Performance assessment of the geosphere barrier of a deep geological repository for spent fuel. The use of interaction matrices for identification, structuring and ranking of features, events and processes

This paper summarises a study where the basic device in the Rock Engineering Systems (RES) approach, the interaction matrix, was used to identify, structure and rank features, events, and processes (FEPs) describing barrier performance and radionuclide behaviour in the far-field of a deep geological repository for spent fuel. The study has shown that it is feasible to use an interaction matrix both for the structuring of the process system (PS) and for visualisation of the PS. The developed documentation system increases the transparency of the system description and makes it possible to trace back the judgements made during the construction of the matrix. This will facilitate review work and future revisions as well as consistent treatment of different issues in the system. This study is a first step in the application of a systematic method based on interaction matrices to establish a structured PS. The next step would be to develop the PS for the remaining parts of the repository system to the same level as has been done for the far-field system.