Method of Applying Graded Approach in Corrective Action Program and Its Safety Effects

increase. 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 sup pressing future CDF.