Study on the hydrogen explosion risk at reactor building during a severe accident

JNES carried out analysis on the hydrogen mixing and explosion at reactor building with CFD code and explosion analysis code to evaluate what exactly has happened at the reactor buildings of the Fukushima Daiichi NPS. Based on the MELCOR severe accident analysis results of Fukushima Daiichi Unit 1 and Unit 3, sensitivity study using the CFD code FLUENT was carried out on the parameter of the release rate, total mass of hydrogen gas, the release path between reactor building and PCV, and so on. Then an analysis using AUTODYN code was carried out to investigate the explosion at the reactor building of Unit 4 as well as Unit 1 and, Unit 3. With those analysis results it became possible to estimate the leaked path and the total amount of leaked hydrogen gas from PCV to reactor building. (author)