Problems in the application of the SSHAC probability method for assessing earthquake hazards at Swiss nuclear power plants

Abstract From 2000 to 2004 a large scale probabilistic seismic hazard analysis (PEGASOS) was created and performed as a research project, sponsored by the Swiss NPP utilities to improve the assessment methodology for seismic risk in support of the plant-specific seismic PRAs. The project followed the methodology of the SSHAC [ Senior Seismic Hazard Analysis Committee (SSHAC), 1997. Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts. NU-REG/CR-6372 ] procedures at its most elaborate way—level 4. Before practical implementation was to occur, a detailed review was performed including validation tests and analysis of uncertainty propagation. This paper presents the main results of the review. The review revealed that current PSHA (Probabilistic Seismic Hazard Analysis) methodology as based on logic trees, in conjunction with the SSHAC procedures, potentially leads to a significant overestimation of the seismic hazard in areas with low seismic activity due to the inherent possibilities of unconstrained accumulation of uncertainties. The preliminary results of the project did not pass any of our logical geological–scientific benchmark tests used in our attempts to perform a validation process of the PEGASOS analysis method. Some of the problems encountered are of generic nature and shall be studied carefully before making the decision of whether or not the Swiss nuclear power industry will adopt the recommended use of SSHAC-procedures as a basis for the evaluation of the seismic hazard for individual nuclear power plant seismic PRA without correction.

[1]  J.B. Radziminski,et al.  Civil Engineering Department , 1982, Frontiers in Education Conference, 1982. Proceedings.

[2]  Julian J. Bommer,et al.  The attenuation of ground accelerations in Europe , 1991 .

[3]  Jocelyn Mitchell,et al.  Methodology for Assessment of Uncertain Input Data for a Level-3 PRA Analysis of a Nuclear Reactor Accident using MACCS2 , 2004 .

[4]  P. Smit.  Datenerfassung und Bestimmung der Abminderung der Bodenbewegung bei Erdbeben in der Schweiz , 1996 .

[5]  Robert J. Budnitz,et al.  Recommendations for probabilistic seismic hazard analysis: Guidance on uncertainty and use of experts , 1997 .

[6]  J.-U. Klügel,et al.  Challenges to future Seismic PRA , 2004 .

[7]  A. D. Swain,et al.  Handbook of human-reliability analysis with emphasis on nuclear power plant applications. Final report , 1983 .

[8]  Jeff Gill,et al.  Bayesian Methods : A Social and Behavioral Sciences Approach , 2002 .

[9]  G. R. Toro,et al.  Model of Strong Ground Motions from Earthquakes in Central and Eastern North America: Best Estimates and Uncertainties , 1997 .

[10]  Ellis L. Krinitzsky,et al.  Earthquake probability in engineering — Part 1: The use and misuse of expert opinion. The Third Richard H. Jahns Distinguished Lecture in Engineering Geology , 1993 .

[11]  Göran Ekström,et al.  Evidence of bias in estimations of earthquake size , 1988, Nature.

[12]  Vinh N. Dang,et al.  Probabilistic Safety Assessment and Management , 2004 .

[13]  Ellis L. Krinitzsky,et al.  Earthquake probability in engineering—Part 2: Earthquake recurrence and limitations of Gutenberg-Richter b-values for the engineering of critical structures: The third Richard H. Jahns distinguished lecture in engineering geology , 1993 .

[14]  Robert R. Youngs,et al.  Implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates , 1985 .

[15]  L. J. O'Brien,et al.  The correlation of peak ground acceleration amplitude with seismic intensity and other physical parameters , 1977, Bulletin of the Seismological Society of America.

[16]  F. Scherbaum,et al.  On the Conversion of Source-to-Site Distance Measures for Extended Earthquake Source Models , 2004 .

[17]  Robin K. McGuire,et al.  New seismic design spectra for nuclear power plants , 2001 .

[18]  K. Campbell,et al.  Updated Near-Source Ground-Motion (Attenuation) Relations for the Horizontal and Vertical Components of Peak Ground Acceleration and Acceleration Response Spectra , 2003 .