Development of an overall correlation model for cesium chemisorption onto stainless steel

Nakajima, Kunihisa  ; Suzuki, Eriko   ; Osaka, Masahiko  

Severe accident (SA) analysis codes predicted that a large amount of cesium (Cs) chemisorbed onto stainless steel would be localized in the upper region of reactor pressure vessels (RPVs) in Fukushima Daiichi Nuclear Power Station because the RPV internals such as steam dryer and steam separator have large surface areas and would have experienced relatively high temperature. However, the current Cs chemisorption model incorporated into SA analysis codes cannot accurately reproduce experimental results such as temperature dependence. Therefore, JAEA has constructed an improved Cs chemisorption model validated above 1073 K where a Cs silicate was mainly formed as Cs-chemisorbed compound. On the other hand, recent study in JAEA indicated that the chemisorption rate was much higher than that expected from the improved model in a relatively low temperature region, around 873 K. Such an enhancement was suggested to be resulted from formation of a Cs ferrate. Thus, a lower temperature model validated in the temperature region where the main Cs-chemisorbed compound was a Cs ferrate was constructed. In this study, an overall correlation model combined the higher and the lower temperature models was developed by considering fraction of the Cs silicate and the Cs ferrate.