Uncertainty Quantification of Seismic Response of Reactor Building Considering Different Modeling Methods

After the 2011 Fukushima accident, the seismic regulations for nuclear power plants (NPP) in Japan have been strengthened to include countermeasures far beyond design-basis accidents. The importance of seismic probabilistic risk assessments, therefore, have been the focus of deserved attention. Generally, an uncertainty quantification has been a very important undertaking to assess for fragility in NPP buildings. Therefore, this study focuses on the reduction in epistemic uncertainty by aiming to clarify the seismic-response effects on NPP buildings based on different modeling methods. As a first step in this study, the authors compared the seismic-response effects using two modeling methods of analysis. To evaluate the seismic response, an analysis was performed on two building model types; these being the three-dimensional (3D) finite-element model and the sway-rocking model with a conventional lumped mass system. To input a ground motion, the authors adopted 200 types of simulated seismic ground motions, generated by fault-rupture models, using stochastic seismic source characteristics. For the uncertainty quantification, we conducted a statistical analysis of the seismic responses acquired from the two modeling methods based on the building response each ground-motion input, and quantitatively evaluated the uncertainty response by considering the different modeling methods. We found a clear difference in the modeling methods near the floor and wall openings. We also imparted our knowledge on these 3D effects for the seismic-response analysis.