Validation strategies for licensing nuclear waste repositories in salt formations in Germany

The Gorleben salt dome in Germany has been selected as a potential site for a radioactive waste repository to be constructed within a salt dome. Licensing of such a nuclear waste repository requires the demonstration of the post-closure safety of the facility. This involves extensive use of models to assess the potential future evolution of the site with respect to thermal-geomechanical effects, behaviour of the waste, release of radionuclides and their migration through the geosphere and uptake by man. Since observations of the relevant processes will not be available over the long time period involved, confidence-building measures are needed to convince the authorities as well as the public, that the repository is safe. Part of this process is model testing, usually referred to as validation, which requires the design of appropriate experiments and data sampling, both to be carried out during site characterization as well as in the underground facilities to be constructed. With rock salt as host formation, a number of specific phenomena and processes have to be considered. Models for the creep of salt and compaction of backfill material and seals due to heat and pressure as the most important processes in the near-field have to be tested against in-situ experiments and supporting laboratory experiments. Appropriate laboratory experiments are also carried out to validate geochemical models used to determine the degradation of the waste form and the solubility of the radionuclides under the conditions of a brine environment. (authors). 19 refs., 2 figs