Fission products chemistry in achieving reliable LWR source term prediction; An Outlook to Cs-Cr vapor species interaction

Rizaal, M.   ; Nakajima, Kunihisa  ; Karasawa, Hidetoshi; Miwa, Shuhei  

In our research group, we devoted fundamental study on fission products (FP) in Cesium (Cs) and iodine (I) chemistry due to their high impact on the overall source term. In a severe accident, the retention or release of Cs and I is largely affected by chemical interaction with materials in the reactor. The interaction phenomena taking place from high- to low-temperature conditions were studied to understand their chemical behavior. We have succeeded in elucidating some underlying phenomena (particularly Cs) and summarized them in an FP chemistry database ECUME. In the upcoming version of the ECUME database, we aim at extending the application into Accident Tolerant Fuel (ATF) cladding materials such as chromium (Cr)-coated Zircaloy. Upon ATF cladding's introduction to the light water reactor, various chemical impacts on the source term can be expected, such as suppression of hydrogen generation and changes in the vessel/containment atmosphere during severe accidents. In the case of Cr-coated Zircaloy, the chromium may react with cesium in an oxidizing atmosphere to form the low-volatile Cs compound of CsCrO. This event could significantly influence the transport behavior of cesium and iodine. At the present workshop, we will discuss the interaction phenomena among Cs and Cr vapor species under specific accident progression scenarios within thermodynamic consideration. Experimental investigations are planned in the future to confirm the findings reported in this preliminary work.