A Study on Multi-Unit Initiating Event

Current situation in Korea has raised public's concern on multi-unit risk. However, there are few researches conducted to estimate multi-unit risk since the safety evaluation has been performed based on each unit. Korea Institute of Nuclear Safety (KINS) has started a long-term research aimed at developing a regulatory framework for multi-unit risk in 2017. As part of research, Kim et al. showed research results on multi-unit initiating events focusing on developing a framework to identify multi-unit initiating events. This paper, as a part of subsequent research, introduces a systematic process to identify the comprehensive sets of multi-unit initiating events and to estimate their frequencies. This research mainly consists of three parts. First part explains the process to identify the comprehensive sets of initiating events using operational data in Korea and results of failure mode and effect analysis (FMEA) for shared SSCs (Structure, System, and Components). Second part explains the screening process for the multi-unit initiating events. Since there is still debate on the concept of site-year, some assumptions were made to estimate the multi-unit initiating event frequency. Although the estimated multi-unit initiating frequency is not actual value, it is expected that more precise value can be estimated when assumptions made during calculations have technical backgrounds.