Host: The Japan Society of Mechanical Engineers
Name : The 30th International Conference on Nuclear Engineering (ICONE30)
Date : May 21, 2023 - May 26, 2023
During the accident at the Fukushima Daiichi Nuclear Power Plant, venting was performed at Unit 1, and vent gas was released into the environment through the Unit 1 and Unit 2 (Unit 1/2) exhaust stack. Post-accident investigations revealed that some vent gas flowed back into the Unit 1/2 standby gas treatment system (SGTS) piping, and some of the piping was unexplainably highly contaminated. Flow analysis in the SGTS piping during venting was performed using the RELAP5 code to elucidate the causes of these problems. The plant condition at that time was estimated by reproducing the flow condition that was estimated based on the measurement results. Furthermore, steam condensation of the vent gas was evaluated to investigate the cause of the localized high contamination. The applicability of the RELAP5 codes to this analysis is unknown since the analysis conditions are different from those assumed in usual RELAP5 calculations. This paper presents the accident analysis results using the RELAP5 code and the correlations equipped in RELAP5 to discuss the causes of the localized high contamination and the validity of the RELAP5 calculations.
