Kapitel 1 Introduktion Kapitel 2 Förläggningsplats Kapitel 3
Krav och konstruktionsförutsättningar Kapitel 4
Kvalitetssäkring och anläggningens drift Kapitel 5
Anläggnings- och funktionsbeskrivning Kapitel 6
Radioaktiva ämnen i anläggningen Kapitel 7
Strålskydd och strålskärmning Kapitel 8
Säkerhetsanalys
Repository production report
Design premises KBS-3V repository report Spent fuel report
Canister production report Buffer production report Backfill production report Closure production report
Underground opening construction report Ramprogram för detaljundersökningar vid uppförande och drift
FEP report
Fuel and canister process report
Buffer, backfill and closure process report Geosphere process report
Climate and climate related issues Model summary report
Data report
Handling of future human actions Radionuclide transport report Biosphere analysis report
Site description of Forsmark (SDM-Site)
Samrådsredogörelse
Metodik för miljökonsekvens- bedömning
Vattenverksamhet Laxemar-Simpevarp
Vattenverksamhet i Forsmark I Bortledande av grundvatten Vattenverksamhet i Forsmark II Verksamheter ovan mark Avstämning mot miljömål
Comparative analysis of safety related site characteristics
Bilaga SR
Säkerhetsredovisning för slutförvaring av använt kärnbränsle
Bilaga AV
Preliminär plan för avveckling
Bilaga VP
Verksamhet, organisation, ledning och styrning
Platsundersökningsskedet
Bilaga VU
Verksamhet, ledning och styrning Uppförande av slutförvarsanläggningen
Bilaga PV
Platsval – lokalisering av slutförvaret för använt kärnbränsle
Bilaga MKB
Miljökonsekvensbeskrivning
Bilaga AH
Verksamheten och de allmänna hänsynsreglerna Bilaga MV
Metodval – utvärdering av strategier och system för att ta hand om använt kärnbränsle
Toppdokument Begrepp och definitioner
A nsök an enligt k ärntekniklagen
Bilaga SR-Site Redovisning av säkerhet efter förslutning av slutförvaret Bilaga SR-Drift Säkerhetsredovisning för drift av slutförvars- anläggningen
Svensk Kärnbränslehantering AB Swedish Nuclear Fuel
and Waste Management Co
Technical Report
TR-08-05
Site description of Forsmark at completion of the site
investigation phase
SDM-Site Forsmark
Svensk Kärnbränslehantering AB
December 2008
Site description of F orsmark at completion of the site investigation phase –
SDM-Site ForsmarkSite description of Forsmark at completion of the site
investigation phase
SDM-Site Forsmark
Svensk Kärnbränslehantering AB
December 2008
A pdf version of this document can be downloaded from www.skb.se.
ISSN 1404-0344
SKB TR-08-05
Preface
The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site characterisation at two different locations, the Forsmark and Laxemar-Simpevarp areas, with the objective of siting a deep geological repository for spent nuclear fuel. An integrated component in the characterisation work is the development of a site descriptive model (SDM) that constitutes a description of the site and its regional setting. The model addresses the current state of the geosphere and the biosphere as well as the ongoing natural processes that affect their long-term evolution.
The site descriptive model concluding the surface-based investigations at Forsmark, SDM-Site, is compiled in the present report. Prior to the SDM-Site report, three versions of a site descriptive model have been completed for the Forsmark area. Version 0 established the state of knowledge prior to the start of the site investigation programme. Version 1.1, which was essentially a training exercise, was completed during 2004 and version 1.2 in June 2005. Version 1.2 of the SDM, a preliminary site description, concluded the initial site investigation work.
Three analytical and modelling stages have been carried out during the complete site investigation work. An important component of each of these stages has been to address and continuously try to resolve uncertainties of importance for repository engineering and safety assessment. Stage 2.1 aimed to provide feedback from the modelling group to the site investigation team to enable completion of the site investigation work. Stages 2.2 and 2.3 have established the different discipline-specific models, which are combined into the framework of the integrated site descriptive model, SDM-Site.
A synthesis of the SDM-Site report that focuses on model integration and the current understanding of the site is presented in chapter 11. In essence, this chapter serves as an executive summary.
The overall objective of the site descriptive modelling work at Forsmark is to develop and document an integrated description of the site, based on data from the complete site investigation work, as a basis for a site-adapted design of the final repository (Layout D2) and for assessment of the repository’s long-term radiological safety (SR-Site).
The site descriptive modelling work performed within the Swedish site characterisation programme is conducted by multi-disciplinary project groups and associated discipline-specific working groups.
All individuals and expert groups contributing to the projects are gratefully acknowledged, and espe- cially the Forsmark multi-disciplinary project group, for making this report possible. Specifically, the following individuals and expert groups contributed to this final report:
• Kristina Skagius – project leader, editor and site synthesis.
• Lennart Ekman – site investigation data.
• Björn Söderbäck – site evolutionary aspects, abiotic and biotic properties of the surface system.
• Sten Berglund and other members of the SurfaceNet group – abiotic and biotic properties of the surface system.
• Michael Stephens – geology (deterministic modelling and integrated model), site synthesis and Appendix 4.
• Raymond Munier – geology (discrete fracture network modelling).
• Jan Sundberg and John Wrafter – thermal properties.
• Rune Glamheden – rock mechanics.
• Sven Follin – hydrogeology and site synthesis.
• Marcus Laaksoharju, John Smellie and Eva-Lena Tullborg – hydrogeochemistry.
• James Crawford – transport properties.
• Anders Lindblom – production of maps and figures.
The members of the multi-disciplinary project group completed Appendices 2 and 3.
Johan Andersson is specifically acknowledged for his ambitious and devoted efforts as a driving force for the confidence assessment work and as the editor of the report documenting the outcome (SKB R-08-82).
The report has been formally reviewed by the following members of SKB’s international site inves- tigation expert review group (Sierg): Per-Eric Ahlström (Chairman); Jordi Bruno (Amphos, Spain);
John Hudson (Rock Engineering Consultants, UK); Ivars Neretnieks (Royal Institute of Technology, Sweden); Lars Söderberg (SKB); Michael C. Thorne (Mike Thorne and Associates Ltd, UK); Roland Pusch (GeoDevelopment AB); Thomas W Doe (Golder Associates Inc.); John Cosgrove (Imperial College, London); Alan Hooper (Alan Hooper Consulting Limited). The Sierg group provided many valuable comments and suggestions for this work. However, it is not to be held responsible
for any remaining shortcomings of the report.
Anders Ström
Site Investigations – Analysis
Summary
The Swedish Nuclear Fuel and Waste Management Co., SKB, has undertaken site characterisation in two different areas, Forsmark and Laxemar-Simpevarp, in order to identify a suitable location for a geological repository of spent nuclear fuel according to the KBS-3 method. The site investigations have been conducted in campaigns, punctuated by data freezes. After each data freeze, the site data have been analysed and modelling has been carried out with the overall purpose to develop a site descriptive model (SDM). The site descriptive model is used by repository engineering to design the underground facility and to develop a repository layout adapted to the site. It is also essential for safety assessment, since the model is the only source for site-specific input. Another important use of the site descriptive model is in the environmental impact assessment.
An SDM is an integrated model for geology, thermal properties, rock mechanics, hydrogeology, hydrogeochemistry, bedrock transport properties and a description of the surface system. The site descriptive model compiled in the current report, SDM-Site, presents an integrated understanding of the Forsmark area at the completion of the surface-based investigations, which were conducted at Forsmark during the period 2002 to 2007. It also provides a summary of the abundant underlying data and the discipline-specific models that support the site understanding. The description relies heavily on background reports that address, in particular, details in data analyses and modelling in the different disciplines.
The Forsmark area is located in northern Uppland within the municipality of Östhammar, about 120 km north of Stockholm. The candidate area for site investigation is located along the shoreline of Öregrundsgrepen, within the north-western part of a major tectonic lens that formed between 1.87 and 1.85 billion years ago during the Svecokarelian orogeny. The candidate area is approximately 6 km long and 2 km wide. The north-western part of the candidate area lacks hydraulically conductive, gently dipping fracture zones at potential repository depth and was selected as the target area for the complete site investigation work, following the initial investigations at the site.
Prior to the presentation of the SDM-Site report, three versions of a site descriptive model have been completed for the Forsmark area and presented for peer review. The last version, referred to as version 1.2, was a preliminary site description that concluded the initial site investigation work and was presented in 2005. This preliminary site description formed the basis for a preliminary safety evaluation (PSE) of the Forsmark area, a preliminary repository layout (step D1), and the first evalua- tion of the long-term safety of this layout for KBS-3 repositories in the context of the SR-Can project.
The final site descriptive model, SDM-Site, builds on a coordinated geological model in 3D, into which other discipline-specific models have been integrated without any major conflicting interpre- tations. In particular, the thermal properties of the bedrock at the site have been coupled to identified rock domains in the geological model and an integrated model that links the current stress regime, the hydrogeology and the chemistry of the groundwater to fracture domains and fracture zones in the geological model has evolved. These mutually consistent results demonstrate that a fundamental understanding of the current state of conditions and the on-going processes in the Forsmark area, from the surface down to potential repository depth, has been achieved. In addition, the properties of the area can be explained in the context of an understanding of the past evolution, throughout a long period of geological history. This integrated understanding of the area is presented in chapter 11 of this report and this chapter serves as an executive summary.
A systematic assessment of the confidence in the model, including treatment of uncertainties and evaluation of alternative interpretations, has been carried out. This assessment has taken account of the feedback obtained from the work with the preliminary repository layout step D1 and from the safety assessment SR-Can, as well as the feedback obtained on earlier versions of the site
Contents
1 Introduction 13
1.1 Background 13
1.2 Scope and role of the site description 14
1.3 Objectives and strategy 14
1.4 Feedback from reviews and assessments of previous model versions 16
1.5 Setting 16
1.6 Methodology and organisation of the work 20
1.6.1 Methodology 20
1.6.2 Interfaces between disciplines 22
1.6.3 Organisation of work 23
1.6.4 Quality assurance aspects 24
1.6.5 Nomenclature 24
1.7 This report and supporting documents 25
2 Investigations, available data and other prerequisites for modelling 29
2.1 Overview of investigations 29
2.1.1 Investigations and primary data acquired up to data freeze 1.2 29 2.1.2 Investigations and primary data aquired at data freezes 2.1, 2.2
and 2.3 30
2.2 Investigations of the surface system 30
2.2.1 Bedrock geology and ground geophysics 30
2.2.2 Quaternary geology and ground geophysics 32
2.2.3 Surface ecology 32
2.3 Borehole investigations 33
2.3.1 Drilling activities 41
2.3.2 Measurements completed in connection with drilling, geological mapping of drill cores and drill cuttings, and down-hole logging 41 2.3.3 Sampling and analysis of intact rock material for laboratory
investigations 45
2.4 Monitoring 46
2.4.1 Background 46
2.4.2 Monitoring programme 46
2.5 Geographical data 47
2.6 Other data sources 48
2.7 Databases 48
2.8 Model versions prior to stages 2.2 and 2.3 49
2.9 Model volumes and model areas 50
2.9.1 Regional model area and volume 50
2.9.2 Local model area and volume 51
3 Evolutionary aspects of the Forsmark site 53
3.1 Bedrock evolution during the Proterozoic and Phanerozoic eons 53 3.1.1 Bedrock geological evolution in south-eastern Sweden 53 3.1.2 Bedrock geological evolution in the Forsmark area 56 3.2 Palaeoclimate and geological development during the Quaternary period 58
3.3 Seismicity during the Quaternary period 60
3.4 Groundwater evolution during the Quaternary period 62 3.5 Development of ecosystems during the late Quaternary period 63
3.6 Human population and land use 65
4 Surface system and surface-bedrock interactions 67 4.1 State of knowledge at the previous model version 67
4.2 Evaluation of primary data 67
4.2.1 Regolith and Quaternary geology 68
4.2.2 Hydrology and near-surface hydrogeology 72
4.2.3 Hydrochemistry 73
4.2.4 Ecosystems 74
4.2.5 Human population and land use 78
4.3 Modelling of the surface system 79
4.3.1 Hydrology and near-surface hydrogeology 79
4.3.2 Ecosystems 81
4.4 Implications for bedrock modelling 85
4.4.1 Hydrology and hydrogeology 86
4.4.2 Hydrochemistry 89
4.4.3 Solute transport 92
4.5 Summary description of the surface system at Forsmark 95
4.6 Evaluation of uncertainties 98
5 Bedrock geology 99
5.1 State of knowledge at the previous model version 99
5.2 Evaluation of primary data 100
5.2.1 Bedrock geological map at the surface 100
5.2.2 Rock units and possible deformation zones in the sub-surface realm 103 5.2.3 Rock types − properties, alteration, volumetric proportions and
thickness of the subordinate rock amphibolite 107
5.2.4 Ductile deformation 110
5.2.5 Brittle deformation 114
5.2.6 Character and kinematics of deformation zones 122 5.2.7 Identification, character and geological significance of lineaments 124 5.2.8 Character and geological significance of seismic reflection data 128 5.2.9 Character and geological significance of seismic refraction data 131 5.3 Geological models in relation to data resolution 132
5.4 Deterministic model for rock domains 133
5.4.1 Data input 133
5.4.2 Conceptual model 133
5.4.3 Methodology, assumptions and feedback from other disciplines 134 5.4.4 Division into rock domains, geometries and property assignment 135
5.5 Deterministic model for deformation zones 139
5.5.1 Data input 139
5.5.2 Conceptual model 139
5.5.3 Methodology, assumptions and feedback from other disciplines 142 5.5.4 Geometric models and property assignment 144 5.6 Statistical model for fractures and minor deformation zones 153
5.6.1 Division into fracture domains 154
5.6.2 Modelling assumptions 158
5.6.3 Derivation of statistical fracture model 159
5.6.4 DFN models 165
5.7 Integrated geological model 166
5.8 Verification of the deterministic geological models 171
5.8.1 KFM08D 171
5.8.2 Gravity and petrophysical modelling 173
5.9 Remaining uncertainties 173
5.9.1 Deterministic model for rock domains 173
5.9.2 Deterministic model for deformation zones 174 5.9.3 Statistical model for fractures and minor deformation zones 175
6 Bedrock thermal properties 177
6.1 State of knowledge at the previous model version 177
6.2.5 Thermal conductivity vs heat capacity 181 6.2.6 Temperature dependence of thermal properties 182 6.2.7 Pressure dependence in thermal conductivity 182
6.2.8 Coefficient of thermal expansion 182
6.2.9 In situ temperature 183
6.3 Strategy for thermal modelling 184
6.3.1 Conceptual model 184
6.3.2 Modelling approach 185
6.3.3 Modelling assumptions 186
6.3.4 Feedback from other disciplines 187
6.4 Geostatistical analyses and stochastic simulations 187 6.4.1 Thermal Rock Classes (TRC) – Definition, properties
and proportions 187
6.4.2 Geological heterogeneity and division into thermal subdomains 188
6.4.3 Spatial statistical models of lithology 190
6.4.4 Stochastic simulations of lithology 191
6.4.5 Spatial statistical models of thermal conductivity 194 6.4.6 Stochastic simulations of thermal conductivity 196
6.5 Thermal domain model 198
6.5.1 Domain modelling results 198
6.5.2 Evaluation of domain modelling results 202
6.5.3 Summary of rock domain properties 202
6.6 Evaluation of uncertainties 204
6.6.1 Data uncertainty 204
6.6.2 Model uncertainty 204
6.6.3 Summing up 206
7 Rock mechanics 207
7.1 State of knowledge at the previous model version 207
7.2 Evaluation of primary data 208
7.2.1 Laboratory properties of intact rock 209
7.2.2 Laboratory properties of fractures 212
7.2.3 Characterisation of the rock mass quality 212
7.2.4 In situ state of stress 214
7.3 Rock mechanics model 217
7.3.1 Intact rock properties 217
7.3.2 Fracture properties 219
7.3.3 Rock mass properties 220
7.3.4 In situ state of stress 223
7.4 Evaluation of uncertainties 227
7.4.1 Uncertainty in mechanical properties 227
7.4.2 Uncertainty in the stress model 227
8 Bedrock hydrogeology 229
8.1 Context 229
8.1.1 Hydrogeological modelling in the SDM 229
8.1.2 Model development 230
8.1.3 Main characteristics of relevance to the model 231 8.2 State of knowledge at the previous model version 232
8.3 Evaluation of primary data 234
8.3.1 Deterministic versus stochastic features 234
8.3.2 Basic characteristics of the single-hole tests 236 8.3.3 Evaluation of single-hole hydraulic tests 237 8.3.4 Evaluation of hydraulic interference tests 242
8.4 Conceptual modelling 243
8.4.1 Deformation zones and associated hydraulic data 243 8.4.2 Fracture domains and associated hydraulic data 246
8.4.3 The bedrock bordering the target volume 252
8.4.4 The shallow bedrock aquifer 252 8.5 Parameterisation of deformation zones and fracture domains 259
8.5.1 Deformation zones 259
8.5.2 Fracture domains 260
8.6 Flow model calibration 271
8.6.1 Matching the 2006 interference test in HFM14 272
8.6.2 Matching natural groundwater levels 273
8.6.3 Matching hydrochemical profiles in cored boreholes 275
8.7 Bedrock hydrogeological model 280
8.7.1 Visualisations for interpretation of hydrochemistry 283 8.7.2 Visualisations for interpretation of flow and solute transport 287
8.8 Parameter sensitivity analysis 291
8.9 Confidence and remaining uncertainties 293
8.9.1 Groundwater levels in the shallow bedrock aquifer 293 8.9.2 Compartmentalised fracture networks at repository depth 295
8.9.3 Evaluation of PFL-f transmissivity data 295
9 Bedrock hydrogeochemistry 297
9.1 Introduction 297
9.2 State of knowledge at previous model version 298
9.3 Conceptual model 299
9.3.1 Major concepts and model input 299
9.3.2 Working hypothesis on the past groundwater evolution 305
9.4 Hydrogeochemical data 307
9.4.1 Borehole groundwater data 308
9.4.2 Representativity of the data 308
9.5 Explorative analysis and modelling 309
9.5.1 Initial data evaluation and visualisation 310
9.5.2 Mixing calculations 318
9.5.3 Redox modelling 319
9.5.4 Characterisation of microorganisms 322
9.5.5 Characterisation of colloids 324
9.5.6 Gases 325
9.5.7 Studies of fracture fillings 325
9.5.8 Porewater composition in bedrock 328
9.5.9 Groundwater residence time 333
9.5.10 Evaluation of uncertainties in field data and interpretation methods 336
9.6 Hydrogeochemical integrated site model 338
9.6.1 Hydrogeochemical visualisation 338
9.6.2 Consistency with the hydrogeological model 344 9.6.3 Confidence and uncertainty in the integrated hydrogeochemical
model 345
10 Bedrock transport properties 349
10.1 State of knowledge at previous model version 349
10.2 Evaluation of primary data 349
10.2.1 Data and models from other disciplines 349
10.2.2 Transport data 350
10.3 Conceptual model 350
10.4 Transport properties of the bedrock 353
10.4.1 Overview of rock domains and fracture domains 353
10.4.2 Representative transport property data 356
10.4.3 Application of the retardation model 367
10.6 Transport of radionuclides 376 10.7 Field-scale confirmatory testing of transport properties 379
10.7.1 Multiple well tracer tests 379
10.7.2 Single well injection-withdrawal (SWIW) tests 380 10.7.3 Evaluation of tracer test data, interpretation and consequences
for safety assessment 380
10.8 Evaluation of uncertainties 382
11 Current understanding of the site 385
11.1 Surface system 386
11.1.1 Evolution during the Quaternary period 386
11.1.2 Description of the surface system 388
11.1.3 Human population and land use 391
11.2 Rock domains and their associated thermal and rock mechanical properties 391 11.2.1 Rock crystallisation and cooling history 391 11.2.2 Rock composition and ductile deformation 392
11.2.3 Rock domain model 395
11.2.4 Mineral resources 396
11.2.5 Thermal properties 396
11.2.6 Strength and other mechanical properties of intact rock 398 11.3 Deformation zones, fracture domains and fractures 399 11.3.1 Formation and reactivation throughout geological time 399
11.3.2 Deterministic deformation zones 401
11.3.3 Fracture domains, fractures and DFN modelling 404
11.3.4 Fracture mineralogy 407
11.3.5 Mechanical properties of deformation zones and fractures 408
11.4 Rock stress 409
11.4.1 Stress evolution 409
11.4.2 Stress model 409
11.5 Bedrock hydraulic properties 411
11.5.1 Evolution 411
11.5.2 Hydraulic properties of deformation zones and fracture domains 411 11.6 Integrated fracture domain, hydrogeological DFN and rock stress models 415
11.7 Groundwater 416
11.7.1 Evolution during the Quaternary period 416
11.7.2 Groundwater composition 418
11.7.3 Groundwater flow and evolution of groundwater composition 421
11.8 Transport properties 423
11.8.1 Properties of the rock matrix 423
11.8.2 Flow-related properties 424
11.9 Overall confidence 427
11.9.1 Data usage 427
11.9.2 Key remaining issues and their treatment 427
11.9.3 Handling of alternatives 428
11.9.4 Consistency between disciplines 429
11.9.5 Confidence statement 429
12 Conclusions 431
12.1 Fulfilment of objectives 431
12.2 Key remaining issues 431
12.3 Implications for the underground construction phase 431
13 References 433
Appendix 1 Topography and place names in the Forsmark area 449
Appendix 2 Nomenclature 451
Appendix 3 Tables with references to primary data 455 Appendix 4 Properties of deformation zones modelled to intersect the target
volume at –400 to –600 m elevation 497
1 Introduction
1.1 Background
Radioactive waste from nuclear power plants is managed by the Swedish Nuclear Fuel and Waste Management Co., SKB. The Swedish programme for geological disposal of spent nuclear fuel is approaching major milestones in the form of permit applications for an encapsulation plant and a final repository. For siting of the repository, SKB has undertaken site characterisation at two dif- ferent locations, Forsmark and Laxemar-Simpevarp (Figure 1-1). The site investigations have been conducted in campaigns, punctuated by data freezes. After each data freeze, the site data have been analysed and modelling has been carried out with the overall purpose to develop a site descriptive model (SDM). An SDM is an integrated model for geology, thermal properties, rock mechanics, hydrogeology, hydrogeochemistry, bedrock transport properties and a description of the surface system.
The site descriptive model concluding the surface-based investigations at Forsmark, SDM-Site, is compiled in this site description. The report presents the integrated understanding of the Forsmark site at the completion of the surface-based investigations and provides a summary of the models and the underlying data supporting the site understanding. Prior to the SDM-Site, three versions of a site descriptive model had been completed for the Forsmark area. Version 0 /SKB 2002/ established the state of knowledge prior to the start of the site investigation phase. Version 1.1 /SKB 2004/ was essentially a training exercise and was completed during 2004. In June 2005, version 1.2 of the SDM /SKB 2005a/, a preliminary site description, concluded the initial site investigation work (ISI).
Three analytical and modelling stages have been carried out during the complete site investigation work (CSI). An important component of each of these stages has been to address and continuously try to resolve uncertainties of importance for repository engineering and safety assessment.
Sweden
Laxemar-Simpevarp Forsmark
Stockholm
Göteborg
Oskarshamn municipality
Östhammar municipality
Model stage 2.1 /SKB 2006a/ included an updated geological model for Forsmark and aimed to provide feedback from the modelling working group to the site investigation team to enable completion of the site investigation work. Model stages 2.2 and 2.3 have established the different discipline-specific models which are synthesised into the framework of the integrated site descriptive model SDM-Site presented in this report. This concludes the assessment of the surface-based site investigations at Forsmark.
1.2 Scope and role of the site description
Site characterisation should provide all data required for an integrated evaluation of the suitability of the investigated site for a deep geological repository and a fundamental component in the characterisation work is the development of a site descriptive model.
Quality-assured data from site investigations, stored in the SKB database Sicada and the SKB geographic information system (GIS), are the input to site descriptive modelling. The site descriptive model is used by repository engineering to design the underground facility and to develop a repository layout adapted to the site. It is also essential for safety assessment, since the model is the only source for site-specific input. Another important use of the site descriptive model is in the environmental impact assessment.
In order to ensure that all data and information needed for repository design and safety assessment are captured in the site characterisation work, there has been a continuous exchange of information between the various technical activities (Figure 1-2). Based on the preliminary site description (SDM version 1.2), compiled from data collected during the initial site investigation stage (ISI), a preliminary repository layout (step D1) /Brantberger et al. 2006/ was established and a preliminary safety evaluation (PSE) /SKB 2005b/ as well as a full safety assessment (SR-Can) /SKB 2006b/ were conducted (thin red arrows in Figure 1-2). In the course of the work with the design and the safety assessment, requests for new data and/or data with greater precision were raised. This feedback (blue arrows in Figure 1-2) was included in the final programme for the completion of the site investigation phase. In addition to this formal feedback via the site modelling report from stage 2.1 /SKB 2006a/, there has been another, less formalised feedback continuously ongoing from site modelling to the site investigation programme (dashed blue arrows in Figure 1-2). Repository engineering and safety assessment will now update their work based on the final site description, SDM-Site, which concludes the surface-based characterisation work (thick red arrows in Figure 1-2). The products within repository engineering that rely on an input from the site description are: the site engineering report, the layout report and the underground opening construction report. The corresponding reports in the safety assessment work are: the data report and the geosphere process report.
In the SKB programme, a site description is a description of the site covering the current state of the geosphere and the biosphere as well as descriptions of on-going natural processes that can affect their long-term evolution. However, it is not the task of the site description to present any predictions of the future evolution of site conditions. This is completed within safety assessment based on the understanding of the current conditions and of the past evolution as compiled in the site description.
It is also not the task of the site descriptive modelling to evaluate the impact on current site conditions of the excavation or the operation of a repository at the site. This is carried out within the framework of repository engineering and as part of the environmental impact assessment, but again based on input from the site description.
1.3 Objectives and strategy
The overall objective of the current site descriptive modelling work (SDM-Site) at Forsmark is to develop and document an integrated description of the site, based on data from the complete site investigation work, as a basis for a site-adapted design of the final repository (Layout D2) and for assessment of the repository’s long-term radiological safety (SR-Site). The description has to be based on, and demonstrate, a fundamental understanding of the rock and surface system, which is achieved by analysing the reliability and assessing the reasonableness of the assumptions made with
respect to the current state of the Forsmark site and naturally ongoing processes. Furthermore, the work is required to make use of all knowledge and understanding built into previous model versions and of the feedback obtained from the safety assessment SR-Can as well as of other feedback obtained on earlier versions of the site description.
The specific objectives of the work were to:
• analyse the primary data produced within the surface-based site investigation, i.e. including data available at data freezes 2.2 and 2.3,
• describe evolutionary aspects at the site from the time the bedrock formed to the current day,
• develop a complete three-dimensional integrated site descriptive model covering all disciplines,
• perform an overall confidence assessment including systematic treatment of uncertainties and evaluation of alternative interpretations, and
• perform modelling activities in close interaction with safety analysis and repository engineering.
The strategy applied for achieving the stated objectives was to base the site descriptive model on the quality assured, geoscientific and ecological field data from Forsmark that were available in the SKB databases Sicada and GIS at the date defined for data freeze 2.2, i.e. on September 30th 2006. This data freeze contained all data planned to be collected from the target volume, i.e. the rock volume that has been selected as potentially suitable for hosting a final repository (see further section 1.5).
All new data that were available at the date defined for data freeze 2.3, i.e. on March 30th 2007, were used for complementary analyses and verification of the models. Since the site investigation has continued after data freeze 2.3, although to a very much smaller extent, additional data have also emerged after this data freeze. As far as possible, these “late” data have been assessed and Figure 1‑2. Exchange of information between technical activities that provide data to site modelling or make use of the site description. Deliveries from (red arrows) and feedback to (blue arrows) site modelling are highlighted together with the final product from site modelling and the products of other technical activities that rely on this input.
Investigations Main product:
Primary data in Sicada, GIS
Site descriptive modelling Main product:
Site description
Safety assessment Main product:
Safety report
Repository engineering Main product:
Facility description
Initial Site Investigation Stage (ISI)
Preliminary site Description
• SDM 1.1
• SDM 1.2 •Preliminary Safety
evaluation (PSE)
•SR-Can
Step D1 Facility description
• Layout report
• Feedback to site characterisation
Environmental impact Assessment Main product:
EIA report
Environmental Impact Assessment Report Feedback to CSI
Stage 2.1 report Complete Site
Investigation Stage (CSI)
Safety report SR-Site
• Data report
• Geosphere process report
Step D2 Facility description
• Site engineering report
• Layout report
• Underground opening construction report Site description
(SDM-Site)
properties to repository engineering, it was decided to compile the results of the modelling based on data freeze 2.2 into modelling stage 2.2 reports for these disciplines, prior to conducting and reporting the complementary analyses and verification activities using new data in data freeze 2.3.
For the remaining disciplines, the modelling based on data freeze 2.2 and the complementary and verification analyses are compiled into a single background report. The reports supporting the Forsmark SDM-Site are further described in section 1.7.
1.4 Feedback from reviews and assessments of previous model versions
Feedback on previous model versions has been received from downstream users of the models and from reviews of the previous model reports by SKB’s own expert group Sierg, but also from expert groups set up by the authorities SKI (the Insite group) and SSI (the Oversite group). Specifically, the Insite and Oversite groups have continuously followed the progress of the work and the Insite group has regularly provided lists of issues of their concern to be addressed in the modelling work. The handling of the issues raised has been documented by SKB as formal responses to Insite and SKI.
All feedback issues related to the site descriptive modelling of the Forsmark site have been compiled and the remaining issues have been addressed in the modelling work. A main task of the model stage 2.1 work /SKB 2006a/ was to identify and compile remaining important issues/uncertainties and suggest how these should be handled in the forthcoming site investigation and modelling work.
Uncertainties in the preliminary site description /SKB 2005a/, the results of analyses conducted during modelling stage 2.1, and experience from the work with repository layout D1 and the pre- liminary safety evaluation (PSE) for Forsmark formed the input to the compilation of issues. In the SR-Can safety assessment /SKB 2006b/, which was based on the preliminary site description /SKB 2005a/, remaining site characterisation issues of importance for assessing repository safety were identified and provided as feedback to the site investigation and modelling teams. These issues have been addressed in the final stages of site descriptive modelling together with issues of importance for repository design. The results were evaluated as part of the assessment of confidence and uncertainties in the site descriptive model at the conclusion of the surface-based site investigation work /SKB 2008/
and a summary is provided in section 11.9.
1.5 Setting
The Forsmark area is located in northern Uppland within the municipality of Östhammar, about 120 km north of Stockholm (Figure 1-1 and Figure 1-3). The candidate area for site investigation is located along the shoreline of Öregrundsgrepen. It extends from the Forsmark nuclear power plant and the access road to the SFR-facility, a repository for low- and intermediate level radioactive waste, in the north-west to Kallrigafjärden in the south-east (Figure 1-3 and map in Appendix 1).
It is approximately 6 km long and 2 km wide. The north-western part of the candidate area was selected as the target area for the complete site investigation work /SKB 2005c/ (see Figure 1-4 and map in Appendix 1).
The Forsmark area consists of a crystalline bedrock that belongs to the Fennoscandian Shield, one of the ancient continental nuclei on the Earth. The bedrock at Forsmark in the south-western part of this shield formed between 1.89 and 1.85 billion years ago during the Svecokarelian orogeny /SKB 2005a/. It has been affected by both ductile and brittle deformation. The ductile deformation has resulted in large-scale, ductile high-strain belts and more discrete high-strain zones. Tectonic lenses, in which the bedrock is less affected by ductile deformation, are enclosed between the ductile high strain belts. The candidate area is located in the north-westernmost part of one of these tectonic lenses. This lens extends from north-west of the nuclear power plant south-eastwards to the area around Öregrund (Figure 1-5). The brittle deformation has given rise to reactivation of the ductile zones in the colder, brittle regime and the formation of new fracture zones with variable size.
© Lantmäteriverket Gävle 2007 Medgivande I 2007/1092 Forsmark nuclear
power plant
Forsmark nuclear power plant
SFR
Candidate area Regional model area
Figure 1‑4. The north-western part of the candidate area was selected as the target area for the complete site investigation work (modified after Figure 2-15 in /SKB 2005c/).
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0 0,5 2 km
Target area Candidate area
Cored borehole used in SDM version 1.2 bbot tr tttt ä rräskkekeeeeekkkekett
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Zone A2, interpreted location 400 metres depth
500 metres depth North-western part
South-eastern part
KFM02A
0 5 10 km
Area inferred to be affected by higher ductile strain Area inferred to be affected by lower ductile strain (tectonic lens) Major, retrograde deformation zone (DZ)
along the coast (1 = Singö DZ, 2 = splay from Singö DZ, 3 = Eckarfjärden DZ, 4 = Forsmark DZ)
1
Tectonic lens at Forsmark (land, left; under sea, right)
Sea, lake Investigation site for the disposal of highly radioactive nuclear waste Österbybruk
Öregrund Öregrundsgrepen
Kallrigafjärden Gräsö
Gimo Forsmark
nuclear power plant
1 2
3 4
SFR
Östhammar
Hargshamn
Figure 1‑5. Tectonic lens at Forsmark and areas affected by strong ductile deformation in the area close to Forsmark (Figure 4-1 in /Stephens et al. 2007/).
The current ground surface in the Forsmark region forms a part of the sub-Cambrian peneplain in south-eastern Sweden. This peneplain represents a relatively flat topographic surface with a gentle dip towards the east that formed more than 540 million years ago. The candidate area at Forsmark is characterised by a small-scale topography at low altitude (Figure 1-6). The most elevated areas to the south-west of the candidate area are located at c. 25 m above current sea level. The whole area is located below the highest coastline associated with the last glaciation, and large parts of the candidate area emerged from the Baltic Sea only during the last 2,000 years. Both the flat topography and the still ongoing shoreline displacement of c. 6 mm per year strongly influence the current landscape (Figure 1-6). Sea bottoms are continuously transformed into new terrestrial areas or freshwater lakes, and lakes and wetlands are successively covered by peat.
SFR
Candidate area
Figure 1‑7. From site investigations to site description. Quality-assured primary data from site investiga- tions are collected in databases. Data are interpreted and presented in a site descriptive model, which consists of a description of the geometry of different features in the model and the corresponding properties of those features and of the site as a whole (modified after Figure 1-1 in /SKB 2002/).
Investigations
Database
Primary data (measured data, calculated values and conceptual assumptions)
Interpretation of geometries and properties
Site descriptive model
Geology
mechanicsRock
Ecosystem Transport properties
Hydrogeology
Hydrogeo- chemistry
Thermal properties
Geometry
(Structural geology)
Site description
1.6 Methodology and organisation of the work
1.6.1 Methodology
The project is multi-disciplinary, in that it covers all potential properties of the site that are of importance for its overall understanding, for the design of the deep repository, for safety assessment and for the environmental impact assessment. The overall strategy applied in the work (Figure 1-7) has been to develop discipline-specific models by interpretation and analyses of the quality-assured primary data that are stored in the SKB databases Sicada and GIS, and then to integrate these discipline-specific models into a unified site description. The quantitative, discipline-specific models are stored in the SKB model database Simon, from where quality-assured versions of the models can be accessed by the downstream users of the site description. Quality assurance aspects of the modelling procedure are further described in section 1.6.4.
The site descriptive modelling comprises the iterative steps of evaluation of primary data, descriptive and quantitative modelling in 3D, and evaluation of the confidence in the resulting models. Data are first evaluated within each discipline and then the evaluations are cross-checked between the disci- plines. Three-dimensional modelling, with the purpose of estimating the distribution of parameter values in space, as well as their uncertainties, follows. In this context, the geological models provide the geometrical framework for all discipline-specific modelling. The three-dimensional description presents the parameters with their spatial variability over a relevant and specified scale, with the uncertainty included in this description. If required, different alternative descriptions are provided.
Based on experience from earlier SKB projects, e.g. the Laxemar modelling project /Andersson et al.
2002a/, methodologies for generating site descriptive models were developed and documented in discipline-specific strategy reports. The work conducted during the development of the preliminary site description /SKB 2005a/ followed the guide-lines in these reports, which are:
• Geological site descriptive modelling /Munier et al. 2003/,
• Thermal site descriptive modelling /Sundberg 2003a/,
• Rock mechanics site descriptive modelling /Andersson et al. 2002b/,
• Hydrogeological site descriptive modelling /Rhén et al. 2003/,
• Hydrogeochemical site descriptive modelling /Smellie et al. 2002/,
• Transport properties site descriptive modelling /Berglund and Selroos 2004/,
• Ecosystem descriptive modelling /Löfgren and Lindborg 2003/.
In addition, a strategy for achieving sufficient integration between disciplines in producing site descriptive models is documented in a separate strategy report for integrated evaluation /Andersson 2003/.
New experience on methodology issues has been gained during the course of the iterative process of site descriptive modelling and also to some extent by following the progress of international projects, e.g. the AMIGO project /NEA 2004/. When appropriate, this has been built into the
methodologies applied and also, in some cases, resulted in updates to, or amendments of, the strategy reports. The products expected from the geological discrete fracture network (DFN) modelling have been presented in detail and clarified in an updated version /Munier 2004/ of an appendix to the strategy document for geological site descriptive modelling /Munier et al. 2003/. The methodology applied for modelling of thermal properties has been considerably revised as compared with the methodology used previously. The updated strategy is based on stochastic simulations of lithologies and thermal conductivity as described in /Back and Sundberg 2007/. Finally, the strategy for hydrogeological modelling during the CSI stage has been updated to give more focus to assessing and demonstrating the understanding of the hydrogeology and on describing the hydrogeological properties of the potential repository volumes. A first test of the updated strategy was reported in /Follin et al. 2007a/.
According to the strategy report for integrated evaluation /Andersson 2003/, the overall confidence evaluation should be based on the results from the individual discipline modelling and involve the different modelling teams. The confidence is assessed by carrying out checks concerning, for example, the status and use of primary data, uncertainties in derived models, and various consistency checks, for example, between models and with previous model versions. Procedures for this
assessment have been progressively refined during the course of the site descriptive modelling, and applied to all previous versions of the Forsmark site descriptive model. Since the surface-based site investigations are now concluded and the current site descriptive model (SDM-Site) is compiled with the purpose to support a license application to start construction of a spent nuclear fuel repository, the approach has been further developed in order to address more specifically the confidence in the site description.
1.6.2 Interfaces between disciplines
For several of the disciplines involved in the SDM work, e.g. geology, hydrogeology and hydrogeo- chemistry, a distinction is made between the surface system and the bedrock system. The reasons for this distinction are both practical (large amounts of data, different objectives and different users of results) and historical, as the SKB work traditionally has been focused on the bedrock system. The delimitation between the surface and bedrock systems is, of course, artificial and somewhat arbitrary.
Central to the description of the bedrock is the geological model which provides the geometrical context in terms of the characteristics of deformation zones and the rock mass between the zones (see section 1.6.5 for definitions). Using the geometric component in the bedrock geological models as a basis, descriptive models for other geoscientific disciplines (thermal properties, rock mechanics, hydrogeology, hydrogeochemistry and transport properties) have been developed for the bedrock.
Development of these models has, in turn, highlighted issues of potential importance for the bedrock geological model. Another important interface is that between hydrogeology and hydrogeochemistry, which has been handled, for example, by regional palaeo-hydrogeological simulations of variable- density groundwater flow between 8000 BC and 2000 AD.
The interface between the surface and bedrock systems has been considered in the evaluation of shallow and deep groundwater movement, as well as in the groundwater chemistry description. The present conceptualisation of the hydraulic properties of the Quaternary deposits is implemented into the near-surface hydrogeological modelling in the bedrock and also into modelling and evaluation of the impact of infiltration on the present groundwater composition. The shallow groundwater system is modelled so as to include the uppermost part of the bedrock with flow conditions that are consistent with the bedrock hydrogeological model (see Figure 1-8).
The handling of the interfaces between disciplines is described in more detail in chapter 4 (surface system) and chapters 5 through 10 (bedrock system).
Figure 1‑8. Cartoon showing how the modelling of the hydrologic cycle is divided into a surface-based system and a bedrock-based system. The former is modelled with the MIKE SHE numerical modelling tool and the latter with the ConnectFlow numerical modelling tool. Reproduced from /Follin et al. 2007c/.
1.6.3 Organisation of work
The work has been conducted by a project group with representatives of the disciplines geology, thermal properties, rock mechanics, hydrogeology, hydrogeochemistry, transport properties and surface systems. In addition, some group members have specific qualifications of importance in this type of project e.g. expertise in RVS (Rock Visualisation System) modelling, GIS-modelling and in statistical data analysis.
Each discipline representative in the project group was given the responsibility for the assessment and evaluation of primary data, and for the modelling work concerning his/her specific discipline.
This task was then carried out either by the representatives themselves, or together with other experts or groups of experts outside the project group. In this context, discipline-specific networks, set up by SKB, play an important role. These networks are the same for both the Forsmark and Laxemar- Simpevarp site-modelling projects and they are essentially run by the discipline responsible, as assigned by SKB. The purpose of these networks is to carry out site modelling tasks and to provide technical links between the site organisations, the site modelling teams and the principal clients (repository engineering, safety assessment and environmental impact assessment). The discipline-specific, so-called Net-groups actively involved in the site modelling work are identified in Table 1-1.
In addition to traditional project work, the project group has had several workshops together with representatives of the Forsmark site investigation team addressing uncertainties and overall confi- dence in the data gathered and in the models produced. The objectives and scope of the uncertainty and confidence assessment have been modified during the course of the site descriptive modelling, reflecting the state of progress in the modelling work. During the initial site investigation stage, focus was on identifying important uncertainties in model versions 1.1 /SKB 2004/ and 1.2 /SKB 2005a/, and in data supporting these models, in order to guide further data collection and modelling activities. Similarly, the primary objective of the work conducted during modelling stage 2.1 /SKB 2006a/ was to provide feedback to the site investigations, in order to ensure that sufficient information was obtained during the remainder of the complete site investigation stage. The focus of the assessment of the final models included in SDM-Site has been on addressing confidence in the models and to provide arguments for the confidence statements.
Table 1‑1. Discipline‑specific networks involved in site descriptive modelling and their mandates/objectives.
Discipline Net‑group Mandate
Geology GeoNet Provides a forum for the coordination of geological modelling tasks in both the Forsmark and Laxemar-Simpevarp site-modelling projects.
Rock mechanics and
thermal properties MekNet Coordination of modelling tasks for rock mechanics and thermal properties.
Resource for development and maintenance of method descriptions.
Hydrogeology HydroNet Execution of the hydrogeological modelling; constitutes a forum for all mod- ellers within hydrogeology (needs of site modelling and safety assessment and repository engineering).
Hydrogeochemistry ChemNet Models the groundwater data from the sites and produces site descriptive hydrogeochemical models. Integrates the description with other disciplines and makes recommendations for further site investigations.
Bedrock transport
properties RetNet Execution of the transport properties modelling; constitutes a forum for all transport-related modellers within site modelling and safety assessment.
Surface system SurfaceNet Models and describes the surface system by subdiscipline (biotic and abi- otic), models the properties in a distributed way (maps and 3D), models the interdisciplinary processes (over space and time), describes the different ecosystems (conceptually and in site-specific terms), describes and models the flow of matter in the landscape, defines and connects the biosphere objects, and produces site descriptions to support environmental impact assessment (EIA).
1.6.4 Quality assurance aspects
In order to ensure that the site descriptive model builds on qualified data and that the model and sub-models derived from these qualified data are correct and are the models that are delivered to, and employed by, the downstream users, a number of quality assurance (QA) procedures and instructions in the SKB quality assurance system have been followed. The process to progress from collection of primary data to models available to the downstream users, as defined by the QA procedures and routines and applied in the site modelling, is summarised briefly below.
All primary data collected in the field and from laboratory measurements are stored in the SKB databases Sicada and GIS. Before delivery to the database operator, the data are reviewed and approved by the person responsible for the field activity providing the data (activity leader). The database operator transfers the data to the database and then makes an order of the same data from the database. The data export from the database is then checked by the database operator and the activity leader to ensure that no mistakes are made in the transfer of the data to the database. When everything is correct, the data are approved by the activity leader by signing the data. The execution of this process is specified in the SKB QA document SDK-508.
Primary data collected at the site and used in the site descriptive modelling are only extracted from the databases Sicada and GIS. Information regarding the procedures for data collection and circumstances of importance in the interpretation of data is given in the documentation (P-reports) of the data collection activity, but the hard data have to be ordered from the databases. Only data that are approved (signed) are allowed for delivery to users of the data. All orders and deliveries of data from the databases are registered, which means that it is possible to trace back all data deliveries.
The execution of the process of order and delivery of data from the databases is specified in the SKB QA documents SD-112 (Sicada) and SD-113 (GIS).
Errors in data identified during the subsequent analytical and modelling work are reported by the modeller who discovers the error. The errors are compiled in a list that is published on SKB’s internal web site. It is the responsibility of the users of the data to report all errors found and to be updated on the data errors reported. For all errors reported, the type of error is identified and corrective actions are taken. The actions taken are documented in the data error list and corrected data are transferred to the databases according to the procedure described above. The procedure for handling of errors in primary data is specified in the SKB QA document SDK-517.
The discipline-specific models developed within site modelling, using quality-assured data according to the procedures above, are stored in the SKB model database Simon. In this context, the term
“models” refers to, for example, 3D models of the geometry of deformation zones, 2D models of surface objects, DFN model parameters. Before the models are officially released to downstream users, they are approved by the person who is responsible for a specific discipline at SKB. The only models that are allowed for further use by, for example, repository engineering and safety assessment are the approved versions downloaded from the model database. The model database is also used for internal deliveries within the site modelling project. All downloads of models in the database are registered, which means that it is possible to trace by whom, when and which model has been downloaded. Instructions for the use of the model database are compiled in the SKB QA document SDK-115.
The peer review of previous and the current model version conducted by SKB’s own expert group Sierg and by the expert groups set up by the authorities (Insite and Oversite), as well as the list of issues of concern, continuously provided by the Insite group and responded to by SKB, are also important in a quality assurance context (see section 1.4).
1.6.5 Nomenclature
Some definitions are provided here for terms that are of basic importance for the modelling and description of the Forsmark site. Most of these are geological terms that are related to the geometrical framework of the modelling and are, as a consequence, common to all disciplines.
The definitions of geological terms are based on section 2.4 in /Stephens et al. 2007/. Definitions of additional terms are provided in Appendix 2.
Candidate area/volume The candidate area refers to the area at the ground surface that was recognised as suitable for a site investigation, following the feasibility study work /SKB 2000/. The extension at depth is referred to as the candidate volume.
Target area/volume The target area/volume refers to the north-western part of the candidate area and the rock volume beneath that was selected during the site investigation process /SKB 2005c/ as potentially suitable for hosting a final repository for spent nuclear fuel.
Rock unit A rock unit is defined on the basis of the composition, grain size and inferred relative age of the dominant rock type. Other geological features including the degree of bedrock homogeneity, the degree and style of ductile deformation, the occurrence of early-stage alteration (albitization) that affects the composition of the rock, and anoma- lous fracture frequency also help define and distinguish some rock units.
Rock domain A rock domain refers to a rock volume in which rock units that show specifically similar composition, grain size, degree of bedrock homogeneity, and degree and style of ductile deformation have been combined and distinguished from each other. Different rock domains at Forsmark are referred to as RFMxxx.
Deformation zone Deformation zone is a general term that refers to an essentially 2D structure along which there is a concentration of brittle, ductile or combined brittle and ductile deforma- tion. Deformation zones at Forsmark are denoted ZFM followed by two to eight letters or digits. An indication of the orientation of the zone is included in the identification code.
Fracture zone Fracture zone is a term used to denote a brittle deformation zone without any specifica- tion whether there has or has not been a shear sense of movement along the zone.
Fault zone Fault zone is a term used for a fracture zone that shows a shear sense of movement along it.
Fracture domain A fracture domain is a rock volume outside deformation zones in which rock units show similar fracture frequency characteristics. Fracture domains at Forsmark are denoted FFMxx.
1.7 This report and supporting documents
This report presents the integrated understanding of the Forsmark site at the completion of the surface-based investigations and provides a summary of the models and the underlying data sup- porting the site understanding. The report is intended to describe the properties and conditions at the site and to give the information essential for demonstrating this understanding, but relies heavily on background reports concerning details in data analyses and modelling. These background reports and their hierarchy in the SDM-Site reporting are illustrated in Figure 1-9 and further described below.
Chapter 2 in this description of the Forsmark site, SDM-Site, summarises available primary data and provides an overview of previous model versions and other prerequisites for the modelling.
In chapter 3, the current understanding of the development of the geosphere and the surface system through time is described. Chapter 4 summarises the modelling of the surface system, with a focus on aspects of importance for the bedrock system. The integrated description of the surface system is provided in one of the background reports (see Figure 1-9 and text below). Chapters 5 to 10 provides summaries of the modelling of the bedrock geology, bedrock thermal properties, bedrock mechanics, hydrogeology, hydrogeochemistry and bedrock transport properties, respectively.
In chapter 11, the current understanding of the Forsmark site is summarised. It focuses on an integrated description that demonstrates consistency and, as such, it also functions as an executive summary for the SDM-Site. Chapter 12 provides the conclusions from the work in terms of fulfil- ment of objectives and a highlight of the most important issues judged to merit further study prior to and during the underground construction phase, in order to decrease the remaining uncertainties in the description of the target volume. Finally, it should be noted that a geographical map of the Forsmark area is provided in Appendix 1, where the location of different local geographical names that are referred to in the site description can be found.
The site descriptive modelling resulting in the final site description, SDM-Site, has involved two
