This study developed a Multi-Unit PSA (MUPSA) model to evaluate the risk of accidents induced by tsunami hazards at the Hanul Nuclear Power Plant site. To address simultaneous multi-unit damage scenarios, a comprehensive "One-top" model framework was constructed to integrate all units on the site, selecting Loss of Ultimate Heat Sink (LUHS) and Station Blackout (SBO) as primary initiating events based on tsunami wave heights. The model incorporated site-specific plant configuration and design features identified through plant walkdowns, including watertight door installations and potential tsunami ingress pathways such as building openings and penetrations. In addition, the operational priorities of AAC DGs and multi-unit common cause failures (CCFs) were explicitly modeled to enhance the realism and accuracy of inter-unit dependency analysis.

The quantification results revealed that the simultaneous failure of identical structures (e.g., TS-DWST) during tsunami events with wave heights of 10–13 m was the most significant contributor to the Core Damage Frequency (CDF), suggesting the need to refine conservative assumptions regarding simultaneous structural failures or re-evaluate tsunami hazard characteristics. Furthermore, RCP seal failures in specific units were identified as major risk contributors, highlighting the necessity for mitigation strategies and the potential application of mobile equipment. This study provides a technical foundation for future tsunami hazard re-evaluations and is expected to serve as an important reference for establishing regulatory review guidance for MUPSA.