(GRS 162) Einfluß von Stützversatz und anderen technischen Maßnahmen auf die Langzeitsicherheit eines Endlagers im Salinar

The long-term safety of a simplified hypothetical repository in a salt formation is investigated taking into account different technical measures to enhance the performance of the repository. Among these technical measures are non-compacting backfill in drifts, load-reducing packings in boreholes, and simplified containers for direct disposal of spent fuel elements. The non-compacting backfill and the load-reducing packings are shown to reduce the release of radionuclides from the near field and to reduce the potential radiation exposure in the biosphere. The simplified containers are shown to slightly enhance the release of radionuclides and the radiation exposure. The reduction of radiation exposure in the case of non-compacting backfill is under certain parameter constellations drastic. In all the other investigations, the influence on the radiation exposure is within a factor of 10 compared to calculations with reference values. Another part of the report deals with the effect of transmutation strategies to long-term safety of a repository in salt. In this case, a more detailed hypothetical repository is taken into account. Several variants with different inventories have been investigated. The main result is that the reduction of the actinide inventories must be very effective, until a remarkable reduction of the doses occurs. This is mainly due to special effects in the near field of the repository, e. g. solubility limits, which conceal the efforts of inventory reduction by transmutation. The changes in the temperature within the near field as a consequence of the reduced inventories turned out to be of relevance to the release of radionuclides.