Parametric study for impact of in-vessel chemical forms of cesium and iodine on source term and pH of aqueous phase

ソースターム及び液相pHに及ぼすセシウムとヨウ素化学形の影響に係わるパラメータ解析

塩津 弘之  ; 石川 淳 ; 丸山 結 

Shiotsu, Hiroyuki; Ishikawa, Jun; Maruyama, Yu

In order to evaluate the effect of chemical forms of Cs and I on source terms and solution pH in a severe accident of a BWR, parametric analysis was performed with an integral severe accident code, THALES2, developed by JAEA. In the present analysis, THALES2 code was modified to take into account CsOH, CsMoO and CsBO as Cs chemical forms, and CsI and HI as I chemical forms. The severe accident sequence examined was similar to that occurred at unit 3 of the Fukushima Dai-ichi NPP. Due to the effective scrubbing, approximately 90% of the initial core inventory of Cs and I was predicted to be retained in the water pool of the suppression chamber, resulting in limited influence of Cs chemical form on Cs source term. On the other hand, the present analysis indicated that solution pH of the water pool was strongly affected by chemical forms of Cs and I. This outcome implies that chemical forms of Cs and I influence I source term since the formation of volatile I species such as I2 and organic iodine in the water pool depends strongly on solution pH.