Abstract
The purpose of this study is to investigate the effects of the consideration of simultaneous occurrence of seismically induced events in Nuclear Power Plants (NPPs) such as failures of components due to seismic stress, seismically induced fire, and seismically induced internal flooding in seismic probabilistic safety assessment(PSA). The seismic risk is estimated in terms of the Core Damage Frequency (CDF) and the CDF is comprised of occurrence frequencies of accident sequences. In this study, two analytical methods, upper bound approximation (UBA) using minimal cut sets (MCSs) and direct quantification of fault tree using Monte Carlo simulation (DQFM) are selected for comparison. The results showed that the simultaneous occurrence of seismically induced events should be reasonably considered to assess the intersection and the union of these events. In addition, the Great Eastern Japan Earthquake and the Tsunami damaged NPPs on the Pacific Coast of Eastern Japan on March 11, 2011 will be examined in this study.
