Scenario development and analysis for a repository in salt for highly radioactive waste

Within the scope of a safety assessment of a site for a repository in a salt dome, a total of 32 scenarios containing 61 FEPs (features, events, and processes) have been analyzed. A possible method for scening is presented. Three categories for evaluating the potential hazards were chosen to classify the hazards resulting from the FEP, the temporary aspects, and the hierarchy of the barriers modified by the events and processes. A fourth category takes the relevance of the FEP for this site into consideration. Additionally, all four categories are subdivided into evaluation classes. A point system is used to evaluate the FEP in terms of the system of categories. This point system is subdivided into evaluating groups. High scores for an FEP means a high hazard potential. Twelve of the FEPs in the geotechnical scenarios, 1 FEP in the climate scenarios, and 2 in the geological scenarios have the highest scores. The scenarios include processes and events that: - make water available for gas production leading to an increase in pressure, - produce gas by microbial activity, - lead to the development of migration paths and the resulting possibility of radionuclide transport, - cause the surface of the salt dome to rise, and - occur at the margins of continental ice. The other FEPs have low scores, which means a low hazard potential. The FEPs with the highest scores should be included in a safety analysis. The processes with high scores are potential hazards for the near-field of the repository, but not for the biosphere, because no uninterrupted transport route from the repository to the biosphere is observed. These potential hazards exist for only a few thousand years after the repository has been closed if the mine shaft to the repository remains sealed during this period of time. (author)