Multi-Unit Nuclear Power Plant Probabilistic Risk Assessment: A Comprehensive Survey

A growing concern regarding probabilistic risk assessments (PRA) is the impact of dependencies among reactor units co-located at a nuclear power site, especially after the March 2011 Fukushima Daiichi accident. To address these dependencies and identify the critical contributors to the entire site risk, multi-unit probabilistic risk assessment (MUPRA) has been actively developed by various research and regulatory agencies. However, possible inter-unit dependencies in MUPRA have led to some technical issues and challenges associated with the development and modeling of initiating events, accident sequences, end states, and risk metrics relevant to multi-unit sites. This paper provides a comprehensive survey and assessment of the state of current knowledge in MUPRA. The critical recent literature is synthesized and discussed, focusing on three facets: multi-unit event characterization, MUPRA methodological development, and site-based risk metrics and risk aggregation. This survey aims to identify the key issues addressed and challenges faced by the research and development activities of MUPRA, and identifies gaps and opportunities for future research and developments.