Methodology for Deriving Positive Lesson Learning from Troubles Primarily Related to Maintenance in Nuclear Power Plant

Nuclear operators have generally improved their procedures to eliminate human errors that cause troubles during maintenance work. However, it is difficult to anticipate every possible situation and establish appropriate procedures in advance. A new perspective on safety is required for preventing troubles. Although the Safety-II concept has been developed, applying it to maintenance is challenging. This is because the troubles the nuclear operators face in performing maintenance work vary in scale and the difficulty level of solutions. The appropriate problem-solving approach should be based on the complexity. In this study, we aim to propose a systematic and effective analysis method based on the Safety-II concept, focusing on human actions in troubles primarily related to maintenance experienced at nuclear power plants. By combining the Cynefin framework and resilience engineering, a methodology focusing on the complexity is proposed. The analysis flow for the proposed methodology consists of the following steps: (1) organize the timeline by focusing on human actions and changing problems, (2) classify the problem status on the basis of the Cynefin framework, (3) confirm the achievement status of the problem resolution phase, and (4) develop countermeasures of monitoring and responding. Through the analysis of 65 troubles that occurred at nuclear power plants, the effectiveness of the proposed methodology was confirmed.