Quantitative Risk Assessment With CMMC Method on Abnormal Snowfall Incident for a Sodium-Cooled Fast Reactor

Abstract

In general, the ultimate heat sink of a decay heat removal system is the atmosphere for accidental conditions of sodium-cooled fast reactor (SFR) designs in Japan. Therefore, risk assessment of external hazards from the atmosphere is important for SFR. However, along with global warming (GW), the number of significant meteorological disasters has increased. Therefore, it is necessary to focus on meteorological phenomena. Hazard curves were developed to address the possibility of abnormal snowfall. By using the hazard curve data, plant dynamics analyses by continuous Markov-chain Monte-Carlo (CMMC) method were conducted with the assumption of failure due to snowfall. The excess frequency of the coolant temperature was quantitatively examined for the design limitation temperature value. The abnormal snowfall height was evaluated using meteorological data. Assuming the possibility of snowfall increase occurring by 2050, the expected value to reproduce 10,000 years was evaluated, and the plant dynamics analyses were conducted using the snowfall height. In conclusion, abnormal snowfall was found to likely increase by GW. In addition, the CMMC method was implemented using the expected value to reproduce 10,000 years, and its effect on the probability of exceeding the temperature limit as the core damage factor was evaluated. As a result, the probability of exceeding this limit increased when GW was considered.