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The Seismic Research Group is spearheading efforts to modernize the current seismic probabilistic risk assessment (PRA) process to provide the best estimate values of seismic risk.  

NLSSI in Seismic PRA

The first step in advancing the traditional seismic PRA process is the implementation of NLSSI in the calculation of seismic demands. Current state of the art involves the use of linear analysis codes such as SASSI to calculate the seismic demand distributions. The demands for other earthquake intensity levels are then scaled linearly even in the beyond-design basis, where the soil, structure and foundation response is typically nonlinear. 

This study involves modifying the traditional seismic PRA process to include NLSSI analysis, and specifically examining the effects of geometric nonlinearities on the risk of core damage. A simple nuclear power plant (NPP) structure and plant system is considered for the study. Linear SSI analyses are performed using CLASSI and NLSSI analysis is performed using LS-DYNA. A representative seismic hazard for an INL site is used and thirty ground motions are selected and spectrally matched to the Uniform Hazard Spectrum (UHS) corresponding to this hazard. 

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Description of the NPP structure and sample system used for seismic PRA