Risk Analysis Methodology for the Design of a Monitoring System for Fuel Debris Retrieval Operations at the Fukushima Daiichi Nuclear Power Station

To maintain the fuel debris retrieval (FDR) operations at the Fukushima Daiichi Nuclear Power Station, the design of a monitoring system is important. However, there is a scarcity of research that evaluates the specific physical quantities (monitoring items) to be monitored on-site and their significance from both working and safety functions. In this study, we propose a risk analysis method combining objective tree (OT) and failure mode and effect analysis (FMEA), which includes the steps of determining the monitoring items and calculating the criticality ranking tailored to the characteristics of the FDR operations. The proposed method is applied to the partial-submersion method, and the results of the risk analysis are evaluated by nuclear facility design experts. As a result, it was confirmed that the proposed method can be utilized in the design of the monitoring system.