Review of safety assessments of nuclear waste management

This report reviews past safety assessment studies for the disposal of nuclear wastes in mined repositories. Both pre-closure operations and long-term performance after the repository is closed are considered. The methods used in pre-closure studies are relatively well established, and past studies have covered all important accident scenarios and containment failure modes. However, the results of different studies exhibit a spread of up to five orders of magnitude. This can be attributed largely to variations in accident probabilities and cesium release fractions. The techniques used to assess long-term dangers are more variegated. There is, however, a considerable degree of agreement in the results, and the feasibility of safe disposal of high-level wastes in general has been well established. Only a few detailed safety analyses have been conducted for particular sites, however. The most difficult problem in calculating long-term risk is to quantify the probability that different scenarios will occur; approaches to safety assessment which avoid this step tend to be more successful. Comparison of pre-closure and post-closure risks is rendered difficult by a number of factors, in particular the difference in time scale. Those studies which have nevertheless attempted to make such a comparison have been notably unsuccessful in doing so