Interim Results of PEGASOS

Why was there an interim assessment of the seismic hazard in 2011?

As one of the measures taken following the accident at the Fukushima-Daiichi NPP in March 2011, on 1st April 2011 ENSI called for an immediate review of the safety of the Swiss nuclear power plants in the event of earthquakes and flooding; such a review is a legal requirement in these situations. The power plant operators were required to provide, by the end of March 2012, a demonstration of their capability to manage an earthquake, with the resulting ground movement, that would be expected once in 10,000 years at the most, combined with flooding due to dam failure.

The PEGASOS Refinement Project was not sufficiently far advanced at that point to allow the hazard assumptions to be taken over directly from the project. In May 2011, swissnuclear therefore carried out an Intermediate Seismic Hazard evaluation for all relevant power plant and dam sites.

The Intermediate Seismic Hazard analysis is based on the quality-assured results of the PRP available at the time. The analysis is more up to date and more comprehensive than the PEGASOS study (it includes new measurements), but does not represent the final result of the PRP. Given the short time available for carrying out the demonstration, it was not possible to wait for the full PRP results.

At the beginning of July 2012, ENSI confirmed that the demonstration submitted by the operators showed that the Swiss nuclear power plants are capable of surviving a 10,000 year seismic event in combination with flooding with no damage to humans or the environment.

However, the demonstration has only restricted validity. Following completion and review of the PRP, ENSI will redefine the requirements for probabilistic seismic hazard analyses for all sites and, based on this, the power plant operators will have to update the current demonstrations.

Intermediate Hazard