Handling of timescales and related safety indicators

The fundamental objective of a nuclear waste repository is a long-term protection of man and environment. To conduct safety analyses over long period of times, up to the million years, is not a straightforward question. For example, the required demonstration of safety, with respect to the fundamental rules of safety, is out of the scope of any experiment. The safety analysis of a geological disposal system is usually addressed using qualitative and quantitative approaches. But in any case, the evaluation is made for specific time-span and those have to be carefully chosen and discussed in terms of uncertainties, especially for the long term. At ANDRA, a tentative time fractionation has been conducted for geological disposal using two types of approaches: The first one is based on a 'phenomenological' description of a series of situations dependent on the timescale. The second one, the purpose of this paper, proposes to handle timescale using supplementary 'safety indicators'. (authors)