Severe Accident Research in Japan After the Fukushima Daiichi Nuclear Power Station Accident

After the accident at the Fukushima Daiichi nuclear power station in March 2011 (Fukushima accident), several investigation committees in Japan issued reports with lessons learned from the accident, including some recommendations on severe accident research. The review of specific severe accident research issues began after the Fukushima accident in the Atomic Energy Society of Japan (AESJ). AESJ has recently developed a new Thermal Hydraulics Safety Evaluation Fundamental Technology Enhancement Strategy Roadmap (TH-RM) for light water reactor safety improvement and development after the Fukushima accident by thoroughly revising the first version of the Roadmap (TH-RM-1) prepared in 2009. The revision was made by considering the lessons learned from the Fukushima accident. At the same time, the Research Expert Committee on Evaluation of Severe Accident, which was established by AESJ in 2012, has published phenomena identification and ranking tables (PIRTs) for both thermal hydraulics and source term issues in severe accidents based on findings from the Fukushima accident utilizing PIRT methodologies. The present paper reviews severe accident research before the Fukushima accident, lessons learned about severe accident research from the Fukushima accident, severe accident research issues reviewed after the Fukushima accident by AESJ, and current severe accident research activities mostly based on the two above-mentioned AESJ reviews after the Fukushima accident in Japan.