Fukushima Daiichi Nuclear Power Plant Unit 2 Accident analysis considering the thermal stratification and containment leakage

中村 勇気*; 小島 良洋*; 山下 拓哉  ; 下村 健太 ; 溝上 伸也

Nakamura, Yuki*; Kojima, Yoshihiro*; Yamashita, Takuya; Shimomura, Kenta; Mizokami, Shinya

In 2011, at the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, it has been reported that several Units of containment vessel had failed, and large quantity of radionuclides had been released into the environment, however, the detail of accident progression with core melt, reactor and containment vessel failure, has still large uncertainties. Especially for the Unit 2 and Unit 3, even they had succeeded in the initial core cooling, at last lost cooling system and fell into severe accident into large release of the fission product into the environment. To clarify these uncertainties in accident scenario, considering the latest information and several insights, the latest accident scenario for Unit 2 and Unit 3 are studied using the severe accident analysis code in this study. It is shown that both Units would result in the thermal stratification in the containment water which encouraged the containment pressure increase at the early phase of the accident. On the other hand, it would be also possible that containment leakage happened to decrease the containment pressure at the later phase of the accident.