Surface analyses of cesium hydroxide chemisorbed onto type 304 stainless steel

Highlights: • The results of CsOH chemisorption experiments on stainless steel 304 are presented. • Stainless steel 304 was used to simulate reactor structural materials. • Separate effect experiments were performed, to simulate Severe Accident conditions. • A previously unexpected chemisorbed compound was formed CsFeSiO₄. • A relation between the samples Si content and the Cs deposited amount was detected. - Abstract: Chemisorption is of main importance during a Severe Accident (SA) at a light water reactor, as it can influence fission product retention in the reactor vessel. Information on the distribution, composition and properties of such deposits can influence the decommissioning practice after a SA, and could be applied, for example, for the decommissioning of the Fukushima Daiichi Nuclear Power Plant. Moreover such information can enhance the description of the chemisorption models applied in SA codes, consequently improving the source term assessment. This paper will present the results obtained from CsOH chemisorption experiments onto stainless steel samples, used as simulants of reactor structural materials. The samples post-analyses showed that CsOH will absorb onto the surface, reacting preferentially with Si impurities and forming a newly detected compound, CsFeSiO₄. From our results, it can be inferred that Si content in structural materials can determine the amount of radioactive Cs deposited and potentially retained on the reactor vessel after a SA.