Safety Assessment Methodologies

Coordinated Research Project on Improvement of Safety Assessment Methodologies for Near Surface Waste Disposal Facilities (ISAM)

Introduction - The International Atomic Energy Agency (IAEA) Research Coordinated Project on "Improvement of Safety Assessment Methodologies for Near Surface Disposal Facilities" (ISAM) was launched in November 1997 and it has been underway for three years. The ISAM project was developed to provide a critical evaluation of the approaches and tools used in long-term safety assessment of near surface repositories. It resulted in the development of a harmonised approach and illustrated its application by way of three test cases - vault, borehole and Radon (a particular range of repository designs developed within the former Soviet Union) type repositories. As a consequence, the ISAM project had over 70 active participants and attracted considerable interest involving around 700 experts from 72 Member States. The methodology developed, the test cases, the main lessons learnt and the conclusions have been documented and were published as an IAEA publication.

Objectives

The ISAM project had the following objectives:

To provide a critical evaluation of the approaches and tools currently used in the post-closure safety assessment of proposed and existing near surface radioactive waste disposal facilities
To enhance the approaches and tools used
To provide participants with practical experience in the implementation of the approaches and tools
To build confidence in the approaches and tools used

Scope

The project focused on development of consensus on safety assessment methodology for post-closure safety assessment of near surface radioactive waste disposal facilities and its illustration to a number of test cases. The waste types addressed are low and intermediate level waste, that could be generated both in the nuclear fuel cycle and research, industry, medicine, education, etc. The project did not consider safety assessment of deep geological repositories for high-level waste, although many aspects of the safety assessment methodology are similar.

Various methodologies were applied and are being developed to assist in the evaluation of the long-term safety of near surface disposal facilities. Whilst there are some differences in the detail of the methodologies used, many of the more recent ones, such as ISAM, have identified the need to address the following key components:

The specification of the assessment context
The description of the waste disposal system
The development and justification of scenarios
The formulation and implementation of models
The analysis of results and building of confidence

Each of these components were extensively analysed and the conclusions are summarised in the following sub-sections in more detail, with emphasis on the review, enhancement and illustrative application of approaches and tools used for:

Scenario development and justification
Model formulation and implementation, including selection of the input data
Confidence building

Organization

The project was structured along the lines of the working groups and test case groups, which each had a group leader and a number of participants. The overall project was co-ordinated by a co-ordinating group led by a Chairperson and supported by an IAEA Scientific Secretary, as shown in Fig.3

Test Cases: Mr. M. Kozak, Monitor Scientific LLC, United States of America
Vault Test Case: Mr. E. Kelly, British Nuclear Fuels Plc (BNFL), United Kingdom
Radon-Type Facility Test Case: Mr. A. Gouskov, MosNPO "RADON", Russian Federation, supported by Ms. B. Batandjieva (whilst with the Committee on the Use of Atomic Energy for Peaceful Purposes, Bulgaria)
Borehole Test Case: Mr. K. Vivier, Geoconsultants (PTY Limited) (GeoCon) and Mr. J. J. van Blerk, AquiSim Consulting (Pty) Limited, South Africa
The IAEA Scientific Secretary was Mr. C. Torres-Vidal, former Unit Head, Waste Safety Section at the Division of Radiation and Waste Safety.

Activities

Three Working Groups (Scenario, Modelling, and Confidence Building) were set up within the ISAM project to deal with these important aspects of the safety assessment methodology.

Objectives of the Scenario Working Group:

To review existing and currently developing approaches for the development and justification of scenarios
To review the procedures for moving from a consistent FEPs list to a set of justified scenarios
To develop a FEPs list for near surface disposal facilities

Objectives of the Modelling Working Group:

To review approaches used to formalise the process of conceptual model development and justification
To summarise the mathematical models used in safety assessments of near surface disposal facilities
To develop a list of computer codes used to solve the mathematical models
To provide a summary of the parameters and associated data required by the models

Objective of the Confidence Building Working Group:

To review the measures that can be adopted to provide confidence in safety assessments
To summarise the regulatory criteria in various Member States relevant to the safety assessment of near surface disposal facilities
To compile a list of relevant safety indicators
To summarise the methods and tools that have been found useful in performing of sensitivity analyses
To compare the methods used for the presentation of results from safety assessments

In order to test the ISAM safety assessment methodology, it was applied to three example Test Cases based on current practices (vault facility), older practices (RADON facility), and a proposed future disposal option for disused sealed sources (borehole facility)

Outcomes

Development of the ISAM Methodology
The ISAM CRP has resulted in the development of a consistent and transparent safety assessment methodology that can be applied during all stages of the disposal facility life cycle
Interative Character of Safety Assessment
The safety assessment methodology shall be applied in an iterative manner so the components can be reviewed and modified as appropriate. Iteration promotes the examination of improvements to the assessment regardless of how favourable results may initially appear. Subsequent iterations can be used to evaluate whether further improvements are necessary
Development and Illustrative Application of the ISAM FEPs List
The ISAM FEPs list has been successfully developed and represents an important source of FEPs for consideration in the safety assessment of near surface disposal facilities
Illustrative Application of the ISAM Methodology
The ISAM Test Cases, as well as the test cases developed by individual participants, have successfully shown that the ISAM methodology has been widely accepted as a tool upon which to base a near surface disposal facility safety assessment in the development of a site specific safety case. However it shall be emphasised that the level of effort expended on the ISAM Test Cases is significantly less than that required for a complete safety case for an actual site.
Broad Consensus
A broad consensus within the ISAM project relating to a range of technical issues, including the ISAM Safety Assessment Methodology and the associated FEP list, was achieved by the regular attendance of 50-100 participants at the annual ISAM Research Coordination Meetings. The consensus was furthered by active participation in the associated Working Groups and Test Cases meetings. The outcome of the ISAM project has also found broad application in the area of IAEA and national/regional training courses and seminars

Documents

Working Group Documents:

International Atomic Energy Agency. ISAM Programme. Scenario Generation and Justification for the Safety Assessment of Near Surface Radioactive Waste Disposal Systems. IAEA Working Material. Scenario Generation and Justification Working Group. ISAM/SGWG/WD01. Version 1.1, September 2001.

International Atomic Energy Agency. ISAM Programme. Model Formulation, Implementation and Data for Safety Assessment of Near Surface Disposal Facilities. IAEA Working Material. Modelling and Data Working Group. ISAM/MDWG/WD01. Version 0.4, August 2001

International Atomic Energy Agency. ISAM Programme. Confidence Building in the Safety Assessment of Near Surface Radioactive Waste Disposal Facilities. IAEA Working Material. Confidence Building Working Group. ISAM/CBWG/WD01. Version 0.3, September 2001.

International Atomic Energy Agency. ISAM Programme. Vault Safety Case. IAEA Working Material. Vault Safety Case Working Group. ISAM/SCWG/WD01. Version 1.3, September 2001

International Atomic Energy Agency. ISAM Programme. RADON Type Facility Safety Case. IAEA Working Material. RADON Type Facility Safety Case Working Group. ISAM/SCWG/WD02. Version 1.3, October 2001

International Atomic Energy Agency. ISAM Programme. Borehole Safety Case. IAEA Working Material. Borehole Safety Case Working Group. ISAM/SCWG/WD03. Version 1.3, September 2001.

IAEA Publication

International Atomic Energy Agency. Safety Assessment Methodologies for Near Surface Disposal Facilities. Results of a co-ordinated Research Project. Volume I: Review and enhancement of safety assessment approaches and tools; Volume 2: Test cases.

For further information please contact P. Metcalf