LAUSR

The aim of this case study is to evaluate the influence of input seismic motion control point on the fragility curves of some nuclear power plant’s equipment considering (1) a strong soil–structure interaction problem and (2) the variability of the input seismic signals. To this end, a current engineering methodology was implemented for computation efficiency, based on a simplified model representing the largely embedded Unit 7 reactor building of the Kashiwazaki-Kariwa NPP (Japan). Seismic signals were generated with NGA GMPE according to the July 2007 NCOE scenario. In the process, soil non-linearity caused by each seismic signal was taken into account using the equivalent linear method. A study on the uncertainty propagation through the simplified soil–structure system is also presented. It allowed the implementation of an empirical sensitivity analysis to confirm the main results, which suggest that defining the control point of the input motion at the soil surface as prescribed in the French nuclear practice is not appropriate and may lead to biased outcomes when performing non-linear soil–structure fragility analysis. Instead, it should be defined at the “outcropping bedrock” level.