Gaseous and aerosol formations in the pseudo-binary CsI-MoO reaction system

Rizaal, M.   ; 中島 邦久  ; 鈴木 恵理子   ; 三輪 周平  

Rizaal, M.; Nakajima, Kunihisa; Suzuki, Eriko; Miwa, Shuhei

The pseudo-binary CsI-MoO reaction system during transportation in the reactor under severe accident conditions has been investigated by using the JAEA-TeRRa semi-integral test facility. An oxygen gas with approximately 10 mbar of partial pressure was given to argon-steam upstream gas flow during the reaction to study its effect on downstream chemistry between CsI and MoO (Mo/Cs molar ratio of 2.13). The product of CsI-MoO reactions both gas and aerosols were analyzed upon their condensation on type-304L stainless steel sampling coupons at respective temperatures (T= 1150-450 K). Post-test analyses revealed that at a low oxygen potential of -192 kJ/mol (i.e. reference case with argon-steam only), most of the CsI reached downstream (T 400 K) without any reaction with MoO. On the other hand, when oxygen potential was slightly increased to about -144 kJ/mol, the CsI vapor could react with MoO to form cesium polymolybdates (CsMoO and CsMoO) and gaseous iodine which predominated the aerosol and gas that reached the downstream region. Particle size at this location was found to be less than 2.7 m in contrast to the former case having an irregularly large size. The gaseous iodine in the latter case, based on the thermodynamic analyses, was estimated to be hypoiodous acid (HIO) or molecular iodine (I). The results in this study indicated that speciation of both Cs and I with the Mo chemistry during a severe accident could be variedly formed depending on the prevailing oxygen potential.