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Study on chemisorption model of cesium hydroxide onto stainless steel type 304

A large amount of cesium (Cs) chemisorbed onto stainless steel is predicted to be present especially in the upper region of reactor pressure vessel (RPV) during light water reactor severe accident. A chemisorption model was developed for estimation of such amounts of Cs for stainless steel type 304 (SS304) exposed to cesium hydroxide (CsOH) vapor. However, this existing chemisorption model cannot accurately reproduce experimental results and is considered not to be suitable for the estimation of the Cs-chemisorbed amounts under various conditions experienced in Fukushima Dai-ichi nuclear power station. Our recent laboratory study indicated that the surface reaction rate constant used in the exiting chemisorption model depended on both of silicon content in SS304 and concentration of gaseous CsOH as well as on temperature. Therefore, in this study, a modified Cs chemisorption model which accounts for these effects was constructed by combining penetration theory for gas-liquid mass transfer with chemical reaction and mass action law for CsOH decomposition at interface between gaseous and solid phases. As a result, it was found that the modified model was able to adequately describe effects on concentration of CsOH in gaseous phase and Si content in SS304 and more accurately reproduce the experimental data than the existing model.