Technical Report

TR-10-17

Design, production andinitial state of the closure
Svensk Kärnbränslehantering AB

December 2010

Svensk Kärnbränslehantering AB

CM Gruppen AB, Bromma, 2010

Swedish Nuclear Fueland Waste Management Co
Box 250, SE-101 24 Stockholm
Phone +46 8 459 84 00

ISSN 1404-0344
Tänd ett lager:
SKB TR-10-17
P, R eller TR.

Design, production andinitial state of the closure
Svensk Kärnbränslehantering AB

December 2010

Keywords: SKBdoc 1177186, Closure, Safety report, Design premise,
Verification, Verifying analysis, Reference design, Production, Manufacturing,
Inspection, Initial state.
A pdf version of this document can be downloaded from www.skb.se.

Preface
An important part of SKB’s licence application for the construction, possession and operation of
the KBS-3 repository is the safety report. The safety report addresses both safety during operationof the KBS-3 repository facility (SR‑Operation), and the long-term safety of the KBS‑3 repository(SR‑Site).
For the construction of the KBS-3 repository SKB has defined a set of production lines:•

the spent nuclear fuel,•the canister,•

the buffer,•

the backfill,•

the closure, and•the underground openings.

These production lines are reported in separate Production reports, and in addition there is a
Repository production report presenting the common basis for the reports.
This set of reports addresses design premises, reference design, conformity of the reference design
to design premises, production and the initial state, i.e. the results of the production. Thus the reports
provide input to SR‑Site concerning the characteristics of the as built KBS‑3 repository and to
SR‑Operation concerning the handling of the engineered barriers and construction of undergroundopenings.
The preparation of the set of reports has been lead and coordinated by Lena Morén with support
from Roland Johansson, Karin Pers and Marie Wiborgh.
This report has been authored by David Gunnarsson and Roland Johansson.

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Summary
The report is included in a set of Production reports, presenting how the KBS-3 repository isdesigned, produced and inspected. The production reports are included in the safety report for theKBS-3 repository and repository facility.
The report provides input on the initial state of the closure and plugs in underground openings otherthan deposition tunnels for the assessment of the long-term safety, SR-Site. The initial state refers to
the properties of the engineered barriers once they have been finally placed in the KBS-3 repository
and will not be further handled within the repository facility. In addition, the report provides some
input to the operational safety report, SR-Operation, on how the closure and plugs shall be handled
and installed.
The report presents the design premises and reference designs of the closure and plugs and verifies
their conformity to the design premises. It also briefly deals with the production of the closure andplugs. Finally, the initial state of the closure and plugs and their conformity to the reference designs
and design premises are presented.
Design premises for the closure

The design premises are based on regulations; the functions of the KBS-3 repository; the designbasis cases from the assessment of the long-term safety; the design basis events from the assessmentof the operational safety; technical feasibility and the planned production.
The closure is one of the engineered barriers in the KBS-3 repository. The closure is the material
installed in boreholes and underground openings other than deposition tunnels, in order to fill
and close them. In the KBS-3 repository the closure shall sustain the multi-barrier principle bypreventing the formation of water conductive channels between the repository and the surface andby preventing the backfill in deposition tunnels to expand or to be transported out from the deposition tunnels. The closure shall also keep the closure in underlying or adjacent underground openings
in place. In the upper part of the ramp, shafts and boreholes the closure shall significantly obstruct
unintentional intrusion into the repository. The hydraulic conductivity of the installed closure is
the property that is of most importance for its barrier function. Design premises with respect tothe hydraulic conductivity are based on results from assessments of the long-term safety.
The closure plugs have no barrier function in the KBS-3 repository. Their purpose is to provide
mechanical restraint and hydraulic control functions. They are needed as long as the undergroundopening on one side of the plug is unsealed to keep the installed closure material in place. Plugs also
contribute to a feasible, safe and secure installation of the closure.
The closure and plugs shall also be designed to conform to design premises related to production
and operation of the repository facility. With respect to technical feasibility the closure impose
design premises for the main- and transport tunnels and for the lower part of ramp and shafts.
The reference design of the closure and its conformity to the design premises

The closure in main tunnels, transport tunnels and in the lower part of the ramp and shafts has
the same conceptual design as the backfill in deposition tunnels. In practice, neither the material
composition nor the installed density needs to be the same. In main tunnels and transport tunnels
there is no need to prevent buffer expansion and the acceptable hydraulic conductivity is larger
than in deposition tunnels. Nevertheless, the same material as for the backfill in deposition tunnels
is selected at this stage of development, and the verifying analyses presented for the backfill areconsidered relevant to support the conformity of the closure reference design to the design premises.
The only function of the closure of the cavities in the central area is to occupy the space with noother design premise than to prevent substantial convergence and subsidence of the surroundingrock. With respect to this the reference design is compacted crushed rock.

TR-10-175

In the upper part of the ramp and shafts the closure shall significantly obstruct unintentional
intrusion into the repository. To meet this requirement effectively compacted rock fill is chosen as
reference design. In the uppermost 50 m of the ramp and shafts very coarse crushed rock is used forthe closure.
Comprehensive experience of placement and compaction of rock fill is available from road construction, from the construction of hydro power dams and also from SKB’s experiments at Äspö HRL.
Investigation boreholes going deeper than the top sealing have to be sealed. The reference design
is highly compacted bentonite in perforated copper tubes. The assessment of the conformity to thedesign premises is based on results from many years of RD&D work.
The production of the closure

Closure of the repository will, with the exception of some boreholes that have to be sealed earlier,
not take place until all spent nuclear fuel has been deposited. This means that the closure activities
lie well in the future. It also means that the production and installation of the closure will be basedon comprehensive experience from the production and installation of backfill and plug in deposition
tunnels.
The initial state of the closure

The initial state of the closure is the state when all closure material in a specific undergroundopening or borehole is installed and the borehole, rock cavity, shaft or tunnel has been closed. The
initial state will depend on the composition of the closure material, the dimensions and density of theinstalled closure components, the portions of the rock cavity, shaft or tunnel filled with blocks andpellets or rock fill as well as on the dimensions of the rock cavity. For underground openings thatshall be filled with compacted clay blocks and pellets the estimations are based on results presented
for backfill in deposition tunnels. For closure of the other underground openings and for boreholes
the initial state is given by reasonable values of parameters that has been estimated based on resultsfrom experiments and tests or proven experience.

6

TR-10-17

Sammanfattning
Rapporten ingår i en grupp av Produktionsrapporter som redovisar hur KBS-3-förvaret är utformat
samt hur det ska produceras och kontrolleras. Produktionsrapporterna ingår i säkerhetsredovisningen
för KBS-3-förvaret och förvarsanläggningen.
Rapporten redovisar indata om initialtillståndet för förslutningen, inklusive pluggar, i alla berg­
utrymmen utom deponeringstunnlar för analysen av långsiktig säkerhet, SR-Site. Initialtillståndet
avser egenskaperna hos de tekniska barriärerna då de slutligt satts på plats i slutförvaret och inte
hanteras ytterligare inom slutförvarsanläggningen. Dessutom ger rapporten viss information till
driftsäkerhetsredovisningen, SR-Drift, om hur förslutningen och pluggar ska hanteras och installeras.
Rapporten redovisar konstruktionsförutsättningar och referensutformningar för förslutning och
pluggar och verifierar deras överensstämmelse med konstruktionsförutsättningarna. Den behandlarockså kortfattat produktion av förslutning och pluggar. Vidare redovisas initialtillståndet för förslutning och pluggar och deras överensstämmelse med referensutformning och konstruktionsförutsättningar.
Konstruktionsförutsättningar för förslutning och pluggar

Konstruktionsförutsättningarna är baserade på föreskrifter, KBS-3-förvarets funktioner, konstruk­
tionsstyrande fall från analysen av långsiktig säkerhet, konstruktionsstyrande händelser frånredovisningen av driftsäkerhet, teknisk genomförbarhet och den planerade produktionen.
Förslutningen är en av de tekniska barriärerna i KBS-3-förvaret. Förslutningen utgörs av det material
som installeras i borrhål och alla bergutrymmen utom deponeringstunnlar. I KBS-3-förvaret ska
förslutning och pluggar upprätthålla flerbarriärsprincipen genom att hindra att det bildas konduktiva
vattenvägar mellan förvarsområdet och markytan samt hindra att återfyllningen expanderar ut ur ideponeringstunnlarna. Förslutningen ska också hålla förslutningen i de bergutrymmen som ligger
intill och nedanför på plats. I den övre delen av ramp och schakt ska förslutningen avsevärt försvåra
oavsiktligt intrång i förvaret. Den installerade förslutningens hydrauliska konduktivitet är den egenskap som har störst betydelse för dess barriärfunktion. Angivna konstruktionsförutsättningar med
avseende på hydraulisk konduktivitet baseras på resultat från analyser av den långsiktiga säkerheten.
Pluggar som ingår i förslutningen har ingen barriärfunktion i KBS-3-förvaret. Deras uppgift är att
underlätta installation av förslutningen genom att hålla redan installerat material på plats och att
begränsa inflödet av vatten. Pluggarna ska också bidra till att installationen av förslutningen kan
genomföras på ett säkert sätt.
Förslutning och pluggar ska även utformas så att konstruktionsförutsättningar med hänsyn tillproduktion och drift av förvarsanläggningen uppfylls. Med hänsyn till teknisk genomförbarhet ger
förslutning och pluggar konstruktionsförutsättningar för utförande av stam- och transporttunnlar
samt nedre delen av ramp och schakt.
Referensutformning för förslutning och pluggar och överensstämmelse
med konstruktionsförutsättningarna

Förslutningen i stam- och transporttunnlar samt nedre delen av ramp och schakt har i princip samma
utformning som återfyllningen i deponeringstunnlar. I praktiken behöver varken materialsammansättningen eller den installerade densiteten vara densamma. I stam- och transporttunnlar finns inget
krav med hänsyn till att bufferten sväller och tillåtet värde för hydraulisk konduktivitet är högre än
i deponeringstunnlar. I avvaktan på resultat från utvecklingsarbete specifikt för förslutningen har
samma material valts som för återfyllningen i deponeringstunnlar. Detta betyder att de verifierande
analyser som redovisas för återfyllningen bedöms vara relevanta och att referensutformningen för
förslutningen således överensstämmer med konstruktionsförutsättningarna.

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I centralområdet har förslutningen ingen annan funktion än att fylla ut bergutrymmena så att de inte
deformeras. För att klara detta har förslutning med kompakterad bergkross valts som referensutformning.
I övre delen av ramp och schakt ska förslutningen avsevärt försvåra oavsiktligt intrång i förvaret. För
att möta detta krav har välkompakterat bergmaterial valts som referensutformning. I den allra översta
delen av ramp och schakt utförs förslutningen med grovt krossmaterial.
Omfattande erfarenheter av utläggning och kompaktering av bergkross finns från vägbyggen, bygge
av vattenkraftdammar och även från SKB:s experiment vid Äspölaboratoriet.
Undersökningsborrhål som går djupare än toppförslutningen ska förslutas. Referensutformning ärhögkompakterad bentonit i perforerade kopparrör. Erfarenheter och resultat från många års forskningoch utveckling visar att denna utformning uppfyller konstruktionsförutsättningarna.
Produktionen av förslutning och pluggar

Med undantag för vissa undersökningsborrhål kommer förslutning av förvaret inte att påbörjas
förrän allt använt kärnbränsle har deponerats. Detta innebär att utförandet av förslutningen liggerlångt in i framtiden. Det betyder också att produktion och installation av förslutningen kommer
att kunna baseras på omfattande erfarenheter från produktion och installation av återfyllning och
pluggar i deponeringstunnlarna.
Förslutningens initialtillstånd

Förslutningens initialtillstånd är tillståndet när borrhål och alla bergutrymmen har förslutits.
Initialtillståndet kommer att bero av förslutningsmaterialets sammansättning, dimensioner och
densitet på de installerade förslutningskomponenterna, hur stor del av bergutrymmena som fyllts
med block och pelletar alternativt bergmaterial samt måtten på bergutrymmena. För de bergutrymmen som försluts med block och pelletar baseras bedömningen av initialtillståndet på resultat som
redovisats för återfyllning i deponeringstunnlar. För förslutning av övriga bergutrymmen samt av
borrhål redovisas initialtillståndet som rimliga parametervärden som har bedömts med ledning av
resultat från experiment alternativt beprövad erfarenhet.

8TR-10-17

Contents
1
1.1

1.2

1.3

1.4

2
2.1

2.2

2.3

2.4
2.5
3
3.1

3.2

3.3

Introduction
General basis
1.1.1 This report
1.1.2 The design of the closure and plugs
1.1.3 The production of the closure and plugs
Purpose, objectives and limitations
1.2.1 Purpose
1.2.2 Objectives
1.2.3 Limitations
Interfaces to other reports included in the safety report
1.3.1 The safety report for the long-term safety
1.3.2 The safety report for the operational safety
1.3.3 The other production reports
Structure and content
1.4.1 Overview
1.4.2 Design premises
1.4.3 Reference design
1.4.4 Conformity of the reference design to the design premises
1.4.5 Production of the closure and plugs
1.4.6 Initial state of the closure and plugs

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Design premises for the closure
General basis
2.1.1 Identification and documentation of requirements and designpremises
2.1.2 Definition, purpose and basic design of the closure
2.1.3 Definition, purpose and basic design of the plugs
Barrier functions and design considerations
2.2.1 Barrier functions of the closure in the KBS-3 repository
2.2.2 Functions and properties of plugs in the KBS-3 repository andrepository facility
2.2.3 Design considerations
Design premises for the closure
2.3.1 Design premises related to the barrier functions in the KBS-3
repository
2.3.2 Design premises from the other engineered barriers
2.3.3 Design premises related to the production and operation
Design premises imposed by the closure
Design premises for the plugs

15
15

Reference designs
Closure of main tunnels and transport tunnels
3.1.1 Reference design of the closure in main tunnels and transporttunnels
3.1.2 Conformity of the reference closure in main tunnels and transporttunnels to the design premises
Closure of the central area
3.2.1 Reference design of the closure in the central area
3.2.2 Conformity of the reference closure of the central area to thedesign premises
Closure of ramp and shafts below the top sealing
3.3.1 Reference design of the closure in ramp and shafts below the
top sealing
3.3.2 Conformity of the reference closure in ramp and shafts to thedesign premises

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3.4

Top sealing
3.4.1 Reference design for the top sealing
3.4.2 Conformity of the reference top sealing to the design premises
Borehole sealing
3.5.1 Reference design of borehole sealing
3.5.2 Conformity of the reference borehole sealing to the design premises
Plugs
3.6.1 Reference designs of plugs
3.6.2 Conformity of the reference plugs to the design premises

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4
4.1
4.2
4.3
4.4
4.5
4.6
4.7

Production of the closure
Introduction
Closure of main tunnels and transport tunnels
Closure of the central area
Closure of ramp and shafts
Top sealing
Borehole sealing
Plugs

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5
5.1
5.2
5.3

Initial state
Introduction
Initial state of the closure
Material composition
5.3.1 Clay in main tunnels and transport tunnels, the ramp and shafts
up to the top seal
5.3.2 Clay for borehole seals
5.3.3 Copper for borehole seals
5.3.4 Concrete
5.3.5 Rock material
5.3.6 Geometry
Conformity to design premises long-term safety at the initial state

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3.5
3.6

5.4

References

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1

Introduction

1.1

General basis

1.1.1 This report
This report presents the reference design, production and initial state of the closure in undergroundopenings other than deposition tunnels in the KBS-3 repository for spent nuclear fuel. It is included
in a set of reports presenting how the KBS-3 repository is designed, produced and inspected. The
set of reports is denominated Production reports. The Production reports and their short names areillustrated in Figure 1-1. The reports within the set referred to in this report and their full names arepresented in Table 1‑1.
This report is part of the safety report for the KBS-3 repository and repository facility, see Repository
production report, Section 1.2. It is based on the results and review of the most recent long-term safetyassessment and on the current knowledge and technology and results from research and development.

1.1.2 The design of the closure and plugs
The presented designs of the closure and plugs presumes a repository based on the KBS-3 methodwith vertical deposition of canisters in individual deposition holes as further described in Chapter 3
in the Repository production report.

Production reports
Repository
production
reportSpent fuelreport”Engineered barrier” production reports

Canisterproduction
reportBufferproduction
reportBackfill
production
reportClosureproduction
reportUndergroundopenings
construction
reportFigure 1‑1. The reports included in the set of reports describing how the KBS-3 repository is designed,
produced and inspected.
Table 1‑1. The reports within the set of Production reports referred to in this report.
Full title

Short name used within the
Production reports

Text in reference lists

Design and production of theKBS-3 repository

Repository production report

Repository production report, 2010.
Design and production of the KBS-3 repository.
SKB TR-10-12, Svensk Kärnbränslehantering AB.

Design, production and initialstate of the buffer

Buffer production report1

Buffer production report, 2010.
Design, production and initial state of the buffer.
SKB TR-10-15, Svensk Kärnbränslehantering AB.

Design, production and initialstate of the backfill and plugin deposition tunnels

Backfill production report1

Backfill production report, 2010.
Design, production and initial state of the backfill
and plug in deposition tunnels. SKB TR-10-16,
Svensk Kärnbränslehantering AB.

Design, construction andinitial state of the undergroundopenings

Underground openings
construction report

Underground openings construction report,
2010. Design, construction and initial state of
the underground openings. SKB TR-10-18,
Svensk Kärnbränslehantering AB.

1

Commonly referred to as the “Engineered barrier” production reports.

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11

The reference design of the closure and plugs and the reference methods to produce them presented
in this report constitutes solutions that are technically feasible. It is, however, foreseen that the designpremises, the designs as well as the presented methods for production, test and inspection will be further developed and optimised before actual construction of the KBS-3 repository facility commences.
This particularly concerns properties of the closure and plugs that require detailed information on theconditions at repository depth. In this context it should be mentioned that there are alternative designs
that conform to the design premises as well as alternative ways to produce the reference design. In
addition, the safety assessment SR‑Site, as well as future safety assessments, may result in up-dated
design premises. SKB´s objective is to continuously develop and improve both design and production
and adapt them to the conditions at the selected site.

1.1.3 The production of the closure and plugs
The presented production of the closure and plugs in underground openings other than deposition tunnels is based on that there is a system, the KBS-3 system, comprising the facilities required to manage
the spent nuclear fuel and finally deposit it in a KBS-3 repository. The KBS-3 system and its facilities
etc are presented in Chapter 4 in the Repository production report.
The installation of the closure and plugs in underground openings other than deposition tunnels is partof the decommissioning of the KBS-3 repository facility, and commences when the decommissioning
phase of the KBS-3 system and its facilities is initiated.

1.2

Purpose, objectives and limitations

1.2.1 Purpose
The purpose of this report is to describe how the closure and plugs in underground openings other thandeposition tunnels are designed, constructed and inspected in a manner related to their importance forthe safety of the KBS‑3 repository. The report shall provide the information on the design, production
and initial state of the closure and plugs in underground openings other than deposition tunnels required
for the long-term safety report, SR‑Site, as well the information on how to produce and inspect theclosure and plugs required for the safe decommissioning of the KBS-3 repository facility.
With this report SKB intends to present the design premises for the closure and plugs in the KBS-3
repository and demonstrate how they can be designed and produced to conform to the stated designpremises. The report shall present the reference designs and production methods and summarise theresearch and development efforts that supports that the closure and plugs in underground openings
other than deposition tunnels can be produced in conformity to the design premises.

1.2.2 Objectives
Based on the above purpose the objectives of this report are to present:•

the design premises for the closure and plugs,•

the reference design of the closure and plugs,•

the conformity of the reference design to the design premises,•

the planned production,•

the initial state of the closure and plugs, i.e. the expected result of the production comprising as
built data on the properties taken credit for as contributing to, or affecting, the barrier functions
and safety.

1.2.3 Limitations
The Closure production report primarily includes design premises related to the long-term safetyof the KBS-3 repository. The presented reference design must conform to these design premises andconsequently they have in most cases determined the design. Design premises related to other aspects
than safety and radiation protection are only included if they have determined the design of the closure
and plugs or the methods to produce them.
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The Closure production report also includes the design considerations taken with respect to the application of best available technique with regard to safety and radiation protection, and the related designpremises for the design and development of methods to produce the closure and plugs. Motivations forthe presented reference designs and methods as being the best available are reported elsewhere.

1.3

Interfaces to other reports included in the safety report

The role of the Production reports in the safety report is presented in Section 1.2 in the Repository
production report. A summary of the interfaces to other reports included in the safety report isgiven below.

1.3.1 The safety report for the long-term safety
By providing a basic understanding of the repository performance on different time-periods and by theidentification of scenarios that can be shown to be especially important from the standpoint of risk thelong-term safety assessment provides feedback to the design of the engineered barriers and undergroundopenings. The methodology used for deriving design premises from the long-term safety assessment isintroduced in the Repository production report, Section 2.5.2. A more thorough description as well as
the resulting design premises are given in the report “Design premises for a KBS-3V repository basedon results from the safety assessment SR-Can and some subsequent analyses” /­SKB 2009a/, hereinafterreferred to as Design premises long-term safety. These design premises constitute a basic input to thedesign of the closure and plugs in underground openings other than deposition tunnels.
As stated in Section 1.2 this report shall provide information on the initial state of the closure andplugs in underground openings other than deposition tunnels for the long-term safety assessment.
This report shall also provide data concerning the design of the closure and plugs, and the initialstate used in the calculations included in the long-term safety assessment.

1.3.2 The safety report for the operational safety
The production of the closure and plugs in underground openings other than deposition tunnels is partof the decommissioning of the final repository facility. Consequently, this report has no interfaces tothe report for the operational safety. However, it provides information on the design of the closure andplugs and the technical systems used to manufacture, handle, install, test and inspect them for the safe
decommissioning of the repository facility.
1.3.3 The other production reports
The Repository production report presents the context of the set of Production reports and theirrole within the safety report. It also includes definitions of some central concepts of importance forthe understanding of the Production reports.
The Repository production report sets out the laws and regulations and demands from the nuclear
power plant owners applicable to the design of a final repository for spent nuclear fuel. In addition,
it describes the functions of a KBS-3 repository and how safety is provided by the barriers and theirbarrier functions. The report goes on to describe how design premises are derived from laws andregulations, owner demands and the iterative processes of design and safety assessment and design
and technique development respectively. The starting point for the design premises presented in thisreport is the barrier functions and design considerations introduced in the Repository production
report, Chapter 3.
The design and production of the different engineered barriers and underground openings are interrelated. An overview of the design and production interfaces is provided in the Repository production
report, Chapter 4. The design premises imposed by the closure and plugs on the design and productionof the other engineered barriers and underground openings are presented in this report. These designpremises are repeated and verified in the production reports for the engineered barriers and underground openings on which the closure and plugs impose design premises.

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1.4Structure and content

1.4.1 Overview
The general flow of information in the Closure production report can be described as follows:•

design premises,•reference design,•

conformity of the reference design to the design premises,•

production,•

initial state.

The listed bullets are further described in the following sections. In addition, the context of the reportis presented in this chapter.

1.4.2 Design premises
The design premises set out the information required for the design. The design premises for the closure
and plugs in underground openings other than deposition tunnels are presented in Chapter 2 of thisreport. The chapter starts with the definition of the closure and plugs, their purpose and basic design.
After that follows a presentation of the barrier functions the closure shall provide, and the functions theplugs shall provide to contribute to the safety of the final repository and the considerations that shallbe made in the design with respect to the application of a well-tested and reliable technique. Finally,
the detailed design premises for the closure and plugs are given. They state the properties the reference
design shall have to maintain the functions and to conform to the design considerations.
1.4.3 Reference design
The descriptions of the reference designs comprise the closure and plug materials and components andthe installed closure and plugs. The reference designs are presented in Chapter 3. The reference designs
are specified by a set of variables denominated design parameters, e.g. montmorillonite content andblock bulk density. The design parameters shall be inspected in the production and acceptable values forthem are given for the reference designs. The design premises and considerations that have determinedthe design parameters are presented.
1.4.4 Conformity of the reference design to the design premises
An important part of this report is the analyses verifying the conformity of the reference design to thedesign premises. The conformity to each of the design premises given as feedback from the long-term
safety assessment as well as the design premises related to technical feasibility, production and operation is analysed and concluded.
1.4.5 Production of the closure and plugs
The presentation of the production of the closure and plugs comprise an overview of:•

the main parts and different stages of the production,•short descriptions of methods for production, test and inspection.

1.4.6 Initial state of the closure and plugs
In Chapter 5, the initial state chapter, the expected values of the design parameters, and other parameters required for the assessment of the long-term safety, at the initial state are presented. The expectedvalues are based on the current experiences from the production trials, and they are discussed andjustified with respect to the currently available results presented in Chapter 4. Finally, the conformityof the closure and plugs at the initial state to the design premises stated in Design premises long-term
safety is summarised.

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2

Design premises for the closure

In this chapter the design premises for the closure are presented. They comprise the barrier functions
and properties the closure shall sustain in the KBS‑3 repository and premises for the design. The
required functions and design premises are written in italics.

2.1

General basis

2.1.1 Identification and documentation of requirements and design premises
The methodology to derive, review and document design premises is presented in the Repository
production report Chapter 2. The design premises are based on:•international treaties, national laws and regulations,•the functions of the KBS‑3 repository,•

the safety assessment,•

technical feasibility,•

the planned production.

The Repository production report, Section 2.2 includes a presentation of the laws and regulations
applicable for the design of a final repository for spent nuclear fuel. Based on the treaties, laws andregulations SKB has substantiated functions and considerations as a specification of the KBS‑3
repository, and as guidelines for the design of its engineered barriers and underground openings.
In Section 3.6.2 of the Repository production report the barrier functions and properties theclosure shall sustain in order to contribute to the functions of the KBS‑3 repository are presented.
The functions of the plugs are presented in Section 3.8.2 of the Repository production report.
Section 3.9 of the Repository production report introduces the design considerations to be appliedin the design work. The presented barrier functions of the closure, the functions of the plugs and theconsiderations that shall be applied in the design work are repeated in Section 2.2 in this report.
The design premises related to the barrier functions of the closure in the KBS‑3 repository are basedon the results from the latest performed long-term safety assessment and some subsequent analyses.
These design premises for the closure are provided in Design premises long-term safety, and arepresented in Section 2.3.1 in this report. Corresponding design premises for the plugs are presented
in Section 2.5.
Design premises related to technical feasibility refer to the properties the closure and plugs shall haveto fit, and work, together with the engineered barriers and other parts of the final repository during
the production. The general approach to substantiate this kind of design premises is presented in
Section 2.5.1 in the Repository production report and the interfaces to the engineered barriers andother parts in the production are summarised in Sections 4.7.2 and 4.8.2 in the Repository produc‑tion report. In this report, these design premises are presented in Section 2.3.2 for the closure and in
Section 2.5 for the plugs. In Sections 2.4 and 2.6 the design premises the closure and plugs impose
on other parts of the KBS‑3 repository are presented.
Finally, design premises related to the operation of the KBS 3 repository facility and the productionof the closure and plugs are presented in Sections 2.3.3 and 2.5 in this report for the closure andplugs respectively. The methodology to substantiate these kinds of design premises is presented in
Section 2.5.4 in the Repository production report.

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2.1.2 Definition, purpose and basic design of the closure
The closure is one of the engineered barriers in the KBS-3 repository. The closure is the material
installed in boreholes and underground openings other than deposition tunnels, in order to fill andclose them. 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 closure of the final repository includes the filling and sealing of main tunnels, transport tunnels, therock cavities of the central area, the ramp and shafts for transport and ventilation. It also includes sealing of investigation boreholes from the surface and from underground openings in the final repository.
The design premises for the closure in underground openings where the flow of water shall be restricted
are based on the use of compacted bentonite clay blocks and pellets. In underground openings where
there are no restrictions on flow of water the design premises for the closure are based on that it consistsof rock material, and that the material will be compacted at site in the underground opening.

2.1.3 Definition, purpose and basic design of the plugs
The plugs have no barrier function in the KBS-3 repository. The purpose of the plugs is to provide
mechanical restraint and hydraulic control functions. Plugs are needed as long as the undergroundopening on one side of the plug is unsealed to keep the installed closure material in place. Plugs also
contribute to a feasible, safe and secure installation of the closure.
The design premises for the plugs are based on the use of concrete providing the required strength, andthat the concrete is complemented with clay and/or permeable material parts for tightening and drainage.

2.2

Barrier functions and design considerations

In this section the barrier functions of the closure, the functions of the plugs and the design considerations for the closure and plugs are presented. They are based on the functions of the KBS‑3 repository
presented in Section 3.1.2 in the Repository production report and have been divided into:•

barrier functions and properties the closure shall sustain in order for the final repository tomaintain its safety (Section 2.2.1),•

functions and properties the plugs shall sustain (Section 2.2.2),•

issues that shall be considered when developing the design of closure and plugs and methods for
manufacturing, preparation, installation, test and inspection (Section 2.2.3).

2.2.1 Barrier functions of the closure in the KBS-3 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 closure shall:•

prevent that water conductive channels, that may jeopardise the barrier functions of the rock, areformed 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 thefollowing barrier functions.
•

The closure in main tunnels shall prevent that the backfill in deposition tunnels swells/expands oris transported out from the deposition tunnels.

•

The closure shall keep the closure in underlying or adjacent underground openings in place.

16

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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 ofaction, needs and aspirations of future generations. From this follows that:•

The closure in the upper part of the ramp, shafts and boreholes shall significantly obstruct
unintentional intrusion into the 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 canaffect the post-closure performance the closure shall:•be long-term durable and maintain its barrier functions in the environment expected in the final
repository.

2.2.2

Functions and properties of plugs in the KBS-3 repository andrepository facility
In order for the barrier system of the final repository to withstand conditions, events and processes
that may impact their functions, plugs shall:• withstand prevailing hydrostatic pressure at any location where a plug is installed,• limit water flow past the plug until the adjacent rock cavity (tunnel, ramp, shaft etc) is filled
and saturated,• be durable and maintain its functions until the closure in the underground opening in questionis saturated.
In the long-term perspective in the final repository, in order for the repository to maintain the multibarrier principle, the plugs must:•

not significantly impair the barrier functions of the engineered barriers or rock.

These functions and properties shall be secured and maintained during different periods of the
lifetime of the plugs, see further Section 2.4.

2.2.3 Design considerations
This section presents the design considerations that shall be regarded in the design of the closure
and plugs and in the development of methods to manufacture, install, test and inspect them and theircomponents. When a reference design is determined it, together with the design considerations, forms
the basis for the detailed requirements on methods to manufacture, prepare, install and inspect theclosure and plugs.
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 of the closure and plugs and methods for preparation, installation, test and inspection shall be based on proven or well-tried techniques.

The construction, manufacturing, installation and non-destructive tests of the barriers of the final
repository to be dependable, and the following shall be considered.
•

Closure and plugs with specified properties shall be possible to prepare and install with highreliability.

•

The properties of the closure and plugs shall be possible to test and inspect against specified
acceptance criteria.

A reliable production is also required with respect to SKB’s objective to achieve high quality andcost-effectiveness. Regarding cost-effectiveness the following shall be considered.
•

The closure and plug designs and methods for preparation, installation, test and inspection shallbe cost-effective.

•

Closure and plug installation shall be possible to perform at the prescribed rate.

TR-10-1717

Further environmental impact such as noise and vibrations, emissions to air and water, impact on
groundwater and consumption of material and energy shall be considered in the design. Methods toprepare and install the closure and plugs must also conform to the regulations for working environment
and industrial safety. Design premises related to these aspects can generally be met in alternative ways
for designs of closure and plugs that comply with the safety and radiation protection design premises.
Together with design considerations related to efficiency and flexibility they are of importance forthe design of technical equipment used in the production of the closure and plugs. The design of thetechnical equipment is not discussed in this report.

2.3

Design premises for the closure

In this section the design premises for the closure are given. They constitute a specification for thedesign of the closure. The design premises comprise the properties and parameters to be designed
and premises such as quantitative information on features, performance, events, loads, stresses,
combinations of loads and stresses and other information, e.g. regarding environment or adjacentsystems, which form a necessary basis for the design.
The design premises are relating to the barrier functions presented in Section 2.2.1 and to the design
considerations presented in Section 2.2.3. The design premises are also based on, and constitute a
concise summary of, the current results of the design process and feedback from technology development and safety assessment iterations, see Section 2.5.1 in the Repository production report.
The design premises given as feedback from the long-term safety assessment are compiled in Designpremises long-term safety.
The design premises from other engineered barriers given as feedback from the technical development
are based on the reference designs of the other parts of the KBS-3 repository. The design premises
related to the production and operation are preliminary at this stage of development.

2.3.1 Design premises related to the barrier functions in the KBS-3 repository
The design premises related to the barrier functions in the KBS-3 repository are compiled in Table 2-1.
In the leftmost column of the table the barrier functions which form the basis for design premises andthat were presented in Section 2.2.1 are repeated; the middle column contains the closure propertiesand design parameters to be designed and in the rightmost column the design premises as stated in
Design premises long-term safety are given.

18

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Table 2‑1. Barrier functions, properties and parameters to be designed and design premises forthe closure.
Barrier function

Part of closure, property and design
parameters to be designed

Design premises long-term safety

The closure shall prevent that water
conductive channels, that may
jeopardise the barrier functions of therock, are formed between the repository and the surface.

Closure in ramp, shafts and tunnels
other than deposition tunnels below
the level of the top sealing1.
Properties that affect swelling pressure and hydraulic conductivity of thesaturated closure.

Below the location of the top sealing,
the integrated effective connectedhydraulic conductivity of the backfill
in tunnels, ramp and shafts and the
EDZ surrounding them must be lessthan 10–8 m/s. This value need not
be upheld in sections where e.g.
the tunnel or ramp passes highly
transmissive zones.

Material composition: Montmorillonite
content.
Installed density: The dry density andwater content of blocks, pellet fillingand bottom bed, the portions of thetunnel, shaft etc filled with blocks,
pellet filling and bottom bed.

The closure shall be long-term
durable and maintain its barrier
functions in the environment
expected in the final repository.

Closure in the cavities of the central
area.
–

There is no restriction on the hydraulicconductivity in the central area.

Closure in the top sealing (i.e. in thepart of the ramp and shafts close to
the surface).
–

The top sealing has no demands on
hydraulic conductivity.
The depth of the top sealing can beadapted to the expected depth ofpermafrost during the assessment
period, but must not be deeper than
100 m above repository depth.

Boreholes (connected to the suface).
Properties that affect swelling pressure and hydraulic conductivity of thesaturated closure.
Material composition: Montmorillonite
content.
Installed density: The dry density andwater content of clay blocks.

Boreholes must be sealed such thatthey do not unduly impair containmentor retention properties of the repository. This is preliminary achieved if thehydraulic conductivity of the borehole
seal < 10–8 m/s, which is ensured if
the swelling pressure of the seal is> 0.1 MPa. This value need not be
upheld in sections where e.g. holepasses highly transmissive zones.

Closure in boreholes and in ramp,
shafts and tunnels other than deposition tunnels below the level of the top
sealing.
Properties that affect swelling pressure and hydraulic conductivity of thesaturated closure.
Material composition: Montmorillonite
content.
Installed density: The dry density andwater content of blocks, pellet fillingand bottom bed, the portions of thetunnel, shaft etc filled with blocks,
pellet filling and bottom bed.

–

Closure in cavities of the central area. –Installed density.
Closure in the top sealing (i.e. in thepart of the ramp and shafts close to
the surface).
Installed density.

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19

Barrier function

Part of closure, property and design
parameters to be designed

The closure in main tunnels shallprevent that backfill in deposition
tunnels swells/expands or istransported out from the deposition
tunnels.

–
Closure in main tunnels.
Properties that affect the compactability of the saturated closure:
Material composition: Montmorillonite
content.
Installed density: The dry density andwater content of blocks, pellet fillingand bottom bed, the portions of thetunnel, shaft etc filled with blocks,
pellet filling and bottom bed.

The closure shall keep the closure inunderlying or adjacent undergroundopenings in place.

All closure.
Properties that affect the compactabilityof the saturated closure:
Material composition (clay closure):
Montmorillonite content.
Installed density: The dry density andwater content of blocks, pellet fillingand bottom bed, the portions of thetunnel, shaft etc filled with blocks,
pellet filling and bottom bed.

The closure must not significantly
impair the barrier functions of theother barriers.

All closure.
Properties that affect the chemical
conditions around the buffer andcanister:Material composition.

Closure in the upper part of the ramp,
shafts and boreholes shall significantly obstruct unintentional intrusion
into the repository.

–
Closure in the top sealing (i.e. in thepart of the ramp and shafts close to
the surface).
Properties that affect the effectiveness(strength, durability etc) of the top
sealing:
Installed density: Particle size,
strength and compaction of rockmaterial.
Strength of the concrete: Compositionof concrete.

1

Design premises long-term safety

Only low pH (< 11) materials areallowed below the level of the top
seal.
Limits for the composition of the rockmaterial used to close the central area
– is discussed in Design premises
long-term safety Section 3.5.1.

“Top sealing” is the term used for the closure in the part of the ramp and shafts close to the surface.

2.3.2 Design premises from the other engineered barriers
There are no design premises related to technical feasibility imposed on the closure by the otherbarriers.
2.3.3 Design premises related to the production and operation
In this section the design premises for the closure and its components related to their production
and the operation of the KBS-3 repository facility are given. In addition to the design considerations
presented in Section 2.2.3, they are based on the preliminary planned procedure to close the different
kinds of underground openings of the final repository facility.
The design premises related to the production and operation are presented in Table 2-2. In theleftmost column the design considerations from Section 2.2.3 are repeated.

20

TR-10-17

Table 2‑2. Design requirements and premises for the closure related to the production and operation.
Design consideration

Required property

Design premises

The closure shall be based on well-triedor tested techniques.
Closure with specified properties shall bepossible to prepare and install with highreliability.

The closure material must be possible tocompact to required density.

–

The closure components shall be designed
so that installation can be performed withhigh reliability.

–

2.4

Design premises imposed by the closure

In this section the design premises imposed by the closure on the underground openings, i.e. the cavitiesof the central area, the ramp, shafts, tunnels other than deposition tunnels, in order to achieve a technically feasible design and reliable production are given.
In order for the closure to maintain its barrier functions the closure density shall be high enoughthroughout the cross section and length of tunnels, the ramp and shafts. Further it must be possible
to pack the closure material to the required density. To achieve the required density the variation intunnel/shaft geometry must be limited and known.
For underground openings where the flow of water shall be restricted, closure using the same backfill
concept as for deposition tunnels is selected, i.e. backfilling with pre-compacted blocks. The designpremises imposed by the closure on these underground openings concern the same properties of
the underground openings as the design premises imposed by the backfill on the deposition tunnels.
These properties are acceptable inflow and acceptable dimensions and geometry, also see Table 2-2
and 2-3 in the Backfill production report. However, since a lower installed density is anticipated tobe accepted for the closure, the acceptable variations will most probably be larger than those stated
for the backfill in deposition tunnels. At this stage of development of the closure, no quantitative
design premises are given for the acceptable geometries of the underground openings. For the inflow,
10 litres per minute and 100 meter tunnel length is set to an acceptable level.

2.5

Design premises for the plugs

In the final repository during the post closure phase the plugs must not significantly impair the barrier
functions of the engineered barriers or the rock. The design premises related to this requirement arepresented in Table 2-3.
At this stage of development no detailed design premises related to the functions of the plugs during
the decommissioning of the final repository facility are established.
Table 2‑3. Design premises for the plugs related to their properties in the final repository during
the post closure phase.
Required function or property

Property and design parameters tobe designed

Design premises

The plugs must not significantly
impair the barrier functions of theengineered barriers or rock.

Volume and compressibility of theplugs (all parts)

The matrial shall remain in its place andnot decrease significantly in volume.

Concrete plug material composition
Concrete recipie: composition ofbinder and additional ingridients

Only low pH (< 11) materials are allowed
below the level of the top seal.

TR-10-1721

3Reference designs

In this chapter the reference designs of the closure in the different categories of underground openings are presented. In addition to the underground opening to be closed the design will depend on the
different functions of the closure in different parts of the underground opening. This results in thefollowing reference designs which are presented in the following sections:
Section 3.2 – closure of the central area.
Section 3.3 – closure of the ramp and shafts below the level of the top sealing.
Section 3.4 – top sealing.
Section 3.5 – borehole sealing.
Section 3.6 – plugs.
The reference design specifies the current designs of the closure and plugs. The reference designs
shall conform to the design premises presented in Sections 2.3 and 2.5 respectively and they shall betechnically feasible to produce by applying the methods for preparation and installation described in
Chapter 4. The conformity of the references designs to the design premises are presented in connection to the presentations of the reference designs.
An outline of the different kinds of closure and plugs is given in Figure 3-1.
Transport tunnel

Central area

Transport tunnel

Deposition tunnel

Highly transmissive zone

Main tunnel

Rock cavities backfilled with clay.
Rock cavities backfilled with compacted crushed rock.
Backfill of deposition tunnels.
Plug that shall keep the closure in the transport and main tunnels, in the ramp and shafts in place.
Plug, placed where a tunnel, the ramp or a shaft passes highly transmissive zones.
Plug in deposition tunnels, see backfill report.

Figure 3-1. Outline of the closure and plugs in the different categories of underground openings.

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23

3.1

Closure of main tunnels and transport tunnels

3.1.1 Reference design of the closure in main tunnels and transport tunnels
To conform to the design premises the closure in main tunnels and transport tunnels (see Table 2-1)
have the same conceptual design as the backfill in deposition tunnels, see Chapter 3 in the Backfill
production report. Figure 3-1 shows the main tunnels and transport tunnels for which this concept
is the reference design.
3.1.2

Conformity of the reference closure in main tunnels and transporttunnels to the design premises
The same conceptual design as used for the backfill in deposition tunnels is selected as the reference
design of the closure in main tunnels and transport tunnels. In practice, neither the material composition nor the installed density needs to be the same. In main tunnels and transport tunnels there is noneed to prevent buffer swelling/expansion and the acceptable hydraulic conductivity is larger than indeposition tunnels. Nevertheless, the same material as for the backfill in deposition tunnels is selected
at this stage of development, and the verifying analyses presented for the backfill in Chapter 4 in the
Backfill production report are considered relevant to support the conformity of the closure reference
design to the design premises.
SKB has studied the feasibility of several backfilling methods and backfill materials, see e.g.
/­Gunnarsson et al. 2006, Johannesson and Nilsson 2006, Johannesson 2008/. Results from theseinvestigations indicate that also with other materials, e.g. alternative bentonite clay products or
mixtures of bentonite and ballast, the closure in main tunnels and transport tunnels will conform to
the design premises, see Figure 3-2 and 3-3.

3.2

Closure of the central area

3.2.1 Reference design of the closure in the central area
The only function of the closure of the cavities in the central area is to occupy the space with noother design premise than to prevent substantial convergence and subsidence of the surroundingrock. With respect to this the reference design is to use crushed blasted rock that will be placed bytractors in horizontal layers and then compacted.
The following shall be considered when determining a reference design:•

size distribution and shape of rock particles depending on excavation method,•

density of rock fill: loose layering; moderately compacted; or very effectively compacted,•

techniques for compaction; dry and wet,•compressibility and settlement of rock fill,•shear strength of rock fill,•

hydraulic conductivity of rock fill,•

petrological compositions of rock fill.

In /­Pusch 2008/ a condensed description and overview of these items are given. The report presents
experience from road and dam construction as well as results from SKB’s backfilling experiments in
the Prototype Repository Project and the Backfill and Plug Test at Äspö HRL.
The petrological composition is important as the closure must not significantly impair the barrier
functions of the engineered barriers or rock. To guarantee that the rock fill doesn’t contain minerals
in a proportion that could result in a negative impact, a careful inspection and analysis of the mineralcomposition is vital. In the current reference design the rock material will be taken from the rockproduced during excavation of the repository facility. This means that the mineral composition of
the material will be the same as in the surrounding rock. Information on the properties of the rock in
Forsmark is found in /­Stephens et al. 2007, Section 3.4/.

24

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Swelling pressures in 3.5 and 7%
600
Asha (3.5%)500

Asha (7%)
Milos b. (3.5%)

(kPa)

400

Milos b. (7%)
DPJ (3.5%)300

DPJ (7%)
Friedland (3.5%)

200Friedland (7%)
Mix 5 (3.5%)

100

Mix 5 (7%)
0
1000

1100

1200

1300

1400

1500

1600

1700

Dry density (kg/m )3

Swelling pressure in 3.5% and 7%
1000

Mix 1 (3.5%)

900

Mix 1 (7%)

800

Mix 2 (3.5%)
Mix 2 (7%)

(kPa)

700

Mix 3 (3.5%)

600

Mix 3 (7%)

500

Mix 4 (3.5%)

400

Mix 4 (7%)

300

Mix 6 (3.5%)

200

Mix 6 (7%)

100

Mix 7 (3.5%)

01700

Mix 7 (7%)
1800

1900

Dry density (kg/m3)

Figure 3-2. The swelling pressure as a function of dry density for different backfill materials; results at
3.5 and 7% salinity. Details on materials etc are given in /­Gunnarsson et al. 20061/.
Explanation of abbreviations in Figure 3-2 and 3-3:
Asha = India Asha 230, a low-grade Na-bentonite.
Milos b = Milos backfill a low-grade Ca-bentonite.
Dep. CA-N = Deponite CA-N, a non-activated high-grade Ca-bentonite from Milos.
MX 80 = A high grade Na-bentonite from Wyoming.
DPJ = Dnešice-Plzensko Jih, a smectite-rich mixed-layer clay; Ca-bentonite
Friedland = Friedland clay, a smectite-rich mixed-layer clay, Na-bentonite.
SPV = SPV200, a high grade Na-bentonite from Wyoming.
Mx 1 = A mixture of 30% MX 80 and 70% crushed rock (0–5 mm), fine fraction 0%.
Mx 2 = A mixture of 30% SPV and 70% crushed rock (0–5 mm), fine fraction 0%.
Mx 3 = A mixture of 30% Dep. CA-N and 70% crushed rock (0–5 mm), fine fraction 0%.
Mx 4 = A mixture of 40% Dep. CA-N and 60% crushed rock (0–5 mm), fine fraction 0%.
Mx 5 = A mixture of 50% Dep. CA-N and 50% crushed rock (0–5 mm), fine fraction 0%.
Mx 6 = A mixture of 30% Dep. CA-N and 70% sand.
Mx 7 = A mixture of 30% Dep. CA-N and 70% crushed rock (0–5 mm), fine fraction 12%.
1

TR-10-1725

Hydraulic conductivity in 3.5% and 7%

Asha (3.5%)

1.00E-08

Asha (7%)

K (m/s)Milos bf (3.5%)
Milso bf (7%)
Dnesice (3.5%)
Dnesice (7%)

1.00E-10

Friedl. (3.5%)
Friedl. (7%)
Mix 5 (3.5%)
Mix (7%)

1.00E-12
1000

1100

1200

1300

1400

1500

1600

Dry density (kg/m )3Hydraulic conductivity in 3.5% and 7%
Mix 1 (3.5%)

1.00E-09

Mix 1 (7%)
Mix 2 (3.5%)
Mix 2 (7%)
1.00E-10

K (m/s)Mix 3 (3.5%)
Mix 3 (7%)
Mix 4 (3.5%)
Mix 4 (7%)

1.00E-11

Mix 6 (3.5%)
Mix 6 (7%)
Mix 7 (3.5%)
1.00E-12
1750

1800

1850

1900

1950

2000

Mix 7 (7%)

Dry density (kg/m3)

Figure 3-3. The hydraulic conductivity as a function of dry density for different backfill materials. Results
at 3.5 and 7% salinity. Details on materials etc are given in /­Gunnarsson et al. 2006/.

3.2.2

Conformity of the reference closure of the central area to thedesign premises
In the cavities in the central area the rock fill will undergo small self compaction; 5–10 mm according to /­Pusch 2008/. This would be acceptable as there is no restriction of the hydraulic conductivityof the closure in the central area. However, it is important to yield sufficient density of the installed
closure material and the densities that can be achieved based on current experiences are summarised
below.
Comprehensive experience of placement and compaction of rock fill is available from road construction and from the construction of hydro power dams. For road embankments compacted by ordinary
vibratory rollers (5–10 tonnes) common density values are in the range of 2,050 to 2,200 kg/m3/­Pusch 2008/.

26

TR-10-17

For earth dam construction thicker layers and larger boulders than for road construction are accepted.
By using vibrating single-rollers with 6 tonnes weight dry densities of about 2,000 kg/m3 can beachieved /­Pusch 2008/.
SKB has performed backfilling experiments in the “Field test of tunnel backfilling” and the “Backfill
and Plug Test” at Äspö HRL. They involved placement of rock debris from tunnel boring (TBMmuck) with and without compaction. Some tests were made with material that had been stockpiled
without further treatment while crushed muck was used in certain other tests.
Field test of tunnel backfilling included placement and compaction of virgin and crushed TBM-muckin horizontal and inclined (sloping) layers /­Pusch 2008/. Horizontal layers of virgin TBM-muckcompacted by a 5 t vibratory roller had a dry density of 2,430 kg/m3 while crushed muck had
a maximum dry density of 2,210 kg/m3 /­Pusch 2008/. Placement of virgin TBM-muck without
compaction to form inclined layers gave a dry density of 1,600 to 2,120 kg/m3 while compaction
gave 2,210–2,330 kg/m3. Crushed rock gave a dry density of 2,140 kg/m3 of inclined layers.
The Backfill and Plug Test looked into the placement and compaction of crushed TBM-muck toform inclined layers /­Gunnarsson et al. 2001/. The density was found to range between 2,110 and
2,210 kg/m3. These experiments included placement of compacted clay blocks on top of the rock-fill.
TBM-muck was used in the trials at Äspö HRL. The experiences are therefore not in all respects
relevant for the reference design. But as the results are in line with experience from road and dam
construction /­Pusch 2008/ the reference design must be judged to be appropriate and feasible.
Dry densities for rock filling according to the above presented experiences are summarised in Table 3-2.
There is no design premise for restriction of hydraulic conductivity for the closure in the cavitiesof the central area. Nevertheless, the hydraulic conductivity has been estimated. Experiments andtests indicate that compacted crushed rock fill with a dry density of about 2,000 kg/m3 will obtain ahydraulic conductivity in the order of 10–7 m/s. The combined effect of the crown space, i.e. the gap
between the top of the rock fill and the roof of the underground opening, and the dry density of therock fill determine the resulting hydraulic conductivity for the closure in the central area. A preliminary judgement is that a resulting hydraulic conductivity of about 10–5 m/s can be achieved.

Table 3-2. Dry densities for rock fill – results achieved in road and dam constructions and in
backfilling experiments at Äspö HRL.
Horizontal layers compacted by a 5 tonnes vibratory roller
Rock fill material

Dry density, kg/m3

Virgin TBM-muck

2,390–2,470

Crushed TBM-muck

2,100–2,300

Road embankments

2,050–2,200

Dam constructions (6 t vibratory roller)

2,000

Inclined layers
Rock fill material

Dry density, kg/m3

Virgin TBM-muck without compaction

1,600–2,120

Virgin TBM-muck after compaction

2,210–2,330

Crushed TBM-muck

2,110–2,210

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3.3

Closure of ramp and shafts below the top sealing

3.3.1

Reference design of the closure in ramp and shafts below the
top sealing
To restrict water flow below the level where the top sealing starts (see Table 2-1), SKB has chosen
the same conceptual design for the closure in this deeper part of the ramp and shafts as for backfill indeposition tunnels, see the Backfill production report, Chapter 3.
In the reference design the ramp and shafts are backfilled with clay up to –200 meters depth, where
the top sealing starts. The depth of the top sealing is determined by the presence of water conducting
structures and the expected depth of permafrost in Forsmark. Figure 3-4 shows the parts of the ramp
and shafts belonging to the top sealing, the deeper parts filled with clay and the use of plugs in ramp
and shafts.
0m

Rock blocks

Coarsecrushed rockCompacted
crushed rock

–50 m

Clay

–200 mTopsealing

Potential highly
transmissive zone
Clay–500 mPlug, placed where the ramp and shafts passes highly transmissive zones
Plug that shall keep the clay in the ramp and shafts in place
Figure 3-4. Top sealing, the parts of the ramp and shafts filled with clay and the placement of plugs inramp and shafts.

28

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3.3.2

Conformity of the reference closure in ramp and shafts to thedesign premises
Below the level of top sealing the same conceptual design as for the backfill in deposition tunnels is
selected as reference design for closure of ramp and shafts. In practice, neither the material composition
nor the installed density will be the same. In ramp and shafts there is no need to limit buffer swelling/expansion and the accepted hydraulic conductivity is larger than in deposition tunnels. Nevertheless,the same material as for the deposition tunnels is selected as reference material at this stage of development, and the verifying analyses presented for the backfill in Chapter 4 in the Backfill production
report are considered relevant to support the conformity of the reference design for the closure in ramp
and shafts below the top sealing to the design premises.
SKB has studied the feasibility of several backfilling methods and backfill materials. Results fromthese investigations indicate that the design premises for the closure of ramp and shafts below the levelof top sealing could be met also with other backfill materials (clays with less demanding properties or
mixtures of bentonite and ballast), see Section 3.1.2.

3.4

Top sealing“Top sealing” is the term used for the closure of the upper part of the ramp and shafts.

3.4.1 Reference design for the top sealing
To maintain the function to “significantly obstruct unintentional intrusion into the repository”(Section 2.2.1) the ramp and shafts are, from –200 to –50 m depth from the zero level, filled withcrushed rock having a maximum particle size of 200 mm. The rock fill is effectively compacted tominimise self-compaction under its own weight and overburden /­Pusch 2008/.
The depth of the top sealing depends on site-specific conditions, e.g. presence of water conducting
structures and the expected depth of permafrost. In the reference design the top sealing goes down
to a depth of –200 meters. The parts of the shafts and ramp belonging to the top sealing are shown in
Figure 3-4.
The uppermost 50 m of the ramp and shafts is backfilled with very coarse crushed rock that is effectively compacted to minimise self-compaction. The shallowest parts of the ramp and shafts are filledwith fairly well fitted blocks of crystalline rock. Good but not perfect fitting of the blocks eliminatesarching, and possibly occurring open spaces between the rock blocks are not considered to significantly
affect the settlement.

3.4.2 Conformity of the reference top sealing to the design premises
The reference design for the top sealing is to fill the ramp and shafts with crushed rock and rockblocks, i.e. essentially the same material that is used for closure of the central area, see Section 3.2.
The function of the uppermost 50 m of the ramp and shafts is to significantly obstruct unintentional
intrusion into the repository. The selected reference design is judged to maintain this function. The
judgment is based on experience from the quarrying industry and diabase pits which proves thatboring in fractured rock is very difficult and that production of rock blocks for the suggested masonryat the top is an established technique /­Pusch 2008/.

TR-10-1729

3.5

Borehole sealing

A number of investigation boreholes, both holes drilled from the surface and holes drilled fromunderground openings have to be sealed, at the decommissioning of the final repository facility.
With respect to that 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”, only boreholes
going deeper than the top sealing (thus passing –200 meter) have to be sealed. In the layout of the
final repository facility the locations of the boreholes are considered in order to avoid that boreholes
connected to the surface intersect underground openings. Further, deposition tunnels and deposition
holes must not be intersected by any investigation boreholes.
The geometry of a borehole seal is mainly determined by the dimensions of the drilled holes. The
length of surface-based boreholes ranges from a few metres to more than 1,000 metres and the diameter
will range from 56 to 120 mm. The tunnel-based boreholes are expected to have a length of a few
hundred metres and a diameter of 56 to 76 mm. The shallowest parts of the boreholes may have larger
diameters. Some boreholes may be more or less horizontal.
In addition a large number of grouting holes and holes for installation of rock support will be drilledduring construction of the repository, see the Underground openings construction report. However,they do not need to be sealed.
SKB has studied and developed several concepts for borehole sealing. The main principles for sealing
boreholes as well as results from tests and experiments are summarised in /­Pusch and Ramqvist 2007/.

3.5.1 Reference design of borehole sealing
To conform to the design premises for borehole sealing (see Table 2-1) the following reference
design is applied.
Highly compacted bentonite is used where tight seals are needed and cement-stabilised plugs arecast where the boreholes pass through fracture zones, see Figure 3-6 and 3-7. For the reference design
MX-80 bentonite is chosen. To prevent erosion during the installation phase the clay shall be pre-dried
to a water content of about 6% and then compacted to a dry density of 1,900 kg/m3. The clay blocks
are contained in perforated copper tubes that are jointed as they are inserted into the holes. The
copper tubes provide mechanical protection against abrasion in the installation phase. The reference
borehole has a diameter of 80 mm (investigation holes with a original diameter of 76 mm have to
be enlarged) and the perforated copper tube an outer diameter of 76.1 mm and an inner diameter of
72.1 mm (which is a standard dimension). The tubes have a perforation ratio of 50% with 10 mmdiameter holes in order to allow the clay to swell into the volume between the tube and the rock.
Along sections where the borehole passes water-conducting fracture zones the clay could potentiallyerode. In such positions the holes are therefore filled with silica concrete, which is a permeable anderosion-resistant material, see Figure 3-6. These plugs do not need to have a low conductivity but
must be physically stable for supporting the surrounding rock and the clay plugs that rest on themor are located below them. In the construction phase they must be stable and rapidly become strong
enough to carry overlying clay plugs without settling. This is attained by using a fast curing cementbinder. To minimise the negative impact of cement contacting clay plugs, the cement content will
be very low and low-pH cement will be utilised. Further details are found in /­Pusch and Ramqvist
2007/.
The upper part of boreholes connected to the surface will be sealed with material that can sustain theswelling pressure exerted by the clay part and offer resistance to mechanical impact like intrusion,
erosion and glaciations. For the reference design the concept illustrated in Figure 3-5 is selected. The
main components are: rock cylinders, concrete plugs cast on site and anchored in reamed recesses
and well compacted till /­Pusch and Ramqvist 2007/.

30

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Rock cylinder
Concrete plug~100 mCompacted till

Highly compacted bentonite
in perforated copper tubes

Concrete plug

Figure 3-5. Reference concept for sealing investigation boreholes from the surface.

Clay plug in perforated copper tubes

Concrete plug

Fracture zone

Stabilized part of
the fracture zone
Clay plug in perforated copper tubes
Borehole axis
Figure 3-6. Schematic sketch of the construction of concrete plugs in parts where the borehole passes
water-conducting fractures.

TR-10-1731

About 100 m

Ground surface
Trimmed, well fittingrock cylinders
Concrete plug anchored inreamed recesses
Compacted till

one

re z

tu
Frac

Concreteplugged partClay-plugged part
except for intersected
fracture zones

Figure 3-7. The principle for closure of the upper part of a borehole with well compacted till below
concrete and fitted rock blocks.

3.5.2 Conformity of the reference borehole sealing to the design premises
SKB has, in cooperation with Posiva and as part of SKB’s RD&D programme, developed concepts forsealing of long and short boreholes. The concepts are based on the one tested in Stripa and used in SFR
and are postulated to work in both steeply and gently dipping boreholes /­Pusch and Ramqvist 2007/.
Examples of results reported in /­Pusch and Ramqvist 2007/ are summarised below.
•

The long-term tests show that a high degree of swelling and homogenisation is obtained after
10–20 days. The measured mean swelling pressure against the rock for the initial dry density
1,905 kg/m3 of the clay plug core is 2,800 kPa in fresh water and 600 kPa in saline water (Äspö).
After saturation the clay plug will reach a density of 2,025 kg/m3 which corresponds to a dry
density of 1,630 kg/m3. Measurement of the hydraulic conductivity of the clay paste between thecopper tube and rock showed that it was lower than 9×10–13 m/s for saturation and percolation
with fresh water and 2×10–12 m/s for saline water.

•

Plugging the upper end of deep boreholes can be made by use of copper plugs and CBI silica
concrete plugs, both of which can take axial pressures of more than 30 MPa. The shear strengthand deformation moduli of concrete plugs of silica concrete can be significantly improved bymixing in centimetre-sized quartzite fragment.

•

The function of plugs of the investigated type has been fully demonstrated. For the concrete
plugs the recorded strength in full-scale tests has been found to agree well with predicted values
derived from laboratory experiments. For clay plugs a very high degree of homogeneity has been
documented by investigation of several years old plugged boreholes, demonstrating also that theswelling potential and the hydraulic conductivity agree well with predictions.

Tests also show that clays with Na as the major adsorbed cat ion should be used, since Ca-saturated
clay does not expand readily during the saturation phase in either fresh or salt water. They show thatthe density of the soft gel that migrates out through the holes in the copper tube is not sufficient tomake it form a coherent mass, see Figure 3-8. It will therefore settle in the gap between the tube andthe borehole wall especially in salt water. When a Na-clay plug has been saturated and homogenised,
which will happen within a week or two, the density of the outer part of the clay plug is high enough32

TR-10-17

Figure 3-8. Example of quick release of clay through the perforation of copper tubes in a borehole plug insalt water. The clay that migrated out through the perforation did not form a coherent clay gel but settled
as a coagulated dispersed sol in the space between tube and glass vessel /­Pusch and Ramqvist 2004/.

to prevent negative effects on the plug properties (hydraulic conductivity and swelling pressure)caused by ion exchange leading to the calcium saturation /­Pusch and Ramqvist 2004/. For the reference
design MX-80 bentonite is chosen.
The performance and technical design of different types of boreholes drilled during the site
investigation at Forsmark, such as telescopic boreholes, core-drilled boreholes of standard type,
and percussion-drilled boreholes in solid bedrock are described in /­SKB 2005/. Some geometricalborehole characteristics are displayed in /­SKB 2008, Table 2-1 and Table 2-2/.

3.6

Plugs

The plugs shall separate backfilled and closed underground openings from underground openings
that remain to be closed. The plugs shall keep the closure material in the closed parts in place until
the underground opening on the other side of the plug is filled and the material saturated. Plugs arealso used in areas containing conductive features in the rock. The plugs also contribute to a safe andsecure installation of the closure. The plugs must not contain materials that may impair the barrier
function of any of the other barriers.
The design of the plugs will be site specific and depend on the local conditions in the host rock.
What is important at one location may be irrelevant in another. A number of tunnel plug/seal tests
have already been conducted by various organizations interested in deep geologic disposal of spent
nuclear fuel. There also exists a considerable amount of literature on the performance of plugs/seals
installed for other purposes (e.g. mining operations, hydroelectric plants, environmental remediation). These experiences are briefly reviewed in /­Dixon et al. 2009/.

3.6.1 Reference designs of plugs
As stated in the previous section the design of plugs depends on conditions at the site and at thisstage only an overview of the anticipated kinds of plugs and examples of conceptual designs areprovided.

TR-10-1733

Based on the different purposes of the plugs stated in the previous section the plugs can be divided
into the following types.
A. Plugs separating underground openings filled with clay from underground openings filled withcrushed rock.
B. Plugs used where tunnels, the ramp and shafts pass water-bearing structures.
C. Plugs facilitating the installation of closure material in large underground openings e.g. the cavities
in the central area.
Plugs of type A are installed where the transport tunnels, ramp and shafts connect to the central
area. Figure 3-1 outlines the placement of such plugs. For these plugs the same conceptual design
as for the plugs in deposition tunnels is selected as reference design, see Section 7.1 in the Backfill
production report.
Plugs of type B are installed where a main or transport tunnel, or the parts of the ramp and shafts
filled with clay blocks and pellets, intersect fracture zones. An example of such a plug in a shaft is
illustrated in Figure 4-1.
Plugs of type C are installed when needed for construction reasons. The location and design dependon the local conditions

3.6.2 Conformity of the reference plugs to the design premises
A number of studies that examine aspects of closing openings in granitic rock have been conductedsince the early 1980s. Beginning with the first large-scale field tests at the Stripa site and then continuing at the Äspö HRL and Canadian Underground Research Laboratory (URL) facilities, the influenceof plugging material, length of plug, influence of keying features to cut off the EDZ and effect of
excavation technique on seepage have been investigated. Valuable insight and knowledge related toplug construction have been gained in these studies. It should also be emphasised that none of thesedemonstrations were intended to test an optimised design, and in most cases the purpose was to assess
which parameters had the largest impact on the post-construction seepage.
At Stripa both a shaft and a tunnel sealing test was conducted. The tests were designed to determine
the effectiveness of swelling clay-based plugs in limiting water flow at interfaces between concretebulkheads and backfilled excavations. Both sealing trials had the same goal of limiting the movement of water past the plug and evaluating the role of the excavation damaged zone (EDZ) in thisflow. From these two tests it is clear that bentonite used in conjunction with concrete provides aneffective seal. These tests were run for a very short duration; the longer-term behaviour and effects
of groundwater flow on bentonite or fracture-filling materials were not assessed /­Gray 1993 Chapter 3,
Pusch et al. 1987a, b/.
At the Canadian URL several tests related to the sealing and plugging of underground openings wereconducted. The Tunnel Sealing Experiment was a study that was designed to characterise the sealing
potential of two well-constructed bulkheads. The Composite Seal Experiment was originally envisaged as being the first in a series of tests that examined the performance of a number of composite
sealing system designs but only the first of these was completed. The tests at URL confirmed that theuse of bentonite seals is an effective way of reducing the seepage past a plug /­Martino et al. 2003,
Kjartanson and Martino 2004, Dixon et al. 2004/.
More recent tests at Äspö HRL have extended some of the studies conducted at Stripa or the Canadian
URL by incorporating bentonite gaskets into concrete bulkheads or plugs and other structures. The
Backfill and Plug test incorporated both a bentonite gasket in a concrete bulkhead that was keyed
into the rock and also contained bentonite-rich materials in the upper regions of the tunnel adjacent
to it. The seepage past this type of structure at 6 MPa hydraulic head is estimated to be 13.6 L/h. In
the Prototype Repository, a similar approach to plugging the tunnel to the Backfill and Plug Test was
adopted. For references, see the Backfill production report.
Before detailed designs of plugs used in connection to closure are determined, similar development
work will be performed. The experiences gained from the design and installation of deposition tunnelplugs can be applied to shaft plugs. The experiences from plugs in deposition tunnels make it clearthat such a development can be based on conventional technique. More information on verifying
analyses for the selected reference design is found in the Backfill production report, Chapter 8.
34

TR-10-17

4

Production of the closure

4.1

Introduction

Closure of the repository will, with the exception of some boreholes that have to be sealed earlier, nottake place until all spent nuclear fuel has been deposited. This means that the closure activities lie wellin the future. So far SKB has prioritised the development of the backfill and plug in deposition tunnels.
For that reason, this section refers to the Backfill production report for the production of closure formain tunnels and transport tunnels and the ramp and shafts below the level of the top sealing.
For the closure of the central area a short overview is given. This is considered sufficient at thisstage of development, since there are no design premises related to the long-term safety given forthe central area.
As mentioned in Section 3.5, SKB has studied and developed several concepts for borehole sealing.
A short summary of methods to manufacture and install borehole seals used in these tests is given at
the end of this chapter.
Prior to closure of any underground opening, construction features such as road beds and building
components and installations will, as part of the decommissioning, be removed and the undergroundopening cleaned. Routines for these activities remain to be specified.
The main stages for closure of the repository are:•backfilling of and, if necessary, installation of plugs in the outer ventilation shaft,•backfilling of and, where necessary, installation of plugs in main tunnels and transport tunnels,•

installation of plugs where the transport tunnels connect to the central area,•

backfilling of the central area,•

installation of plugs where the central area connects to shafts and ramp,•

backfilling of and, where necessary, installation of plugs in the ramp and remaining shafts; these
activities must be very well coordinated and accomplished gradually,•

installation of top seal.

Borehole seals are installed at suitable occasions before or during the other closure activities.

4.2

Closure of main tunnels and transport tunnels

The manufacturing of components, i.e. blocks and pellets, as well as the handling, and filling can largely
be done using the same methods as those developed for the backfill, see the Backfill production report,
Chapter 5.

4.3

Closure of the central area

The production of the closure material for the central area and its installation includes the following
activities.
•

Blasted rock from the storage of rock from excavated tunnels is transported to the crusher.

•

The blasted rock is cleaned.

•

The blasted rock is crushed and sieved to a pre-determined grain size distribution that facilitatescompaction.

TR-10-1735

•The crushed rock is transported to an intermediate storage at the repository level adjacent to thecentral area.

•

The quality of the material is inspected with respect to weight, mineral composition, grain size
distribution, water ratio and density.

•

The rock fill is placed in the tunnel or rock cavity.

•

The crushed rock is compacted in inclined layers.

All activities are well known from many kinds of construction work. Experience from road and dam
construction as well as results from SKB’s backfilling experiments in the Prototype Repository andthe Backfill and Plug Test are summarised in /­Pusch 2008/. Further details on SKB’s backfilling experiments are reported in a large number of reports; assessments of different backfill concepts are found in/­Gunnarsson et al. 2004/. See also Section 3.3.2.

4.4

Closure of ramp and shafts

During installation of the closure in the ramp the inflow of water will probably be greater than during
installation of backfill in deposition tunnels. The reason is that the ramp will most probably intersect anumber of highly transmissive zones. This has to be solved by means of a water management systemand plugs for wet sections of the tunnels. Such a system will be designed, constructed and tested/­Gunnarsson et al. 2004/.
In shafts other types of compaction technique is used. Here, higher compaction energy can be appliedand higher density obtained than in tunnels. Possible compaction techniques involve: stamping; useof vibrating plates; falling weight and self-compaction by gravity. The water inflow can be greaterfor shafts than for the deposition tunnels. The water coming from below is handled with plugs anddrainage sections in a similar way as for the ramp. The water coming from above is collected to avoid
softening of the backfill surface. A special water interception and collection system for doing this will
be designed. A system for bringing material down in the shaft and past the compaction equipment will
also be developed /­Gunnarsson et al. 2004/.
The self-weight of the closure material in shafts as well as lithostatic, hydrostatic and other stresses
are quite large and as a result some deformations are expected. These deformations, which are mainly
settlement, will be dominated by the elastic and plastic deformation (including creep) of the closurematerial. The magnitude of the settlement will depend on the mechanical properties of the material aswell as the behaviour of plugs along the length of the shafts. The total settlement will be the cumulative
settlement under the backfilling sequence and part of settlement will happen during the construction.
The deformation properties of the materials are stress-dependent; and they will change during thesaturation process and at higher pressures. Prior to closure of shafts detailed design and deformation
calculations will be performed.
Because the compaction work can be done in horizontal layers it is possible to achieve higher densities (and thus lower conductivities) in the shafts than can be achieved in horizontal excavations using
inclined compaction.
One important consideration to repository backfilling and closure is placement of material in thelocations where the excavations intersect a number of highly transmissive zones. These intersections
can either have a permeable closure material such as sand or crushed rock. In such cases the water ofthe fracture zone can flow freely through the backfilled section without impact on adjacent volumes.
Another option is to backfill the intersection area with a material with very low permeability, e.g.
bentonite blocks. In that case the water in the fracture zone flows around the shaft but there arepotential issues associated with this approach (e.g. erosion during placement and longer-term loss ofmaterials into the fracture zone). The first alternative, illustrated in Figure 4-1, is assessed to conformto the design premises and to be the most reliable.
To handle inflowing water in the ramp and shafts drainage systems and temporary plugs are foreseen.
Water that flows along the walls in the ventilation and lift shafts can be taken care of at the connections between the ramp and these shafts. In the skip shaft and the outer ventilation shaft this means is
not available. Therefore measures will be designed, constructed and tested.
36

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Free flowing through shaft

Sand or crushed rock

Filter layers
Hydraulic plug
Filter layers if needed
Clay
Figure 4-1. Concept with permeable closure material where a shaft intersects a highly transmissive zone.

Based upon experience from the backfilling trials e.g. in the Prototype Repository and the Backfill andPlug Test SKB’s opinion is that development work on reliable methods for production and installationof closure in ramp and shafts will be finished in good time before the methods have to be applied/­Gunnarsson et al. 2004/.

4.5

Top sealing

The reference design for the top sealing is to fill ramp and shafts with crushed rock and rock blocks,
i.e. essentially the same material that is used for the closure of the central area.
The uppermost 50 m of the ramp and shafts is sealed with very coarse crushed rock that is effectively
compacted. The activities involved are on the whole the same as for closure of the central area. The
shallowest parts of ramp and shafts will be filled with fairly well fitted blocks of crystalline rock. Theserock blocks are taken from building stone quarries and are shaped to fit to each other at the location.

4.6

Borehole sealing

Borehole sealing can be made at nearly any time and as long as the activities are adapted to themonitoring plan. Holes extending from repository tunnels, rooms etc must be plugged before therooms are backfilled and closed.

TR-10-1737

Sealing of boreholes comprise the following activities /­Pusch and Ramqvist 2007/.
•

Remaining old instrumentation and other obstacles like rock fragments are removed if needed.

•

If needed the borehole is reamed to its original diameter or to any desired new diameter.

•

The borehole walls are stabilised where the borehole pass zones of weakness. This is achieved bywidening the borehole and filling it with silica concrete. A hole of the same diameter as the restof the borehole is drilled through the concrete.

•

The borehole geometry is checked by dummy testing•

Perforated copper tubes filled with highly compacted smectite rich clay are installed. A practicalsolution for use of copper tubes implies 24 m long segments consisting of jointed 2.5 m long parts.
The tensile strength is sufficient, assuming 4-fold safety, and safe attachment to the drill string canbe achieved. The thickness of the tube wall should be 2–3 mm and the outer diameter about 4 mm
smaller than the diameter of the hole. Each 24 m segment is lowered into the desired position, i.e.
in the space between two stabilised fracture zones, and left there. Several segments can be placed inseries without coupling them together. Their weight guarantees that they will rest on the underlying
ones without moving in the axial direction.

•

Concrete plugs are cast at suitable positions, primarily where the borehole is intersected byfracture zones. For minimizing negative impact on contacting clay plugs the cement content in
the concrete will be very low and low-pH cement will be utilised.

•

The borehole is plugged.

The method described above to seal boreholes has worked well, but needs to be tested in holes
deeper than 500 metres /­SKB 2007/.

4.7

Plugs

As mentioned in Section 3.6, a number of plugs will be needed for closure of the repository. The designof these plugs will depend on their purpose and conditions at the location where they are needed.
Development work will be performed before a detailed description of the production and inspectionof these plugs is provided. In the Backfill production report, Chapter 9, some important issues to beconsidered in the production of the plugs are presented.

38

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5

Initial state

5.1

Introduction

The initial state refers to properties of the engineered barriers once they have been finally placed in
the final repository. The initial state of the closure is the state when all closure material in a specificunderground opening or borehole is installed and the borehole, rock cavity, shaft or tunnel has beenclosed. Inflow of groundwater to an underground opening or a borehole and its impact on the closure
is not accounted for in the initial state.
For the assessment of the long-term safety it shall be confirmed that the closure at the initial state
conforms to the design premises related to the barrier functions in the final repository. This will bedone by verification of:•

the conformity of the reference design to the design premises,•

the conformity of the installed closure to the reference design.

The conformity of the reference design to the design premises is discussed in Chapter 3. In this chapter
the initial state of the closure is presented. This chapter also presents information regarding the closurematerials that are of importance for the assessment of the long-term safety.

5.2

Initial state of the closure

The initial state of the closure in the different underground openings and boreholes are presented inTable 5-1. At this stage of development, the closure properties are described as a compilation of reasonable values of some main parameters that can be estimated based on the current results and experiences.
For underground openings that shall be filled with compacted clay blocks and pellets the estimations are
based on the results presented in the Backfill production report. For the underground openings filledwith rock material the estimations are based on the studies referred to in Sections 3.2, 3.4 and 4.3 and forthe boreholes they are based on /­Pusch and Ramqvist 2007/. The volumes of closure materials to be used
are based on information in /­SKB 2009b/. The data given in Table 5-1 are preliminary and carry a degreeof uncertainty.

5.3

Material composition

5.3.1

Clay in main tunnels and transport tunnels, the ramp and shafts up to
the top seal
The material composition of the clay must be such that the density of the installed closure material
has capability to provide the required functions. As illustrated in Figure 3-2 there are several materials that can provide the desired hydraulic conductivity and swelling pressure. The clay used for thereference design of the closure is the same as that used for the backfill in deposition tunnels.
For the construction of plugs low-pH cement will be used. The composition is given in Table 5-3.

5.3.2 Clay for borehole seals
Long term tests described in Section 3.5.2 show that a high degree of swelling and homogenisation
is obtained after 10–20 days. The measured mean swelling pressure against the rock for the initial
dry density 1,905 kg/m3 of the clay plug core is 2,800 kPa in fresh water and 600 kPa in saline water(Äspö). Measurement of the hydraulic conductivity of the clay paste between tube and rock showedthat it was lower than 9×10–13 m/s for saturation and percolation with fresh water and 2×10–12 m/s forsaline water /­Pusch and Ramqvist 2007/.

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39

Table 5-1. The initial state of the closure in the different underground openings and boreholes.
Material

Volume(m3)

Installeddrydensity(kg/m3)

Density Porosityof solid (%)
particles(kg/m3)

Dry weightof installed
closure(tonne)Integrated
hydraulicconductivity(m/s)

Assessments andfurther details

Maintunnels

Clay.
(Note 1)

390,000

1,460

2,780

47.5

569,400< 10–8See Section 3.1.2
in this report andSection 6.1 and 6.2
in the Backfill
production report.

Transport
tunnels

Clay.
(Note 1)225,000

1,460

2,780

47.5

328,500< 10–8See Section 3.1.2 inthis report andSection 6.1 and 6.2
in the Backfill
production report.

Centralarea

Crushedrock

125,000

1,900

2,670

28.8 in the237,500
compacted
rock fill; 100%in the crownspace

about 10–5

See Section 3.2.2

Ramp(up to level– 200 m)Clay.
(Note 1)

115,000

1,460

2,780

47.5

167,900< 10–8See Section 3.3.2
in this report andSection 6.1 and 6.2
in the Backfill
production report.

Shafts(up to level– 200 m)Clay.
(Note 1)

25,000

1,460

2,780

47.5

36,500< 10–8See Section 3.3.2
in this report andSection 6.1 and 6.2
in the Backfill
production report.

Topsealing

Crushedrock

95,000

1,600

2,670

40.1 in the
152,000
compacted
rock fill; 100%in the crown
space

10–1

See Section 3.4.2
in this report andSection 6.1 and 6.2
in the Backfill
production report.
Due to self compaction 10 cm crownspace will develop
above the compacted
rock fill.

Boreholes

Clay,copper,concreteFor
1,630
geometry,(clay)
see
Section 3.5.1

2,780

28.1

< 10–8See Section 3.5.2
in this report.

Plugs

Reinforced
concrete

See Section 10.1
in the Backfill
production report.

Note 1: The clay used for the reference design is the same as that used for the backfill in deposition tunnels.

40

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5.3.3 Copper for borehole seals
The copper is standard ISO R1337 Cu DHP containing 99.9% copper with the density 8,930 kg/m3.
The tensile strength = 60 MPa and Poisson’s ratio = 0.3.
5.3.4 Concrete
Silica concrete will be used in parts of the repository where there are chemical restrictions on theconcrete (pH < 11). Based on experiences from SKB’s borehole sealing tests the composition of asuitable concrete mix is given in Table 5-2.
5.3.5 Rock material
The mineral composition of the rock material will be the same as in the surrounding rock.
Information on the properties of the rock in Forsmark is found in /­Stephens et al. 2007, Section 3.4/.
5.3.6 Geometry
The geometry of the tunnels, the central area, the ramp and shafts are given in /­SKB 2009b/.
The borehole seals are mainly determined by the dimensions of the drilled holes. The length of surfacebased boreholes ranges from a few metres to more than 1,000 metres and the diameter will presumably
range from 56 to 120 mm. The tunnel-based boreholes are expected to have a length of a few hundred
metres and a diameter of 56 to 76 mm. In the reference design the boreholes are enlarged to get a diameter of 80 mm. The shallowest parts of the boreholes may have larger diameters. Some boreholes may
be more or less horizontal. Only boreholes going deeper than the top sealing (thus passing –200 meter)
have to be sealed.
Table 5-2. Concrete composition for plugging of boreholes /­Pusch and Ramqvist 2007/.
Com­ponents

Amount(kg/m3 concrete)

Manufacturer

White cement

60

Aalborg Portland

Silica Fume

60

Elkem

Fine ground α-quartz M300

200

SibelcoFine ground cristobalite M6000

150

SibelcoSuperplasticiser Glenium® 51

4.375 (dry content)

Degussa

Granitic aggregates 0–4 mm

1,700

Jehanders grus

Water

244.27

Local

Table 5-3. Composition for the concrete in the plugs /­Backfill production report, Table 7-2/.
Design parameter

Nominal design[kg/m3 if not specified]

BinderCement CEM I 42.5 MH/LA/SR

120

Silica fume (densified)80

Other components

Water

165

Limestone filler L25

369

Sand 0–8 mm

1,037

Gravel 8–16 mm

558

Superplasticiser Glenium® 51

6.38

Water/cement

1.375 kg/kg

Water/binder

0.825 kg/kg

Water/powder

0.29 kg/kg

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5.4

Conformity to design premises long-term safety at theinitial state

In Chapter 3 the conformity of the reference designs to the design premises stated in Designpremises long-term safety are discussed. In the previous section the conformity of the installed
closure to the reference design is addressed.
SKB’s judgement is that the properties (mainly density) of the installed closure that is necessary toconform to the design premises will be achieved.

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References
SKB’s (Svensk Kärnbränslehantering AB) publications can be found at www.skb.se/publications.

Backfill production report, SKB 2010. Design, production and initial state of the backfill and plugin deposition tunnels. SKB TR-10-16, Svensk Kärnbränslehantering AB.
Buffer production report, SKB 2010. Design, production and initial state of the buffer.
SKB TR-10-15, Svensk Kärnbränslehantering AB.
Design premises long-term safety, SKB 2009. Design premises for a KBS-3V repository based on
results from the safety assessment SR-Can and some subsequent analyses. SKB TR-09-22, Svensk
Kärnbränslehantering AB.
Repository production report, SKB 2010. Design and production of the KBS-3 repository.
SKB TR-10-12, Svensk Kärnbränslehantering AB.
Underground openings construction report, SKB 2010. Design, construction and initial stateof the underground openings. SKB TR-10-18, Svensk Kärnbränslehantering AB.
Dixon D A, Martin J B, Chandler N A, Guo R, 2004. Performance of the clay bulkhead portionof the Tunnel Sealing Experiment (TSX) under ambient temperature conditions. Technical report
06819-REP-01200-10131-R00. Ontario Power Generation, Nuclear Waste Management Division.
Dixon D A, Börjesson L, Gunnarsson D, Hansen J, 2009. Plugs for deposition tunnels in a deep
geologic repository in granitic rock. Concepts and experience. SKB R-09-50, Svensk Kärnbränsle­
hantering AB.
Gray M N, 1993. OECD/NEA International Stripa Project 1980–1992. Overview Volume III:
Engineered barriers. Svensk Kärnbränslehantering AB.
Gunnarsson D, Börgesson L, Hökmark H, Johannesson L-E, Sandén T, 2001. Äspö Hard RockLaboratory. Report on the installation of the Backfill and Plug test. Detailed design of lead-throughs.
SKB IPR-01-17, Svensk Kärnbränslehantering AB.
Gunnarsson D, Börgesson L, Keto P, Tolppanen P, Hansen J, 2004. Backfilling and closure of the
deep repository. Assessment of backfill concepts. SKB R-04-53, Svensk Kärnbränslehantering AB.
Gunnarsson D, Morén L, Sellin P, Keto P, 2006. Deep repository – engineered barrier systems.
Assessment of backfill materials and methods for deposition tunnels. SKB R-06-71, Svensk
Kärnbränslehantering AB.
Johannesson L-E, Nilsson U, 2006. Deep repository – engineered barrier systems. Geotechnicalbehaviour of candidate backfill materials. Laboratory tests and calculations for determining
performance of the backfill. SKB R-06-73, Svensk Kärnbränslehantering AB.
Johannesson L-E, 2008. Backfilling and closure of the deep repository. Phase 3 – pilot tests toverify engineering feasability. Geotechnical investigations made on unsaturated backfill materials.
SKB R-08-131, Svensk Kärnbränslehantering AB.
Kjartanson B H, Martino J B, 2004. Composite Seal Experiment at AECL’s UndergroundResearch Laboratory, 57th Canadian Geotechnical Conference, October 2004, Quebec City.
Martino J B, Dixon D A, Keith S G, Chandler N A, Kjartanson B H, 2003. Sealing studies
at the URL. Proceedings of the 56th Canadian Geotechnical Conference, Winnipeg, Canada,
Sept. 29–Oct. 1, 2003.
Pusch R, Börgesson L and Ramqvist G, 1987a. Final Report of the borehole, shaft, andtunnel sealing test – Volume II: Shaft plugging. Stripa Project Technical Report 87-02, Svensk
Kärnbränslehantering AB.
Pusch R, Börgesson L and Ramqvist G, 1987b. Final Report of the borehole, shaft, and tunnel
sealing test – Volume III: Tunnel plugging. Stripa Project Technical Report 87-03, Svensk
Kärnbränslehantering AB.

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Pusch R, Ramqvist G, 2004. Borehole sealing, preparative steps, design and function of plugs –basic concept. SKB IPR-04-57, Svensk Kärnbränslehantering AB.
Pusch R, Ramqvist G, 2007. Borehole project – Final report of Phase 3. SKB R-07-58, Svensk
Kärnbränslehantering AB.
Pusch R, 2008. Rock fill in a KBS-3 repository. Rock material for filling of shafts and ramps in aKBS-3V repository in the closure phase. SKB R-08-117, Svensk Kärnbränslehantering AB.
SKB, 2005. Preliminary site description. Forsmark area – version 1.2. SKB R-05-18, Svensk
Kärnbränslehantering AB.
SKB, 2007. RD&D Programme 2007. Programme for research, development and demonstrationof methods for the management and disposal of nuclear waste. SKB TR-07-12, Svensk Kärn­
bränslehantering AB.
SKB, 2008. Site description of Forsmark at completion of the site investigation phase.
SKB TR-08-05, Svensk Kärnbränslehantering AB.
SKB, 2009a. Design premises for a KBS-3V repository based on results from the safety assessment
SR-Can and some subsequent analyses. SKB TR-09-22, Svensk Kärnbränslehantering AB.
SKB, 2009b. Underground design Forsmark. Layout D2. SKB R-08-116, Svensk Kärnbränsle­
hantering AB.
Stephens M B, Fox A, La Pointe P, Simeonov A, Isaksson H, Hermanson J, Öhman J, 2007.
Geology Forsmark. Site descriptive modelling Forsmark stage 2.2. SKB R-07-45, Svensk Kärn­
bränsle­hantering AB.

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