NUMO-TR-12-01

Collaboration on Strategies for thedevelopment of a Repository Program

T. Ebashi, K. Kaku, S. Suzuki, S. Kubota,
K. Yoshimura, K. Ishiguro, S. Takeda
NUMO
I. Gaus, S. Vomvoris, A. Martin, L. Johnson
Nagra

July 2012
Nuclear Waste Management Organization of Japan（NUMO）

Ⓒ原子力発電環境整備機構: Nuclear Waste Management Organization of Japan, 2012
All parts of this work are protected by copyright. No parts of this publication may be
reproduced, stored in the retrieval system, or transmitted, in any form or by anymeans, without the prior permission of NUMO. Inquiries about copying and reproduction
should be addressed to:
Science and Technology Department
Nuclear Waste Management Organization of Japan
Mita NN Bldg. 1-23, Shiba 4-chome, Minato-ku, Tokyo 108-0014 JapanNUMO-TR-12-01

Collaboration on Strategies for thedevelopment of a Repository
ProgramT. Ebashi, K. Kaku, S. Suzuki, S. Kubota,
K. Yoshimura, K. Ishiguro, S. Takeda
NUMO
I. Gaus, S. Vomvoris, A. Martin, L. Johnson
Nagra2011 年 3 月
原子力発電環境整備機構
July 2012
Nuclear Waste Management Organization of Japan（NUMO）

Table of Contents
1 Introduction .....................................................................................................................................1
1.1 Background of this study ...........................................................................................................1
1.2 Overview of the collaborative study ..........................................................................................1
2 Provisional activities for the DI stage .............................................................................................3
2.1 Introduction ................................................................................................................................3
2.2 Boundary conditions ..................................................................................................................3
2.3 General remarks ........................................................................................................................5
2.4 Objectives of DI activities ..........................................................................................................6
2.5 DI activities ................................................................................................................................6
2.5.1 Overview .............................................................................................................................6
2.5.2 Available information from the PI stage ..............................................................................82.5.3 Step 1: Activities before access construction......................................................................8
2.5.4 Step 2: Activities during construction of the access ..........................................................142.5.5 Step 3: Activities in the host formation ..............................................................................18
2.5.6 Step 4: Final evaluation and reporting of the DI stage .....................................................20
2.6 Outlook ....................................................................................................................................22
3 Uncertainty management in the safety case ................................................................................24
3.1 Introduction ..............................................................................................................................24
3.2 Identification of safety-relevant uncertainties ..........................................................................26
3.3 Description and quantification of uncertainties .......................................................................34
3.4 Assessing the impacts of uncertainties ...................................................................................36
3.5 Avoidance, reduction and mitigation of remaining uncertainties ............................................40
3.6 Issues to be considered in the future ......................................................................................42
4 Definition and concept of Demonstration .....................................................................................44
4.1 Definition of demonstration......................................................................................................44
4.2 Demonstration concept............................................................................................................49
5 Overall conclusions ......................................................................................................................55
Acknowledgements .........................................................................................................................56
References ......................................................................................................................................57
Appendix A: Main topics studied between FY2008 and FY 2010 ...................................................60

List of Figures
Figure 2.1 Site investigation stages for the HLW disposal program in Japan ................................. 5
Figure 2.2 Outline of the provisional activities for the DI stage ...................................................... 7
Figure 3.1 The cyclical strategy for identification, avoidance, reduction and assessment of
uncertainties (adapted from Figure 6-9 of Posiva 2008) .......................................... 26
Figure 3.2 Safety functions (bold), safety function indicators and safety function indicator criteria
for the KBS-3V buffer (SKB, 2006a) ......................................................................... 28
Figure 3.3 Use of safety functions, indicators and criteria for the evaluation of the safetyrelevance of the process of buffer erosion and its associated uncertainties ........... 28
Figure 3.4 Illustration of iterative nature of the planning of model calculations to support
judgments as to whether or not safety function indicator criteria are upheld ........... 29
Figure 3.6 Examples from the ONDRAF/NIRAS hierarchy of safety statements (after Table 1 ofSmith et al. 2009) ...................................................................................................... 31
Figure 3.7 Example of the propagation of uncertainties related to a change of climate through ahierarchy of safety statements (after Figure 10 of Smith et al. 2009) ...................... 32
Figure 3.8 Examples of probability density functions and a more speculative "what-if?" value(after Figure A1.2 of Nagra (2002)) .......................................................................... 35
Figure 3.9 Ranges of parameter uncertainty (adapted from Smith et al 2009) ............................. 36
Figure 3.10 Binary combinations of buffer and canister scenarios considered in the SR-Can
safety assessment .................................................................................................... 39
Figure 3.11 The coupling between Research and Technical Development (RTD) work, planning,
performance targets/target properties and safety analysis ...................................... 41
Figure 3.12 Top-down identification of processes, conditions and factors affecting controlling thesafety functions, and the bottom-up propagation of uncertainties ........................... 43
Figure 4.1 A possible demonstration concept for NUMO consisting of four parallel tracks .......... 50
Figure 4.2 Timing of the demonstration activities according to NUMO's stepwise repository
development approach (A darker shade indicates a higher intensity of activities) .. 54

List of Tables
Table 3.1 Example of a listing of assumptions related to the modeling of matrix diffusion, andidentification of possible alternative assumptions .................................................... 33
Table 3.2 Buffer and canister scenarios considered in the SR-Can safety assessment, indicating
which are judged to be residual (adapted from SKB (2006a)) ................................. 38

1 Introduction
1.1 Background of this study
The Nuclear Waste Management Organization of Japan (NUMO, hereafter) has selected an
open solicitation approach for the site selection process in Japan, both for the high-level waste
repository (open call in 2002) and the TRU repository (open call in 2008). Such an approach,albeit flexible, poses a special challenge for NUMO's repository design team.
A detailed repository design must be tailored to the given geological and surface environment,
not least to take advantage of the potential for optimization. The repository design must
fulfill a broad range of requirements resulting, for example, from the long-term safety goals,
engineering practicality and socio-economic issues. The special challenge for NUMO's designteam is to be able to specify a number of different designs for sites in different geological andgeographical settings and, moreover, to be able to finalize such designs within a very limited
time period.
Regarding the Swiss radioactive waste disposal program, Nagra has built up a long experiencethrough the investigation of a wide range of geological environments for both the HLW and
L/ILW. As a consequence it was agreed to set up a collaborative study aimed at transferring
relevant knowledge from the Swiss geological disposal program to the Japanese disposal
program in first instance. Later in the project, where this was relevant for NUMO, also
experience from other European implementers was drawn upon.

1.2 Overview of the collaborative study
The repository concept (RC) collaborative study was initiated in 2001, mainly as a technicalknowledge transfer between the implementing organizations of Japan and Switzerland. The
focus was on developing a methodology for tailoring repository concepts to a broad range ofsite environments. The outcome of the study between 2001 and 2003 is summarized in
NUMO (2004).
The RC collaborative study was then continued and expanded to cover a wide range of topics
from the strategic to the technical level. Every year joint team meetings have been organizedin Switzerland and in Japan. These were supplemented by a number of working meetings alsoin Switzerland and Japan. The working meetings allowed the members of the NUMO-Nagra
team to exchange, discuss, and further develop ideas and concepts applicable to the Japaneseenvironment. The main meetings also discussed work performed by contractors and guided
future developments.
1

The 2nd phase of the RC study was completed in FY 2007. The main results of this phase are
discussed in Kurikami et al. (2009) and can be summarized as follows:

Development of the roadmap for the preliminary investigation (PI) stage in Japan

Identification of issues for the scenario development methodology of NUMO

Discussion/suggestion for requirements management system of NUMO

In its 3rd phase, the RC collaborative study was expanded to develop the above topics fromthe strategic to the technical level. The 3rd phase covers FY 2008 to FY 2010.
The goal of this report is to summarize the main results of the study during the 3rd phase. For
each of the fiscal years covered in this report, Appendix A shows the main topics investigatedas part of the RC study collaborative study. From the list described in Appendix A, theoutcomes of development and the International workshop on Requirement Management
Systems have already been published (Suzuki et al., 2008: Suzuki et al., 2010a: Suzuki et al.,2010b: NUMO, 2011a). Also, the outcomes of the International workshop on scenario
development methodology have already been published (Ebashi et al., 2010).
From the list of topics covered under the collaboration, in terms of the following points, thesome topics are selected for this summary report and described in more detail.


Exclusion of topics already published by some form
Focus on technical and important topics in initial stage of NUMO’s about 100-years
program

Chapter 2 summarizes the activities for the Detailed Investigation (DI) stage based on theboundary conditions and the DI objectives.
In Chapter 3 aspects of the management of uncertainties in safety assessment are discussed.
In Chapter 4 the definition and concept of demonstration in general are discussed.
Chapter 5 contains the conclusions of the collaborative study.

2

2 Provisional activities for the DI stage
2.1 Introduction
In this chapter a provisional DI activities is described. The DI activities was developed in aseries of working meetings, discussed and finalized during the Joint Team Meetings. In FY'06
and FY'07, the NUMO-Nagra team developed a activities for the PI phase (Kurikami et al.,2009). In FY’08, this work was extended to the activities for the DI stage.
During the DI stage, NUMO will construct an Underground Investigation Facility (UIF) to thehost rock. The NUMO-Nagra team has gone through the expected work processes during the
DI stage and developed a provisional DI activities. The activities covers all major groups ofactivities expected during the DI stage, namely additional surface-based investigations,construction of the access, excavation of experimental tunnels and performing tests
underground. This activities will contribute to the understanding of the type of activities thatwill need to take place in the DI stage in a comprehensive manner. It should be noted that theactivities developed is site-generic and more detailed work will be required once the site
conditions become more concrete. In addition, NUMO has showed the basic idea for DI stage
in FY’11 (NUMO, 2011b), and then it is based on this activities.

2.2 Boundary conditions
Figure 2-1 shows NUMO's activities during the site investigation stages. The DI stage is when
NUMO goes underground to conduct detailed investigations. It is also important to point out
that NUMO, most probably, will have to purchase the surface land; this will be a majordecision for NUMO.
The following (assumed) boundary conditions have been applied in this development:
Although there is no official duration, it is expected that the DI stage will take approximately
15 years
After the DI stage, NUMO will select a repository site and start to prepare the licensing
Field work will be carried out continuously even during licensing (but may not be called DI)
The activities that NUMO is required to complete in the DI stage are defined in Article 8 of
the Final Disposal Act.

3

Final Disposal Act: Selection of a Site for Repository Construction

Article 8.

The Organization shall, when it intends to select a site for repository construction, carry out inadvance the detailed investigation in accordance with the final disposal plan and the approved implementation
plan of the Organization with respect to the matters mentioned in the following items in the detailed
investigation areas under Article 5, paragraph 2, item (iii), as stated in the said approved implementation plan:(i)matters concerning the strength of rocks that make up a geological formation where the final
disposal will be carried out (to be referred to in this article as the “subject geologicalformation”) and the physical properties of the said subject geological formation in the saiddetailed investigation areas;(ii)

matters concerning hydrogen ion concentration in the said subject geological formation andother chemical properties of the said subject geological formation;(iii)

matters concerning the details of groundwater flows, if any, in the said subject geologicalformation; and(iv)

other matters specified in the Ordinance of the Ministry of Economy, Trade and Industry.

Subject to the provisions of the Ordinance of the Ministry of Economy, Trade and Industry, when the
Organization has carried out the detailed investigation in accordance with the provisions of the preceding
paragraph, it shall, based on the results of the detailed investigation, select a site for repository construction
from among those detailed investigation areas with respect to which the said detailed investigation has been
carried out and which are deemed to meet all of the following criteria:(i)

it is expected that underground engineered facilities in the said subject geological formation
are unlikely to be exposed to unusual pressure, and in other respects, the physical propertiesof the said subject geological formation are expected to be suitable for the construction of a
final disposal facility;(ii)

it is expected that underground engineered facilities in the said subject geological formation
are unlikely to be exposed to unusual corrosive action, and in other respects, the chemical
properties of the said subject geological formation are expected to be suitable for theconstruction of a final disposal facility;(iii)

it is expected that groundwater or groundwater flow in the said subject geological formationis unlikely to disturb the functions of underground engineered facilities; and(iv)

other matters specified in the Ordinance of the Ministry of Economy, Trade and Industry.

4

Figure 2.1 Site investigation stages for the HLW disposal program in Japan

2.3 General remarks
The legal requirements contain essential aspects that need to be addressed in a DI activities,
but additional considerations are needed for its development, as described herein. A key
challenge in the DI stage is the integration of excavation activities with the requirements of(most probably) building a safety case for a license application of this site. It is required tohandle scientific work in harmony with ongoing excavation work without jeopardizing theobjectives of the DI.
The site characterization during the DI is a continuation of the one performed in the PI stage,
but expanded to include both surface-based and underground investigations. The undergroundconstruction itself, combined with mapping, represents an important component of thedetailed characterization activities because any underground excavation is, at least temporarily,
a major disturbance to the overall geological system, and a monitoring program is needed.
Another potential use of the underground space is to carry out specific tests. However, adetailed test program can be developed only after the repository site, the host rock and arepository concept have been determined. It is also necessary to consider what tests should bedone in an underground facility at the site – and what could be done elsewhere.
A activities structure similar to the PI roadmap (Kurikami et al., 2009) is suggested for the DI
stage. This structure includes the main processes, their interactions and the key decision
points.

5

2.4 Objectives of DI activities
The activities are developed with the following objectives in mind:
Confirm that the Detail Investigation Areas (DIA) fulfils all of the legal and NUMO
requirements

Provide sufficient input for preparing the licence application with its safety case forthe repository – even if some complementary activities may be needed. The input for
the licence application preparation would include for example confirming that the
thickness and extent of the selected host rock are sufficient to accommodate theplanned waste volumes and that the investigations provide sufficient input for thebasic/detailed design of the repository.

2.5 DI activities
2.5.1 Overview
The proposed DI activities is shown in Figure 2.2. It is structured in a similar manner to the PI
roadmap (Kurikami et al., 2009). It contains the main steps as well as the input required foreach step and the products expected as an output.

6Input from prevous step/stage

Activities

Expected outcome

Step 1: Activities before access construction* SDM 1.0
* Preliminary repository concept* Preliminary safety assessment* Issues remaining from PI

1.1 Initial planning and characterisation * Completed surface basedof monitoring
investigations
1.2 Initial planning of testing in the host * Preliminary plans for undergroundrock and elsewherecharacterisation and monitoring
1.3 Complementary surface-based* Preliminary plans for undergroundinvestigations
testing
1.4 Initiation of baseline monitoring* Plans for tests in generic URLs
1.5 Update SDM* Baseline monitoring system on site
1.6 Detailed design of access and* Updated SDM 2.0
surface facilities* Detailed design of access includingtime schedule

Step 2: Activities during construction of access* Detailed design of the access* Plan for undergroundcharacterisation and monitoring* Assessment of activities in other
URLs (Japan or overseas)

2.1 Construction of access tunnel or
shaft to reach host formation
2.2 Characterisation of monitoring
during access construction
2.3 Assessment of findings during
access construction
2.4 Revision of underground test andcharacterisation plan

* Completed access and including
characterisation and monitoring* Installed and initiated undergroundmonitoring* Monitoring data from the surface* Updated SDM 3.0 in the access andtesting volume* Updated test plan
* Updated characterisation andmonitoring plan

Step 3: Activities in the host rock formation*Revised underground testing and
3.1 Construction of test (and potential
characterisation plancharacterisation) tunnels*Monitoring concept of the near-field 3.2 Continued characterisation andmonitoring*Method statements for excavation 3.3 Implementation of tests
of test and disposal tunnels*Completed test and characterisation
tunnels*Completed characterisation activities*Installed and initiated monitoring
system*Results of tests and their interpretation

Step 4: Final evaluation and reporting of the DI stage
Updated SDM 4.0
Detailed repository design
Updated safety case

Figure 2.2 Outline of the provisional activities for the DI stage

7

2.5.2 Available information from the PI stage
The work carried out in the PI stage, e.g. as outlined in the "fundamental activities of the PI
stage", provides crucial information for the planning and execution of the DI stage. This
information includes:
SDM (Site Descriptive Model) version 1.0 (SDM 1.0 hereinafter): The SDM after
completion of the PI stage should include the geometry of the host formation, the location oflayout-determining features, and a statistical description of key host formation properties,
groundwater composition, migration properties, rock engineering properties and dilution in
aquifers/surface waters. It will also include a description of the evolution of the site
conditions, e.g. uplift/erosion, ongoing and past geochemical processes, faulting, etc. and aquantification of key uncertainties related to PI targets.
A preliminary repository design: The design should be based on SDM 1.0 and should fulfil
the specified requirements. The engineering feasibility with respect to the requirements
should be assessed and issues/uncertainties requiring resolution should be identified.
A preliminary safety assessment: The safety assessment should be based on SDM 1.0 andthe preliminary repository design. It should provide a list of safety arguments and outstanding
issues.
Issues remaining from PI: An outline plan for resolving remaining issues, i.e. a generalcharacterization, testing and technical development plan for the DI stage. Such a plan would
include approaches for verification of assumptions made regarding rock conditions andengineering feasibility (to be executed during the DI stage), characterisation targets for the DI
stage, required R&D topics for DI, remaining issues relating to long-term safety, engineering
design and site understanding as identified when developing the preliminary safety case andan assessment whether further resolution of these issues is needed (input from the preliminary
safety case).
Safety-related restrictions on underground access: Such restrictions would be based on theselected repository concept and could relate to location of access, groundwater control,chemicals that could be used, etc.
2.5.3 Step 1: Activities before access construction
The following activities are foreseen the construction of the access tunnel or shafts.


Step 1.1

Initial planning of characterisation and monitoring during DIStep 1.2

Initial planning of testing in the host rock and elsewhere8

Step 1.3

Complementary surface-based investigations (additional borehole &
geophysical surveys)



Step 1.4

Initiation of baseline monitoring

Step 1.5

Update SDM 2.0

 Step 1.6
Detailed design of access
These are further outlined in the following sections.
Step 1.1 Initial planning of characterization and monitoring during DI
While planning of the DI already starts as part of the DIA selection (i.e. at the PI stage), a
more detailed, although still preliminary, planning of the characterisation and monitoring
during DI is needed once the DIA selection is made.
Issues to be considered:
The following items should be considered in the characterization and monitoring planning:Key remaining issues from PINeed for complementary surface-based investigations. It is very likely that complementarysurface-based investigations (boreholes and geophysical surveys) will be needed in the DI
stage. The main objective of these investigations would be to support the detailed repository
design in rock volumes not directly reached by the underground excavations carried out in
the DI stage. This also means that the scope and intensity of these investigations will dependon the DI objectives, the type of host rock and the understanding of the host rock

What characterisation is needed for the detailed design of the access volume?



Need for characterisation during access construction (relevance depends on the importanceof understanding the overlying formations).



Assessments whether remaining issues require specific characterisation or specific tests insitu in the host formation

Assessment of needs/objectives of monitoring the impact of construction (mechanical,
hydraulic, chemical)



Need for extended surface-based characterisation - will the deep access sufficiently cover thefootprint of the repository? (Depends on DIA objectives).

Should there be a characterisation loop around the first repository panels (depends on DIA
objectives).

It should also be noted that the list of issues assumes that the objective of the DIA stage is not
only to show that the DIA fulfils the legal requirements, but also that the DIA should lead todetailed design of the repository.

9Required input
The following input is required for the planning:Feedback from design and safety assessment

Safety-related restrictions on underground access (location of access, groundwater control,chemicals, e.g. low-pH grout, etc.)

Outcome
The expected outcome of the planning is:

A programme for the complementary surface-based investigations

Preliminary plans for underground characterization and monitoring

Step 1.2: Initial planning of testing in the host rock and elsewhere
In addition to the initial planning of characterisation and monitoring during DI, there is also aneed for initial planning of testing in the host rock and elsewhere, even if such tests would
typically only start when the excavation has reached the host rock at relevant depths. It should
also be realised that the initial test plan might be substantially revised based on the findings
made during the underground excavation.
Issues to be considered
The following issues should be considered in the initial test planning:Key remaining issues from PIAssessment whether remaining issues requires specific tests in the host formation (e.g.
interaction between EBS and rock, demonstration of construction technologies,
demonstration of operating technologies (transportation and emplacement), demonstration ofclosure technologies (plug, backfill, borehole sealing, etc.))

Is it necessary to perform the test at the site – or could it be done at another URL?



Will the test provide results in time for the completion of the DI stage?



Are there tests that could help guide the implications of the concept of "performance
confirmation monitoring", e.g. THMC processes, metal corrosion.

Required input
The following input is required:

Feedback from design and safety assessment

Initial planning of characterisation and monitoring during DI (Step 1.1 above)

Safety-related restrictions on underground access (location of access, groundwater control,chemicals, e.g. low pH grout, etc.).



Assessment of on-going and planned tests at URLs in Japan and abroad.

10Outcome
The following outcome is expected:
Preliminary plans for underground testing, with justificationPlans for trial-and-error type testing in generic URLs that may or may not be confirmed laterat the DI site.

Step 1.3: Complementary surface-based investigations
Step 1.3 involves the actual performance of the surface-based investigations. However, it
should be noted that these investigations do not necessarily end once underground excavation
starts. There may be good reasons to continue with some surface-based investigations duringlater steps.
Issues to be considered
The basic issue to be considered is the timing and logistics of the investigations, i.e. when are
the results needed. It should be noted that surface-based investigations do not necessarily end
once underground excavation starts. There may be good reasons to continue with somesurface-based investigations during later steps. The following should be considered:

Information needs for the detailed design of the access (e.g. pilot hole in the proposed shaft).
These investigations clearly need to be completed and evaluated in time for the detailed
design of the access

Additional boreholes needed for baseline monitoring purposes – these boreholes also need tobe completed and instrumented prior to the start of the excavation

Investigations aimed at more detailed coverage of the potential repository volume. These
investigations can probably be conducted in parallel with access construction.

Required input
Performance of the complementary surface-based investigations requires the programme forthe complementary surface-based investigations developed in Step 1.1.
OutcomeThe outcome of this step is the completed investigations with their results.

Step 1.4: Initiation of baseline monitoring
If not earlier, baseline monitoring needs to be initiated prior to the potential disturbances
caused by the excavation activities. To a large extent, the monitoring would be a continuationof the monitoring (potentially) initiated during the later stages of the PI stage.
Issues to be considered
The following issues should be considered:11Monitoring should be seen as part of the characterisation programme – not as a separate
activity!

Some of the monitoring should have been initiated in the PI stageAdditional borehole drilling might be required if the boreholes already drilled for site
investigation are not sufficient for baseline monitoring (see Step 1.3).

Required input
The following input is required:Preliminary plans for underground characterisation and monitoring (see Step 1.1)



Existing monitoring programme from the PI stageSpecification and location of existing boreholes that could be used for monitoring in the DIA

Requirements for baseline conditions from safety assessment and repository design
perspectives.

OutcomeThe outcome is the baseline monitoring system on site.

Step 1.5: Update SDM 1.0 to SDM 2.0
The information obtained from the characterisation work prior to excavation should be
evaluated and assembled in an updated SDM 2.0.
Issues to be considered
The basic issue to be considered is how to update the SDM such that it can be used as input
for the detailed design of the underground access. This means that it will focus on rockformations along the access and may be less ambitious regarding other formations, even if
they are eventually very important for the safety case and the detailed design of the entire
repository. Furthermore, the description in the access formations might have a much higher
geometric resolution compared to the SDMs developed during the PI stage.
Required input
The following input is required:

SDM 1.0 from the PI

Findings from additional characterisation (see Step 1.4) and monitoring (see Step 1.5) before
the start of the detailed design work.

OutcomeThe basic outcome of this step is the updated SDM 2.0, with the focus on the details of thevolume in the vicinity of the underground excavation access.

12

Step 1.6: Detailed design of access and surface facilities
The final step prior to excavation is the detailed design of the access and the surface facilities.
Issues to be considered
There are several issues to be considered in the detailed design of the access, including:

Detailed design of the surface facilities for DI (e.g. facilities for tunnel/shaft construction,
excavation muck storage, water treatment facility, pipeline for groundwater discharge)Estimation of required land area for DI activities and purchase of the land

Developing the preliminary design into a detailed design that can be readily applied by theconstructorEnsuring proper integration between the excavation work and the characterization activities.
This has proved to be a real challenge based on the experience of e.g. SKB at the Äspö HRL,AECL at their URL and Posiva at ONKALO. There is an inevitable conflict between, on the
one side, the constructor who usually has a considerable incentive to complete the access as
quickly as possible and, on the other side, recognising that the underground excavations are
made for a very specific purpose – and not only for completing the underground facilities.
Careful attention to contractual agreements and incentives is needed

Restrictions related to long-term safety (e.g. formations that must not be penetrated,materials that might not be acceptable, and long-term safety requirements on the access suchas the EDZ)

Type of access (e.g. ramp or shaft or both).

Required input
The following input is required for the detailed design of the access:Detailed scale SDM for the access volume (see Step 1.5)

Detailed engineering requirements (to be identified based on the updated SDM)



Requirements/restrictions regarding long-term safety (to be identified based on the updated
SDM)Preliminary plans for underground characterisation and monitoring during accessconstruction (see Step 1.1)

How will the access be used for repository construction or operation at a later stage? Thismight affect the decision between a ramp or a shaft and also what kind of restrictions might
apply.

Outcome
The following outcome is expected from the detailed design:13

Detailed design of the access, integrated with a plan for underground characterisation andmonitoring

Detail time schedule for access excavation.

2.5.4 Step 2: Activities during construction of the access
The following activities are foreseen during access construction:


Step 2.1:

Construction of an access tunnel or shaft to reach the host formation



Step 2.2:

Characterisation and monitoring during access construction

Step 2.3:

Assessment of findings during access construction – update of SDM 2.0,
consideration of whether safety case and critical issues in safety casehave been addressed

Step 2.4:

Revision of the underground characterisation and test plan.
(Decision to proceed with the DIA).

These are further outlined in the following sections.
Step 2.1: Construction of an access tunnel or shaft to reach the host formation
Based on the detailed design developed in Step 1.6, construction should proceed, while still
meeting the expectations of characterisation and monitoring.
Issues to be considered
The following issues should be considered during the access construction:Constructing the access and implementing the characterisation and monitoring plan

Handling "surprises". There will be surprises, e.g. the construction will encounter formations
or conditions that were not fully anticipated in SDM 2.0. Such situations should not be
regarded as catastrophic, but instead be anticipated and measures prepared for handling them,e.g. by applying the "observational method"Meeting the construction schedule without jeopardising the objectives of the DI in generaland the underground characterisation and monitoring plan in particular (see previous
comments in Step 1.6).

Required input
The basic input required for this step is the detailed design developed in Step 1.6.

14

Outcome
The basic outcome of this step is the completed access and the characterisation andmonitoring associated with this.
Step 2.2: Characterization and monitoring during access construction
It is highly likely that rock characterisation and monitoring will be a crucial activity during
access construction.
Issues to be considered
The following issues should be considered for the characterisation and monitoring during
access construction:

Carrying out the characterisation and monitoring plan without unduly disturbing the
excavation work

Being able to adjust the plan based on new findings and surprisesMonitoring of the potential perturbations in the geosphere caused by the undergroundconstruction.

Required input
The basic input required is the plan for the underground characterisation and monitoring (seeStep 1.3).
OutcomeThe outcome of this step is:Completed characterisation activities



Installed and initiated underground monitoring

Monitoring data from the surface.

Step 2.3 Assessment of findings during access construction
The findings during access construction need to be evaluated and assessed, not only in termsof an updated SDM, but potentially also in terms of an updated repository design and updated
safety assessment.
Issues to be considered
The following issues should be considered for this step:Is there a need for a detailed SDM in the local host volume for potential test tunnels?

Consideration of whether the safety case and critical issues in the safety case require revisionAssessment of disturbances caused by the excavation (e.g. estimation of macroscopic
hydraulic properties of the rock formations using the water inflow rate along the access,assessment of buffering of infiltrating groundwater)15

Are the disturbances affected by local phenomena (such as "skin" or grouting) – or do theytell something about the site?

Required input
The basic input required for this step is the results of characterisation and monitoring during
access construction (see Step 2.2).
OutcomeThe outcome of this step is:Update of the SDM 3.0 in the access and testing volumeUpdated needs for underground tests - are there remaining uncertainties regarding the site
conditions that are highly relevant for safety or design?

Step 2.4: Revision of the underground test and characterization plan
The findings from the access construction characterisation and from other activities are likely
to suggest that the preliminary underground test plan (Step 1.2) needs to be updated andrevised.
Issues to be considered
Issues to be considered in the test plan revision include:

Are there continuing characterisation and monitoring needs?



Should there be specific characterisation tunnels around the first disposal panels and what
investigations should be carried out?

Can remaining uncertainties in the site conditions that are highly relevant for safety or design(see Step 2.3) be resolved by underground tests?



Are there other needs for underground tests from a safety or engineering point of view?

Is there a special need for demonstration in addition to the purely technical needs?

Will the relevant tests, i.e. the ones that meet needs, produce results in time for thecompletion of the DI stage?



Are tests really needed in the host formation? What can be achieved by testing in other
URLs?



Advantage of parallel tests underground and at the surface for comparison purposesWill tests provide results in time for the completion of the DI stage?

Required input
The basic input required is:Results of Step 2.3



Other needs for underground tests
16

Assessment of activities in other URLs (in Japan or elsewhere).

OutcomeThe basic outcome of this step is:Updated test planUpdated characterisation and monitoring plan.

Examples of tests on the actual rock conditions
Example of issues related to testing the actual rock conditions that could be important forresolving by underground tests include:Mechanical stability (rock stress and rock mechanical responses), detailed migration paths in
the near-fieldGeochemical processes.

Examples of geosphere tests that would serve such needs include:Mechanical tests (e.g. mechanical and thermal property tests on rock samples, initial stressmeasurements)

Hydraulic tests in boreholes (pressure, conductivity, fracture contribution to groundwater
flow, gas permeability, gas breakthrough pressure)

Geochemical investigations (redox conditions/buffering capacity, high-pH buffering capacity,
groundwater history, groundwater dating)

EDZ measurements (hydraulic properties, depth, etc.)Geophysical tests to detect features in the host rock (identification of detection limit –distance, size, and feature).

Examples of EBS tests
Examples of issues related to the EBS to be considered when planning EBS tests include:

Aspects of EBS design that would be good to test in situ

THM processes in the EBS and its interaction with the host rock.

However, it must be noted that many of these tests could be done at other URLs and the tests
may take too long to complete during the DI stage (depends on the objectives of the DI stage,see Section 2.4). This means that NUMO needs to think about critical EBS tests that could be
conducted at other URLs already during the LS and PI stages. EBS tests carried out at the17

DIA stage would typically be confined to confirming the applicability of results obtained
from more elaborate and time-consuming tests carried out previously.
Examples of EBS tests include:

Demonstration test of EBS transportation and emplacement in the host rock (operational test),
if possible with a prototype remote handling system to check engineering practicality andcycle time, etc.

Designing and testing the measures taken against potential operational hazards, e.g. derailing,
canister drop, rock fall, flooding, fire, recovery of emplaced EBS, etc.



EBS behaviour test: buffer saturation test, THM coupling test, canister corrosion test, gas
generation and migration test, material interaction study (e.g. bentonite-cement).

Examples of other tests
There will also be other tests to consider, notably focusing on demonstration and repository
operations. Examples of issues to be considered include:Testing aspects of the repository components (e.g. drilling deposition holes, backfilling,plugs, borehole sealing, etc.)

Demonstration of the practicalities of repository operation

Needs from public relation.

Examples of other tests include:

Sealing technologies (e.g. grouting, temporary plug, borehole sealing)Repository closure technologies (backfilling, permanent plug, feasibility of long-termmonitoring concept and technologies).

2.5.5 Step 3: Activities in the host formation
At least the following activities are foreseen when the access has reached the host formation:


Step 3.1:

Construction of test and (potential) characterisation tunnels

Step 3.2:

Continued characterisation and monitoring

Step 3.3:

Implementation tests

These are further outlined in the following sections.
Step 3.1: Construction of test tunnels and (potential) characterization tunnels

18

Clearly, test tunnels and potential characterisation tunnels need to be excavated according toplan. Furthermore, the excavation experience itself also provides important input for thedetailed design of the repository.
Issues to be considered
The following issues should be considered:Ensuring that the test and characterisation tunnels are constructed to meet test objectives

Testing logistics

Considering the potential use of the test and characterisation tunnels for future near-field
monitoringTesting excavation methods for disposal tunnels

Feasibility of an exploration tunnel around the repository area

Worker safety (ventilation, fire, etc.).

Required input
The following input is required for this step:

Revised underground testing and characterisation plan (see Step 2.4)



Monitoring concept for the near-fieldMethod statements for excavation of test tunnels and actual disposal tunnels.

Outcome
The main outcome of this step is:Completed test and characterisation tunnels

Experience gained from the excavation.

Step 3.2: Continued characterization and monitoring
Characterisation and monitoring continue. Depending on the plans, characterisation may be
carried out using boreholes drilled from underground, potentially complemented by acharacterisation loop around the first repository panels. One possibility is to excavate
exploratory tunnels around the planned disposal area. This allows direct confirmation of thehost formation, e.g. extent, location and impact of features, etc.
Issues to be considered
The following issues should be considered:

Carrying out the characterisation and monitoring plan in the host rock and elsewhere without
unduly disturbing the excavation work

Being able to adjust the plan based on new findings and surprises

19

Monitoring of EDZ development or a mine-by test with the progress of excavation of the test
tunnel

In the event that an exploratory tunnel is constructed around the planned disposal area, thetime schedule must be well planned as the excavation may take quite a long time considering
the interaction with investigation work, e.g. mapping of tunnel surface, potential tests forcharacterising features.

Required input
The basic input required is the revised underground testing and characterisation plan (seeStep 2.4)
OutcomeThe outcome of this step is the completed characterisation activities and the installed andinitiated monitoring system.
Step 3.3: Implementation of the tests
Implementation of the tests is likely to involve several issues, but at this early stage ofplanning only a few can be listed.
Issues to be considered
The basic issue to be considered is carrying out the tests according to plan.
Required input
The main input required is the revised underground testing plan (see Step 2.4) and thecompleted test tunnels (see Step 3.1).
OutcomeThe outcome is the results of the tests.

2.5.6 Step 4: Final evaluation and reporting of the DI stage
While evaluation and reporting are needed throughout the DI stage, it is also important toenvisage the activities needed for the final evaluation and reporting. The following steps areenvisaged:

Step 4.1

Updated SDM 4.0



Step 4.2

Detailed repository designStep 4.3

Updated safety case

These are further outlined in the following sections.

20

Step 4.1: Updated SDM 4.0
All the findings on the rock characteristics and monitored changes during the DI stage need tobe evaluated and documented in an updated SDM 4.0.
Issues to be considered
At least the following issues need to be considered:Addressing targets and issues in previous plansEnsuring fulfilment of engineering and performance assessment needs.

Required input
The following input would be required:

Findings from characterisation, monitoring and construction experienceFindings from tests.

OutcomeThe outcome of the step would beAn updated SDM – with the focus on the detailed data on the rock formations



Assessment of confidence over the entire footprint – is there a need for more surface-based
investigations prior to the licence application?

Step 4.2: Detailed repository design
If the DI stage includes detailed repository design, this design needs to be developed.
Issues to be considered
Issues to be considered in the detailed repository design include:

Revising the repository design based on the results of the tests performed (includingtransportation/emplacement of the EBS)How will the repository be designed (including layout), considering all safety-related
restrictions and the desired repository capacity (including potential for TRU waste).

Required input
At least the following input is required:Updated SDM 4.0

Construction experience from the DI

Findings from activities during DI stage.

OutcomeThe outcome should include:

A detailed repository design building on the most recent SDM 4.0 and findings from the tests

21

A suggested approach for constructing the repository in accordance with the detailed design.

Step 4.3: Updated safety case
Since the DI stage should lead to the licence application, the safety case needs to be updatedwith the findings from the DI stage.
Issues to be considered
The following issues should be considered:Conclusions to be drawn from the various tests carried out during DIAre there any findings during DI that would dramatically change the safety case?

Feedback to the repository construction stage.

Required input
The following input is required:Updated SDM 4.0 (see Step 4.1)

Detailed repository design (see Step 4.2)

Findings from activities during DI stage.



Any relevant scientific and technical information available at this stage (e.g. lab tests,
generic URL, natural analogues, domestic and overseas safety assessment studies).

OutcomeThe outcome of this step should include:Updated safety case based on findings from the DI stage



List of issues and further investigations (if any) that need to be completed prior to the licenceapplication

Feedback to the repository construction stage.

2.6 Outlook
This activities provides a framework for the activities that will need to be implemented in the
DI stage. It describes the basic activities and the required feedback between activities needed
during the DI stage as they can be defined and anticipated in this early stage of the
programme.

22

As the programme matures, the repository concept will be selected and insight will be gained
into the potential host rock and sites that will become DI areas, the type of activities will
become more concrete and the effort needed to conduct them can then be specified.
However, the structures that will need to be in place before the start of the DI stage, in order
to conduct the activities will need to be well though off in advance. This would require to:Further specify the objectives and scope of the DI stage

Further elaborate on the iteration and feedback between site characterization, undergroundexcavation experience, detailed underground design and safety assessment.

23

3 Uncertainty management in the safety case
3.1 Introduction
There are multiple uncertainties in describing the evolution and performance of a geologicalrepository. For example, the evolution of a repository over the time frame of interest in asafety case generally involves a large number of coupled and sometimes complex phenomena,some of which are incompletely understood or characterized. Uncertainties may affect theinitial state of the system (e.g. uncertainties regarding the presence of fabrication defects).
They may also affect the rates of processes and the timing of events in the course of therepository evolution. Additionally, there may be uncertainty in whether or not a process or
event will actually occur, and/or the extent of its impact on evolution and performance.
Uncertainties may be aleatory or epistemic in nature. Aleatory uncertainties are those thatcannot be reduced by more accurate measurements, and are associated with features, events orprocesses that show natural variability. Uncertainties may also be epistemic, i.e. associatedwith ignorance or lack of knowledge, and may in principle be reduced e.g. by performing
observations or measurements. According to OECD/NEA (2004a):"Overall, the distinction between aleatory and epistemic uncertainties is not always clear, andboth can be treated mathematically in the same way."
The overall strategy for the management of uncertainties can be summarized in four words:
identify, avoid, reduce and assess. According to Posiva (2008):"Identification and communication of uncertainties are usually an essential part of all thereports related to the development of the safety case. The development of the disposal system isbased on the idea of robustness, which means avoiding concepts and components the behaviourof which would be difficult to understand and predict. The stepwise implementation process of
the repository allows the reduction of uncertainties by means of continuous RTD efforts.
However, some uncertainties will always remain and have to be assessed in terms of theirrelevance to the final conclusions on safety."
This strategy is applied iteratively through the various stages of a repository programme, andprovides guidance to site characterisation, concept development and scientific research insupport of the safety case.
The cyclical nature of uncertainty management is depicted in Figure 3.1, the elements ofwhich are used to structure the present chapter. Uncertainties with potential safety relevancemust first be identified. The identification of uncertainties is dealt with in Section 3.2. They

24

must then be described or quantified to the extent necessary to assess their impacts. The
description and quantification of uncertainties is covered in Section 3.3. Assessment of impact
is discussed in Section 3.4. Those that are shown to have impacts that could compromise
repository safety must be:Reduced, e.g. by developing a better understanding of uncertain processes

Mitigated by making the repository concept less sensitive to particular uncertainties, e.g. by
the conservative dimensioning of some repository barriers; or

Avoided, e.g. by the use of well understood materials that are less subject than others to
uncertain processes.

Avoidance, reduction and mitigation of uncertainties are discussed further in Section 3.5.
The final aim of the strategy is the identification and characterisation of a site anddevelopment of a concept for which adequate levels of safety can be shown in spite of any
residual uncertainties.
The descriptions in Sections 3.2 to 3.5 are not intended to be comprehensive. All programmes
follow a similar overall strategy for uncertainty management, but the approaches adopted
differ in detail, and Sections 3.2 to 3.5 simply provide a few examples of recent developments,
some of which are still under active development.
Finally, Section 3.6 provides ideas for future work resulting from the NUMO-Nagra
collaboration.

25

INITIAL SYSTEM UNDERSTANDING

What are the sources of
uncertainty?

Which are potentiallysafety-relevant and how are theypotentially safety-relevant?

Identify, avoid
reduce, assess

TKS PROGRAMME

How can degrees of uncertainty bedescribed/quantified?

What are the impacts of individual
uncertainties on system
performance and saftey?
Can/need individual uncertainties be
avoided, reduced or their effects mitigated?

Yes

No
What is the combined impact of all identified
uncertainties on system performance and safety?

SAFETY CASE

Figure 3.1 The cyclical strategy for identification, avoidance, reduction and assessment of
uncertainties (adapted from Figure 6-9 of Posiva 2008)

3.2 Identification of safety-relevant uncertainties
For organizing a safety assessment, it is often convenient to categorize the uncertainties that
affect the evaluation of safety indicators such as dose as "scenario", "model" or "parameter".
It should be noted, however, that the distinctions between these classes is not always welldefined. For example, according to Nagra (2002):"It is recognized that there is an overlap between the different categories of uncertainty andallocation to a particular category is an operational matter that may involve a subjective
decision."
As discussed in the previous chapter, scenarios are often defined in terms of the broad
evolution of the main safety functions provided by a repository over time. The scenario
uncertainties are those that lead to significantly different possibilities for the evolutions of the26

safety functions. Systematic methods for the identification of such uncertainties are being
developed in several national programmes.
SKB has developed a methodology based on the concepts of safety functions and theirassociated indicators and criteria, defined as follows and based on SKB (2006a):
Overall safety functions of the repository are containment and retardation
These are differentiated into a number of lower-level safety functions for the main repository
components
Safety function indicators are measurable or calculable property of the repository
component associated with each (lower-level) function
Safety function indicator criteria are defined such that, if a safety function indicator fulfils acriterion, then the corresponding safety functions in is upheld.
As an example, safety functions, indicators and criteria for the buffer identified in the SKB
SR-Can safety assessment are shown in Figure 3.2.
The use of these concepts in the identification of safety-relevant uncertainties is illustrated in
Figure 3.3, which considers the process of buffer erosion due to the penetration of low ionicstrength groundwater to repository depth. This process could occur, for example, in
association with glacial advance or retreat above the repository. If erosion occurs, it willaffect buffer density and in turn the buffer swelling pressure which, as shown in Figure 3.4, isa safety function indicator associated with the buffer safety functions of limit advective
transport. If these safety functions are lost the supply of corroding sulphide will increase
substantially, which in turn enhances canister corrosion to an extent that the integrity of thecanister (another safety function) may be lost. Loss of buffer density will also affectelimination of microbes and preventing canister sinking. The degree of erosion that mightoccur over time is, however, subject to numerous uncertainties, which must be taken into
account when evaluating with model calculations whether the criteria for these safety function
indicators are upheld.

27

Figure 3.2 Safety functions (bold), safety function indicators and safety function indicator
criteria for the KBS-3V buffer (SKB, 2006a)
The colour coding shows how the functions contribute to the canister safety functions corrosion barrier (red), withstand isostatic load (green), withstand shear load (blue) - or toretardation (yellow). Many functions contribute to both the canister corrosion barrier function
and retardation (red box with yellow board) (after Figure 9-2 of SKB 2006a)

Figure 3.3 Use of safety functions, indicators and criteria for the evaluation of the safetyrelevance of the process of buffer erosion and its associated uncertainties

In the case of buffer erosion, there are two more specific questions to be addressed by model
calculations in order to answer the more general question of whether relevant criteria areupheld:1)

How much buffer could be lost due to erosion?

2)

How much buffer would have to be lost such that the criteria on maximum hydraulicconductivity and minimum swelling pressure would no longer be upheld?

A buffer erosion model has been developed in order to address the first of these questions(Neretnieks et al., 2009). This is subject to numerous uncertainties in both the understandingof the erosion process itself, and in the parameters to be assigned to the model. The same is28

true of the calculations of buffer homogenisation following mass loss that are performed inorder to answer the second of the questions (Åkesson et al., 2010).
Based on the model calculations, and taking all these uncertainties into account, the questionof whether the density-related safety function indicator criteria are always upheld isconsidered. If, in spite of the uncertainties, the answer is confidently judged to be yes, thenthe buffer erosion process need not be considered further in the safety assessment. If thisjudgement cannot be made with confidence, then the possibility of the loss of one or more
buffer safety functions must be considered as alternative buffer scenarios in the safetyassessment.
The planning of model calculations to support judgements as to whether or not safety function
indicator criteria are upheld is iterative, as illustrated in Figure 3.4.

Figure 3.4 Illustration of iterative nature of the planning of model calculations to support
judgments as to whether or not safety function indicator criteria are upheld

For example, calculations of the corrosion lifetime of the KBS-3 copper canisters (i.e.
calculations of whether, and for how long, the safety function indicator that the copper
thickness > 0 over the entire canister surface is upheld) will be based on certain calculation
premises, e.g. that the repository buffer and backfill perform their respective safety functions,
implying that diffusion is the dominant transport process in the repository near field, that the29

deposition hole positions are chosen according to appropriate rock suitability criteria (RSC),
etc. However, calculation of buffer erosion of the type described above may indicate thatthese premises are not necessarily fulfilled at all canister positions for all relevant times and,for example, copper corrosion in conjunction with advective conditions in the buffer may
need to be considered in some deposition holes. A general scheme for iterative planning ofsuch calculations is illustrated in Figure 3.5.

Figure 3.5 General scheme for the iterative planning of model calculations

ONDRAF/NIRAS has developed a different, though related, methodology based on theconcept of a hierarchy of safety statements. As shown in Figure 3.6, the statements at a higher
level are very general and concern aspects of the safety concept whereas lower levelstatements concern detailed aspects related to the phenomenological understanding of thesystem. The lower statements are directly supported by the evidence from the scientificunderstanding of the site and repository concept. The statements are developed in a top-downmanner, with lower-level statements being those that need to be substantiated in order tosubstantiate, or at least increase confidence in, the higher-level statements.
The uncertainty analysis systematically examines perturbing phenomena and associateduncertainties potentially affecting the validity of each of the lowest-level safety statements,
and the propagation of these uncertainties from one statement to another. Any uncertainty that
calls into question the validity of lowest-level statements may also call into question thehigher-level statements that the low-level statements underpin. In this way, uncertainties may
30

propagate through the hierarchy of statements, from the bottom-up. Any uncertainty
propagating as far as safety statements representative of the safety functions of the disposal
system gives rise, potentially, to altered evolution scenarios and is thus categorised as a
scenario uncertainty. (Smith et al, 2009).

Figure 3.6 Examples from the ONDRAF/NIRAS hierarchy of safety statements (after Table 1 ofSmith et al. 2009)

The propagation of uncertainties from lower-level safety statements towards higher-levelstatements is illustrated in Figure 3.7, for the example of uncertainties associated with theimpact of climate change on the Boom Clay host rock. Subject experts are asked whether, forexample, cracks in the Boom Clay could develop as a result of permafrost penetration. If theanswer is yes, the hierarchy of statements is examined to assess whether this could
conceivably affect the validity of the highest-level statements concerning the Boom Claysafety functions (i.e. compromise the safety function of the Boom cay of limiting water flow
and ensuring diffusion-dominated transport).
31

It should be noted that, though not yet attempted, the concept of safety function indicator
criteria could be incorporated in the ONDRAF/NIRAS methodology, i.e. criteria could
possibly be developed that, if upheld, would imply that a given statement can be considered
substantiated.

Figure 3.7 Example of the propagation of uncertainties related to a change of climate through ahierarchy of safety statements (after Figure 10 of Smith et al. 2009)

Uncertainties that do not propagate to the highest-level statements may nevertheless affecthow specific processes are modelled in a given scenario, and the values assigned to model
parameters. These are, respectively, the model and parameter uncertainties. In general, theidentification of model and parameter uncertainties relies heavily on the use of expert
judgement by subject specialists.

32

To identify model uncertainties, it can be helpful to list systematically all the assumptions that
underlie a particular model, and then to consider whether these assumptions are fully justified,or whether alternative assumptions need to be considered. An example of such a listing isgiven in Table 3.1 for the case of matrix diffusion.
Table 3.1 Example of a listing of assumptions related to the modeling of matrix diffusion, andidentification of possible alternative assumptions

In the case of parameter uncertainties, to focus discussion with experts and to reduce thepossibility of important uncertainties being overlooked, it can be helpful to identify"checklists" of the important causes of such uncertainties. For example, ONDRAF/NIRAS
have identified as important sources of uncertainty in the parameter values used in its
assessment models (Section 2.2.4 of Smith et al., 2009):


The applicability of the phenomenological data obtained from observations or laboratory
experiments over relatively short intervals of space over the larger spatial scales of interest insafety assessment.



The applicability of the phenomenological data representative of the host formation in one
location in another location or a larger zone. Transferability considers up scaled data as its
starting point, which increases the uncertainty and thus broadens the parameter ranges.



The impact on the phenomenological data obtained today of phenomena occurring over timethat may affect the disposal system, such as phenomena triggered from within the disposal
system (for example, the effect of the thermal phase on clay properties) or external events(for example, human intrusion or climate changes). The analysis of the impact of evolving
conditions on phenomenological data uses as a starting point data that have undergone an up
scaling and/or a transferability process, and further increases the uncertainty, thus
broadening the parameter ranges. This analysis requires the knowledge of the evolution of
the system components, of its geological coverage and of the biosphere.

33

There are, however, other sources of parameter uncertainty that should not be overlooked,
such as measurement errors and incomplete datasets.

3.3 Description and quantification of uncertainties
Depending on whether the safety assessment adopts a probabilistic or deterministic approach(or a combination of both, see Section 3.4), parameter uncertainties may be quantified interms of probability density functions or in terms of discrete alternative values. Scenario andmodel uncertainties will typically be described in terms of the "degree of belief" in the various
alternative scenarios or models that have been identified.
In general, the quantification of uncertainties in terms of numerical probabilities is only
attempted in the case of parameter uncertainties. Scenario and model uncertainties are often
described in terms of a qualitative judgement as to whether a given alternative is, for example,
likely, unlikely, very unlikely, etc. In some cases, however, (e.g. in the U.S. programmes)
model and scenario uncertainties have been represented in terms of additional parameters, towhich probabilities have been attached.
Figure 3.8, from Nagra's Project Opalinus Clay illustrates some of the probability density
functions (PDFs) commonly used to quantify parameter uncertainties. Where possible,
support for parameter values and PDFs is sought from a wide range of sources, including
laboratory and field experiments and observations from nature, in order to ensure that therange of parameter uncertainty is reliably bounded. In order to test the robustness of thesystem with respect to parameter uncertainty, "what if?" parameter values that lie outside therange of possibilities supported by observations and experiments and for which it is thus
meaningless to make a statement about their probability of occurrence may also be consideredin safety assessment.

34

Figure 3.8 Examples of probability density functions and a more speculative "what-if?" value(after Figure A1.2 of Nagra (2002))

Discrete alternative parameter values may be described using terms such as "best estimate","optimistic" or "pessimistic". Alternative, ranges may be defined, within which all parametervalues are considered equally probable. This is, for example, the approach currently being
considered by ONDRAF/NIRAS (Smith et al., 2009). The uncertainty treatment of
ONDRAF/NIRAS includes a non-parametric protocol to quantify the uncertainties of aparameter on the basis of the expert knowledge. Uncertainty ranges are defined, within which
all parameter values are considered equally probable.
Following this protocol,
ONDRAF/NIRAS ask their subject experts to specify two ranges for parameter values, taking
into account the various sources of parameter uncertainty described in Section 3.2. These
ranges, also illustrated in Figure 3.9, are:

The source range is the range of values outside of which the parameter value is very
unlikely to lie, considering current knowledgeThe expert range is the range of values within which experts expect the parametervalue to lie.

35

"Expert range""Source range"

x1

x2

x3

x4

X

Figure 3.9 Ranges of parameter uncertainty (adapted from Smith et al 2009)
Figure 5 – Illustration of the source and expert ranges for a hypothetical param eter x.

These ranges can be linked to subjective, common-language terms such as "expected", "notreally expected" or "not expected", which can facilitate the communication of their meaning.
Furthermore, concepts such as "imprecision", "vagueness", "incompleteness" and "conflicting
evidence" can be taken into account in defining the source range, which are not readily
describable using probabilities. Despite the qualitative character of this elicitation process, theranges estimated by experts have to be justified by multiple lines of evidence. Currently
ONDRAF/NIRAS uses expert and source ranges in safety calculation cases in order toperform sensitivity analysis and identify critical issues. It gives guidance to prioritize the
RD&D program. Expert ranges are used in the framework of the reference scenario whilesource ranges would give an indication of the robustness of the system.
It is important when describing parameter uncertainties to consider how uncertainty in one
parameter is linked to, or correlated with, uncertainties in others. For example, uncertainties
in the sorption coefficients of each radionuclide species cannot, in general be describedindependently. In particular, they are all affected by uncertainties in groundwater chemistry,and so, for example, a high sorption coefficient or one species will tend to be correlated withhigh sorption coefficients of other, chemically similar species. As a further example, highvalues of near-field flow, which for example can strongly affect radionuclide release acrossthe near-field/geosphere interface, will tend to be accompanied by low values of the overall
transport resistance of the host rock, especially since it is often the rock immediately aroundthe engineered barriers that main contribution to this transport resistance.

3.4 Assessing the impacts of uncertainties
Safety assessments treat uncertainties primarily by defining and analysing a wide range ofassessment cases – i.e. specific model realisations of different possibilities or illustrations of
how a system might evolve and perform. The cases, which may be analysed deterministically,
probabilistically or by some combination of these approaches, each address the impact ofsome particular uncertainty or combination of uncertainties. Categorisation of uncertainties
can provide a basis for organising such cases.
36

In a deterministic approach, parameter values for each case are individually specified. In aprobabilistic approach, parameter values sampled randomly from probability density
functions (PDFs). Probabilistic calculations explore the full extent of a defined parameter
space. Deterministic calculations explore just a few locations in parameter space.
In general, alternative models and alternative scenarios are not integrated within the set ofprobabilistic calculations (although, as noted earlier, this can be done by representing modeland scenario uncertainties in terms of additional parameters, to which probabilities areattached). Rather, discrete sets of calculations are calculated for each alternative scenario and,within each scenario, for each alternative subsystem model.
Correlations, discussed above in the context of describing and quantifying uncertainties, need
to be taken into account when defining the defining deterministic calculation cases, or whensampling probabilistically from PDFs. Similarly, when defining the models and scenarios tobe analysed, possible combinations of alternative model assumptions and alternative scenarios
need to be considered, taking into account the likelihood of occurrence of such combinations.
As an example, Table 3.2 shows some alternative scenarios for buffer and canister evolution
considered in the SR-Can safety assessment. Based on an extensive analysis of current
understanding of relevant processes, the scenarios were classified as "likely", "less likely" or"residual", where only those classified as "likely" or "less likely" were considered to have any
appreciable probability of occurrence, and so needed to be taken into account in evaluatingcompliance with Swedish regulatory risk targets.

37

Table 3.2 Buffer and canister scenarios considered in the SR-Can safety assessment,
indicating which are judged to be residual (adapted from SKB (2006a))
Only those indicated by an asterisk are judged to have an appreciable probability ofoccurrence

The residual scenarios were considered individually as hypothetical "what-if?" situations.
However, because of the hypothetical nature of individual residual scenarios combinations ofresidual scenarios were not considered (green combinations in Figure 3.10). Other possible
binary combinations of scenarios were, however, systematically considered. Three were
eliminated from inclusion from the risk assessment (yellow combinations in Figure 3.10), forreasons summarized in the notes in Figure 3.10. Only one combination remained to be
included in the risk assessment, namely erosion of the buffer leading to advective conditions
around one or more canisters, combined with corrosion failure of these canisters (the red
combination in Figure 3.10).

38

Figure 3.10 Binary combinations of buffer and canister scenarios considered in the SR-Can
safety assessment(simplified version of Table 12-5 of SKB (2006a))

This issue of risk dilution needs to be considered when performing probabilistic calculations
to assess compliance with mean dose or risk targets. Risk dilution denotes the situation wherea higher degree of uncertainty in input parameters, i.e. a broader input distribution, leads to alower mean value of an output quantity, e.g. mean dose or risk. As noted in SKB (2006a):"A seemingly paradoxical situation arises where less knowledge implies a safer repository if
the mean value to a highly exposed individual at a certain point in time is used as the safety
indicator. Less knowledge will spread the dose over more individuals and over longer times."
The issue in an inevitable consequence of mean dose or risk targets and cannot therefore be
avoided if compliance with such targets is required by regulations. However, it is important toacknowledge and discuss the issue in the documentation of the safety assessment and safety
case.
Not all uncertainties are treated by developing specific calculation cases or probabilistic
realisations to illustrate their impacts. Some are treated using model assumptions or
simplifications that are conservative, meaning that they tend to over-estimate evaluated doses

39

or risks. Parameter values can also be selected conservatively or pessimistically1. Such an
approach is necessary, for example, if there is no adequate model or dataset to evaluate theimpact of a particular process, but simply omitting the process is confidently expected to leadto conservative results. The conservative or pessimistic treatment of at least someuncertainties is also acceptable within a safety case given that regulatory safety criteria
generally refer to dose or risk limits, the demonstration of compliance with which requires
only bounding estimates of these safety indicators.
Identifying what is a conservative assumption or approach is not, however, always
straightforward - what is conservative with respect to one process may not be conservativewith respect to another competing process. Furthermore, a purely conservative approach does
not give a basis for deciding which uncertainties are the most important in terms of
performance. Neither does it allow different design, operational or siting variants to becompared. Identification of critical uncertainties and open siting or design issues is necessary,particularly at early programme stages, in order to guide the strategy for addressing themduring future stages (Section 3.5). Excessive conservatism or pessimism may also make it
impossible to satisfy relevant regulatory criteria. The use of conservative and pessimistic
assumptions for the treatment of uncertainties thus tends focus on those uncertainties forwhich the effort in reducing them by further research and technical development is notdeemed to justify the likely gains in calculated performance - the lack of a suitable model ordataset often reflects the fact that a process is not easily amenable to reliable scientificinvestigation.
There may, however, be some conservatively omitted processes for which there are judged to
be good prospects for more realistic modelling (and gains in calculated performance) at laterstages of the programme. These are termed "reserve FEPs" in, for example, Swiss safetyassessments, and their existence can provide a qualitative safety argument complementing
calculated doses or risks.

3.5 Avoidance, reduction and mitigation of remaining uncertainties
A key role of the safety case, which includes an assessment of the impact of uncertainties, isto provide guidance to the programme of research and technical development, including site
selection and characterisation. In particular, it will indicate which, if any, uncertainties havethe potential to weaken the safety case, and thus need to be avoided, reduced or their effects
1

The term "pessimistic" is sometimes used (e.g. in Nagra 2002) to refer to values that, within the range of possibilities
according to current scientific understanding, give rise to the highest consequences. The term "conservative" refers tovalues that are outside that range (e.g. assigning zero sorption to migrating species that are known to sorb to some extent,even though the degree of sorption may be uncertain).

40

mitigated. This role has been recognised by the OECD/NEA in the Safety Case Brochurepublished in 2004 (OECD/NEA 2004b):"The synthesis should … consider the limitations of currently available evidence, arguments
and analyses …. This includes the strategy by which any open questions and uncertainties
with the potential to undermine safety will be addressed and managed.""At the earliest stages of a programme, there may be many such open questions anduncertainties, and the safety case should make clear the view of the developer that there aregood prospects for dealing with these in the course of future stages, e.g. by sitecharacterisation and optimizatioin of system design, and set out the strategy by which thiswill be achieved."
The feedback from the safety case to research and technical development is recognised in the
programme descriptions and illustrative flowcharts produced by implementing organizations.
Figure 3.11 is an example from the Finnish programme.

Figure 3.11 The coupling between Research and Technical Development (RTD) work, planning,
performance targets/target properties and safety analysis(after Figure 6-1 of Posiva (2009)).

41

The figure shows that the feedback occurs not only in the form of results of safety analysis(e.g. calculations of dose for a range of calculation cases illustrating the impact of different
scenario, model and parameter uncertainties), but also at the stage of subsystem performance
evaluation and scenario formulation, when the assessment of the achievability of performancetargets (for the EBS) or target properties (for the rock), these being similar to the safetyfunction indicator criteria used in the Swedish programme. In particular, undertaking thisassessment is likely to highlight any deficiencies or uncertainties in the models and parametervalues used to evaluate whether criteria are upheld, such as the model of buffer erosion citedin Section 3.2.
The safety case also provides an important platform for discussion with the regulator
regarding those uncertainties that the regulator considers to be important to address, e.g. prior
to the granting of a licence. In some countries, including Sweden, Finland and the U.S., theregulator and its advisory groups, based in part on their review of safety assessments as wellas the implementer's research plans, compiles a Tracking Issue List (TIL). Such lists identify
issues that, in the regulators view, remain unresolved, as well as others that can be consideredclosed once certain conditions have been fulfilled. Resolved issues may also be retained in thelist so as to maintain a complete and open record of the issue resolution process.

3.6 Issues to be considered in the future
As a framework for the application of assessment models, the scenario development tools
could, however, be further refined and extended to deal with model and parameter
uncertainties, and hence the development of a range of calculation cases for safety assessment.
More specifically, the approach to identify uncertainties as well as if and how they affect thesafety functions needs further development. As part of scenario development, it has been
proposed to identify:
 The safety functions of the disposal system, e.g. containment of radionuclides by theover pack Processes that influence these safety functions, e.g. corrosion of carbon steel
 Environmental conditions that affect the occurrence or rate of such processes, e.g.
temperature
 Factors that affect these environmental conditions, e.g. heat generation by the waste, or
the thermal conductivities of repository materials.
The above are likely to be identified in a top-down fashion, starting with the safety functions,as shown on the left-hand side of Figure 3.12.

42

Figure 3.12 Top-down identification of processes, conditions and factors affecting controllingthe safety functions, and the bottom-up propagation of uncertainties

A logical way to identify uncertainties with the potential to affect the safety functions could
be to begin with factors that affect the environmental conditions, and consider first theuncertainties in these, e.g. in the rate of heat generation by the waste, or the magnitudes of thethermal conductivities of repository materials. Next, the implication of these uncertainties for
uncertainties in the environmental conditions – the evolution of temperature in this example –could be considered. Then, the implications of uncertain environmental conditions for
uncertainties in processes affecting the safety functions could be considered – the rate of steel
corrosion in this example. Finally, the implication of uncertainties in processes – the rate ofsteel corrosion in this example – on the evolution of the safety functions could be assessed. A
new scenario could arise, for example, if the uncertainty in steel corrosion rate is such thatover pack failure during the repository thermal phase is judged to be a possibility. Criteria
could be developed specifying, for example, how rapid a processes such as steel corrosion
would need to be in order to generate a new scenario, such as over pack failure during thethermal phase.
This top-down/bottom up approach has clear similarities to the ONDRAF/NIRAS approachsummarized in Section 3.2, and builds on the approach already partly developed by NUMO
(NUMO, 2011b). Care must, however be taken to ensure that no significant sources of
uncertainty are overlooked. In particular, uncertainties in the initial state (e.g. possibility of
initial defects in the overpack) must be captured, and this is likely to require further
development of the approach outlined above.

43

4 Definition and concept of Demonstration
4.1 Definition of demonstration
The issue of demonstration in radioactive waste management is practically as old as theradioactive waste management programmes themselves. The first demonstration experiments
were initiated in the late seventies, few examples being: the Climax mine experiment (1978 –1983) by the US DOE in Nevada, USA, which focussed on demonstrating the capability tohandle and package spent fuel and to emplace it in storage holes about 400 meters below thesurface in crystalline rock; the G-Tunnel experiment (1979–1990) also by USDOE in Nevada;
the Stripa mine (1976–1992) in Sweden, which evolved to become the first multinational
cooperation experiment on issues of geological disposal demonstration.
A discussion on the definition and role of demonstration in radioactive waste management
was initiated by OECD/NEA in the beginning of the 80s resulting in a report summarising theconclusions and state-of-the-art at that time (OECD/NEA, 1983). It was recognised from the
beginning that whereas the definition of demonstration in "research" is clear and wellunderstood, in "applied science", part of which is the management of radioactive waste andthe geological disposal, demonstration should be understood in a broader text. In researchdemonstration is defined as the verification by experiment of one or a set of assumptions.
Although research is one of the key components in applied science, the definition ofdemonstration also incorporates attributes such as:Scientific and engineering considerations

Engineering competence

Quality of construction

Skill of operators.

Hence, demonstration here includes the commonly used notion for the scientific part andexpands to include, what we will refer to in the rest of this chapter as, "know-how". In thecase of radioactive waste disposal, an organization can demonstrate "know-how" by showingthat:

It has the tools and methods to characterise the site, to design and build the repositoryIt has the necessary database and knowledge to evaluate the repository system and ensurethat it will meet the required performanceIt has the organizational structures and the capabilities to implement the process ofdeveloping and realising a geological repository.

44

In the above definition the reader should note that, "tools and methods" is used here in a broad
sense and it includes the testing equipment, the testing and interpretation methods, thenumerical tools, the machinery and manufacturing processes etc. Also the term "database" isused in a broad sense and it includes the data (from quality assured laboratory tests and field
investigations), the methodology to develop a quality assured assessment basis(conceptualisation of processes, treatment of events and features, formulation of scenarios andassessment cases, treatment of uncertainty) etc.
A more difficult aspect of demonstration in geologic disposal results from the considerationof time scales, which extend to periods of hundreds of thousands of years. The OECD/NEA
treatment introduces and clearly differentiates between:
Direct demonstration, which refers to aspects that can be demonstrated within the short timescale, andIndirect demonstration, which refers to aspects that correspond to much longer time scales.
Long-term safety of the geological repository system, i.e. demonstration that the repository
system (engineered and geologic barriers) will meet the required performance criteria,belongs to the second category of demonstration. The demonstration of geological disposal ofradioactive waste, according to the OECD/NEA (1983) definition includes then two steps:
Direct demonstration, which aims at proving (showing) that the system could be:


Built



Operated andClosed safely andAt acceptable costs, using available technology and engineering experience.

Indirect demonstration, which requires to make a convincing evaluation of the system's
performance and long term safety on the basis of predictive analyses confirmed by a body ofavailable data and evidence.
Although the first type of demonstration is amenable to "proof", the second type is not,because of the time-scales involved. Thus, for the second it can be said paraphrasing
OECD/NEA (1983) that: "As usual in similar situations, it will be the role of competent
national authorities to critically examine the scientific and technical evidence provided for thelong term safety and reliability of high level waste disposal concepts. They will have tosatisfy themselves that the nature and extent of this evidence (what is now referred to as the
Safety Case) show a sufficiently deep understanding of the problems involved and that the
proposed solutions can meet long term safety objectives."45

In 2001, a working group under the auspices of the OECD/NEA Radioactive Waste
Management Committee examined the definition of demonstration with respect to activities
being performed at underground research laboratories or facilities (OECD/NEA, 2001). It
proposed the following definition:

Demonstration is the illustration, at full scale and under real and/or simulated repository
conditions, of the feasibility of the repository design and of the behaviour andperformance of various (or all) of the components of the repository.

For a radioactive waste management programme to be at the stage of considering its own
demonstration activities at underground laboratories, normally the implicit assumption is thatit has made advances in the development of the repository system considered as well as thepotential geological barriers. Thus, the definition above can be too restrictive for the earlier
stages of the repository development programme, a focus which was beyond the scope of the
OECD/NEA (2001) report. The definition neither considers the differentiation between direct
and implicit demonstration nor the demonstration activities that precede the stage ofdevelopment of underground testing or characterisation facilities.
In the late 90s the notion of demonstration was given a much more prominent position andbecame one of the additional components in the research and development activities of thevarious programmes, which are now referred to as RD&D plans. However no specificdefinition of demonstration has been adopted in those RD&D plans, rather the common
implication that demonstration activities predominantly focus on "engineering" demonstration,
part of the direct demonstration activities mentioned above. An examination of the specificactivities however, shows that they correspond to a much broader range than this "traditional"
engineering demonstration and also include research aspects.
Nagra in its recent RD&D report (Nagra, 2009) discusses the concept of demonstration as
follows: "The concept of demonstration exists at several levels in the context of repository
development. The first could be described as demonstration of the feasibility of key
technological elements. An example in Nagra's RD&D programme involves studies of
emplacement of pelletized bentonite at large-scale, which have been pursued at Mont Terriand elsewhere. The next level involves demonstration that full-scale components can be
manufactured e.g. the SKB copper canister (SKB, 2006b). The final level involves
demonstration of integrated operations at full-scale (e.g. the requirement that Nagra
demonstrate canister retrievability prior to receiving the nuclear operation licence for therepository)." A comparison with the OECD/NEA definition would place this discussion of theconcept of demonstration to the "direct demonstration" defined in the early 80s. Indirect

46

demonstration would be performed through the Safety Case, as is the current practice in allother programmes.
SKB introduced the term demonstration in its RD&D programme with the RD&D report in1992 (SKB, 1992). The term was dedicated to the "demonstration deposition". In the next 3-yr
RD&D report, demonstration was focused on experiments at the Äspö undergroundlaboratory (SKB, 1995). In the most recent RD&D report (SKB, 2010), the role ofdemonstration as the site license application is being finalised, is reflected upon as follows:" By means of demonstrations at our laboratories, we have shown on a full scale that we canmanage the different steps from fabricating and depositing canisters to closing and sealing
tunnels. We believe the time has now come to proceed to the next stage in the Nuclear Fuel
Programme and, after a due licensing process, commence the actual construction of the
facilities in the KBS-3 system.
The remaining development work requires extensive technical resources. SKB’s ownlaboratories – the Äspö HRL, the Canister Laboratory and the Bentonite Laboratory – arebuilt and equipped for full-scale tests, demonstrations and dress rehearsals. Other facilities,
such as Posiva’s Onkalo facility in Finland and our underground facilities and laboratories in
Europe, will also be valuable for our development work.
We are now at a point where we are about to start putting the results of many years of
research, development and demonstration to practical use in industrial processes in new
facilities."
Although the proposed repository site is located at Forsmark, SKB's policy is that research,technology development, long-term experiments and demonstration will primarily be based atthe Äspö HRL, at least until start of operation in mid 2020s. The focus of the activities at
Forsmark will be on underground construction, detailed investigations, update of the SDM etc.
The programme for the detailed investigations will also include activities of a more researchcharacter but directly related to the specific conditions at the Forsmark site, for example:Size and orientation of rock stress and rock mechanics issues related to high rock stresses

Thermally induced spalling in deposition holes – although SKB will primarily follow the
POSE-project conducted by Posiva in ONKALOGroundwater chemistry with focus on sulphide content and degree of oxidation of fractureminerals

Biosphere studies.

47

Reflecting on the experience from SKB, one can recognise that although full-scale testing(corresponding to the more "standard" use of the term demonstration) is a necessarycomponent of technology development:Full-scale testing is never "only" about demonstration, i.e., there is valuable scientific orengineering knowledge that can be gained and provide feedback to the designs and/or the
long-term safety assessment



Early Full-scale tests are needed to advance technology development to meet challenges in
implementation, i.e., whereas a specific design may appear advantageous on paper or at
small scale, its implementation as an industrial process is not trivial and could have safety
implications which would require further developments – ones that can only be realised witha full-scale demonstration not be as straightforward

While early solutions may later be revised – lessons learned from "old concepts" are still
essentialDemonstrating, by use of the full-scale tests, is essential for showing stakeholders how thesystem will look like and that it can be achieved, and such early demonstrations may beessential for the acceptance of the repository development programme

Full-scale tests and a demonstration facility is needed also after site is selected

In seeking a succinct definition that would reflect the current understanding on"demonstration" it is proposed here to combine elements of the definitions of demonstrationin the two OECD/NEA documents, and modify them according to the implementation ofdemonstration in the RD&D plans of other programmes. The resulting definition is shown inthe box below and it is the one that will be used throughout the remaining of this chapter.

48

Demonstration encompasses all activities that increase confidence in the safety andfeasibility of a proposed repository system. It includes those activities that:i) Directly illustrate under real and/or simulated repository conditions, the feasibility of
the repository design and of the behaviour and performance of the various
components of the repository, as well as, the know-how to characterise, built, operateand close safely the repository  collectively referred to as direct demonstration,andii) Aim at a convincing evaluation of the system's performance and its long term safety
on the basis of an assessment of its future evolution confirmed by a body of available
data and evidence  collectively referred to as indirect demonstration.

4.2 Demonstration concept
In developing NUMO's demonstration concept the basic approach was to elaborate andconsolidate in a systematic manner the activities that NUMO should perform according to thedefinition in Section 7.1, considering at the same time the boundary conditions and the historyof the radioactive waste disposal programme in Japan.
NUMO was established as the implementer and entrusted with the realisation of geologicalrepositories for specified waste (HLW and later TRU) in Japan in 2000. Up to that point theradioactive waste programme had been managed and driven by JAEA (formerly PNC and
JNC). Thus, NUMO was fortunate in being able to utilise the momentum that already existed
without starting from "scratch". The main emphasis however up to that point was on generic
aspects of geological disposal and on the "demonstration" of its feasibility in Japan, with mainemphasis on scientific and applied research aspects. NUMO had to initiate thus additional
activities that focussed on expanding the know-how to the implementation, as opposed to theresearch, aspects of the geological disposal.
The volunteer approach adopted in Japan requires the maximum degree of flexibility fromNUMO with respect to the specific disposal concept to be evaluated, which has to be tailoredto the yet unknown geologic formation(s) and geographic conditions of the volunteers.
NUMO has been using as starting concepts those developed in the H-12 report, but has also
examined alternative concepts. This situation makes it a lot more challenging to narrow down
the scope of long-term large/full-scale demonstration experiments.

49

Considering these boundary conditions, a four track demonstration concept canvassing thewhole spectrum of demonstration activities was proposed during the NUMO-Nagra
collaboration. The four tracks proposed are shown in Figure 4.1 and are:

Demonstration of know-howIllustration of repository system components

Demonstration of the engineering systems and engineering processes



Demonstration of the long-term safety assessment.

A definition of each of these tracks and a description of the different areas each one covers isgiven below.

Demonstration of know-how
Illustration of repository system components
Demonstration of engineering systems and processes
Demonstration of long-term safety

Figure 4.1 A possible demonstration concept for NUMO consisting of four parallel tracks

Track 1: Demonstration of know-how
Demonstration of know-how is broadly defined and it includes all activities that show that
NUMO is in the position to:Characterise a site, for example,



Develop and execute an investigation planManage field activities ensuring that high-quality results are obtained

Evaluate the results from different disciplines and develop a consistent model (conceptualand eventually numerical) for the site, as a basis for engineering design and performanceassessment, etc.

Tailor existing, or develop new, repository concepts appropriate for a specific volunteer site,
for example has the,50Engineering capabilities to assess concepts with respect to their feasibility, their operational
and long-term safety, and their life-cycle costsCapabilities to manage the development of new concepts, if requiredCapabilities to plan and integrate the transportation of the considered wastes to the specificsite, etc.

Assess the long-term performance of proposed repository concepts, for example:

Has the methodology to develop the scenarios for the possible repository evolutions in a site(including evolution of the wastes, the engineered barriers, the geosphere etc.)Have the "tools" and methods to evaluate the different scenarios for their compliance withthe regulatory stipulations (long-term radiological safety, environmental impact etc.)

Has the methodologies and knowledge to develop site-specific Safety Case, etc.

Manage effectively and efficiently the whole process of step-wise repository development, forexample:

Has the internal organizational structure and related quality-assured process

Has the appropriate trained staff and, in addition, access to external qualified resources, as
they may be neededHave the mechanisms to ensure transparency of decision taking, continuity of knowledge
and know-how throughout the whole programme, etc.

It should be noted that the list of examples above is exemplary and not exhaustive.
Track 2: Illustration of repository system components
System components is used herein to describe different parts of the repository concept, forexample, over pack and other engineered barriers like bentonite buffer, or also, more broadly,
equipment that will be used in the repository operations, such as emplacement of the overpack and the engineered barriers, retrievability etc. The term chosen for this track is
illustration, instead of demonstration, to differentiate between the engineering demonstrations
that are included under Track 3 and will most probably be part of the requirements to obtainan operation license.
Because the time of the repository operation is several decades away it is expected that further
improvements in technology or engineering will occur and will be considered, even if one hasa specific disposal concept as a reference. In fact it is one of the advantages of the stepwise
implementation that within a repository programme one has indeed the possibility to further
improve the designs chosen. Therefore at an early stage, such as the one that NUMO is inright now, it would not make sense to strive for a demonstration of the actual system that will51

be used in the (intermediate) future. Nevertheless, lessons can be learned by initiating
experiments on, or technological developments of system components that will be integrated
in the further development of the system components. For these illustration experiments, theactual details of the components, for example geometry, need not be a strict representation of
the final design, rather they need to capture the main characteristics that one would like to test
and show.
Numerous examples of such experiments and projects exist, for example:


The in-situ part of FEBEX (Full-scale Engineered Barrier Experiment), from which valuablelessons were obtained for the buffer emplacement process and which led to the study of otheremplacement processes such as pelletized buffer, or the "mock-up" part of FEBEX, which
has been providing valuable data on up scaling THM processes since 1997

The GMT (Gas Migration Test), which provided feedback both on the engineering design(sand/bentonite emplacement in the annulus around disposal cell of silo-type) but also on
testing and up scaling models for the description of gas migration through such systems

The range of all the experiments initiated within the ESDRED project (ESDRED, 2009),
such as the emplacement machines for Andra's concept, or the large scale test of bentonite
behaviour at the surface facilities at Mol, etc.

A lot of these illustration experiments can be performed in a surface facility, in particular
those that represent components of the repository at a 1:1 scale, even if this is done withartificial materials or with first "prototypes" machines.
Track 3: Demonstration of engineering systems and process
Under this track, the demonstration activities are very similar to the ones expected under the"standard" definition of demonstration. The demonstration is direct, it involves almost
exclusively designs considered in the reference case and which are part of the Safety Case.
The geometric scale, the host rock and the related environmental conditions, and theengineering processes (for example material flow, emplacement rate etc.) are an image of the
anticipated operations. This is also true for the surface-related operations, such astransportation, encapsulation (if applicable), bentonite block manufacturing (if applicable) etc.
The main purpose of this type of demonstration is to obtain a licensing application to proceedwith this particular disposal concept and disposal process.
Track 4: Demonstration of long-term safety
A separate track is dedicated to the demonstration of long-term safety to draw special
attention because, as discussed in Section 4.1, this is an indirect demonstration. As such, it
can only be achieved through the preparation of a "convincing evaluation of the system's
52performance and long term safety on the basis of predictive analyses confirmed by a body ofavailable data and evidence". The decision of whether the demonstration of long-term safety
has been achieved will be finally made by the national authorities, which have to criticallyexamine the scientific and technical evidence provided. Although they may also request
support, in terms of review, from international bodies, at the end they will have to satisfy
themselves that the nature and extent of this evidence (what is now referred to as the Safety
Case) show that the proposed solutions can meet the long-term safety objectives. It is ofoutmost importance that during the repository development period up to licensing, theauthorities have also build-up and accumulated the required know-how and they are
considered the established competent independent body that can make this important decision.
There are many similarities between Track 4 and Track 1, because at the end the developmentof the Safety Case for the demonstration of long-term safety requires convincingly showingthat you have the know-how and the data to do so. Under this track, NUMO has todemonstrate that it has the capability:
To obtain the necessary data, for example,
Specific site dataLaboratory data (either from the literature, after evaluating their quality, or through theinitiation of additional necessary experiments).

Demonstration track

The list above is not exhaustive but is intended to assist in defining what has to be done todemonstrate long-term safety. An important element here is the step-wise iterative approach
followed, which also implies that there will be more than one Safety Case, or more than one
versions of a Safety Case, as the repository development progress. As a result, demonstrationof long-term safety is a process that will extend through all the stages of the repository
culminating with the one that will enable the final step of the programme, namely therepository closure.

Know-howIllustration
Engineering processes
Long-term safety (indirect demonstration)
LS

PI

DI-1

DI-2

Construction

53

Figure 4.2 Timing of the demonstration activities according to NUMO's stepwise repository
development approach (A darker shade indicates a higher intensity of activities)

The timing and intensity of demonstration activities along the four tracks proposed above
vary according to the major stages in the repository development. Figure 4.2 shows
schematically that, activities for:Track 1 can start (and already have started) before the literature survey stage and willcontinue with the same intensity until the choice of the DI area(s). After the selection of thelocation of an on-site UIF demonstration of know-how will continue but with a much lower
intensity, mainly focussing on new methods or techniques specific to the repository concept.
Track 2 can also start before the literature survey stage. The intensity of the corresponding
activities should reach its "highest" during the PI stage, the expectation being that these
activities will facilitate communication with the various stakeholders as the process of"narrowing-down" to the DI areas takes place. With the construction of NUMO's UIF, or if
the possibility to perform such activities in other generic testing facilities in Japan arises,
there will also be a shift of the nature of these activities from Track 2 to Track 3.
Track 3 should start after sites have been identified and preliminary site-specific repository
concepts can be developed. The activities are expected to intensify before applying for therepository construction license and to continue, at a reduced intensity, during the construction
and operation in case modifications of engineering system components or engineering
processes that have been already licensed by the authorities are considered, and they should
be demonstrated in advance.
Track 4 can start (and already have started) before the literature survey stage and theirintensity will be quite high during the DI Stage – in the first part of the DI stage to support the
selection of the site(s) for underground construction and in the second part to support thelicense application. They will continue throughout the repository operation, albeit with much
lower intensity, and short-duration peaks for supporting the "confirmation" milestones
expected in the programme or for the closure application.

54

5 Overall conclusions
Based on Nagra's experience through investigation of a wide range of geologicalenvironments for both the HLW and L/ILW, the repository concept (RC) collaborative study
was initiated in 2001. Its initial aim was mainly organising a technical knowledge transfer
between the implementing organizations of Japan and Switzerland. The focus was on
developing a methodology for tailoring repository concepts to a broad range of geological andgeographical environments. Over the years the project evolved, a broad range of issues has
been studied, and also experiences from other European implementers were included wherethese were found useful for NUMO.
This report summarizes three of the specific areas studied and advances made through thiscollaboration in the period FY 2008 to FY 2010, namely:
 Development of NUMO’s DIA activities
 Uncertainty management in safety case
 Demonstration concept.
The project allowed the development of a multi-year continuous platform for a compact,
efficient and quick information exchange. As such the collaboration could be seen by NUMO
as a portal to European implementer developments, which could be interpreted in the light of
NUMO's needs based on the fact that through the years a detailed mutual understanding ofeach other’s programs developed.
Developments in some areas will continue to keep abreast of the best available technology at
the international level, but instruments and technologies will also be tailored for application
within the Japanese environment. Especially, based on the DI activities described in thisreport, it is necessary to embody the planning and activities in practical manner, in responseto the specific site characterization.

55

Acknowledgements
The authors value the contributions from a wide range of RC Collaboration Team members.
In particular, we would like to express our gratitude to the Nagra Technical Support Team, Dr.
H. Kurikami (current JAEA) and Mr. K. Wakasugi (current JAEA) for their contributions toboth project coordination and technical development. It should also be noted that the work
was performed with extensive contributions from the Nagra Technical Support Team,
including Dr. P. Smith (SAM), Dr. J. Andersson (SKB), and Dr. H. Kawamura (Obayashi).

56

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Appendix A: Main topics studied between FY2008 and FY 2010
FY 2008•

Review of NUMO's fundamental activities in the PI stage (Action Plan)•

Provisional activities for the DI stage•

Assessment of the potential for reducing the I-129 releases from a TRU repository•

Concept for repository closure•

Scenario analysis work frame: review and suggested future activities•

R&D work for the radioactive waste disposal programme•

Case studies of design changes•

Nagra's technical information management system.

FY 2009•

International workshop
methodology•

International workshop for stakeholders on Requirement Management Systems•

Review of the NUMO 2009 report.

between

implementersonscenariodevelopment

FY 2010•

Kick-off meeting of the International review of the NUMO 2010 report and reviewof the roadmaps•

Treatment of uncertainties in the safety case•

Overview of R&D programmes of implementing organizations•

Role of demonstration in an implementer’s program•

Summary report on RC collaboration (draft).

60