Fukushima Daiichi Nuclear Power Plant Accident Analysis Considering the Thermal Stratification and Containment Leakage

Abstract

During the Fukushima Daiichi Nuclear Power Plant accident in 2011, it was reported that several units of the containment vessel had failed, and a large quantity of radionuclides had been released into the environment. However, the detailed accident progression of such a containment failure, which includes core melt, reactor vessel failure and following containment vessel behavior, still has large uncertainties. Especially for Unit 2 and Unit 3, they had succeeded in the initial core cooling, but at last lost their cooling system and fell into the severe accident to release fission products into the environment. Nowadays, much information has been obtained by the internal inspection into the containment of Fukushima Daiichi Nuclear Power Plant. To clarify the uncertainties in the accident scenario, considering the information and several insights already obtained by previous research, the latest accident scenarios in Unit 2 and Unit 3 of the Fukushima Daiichi Nuclear Power Plant accident are suggested and tested by the severe accident analysis code, MAAP* in this study. It is shown that Unit 2 and Unit 3 both accident scenarios would have resulted in the thermal stratification in the suppression pool which encouraged the containment pressure response in the early phase of the accident. In addition, containment vessel leakage would have occurred, affecting the containment depressurization.