Development of Level 1 Internal Event Single-unit PSA Models for Multi-unit Risk Profiles

The Multi-Unit Risk Research Group (MURRG) sponsored by the Korean regulatory authority has been developing multi-unit probabilistic safety assessment (MUPSA) models since 2017. To implement the MUPSA, individual models, so-called single-unit PSAs (SUPSAs) need to be prepared first. In this paper, we introduce and summarize the processes and results regarding a level 1 internal event single-unit PSA model for four reactor types: WH600, WH900, OPR1000, and APR1400, which are found at a specific site. All models were developed for full-power (FP) and low-power-shutdown (LPSD) modes. For the LPSD mode, the mid-loop operation corresponding to plant operation state (POS) 5 was chosen for its high-risk contribution. Although existing models were available, most of models are newly created or restructured due to (1) updates to recent design modifications, (2) the need to maintain consistency between reactors with respect to naming conventions, initiation of event frequencies, failure or human error data, and major modeling assumptions, and (3) the need to characterize the specialties for each reactor in a MUPSA model. To compare these models’ consistency and specialty, we attempted to cross-check the quantification results of each PSA model. Some insights regarding core damage frequency (CDF), top-ranked initiating events, and minimal cutsets (MCS) will be addressed.