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POSIVA 2012-15
December 2013
POSIVA OY
Olki luoto
FI-27160 EURAJOKI, F INLAND
Phone (02) 8372 31 (nat. ) , (+358-2-) 8372 31 ( int. )
Fax (02) 8372 3809 (nat. ) , (+358-2-) 8372 3809 ( int. )
Jorma Autio
Md. Mamunul Hassan
Petri ikka Karttunen
Paula Keto
B+Tech Oy
Backfill Design 2012
ISBN 978-951-652-196-4ISSN 1239-3096
Tekijä(t) – Author(s)
Jorma Autio, Md. Mamunul Hassan, Petriikka Karttunen, Paula Keto, B+Tech Oy
Toimeksiantaja(t) – Commissioned by
Posiva Oy
Nimeke – Title
BACKFILL DESIGN 2012 Tiivistelmä – Abstract
This report describes both the concept and the detailed design of backfilling in KBS-3V deposition tunnels. The purpose of the backfill is to keep the buffer in place, maintain favourable and predictable conditions for the buffer and the canister, and also favourable rock mechanical, hydrological and geochemical conditions in the near-field and to retard the transport of released radionuclides in case of canister failure. In addition to the description of the overall backfill design, detailed designs for the components of the backfill (foundation, block and pellet fill) are provided in this report. The deposition tunnel end plug design is not presented in this document. In the backfill design, the deposition tunnels are to be filled with a foundation layer material, precompacted clay blocks and extruded bentonite pellets. The foundation layer consists of Milos bentonite granules, which are compacted in situ in order to level the deposition tunnel floor, providing an even and stable base for the block filling. On the foundation layer, a rigid assemblage of overlapping layers of pre-compacted blocks made of Friedland clay are installed. The void space between the blocks and the rock wall is filled with extruded pellets made of bentonite similar to raw material of Cebogel QSE product.
Avainsanat - Keywords
Backfill, bentonite, block, design, foundation layer, Friedland clay, KBS-3V, pellet.
ISBN
ISBN 978-951-652-196-4 ISSN
ISSN 1239-3096 Sivumäärä – Number of pages
80 Kieli – Language
English
Posiva-raportti – Posiva Report Posiva Oy Olkiluoto FI-27160 EURAJOKI, FINLAND Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Raportin tunnus – Report code
POSIVA 2012-15
Julkaisuaika – Date
December 2013
Tekijä(t) – Author(s)
Jorma Autio, Md. Mamunul Hassan, Petriikka Karttunen, Paula Keto, B+Tech Oy
Toimeksiantaja(t) – Commissioned by
Posiva Oy
Nimeke – Title
LOPPUSIJOITUSTUNNELIEN TÄYTÖN SUUNNITELMA 2012
Tiivistelmä – Abstract
Tämä työ sisältää KBS-3V-loppusijoitustunnelin täytön käsitteellisen ja yksityiskohtaisen suunnitelman. Täytön tarkoituksena on pitää puskuri paikallaan sekä ylläpitää suotuisia ja ennus-tettavissa olevia olosuhteita puskurille ja kapselille. Lisäksi täytön tarkoituksena on ylläpitää suotuisia kalliomekaanisia, hydrologisia ja geokemiallisia olosuhteita loppusijoitusreiän lähi-alueella sekä rajoittaa kanisterivikatapauksessa vapautuvien radionuklidien kulkeutumista. Yleisellä tasolla olevan täyttösuunnitelman lisäksi kaikille täyttökomponenteille (lattia-, lohko- ja pellettitäyttö) on tässä raportissa esitetty yksityiskohtaiset suunnitelmat. Loppusijoitustunnelin päätytulpan suunnitelmaa ei ole esitetty tässä dokumentissa. Loppusijoitustunneli on suunniteltu täytettäväksi lattiatäyttömateriaalilla, esipuristetuilla savi-lohkoilla sekä pelletöidyllä bentoniitilla. Lattiatäyttömateriaali koostuu alkuperältään Milokselta olevasta granuli-muotoisesta bentoniitista. Materiaali tiivistetään ja sen avulla muodostetaan tasainen ja kantava pohja lohkotäytölle. Lattiatäytön päälle asennetaan limittäin ja kerroksittain esipuristettuja Friedland-savesta valmistettuja lohkoja, jotka muodostavat tiiviin pinon. Tunneli-seinämän ja lohkopinon välinen rako täytetään pelletöidyllä bentoniitilla, joka on valmistettu Cebogel QSE -pellettien raaka-aineen kaltaisesta materiaalista.
Avainsanat - Keywords
Bentoniitti, Friedland-savi, KBS-3V, lattiatäyttö, lohko, pelletti, suunnitelma, täyttö.
ISBN
ISBN 978-951-652-196-4 ISSN
ISSN 1239-3096 Sivumäärä – Number of pages
80 Kieli – Language
Englanti
Posiva-raportti – Posiva Report Posiva Oy Olkiluoto FI-27160 EURAJOKI, FINLAND Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)
Raportin tunnus – Report code
POSIVA 2012-15
Julkaisuaika – Date
Joulukuu 2013
FOREWORD The backfill design presented in this report is based on design work started by Jorma Autio (B+Tech Oy) in 2011. Md. Mamunul Hassan (B+Tech Oy) provided detailed descriptions of block filling designs, and all the design work connected with this topic was carried out by him. Paula Keto (B+Tech Oy) edited the report in 2012 to be in accordance with the Backfill Production Line report and wrote sections concerning design requirements. Petriikka Karttunen and Leena Kiviranta (B+Tech Oy) contributed to the content of the report and handled review comments together with Paula Keto. Xavier Pintado and Jorma Autio from B+Tech Oy reviewed the report as B+Tech’s internal reviewers. Petri Koho and Petri Korkeakoski from Posiva Oy acted as the client’s representatives and provided review comments. Timo Kirkkomäki (Fortum Oyj) provided information presented in Appendix 1, Olli Salo from Saanio & Riekkola Oy wrote Appendix 2 and Leena Kiviranta and Petriikka Karttunen from B+Tech Oy wrote Appendix 3. Rick McArthur corrected the language. The official review of the report was done by Markku Juvankoski (VTT), Heini Laine (Saanio & Riekkola Oy) Petri Korkeakoski and Jukka-Pekka Salo from Posiva Oy. In addition, unofficial review comments were provided by David Dixon (AECL) and Aimo Hautojärvi (Posiva Oy). Thanks are due to all the experts mentioned above for contributing their design expertise, and for their help in writing this report.
ABBREVIATIONS AND DEFINITIONS Arch/arch zone The uppermost part of the deposition tunnel, the arched
tunnel roof.
Backfill Backfill is the material or materials used to fill deposition tunnels.
Block filling The backfill component which occupies the largest volume of the deposition tunnel. Consists of pre-compacted blocks.
Block filling degree Block filling degree is defined as the ratio of the volume of blocks divided by the theoretical (i.e. nominal) volume of the tunnel. If block filling degree is defined from the realised tunnel volume, this is noted separately in the sentence.
Block layout An arrangement which allows the largest volume of a deposition tunnel to be filled with pre-compacted blocks. There are two block layouts: one for the Loviisa deposition tunnels and one for Olkiluoto deposition tunnels.
Block orientation system There are two different block orientation systems (A and B). In each system every block is in same direction. When an A layer is installed on top of a B layer, the blocks overlap and vertical gaps do not span more than a single block layer.
Buffer Compacted bentonite blocks and pellets surrounding the copper canister in the deposition hole.
Bulk density Bulk density is the ratio of the total mass of dry solids and water to the bulk volume and calculated as ρb = (ms+mw/Vs (kg/m3).
Cebo Holland BV Supplier of bentonite raw material.
Cebogel QSE Cylindrical, compacted bentonite rod product manufactured by Cebo Holland BV consisting of 100% activated sodium bentonite.
Central tunnel A tunnel which provides access to deposition tunnels. A repository always has two parallel central tunnels. The cross-sectional area of a central tunnel is larger than the cross-sectional area of a deposition tunnel.
Chamfer A bevel in the uppermost part of a deposition hole which makes installation of the canister easier.
Conceptual design Backfilling design at a general level.
Degree of water saturation, Sr (%) The degree of water saturation is the ratio between the
volume of the pore water and the pore volume.
P
wr V
VxS 100
Deposition hole The vertical hole where the disposal canister and the surrounding buffer are emplaced in the KBS-3V concept.
Deposition tunnel The tunnel, where deposition holes are located in the KBS-3V concept.
Deposition tunnel plug A plug made of low pH concrete and filter and sealing materials. The plug is installed in the mouth of a deposition tunnel after the backfill has been installed.
Design basis Performance targets and target properties for the repository system.
Design boundary A boundary which separates design entities. Examples include the boundary between the backfill and buffer designs, and the boundary between the backfill and the plug designs.
Design requirement Design requirements are ultimately defined so as to enable the achievement of the performance targets in the expected scenarios.
Design specification Design specifications are firm, quantitative specifications for the design based on the performance targets and design requirements.
DFN Discrete Fracture Network model.
Disk block Disk-shaped buffer blocks located above and below the canister in a deposition hole.
Dry density Dry density is the ratio of the dry solid mass to the bulk volume and calculated as ρd = ms/Vs (kg/m3).
EMDD Effective Montmorillonite Dry Density (kg/m3):
)))/(*(1()1(
solidsd
d
FxFEMDD
where F is ratio of
non-swelling minerals, ρd is dry density, and ρsolids is density of solid particles (unit weight).
Excavation tolerance The allowed deviation (+/- in mm) from the theoretical excavation line.
EYT Safety class. Means no significance for nuclear safety.
Foundation layer/bed Layer of backfill material used for levelling of the tunnel floor.
Friedland clay Friedland clay is smectite-rich clay from North-Eastern Germany, quarried and sold as a product by FIM Friedland Industrial Minerals GmbH.
GD Government Decree.
Grouting The sealing of water-conducting rock fractures by injecting grouting material into the fractures. Grouting is used to minimise water inflow into the excavated volumes.
Grouting criteria A limit value for the rate of groundwater inflow (L/min). If the inflow rate exceeds this limit, grouting is recommended.
High-grade bentonite Bentonite with a high smectite content (>75 %).
Homogenisation When backfill densities across the tunnel cross-section are homogenised to such extent that the material properties in all parts of the tunnel cross section fulfill the design requirements set for the backfill.
Host rock The surrounding bedrock.
Hydraulic conductivity A property of rock or any other material (m/s) which determines the flow rate of water per unit area caused by a given hydraulic gradient.
Hydrostatic pressure The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above. In this case, the hydrostatic pressure results from the presence of groundwater in bedrock.
Initial state Initial state is the state in which a given component has been emplaced according to its design and remains after intentional engineering measures and executed controls have been completed.
Installation tolerance The degree of accuracy acceptable when an object (a backfill component) is being installed.
LO1-2 Loviisa reactor units 1 and 2. Type VVER 440.
Manufacturing tolerance The degree of accuracy that is acceptable when an object (a backfill component) is being manufactured.
Minelco granules Bentonite product excavated from Milos, Greece, by S&B Industrial Minerals SA and processed by Minelco AB. Consists of high-grade Na-activated Ca-bentonite.
Na-bentonite Bentonite in which the exchangeable cation is primarily sodium.
ONKALO The Olkiluoto Underground Rock Characterisation Facility.
ONKALO demonstration (DEMO) tunnel A demonstration tunnel excavated in the Olkiluoto
repository at a depth of 420 m.
OL1-4 Olkiluoto reactor units 1 - 4. OL1 and OL2 are BWR-reactors in operation, OL3 is EPR-type (in construction) and OL4 is so far only a decision-in-principle.
Operational phase The operation phase of the repository for spent nuclear fuel before the repository and the whole disposal facility is closed and sealed.
Pellet Pieces of compressed clay. Shape and size can vary depending on pelletizing technique.
Performance target The performance targets form the basis for the definition of the design requirements that are subsequently implemented.
Pilot hole/Probe hole A survey hole drilled into rock located within the tunnel profile before tunnel excavation.
Porosity Porosity (n) is the ratio between the pore volume (Vp) and
the bulk volume (V) of the soil. V
Vn p also
e
en
1,
where e is void ratio.
Post-grouting Grouting carried out after a tunnel section has been excavated.
Pre-grouting Grouting carried out before the excavation of a tunnel section.
Realised cross-section The measured cross-sectional area of a tunnel after it has been excavated.
Realised tunnel volume The measured tunnel volume after excavation.
Repository Part of the disposal facility consisting of deposition tunnels and holes.
RSC Rock Suitability Criteria. The aim of the RSC is to define suitable rock volumes for the repository, deposition tunnels and deposition holes.
Safety functions Safety functions are the main roles for each barrier.
Saturation The process during which the pore space of the material is filled with pore water up to degree of saturation (Sr )100 %.
Saturated state Describes the state of the soil when the degree of saturation Sr of the soil is 100 %.
Self-sealing The ability of bentonite to repair and fill the channels formed by flowing water.
SKB Svensk Kärnbränslehantering AB, Swedish Nuclear Fuel and Waste Management Co.
STUK Radiation and Nuclear Safety Authority Finland.
Swelling pressure Pressure which results from the swelling of material without change of volume.
TDS Total Dissolved Solids (g/L).
Theoretical excavation line The theoretical excavation line shows the designed geometry of the rock surfaces in an excavated tunnel.
Theoretical tunnel volume The exact volume of a tunnel as designed (without variations in tunnel volume for instance due to drill & blast technique).
Void ratio Void ratio (e) is the ratio between the pore volume (Vp) and the volume of solids (Vs) and is calculated as e = Vp/Vs (dimensionless).
Water content Water content is the ratio between the mass of water and the mass of solid substance in a material and is calculated as w = 100 x (mw/ms) (%).
YVL Finnish nuclear regulatory guides. YVL refers to the Finnish word “ydinvoimalaitos”.
1
TABLE OF CONTENTS ABSTRACT
TIIVISTELMÄ
FOREWORD
ABBREVIATIONS AND DEFINITIONS
1 INTRODUCTION ................................................................................................... 3 1.1 Background .................................................................................................... 3 1.2 Purpose and objectives .................................................................................. 5 1.3 Limitations ...................................................................................................... 6 1.4 References ..................................................................................................... 6
2 DESIGN BASIS ..................................................................................................... 7 2.1 General ........................................................................................................... 7 2.2 Design basis related to safety functions in the KBS-3 repository ................... 7
2.2.1 Safety functions, performance targets and design requirements ........ 7 2.2.2 Design specifications derived from the safety functions, performance targets and design requirements .................................................................... 8
2.3 Boundary conditions ..................................................................................... 12 2.3.1 Inflow conditions ............................................................................... 12 2.3.2 Groundwater pressure ...................................................................... 14 2.3.3 Groundwater salinity ......................................................................... 14
2.4 Tunnel dimensions and volumes .................................................................. 16 2.5 Interface with other barriers .......................................................................... 19
2.5.1 Interface with the buffer and the deposition hole .............................. 19 2.5.2 Plug – backfill interface ..................................................................... 22
2.6 Backfilling rate .............................................................................................. 23
3 BACKFILL - CONCEPTUAL DESIGN ................................................................. 25 3.1 Backfill components ...................................................................................... 25 3.2 Backfill materials ........................................................................................... 26
4 BACKFILL - DETAILED DESIGN ........................................................................ 29 4.1 General ......................................................................................................... 29 4.2 Design of the foundation layer ...................................................................... 29
4.2.1 Design requirements ......................................................................... 29 4.2.2 Materials ........................................................................................... 29 4.2.3 Dimensioning .................................................................................... 30 4.2.4 Design ............................................................................................... 31
4.3 Design of block filling .................................................................................... 32 4.3.1 Design requirements ......................................................................... 32 4.3.2 Materials ........................................................................................... 32 4.3.3 Dimensioning .................................................................................... 33 4.3.4 Block design ...................................................................................... 34 4.3.5 Design of the block layout ................................................................. 35
4.4 Pellet filling design ........................................................................................ 37 4.4.1 Design requirements ......................................................................... 37 4.4.2 Materials ........................................................................................... 37 4.4.3 Dimensioning .................................................................................... 39 4.4.4 Design ............................................................................................... 39
4.5 Volumes and masses ................................................................................... 40 4.6 Performance ................................................................................................. 43
2
5 SUMMARY .......................................................................................................... 45
REFERENCES ............................................................................................................. 47
LIST OF APPENDICES ................................................................................................ 51
3
1 INTRODUCTION 1.1 Background Posiva's spent nuclear fuel disposal is based on the KBS-3V concept and on the characteristics of the Olkiluoto site. In the KBS-3V concept, the spent fuel elements are disposed in copper-iron canisters, surrounded by bentonite buffer in the vertical deposition hole. There are several deposition holes in one deposition tunnel (see Figure 1-1). After all canisters have been disposed in a deposition tunnel, the tunnel will be filled with backfilling material (Figure 1-1) and the deposition tunnel will be closed with a plug. The disposal operation is planned to take place at a rate where one or two deposition tunnels will be filled in a year. After all deposition tunnels in a deposition panel are backfilled and plugged, the central tunnels and other openings in the panel will be backfilled and plugged, i.e. closed. The whole KBS-3V disposal system and its subsystems include safety functions determined by taking into account the regulatory requirements. From the safety functions, performance targets for each subsystem have been defined. These form the design basis of each subsystem. The performance targets and design requirements derived from them have been compiled in the Design Basis (p. 19, 54-56). This report belongs to series of design reports together with the Canister Design (Raiko 2012) and Buffer Design (Juvankoski 2012). This report describes the backfill design. Production (excavation, processing, transport, manufacturing and installation) is described in the Backfill Production Line report, (Chapter 4). Additionally, the initial state and fulfillment of design requirements are described in the Backfill Production Line report (Chapter 5). The long-term performance of the backfill design is discussed in the Performance Assessment. The connection between these reports is shown in Figure 1-2.
Figure 1-1. (Left) A schematic presentation of the KBS-3V design showing the location of the repository at Olkiluoto island, access routes, part of the central tunnel and deposition tunnel with deposition holes. (Right) Multi-barrier principle of a KBS-3V deposition tunnel 1: Backfill, 2: Buffer, 3: Canister and 4: Surrounding bedrock (Posiva 2012).
4
A backfill design for deposition tunnels in a KBS-3V repository consisting of a foundation layer, pre-compacted blocks and pellets was presented in Hansen et al. (2010, Chapter 5). Further development of this design was motivated by changes in requirements, new information on the performance of backfill components, uncertainties about the way in which the preceding design would function and its performance, and the potential advantages which could result from adopting new conceptual and dimensioning principles. 1.2 Purpose and objectives
The purpose of this report is to present the current backfill design. The objectives of this report are to present: - Basis for the design, - Conceptual design of the backfill, - Detailed design for the backfill components (foundation layer, backfill blocks and
the pellet filling), and to - Present the design for the block layout.
*The complete TURVA 2012 safety case portfolio reporting is described in the Design basis. Figure 1-2. The reports connected to this report. The reports in the orange box are the background reports or research, design and development work, that are described in the production line report. The reports in the green and blue boxes are as defined in the TURVA 2012 portfolio. The grey box includes the reports within the application for construction license, in TURVA 2012 portfolio or within the PSAR topical reports.
5
The report also presents the main differences between the 2009 design (Hansen et al. 2010, p. 37) and the current design and the background behind the design updates and material selection. 1.3 Limitations Backfill design 2012 describes both the concept and the detailed design of backfilling in KBS-3V deposition tunnels. In addition to the description of the backfill design, detailed designs for the components of the backfill (foundation, block and pellet fill) are provided in this report. The data used in this report is the same that has been used for the Backfill Production Line report. The production of the backfill including material acquisition, manufacturing and installation of components are outside the scope of this report, as is the plug design aspects. These topics are described in the Backfill Production Line report (Chapters 8, 9 and 10). For the purposes of this report, the boundary between the buffer and the backfill has been defined to be such that buffer is limited to -400 mm from the theoretical tunnel floor surface. All filling above this limit belongs to the backfill by definition regardless of the design of the filling. The design of the backfill in the upper part of the deposition hole and chamfers is described in Juvankoski (2012, p. 35-37) and in Buffer Production Line report (p. 20-23), as is the manner in which rejected deposition holes will be filled. 1.4 References In this report the TURVA-2012 safety case portfolio reports and production line reports have been referred to using italicized shortened names of the reports (e.g. Backfill Production Line report and Performance Assessment). Detailed reference information of these TURVA-2012 safety case portfolio reports and production line reports is found from the beginning of the reference list (Chapter 6). Referring to other than above mentioned documents is done using Harvard style and reference list in alphabetic order is found below the TURVA-2012 safety case portfolio reports and production line reports in Chapter 6.
6
7
2 DESIGN BASIS 2.1 General The design basis for the backfill design presented in this report is divided into the following topics: - Design basis related to safety functions in the KBS-3 repository - Boundary conditions - Tunnel dimensions and volumes - Interfaces to other barriers
2.2 Design basis related to safety functions in the KBS-3 repository 2.2.1 Safety functions, performance targets and design requirements The closing structures of the deposition tunnels consist of backfill and end plugs. The backfill considered in this report is the material or materials that is/are used for backfilling the deposition tunnels. Plugs will be placed at the mouth of the deposition tunnels. The deposition tunnel end plug is discussed in the Backfill Production Line report (Chapter 7). Any backfill materials or plugs used in parts of the repository other than the deposition tunnels are discussed in the Closure Production Line report (Chapter 3). The principles and reasoning behind the long-term safety related requirements are based on STUK’s YVL guides and other stakeholder requirements, including Finnish laws. These are described in detail in Design Basis and considered in Posiva’s safety concept. The safety concept is a conceptual description of how safe disposal of spent nuclear fuel is achieved using the KBS-3 method, taking into account the characteristics of the Olkiluoto site. Based on this concept, safe disposal is achieved by long-term isolation and containment. Another key element is the multibarrier principle that has been defined in the Government Decree GD 736/2008 (Section 11: Multibarrier principle): “The long-term safety of disposal shall be based on safety functions achieved through mutually complementary barriers so that a deficiency of an individual safety function or a predictable geological change will not jeopardise the long-term safety”. The deposition tunnel backfill is one of the engineered barriers in the KBS-3V system along with the canister, the buffer bentonite and sealing structures used in closure of the repository. The role of backfill materials and sealing structures according to STUK-YVL Guide D.5 (Draft 4, 17.3.2011, Section 4.2, 405) is to “limit transport of radioactive substances through excavated rooms”. The deposition tunnel backfill is classified to safety class EYT meaning that the backfill has no significance for nuclear safety. The safety classification is described in YVL Guide B.2 (Draft 4, 21.9.2011, Section 3.1, p. 4-6). According to Posiva (Design Basis, Chapter 9), the deposition tunnel backfill (and the plug) have the following safety functions:
8
- Contribute to favourable and predictable mechanical, geochemical and hydrogeological conditions for the buffer and canisters,
- Limit and retard radionuclide releases in the possible event of canister failure, and - Contribute to the mechanical stability of the rock adjacent to the deposition tunnels.
According to Government Decree 736/2008 safety functions shall effectively prevent releases of radioactive materials at least several thousand years and further based on YVL Guide D.5 (Draft 4, 17.3.2011, Section 4.2, 408, p. 7), the time-scale is further defined to be at least 10 000 years. The long-term safety related requirements are divided into performance targets and target properties. Target properties have been defined for the host rock. Performance targets have been defined separately for each engineered barrier, i.e. for the canister, buffer, deposition tunnel backfill and end plug, and for closure backfill materials and sealing structures placed in other parts of the repository. The performance targets and corresponding design requirements set for the deposition tunnel backfill are presented in Table 2-1. The rationales behind these are discussed in the Design Basis (Sections 9.1 and 9.2). 2.2.2 Design specifications derived from the safety functions, performance
targets and design requirements The design specifications for the backfill are presented in Table 2-2. Design specifications are firm, quantitative specifications determined for the design based on the performance targets and design requirements. The reasoning behind the design specifications is given below. Montmorillonite content and density The reasoning behind the limits for the montmorillonite content and the dry densities of backfill materials presented in Table 2-2 is based on the idea that the system will be able to fulfill the performance criteria. One means of evaluating density-related performance is through the use of the effective montmorillonite content (EMDD) parameter discussed in the Backfill Production Line report (p. 13). Desired properties can be achieved with the design by determining the right combination of smectite content and dry density for the backfill components. For this the natural range of smectite content needs to be known as well as to what dry density the components can be manufactured and installed. For example, based on block manufacturing tests described in the Backfill Production Line report (p. 79) for Friedland clay, fairly high dry densities (>2000 kg/m3) have been gained for this particular material. Therefore, the material can be used in this application, although the montmorillonite content is fairly low (30-38 %, see Backfill Production Line report, p. 79). Batches having the smectite content less than the specified lower limit will not be accepted for the backfill production. This will be ensured with quality assurance and control measures described in the Backfill Production Line report (p. 41-50).
9
Geometry The reasoning behind the specifications given for the backfill geometry is that the proportion of backfill components in the tunnel cross-section shall be suitable to provide sufficient swelling and hydraulic properties. In addition, the backfill as a structure should provide sufficient structural stiffness to prevent buffer heave also when the backfill is in unsaturated state. Other things to consider in the geometry are for example installation tolerances of the pellets and the ability of the pellets to protect the blocks from erosion. In addition, the tunnel geometry and especially excavation tolerances affect the maximum thickness of the foundation layer and the pellet filling. See Table 2-1. Chemical properties The limits for organics, sulphur and sulphide contents of the backfill materials were set because they may affect the canister corrosion rate. Backfill specific limits have not yet been determined and therefore the limits are the same as for buffer material (see Table 2-2). The design specifications for buffer have been presented in Juvankoski (2012) (Table 3-1, p. 20).
T
able
2-1
. Per
form
ance
targ
ets
and
desi
gn r
equi
rem
ents
def
ined
for
the
back
fill
. Req
uire
men
ts c
once
rnin
g on
ly p
lugs
are
not
incl
uded
(D
esig
n B
asis
).
Per
form
ance
tar
get
s D
esig
n r
equ
irem
ents
D
efin
itio
n
The
sea
ling
stru
ctur
es o
f th
e de
posi
tion
tunn
els
cons
ist
of b
ackf
ill a
nd
plug
s. B
ackf
ill is
the
mat
eria
l or
mat
eria
ls th
at is
/are
use
d fo
r ba
ckfil
ling
the
depo
sitio
n tu
nnel
s. T
he p
urpo
se o
f th
e ba
ckfil
l is
to k
eep
the
buffe
r in
pla
ce,
mai
ntai
n fa
vour
able
and
pre
dict
able
con
ditio
ns f
or t
he b
uffe
r an
d th
e ca
nist
er,
and
also
fav
oura
ble
rock
mec
hani
cal,
hydr
olog
ical
an
d ge
oche
mic
al c
ondi
tions
in th
e ne
ar-f
ield
and
to r
etar
d th
e tr
ansp
ort
of r
adio
nucl
ides
if th
e ca
nist
er s
tart
s le
akin
g.
The
mai
n co
mpo
nent
of t
he b
ackf
ill m
ater
ial s
hall
cons
ist o
f nat
ural
sw
ellin
g cl
ays.
Per
form
ance
Unl
ess
othe
rwis
e st
ated
, th
e ba
ckfil
l an
d pl
ugs
shal
l fu
lfill
the
perf
orm
ance
tar
gets
list
ed b
elow
ove
r hu
ndre
ds o
f th
ousa
nds
of y
ears
in
the
expe
cted
rep
osito
ry c
ondi
tions
exc
ept f
or in
cide
ntal
dev
iatio
ns.
The
bac
kfill
sha
ll be
des
igne
d to
be
self-
seal
ing
afte
r in
itial
ins
talla
tion
and
self-
heal
ing
afte
r an
y hy
drau
lic o
r m
echa
nica
l dis
turb
ance
s.
Hyd
rau
lic a
nd
tra
nsp
ort
pro
per
ties
T
he b
ackf
ill s
hall
limit
adve
ctiv
e flo
w a
long
the
depo
sitio
n tu
nnel
s.
The
bac
kfill
sha
ll be
so
desi
gned
tha
t its
hyd
raul
ic c
ondu
ctiv
ity o
ver
the
who
le
cros
s-se
ctio
n of
the
back
fille
d tu
nnel
will
be ≤1
x10-1
0 m/s
afte
r fu
ll sa
tura
tion
Ch
emic
al p
rop
erti
esT
he c
hem
ical
com
posi
tion
of t
he b
ackf
ill a
nd p
lugs
sha
ll no
t je
opar
dise
th
e pe
rfor
man
ce o
f the
buf
fer,
can
iste
r or
bed
rock
. B
ackf
ill
mat
eria
ls
shal
l be
se
lect
ed
so
as
to
limit
the
cont
ents
of
ha
rmfu
l su
bsta
nces
(or
gani
cs,
oxid
isin
g co
mpo
unds
, su
lphu
r an
d ni
trog
en c
ompo
unds
) an
d m
icro
bial
act
ivity
. S
up
po
rt o
f o
ther
co
mp
on
ents
of
the
dis
po
sal s
yste
m /
mec
han
ical
pro
per
ties
T
he b
ackf
ill s
hall
keep
the
buffe
r in
pla
ce.
To
keep
the
buf
fer
in p
lace
, th
e de
sign
of
the
back
fill h
as t
o ta
ke in
to a
ccou
nt,
on
the
one
hand
, th
e co
mpr
essi
bilit
y an
d st
ruct
ural
stif
fnes
s of
the
bac
kfill
, an
d, o
n th
e ot
her
hand
, th
e bu
ffer
swel
ling
pres
sure
and
the
fric
tion
of b
uffe
r ag
ains
t th
e de
posi
tion
hole
wal
ls.
The
bac
kfill
sha
ll co
ntrib
ute
to p
reve
nt u
plift
ing
of t
he c
anis
ter
in t
he
depo
sitio
n ho
le.
(sam
e as
abo
ve)
The
ba
ckfil
l sh
all
cont
ribut
e to
th
e m
echa
nica
l st
abili
ty
of
the
depo
sitio
n tu
nnel
s.
In th
e in
itial
sta
te th
e ba
ckfil
l sha
ll ha
ve a
goo
d co
ntac
t with
the
host
roc
k.
10
T
able
2-2
. Des
ign
spec
ific
atio
ns fo
r de
posi
tion
tunn
el b
ackf
ill.
1 P
ER
FO
RM
AN
CE
M
on
tmo
rillo
nit
e co
nte
nt:
T
he m
ontm
orill
onite
con
tent
of F
riedl
and
clay
blo
cks
shal
l be
30-3
8%.
The
foun
datio
n la
yer
and
pelle
ts s
hall
cons
ist o
f ben
toni
te w
ith m
ontm
orill
onite
con
tent
bet
wee
n 75
-90%
D
ry d
ensi
ty:
The
dry
den
sity
of F
riedl
and
clay
blo
cks
shal
l be
with
in th
e ra
nge
of 1
990-
2070
kg/
m3 .
T
he d
ry d
ensi
ty o
f th
e fo
unda
tion
laye
r sh
all b
e w
ithin
the
rang
e of
115
0-13
50 k
g/m
3 .
The
dry
den
sity
of
the
pelle
t fill
sha
ll be
with
in th
e ra
nge
of 9
00-1
100
kg/m
3 G
eom
etry
: T
he b
ackf
ill b
lock
s sh
all h
ave
follo
win
g di
men
sion
s: 5
50 x
470
x 3
30 m
m. T
he m
anuf
actu
ring
tole
ranc
e sh
all b
e -1
mm
/ +
2 m
m.
The
blo
ck fi
lling
deg
ree
(fro
m th
e th
eore
tical
/nom
inal
cro
ss-s
ectio
n) s
hall
be >
80%
.
The
gap
wid
th b
etw
een
the
bloc
ks a
nd t
he t
heor
etic
al t
unne
l wal
l/roo
f sh
all b
e 10
0 m
m.
The
pel
let
fill s
hall
fill t
he r
emai
ning
ope
n ga
p be
twee
n th
e bl
ocks
and
roc
k.
The
thi
ckne
ss o
f th
e fo
unda
tion
bed
shal
l be
max
imum
+15
0 m
m a
bove
the
the
oret
ical
flo
or l
ayer
. C
onsi
derin
g ex
cava
tion
tole
ranc
e of
+40
0 m
m, t
he m
axim
um th
ickn
ess
of th
e fo
unda
tion
laye
r is
550
mm
.
2 C
HE
MIC
AL
PR
OP
ER
TIE
S
2.1
BA
CK
FIL
LT
he o
rgan
ics
cont
ent i
n th
e ba
ckfil
l sha
ll be
low
er th
an 1
wt-
%.
The
tota
l sul
phur
con
tent
in th
e ba
ckfil
l sha
ll be
less
than
1 w
t-%
, with
sul
phid
es m
akin
g, a
t mos
t, ha
lf of
this
.
11
12
2.3 Boundary conditions This section describes the environment-related boundary conditions most relevant for the backfill design. The performance of the backfill is affected by the inflow conditions, the groundwater pressure and the groundwater salinity. Other boundary conditions, such as the rock types and the temperature evolution of the repository are described in the Performance Assessment (Sections 2.2.1, 5.2 and 7.2.1). 2.3.1 Inflow conditions The expected groundwater inflow conditions to open repository tunnels and deposition holes are described in detail in the Backfill Production Line report (p. 15-16 and appendix 4 on p. 125-144). The expected natural groundwater conditions assigned to the repository are based on inflow estimates from a hydrogeological DFN model 2008 in open tunnels presented in Hartley et al. (2010). Recently, the hydrogeological DFN model has been revised (Hartley et al. 2012). However, initially the inflow conditions also depend on the results of grouting and the rock suitability criteria (RSC) applied to deposition tunnels. According to the rock suitability criteria (McEwen et al. 2012, p. 78), developed from the results of backfill stability tests using large-scale mockups, the maximum local (fracture related) inflow to a deposition tunnel is estimated to be 0.25 L/min. This value was originally set based on field tests up to ½ tunnel scale where water throughflow and erosive activity were reported by Dixon et al. (2008a & 2008b). Based on these test results it was stated in the Backfill Assessment report 2009 (Keto et al. 2009, p. 87) that water inflow at a single point does not seem to affect the erosion very much if a preferential pathway forms in the pellet-rock contact and inflow rates are moderate (<0.5 l/min). Since data existed from the ½ scale tests with inflow of 0.25 L/min (Dixon 2008b, p 50), this was suggested as the conservative limit for the fracture related inflow. Later in 2011, more tests were performed in Äspö with inflow of 0.1 and 0.25 L/min simulating the inflow from a fracture (Dixon et al. 2011, p. 40). In first two tests with the inflow of 0.1 and 0.25 L/min from a simulated fracture, a single water pathway eventually developed at the pellet-wall contact (Dixon et al. 2011 p. 31) and the conclusion was that the overall short-term stability of the system is not likely to be compromised by the presence of a single flow feature providing 0.25 L/min or less (Dixon et al. 2011 p. 31). In the latter two tests, water inflow was introduced to the system behind a partially saturated clay region. This resulted in pressure buildup and temporary increase in erosion of the pellet fill, linked to the outburst of the water and following decrease in the pressure within the system. However, the results from the Dixon et al. (2011) were performed using Milos B blocks resulting in slightly higher EMDD 1200 kg/m3 compared to earlier studies with low density Friedland clay blocks with EMDD of 1140 kg/m3 (Dixon et al. 2011, p 41). The influence of a difference in material type on piping and erosion has not been assessed. No total inflow limitation has been determined for the whole tunnel. An informally defined grouting criterion is 0.2 L/min, so whenever higher leakages are observed in a probe hole, pre-grouting before excavation of that section will occur. If necessary, post-grouting (after excavation) can also be performed. If the inflow from a single fracture is still >0.25 L/min after grouting, the RSC-criterion is not fulfilled and the use of the deposition tunnel will be re-evaluated (McEwen et al. 2012, p. 78). The maximum
13
inflow allowed into a deposition hole is 0.1 L/min (Hellä et al. (2009, p. 42). No grouting is allowed in deposition holes and if grouting material is observed in a deposition hole it will not be accepted (McEwen et al. 2012, p. 76). Based on the natural groundwater conditions and the information presented above, four different inflow cases have been defined for backfill design purposes (see Figure 2-1) (Backfill Production Line report, p. 139-141): - Wet tunnel case 1: Natural groundwater inflow to the whole deposition tunnel is 5
L/min. In this case, the majority of the inflow (>1 L/min) comes from one fracture accompanied by fractures with smaller inflows (0.1 L/min or less) in a tunnel section with length of 20-30 m. The probability that the inflow to the tunnel is higher than 5 L/min is ~20 %.
- Wet tunnel case 2: Same as case 1, but the inflowing fracture has been grouted limiting the total inflow to the whole deposition tunnel to ~1 L/min.
- Typical tunnel case: Natural groundwater inflow to the whole deposition tunnel is 0.5 L/min. The inflow comes from a group of fractures with an inflow of 0.1 L/min or less. The probability that the inflow to the whole tunnel is higher than 0.5 L/min is ~50 %.
- Dry tunnel case: Natural groundwater inflow to the whole deposition tunnel is <0.01 L/min. The probability that the flow is equal to 0.01 L/min or lower than this is ~22 %.
Taking into account the possibility that a significant number of inflowing fractures are located near each other, a case where the majority of the total inflow to the open backfill front comes through a single flow path in the backfill can be considered as the worst case scenario for the installation of backfill. This scenario can be justified by the fact that merging of originally separate inflow paths has been seen in tests performed for the backfill at Äspö and Riihimäki (see e.g. Dixon et al. 2011a, p. 26-30, Keski-Kuha et al. 2012, p. 62) and therefore cannot be ruled out. For example, if the inflows from one 20-30 m long tunnel section were combined into one pathway, it would be possible that the inflow through this pathway would be ~0.5 L/min. This amount of water is sufficient to disturb the installation of backfill and should be handled with some technical solution.
14
Figure 2-1. The inflow cases taken into account in the backfill design are (Backfill Production Line report, p. 139-141): 1) Wet tunnel case 1 with total inflow of 5 L/min to the whole deposition tunnel before grouting. 2) Wet tunnel case 2 representing the same case as wet tunnel case 1, but after grouting having total inflow to the whole tunnel of 1 L/min. 3) Typical tunnel case with total inflow of 0.5 L/min. 4) Dry tunnel case with total inflow of 0.01 L/min to the whole deposition tunnel. 2.3.2 Groundwater pressure The prevailing groundwater pressure at the repository level is approximately 4.1 MPa (Performance Assessment, p. 281). 2.3.3 Groundwater salinity
Based on Löfman et al. (2010, p 51), the initial salinity of groundwater at repository level is 12 g/L (TDS) on average. The evolution of salinity has been studied by Löfman & Poteri (2008, p. 32) and Löfman & Karvonen (2012). Based on the model, the
15
maximum salinity increases until the end of the operational period, after which it starts to decrease (see Figure 2-2). The maximum salinity in the reference volume (repository level and ±50 m from the repository level) is 35-45 g/L (TDS) depending on the model variant (see Figure 2-2) (Figures 5-14, 5-15 and 5-16 in Löfman & Karvonen, 2012 and Performance Assessment, p. 122). Even under the most pessimistic assumptions of the parameters affecting salt transport, the salinities will remain below 70 g/L (TDS) (Performance Assessment, p. 122). According to Fig. 2-2, the long-term average value in the temperate period (first 10 000 years) can be estimated to be 10-15 g/L after which the salinity decreases below 10 g/L. The maximum salinity value estimated for the repository level is 20−25 g/L (Performance Assessment, p. 122). During the operational period, the estimated minimum salinity at the repository level remains above 1 g/L (TDS) (Performance Assessment, p 124). During the first 10 000 years, the salinity at the repository level may decrease below 1 g/L and at some locations even dilute water conditions (<0.4 g/L) may take place (Performance Assessment, p 202-203). Later on, dilute water conditions are expected to take place during glacial conditions (Performance Assessment, p. 304-305). The requirement concerning salinity of the groundwater in the host rock is as follows (Design Basis, p. 65): “Groundwater at the repository level shall have limited salinity so that the buffer and backfill will maintain a high enough swelling pressure. Therefore the groundwater salinity (TDS, total dissolved solids) at the repository level shall, in general be below 35 g/L but local or temporal variations up to 70 g/L can be allowed.” Based on this requirement and the natural variation of groundwater salinities presented above, the salinities against which the properties of the backfill are evaluated are tap water, 10 g/L, 35 g/L and 70 g/L (TDS).
16
Figure 2-2. Salinity evolution during the excavation and operation period, and after closure until 50 000 years after starting of ONKALO construction. The maximum, minimum and average salinity in the reference volume for different model variants (Löfman & Karvonen 2012, p. 109). 2.4 Tunnel dimensions and volumes The cross-sections of the deposition tunnels for spent fuel from Olkiluoto (OL) and Loviisa (LO) are presented in Figure 2-3. The theoretical cross-section of the deposition tunnels for Olkiluoto 1, 2 and 3 canisters is 14.00 m2 and for Loviisa canisters 12.61 m2
(Saanio et al. 2010, p. 69). The corresponding values when chamfers in the lower corners of the tunnel profile are excluded are 14.1 m2 and 12.7 m2, respectively (chamfers are marked with a dashed line to Figure 4-4). The width of the tunnel is 3500 mm for both of the tunnel types, but the height is 4400 mm for Olkiluoto tunnel type and 4000 mm for Loviisa tunnel. There are variations in the tunnel cross-section due to technical limitations of the drill and blast excavation method. The blasting holes are always drilled with a small inclination outwards (look out angle) from the theoretical profile. In practice it means that the volume of the tunnel is always smaller in the location where the drilling has started compared to the location where the drill holes ends (see Figure 2-4). The maximum tolerances to be taken into account in the backfill design are the ones determined for the ONKALO demonstration tunnel, i.e. 400 mm for the floor and 300 mm for the walls/arch (see Figure 2-5 as an example) (Underground Openings Production Line report). Taking into account the maximum excavation over-break of +36 %, the maximum cross-section (or unit volume) for OL1-3 tunnels is 19.04 m2 and for Loviisa tunnels 17.14 m2. However, in the block layout design it was assumed that
17
similar to the profile in the ONKALO demonstration tunnels, there are no small rock chamfers in the lower corners of the tunnel profile as shown in Figure 2-5, but the lower corner in the profile are assumed to form an angle of 90° (chamfers are also marked with a dashed line to Figure 4-4). Therefore, the backfill densities and block filling degrees have been calculated using slightly bigger tunnel cross-sections (for OL1-3 used maximum cross-section is 19.18 m2 and for LO1-2 17.53 m2) (see Section 4.5 for volumes and masses). The maximum length of deposition tunnels is set to 350 m (Saanio et al. 2010, p 68). The total number of deposition tunnels in the repository for spent fuel from OL1-4 and LO1-2 is 197 and the total length is 58 400 m (Kirkkomäki 2012, p. 42), leading to an average length of 296.3 m. The theoretical total volume of deposition tunnels (excluding deposition holes) is roughly 874 000 m3 (see Appendix 1). The total theoretical volume to be backfilled (total theoretical volume of deposition tunnels excluding volume of plugs and volume between the plug and central tunnel) is ~735 000 m3 (Appendix 1). Taking into account the average excavation over breakage of +18 %, the total volume to be backfilled is 860,000-870,000 m3 (Appendix 1). Deposition holes are drilled into the floor of the deposition tunnel. The diameter of the hole is 1750 mm and the depth varies for different canister types and is approximately 6.6 m for Loviisa LO1-2 canisters, 7.8 m for Olkiluoto OL1-2 canisters and 8.3 m for OL3 canisters (Saanio et al. 2010, p. 69). The distance between the holes is 7.3 m (LO1-2), 9.1 m (OL1-2) and 10.8 m (OL3) assuming a distance of 25 m between adjacent deposition tunnels (Ikonen 2009, p. 28). The average distance between deposition holes is ~10 m. The number of rejected canister positions is estimated to be ~20 %, based on RSC estimations (Kirkkomäki 2012, p. 11). The filling of rejected deposition holes is described in the Buffer Production Line report (p. 106) and Juvankoski (2012, p. 61).
18
Figure 2-3. Theoretical cross-sections for Olkiluoto and Loviisa deposition tunnels (Saanio et al. 2012, p. 64).
Figure 2-4. Schematic illustration showing the effect of the drill and blast technique on the tunnel geometry (Backfill Production Line report, p. 19).
19
Figure 2-5. The solid black line presents the theoretical cross-section and the dotted green line the cross-section based on maximum tolerances for the OL1-3 deposition tunnels (Backfill Production Line report, p. 20). 2.5 Interface with other barriers 2.5.1 Interface with the buffer and the deposition hole The backfill is in contact with the buffer and the walls of the deposition hole. The buffer consists of bentonite with montmorillonite content between 75-90 % (Juvankoski 2012, p. 30, Buffer Production Line report, p. 26). The reference bentonite is MX-80 Na-bentonite from Wyoming, USA, but other bentonite products have also been considered as alternatives (Juvankoski 2010, p. 25, Juvankoski 2012, p. 30). The dry density of the homogenised buffer (i.e. dry density taking into account the gaps between the buffer and rock and between buffer and the canister) varies between 1591-1595 kg/m3 (Buffer Production Line report, p. 118) and the corresponding bulk density of saturated buffer varies between 2012-2015 kg/m3 (Buffer Production Line report, p.118). Initially the dry density of ring shaped buffer blocks is 1752 kg/m3 and disk blocks 1701 kg/m3 (Buffer production line report, p. 117). The initial gravimetric water content of the buffer blocks is 17 % and when saturated 26-27 % (Buffer Production Line report, p. 117-118). Taking into account that the bulk density of saturated buffer is <2050 kg/m3 and montmorillonite content of max 90 %, the swelling pressure from the buffer is in the base case <15 MPa (Buffer Production Line report, p. 23-24). The design boundary between buffer and backfill is presented in Figure 2-6. The buffer is limited to -400 mm from the theoretical excavation surface at the tunnel floor (Backfill Production Line report, p. 20, Buffer Production Line report, p. 29 and
20
Juvankoski 2012, p. 180) and buffer thickness is 2500 mm above the canister (Buffer Production Line report, p. 33, Juvankoski 2012, p. 185). Depending on the position of the rock surface between the theoretical excavation line and the -400 mm line representing the maximum excavation tolerance, there will be in some cases a need to fill the upper part of the deposition hole with buffer type of material (Backfill Production Line report, p. 20-21). This volume is filled up to the rock surface with filling components having the same material composition and density as the buffer blocks have. The installation, production and quality control of these components follow the production line of buffer components (presented in the Buffer Production Line report, Chapter 5). The upper part of the deposition holes for OL1, OL2 and OL3 canisters are notched with a chamfer to facilitate the emplacement of canisters (Juvankoski 2010, Buffer Production Line report, p. 49-50, Juvankoski 2012, p. 35), see Figure 2-7 for dimensions. In case of OL3 chamfer, the lower part of the chamfer (below -400 mm level) belongs to buffer and the upper part (above -400 mm level up to the rock surface) to backfill. The chamfer for OL1-2 is completely above the -400 mm level and belongs to backfill. However, the chamfers are filled up to the rock surface with a buffer-type material (see Buffer Production Line report, p. 29-31, Juvankoski 2012, p. 35). The production, installation and quality control of the chamfer components follow the production line of buffer components (presented in the Buffer Production Line report).
21
Figure 2-6. Design boundary between the buffer and the backfill for the Loviisa spent fuel canisters (upper figure) and for the Olkiluoto spent fuel canisters (lower figure) (Backfill Production Line report, p. 22, Buffer Production Line report, p. 30).
22
Figure 2-7. Cylindrical shaped chamfers for OL1-2 (right) and OL3 (left) deposition holes (Buffer production line report, p. 51, Juvankoski 2012, p. 37). In the OL3 case the depth of the chamfer (h) from the surface of the foundation layer is 0.900 m and radius (r) is 0.825 m. The height of the buffer block (t) in the chamfer for OL3 is 0.350 m. In the OL1-2 case the depth of the chamfer from the surface of the foundation layer (h) is 0.520 m and radius (r) is 0.825 m. For other dimensions see the Buffer Production Line report (p. 52) and Juvankoski (2012, p. 37). 2.5.2 Plug – backfill interface The current deposition tunnel end plug design is presented in the Backfill Production Line report (Chapter 7). In general, the current deposition tunnel plug design is based on SKB plug design (SKB 2010) that has been downscaled to the size of Finnish deposition tunnels and modified to fulfill the Finnish requirements set for the deposition tunnel plug. The boundary between the deposition tunnel plug and backfill is the contact between the innermost concrete beam on the deposition tunnel side and the backfill as shown in Figure 2-8. The contact area is the cross-sectional area of the deposition tunnel, which is at theoretical cross-section case 14.00 m2 for OL1-3 tunnels and 12.61 m2 for LO1-2 tunnels (Saanio et al. 2010, p. 69).
23
Figure 2-8. Illustration of the reference design of the deposition tunnel plug for OL1-3 size tunnel (Backfill Production Line report, p. 98). 2.6 Backfilling rate The assumed backfilling rate is roughly 5 m in 24 hours, consisting of following activities (Backfill Production Line report, p. 77-78): - Installation of the foundation layer (~1 working shift per 5 m), - Installation of blocks (8-10 hours per 5 m) and - Installation of pellets (3-4 hours per 5 m).
The basic assumption for the backfilling sequence is that in dry tunnel conditions the backfilling will be made in 40-metre long sections. If no other operations in the tunnel are taken into account, the backfilling of a 40-metre long section would take 8 days and of a 300 metre long tunnel 60 days (3 shifts per day, continuous operation). However, the total duration depends on the duration of the buffer/canister related operations and preparations taking place in the tunnel (for example clearing of temporary infrastructure etc.). For a 40-metre long section, the preparations prior to backfilling can be estimated to take 48 hours (Backfill Production Line report, p. 78, Saanio et al. 2012, p 108-109). These preparations include dismantling of the remaining infrastructure at this tunnel section, removal of temporary buffer related structures and cleaning of impurities from the rock surface (Saanio et al. 2012, p 108-109). Considering that the installation of canister and buffer for four deposition holes would take at maximum four days (Tanskanen 2009, p. 52), the total duration of operations for a 40 meter long section would be 14 days and approximately 100 days for a 300-metre long tunnel with 26 deposition holes (Backfill Production Line report, p. 77). Considering continuous campaign (3 shifts per day, working on weekends), the tunnel would be filled within 3-4 months (Backfill Production Line report, p. 77). However, in case the inflow to the tunnel is high enough to disturb the backfill operations, the backfill sequence will be modified case by case and the total duration of the backfill operations depend on what technical solutions are needed for controlling the water inflow.
24
25
3 BACKFILL - CONCEPTUAL DESIGN 3.1 Backfill components In principle, the conceptual design has not been changed from the 2009 backfill design presented in Hansen et al. (2010, p. 37-39). The backfill consists of three main components as shown in Figures 3-1 and 3-2: - Pre-compacted backfill blocks filling the majority of the tunnel, - Foundation layer providing a stable and level foundation for the block assemblage,
and - Pellets used for backfilling the remaining empty space between the blocks and the
rock. While the backfill design concept has not changed, the detailed design of these components has evolved since 2009. Each of these components are described in detail in Sections 4.2 (Foundation layer), 4.3 (Backfill blocks) and 4.4 (Pellets). In addition, the number of material alternatives has been reduced for each component. The backfill materials are described in Section 3.2 (Backfill materials).
Figure 3-1. A schematic figure showing the main deposition tunnel backfill components: foundation layer, backfill blocks and pellets (Backfill Production Line report, p. 25). The tunnel size shown is for spent fuel from Olkiluoto. The inner black dotted line is showing the theoretical excavation profile and the outer, the maximum possible cross-section of the tunnel assuming tolerances of 400 mm for the floor and 300 mm for the walls/roof. In reality the rock surface will be located between these two lines (an example is illustrated in the figure).
26
Figure 3-2. A schematic figure showing the main components of the backfill and the location of the deposition tunnel plug (Backfill Production Line report, p. 26). 3.2 Backfill materials The material selection is beyond the scope of this report, but the decisions on the material selection had already been made by Posiva based on data collected at the time for the alternatives discussed in Hansen et al. (2010, Chapter 3): 40/60 mixture, 50/50 mixture (comprising of 40 and 50 wt-% of Na-activated Ca-bentonite from Milos, Greece and 60 and 50 wt-% crushed rock with grain size of 0-4 mm), Friedland clay from Germany, IBECO RWC-BF bentonite from Milos, Greece and bentonite pellets. One material for each backfill component was selected and the chosen backfill materials and design specifications set for the montmorillonite contents are presented in Table 3-1. The reasoning for these selections is discussed below. The decisions were based on comparisons of fulfillment of the dry density and EMDD criteria set for these materials after assessing their mineralogical and chemical properties, hydraulic and swelling properties, self-sealing and homogenisation as well as volume change cababilities. The initial data used in the comparison is presented in Johannesson & Nilsson (2006), Karnland et al. (2006), Wimelius & Pusch (2008), Sandén et al. (2008) Olsson & Karnland (2009), SKB (2010), Johannesson et al. (2010), Kumpulainen & Kiviranta (2010) and Schatz & Martikainen (2012) providing information on the mineralogy, chemistry, physical properties and dry density gained for these materials in backfill blocks, foundation layer and pellets. Based on this comparison, the only material that had uncertainties in fulfilling the dry density criteria was the 40/60 mixture.
27
Table 3-1. The design specifications for the mineralogical composition of the clay materials to be used in deposition tunnel backfill.
Component Materials
Montmorillonite content
Min Average Max Notes
Backfill blocks Friedland clay, Germany % 30 34 38 Margin of error ±2 %, possible variance 28-40%
Foundation layer Bentonite granules from Milos, Greece % 75 80 90 Includes margin of error
Pellets Bentonite pellets from Milos, Greece % 75 80 90 Includes margin of error
Backfill block material In the process of determining the reference material for backfill blocks for Posiva’s repository concept, consideration was given to upgrading the clay used in the manufacture of backfill blocks to a material with higher smectite content than is present in the Friedland clay. Specifically, SKB’s backfill block material, IBECO RWC-BF (SKB 2010) was evaluated. Use of this material would result in an increase in the swelling capacity of the system for a given installed density. However, the higher dry density achieved in the manufacture of Friedland clay blocks (average dry density of 2030 kg/m3 at 6 % water content (Hansen et al. 2010, p. 29-30)), relative to the 1650 kg/m3 dry density achievable using the IBECO RWC-BF clay (Johannesson et al. 2010, p. 16), meant that there was very little difference in the EMDD (effective montmorillonite dry density) of these two block types. Calculating from the smectite content of the IBECO RWC-BF of 58 % defined by Olsson & Karnland (2009, p. 23) and dry density of the blocks (Johannesson et al. 2010, p. 16), the EMDD achieved for these IBECO RWC-BF blocks is 1060 kg/m3. Considering even the minimum dry density of Friedland clay blocks (1990 kg/m3) and smectite content of 28 %, the EMDD for these blocks is 1150 kg/m3 (Backfill Production line report, p. 79). This means that these two materials should exhibit very similar swelling pressure and hydraulic conductivity properties. Therefore, Friedland clay has remained the reference material for Posiva’s backfill block. SKB’s IBECO RWC-BF material is being kept as an alternative, but was not taken into account in the latest Posiva’s safety case (TURVA-2012). Foundation layer material In the 2009 design (Hansen et al. 2010) the two alternatives identified for foundation layer materials were (a) mixture of bentonite and ballast (40/60) and (b) bentonite pellets (or granules). Due to uncertainties in achieving the required dry density 1750 kg/m3 for the 40/60 mixture (Hansen et al. 2009, page 57) with in situ compaction in full-scale tests with a bentonite/crushed rock mixture with 30 % bentonite content (Hansen et al. 2009. p. 30) and uncertainties associated with self-sealing, volumetric swelling capacity and homogeneity of the material identified in newer data presented in Schatz & Martikainen (2012, p. 44, 61, 78, 101), the 40/60 mixture is no longer recommended for the foundation layer.
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The foundation layer options were then reduced to bentonite granules or pellets. As bentonite from Milos, Greece had been identified as the reference clay for use in the foundation layer, the pellet and granular forms were further assessed. The difference between the pellets and granules is only in the processing of bentonite (granules are raw bentonite and pellets are produced by pelletising the same material). For the 2012 deposition tunnel backfill design (this report), Milos bentonite granules were selected as the foundation layer material instead of bentonite pellets. This is due to the slightly better in situ compaction properties of the Milos bentonite granules compared to bentonite pellets (field tests performed by Wimelius & Pusch (2008, p. 41, Appendix 4)). An example of such a product that has also been used in the field tests (see e.g. Appendix 2) is the bentonite granules produced by Minelco AB. Bentonite pellets The selection for pellet material for use in deposition tunnel backfilling was kept the same as in the 2009 design reported by Hansen et al. (2010), i.e. bentonite from Milos, Greece, since most of the field and laboratory tests had been so far performed with Cebogel QSE pellets. Mineralogy and chemistry of the selected materials The mineralogy and chemistry of some suitable backfill materials as well as their physical properties are described in detail in the Backfill Production Line report. The key parameter associated with the behavior of the components of the deposition tunnel backfill is the acceptable range of smectite content of the materials. The average montmorillonite content and their acceptable variations in the clay materials selected for the current design are presented in Table 3-1. The design specifications for chemical properties are presented in Table 2-2.
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4 BACKFILL - DETAILED DESIGN 4.1 General The detailed design of the different backfill components presented in this chapter has been developed based on the conceptual design (Chapter 3) and design requirements described in Section 2.2.2. 4.2 Design of the foundation layer 4.2.1 Design requirements The foundation layer has the performance targets of the backfill, for example the hydraulic conductivity of the layer shall be <1x10-10 m/s (see Chapter 2, Table 2-1). In addition, the foundation layer shall provide stable and level surface for the block assemblage. So far, no exact values have been set for the levelness of the layer. This shall be done later when more data is available from installation tests done with both components (foundation layer and blocks) present in the test. However, the aim is to produce as level surface as reasonably possible. 4.2.2 Materials The material selected for the foundation layer is bentonite granules from Milos (see Section 3.2). The mineralogy, chemistry and physical properties of an example material are described in the Backfill Production Line report (p. 26-28). The compaction of an example foundation layer material (Minelco granules) and other bentonite materials has been studied using both conventional, fixed-energy techniques (e.g. Standard Proctor Compaction, Modified (Heavy) Proctor Compaction), as well as in field tests using fixed method compaction (e.g. vibratory plates by Wimelius & Pusch (2008, Appendix 4); heavy vibratory roller at Riihimäki (Appendix 2)). These tests have all shown that while density achieved increases with compactive effort applied, the density achieved by bentonite clay materials are little affected by the presence of water. An example of this lack of moisture sensitivity is shown in Figure 4-1. This means that there is a considerable degree of flexibility regarding the acceptable moisture content in foundation layer materials, easing the quality control requirements for this parameter. Other factors such as the effects of granularity on the compaction characteristics and densities practically achievable in a deposition tunnel are still topics that will require further study. The achieved density results obtained in a large installation trial conducted by Wimelius & Pusch (2008, Appendix 4) were selected to be used as the reference density for the foundation layer portion of the deposition tunnel backfill. This corresponds to an as-placed average dry density of 1250 kg/m3 (Wimelius & Pusch 2008, p. 43).
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Figure 4-1. Example of a standard Proctor compaction test result for Minelco granules (see Appendix 2 for results from Riihimäki foundation layer compaction tests). The relatively flat shape of the curve is due to the high smectite content of the material. The yellow dashed line is the zero air void line showing the water content at full saturation. 4.2.3 Dimensioning The dimensioning of the foundation layer is based on: - The dimensions of the tunnel floor (see Chapter 2 and Section 4.2.4 for details). - Dry density reached in field tests by Wimelius & Pusch (2008, p. 43): 1250 kg/m3
(+/- 100 kg/m3). In addition, a new set of field tests were performed in Riihimäki during 2011 verifying that this dry density can be reached, although there is a need for further optimisation of the compaction process and the equipment used in the tunnel conditions (Appendix 2).
- Hydraulic conductivity data by Johannesson & Nilsson (2006, Appendix 1, p. 51)
for Milos bentonites suggests that hydraulic conductivity <1x10-10 m/s is reached in the initial state even for the lowest expected initial dry density of 1150 kg/m3. According to newer data the hydraulic conductivity of Minelco granules compacted to dry densities between 1180 and 1210 kg/m3 varies between 1.1x10-10 m/s and 5.5x10-11 m/s (see Appendix 3).
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4.2.4 Design The top surface of the foundation layer is 150 mm above the theoretical excavation line, i.e. the foundation layer always has a thickness of at least 150 mm. The total local thickness of the foundation layer depends on the realised rock surface at the tunnel floor after excavation. The maximum allowed excavation tolerance at the floor is +400 mm from the theoretical excavation line (see Figure 4-2). This means that the thickness of the foundation layer varies between 150 and 550 mm, the average being 350 mm. The foundation layer material is Milos bentonite granules (see Section 3.2 Selection of backfill materials and the Backfill Production Line report, Section 3.2.1). The average dry density of the foundation layer is assumed to be 1250 kg/m3 (±100 kg/m3). This is based on field tests performed in the Äspö bentonite laboratory (Wimelius & Pusch 2008, p. 43). The main difference between the 2009 design (presented in Hansen et al. 2010, p. 49, 51) and updated design (this report) is the increased maximum thickness of the foundation layer from 380 mm (Hansen et al. 2010, p. 51) to 550 mm (see Figure 4-2). This increase is due to the fact that the design was adapted to the excavation tolerances applied for the ONKALO demonstration tunnels (for details see Section 2.4 Tunnel dimensions and volumes). The processing of the foundation layer material prior to installation and installation of the foundation layer are described in Backfill Production Line report (Section 4.8.1).
Figure 4-2. Basic dimensions of the foundation layer assuming a maximum excavation tolerance of 400 mm. The thickness of the layer varies between 150 mm and 550 mm.
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4.3 Design of block filling 4.3.1 Design requirements The block filling component has the performance targets of the backfill, see Chapter 2. As the component with highest initial dry density, the aim of block installation is to fill as much of the tunnel volume with blocks as possible. There are however, some limitations and conditions set for the design of this component: - The block size should be adapted to the tunnel dimensions (see Chapter 2) so that a
100 mm gap would be left between the outermost block row and the theoretical excavation surface. This dimension was suggested by Wimelius & Pusch (2008, p. 62) as being needed to permit operation of the tools required for pellet installation.
- In addition to operational-related reasons, a sufficiently wide pellet filled gap shall be left between the blocks and the rock. This gap is needed in order to decrease the risk of erosion of backfill blocks due to internal piping during the installation and early saturation phase by directing the water flow in the pellet fill. Based on a limited number of large-scale simulation tests, Dixon (2008b p. 69) estimated that where the pellet fill was typically <100 mm in thickness, a vulnerability to internal piping exists at point inflows of 0.25 l/min or more. However, in tests with pellet fill thickness ~150 mm this vulnerability seems to be reduced and a more stable behavior of system was observed (Dixon et al. 2008, p. 69). Taking into account the excavation tolerance (300 mm) set for the tunnels in Posiva’s concept and the uncertainties linked to homogenization of the block/pellet system, the thicker (150 mm), pellet fill dimension is not necessarily needed. The current guideline for the gap between the blocks and the theoretical excavation line is therefore defined as being ≥100 mm. This is a compromise that aims for as high a block filling degree as possible without compromising the mechanical stability of the system.
- Only one block size would be manufactured. However, the blocks could be cut in half if necessary.
- The block assemblage should have same dimensions (width and height) throughout the tunnel, i.e. the width and height would not be tailored to tunnel sections with different cross-sections. This is justified by the efficiency of the installation process and simple and reliable quality control process compared to an alternative where the block layout would be tailored to each tunnel section.
- The block filling degree should be as high as possible, within the constraints described above with special attention given to the block fill in the tunnel roof region. This high degree of block filling will increase density homogenisation rate in backfill and gain as high initial dry density for the backfill as possible.
- Blocks should overlap in 1-2 dimensions to gain better physical stability and rigidity for the block assemblage. This will decrease the risk of buffer swelling into the backfill and enhance operational safety.
4.3.2 Materials The material selected for the backfill blocks is Friedland clay, from Germany (see section Section 3.2). The mineralogy, chemistry and physical properties of the material are described in detail in the Backfill Production Line report (Sections 3.2.2,).
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4.3.3 Dimensioning The block width was dimensioned taking into account the width of the OL1-3 and LO1-2 tunnels (3500 mm) and the required 100 mm gap between the block assemblage and the theoretical rock surface. The height of the block was adapted to the tunnel height to allow as high block filling degree at the roof as possible. The dry density of the block was determined to be 2030 kg/m3 (+/- 40 kg/m3) based on experiences from full scale block compaction tests (Backfill Production Line report, p. 33). Two types of block dimensional tolerance were considered: manufacturing tolerances and installation tolerances. The maximum manufacturing tolerances for backfill blocks are from -1 mm to +2 mm (see Chapter 2, Design specifications) and the dimensions achieved result in average manufacturing variance range from -0.5 mm to +1 mm (Backfill Production Line report, p. 63-64). The blocks are assumed to be perfect rectangular prisms, i.e. their sides are assumed to be perfectly parallel. This in turn means that due to manufacturing tolerances, the empty space between any two blocks is at maximum 6 mm, and at minimum 0 mm (perfect blocks), and in average 3 mm. However, the variation from the nominal dimensions of block observed in block manufacturing tests have been in practice 0 mm in the width and length of the block and the variation has been present only in the height of the block (Backfill Production Line report, p. 64). Installation tolerances will also result in empty spaces between blocks, and gaps of this type will vary depending on the installation technique employed. Since the tolerances for the selected installation method are not verified in practice, the conservative approach used in this report is that the total tolerance is 5 mm in all vertical interfaces, leading to a void volume of 1.7 % within the whole block volume. The 5 mm tolerance is based on the gap width measured in the Riihimäki field test for a block assemblage made with blocks with a size of 300 x 300 x 150 mm and the manufacturing tolerance of ±1 mm (Riikonen 2009, p. 165). The range of measured gap widths was 0-5 mm, but the block installation was made by hand. For comparison, the total void volume measured for a fork truck placed block assemblage in the Äspö bentonite laboratory was 1.5 % (Wimelius & Pusch 2008, p. 48). The blocks used in that demonstration were made of concrete, with quite rough manufacturing tolerances hence the results obtained can be considered to be conservative. In horisontal joints the total tolerance is assumed to be 0 mm. More information on the total tolerance will be gained in further backfill installation tests. The top level of the foundation layer is always +150 mm above the theoretical tunnel floor level, and the block assemblage is built on top of this level. Since only one block size is to be used in deposition tunnel backfilling, the overlapping of the rows in the block assemblage is created by changing the direction of block in the assemblage.
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The longitudinal section of the block layout is dimensioned so that the steepness of the block front is approximately 45 degrees. This is a preliminary assumption and was used in outlining the design requirements for the block installation equipment. 4.3.4 Block design The dimensions of the backfill blocks are 550 x 470 x 330 mm as shown in Figure 4-3. Based on previous block production tests reported in Hansen et al. (2010), the estimated average dry density for backfill blocks of this dimension is 2030 kg/m3 (estimated from density of 2150 kg/m3 and water content of 6 % given in Hansen et al. 2010, p. 29-30) for blocks of comparable size. The range of dry density differences achieved is estimated to be ±40 kg/m3, which can be considered as conservative since in previous tests the range measured was ±25-30 kg/m3 (see Backfill Production Line report, p. 64). The gravimetric water content of the blocks is 9 % (±0.5 %) (Backfill Production Line report, p. 32). The other basic block properties are summarised in Table 4-1.
Figure 4-3. Dimensions of the backfill block (Backfill Production Line report, p. 33). Table 4-1. Basic block properties based on a block size of 550 x 470 x 330 mm (-1 mm/+2 mm) (Backfill Production Line report, p. 33).
Min Average Max
Volume m3 0.0847 0.0853 0.0865
Dry density kg/m3 1990 2030 2070
Dry mass kg 169 173 179
Water content % 8.5 9 9.5
Wet mass kg 183 189 196
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4.3.5 Design of the block layout The block layout for an Olkiluoto deposition tunnel cross-section (Figure 4-4, left) comprises of 12 layers of blocks. Block Orientation System-A is used for layers 1, 3, 5, 7 and 9 with six blocks in each layer, and Block Orientation System-B is used for layers 2, 4, 6, and 8 with seven blocks in each layer. At layer 10, where the arched zone of the tunnel starts, Block Orientation System-B has to be used to achieve the largest block filling degree, and layer 10 (six blocks), layer 11 (five blocks), and layer 12 (four blocks) all use Block Orientation System-B. The total number of blocks in the Olkiluoto tunnel cross-section is 73. As the height of the Loviisa deposition tunnel is slightly lower than that of the Olkiluoto deposition tunnel, only 11 layers of blocks are required (Figure 4-4, right). Block Orientation System-A is used for layers 1, 3, 5, and 7 with six blocks in each layer, and Block Orientation System-B is used for layers 2, 4, 6, and 8 with seven blocks in each layer. At layer 9 (six blocks), where the arched zone of the tunnel starts, Block Orientation System-B has to be used to achieve the largest block filling degree, and it is also used in layer 10 (five blocks). Block Orientation System-A is used in layer 11 (three blocks). The total number of blocks in the Loviisa tunnel cross-section is 66. Assuming a 5 mm total tolerance in all vertical interfaces, the remaining gap between the blocks and the theoretical tunnel cross-section using the current block installation geometry would be 87.5-90 mm. This is slightly less than the 100+ mm defined in the design. In order to maintain the minimum 100 mm tolerance, the block dimensions will need to be adjusted slightly. However, from a practical point of view, such size adjustment should only be made when data from the block manufacturing and installation tolerances with the single block installation method are available. The block filling degree from the theoretical (nominal) tunnel volume and what would be present in an average realized tunnel volume (+18 % from the theoretical volume) is 85.9 % and 72.8 % respectively for the OL1-3 tunnels. The Loviisa LO1-2 tunnels will exhibit 86.2 % and 72.5 % for the nominal and average realized tunnel volume (+19 % from the theoretical volume) conditions respectively (see Section 4.5 for volumes and masses). It should be noted that as stated in Section 2.4 (tunnel dimensions and volumes), it was assumed for this design that the theoretical tunnel cross-section is 14.1 m2 instead of 14 m2 presented in Saanio et al. (2010). The difference comes from the small chamfers in the lower corners of the theoretical tunnel cross section (marked with a dashed line to Figure 4-4). Since these chamfers were excluded from the ONKALO demonstration tunnel profiles, they were also excluded in the block layout design. The longitudinal section of block layout is presented in Figures 4-5 and 4-6 for OL1-3 and LO1-2 tunnels, respectively. In order to produce the overlapping of blocks in longitudinal section, portions of the first block row at the tunnel end need to be prepared from blocks cut in half. The details of the block layout will be updated when new data is available on the manufacturing and installation of the backfill components.
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Figure 4-4. Cross-section of the backfilled tunnel in the Olkiluoto case (on left) and Loviisa case (on right). The outer solid line presents the tunnel profile with maximum over excavation of +400 mm in the floor and +300 mm in the walls/roof. The inner solid line presents the theoretical excavation line (Backfill Production Line report, p. 36).
Figure 4-5. Longitudinal section for OL1-3 tunnels.
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Figure 4-6. Longitudinal section for LO1-2 tunnels. 4.4 Pellet filling design 4.4.1 Design requirements The pellet fill is used for filling the empty space between the backfill blocks and the rock. Another function for the pellet fill is to act as a water storage medium during the installation phase of the backfill. This water retention capacity helps in preventing problems with the water inflows during the installation of the backfill, e.g. formation of piping channels and erosion of backfill blocks. In addition, the pellet fill with sufficient water storing capacity helps distribute the water more uniformly in the backfill in later stages of the saturation process. The pellet filling has the long-term performance targets of the backfill (see Chapter 2). However, right after installation and prior to saturation of the system some of these requirements are not yet met. Along with saturation of the system, the backfill blocks will compress the pellets to a density state where the performance targets set for the backfill are met also for the pellet fill. 4.4.2 Materials The selected pellet material is an extruded type of bentonite pellet from Milos. An example of this pellet type is Cebogel QSE pellets used earlier in many of the field tests by Posiva and SKB (Riikonen 2009, Dixon et al. 2011a, 2011b). This pellet type has an advantage of good water storing capacity as seen in tests by Sandén et al. (2008, p. 41). The mineralogy, chemistry and physical properties of the Cebogel QSE pellets are described in the Backfill Production Line report, (p. 30-31). As an example, the dimensions of Cebogel QSE pellets manufactured with the extrusion method are shown in Figure 4-7. The length of the Cebogel QSE pellets of this particular batch varied more than typically observed. It should be noted that, if needed,
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the pellet length can be controlled in the manufacturing process by cutting and selective screening. Kim et al. (2012, p. 46) found that the Cebogel QSE product had an individual pellet bulk density of approximately 2070 kg/m3 at a gravimetric water content of 15.6 %. This corresponds to a dry density (individual pellet) of approximately 1800 kg/m3. The EMDD of an individual Cebogel QSE pellet is approximately 1600 kg/m3 (Kim et al. 2012, p. 46). Based on crushing tests, the Cebogel QSE pellets showed reasonably good crush strength compared to other pellets tested (see Kim et. al. 2012, p. 54).
Figure 4-7. Length and diameter distributions of Cebogel QSE pellets as percentages of the total number of measured pellets.
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4.4.3 Dimensioning The empty space between the blocks and the surrounding rock (see Figure 4-4) provides the geometrical constraints for the pellet fill. The achieved as-placed dry density of the pellet fill depends on the dry density of individual pellet but also on the installation equipment and the working procedure. There are following limitations and conditions affecting the minimum and maximum thickness of the pellet fill: - Tunnel dimensions (Fig. 4-4). - Excavation tolerance of 300 mm (Fig. 4-4). - Dimensions of the block layout (Fig. 4-4). - Minimum space needed to install the pellets. At least a 100 mm gap shall be left
between the outermost block row and the theoretical excavation surface. This dimension was suggested by Wimelius & Pusch (2008, p. 62) as being needed to permit operation of the tools required for pellet installation.
- In addition to operational-related reasons, a sufficiently wide pellet filled gap shall be left between the blocks and the rock. This gap is needed in order to decrease the risk of erosion of backfill blocks due to internal piping during the installation and early saturation phase by directing the water flow in the pellet fill. Based on a limited number of large-scale simulation tests, Dixon (2008b p. 69) estimated that where the pellet fill was typically <100 mm in thickness, a vulnerability to internal piping exists at point inflows of 0.25 l/min or more. However, in tests with pellet fill thickness ~150 mm this vulnerability seems to be reduced and a more stable behavior of system was observed (Dixon et al. 2008, p. 69). Taking into account the excavation tolerance (300 mm) set for the tunnels in Posiva’s concept and the uncertainties linked to homogenization of the block/pellet system, the thicker (150 mm), pellet fill dimension is not necessarily needed. The current guideline for the gap between the blocks and the theoretical excavation line is therefore defined as being ≥100 mm. This is a compromise that aims for as high a block filling degree as possible without compromising the mechanical stability of the system.
4.4.4 Design The thickness of the pellet fill depends on the block assemblage and the realized tunnel volume. The maximum excavation tolerance of +300 mm beyond the theoretical tunnel together with the current block layout and a 100 mm minimum gap between the backfill blocks and the tunnel profile means that the maximum pellet thickness along the walls is 400 mm and the minimum is 100 mm. From these limits, an average pellet thickness of 250 mm results. In the roof section the maximum pellet thickness varies as presented in Figure 4-4 and is at maximum 635 mm. At the blind end of deposition tunnel it is presumed that there will be a gap between the block pile and the end wall. The gap size will vary as the result of the uneven face of the rock at the end of the tunnel and will be between 100 and 400 mm. This gap will be filled with pellets in two phases during block installation. In the first phase, pellets will be filled after the block pile attains half of the tunnel height. The rest of the pellets will be installed after the block pile has reached the final height.
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Previous field tests, reported by Wimelius & Pusch (2008, p. 51, 55, 60, 66), Sandén et al. (2008, p. 29, 30, ) and Dixon et al. (2008a, p. 23) achieved as-placed dry density range of 900-1100 kg/m3 for the installed pellet fill. Water was added to the pellet fill during installation to improve placement effectiveness, and based on previous experience from field tests presented in Keski-Kuha et al. (2013), the initial as-placed water content (including construction water) of the pellet fill is expected to be on average 27.5 % (±10 %). 4.5 Volumes and masses The volume and masses for each component per metre of tunnel length and for a 300 m long tunnel are presented in Tables 4-2 and 4-3 for OL1-3 and LO1-2 cases respectively. The variations in the amount of pellets and foundation layer are due to variations in the tunnel volume (see Chapter 2).
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Table 4-2. Volumes and masses of backfill component for one tunnel metre and for a 300-m long tunnel for the OL1-3 canisters. The max case refers to a case with maximum possible tunnel volume and the minimum case to a case with theoretical tunnel volume. Excavation tolerances Max Average Min
Roof and walls mm 300 150 0
Floor mm 400 200 0
Cross‐section areas from the design
Theoretical tunnel cross-section* m2 14.10 14.10 14.10
Realised cross-section with tolerances m2 19.18 16.64 14.10
Over-break-% % 36.00 18.00 0.00
Volumes per one tunnel metre
Blocks (with gaps) m3 12.32 12.32 12.32
Blocks (without gaps) m3 12.11 12.11 12.11Gaps between the blocks (1.7 % of the total block volume) m3 0.21 0.21 0.21
Foundation layer m3 2.26 1.39 0.53
Pellets m3 4.60 2.93 1.26
Total volume of all backfill components m3 19.18 16.64 14.10
Block filling degrees Block filling degree from theoretical/nominal tunnel volume % 85.89
Block filling degree from realised tunnel volume % 63.15 72.79 85.89
Initial as-placed dry densities
Blocks kg/m3 2030 2030 2030
Pellets kg/m3 1000 1000 1000
Foundation Layer kg/m3 1250 1250 1250
Total dry masses per 1 m
Blocks kg 24 584 24 584 24 584
Pellets kg 4596 2926 1255
Foundation Layer kg 2825 1741 656
Total mass of all backfill components kg 32 005 29 251 26 496
Total dry masses per 300 m
Blocks tons 7375 7375 7375
Pellets tons 1379 878 377
Foundation Layer tons 848 522 197
Total masses of all components tons 9602 8775 7949Average dry density after saturation and homogenisation kg/m3 1669 1758 1879
*Excluding small chamfers at the lower corners in the tunnel profile.
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Table 4-3. Volumes and masses of backfill component for one tunnel metre and for a 300-m long tunnel for the LO1-2 case. The max case refers to a case with maximum possible tunnel volume and the min case to a case with theoretical tunnel volume. Excavation tolerances Max Average Min
Roof and walls mm 300 150 0
Floor mm 400 200 0
Cross‐section areas from the design
Theoretical tunnel cross-section* m2 12.70 12.70 12.70
Realised cross-section with tolerances m2 17.53 15.11 12.70
Over-break-% % 38.00 19.00 0.00
Volumes per one tunnel metre
Blocks (with gaps) m3 11.14 11.14 11.14
Blocks (without gaps) m3 10.95 10.95 10.95Gaps between the blocks (1.7% of the total block volume) m3 0.19 0.19 0.19
Foundation layer m3 2.26 1.39 0.53
Pellets m3 4.13 2.58 1.04
Total volume of all backfill components m3 17.53 15.11 12.70
Block filling degrees Block filling degree from theoretical/nominal tunnel volume % 86.23
Block filling degree from realised tunnel volume % 62.48 72.46 86.23
Initial as-placed dry densities
Blocks kg/m3 2030 2030 2030
Pellets kg/m3 1000 1000 1000
Foundation layer kg/m3 1250 1250 1250
Total dry masses per 1 m
Blocks kg 22 230 22 230 22 230
Pellets kg 4126 2581 1035
Foundation layer kg 2825 1741 656
Total mass of all backfill components kg 29 181 26 551 23 921
Total dry masses per 300 m
Blocks tons 6669 6669 6669
Pellets tons 1238 774 311
Foundation layer tons 848 522 197
Total masses of all components tons 8754 7965 7176Average dry density after saturation and homogenisation kg/m3 1665 1757 1884
*Excluding small chamfers at the lower corners in the tunnel profile.
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4.6 Performance The initial state and the compliance with the design requirements of the deposition tunnel backfill are discussed in the Backfill Production Line report (Chapter 5) and Description of the Disposal System (Chapter 8). The long-term performance is discussed in the Performance Assessment (Chapter 3). For OL1-3 tunnels, dry density of backfill at initial state varies between 1608 and 1924 kg/m3, the average being 1758 kg/m3
. For LO1-2 tunnels, the dry density of backfill at initial state varies between 1603-1928 kg/m3 with an average of 1757 kg/m3
.
The majority of the variance comes from the excavation tolerances and if smaller density variance is required, the best option would be to optimise the tunnel excavation techniques (Backfill Production Line report, p. 81). The initial range for EMDD (effective montmorillonite dry density, kg/m3) gained with the design comes from the range of initial component dry densities, excavation tolerances and range in the smectite content of the backfill materials (Backfill Production Line report, p. 83). After saturation and homogenisation, the estimated EMDD for the design is between 1000-1300 kg/m3 as shown in Figure 4-8 and 4-9 for OL1-3 and LO1-2 tunnels respectively (Backfill Production Line report, p. 83).
Figure 4-8. Average effective montmorillonite dry density (EMDD) for the Olkiluoto case taking into account the montmorillonite content in all backfill components (Backfill Production Line report, p. 83).
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Figure 4-9. Average effective montmorillonite dry density (EMDD) for the Loviisa case taking into account the montmorillonite content in all backfill components (Modified based on Backfill Production Line report, p. 84). The hydraulic conductivity provided by the design is between 1x10-11 and 1x10-12 m/s in a variety of groundwater salinities (up to 70 g/L) (Backfill Production Line report, p. 87). At the initial state conditions, the swelling pressure of the backfill components will range from few hundred kPa up to 6-7 MPa (Backfill Production Line report, p. 91). However, assuming density homogenisation of the backfill, the range of swelling pressure developed is expected to be 1-3 MPa (Backfill Production Line report, p. 91). The main uncertainty in longer-term backfill performance is related to the manner in which homogenisation of the system components occurs. There is positive laboratory scale data available on the homogenisation (see Backfill Production Line report), but more information is needed from larger-scale tests and numerical modeling to verify that sufficient homogenisation takes place in the backfill. The uncertainties in achieving the estimated initial state are largely dependent on block installation technique (not yet tested in practice) and whether the quality control measures put into place during backfill installation can ensure that each of the backfill components meets their initial state requirements.
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5 SUMMARY This report has presented the design basis for the KBS-3V deposition tunnel backfill as well as the backfill design 2012. The purpose of the backfill is to keep the buffer in place, maintain favourable and predictable conditions for the buffer and the canister, and also favourable rock mechanical, hydrological and geochemical conditions in the near-field and to retard the transport of released radionuclides in case of canister failure. In practice this means that the backfill shall consist of material with swelling ability and good long-term stability in the expected repository conditions. The deposition tunnel backfill design concept has remained fundamentally unchanged since the previous backfill design (2009) reported in Hansen et al. (2010). The backfill consists of three main components: a foundation layer, clay blocks and bentonite pellet filling. The main differences between this design and the 2009 design are the following: - No alternative materials are presented for the backfill components. - The block size has been optimised to provide higher block filling degree, aiming for
a better system homogenisation. - The block layout has been updated to have overlapping of blocks in two dimensions
to provide more stable and rigid backfill. This aims for decreasing the risk for swelling of buffer into backfill and for better physical stability and therefore better operational safety during installation.
The backfill materials are Friedland clay for backfill blocks, Milos bentonite granules for the foundation layer and extruded Milos bentonite pellets for the pellet filling. The selection of the materials was done by Posiva in 2011 based on the data available on the materials at that time. The selected materials are described in detail in the Backfill Production Line report. The block filling degree gained with the new backfill placement design is >85 % from the theoretical/nominal tunnel volume. From the average realized tunnel volume, the block filling degree is >72 % providing an average dry density of ~1760 kg/m3. The initial state and compliance to design requirements is presented in the Backfill Production Line report. The long-term performance is described in the Performance Assessment. The main uncertainty linked to the backfill performance is linked to the homogenisation of the system. There is supporting laboratory scale data available on backfill homogenisation (see Backfill Production Line report), but more information is needed from larger-scale tests and numerical modeling to verify that sufficient homogenisation takes place in the backfill. The uncertainties in achieving the initial state are mostly linked to block installation technique (not yet tested in a repository environment) and whether the quality control measures are sufficient to ensure system compliance with the design specifications.
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47
REFERENCES SAFCA and PRL report references throughout the report: Backfill Production Line 2012 – Design, production and initial state of the deposition tunnel backfill and plug. Posiva Oy, Eurajoki, Finland. Posiva 2012-18. Buffer Production Line 2012 – Design, production and initial state of the buffer. Posiva Oy, Eurajoki, Finland. Posiva 2012-17. Closure Production Line 2012 – Design, production and initial state of underground disposal facility closure. Posiva Oy, Eurajoki, Finland. Posiva 2012-19. Olkiluoto Site Description 2011, Posiva Oy, Eurajoki, Finland. Posiva 2011-02. Safety case for the disposal of spent nuclear fuel at Olkiluoto – Performance Assessment 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-04. Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto – Design Basis 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-03.
Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto – Description of the Disposal System 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-05.
Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto – Features, Events and Processes 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-07.
Underground Openings Production Line 2012 – Design, production and initial state of the underground openings. Posiva Oy, Eurajoki, Finland. Posiva 2012-22. Pending. References in alphabetical order (other than SAFCA and PLR reports): Dixon, D., Anttila, S., Viitanen, M. & Keto, P. 2008a. Tests to determine water uptake behavior of tunnel backfill (Backlo Tests at Äspö). Svensk Kärnbränslehantering AB, Stockholm, Sweden. SKB R-08-134. Dixon, D., Lundin, C., Örtendahl, E., Hedin, M. & Ramqvist, G. 2008b. Deep repository – Engineered Barrier System: Half-scale tests to examine water uptake by bentonite pellets in a block-pellet backfill system. Svensk Kärnbränslehantering AB, Stockholm, Sweden. SKB R-08-132. Dixon, D., Jonsson, E., Hansen, J., Hedin, M. & Ramqvist, G. 2011a. Effect of Localized Water Uptake on Backfill Hydration and Water Movement in a Backfilled Tunnel: Half-Scale Tests at Äspö Bentonite Laboratory. Svensk Kärnbränslehantering AB, Stockholm, Sweden. SKB R-11-27.
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Dixon, D., Sandén, T., Jonsson, E. & Hansen, J. 2011b. Backfilling of deposition tunnels: Use of bentonite pellets. Svensk Kärnbränslehantering AB, Stockholm, Sweden. SKB P-11-44. Government Decree (736/2008) on the safety of nuclear waste. Issued in Helsinki 27 November 2008. Finnish Acts of Parliament. Hansen, J., Korkiala-Tanttu, L., Keski-Kuha, E. & Keto, P. 2010. Deposition tunnel backfill design for a KBS-3V repository. Posiva Oy, Olkiluoto, Finland. Working Report 2009-129. Hartley, L., Hoek, J., Swan, D. & Roberts, D. 2010. Hydrogeological discrete fracture network modeling of groundwater flow under open repository conditions. Posiva Oy, Eurajoki, Finland. Working Report 2010-51. Hartley, L., Appleyard, P., Baxter, S., Hoek, J., Roberts, D. & Swan D. 2012. Development of a hydrogeological discrete fracture network model for the Olkiluoto Site: Descriptive model 2011. Posiva Oy, Eurajoki, Finland. Working Report 2012-32. Hellä, P. (ed.), Ikonen, A., Mattila, J., Torvela, T. & Wikström, L. 2009. RSC-Programme – Interim Report. Approach and Basis for RSC Development, Layout Determing Features and Preliminary Criteria for Tunnel and Deposition Hole Scale. Posiva Oy, Olkiluoto, Finland. Working Report 2009-29. Ikonen, K. 2009. Thermal dimensioning of the repository for spent fuel. Posiva Oy, Eurajoki, Finland. Working Report 2009-69. Johannesson, L-E. & Nilsson, U. 2006. Deep repository – engineered barrier systems. Geotechnical behavior of candidate backfill materials. Laboratory tests and calculations for determining performance of the backfill. Svensk Kärnbränslehantering AB., Stockholm, Sweden. SKB R-06-73. Johannesson, L-E., Sanden, T., Dueck, A. & Ohlsson, L. 2010. Characterization of a backfill candidate material, IBECO-RWC-BF. Svensk Kärnbränslehantering AB, Stockholm, Sweden SKB R-10-44. Juvankoski, M. 2010. Description of basic design for buffer. Posiva Oy, Eurajoki, Finland. Working Report 2009-131. Juvankoski, M. 2012. Buffer Design 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-14. Karnland, O., Olsson, S. & Nilsson, U. 2006. Mineralogy and sealing properties of various bentonites and smectite-rich clay materials. Svensk Kärnbränlehantering AB, Stockholm, Sweden. SKB TR-06-30.
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Keski-Kuha, E., Nemlander, R. & Koho, P. 2013. Flow-through, open-front and saturation tests of pre-compacted backfill blocks in a quarter-scale test tunnel. Posiva Oy, Eurajoki, Finland. Working Report 2012-41. Publication pending. Keto, P., Dixon, D., Gunnarsson, D., Johansson, E., Börgesson, L. & Hansen, J., 2009. Assessment of backfill design from KBS-3V repository. Posiva Oy, Olkiluoto, Finland. Working Report 2009-115. Kim, C-S., Man, A., Dixon, D.A., Holt, E. & Fritzell, A. 2012. Clay-Based Pellets for Use in Tunnel Backfill and as Gap Fill in a Deep Geological Repository: Characterisation of Thermal-Mechanical Properties, Nuclear Waste Management Organisation, Technical Report NWMO TR-2012-05, Toronto. Kirkkomäki, T. 2012. Loppusijoituslaitoksen asemointi ja vaiheittainen rakentaminen 2012. Posiva Oy, Eurajoki, Finland. Working Report 2012-69. Koskinen, V. 2012. Uniaxial backfill block compaction. Posiva Oy, Eurajoki, Finland. Working Report 2012-21. Kumpulainen, S. & Kiviranta, L. 2010. Mineralogical and chemical characterization of various bentonite and smectite-rich clay materials. Part A: comparison and development of mineralogical characterization methods. Part B: mineralogical and chemical characterization of clay materials. Posiva Oy, Olkiluoto, Finland. Working Report 2010-52. Leoni, M. 2013. 2D and 3D finite element analysis of buffer-backfill interaction. Posiva Oy, Eurajoki, Finland. Posiva 2012-25. Publication pending. Löfman, J. & Poteri, A. 2008. Groundwater Flow and Transport Simulations in Support of RNT-2008 Analysis. Posiva Oy, Olkiluoto, Finland. Working Report 2008-52. Löfman, J., Mészéros, R., Keto, P., Pitkänen, P. & Ahokas, H. 2010. Modelling of Groundwater Flow and Solute Transport in Olkiluoto – Update 2008. Posiva Oy, Eurajoki, Finland. Working Report 2009-78. Löfman, J. & Karvonen, T. 2012. Simulations of Hydrogeological Evolution at Olkiluoto. Posiva Oy, Eurajoki, Finland. Posiva 2012-35. McEwen, T. (ed.), Aro, S., Hellä, P., Kosunen, P., Käpyaho, A., Mattila, J., Pere, T. & RSC working group. 2012. Rock suitability classification, RSC-2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-24. Olsson, S. & Karnland, O. 2009. Characterisation of bentonites from Kutch, India and Milos, Greece – some candidate tunnel back-fill materials? Svensk Kärnbränlehantering AB, Stockholm, Sweden. SKB R-09-53.
Posiva Oy. 2012. Image gallery. www.posiva./en/databank/image_gallery/. Referred in 15.2.2012.
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Raiko, H. 2012. Canister Design 2012. Posiva Oy, Eurajoki, Finland. Posiva 2012-13.
Riikonen, E. 2009. Flow-through and wetting tests of pre-compacted backfill blocks in a quarter-scale test tunnel. Posiva Oy, Eurajoki, Finland. Working Report 2008-89. Saanio, T. (ed.), Ikonen, A., Keto, P., Kirkkomäki, T., Kukkola, T., Nieminen, J. & Raiko, H. 2010. Outline Design of the Disposal Facility 2009. Posiva Oy, Eurajoki, Finland. Working Report 2010-50. Saanio, T. Ikonen, A., Keto, P., Kirkkomäki, T., Kukkola, T., Nieminen, J. & Raiko, H. 2012. Design of disposal facility 2012. Posiva Oy, Eurajoki, Finland. Working Report 2012-50. Sandén, T., Börgesson, L., Dueck, A., Goudrazi, R. & Lönnqvist, M. 2008. Deep repository – Engineered barrier system; Erosion and sealing processes in tunnel backfill materials investigated in laboratory. Svensk Kärnbränlehantering AB, Stockholm, Sweden. SKB R-08-135. Schatz, T. & Martikainen, J. 2012. Laboratory tests and analyses on potential Olkiluoto backfill materials. Posiva Oy, Eurajoki, Finland. Working Report 2012-74. SKB. 2010. Design, production and initial state of the backfill and plug in deposition tunnels. Svensk Kärnbränlehantering AB, Stockholm, Sweden. SKB TR-10-16. SKB 2011. Long-term safety for the final repository for spent nuclear fuel at Forsmark. Main report of the SR-Site project. Volumes I-III. Stockholm, Sweden: Swedish Nuclear Fuel and Waste Management Co. (SKB) Technical Report TR-11-01. 893 p. ISSN 1404-0344. Tanskanen, J. (ed.) 2009. Facility description 2009 (in Finnish). Posiva Oy, Eurajoki, Finland. Working Report 2009-123. Wimelius, H. & Pusch, R. 2008. Backfilling of KBS-3V deposition tunnels – Possibilities and Limitations. Svensk Kärnbränslehantering AB, Stockholm, Sweden. SKB R-08-59. YVL Guide D.5. Regulatory Guides on nuclear safety (YVL). Nuclear waste disposal.OHJE YVL D.5, Luonnos 4 /17.3.2011.
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LIST OF APPENDICES
1. Deposition tunnel volumes (OL1-4 and LO1-2 case). 2. Foundation layer field tests in Riihimäki 3. Laboratory tests for materials used in Riihimäki foundation layer tests
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APPENDIX 1: Deposition tunnel volumes, OL1-4 and LO1-2 These volumes have been defined by Timo Kirkkomäki/Fortum Oyj (9/2012) from the 3D model of the repository (9000tU layout, including tunnels from OL4).
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6 7 APPENDIX 2: Foundation layer field tests in Riihimäki
Laatija Olli Salo
Tarkastajat
Petri Koho (Posiva Oy) Nina Sacklén
Hyväksyjä
Reijo Riekkola
pvm. 4.6.2013
pvm. 4.7.2013
pvm.
4.7.2013 Backfill Design 2012 –raportin liite loppusijoitustunnelin lattian asennuskokeista.
Asiakirjatunnus PROJEKTI-1161-02/2013
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1 INTRODUCTION The main purpose of the foundation layer in deposition tunnel backfill is to establish a levelled plane surface for the bentonite block assemblage. In addition, foundation layer prohibits water flow in rock backfill interface. During construction of the foundation layer on site, the confined space set its own boundary conditions for the dimensions of the equipment and applicable working methods. Regardless of the limiting factors, the foundation layer has to have high enough density to prevent the water flow in the material as well as in the backfill material rock interface. Before installation of the bentonite blocks the foundation layer surface can be machined to attain as levelled foundation for the assemblage of blocks as possible. The foundation layer has to preserve its stability also after installation of the blocks to enable the designed block filling degree, even if the foundation layer gets wet during backfilling operations. Foundation layer materials and design approaches have been studied before by Wimelius & Pusch (2008) in laboratory scale. The aim of this experimental study is to: Show that predefined criteria regarding foundation layer density is possible to attain
in full scale Define the load bearing capacity of the foundation layer Determine if there are other factors to consider before a functional foundation layer
is possible to construct Examine different working methods in the construction of a foundation layer.
The experimental full scale study was intended to model the actual tunnel environment. The width of the test fields was the same as in deposition tunnel and the used equipment was chosen to fit in the excavation profile of the actual tunnel. Some limitations had to be done because of the viability of research and weather conditions. Things that were not observed during testing: Foundation layer's ability to absorb water Swelling of the field after wetting.
No counter weights (block assemblage) were used over the fields to enable measuring and observation of the test fields.
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2 EXPERIMENTS 2.1 Test description The experimental study of the deposition tunnel foundation layer construction comprised of three phases. First phase, the laboratory testing, took place in august 2011. Second phase, the working method field tests (WMFT), commenced 14.9.2011 and lasted until 24.10.2011. The last phase, the field tests (FT), commenced right after dismantling WMFT:s and lasted until 15.11.2011. In the laboratory testing preliminary water content values were determined for the materials. In the WMFT phase, execution of the test fields was studied and in the FT phase the information from WMFT phase was further refined. In the empirical testing phases (WMFT and FT) also different working methods, construction tools and measuring equipment were examined. The reference material for the testing is high quality sodium activated calcium bentonite from Milos, Greece (MG) and the other tested material is a mixture of crushed rock and AC200 bentonite (CRB, mixing ratio 50:50). Both materials had been investigated before. The bentonite content of crushed rock bentonite was increased by 10% from previously used 40% to improve the performance of the foundation layer in long-term (Hansen et al. 2010). The large scale testing for granulated bentonite from Milos was done previously at laboratory in Sweden by SKB (Wimelius & Pusch 2008). The aim was to gain as high density for the layers as possible with the in situ compaction techniques. Tested materials have different target densities that were set to approximately 85-90% of the material specific Proctor maximum dry density, based on the assumption that larger dry densities would be difficult to achieve with in situ compaction techniques. These target densities were 1640 kg/m³ for the crushed rock bentonite and 1250 kg/m³ for the Milos granules. In addition, dry density of ~1250 kg/m3 had been already gained in earlier field tests by Wimeilus & Pusch (2008). Based on the data presented in Johannesson & Nilsson (2006) the dry density of 50:50 CRB should be at least 1560 kg/m³. This limit was set based on deformation properties. For hydraulic conductivity (1x10-10 m/s), dry density of 1420 kg/m³ was found to be sufficient (Johannesson & Nilsson 2006). Similar properties had not been determinced for Milos granules, but based on laboratory data for other Miloan bentonites (Martikainen & Schatz 2011, Johannesson & Nilsson 2006, Johannesson et al. 2010), the material should be able to fulfil the dry density of 1250 kg/m³. The load bearing capacity and density of the fields were measured daily. Also visual observations were made and recorded during observation period. 2.2 Laboratory testing The main goal for the laboratory testing was to determine the water content of the materials for the field testing phase. Preliminary mixes were done for multiple different water contents and the maximum achievable dry density was determined with Proctor
56
compaction test. Also ICT (intensive compaction tester) was used to determine the work needed to achieve specified density result with different water contents. Water content was measured with conventional oven, infrared and microwave oven drying, conventional oven drying being the reference solution. Images of the laboratory testing phase are presented in Figure 1.
Figure 1. Images from laboratory testing phase. Proctor compaction device (left), ICT –cylinders (middle), water content sample from microwave oven (right). 2.3 Test fields Test fields were built to a large tent which served as a weather shelter during testing period. In the WMFT phase two fields (3,5 m by 5 m) were built, one for each tested material. The nominal thickness of the WMFT was 550 mm. The inclination of the slope ramp to the field top was approximately 33 %. The long borders of the fields were sustained with concrete elements. The L –shaped, 2 meter long elements were fixed with compacted crushed rock to the asphalt base. In the FT phase two 550 mm and two 150 mm thick fields were built. The external dimensions and inclination of the slope ramps of all of the fields remained same as in the WMFT phase. Test field layout in the FT phase is presented in Figure 2.
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Figure 2. Layout of the test fields in the FT phase. MG stands for Milos granules and CRB is an abbreviation for chrushed rock bentonite. 2.4 Test conditions Duration of the WMFT phase was from 14.9.2011 to 24.10.2011. Average temperature during the WMFT was 7.9 ± 3.9 °C and the minimum temperature -1.6 °C. Artificial watering system in the WMFT:s was in use during 29.9. - 24.10.2011. Because of problems with weather data equipment no weather data was collected between 19.9.2011 and 14.10.2011. Duration of the FT phase was from 25.10.2011 to 15.11.2011. Average temperature during the WMFT was 5.8 ± 3.0 °C and the minimum temperature -4.6 °C. Artificial watering system in the FT:s was in use during 28.10. - 15.11.2011 for 550 mm fields and during 31.10. - 15.11.2011 for 150 mm fields. The weather data during FT:s is presented in Figure 3.
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Figure 3. Weather data inside the testing tent during the FT:s. Continuous line, temperature in °C and dotted line relative humidity in %. 2.5 Preparations Materials were mixed and the water content was adjusted to predefined optimum (see Section 2.7 for detailed information) in a batching plant before spreading the materials to the fields for compaction. The water addition rate was adjusted depending on the material. The added water was drinkable freshwater. The added water was weighted and dispensed as a fine water mist to the mixer with four nozzles presented on the right in Figure 4.
Figure 4. The mixer and the nozzles used for dosing water.
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In the WMFT and the FT phase saline water was conducted with land drain carpets to the asphalt bentonite interface. The aim was to study the effect of saline water to the installed foundation layer. Also the effect of dripping water on foundation layer was tested. Salinity of the conducted water during the WMFT and the FT was 2.15 ± 0.09% or 21,5 g/l TDS. Average water flow rate under the fields during the WMFT phase was 0.211 l/min and in FT phase 0.201 l/min. Land drain carpet was covered with filter clothes from both sides to prevent clogging of the plastic net. Conceptual image of the land drain carpet is presented in Figure 5. Saline water was mixed and warmed (to prevent freezing) in water container before dispensing to the fields. The target water flow was set to 0.250 l/min for each field in both of the testing phases. The artificial watering system of the FT phase is presented in Figure 6. The water distribution system of the WMFT phase was similar. The saline water didn’t freeze during testing period.
Figure 5. The structure of the land drain carpet used for conduction of saline water to bentonite fields.
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Figure 6. Artificial watering system flow chart in FT phase. 2.6 Working methods and equipment The WMFT fields were compacted in three compaction layers. In the FT phase two compaction layers were used (300 mm / 250 mm). In FT- phase thinner 150 mm fields were compacted at once. In the FT phase the surface of the first compacted layer was disrupted with excavator bucket corner before compaction of the final layer to make the structure more solid. All construction equipment were chosen considering the size of the deposition tunnel. Mini excavator was used for deployment of the materials and dismantling of the test fields. Different sizes of vibratory rollers (from 7 to 13 tons) were used during testing period. A 480 kg vibrating plate was tested for compaction of the border areas of the test fields. Some of the compaction equipment used during testing are presented in Figure 7.
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Figure 7. Compaction equipment used during testing. Sand and water volumeters tests were used to determine water content and the density of the compacted field surface layer. Measured values were used to calibrate the Troxler moisture density gauge results. Troxler was used to evaluate the compaction results and to monitor the development of wet density results during the test period (Figure 8). Loadman and plate loading tests were used to monitor the load bearing capacity of the fields. Loadman was used for continuous monitoring and plate loading test for calibration of the Loadman results. Field and layer thicknesses as well as measuring points were defined with a tachymeter.
Figure 8. Troxler, moisture density gauge used for evaluation of the compaction results.
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2.7 Tested materials Dry density curve as a function of water content for Milos granules is presented in Figure 9. ICT –compaction test results for Milos granules are presented in Table 1. Average grain size distribution for the Milos granules is presented in Figure 10. Grading curve is a composite of dry sieving and laser diffraction based test results. Dry sieving was used to obtain grain size distribution results for sieve sizes from 0,063 mm upwards and laser diffraction method for smaller grain sizes.
Figure 9. Proctor compaction test results, Milos granules.
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*The water content was chosen from the dry end of the optimum water content curve regarding workability. If the water content was lower, the material dusted and the compaction turned out to be challenging. If the water content was too high the material begun to stick to the working equipment.
Table 1. ICT -test results for MG. ICT pressure used was 300 kPa. Water content [%] ICT rounds Dry density [kg/m³] 15,40 % 200 1365,2 17,38 % 200 1310,6 19,15 % 200 1288,7 20,64 % 200 1312,4 20,64 % 21 1265,3 21,12 % 200 1292,4 21,12 % 23 1260,3 21,33 % 200 1276,2 23,99 % 200 1292,8 25,09 % 16 1241,9 27,41 % 200 1302,2 28,18 % 39 1244,0 29,78 % 31 1253,9 29,94 % 200 1326,5
Figure 10. Grain size distribution curve for Milos granules (batch 7.9.2011). In the WMFT phase water content of the MG was 25.2 ± 0.5 % (target 25 %*). The water content of delivered MG before water addition (measured from batch 17.10.2011, FT phase) was 13.3 ± 0.9 %. Measured FT phase water content was 26.6 ± 1.0 % (target 27.5 %*).
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Dry density curve as a function of water content for CRB is presented in Figure 11. ICT –compaction test results for crushed rock bentonite are presented in Table 2. Wet sieving results for the Olkiluoto crushed rock is presented in Figure 12.
Figure 11. Proctor compaction test results, crushed rock bentonite. Table 2. ICT -test results for CRB. ICT pressure used was 300 kPa. Water content [%] ICT rounds Dry density [kg/m³] 8,90 % 100 1581,8
10,07 % 100 1531,6
10,30 % 100 1521,0
10,32 % 90 1602,5
13,49 % 100 1613,7
14,34 % 100 1616,3
15,29 % 67 1660,6
16,54 % 100 1599,2
18,61 % 100 1653,5
20,56 % 100 1627,5
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Figure 12. Grain size distribution for the Olkiluoto crushed rock. In the WMFT phase water content of the CRB was 15.4 ± 0.3 % (target 15.6 %). Water content of crushed rock stored in a weather sealed stock pile outside was 5.5 ± 0.3 % and water content for the AC200 bentonite before mixing was 11.6 ± 0.6 %. Measured FT phase water content was 15.3 ± 0.4 % (target 15.6 %).
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DISTRIBUTION:
3 RESULTS AND OBSERVATIONS Measured average densities for the 550 mm test fields in field test phases are presented in Table 3. Measured dry densities as a function of measurement depth for the 550 mm test fields are presented in Figure 13 for the WMFT phase and in Figure 14 for the FT phase. In both field test phases can be observed a trend that after a well compacted layer surface the material loosens before lower compaction layer. Accurate information about the actual density of the lower layers after compaction of the upper layer was not possible to obtain with the measurement equipment in use. Table 3. Average dry density of test fields. Target density for Milos granules was 1250 kg/m³ and for chrushed rock bentonite 1640 kg/m³. Dry density and range [kg/m³] Material WMFT FT
MG 1249 ± 39 1226 ± 63**
CRB 1653 ± 55 1512 ± 87**
Figure 13. Average dry densities as a function of depth in WMFT phase.
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DISTRIBUTION:
Figure 14. Average dry densities as a function of depth in FT phase. Compaction methods were refined after the WMFT phase and the amount of compaction layers was reduced to two partly due to layering phenomenon (Figure 15) and partly because of the high compaction capacity of the used equipment. In the FT phase density results were lower although the structure was more solid due to disruption of the surface between compaction of the layers.
Figure 15. Layering phenomenon in WMFT phase. Both of the fields were compacted in three layers. During dismantling of the fields excavator bucket revealed boundary surfaces of the compaction layers. Crushed rock bentonite on the left and Milos granules on the right side.
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Because of deficient testing arrangement of 150 mm test fields, no conclusions can be drawn from the test results of the thinner fields. Thinner fields were poorly compacted and water destroyed both fields relatively quickly. In the field test phases the average load bearing capacity measured for the MG was 101.2 ± 25.7 MN/m² and for the CRB 142.8 ± 22.8 MN/m². The development of load bearing capacity as a function of time during water conduction is presented in Figure 16 for the WMFT phase and in Figure 17 for the FT phase.
Figure 16. Load bearing capacities of the tested materials as a function of time in WMFT phase.
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Figure 17. Load bearing capacities of the tested materials as a function of time in FT phase. Before dismantling of WMFT fields, only small cracking of the surface was visible. Dry surface layer preserved its load bearing properties well. In Figure 16 can be seen that the materials were compacting because of dynamic Loadman testing. Because of the shorter monitoring period, no conclusions should be made on development of the load bearing capacity for the FT fields. It can be noted that the allowable open time in densities achieved in FT phase is long enough for both of the materias in construction point of view. In the end of FT -phase water was conducted to the surface of the 550 mm fields for 24 hours. Water softened the surface quickly and load bearing capacity dissipated under the wetted area to approximately 150 mm depth from the surface. In Figure 18 are presented measured elevations of the test fields and the actual thicknesses of the fields in FT -phase. Measured thicknesses were for MG 486 ± 25 mm / 134 ± 26 mm and for CRB 507 ± 32 mm / 148 ± 31 mm.
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Figure 18. Measured thicknesses of the test fields in FT phase. In plan view concrete element sustained 550 mm fields on the right and unsupported 150 mm test fields on the left. In section view 550 mm test fields on top and 150 test fields on bottom.
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4 CONCLUSIONS AND RECOMMENDATIONS Based on the field tests performed, it is clear that appointed target densities are possible to attain in full scale but uniform compaction of the material needs more investigation. Handling of the CRB was better compared to MG in water contents used during testing. Before WMFT phase the target water content of the MG was raised because the material dusted and was challenging to work. The water content target for the MG was raised again before FT phase. Workability of the MG was improved but signs of adherence of the material to working equipment became noticeable. Regardless of the workability challenges, target density was achieved with MG with greater degree of success. Water content targets of the tested materials should remain the same as in FT phase in future studies. Adequate evenness of the field surface may not be possible to achieve without post machining. Boarder areas will be difficult to compact and level in tunnel environment. High load bearing capacity in the end of the elongated follow up time in WMFT phase suggests that the foundation layer could be possible to build in longer sections than planned. Compacting in longer sections could also ease the execution of the compaction work. More testing should be done to verify this statement. Based on the observations done during the compacting, the interlocking between layers was defective. Mechanical roughening or other procedure will eliminate this problem.
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REFERENCES
Hansen, J., Korkiala-Tanttu, L., Keski-Kuha, E. & Keto, P. 2010. Deposition Tunnel Backfill Design for a KBS-3V Repository. Working Report 2009-129, Posiva Oy.
Martikainen, J. & Schatz, T. 2011. Laboratory Tests to Determine the Effect of Olkiluoto Bounding Brine Water on Buffer Performance. Working Report 2011-68, Posiva Oy.
Johannesson, L-E. & Nilsson, U., 2006. Deep repository – engineered barrier systems. Geotechnical behavior of candidate backfill materials. Laboratory tests and calculations for determining performance of the backfill. SKB R-06-73, Svensk Kärnbränslehantering AB.
Johannesson, L-E., Sanden, T., Dueck, A. & Ohlsson, L., 2010. Characterization of a backfill candidate material, IBECO-RWC-BF. Baclo Project – Phase 3. Laboratory tests. SKB R-10-44, Svensk Kärnbränslehantering AB.
Wimelius, H. & Pusch, R. 2008. Backfilling of KBS-3V deposition tunnels – possibilities and limitations. SKB R-08-59, Svensk Kärnbränslehantering AB.
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DISTRIBUTION:
APPENDIX 3: Laboratory tests for materials used in Riihimäki foundation layer tests
Author Petriikka Karttunen, Leena Kiviranta
Reviewed by
Petri Koho
Approved by Project manager Leena Kiviranta
date 14.12.2012
date
22.3.2013 date
11.2.2013 TECHNICAL MEMO: Laboratory tests for materials used in Riihimäki foundation layer tests PROJECT: 171 – Backfill productionline work in 2012 SUBPROJECT: Riihimäki tests CLASS (in M-Files): Technical memo 1 Materials Tested materials were Minelco granules and mixture of crushed rock and bentonite AC200. Minelco granule Type: Granular Na-activated Ca-bentonite B+Tech ID: Be-Mi-BT0015-Gr-R Material was delivered to B+Tech on 17.8.2011. Characterization results of the material are presented in Kiviranta & Kumpulainen 2011. Crushed rock Type: Granular crushed rock B+Tech ID: CR-BT0002-Gr-R Material was delivered to B+Tech on 29.8.2011. AC200 bentonite Type: Powdered Na-activated Ca-bentonite B+Tech ID: Be-Mi-NaA-BT0016-Po-R Material was delivered to B+Tech on 29.8.2011. Characterization results of the material are presented in Appendix 1.
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2 Methods Swelling pressure, hydraulic conductivity, water ratio and bulk density were measured by methods described in Kiviranta & Kumpulainen (2011), except the samples were saturated using constant head method instead of peristaltic pump. In constant head method, the saturation solution was allowed to flow through one of the bottom ports of the measurement cell at a low hydrostatic pressure (~ 16 kPa) while upper opposite port was open for approximately 7 days. After that, the saturation solution was allowed to flow also through one of the upper ports of the measurement cell, while both opposite ports were closed. Total saturation time varied between 3-8 weeks for different samples but in all measurements it was checked that the swelling pressure had reached steady state before hydraulic conductivity measurement was started. Samples 1-3 were measured in measurement cells with diameter of 35 mm and samples 4-7 in measurement cells with diameter of 100 mm. The 100 mm cell size was selected for samples 4-7 because the largest particles in crushed rock had a diameter near 10 mm. In swelling pressure and hydraulic conductivity measurements, the samples were saturated using Posiva reference solution prepared by dissolving CaCl2 and NaCl to deionized water at a Ca2+/Na+ mass ratio of 1:1 to form a total dissolved solids (TDS) content of 35 g/L. 3 Results The results of swelling pressure and hydraulic conductivity measurements are presented in Table 1. Table 1. Swelling pressure (SP), hydraulic conductivity (HC), dry density (ρdry), bulk density (ρbulk) and water ratio (w=mass of water divided by dry mass*100 %) results. ID Material Target
ρdry (g/cm3)
Sample height (mm)
SP [KPa]
HC at 20°C [m/s]
w [%] after test
Calculated from w after test
Immersion method after test
ρdry
(g/cm3) ρbulk
(g/cm3) ρdry
(g/cm3) ρbulk
(g/cm3) 1 Minelco
Granule 1.23 16.32 486 5.52*10-11 41.48 1.29 1) 1.83 1.21 1.72
2 Minelco Granule
1.25 15.97 453 1.04*10-10 45.59 1.23 1) 1.79 1.18 1.72
3 Minelco Granule
1.27 15.90 443 3) 9.55*10-11
3) 42.08 1.28 1) 1.82 1.23 1.74
4 AC200-Crushed rock (50:50)
1.50 38.91 216 5.40*10-11 30.57 1.49 2) 1.95 1.44 1.88
5 AC200-Crushed rock (50:50)
1.50 38.86 189 1.26*10-10 30.18 1.50 2) 1.95 1.44 1.88
6 AC200-Crushed rock (50:50)
1.65 38.85 455 2.70*10-11 25.42 1.62 2) 2.03 1.58 1.98
7 AC200-Crushed rock (50:50)
1.80 50.20 1799 1.11*10-12 20.72 1.75 2) 2.11 1.66 2.00
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1) Grain density result for Minelco granule was based on Kiviranta & Kumpulainen (2011). 2) Grain density results for AC200 and crushed rock were based on Schatz & Martikainen (2012). 3) A small (diameter of 0.5 cm, weight of 0.6 g) piece of rock which was assumed to be contamination was found from sample 3, which may have affected the swelling pressure and hydraulic conductivity results. 4 References Kiviranta, L. & Kumpulainen, S. 2011. Quality control and characterization of bentonite materials. Posiva Oy, Eurajoki, Finland. Working Report 2011-84. Schatz, T. & Martikainen, J. 2012. Laboratory Tests and Analyses on Potential Olkiluoto Backfill Materials. Posiva Oy, Eurajoki, Finland. Working Report 2012-X. To be published. Appendices Appendix 1: Characterization results of Be-Mi-NaA-BT0016-Po-R
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Appendix 1: Characterization results of Be-Mi-NaA-BT0016-Po-R
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LIST OF REPORTS
POSIVA-REPORTS 2012
_______________________________________________________________________________________
POSIVA 2012-01 Monitoring at Olkiluoto – a Programme for the Period Before Repository Operation Posiva Oy ISBN 978-951-652-182-7 POSIVA 2012-02 Microstructure, Porosity and Mineralogy Around Fractures in Olkiluoto
Bedrock Jukka Kuva (ed.), Markko Myllys, Jussi Timonen, University of Jyväskylä Maarit Kelokaski, Marja Siitari-Kauppi, Jussi Ikonen, University of Helsinki Antero Lindberg, Geological Survey of Finland Ismo Aaltonen, Posiva Oy ISBN 978-951-652-183-4
POSIVA 2012-03 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Design Basis 2012 Posiva Oy ISBN 978-951-652-184-1 POSIVA 2012-04 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Performance Assessment 2012 Posiva Oy ISBN 978-951-652-185-8 POSIVA 2012-05 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Description of the Disposal System 2012 Posiva Oy ISBN 978-951-652-186-5 POSIVA 2012-06 Olkiluoto Biosphere Description 2012 Posiva Oy ISBN 978-951-652-187-2 POSIVA 2012-07 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Features, Events and Processes 2012 Posiva Oy ISBN 978-951-652-188-9 POSIVA 2012-08 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Formulation of Radionuclide Release Scenarios 2012 Posiva Oy ISBN 978-951-652-189-6
POSIVA 2012-09 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Assessment of Radionuclide Release Scenarios for the Repository System 2012 Posiva Oy ISBN 978-951-652-190-2 POSIVA 2012-10 Safety case for the Spent Nuclear Fuel Disposal at Olkiluoto - Biosphere Assessment BSA-2012 Posiva Oy ISBN 978-951-652-191-9 POSIVA 2012-11 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Complementary Considerations 2012 Posiva Oy ISBN 978-951-652-192-6 POSIVA 2012-12 Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto - Synthesis 2012 Posiva Oy ISBN 978-951-652-193-3 POSIVA 2012-13 Canister Design 2012 Heikki Raiko, VTT ISBN 978-951-652-194-0 POSIVA 2012-14 Buffer Design 2012 Markku Juvankoski, VTT ISBN 978-951-652-195-7 POSIVA 2012-15 Backfill Design 2012 Jorma Autio, Md. Mamunul Hassan, Petriikka Karttunen, Paula Keto, B+Tech Oy ISBN 978-951-652-196-4
