是正処置プログラムへの等級別扱い適用の手法と安全上の効果

抄録

　One of the purposes of the Corrective Action Program (CAP) in nuclear power plants (NPPs) is to suppress any future increase in Core Damage Frequency (CDF), which represents a large part of safety affected by the issues associated with cause correction. The application of the graded approach in choosing the issues to be corrected could enhance the CAP effectiveness in suppressing CDF increase. In Japan, the significance scale used in the CAP is poorly correlated with CDF, and the CAP is not focusing on the significant risk issues. First the gap between the significance used in traditional Japanese CAP and risk-informed significance is clarified in this paper. Second, a CAP process model with two conditions of potential safety issues depending on whether the cause is removed or not is prepared. This model can explain how the CAP works to suppress the recurrence of safety issues. Third, using this model, the trend that the CDF is increased by the safety issues is parametrically simulated. Simulation results show that the CAP using risk-informed significance can reduce the CDF increase by 40％ over 20 years. For the NPPs that have long been using an inappropriate significance scale, the application of risk-informed significance in CAP is one of the most effective actions for suppressing future CDF.