Wettability of Liquid Cesium Halides on Oxide Single Crystals

The wettability of liquid-state volatile fission products （ FPs ） for solid-state fuels is important for the evaluation of FP release behavior during severe accidents. Previously, we have reported that liquid CsI exhibits extremely high wettability with a contact angle of virtually 0 ° on a polycrystalline UO 2 surface ［ K. Kurosaki et al., Sci. Rep. 7, Article number: 11449 （ 2017 ）］ and a single-crystalline yttria-stabilized zirconia （ YSZ ） surface ［ H. Ishii et al., J. Nucl. Sci. Technol. 55, No. 8, 838 – 842 （ 2018 ）］ . Here, based on the previous studies, we investigate the wettability of liquid cesium halides （ CsCl, CsBr ） on single-crystalline YSZ, TiO 2 , and MgO. We observe the high wettability of liquid cesium halides on single-crystalline YSZ and TiO 2 with contact angles of nearly 0 ° in all cases. However, liquid cesium halides exhibit completely different wettability on single-crystalline MgO, where the contact angles are measured to be 50 ° , 44 ° , and 25 ° for CsCl, CsBr, and CsI, respectively. Similarly to UO 2 , YSZ and TiO 2 are non-stoichiometric compounds containing oxygen defects, while MgO is a stoichiometric line compound. Thus, it is assumed that the oxygen defects play a role in the high wettability of liquid CsI on solid UO 2 .