Recent advancements of probabilistic risk assessment methodologies and risk monitoring usages in Japan

KURAMOTOTakahiro 

Design Service Department, Nuclear Engineering, Ltd., 1-3-7 Tosabori Nishi-ku, Osaka 550-0001, Japan (tkuramoto@neltd.co.jp)

Abstract: The importance of Probabilistic Risk Assessment (PRA) has been highlighted not only for internal events but also for external events following the Fukushima Daiichi NPP accident in Japan. The Standards Committee of Atomic Energy Society of Japan (AESJ) is currently working on the development of the PRA implementation standards concerning the individual external events. At the same time, the Committee is studying on how to assess the combinations of external events, and has started the development of the PRA implementation standards for such hazard combinations. Besides the implementation of PRA as the quantitative risk assessment, we are studying the risk assessment procedures for various types of potential external hazards. This paper describes the Japanese recent advancements on PRA methodologies by focusing on the PRA standards, which are being developed by AESJ.

The Japanese utilities also recognize that the risk information should be used to enhance the rationality and accountability of safety-related activities, and to realize efficient management of NPPs. "Risk Monitoring" is one of the essential applications of PRA and safety-related activities. This paper describes the Japanese current status of "Risk Monitoring" usages especially on "Shutdown risk evaluation for every outage".

Keyword: Probabilistic Risk Assessment (PRA); PRA implementation standard; risk monitoring