Interaction of Liquid CsIO3 with a Polycrystalline UO2 Solid Surface

Understanding the behavior of melted volatile fission products （ FPs ） on the fuel contributes to the precise assessment of the release behaviour during a severe nuclear accident. A previous study revealed that liquid CsI shows abnormally high wettability with measured contact angles of almost zero degrees against the polycrystalline UO 2 solid surface. ［ K. Kurosaki et al., Sci. Rep. 7, Article number: 11449 （ 2017 ） . ］ . In this study, we focus on the melting behavior of CsIO 3 and revealed that liquid CsIO 3 also shows high wettability on the polycrystalline UO 2 solid surface. However, after melting, CsIO 3 decomposed and only Cs reacted with the polycrystalline UO 2 solid surface and I was only ab-sorbed on the solid surface. When the CsI had melted on the polycrystalline UO 2 solid surface, both Cs and I were able to penetrate inside the UO 2 pellets. In short, when Cs and I exist as CsIO 3 , Cs and I will be separately released during severe accidents. These findings suggest that the release mecha nisms of Cs and I could be strongly affected by the chemical species in the irradiated fuels.