The repository depth is selected to conform to the design basis to find large enough volumes fulfilling the specific requirements on positioning deposition drifts. The deposition areas and positioning of the deposition drifts shall conform to design basis for favourable and stable thermal, mechanical and hydrogeological conditions. The deposition drifts as well as other tunnels, ramp/access tunnel and shafts are designed to conform to design basis regarding limitation of the excavation damaged zone (EDZ). Finally, the amounts of engineered and residual materials in different parts of the underground facilities are quantified. The KBS-3H reference method is to drill a pilot hole that is reamed to full drift size, with an additional intermediate reaming step. The reference method for excavating the deposition drifts are full-face horizontal push-reaming techniques. Post-grouting with the Mega-Packer will be used for managing major inflows in the deposition drifts. 3.9 Design considerations In this section the design considerations that shall be regarded in the design are presented. These mainly affect the development of methods to manufacture and handle the engineered barriers and to construct the underground openings and are similar for similar types of openings in all parts (panels/deposition areas) of the KBS-3H repository.

58 50 The system of barriers and barrier functions of the final repository shall withstand failures and conditions, events and processes that may impact their functions. Hence the following shall be considered. The designs and methods for manufacturing, installation, test and inspection shall be based on well-tried or tested technique. The construction, manufacturing, deposition and non-destructive tests of the barriers of the final repository shall be dependable, and the following shall be considered. Engineered barriers, underground openings and plugs with specified properties shall be possible to manufacture and install with high reliability. The properties of the engineered barriers, underground openings and plugs shall be possible to inspect against specified acceptance criteria. A reliable production is also required with respect to SKB s and Posiva s shared objectives to achieve high quality and cost-effectiveness. Regarding cost-effectiveness, the following shall be considered. The designs and methods for manufacturing, installation, test and inspection shall be cost-effective. Installation and construction shall be possible to perform in the prescribed rate. Further, with respect to requirements in the Swedish Environmental Code /SFS 1998:808/, 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 prepare and install the engineered barriers and plugs, and to construct the underground openings, must also conform to requirements in the Swedish Work Environment Act /SFS 1977:1160/ and regulations for occupational safety. Design premises related to these aspects can generally be met in alternative ways for designs that conform to the safety and design basis related to radiation protection. In Posiva s VAHA system, the design considerations are mainly incorporated at Level 4 (design requirements), which includes requirements to the design that can be verified before or at installation. The Level 4 requirements, updated for KBS-3H, can be found in Posiva (2016a, c.f. Appendix A therein) Logistics of the KBS-3H repository system The overall logistics of the KBS-3H repository system overall coincides and conforms with that of the reference alternative KBS-3V. The differences arise in the horizontal deposition of the spent fuel canisters in preassembled supercontainers and the way the supercontainers are separated and protected in the deposition drift. This difference comes with different demands on handling of buffer masses and also in the way the deposition drifts are excavated and sequentially sealed off in compartments. The basic logistical flow in conjunction with preparation and disposal of a KBS-3H deposition drift is illustrated in the flow chart shown in Figure 3-2. The flow chart is divided in three consecutive phases; preparation of drift, filling of first compartment and filling of second compartment.

59 51 Preparation of drift includes all activities that will be performed and finalized before deposition of the preassembled supercontainers commences in the drift, including excavation works, characterization work and inflow measurements. In this phase the deposition drift usage (drift layout) is analysed and decided, with positioning of all components. Filling of first compartment and filling of second compartment, respectively, includes all activities for installation of filling components, emplacement of distance blocks, deposition of supercontainer, installation of plugs, water filling and with removal of the air evacuation and water filling pipes as the last activity. The cyclic emplacement of distance blocks and deposition of the supercontainer constitutes a linked activity that is repeated until the compartment is filled with the number of supercontainers as determined in the drift layout. The initial state for each compartment is the situation existing after the compartment has been water filled and the air evacuation and the water filling pipes have been removed.

60 Figure 3-2. Flow chart illustrating the basic logistical flow in conjunction with preparation and disposal of an KBS-3H deposition drift. 52

61 53 4 THE KBS-3H PRODUCTION LINES 4.1 Facilities related to disposal Definition and scope The KBS-3 system (irrespective of whether vertical or horizontal deposition is employed) entails a disposal facility including the underground part and the necessary above-ground buildings (e.g. for ventilation). In addition, there will be a central facility for interim storage and encapsulation of spent nuclear fuel and a system for transportation of canisters with spent nuclear fuel. Deliveries to the above-mentioned facilities need to be considered as part of the associated production. It is important to establish routines for qualification of suppliers, as well as for inspections of the activities performed by the suppliers. The deliveries are included in the production lines, see Section 4.2. The facilities of the KBS-3 system, the delivery of spent nuclear fuel to it, and the route of the spent fuel through the facilities are illustrated schematically and generically in Figure 4-1. The figure also gives an overview of the deliveries of components required to produce and construct the engineered barriers and underground openings of the KBS-3 repository and tentatively illustrates their routing through the facilities to their final installation in the KBS-3 repository. This section only provides a brief description, since all KBS-3H-specific production aspects are handled in detail in the individual Production reports. Posiva s encapsulation facility is described in detail by Kukkola (2012) and Palomäki and Ristimäki (2013) (covering also the disposal facility), and the transports in e.g. Suolanen (2012). See also KBS-3H facility description (Posiva 2016e) Interim storage, encapsulation and transportation Purpose and main parts The purpose of the interim storage facility for spent nuclear fuel and encapsulation plant is to: store the spent nuclear fuel until its decay power has decreased to levels suitable for deposition in a KBS-3 repository, select assemblies for encapsulation, encapsulate them and deliver sealed canisters for transportation to the KBS-3 repository facility. The interim storage facility for spent nuclear fuel and encapsulation plant consists of two main parts. The interim storage part comprises pools for wet storage. The spent nuclear fuel is placed in storage canisters in the pools. The encapsulation part comprises pools to receive transport canisters with spent fuel from the storage part, and positions for drying of the spent nuclear fuel, placement in the canister and sealing of the copper canister by welding the copper lid to the copper overpack (copper shell in SKB s terminology).

62 54 The purpose of the transport system is to transport the canisters containing the encapsulated spent nuclear fuel from the interim storage facility and encapsulation plant to the KBS-3H repository facility in such a way that they are ready and fit for deposition upon arrival. The transfer of canisters from the canister interim storage at ground level to the reloading station and assembly of supercontainers are detailed in the supercontainer production report (Posiva 2016c). Main activities The main activities of the interim storage facility for spent nuclear fuel and encapsulation plant are to: receive and inspect the spent fuel from the nuclear power plants, store and monitor the spent nuclear fuel, select fuel assemblies for encapsulation, transfer the selected assemblies to the encapsulation part of the facility, prepare, inspect and dry the spent fuel to be encapsulated, place the spent fuel assemblies in the canister, seal the canister, inspect the sealed canister and approve it for transportation, place the canister in transportation casks for transport to the KBS-3 repository facility. Specifically for Posiva, the existing Castor TVO spent fuel transport cask (or similar to that) is used to transfer the spent fuel from the Olkiluoto KPA interim storage to the encapsulation plant. The existing transport trailer is used for the transport. No new arrangements are necessary. The spent fuel transport cask is filled with water (wet transport) during the transfer. The water-filled spent fuel transport cask is then returned to the KPA interim storage. The fuel transfer takes place inside the designated power plant area, so there is no need for spent fuel transport on public roads on this case (Kukkola 2012). The spent fuel transport casks are received and handled at the encapsulation plant. The spent fuel is unloaded from the spent fuel cask in the fuel handling cell. The fuel assemblies are introduced into the disposal canister. The disposal canister is then transferred into the canister interim storage. After storage, the canister is transferred into the repository (reloading station) with the help of the canister shaft lift (Kukkola 2012) The KBS-3H disposal facility Purpose and main parts The KBS-3H disposal facility is the facility required to establish the KBS-3H repository. The KBS-3H disposal facility is divided into a non-nuclear facility and a

63 55 nuclear facility, respectively. The final repository is constructed, and encapsulated spent nuclear fuel is handled, within the nuclear facility. The KBS-3H disposal facility consists of the underground openings, the constructions and buildings above and below ground and the technical systems and equipment within the facility required to construct the KBS-3 repository and operate the facility. The finished parts of the KBS-3H repository lie within the KBS-3 disposal facility. The KBS-3 disposal facility with finished parts of the KBS-3 repository is illustrated in Figure 1-1. Figure 4-1. The KBS-3 system and its facilities and an overview of materials flows through the system as part of the production of the KBS-3 repository. Schematic and generic illustration of surface and underground facilities and their layouts.

64 56 Main activities The main activities within the nuclear facility of the KBS-3 disposal facility are roughly divided into rock construction works and detailed investigations of the rock followed by deposition works. To facilitate the regulated nuclear operation of the facility, and to keep the handling of the canister and the other engineered barriers in a clearly defined area, partition walls physically separate the deposition works from the rock construction works. On the rock construction works side of the partition wall main (central) tunnels are excavated and deposition drifts are excavated and prepared for deposition works. On the deposition works side supercontainers are deposited and buffer distance blocks, filling components and plugs are installed in the deposition drifts. As new main/central tunnels and deposition drifts are constructed and prepared for deposition, new partition walls are installed. The partition wall is always placed so that construction and deposition works are physically separated. Transports to and from the construction side may pass closed deposition drifts. The main activities of the rock construction works are illustrated in Figure 4-2. Each of these main activities comprises several stages, e.g. drilling, blasting, removal of rock debris etc. Figure 4-2. The main activities of the rock construction work. Each main activity comprises several stages. The deposition works comprises a deposition sequence which includes positioning of supercontainers in the deposition drift, installation of distance blocks and strategic positioning of filling components and plugs (compartment plug and drift plug). The main activities of the deposition sequence are illustrated in Figure 4-3. When the last supercontainer has been emplaced the drift plug is installed at the entrance of the drift. The installation of the supercontainer, the distance blocks, the filling components and the plugs, with all their stages and subactivities, are described in the supercontainer production report (Posiva 2016d, c.f. Section 5.4 therein), the buffer and filling components production report (Posiva 2016b, c.f. Section 5.4 therein) and the plug production report (Posiva 2016c, c.f. Section 5.4 therein), respectively.

65 57 Figure 4-3. The main activities of the deposition sequence. 4.2 The production and the production lines In the following sections, overview accounts are provided of the reference design, conformity of reference design to design basis, the production and initial state for the KBS-3H-specific production lines, i.e. for the buffer and filling components (Section 4.5), the supercontainer (Section 4.6), the plugs (Section 4.7) and for the underground openings construction (Section 4.8). In addition, the interfaces in design and interfaces in production are accounted for. The latter two aspects are the only aspects accounted for related to the 3V production lines which also are common to KBS-3H, i.e. for the spent fuel (Section 4.3), the canister (section 4.4) and closure (Section 4.9) production lines. Detailed accounts of the latter production lines are presented in the respective KBS-3V production reports, c.f. Table The production The production of the engineered barriers comprises: the specification of the design of the components to be delivered, the methods to manufacture and inspect the specified designs, a physical production line that delivers components and ultimately engineered barriers that conform to the specified designs. The production lines refer to all the activities and stages required to produce the engineered barriers and install them in the KBS-3H repository. For the underground openings, the specified design is the result of the application of a design methodology in order to successively, as more detailed information becomes available, adapt the design to the conditions at the site. Methods for inspection comprise methods to investigate the host rock before the construction is initiated, methods to control the constructions as well as inspection of the as built underground openings. No explicit production line is outlined for the underground openings, but the methods to excavate the different underground openings and their ability to result in underground openings that conform to the design basis are indicated The production lines There are production lines for each of the engineered barriers of the KBS-3H repository. An overview of the main parts of the production lines of the engineered barriers is given in Figure 4-5. The figure also illustrates the main parts of the handling of the spent fuel and its relationship to the construction of the underground openings. Each main part, as

66 58 illustrated in Figure 4-5, is in the respective engineered barrier production report further divided into stages in the handling and production, respectively. For each stage the properties and design parameters Figure 4-5. Overview of the main activities in the handling of the spent fuel, the production of the KBS-3H engineered barriers and the construction of the KBS-3H underground openings (SKB 2012). of the engineered barriers that are affected and inspected within the stage are presented in the respective production line report Design and production line interfaces As mentioned in Section there are design basis imposed by the spent fuel or individual engineered barriers on other engineered barriers or underground openings related to technical feasibility. This implies that the different parts of the final repository must fit, and work, together during the production of the KBS-3 repository. These interfaces are in Sections 4.3 to 4.9 introduced for the spent fuel line, the production lines of the engineered barriers and the construction of the underground openings. For each of the engineered barriers and underground openings the design basis related to the technical feasibility imposed by other parts of the KBS-3H repository is summarised, whereas detailed descriptions are given in the respective production report.

67 59 In many cases the interfaces between the production lines result from the design basis that the different parts of the KBS-3H repository mutually impose on each other and/or are consequences of interfaces between the production lines, as outlined in the ensuing sections. In addition to design basis related to technical feasibility, there are design interfaces related to the functions that the different parts of the KBS-3H repository need to sustain and maintain in the long-term time perspective. These interfaces and interdependencies are related to the long-term evolution of the KBS-3H repository and are presented in detail in the KBS-3H Design Basis report (Posiva 2016a) and not discussed further in this report. 4.3 The spent fuel line Overview The main parts of the spent fuel line are illustrated in Figure 4-5, and an overview of all stages is given in the Posiva and SKB spent fuel reports; SKB (2010b) and Raiko et al (2012), respectively. The spent fuel line starts with the delivery of the spent nuclear fuel assemblies to the ISFEP and ends when the spent fuel assemblies are finally placed in the canister and the steel lid is finally put on the cast iron insert and welded in place Interfaces between the design of the KBS-3H repository and its barriers and the handling of the spent fuel The design of the KBS-3 repository will impose requirements on the selection of fuel assemblies for encapsulation. The assemblies shall be selected so that criticality cannot occur in the canister and so that the total decay power in a canister and the radiation on the canister surface do not exceed specified values, see SKB (2010b) and Raiko et al (2012, c.f. Section therein). Gases and liquids encapsulated together with the spent nuclear fuel may cause corrosion of the canister. The canister thus imposes that the fuel assemblies shall be dried and the air in the canister exchanged for inert gas before sealing of the canister, see SKB (2010b) and Raiko et al (2012, c.f. Section therein) Production line interfaces The spent fuel line has an interface to the canister production line. The production of the canister and the handling of the spent nuclear fuel merge in the encapsulation plant. The selection and inspection of fuel assemblies to be encapsulated are described in the SKB and Posiva spent fuel reports, see SKB (2010b) and Raiko et al (2012), respectively. After the assemblies have been selected, but before they are placed in the canister, they are dried. After the assemblies are placed in the canister a gas tight steel lid is put on the cast iron insert and the atmosphere in the canister is shifted. The drying of the fuel assemblies, the placement of them in the canister and the exchange of gas including the

68 60 related inspections are presented in the SKB and Posiva spent fuel reports, see SKB (2010b) and Raiko et al (2012). 4.4 The canister production line Overview The main parts of the canister production line are illustrated in Figure 4-5, and an overview of all stages is given in the Posiva (Raiko et al 2012) and SKB (SKB 2010c) canister production reports, respectively. The canister production line starts with the ordering, manufacturing and delivery of components for the cast iron insert and copper shell and ends when the canisters are installed in the supercontainer, c.f. Section Design interfaces The spent fuel and the combined superimposed loads of the swelling buffer, groundwater pressure and ice sheet impose design basis on the canister. The fuel channels of the cast iron insert shall also be designed with respect to the dimensions of the largest BWR and PWR assembly to be deposited, see Section and the Posiva and SKB canister production reports, see (Raiko et al 2012) and (SKB 2010c). Furthermore, with respect to the prevention of illegal diversion of nuclear material, each canister shall be marked by a unique identity number, see Posiva and SKB canister production reports. After the steel lid is finally attached on the cast iron insert it is not possible to inspect individual assemblies any more. Consequently, after this activity the canister is regarded as a unit in the inspection of nuclear material, and the individual identification codes of each assembly and the information of each assembly is linked to the canister they have been encapsulated in Production line interfaces The canister production line has interfaces to the spent fuel line, the supercontainer production line and the buffer and filling components production line, respectively. The spent fuel imposes that the dimensions of the fuel channels shall be inspected and approved prior to placement of the assemblies in the canister. Further, the canister shall be marked and the canisters route through the KBS-3H system after the spent fuel assemblies have been finally placed in the canister shall be documented to conform to regulations related to nuclear safeguards. The interface to the buffer and filling components and supercontainer production line reports are presented in Section and 4.6.3, respectively.

69 The buffer and filling components production line Overview of design The main parts of the buffer and filling components production line are illustrated in Figure 4-5, whereas a detailed overview of all stages of production is given in the buffer and filling components production line report (Posiva 2016b). The buffer and filling components production line involves the ordering, excavation and delivery of buffer material and ends with the installation of the supercontainer, distance blocks and filling components in the deposition drift, including introduction of bentonite pellets in the void section between the transition block and the plug (either compartment or drift plug). The KBS-3H buffer and filling components are divided in the buffer components (solid cylinder and ring-shaped bentonite blocks) of the supercontainer and distance blocks and the filling components (solid cylinder bentonite blocks and bentonite pellets) used to fill the remaining voids of the deposition drift, as outlined in more detail below. Reference design of buffer and filling components The KBS-3H buffer components include blocks inside the supercontainer and the distance blocks (Figure 4-6) placed between supercontainers. The supercontainer (Figure 4-11) consists of the following components, see also Section 4-6 for design and specifications: - Spent fuel canister (copper canister), - Bentonite buffer, - Perforated titanium shell. The buffer components of the supercontainer consist of solid cylindrical and ringshaped blocks that contains the waste canister. The reference dry densities and water contents of the supercontainer buffer components are presented in Table 4-1 whereas supercontainer dimensions are given by Table 4-5. Table 4-1. Dry densities and water contents of reference buffer blocks inside the supercontainer. 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

70 mm 500 mm Figure 4-6. Schematic drawing of the distance blocks between the supercontainers (distance blocks) and feet design, 1 = distance block, 2 = perforated sheet connecting the feet, 3 = foot. The width of the perforated sheet is 175 mm. Crossections parallel (a) and orthogonal (b) to the drift axis. Table 4-2. 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 Outer diameter: 1,765 ± 1 The distance blocks are placed between the installed supercontainers in a drift. The reference design of the blocks is presented in Table 4-2 and Figure 4-6. The water content of the distance blocks is higher than in the supercontainer blocks in order to prevent cracking induced by humidity during operation. The length of each distance block section is determined by the modelled temperature field and varies depending on the thermal properties of the rock and bentonite, type of canister and repository layout. Posiva s reference distance block lengths for various canister types are illustrated in Figure 4-7.

71 63 Figure 4-7. Different distance block alternatives for Finnish spent fuel canisters. 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. The sensitivity of the buffer density to various parameters was analysed as reported in (Posiva 2016b). 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 is within the allowed range of 1,950 2,050 kg/m 3. The updated KBS-3H drift design includes five types of filling components with basically the same design within the compartment and drift plug, respectively, c.f. Figure 4-8: a) Filling components on the sealed side of the compartment and drift plugs consisting of transition blocks and pellet filling b) Filling in positions of inflow. c) Filling on entrance side of compartment plug consisting of transition block and pellet filling. d) Filling at drift end. e) Filling of the remainder of the pilot hole With regards to situation b above respect distances between the flowing fracture and the adjacent distance block is dependent on the inflow rate and the angle of the fracture relative to the drift axis centreline, the higher the inflow and the lower the angle, the longer the respect distance, and hence the length of the filling block in question. Nomograms and tabulations for dimensioning various situations are presented in (Posiva 2016b, c.f. Section 3.4 therein). The reference design of the filling blocks is given by Table 4-3.

72 64 Figure 4-8. KBS-3H drift design with different filling components. Distance blocks, which are part of buffer, are presented in grey colour. Table 4-3. Reference blocks used for filling and transition blocks. Notably, the filling blocks have the same design as the distance 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 For the filling components associated with the drift plug and compartment plug ( a and c above) the design on the sealed side of the plug, c.f. Section 4.7, is identical and 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 (and compartment) plug to distance block with a density gradient. The transition blocks can be composed of several smaller blocks in a similar way as distance blocks. The compaction method is based on isostatic compaction (Posiva s reference method) and the dimensions of blocks will subsequently be optimized. 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 (containing transition blocks and pellets, see Figures 4-9 and Figure 4-10, and the associated compression of the pellet filling. Since the pellet filling has much lower density than the transition blocks there

73 65 Figure 4-9. Design of filling adjacent to the drift plug (the same design applies for the compartment plug). The length of the transition zone is equal to the length of transition block plus the length of pellet filling. Figure 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. Please note that the accounting of the pellet filling and the transition block is not made with a unified relative length scale. will evidently develop a transition of density between the distance block and the plug where the density gradually increases towards the closest distance block. The required length of the transition zone and the resulting maximum swelling pressure at saturation on the plug are dependent on the friction angle as seen in Table 4-4. Table 4-4. Length of transition block, transition zone and resulting swelling pressure on plug with respect to friction angle. Friction angle φ Total length of Length of transition transition zone LT block L 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 Swelling pressure exerted on the plug

74 66 Additional aspects of the reference design (incl. mineralogy, grain size) are presented in (Posiva 2016b, c.f. Section 3.5 therein). Conformity of reference design to design basis Material properties In Posiva s VAHA requirements, the montmorillonite content and the allowed content of organic carbon, sulphides and total sulphur of the bentonite are stated. The montmorillonite content shall be sufficient for the buffer material 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 expose 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. Initially installed mass and density at saturation The design basis stipulates that the saturated buffer density shall be higher than 1,950 kg/m 3, i.e. sufficiently high for example to limit microbiological activity and less than 2,050 kg/m 3 to prevent too high impact by shear on the canister. The conclusion of the performed design calculations and sensitivity analyses (Posiva 216b, c.f. Sections 4.1 through 4.5 therein), is that 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. Thermal constraints 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. Also, the distances between canisters are selected to conform to this performance target. The increase in temperature will be largest for a buffer with a low thermal conductivity, i.e. for a dry buffer and an inner annular gap between the canister and the 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 of the maximum temperature is 93.0 C, which ensures that the maximum temperature in the buffer stays well below 100ºC. Maintaining swelling pressure, hydraulic conductivity and shear strength After swelling the buffer shall uphold the allowed minimum swelling pressure, the allowed maximum hydraulic conductivity and the allowed minimum shear strength in an ambient groundwater salinity of 70 g/l (TDS) (NaCl 1.2 M). The buffer property

75 67 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, it is confirmed that at a saturated density of 1,950 kg/m 3 to 2,050 kg/m 3 is achieved, the hydraulic conductivity will be less than 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 shell into the annular space between rock and supercontainer and associated radial density variation is currently subject to research. The shear strength of the buffer will depend on the density and the dominant cation of the bentonite. High density and ion exchange (from sodium to calcium cation) 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 exhibit the shear strength presumed for the shear load case analysed in SKB (2010b, c.f. Section 4.5 therein). The production, assembly, transportation, handling and installation of the buffer and filling components A production procedure applicable to MX-80 sodium bentonite is presented in (Posiva 2016b). The manufacturing of blocks and pellets is however 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 interim storage of the components, the preparation of the drift, assembly of the supercontainer, the installation of the supercontainer and various buffer and filling components into the deposition drift, removal of any temporary elements from the deposition drift and finally completing the filling procedure by plugging the drift. Manufacturing of buffer and filling components and installation has been carried out and it has been verified that the components can be produced and installed as planned (Posiva 2016b, Kronberg 2015). Initial state of the buffer and filling components The initial state of the buffer is the state when all the auxiliary equipment used during installation has been removed and all buffer and filling components have been installed in the deposition drift and when the compartment or entire drift has been sealed by a plug. Artificial wetting (DAWE) of the deposition drift or inflow of groundwater to the drift and their impact on the buffer are not accounted for in the initial state. For the assessment of the long-term safety it is confirmed that the buffer at the initial state conforms with the design basis related to the barrier functions in the repository. The

76 68 conformity of the reference design with the design basis and conformity of the installed buffer with the reference design has been demonstrated (Posiva 2016b, Kronberg 2015). 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 in almost all possible combinations of acceptable deposition drift dimensions and buffer block, filling block and pellet densities and geometries used here Design interfaces In order to achieve the desired swelling pressure of the bentonite buffer in the supercontainer section, the buffer sets design basis on the diameter of the deposition drift, indirectly on the diameter of the supercontainer (shell) and the resulting annular space between the two. A similar optimization exists between the diameters of the distance blocks, filling blocks and transition blocks and the deposition drift. The canister, furthermore, imposes that the buffer blocks within the supercontainer shall have a cylindrical hole large enough to allow emplacement of the canister. The dimensions and tolerances of the buffer shall, in relation to the Supercontainer shell and the canister, be such as the buffer can be placed inside the Supercon-tainer shell and later allow for installation of the canister, c.f. Section 4.6 which in turn imposes design basis on the deposition drift, c.f. Section Production line interfaces The buffer and filling components production line has interfaces to the canister production line and to the construction of underground openings, i.e. preparation of deposition drifts. The production line of the canister and buffer merge in the final KBS- 3H repository facility in connection to the deposition. The installation of the buffer and filling components comprises several stages as described in the buffer and filling components production report, see (Posiva 2016b, c.f. Section 5.5 therein). Once the supercontainer (shell, buffer blocks and canister) has been assembled, c.f. Section 4.6.1, it is ready for deposition in the deposition drift. The inter-faces to the production lines of the supercontainer and construction of underground openings are described in Section and 4.8.3, respectively. 4.6 The supercontainer production line Overview of design of supercontainer Reference design

77 69 The supercontainer is not a barrier in itself but serves as the pre-assembled carrier/container of the two principal barriers, the canister and the buffer, held together by an outer perforated metal shell. The components making up the supercontainer production line are briefly outlined in Figure The supercontainer is made up of the following components: Canister (copper/cast iron steel canister) containing the spent fuel Bentonite buffer Metallic perforated shell (titanium) The supercontainer is shown in Figure 4-11, showing the spent fuel canister surrounded by the bentonite buffer blocks and the outer cylindrical perforated metallic shell. Detailed design drawings for the supercontainer have so far not been developed for titanium. However, full size prototypes of the supercontainer were developed for the testing and demonstrations of the deposition machine at the Äspö Hard Rock Laboratory. The prototypes were designed and manufactured in carbon steel and stainless steel, to be used with a dummy buffer made of concrete in order to verify the transportation technique. The supercontainer reference design is therefore not necessarily optimized. The design may therefore at a later stage be changed, provided that it can be demonstrated that the new design conforms to the design basis. The verification of the reference design shall demonstrate the conformity of the reference supercontainer to the design basis. The design parameters shall be inspected in the production to verify that the delivered supercontainer conforms to the reference design. If the supercontainers are manufactured, assembled, handled and deposited such that their properties, when deposited, lie within the specification of the reference design, the deposited supercontainers conform to the design basis. Figure Exploded view of the supercontainer showing its different components.

78 70 Supercontainer specifications The supercontainer shell is a perforated metallic cylinder with solid circular end plates and is provided with five pairs of feet. The feet are located under the joints between the bentonite blocks, facing the drift floor. The thickness of the perforated cylinder and end plates shall be 6 mm. The cylinder is perforated to a degree of approximately %. The perforation is made up of holes with a diameter of 100 mm. With the geometrical requirements set up for the deposition drift, SKB (2012, c.f. Section 3.4 therein), the maximum allowed diameter of the supercontainer is 1,761 mm. 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. The dimensions and of the supercontainer shell with tolerances for the different canisters (end plates and feet excluded) and total weights (with end plates) are listed in Table 4-1. Table 4-5. Dimensions, manufacturing tolerances and weights for the supercontainer, assuming use of titanium for the shell. Outer diameter [mm] Inner diameter [mm] Length [mm] Approx. weight of shell [kg] Total weight [kg] SKB PWR/BWR 1, /-2 1,749 5, / ,490/42,590 Posiva BWR 1, /-2 1,749 5, / ,760 Posiva VVER 1, /-2 1,749 4, / ,290 Posiva EPR 1, /-2 1,749 5, / ,750 Conformity to reference design The following load cases were analysed; Normal load case (Load case 1a): The supercontainer rests against the drift wall on all feet i.e. the load is distributed evenly on all feet. Extreme load case (Load case 4b): There is a possibility that the deposition drift has a vertical step of 5 mm, which implies that the supercontainer will only rest on the two outermost pairs of feet. Cyclic strain-controlled fatigue From the results, it is concluded that all calculated stresses, strains and deformations are acceptable. All stresses are below the yield stress limit and no plastic strains are noted. The calculation on the fatigue life of the titanium details indicates that approximately 1,100 loading cycles can be carried out before failure. This gives a good safety margin, as the supercontainer will, at a maximum, be exposed approximately 200 loading cycles whilst loaded into the deposition drift.

79 71 Other aspects analysed were the supercontainer shell material and the shell perforation pattern. Manufacturing The production system for the manufacturing of supercontainers comprises a network of suppliers who manufacture the supercontainer shell and an assembly facility (reloading station) where the assembly and final inspections will be carried out. Foreseen parameters to inspect during manufacturing include; material properties, dimensions, shape and welds. Manufacturing of a titanium supercontainer shell has not been carried out yet. So far only two prototype supercontainers have been manufactured for the testing/demonstrations of the deposition machine, one in carbon steel and one in stainless steel. The performed manufacturing has however verified that it is possible to manufacture supercontainer shells within specified tolerances. Assembly In Posiva s case the assembly is performed in the reloading station without employing a radiation shielded handling cell, for more details see (Posiva 2016d). The assembly of the supercontainer will in SKB s case be carried out in a radiation shielded handling cell at the reloading station. The reloading station will be equipped with necessary lift arrangements for handling of the different components. The assembly is performed with the supercontainer in a vertical position. To enable lifting and tilting from vertical to horizontal position and transport of the supercontainer after assembly, the supercontainer is placed in a so-called transport tube, c.f. Figure Figure Illustration of the supercontainer assembly.

80 72 Deposition equipment The supercontainer and the interlaced bentonite distance blocks, as well as filling blocks and transition blocks are installed using a deposition machine employing application of water cushion technology (Halvarsson 2008) and (Kronberg 2015). The deposition machine is presented in (SKB 2008, c.f. Sections 4.1 and 4.2 therein). Figure 4-13 shows a 3D illustration of the set-up of the equipment manufactured for the deposition tests performed at the -220 m level at the SKB Äspö HRL during 2007 for full scale verification that the KBS-3H transport concept employing water cushion technology can be shown technically feasible. Figure D lay-out of KBS-3H deposition equipment Design interfaces The required thickness of the buffer blocks in relation to canister geometry imposes design basis on the supercontainer (with its cylindrical shell) the latter which in turn imposes design basis on the geometry of the deposition drifts and on the plugs. Specifically, the outer diameter and the length of the supercontainer impose design basis on the geometry and shape (minimum dia-meter, straightness and undulation) of the underground openings (deposition drift). Other design basis imposed by the supercontainer includes those related to handling of the buffer and the canister. The spent fuel canister imposes design basis on the supercontainer in that it should be able to host four canister varieties of five different lengths, as furnished by the Posiva (N=3) and SKB (N=2, of identical length) programmes, respectively.

81 Production line interfaces The supercontainer production line has interfaces to the canister, buffer and filling components production lines and to the construction of underground openings, i.e. preparation of deposition drifts. The assembly of the supercontainer, including installation of the canister and the buffer, comprises several stages as described in the supercontainer production report, see Posiva 2016d, c.f. Chapter 6 therein. After the cylindrical bottom end block and the ring-shaped buffer blocks have been introduced in the metallic shell of the supercontainer, the canister is inserted followed by emplacement of the cylindrical top end block followed by the solid titanium end plate. Once the supercontainer has been assembled, it is ready for deposition in the deposition drift. The interface to the construction of underground openings is presented in Section The production of plugs Overview of plug design The compartment plugs are used to hydraulically separate sections (~150 m long) 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. Reference design The compartment plug and the drift plug both consist of three main components, c.f. Figure 4-14: Fastening ring Collar (with bushings/lead-throughs for watering and air evacuation pipe) Cap (with connection for pellet filling) The lead-throughs/bushings for artificial watering and air evacuation pipe facilitate the DAWE procedure, see SKB (2012),Kronberg (2015) and Posiva (2016c), for administering artificial water after completed disposal in a given compartment of a deposition drift, c.f. Figure 4-14c. 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 m level at Äspö HRL (SKB 2012).

82 74 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) and Kronberg (2015). 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. Figure a) Overview of a typical KBS-3H deposition drift, b) Vertical section through a KBS-3H plug with its different components, c) perspective view of watering and air evacuation pipes. This presented example in (a) is based on the SKB layout (only one central/main tunnel, and the deposition niche located between the main tunnel and the deposition drift). In Posiva s case the deposition niche is positioned between the two parallel central tunnels.

83 75 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. The fastening ring is V-shaped, 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 overall principle of the plugs is shown in Figure 4-14b. Plug specifications The geometrical specifications of the plug with its different components are shown in Figure 4-8. In the following brief accounts of the various plug components are presented. Detailed accounts are provided in (Posiva 2016c), including proposed modified designs due to the complexity of the design (e.g. novel welding solutions and proposed use of casting). Notch approx. Ф2350 Ф2250 Ф1850 Ф1440 Ф Figure Section view of the Plug showing the main dimensions in mm. Fastening ring: is rigid, form stable and V-shaped, positioned in the circumpheral notch cut out in the rock around 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 is performed before commencing deposition in the drift. The fastening ring is not allowed to protrude outside the rock surface of the drift while this would interfere with the subsequent deposition activities.

84 76 Collar: is V-shaped in order to fit to the inside of the fastening ring, see Figure The collar will carry the load from the cap to the rock via the fastening ring and the grouting. The collar is also designed 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 pipe, see also section Cap: is dome-shaped and is attached to the collar by welding. The shape of the cap is chosen to achieve an even distribution of stress. The cap is also equipped with a filling pipe (DN100) for administering bentonite pellets from the outside once the cap has been installed. Lead-throughs for wetting and evacuation of air: allowing filling up of the annular space between the deposition drift wall and the supercontainer/distance block/filling components inside a sealed compartment with water. The water filling pipes are extending approximately two metres into the drift, passing the pellet section and underneath the transition block. 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 an air evacuation pipe (maximum length 150 m). Due to considerations of safety after closure, titanium has been selected for the metallic parts of the plugs. The plugs shall be manufactured in Titanium Grade 3 or Grade 12 (ASTM), c.f. Table 4-6. Titanium Grade 3 and 12 have similar mechanical properties and either material can be chosen depending on availability. Mechanical properties of Titanium Grade 3 and 12 are shown in Table 4-6. Table 4-6. 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) 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 formula, yet to be determined, will be devised such that it will have the required strength and tightness to conform to the design basis. Table 4-7 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 made at the time that the maximum swelling pressure will be 5 MPa.

85 77 Table 4-7. Estimated weight of compartment plug and drift plug components when manufactured in titanium including the corresponding grouting volumes. Fastening ring [kg] Collar [kg] Cap [kg] Total weight Compartment plug Drift plug [kg] Grout [m 3 ] Conformity to reference design The compartment plug and the drift plug shall be designed in accordance with European Steel Code EC3 employing partial factors provided in (Posiva 2016c, c.f. Section therein). Assumed load conditions for the compartment plug is that it shall be able to withstand a hydrostatic pressure of 5 MPa (500 m water column). The added swelling pressure of the bentonite shall not be taken into account. It is further assumed that by the time the swelling pressure has developed, the complete drift will be filled and sealed. The drift plug shall be able to withstand a hydrostatic pressure of 5 MPa plus an added uniform swelling pressure of c. 1.4 MPa resulting from the swelling of buffer and filling components, the latter figure from (Posiva 2016b). Both types of plugs shall be water tight. Axi-symmetric numerical model calculations have been conducted to assess the load situations for both types of plugs employing both linear and non-linear material models. A full account of model geometries, material properties, boundary conditions, meshing and model cases are presented in (Posiva 2016c). The preliminary FEM calculations performed for the drift plug, based on a modified version of the compartment plug, using titanium, show that the design has potential to constitute a viable solution enabling fulfilment of the high requirements applicable once the deposition process is completed. The drift plug analysis presented in (Posiva 2016c) is considered conservative with regards to the swelling pressure. The final design for the drift plug is expected not to differ all that much from that of the compartment plug, other than with regards to the thickness of the cap to withstand the swelling pressure. The mechanical strength of the compartment plug design was checked during the test installation conducted during the winter 2008/2009 at the -220 m level of the Äspö HRL demonstrating in situ at full scale that the compartment plug can withstand a hydrostatic pressure of 5 MPa (SKB 2012). Laboratory tests have been performed with the objective of obtaining information about the development of swelling pressure from the bentonite buffer and the corresponding required pulling force required to loosen the pipe resting on small support inside the test cell (SKB, 2012). The tests showed that removal of pipes after completed water filling should not be an issue even though the swelling pressure acting on the pipe increases rapidly. It is however assumed that the pipes will be removed within 24 hours after water filling. Pipe removal was also demonstrated in situ at full scale during the installation of the KBS-3H Multi Purpose Test (MPT) at the Äspö HRL. The air

86 78 evacuation pipe was in this case, however, only c. 20 metres long, compared to the maximum assumed length of 150 metres for a single compartment. With regards to the metallic parts of the plugs, titanium is expected to be the most inert material, having the lowest corrosion rate, the lowest hydrogen production rate and is also has good mechanical properties. Titanium has therefore been selected as the reference metallic material for the plugs. Low ph-concrete with ph<11 shall be used for grouting around the fastening ring to minimize any negative impact on the barriers. No customised recipe been developed for this application and is yet to be developed and tested. The accepted water volume to pass the respective plug (water tightness) is dependent on the acceptable transport rate of clay material out from the deposition drift during the sealing phase. A specific number remains to be determined. Manufacturing of the plugs The manufacturing of the plugs is made in an external workshop. The plug components are manufactured from titanium plates where the manufacturing consists of a number of steps. SKB/Posiva intends to apply conventional and generally applied methods both for the involved processes and inspections. The manufacturing of the metallic parts includes the following key steps: Verification of all relevant measures. Welding Nondestructive testing of welds Heat treatment (Stress relief) Machining of surfaces to their final measures Check and documentation of measures Preparation of assembly welds Marking of the different parts In order to verify that the different components fit to each other a preassembly of the plugs will be performed in the workshop before delivery, without employing assembly welds. The inspection plan for the plugs will at a minimum address the following aspects; Material properties Dimensions Shape Welds Preassembly

87 79 Installation of the plugs The installation/assembly of the plugs will be carried out inside the deposition drift. Manual installation of compartment plugs has been demonstrated in tests carried out during the winter 2008/2009 and during the MPT, both carried out at Äspö HRL. It is projected that future installations will be performed with some kind of remotely controlled handling device, including automatization of welding. The preparation of the drift includes excavation of the notches followed by casting of the fastening ring with concrete and installation of the air evacuation pipe (notably a temporary bridge over the fastening ring is required to enable passage by the deposition machine). The closure of the compartment (or drift) includes installation of the collar with pipes that run through it and installation of the cap. Once all welding is finalised, the interfaces between the plug and concrete and between the concrete and the rock surface are contact grouted using the preinstalled injection tubes. Directly after the cap has been installed, the void between the plug and the transition blocks is filled with pellets. After filling the pellets, the filling connection is closed, as well as the drainage pipe in the collar in its lowest part, and the water filling starts. The water filling is continued until water comes out through the air evacuation pipe. Immediately after closing of the valves the water supply lines are disconnected and the removal of pipes commences. A detailed account of the installation process including the various inspections to be made are given in (Posiva 2016c). Initial state of plugs The initial state of the compartment plug and the drift plug is the state when the water filling has been completed, all penetrating pipes have been retracted and the leadthroughs have been sealed. For the assessment of the long-term safety it shall be confirmed that the plugs at the initial state conforms to the design basis related to the barrier functions in the final repository. The confirmation is made through verification of: the conformity of the reference plugs to the design basis, the conformity of the installed plugs to the reference design. The plug properties to be designed to conform to the design basis related to the properties in the KBS 3H repository are: material composition, strength water tightness gas tightness Tabulations of parameters defining the initial state of the plugs, compared with the corresponding reference design values are presented in (Posiva 2016c, c.f. Chapter 7 therein.)

88 80 Manufacturing inspections of the plugs will verify that the material properties conform to the specified values needed to withstand the anticipated loads. The proposed materials are in accordance with the American Society for Testing and Materials (ASTM) standard, hence the property variations are small. Manufacturing inspections of the plugs shall verify that dimensions conform to the specified values. Plugs manufactured so far for performed in situ tests have verified that it is possible to manufacture plugs within specified tolerances. It is however noted that plugs have so far only been manufactured of carbon steel. The compartment plug shall maintain its hydraulic isolation capacity during the installation phase and the drift plug shall as a minimum maintain its hydraulic isolation capacity as long as the adjacent central/main tunnels are not backfilled and saturated. Performed in situ tests have verified that it is possible to reach the acceptance criteria (a tentative leakage criterion of 0.1 L/min) for water leakage through the plugs. Low-pH concrete was however not used in any of the tests (still to be tested). Actual water leakage can be measured in conjunction with the water filling of the compartment Design interfaces The various steps in the plug production line are described in brief in Figure 4-5 and are described in detail in the plug production line report, c.f. (Posiva 2016c). In the final repository, during the post closure phase, the plugs must not significantly impair the barrier function of the engineered barriers or rock. Design basis is imposed by the buffer and filling components (and indirectly by drift dimensions) while the compartment and drift plugs are important for the properties and function of the buffer and filling components, above all to keep the components in place. This implies that the requirements for the drift plug are considerably higher than those for the compartment plug, c.f. (Posiva 2016c). The plugs in turn impose demands on the rock and the construction of the deposition drift. This includes design basis related to inflow, strength of the rock and fracturing at the positions of the plugs and preparation of v-shaped notches to host the fastening ring, c.f. Figure Production line interfaces The plug production line includes a series of activities which includes selection of optimal positions for the plugs, preparation of the v-shaped notch in the drift wall and mounting of the fastening ring followed after deposition by mounting of the collar and the cap, c.f. (Posiva 2016c). Alongside the plug installation work, attachment of the pipe for air evacuation is made to the drift wall of the compartment with lead-throughs associated with the respective plug. The buffer and filling components production line and the plug production line merge in conjunction with the installation of the plug and the subsequent administering of bentonite pellets between the transition block and the plug, c.f. the Buffer and Filling components production report (Posiva 2016b).

89 Construction of the underground openings Overview of design of underground openings The construction of the underground openings comprises site adaptation of the design and description of the application of the methods to excavate and inspect (as built) the underground openings. The construction of the underground openings also includes the preparation of the underground openings for the installation of supercontainers and other drift components and closure. The underground openings here comprise: the actual location and spatial geometry of the openings the rock surrounding the openings that is affected by the construction works; and engineered materials for sealing and rock support, and residual materials from performance of activities in the KBS-3H disposal facility, that remain in and on the rock bounding the openings at deposition and closure. The void spaces of the underground openings as such do not contribute to the safety of the KBS-3H repository and do not have any barrier functions. However, the locations of the deposition areas and deposition drifts with respect to the ambient geological, thermal, hydrogeological, mechanical and chemical properties of the rock are important for the performance of the rock as a barrier and thus for the safety of the final repository. In order to answer up to the above requirement the repository shall; accommodate the sub-surface part of the repository facility with the number of approved supercontainer sections that are required to deposit all canisters with spent nuclear fuel (from the approved programme). Provide thermally favourable conditions; provide mechanically stable conditions; provide favourable hydrogeologic and transport conditions provide chemically favourable conditions be designed so that they do not significantly impair the barrier functions of the rock (for example through development of EDZ) or the engineered barriers (for example water flow affecting the buffer erosion) allow the deposition of canister, buffer and plugs to the drifts with the desired barrier functions; allow the installation of closure to the other underground openings with the desired barrier functions. be designed so that breakdowns and mishaps (e.g. caving in and flooding) in conjunction with the nuclear operations are prevented. In order to meet up to the set-up requirements the following design considerations are adhered to; Excavation, sealing and rock reinforcement shall be based on well-tried or tested techniques.

90 82 The underground openings shall be designed and constructed using methods so that they, with reliability, provide the desired rock conditions. The properties of the underground openings shall be possible to inspect against specified criteria. Detailed accounts of the design basis applicable to underground openings construction are tabulated in (Posiva 2016e, c.f. Section 2.3 therein). SKB and Posiva will apply the Observational Method for adaptation of the repository to the site conditions, so that the as-built layout and underground openings conform to the design basis. Details about the observation method and how it is planned to be applied is given in (Posiva 2016e, c.f. Section 3.2 therein). The development of the repository is divided in two different phases; repository construction (repository accesses, central/service area) and repository operation (successive development of deposition areas). In case of the latter, three separate activities may be identified in the development of an individual deposition area: 1. Investigation of the detailed site conditions and adaptation of the layout to those conditions; 2. Investigation and construction of deposition drifts with control programme; and 3. Deposition works including deposition of supercontainers and installation of buffer, filling components and plugs. The planned stepwise development of the deposition areas with systematic documentation of as-built conditions will enable systematic auditing of the design and construction activities, c.f. (Posiva 2016e, c.f. Sections 3.4 and 3.5 therein). Reference design and conformity to design basis The reference design is based on one possible layout of the underground disposal facilities at Olkiluoto (Figure 4-16) and at Forsmark, respectively. The reference design also provides an estimation of material quantities required for rock support and grouting based on the layout. The site-specific basis for the reference design is site characterisation data, site descriptive models and geotechnical information, which have been interpreted and evaluated in a site engineering report (SER) for KBS-3V. Posiva s SER for the Olkiluoto site is presented in (Posiva 2012e) with the corresponding Forsmark SER presented in (SKB 2009b). In the following sections the reference design and its conformity to the design basis is presented. The design basis related to the functions of the repository is presented under the headers, details provided in (Posiva 2016e, c.f. Chapter 4 therein): repository depth; deposition areas; pilot holes; deposition drifts and supercontainer sections; other underground openings; and engineered and residual materials.

91 83 Repository depth Application of the above rationale resulted in a depth range of 450 m to 500 m according to SKB (SKB 2009a) and in minimum depth 400 m according to Posiva (Posiva 2012b). The in situ stress magnitude and the fracture frequency of waterbearing fractures were the governing conditions. Figure KBS-3H-layout for a final repository facility in Olkiluoto (see Posiva 2016e, c.f. Appendix 1 therein). Deposition area - placement of deposition drifts and supercontainer sections The positioning of these components is dependent on thermal, mechanical and hydrogeological conditions. Thermal: Nominal (centre to centre) horizontal distance from deposition drift to another (drift spacing) is 25 m in Olkiluoto and alternatively 30 m or 40 m in Forsmark. Mechanics: supercontainer sections are tentatively not allowed to be placed closer than 100 m to deformation zones with a trace length longer than 3 km (SKB). Tentatively a supercontainer section shall not intersect the respect volume of layout determining feature (LDF), hydrogeological zone or brittle deformation zone (Posiva). Tentatively deposition drifts shall not intersect the respect volumes of LDFs (Posiva). SKB does not have the corresponding requirement. Canister positions should, as far as reasonably possible, be selected so that they do not have potential for shear larger than the canister can withstand. In order to mitigate the impact of potential future earthquakes, canister positions are selected so that they do not intersect discriminating fractures, so-called Large fractures. Criteria to be applied in selecting canister positions from this point of view is addressed in Posiva 2016h).