Influence of in-vessel melt progression on uncertainty of source term during a severe accident

シビアアクシデント時におけるソースタームの不確かさに及ぼす炉心溶融進展挙動の影響

伊藤 裕人; Zheng, X. ; 玉置 等史 ; 丸山 結 

Ito, Hiroto; Zheng, X.; Tamaki, Hitoshi; Maruyama, Yu

The influence of the in-vessel melt progression on the uncertainty of source terms was examined in the uncertainty analysis with integrated severe accident analysis code MELCOR (Ver. 1.8.5), taking the accident at Unit 2 of Fukushima Daiichi Nuclear Power Plant as an example. The 32 parameters selected from the rough screening analysis were sampled by Latin hypercube sampling technique in accordance with the uncertainty distributions specified for each parameter. The uncertainty distributions of the outputs were obtained through the uncertainty analysis with an assumption of the failure of drywell, including the source terms of the representative radioactive materials (Cs, CsI, Te and Ba), the total mass of in-vessel H generation and the total debris mass released from the reactor pressure vessel to the drywell. Based on various types of correlation coefficient for each parameter, 9 significant uncertain parameters potentially dominating the source terms were identified. These 9 parameters were transferred to the subsequent sensitivity and uncertainty analyses, in which the influence of the transportation of radioactive materials was taken into account.