Study on FP chemistry for improvement of LWR source term

軽水炉ソースターム評価のためのFP化学研究

Rizaal, M.   ; 中島 邦久  ; 唐澤 英年; Luu, V. N. ; 三輪 周平  

Rizaal, M.; Nakajima, Kunihisa; Karasawa, Hidetoshi; Luu, V. N.; Miwa, Shuhei

Our research focused on, but is not limited to, cesium (Cs) and iodine (I) chemistry due to their high impact on the overall source term. The retention or release of both elements is largely affected by chemical interaction with materials that are present in the reactor. To understand their chemistry during transport in the event of a nuclear severe accident (SA), we studied the interaction phenomena taking place from high- to low-temperature conditions. We have succeeded in elucidating these phenomena (particularly Cs) and summarized them in a fission product (FP) chemistry database ECUME. This database not only could deepen our understanding of the mechanism of Cs and I chemistry in an SA, but could also improve source term analysis. Improvement in the reaction between Cs vapor and stainless steel was shown by the use of the ECUME database in SA analysis code SAMPSON. Better reproducibility of Cs retention at high temperatures of the large-scale experiment was obtained, in contrast to using the MELCOR Cs interaction model (i.e. widely used model in SA code) that was worse in reproducing such phenomenon. Taking into consideration of near-term implementation of Accident Tolerant Fuel (ATF) materials such as chromium (Cr)-coated Zircaloy, further study on the interaction with FP would be important to ensure the material impact on source term because the reaction between Cs and Cr can be thermodynamically expected.