Sets of response-history analyses for a sample nuclear power plant (NPP) hosting a boil water reactor were conducted to investigate the impact of uncertainty on seismic risk of NPPs. The first set of analyses involves a series of numerical models to include the uncertainty in soil properties, strength and damping of structures, and damping of equipment in the sample NPP. The second set involves a numerical model with best-estimate mechanical properties. The results indicate that seismic risk of the sample NPP is underestimated when the uncertainties in mechanical properties of soil, structures and equipment are not considered in the analysis. Based on the analysis results, a simplified procedure using best-estimate model only is proposed to address uncertainty in mechanical properties of NPP components in SPRA.
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