Severe accident practices and programmes in Switzerland

In Switzerland over the last few years a number of evaluations on the subject of severe accidents have been performed and further work on plant specific PSAs is under way. Emphasis at first was placed on emergency planning and thus on the source term. Now the priorities are shifting to provisions in the plants to reduce the probability and consequences of severe accidents. Since all defense against severe accidents has to start from the design basis, this basis is again under review. However, major technical extensions of the design basis are considered to give diminishing returns from a cost-benefit standpoint. In order to further reduce the risk from severe accidents involving major core damage, new technical and organisational provisions are under consideration a) to give the operators additional means to influence a severe accident sequence and b) to mitigate its consequences. Since the Swiss NPPs are of different design, evaluations and possible solutions vary considerably between plants. (author). 1 tab