PEGASOS Milestones

A review by the Swiss Federal Nuclear Safety Inspectorate HSK – now ENSI – shows that the probabilistic seismic hazard analyses for the Swiss nuclear power plants no longer meet the state of the art in certain respects (e.g. advances in the USA).

December 1998 HSK starts on the development of the PSHA (Probabilistic Seismic Hazard Assessment) guidelines; these are based on the most recent recommendations from the USA and go beyond the existing status of technology.

June 1999  HSK calls for the power plant operators to prepare a new PSHA based on the novel American SSHAC Level 4 approach; this is aimed at ensuring the independence of the experts involved in the assessment.

March 2000

The power plant operators submit the first draft of the project plan for the PSHA for the power plants in Switzerland (PEGASOS).

2001-2004 The PEGASOS project is carried out under the lead of Nagra and is reviewed by HSK. The work of the experts as part of the project is completed in November 2004

2004-2006  The PEGASOS results are evaluated by the power plant operators and additional investigations are carried out.

June 2005 Based on the PEGASOS results, HSK defines the seismic hazard assumptions for PSA studies (20% reduction of the accelerations at the NPP sites as estimated by PEGASOS).

November 2006 Intensive discussions take place on a national and international level of the methods used for seismic hazard analyses for nuclear power plants.

2007 Planning of the PEGASOS Refinement Project (PRP) and the start of ground investigations at the power plant sites.

2008-2012  The PRP is carried out under the lead of swissnuclear and is reviewed by ENSI and an independent Technical Review Team of swissnuclear.

April 2011 Following the Fukushima accident, ENSI calls for a demonstration of the preparedness for a 10,000 year earthquake by the end of May 2011 and of the preparedness for such an earthquake in combination with a dam break by the end of March 2012.

End May 2011  swissnuclear prepares an Intermediate Seismic Hazard analysis based on the quality-assured data, models and practices from the PRP available at the time.

July 2012 Following its review of the safety demonstrations, ENSI confirms that the Swiss NPPs can survive a 10,000 year earthquake in combination with flooding with no damage to humans and the environment.

Oktober 2012  Verlängerung des Projektes um sechs Monate zur Auswertung von neu verfügbaren
Abminderungsmodellen und Durchführung von weiteren Überprüfungen der im PRP
verwendeten Modelle auf Ihre Verwendung in Regionen mit eher schwacher bis mittlerer Erdbebenstärke. 

16/17 May 2013 Completion of the expert models of the PRP.

Summer 2013  Calculation of hazard curves and completion of quality assurance and documentation. 

20 December 2013

Final report submitted to ENSI for review.

2. Semester 2014 Following its review, ENSI will redefine the requirements for probabilistic seismic hazard assessments for all the power plant sites. Based on this, the operators will update their present safety demonstrations.