Study of ongoing applications of risk-informed regulation

JNES has been doing various activities to stimulate the introduction of Risk Informed Regulation to the safety regulation of nuclear power plants (NPPs) in Japan. Some applications are already incorporated, such as the regulatory review of Maintenance Programs, Significance Determination Process and Accident Sequence Precursor (ASP) study. As for the regulatory review of Maintenance Program, JNES established review points to assess utilities' evaluation about the effectiveness of their maintenance programs based on the actual occurrences in their NPPs. Currently, the results obtained from PSA during power operation are used to evaluate noteworthiness of findings and occurrences. As one of enhancement of SDP procedures, JNES investigated to expand the scope of PSA to plant shutdown condition and made trial evaluation models both for a representative PWR plant and a representative BWR plant in 2011. Incidents and troubles occurred both in Japan and abroad have a potential to be investigated in ASP study. Among 250 events occurred in Japan in 2009, twenty-five events remained trough qualitative screening process and one event, that is a loss of electric power event at a BWR4 plant, was selected to review because its conditional core damage probability (CCDP) exceeds the decision criterion of 1x10^-7 which is tentatively determined referring to ASP study of USNRC and operation experiences of NPPs in Japan. Via a similar process, CCDPs of eight events, which remained in the primary screening process among 41 events occurred in the foreign countries, were evaluated and one event were reported as an important event because its CCDP exceeds the decision criterion. (author)