Approach and challenges for the seismic hazard assessment of nuclear power plants: the Swiss experience

The PEGASOS project, a new state-of-the-art probabilistic seismic hazard assessment for the nuclear power plant sites in Switzerland has been carried out from 2000 to 2004. The quantification of the epistemic uncertainty and aleatory variability in seismic hazard at the four Swiss nuclear power plant sites was the key aspect of the PEGASOS project. After the completion of the project, the Swiss utilities decided to perform a refinement of the study by collecting additional data and using new advances in science, especially in the field of ground motion modeling, to further reduce the identified uncertainties. This paper gives an overview of the different components of the project, the used approaches and also identifies some new challenges for the scientific community. An important aspect being: the adjustment of ground motion prediction equations in order to make them applicable to the study region. The importance of those adjustments and their significant impact on PSHA results are also illustrated.