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Japan Atomic Energy Agency

Geological Isolation Research and Development

Development of a Computer Tool to Support Scenario Analysis for Safety Assessment of HLW Geological Disposal


Jun. 19, 2007

Research and development of advanced safety assessment methods for the geological disposal of High Level Waste (HLW) is being undertaken by the Geological Isolation Research and Development Directorate. As part of this R&D a computer tool named "FepMatrix" has been developed to support performance assessors in carrying out scenario analyses.

When developing scenarios for safety assessments, interactions between "Features", "Events" and "Processes" (hereafter termed "FEPs") that characterize and/or affect a repository system are analyzed. The relationships between these interactions and impacts on the safety of the repository system are described.

The existing FEP analysis methodology involves using "Process Influence Diagrams" (hereafter "PIDs") to analyze interactions between hundreds of FEPs. However, a PID has a spider's web-like structure and is too complicated for the public to understand. Additionally, human error is apt to occur during the interpretation of such diagrams.

To solve these problems, a new approach to understanding the relationships between FEPs has been developed, based on describing the relationships in the "Rock Engineering System" (hereafter "RES") matrix. The method involves using the RES matrix to arrange FEPs according to fixed rules and is the basis for the computer tool "FepMatrix".

The relationships between FEPs that are portrayed using FepMatrix are managed using electronic files, enabling performance assessors to share information efficiently. The tool also provides an effective means for accumulating and managing knowledge for use in the future safety assessment of geological disposal. The potential for human error is decreased because the tool may construct connecting lines between FEPs automatically.

The method and FepMatrix are applicable not only to scenario analysis aimed at the geological disposal of HLW, but also to scenario analysis concerned with other wastes. Furthermore, it is expected that the tool will be applicable more broadly in other fields, such as evaluating the consequences of a natural disaster.

This tool is described in detail in JAEA's report, JAEA-Data/Code 2007-005. Moreover, FepMatrix is offered as a program which can be used by external experts. Please consult the PROgram and Database retrieval System"PRODAS" at JAEA's Internet homepage (http://prodas.jaea.go.jp/) for details about how FepMatrix may be acquired.

Note: The report and FepMatrix are offered in Japanese only.