Evaluation of Cs deposition mechanism between shield plugs, 1; Estimation of Cs deposition by FP behavior models using for severe accident analysis

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

We are investigating the Cs accumulation mechanism between shield plugs observed in the Fukushima Daiichi Nuclear Power Plant accident. Previously, it was thought that there was no gas flow path in the gap between the shield plugs, but it was found that a high concentration of Cs-137 was accumulated. Also, the Nuclear Regulatory Commission clarified that the deformation of the shield plug due to gravity causes the formation of a gas flow path. In this study, the chemical adsorption rate of CsOH aerosol on concrete was added to the FP transfer behavior analysis module of the severe accident analysis code SAMPSON, and a trial analysis was performed on the shield plug of Unit 2. Then, the effects of gap spacing between shield plugs, gas flow velocity, gas temperature, CsOH aerosol concentration, etc. on Cs accumulation are evaluated, and the main mechanisms of Cs accumulation are examined.