Fukushima Daiichi Nuclear Power Plant 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

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