Temperature-dependent Variations of the Interface between UO2 and Zr

Temperature-dependent variations of the interface between uranium dioxide and zirconium in UO2 -Zr systems were studied using X-ray photoelectron spectroscopy. The surface of the uranium dioxide sample was oxidized to hyperstoichiometric UO (2+x) composed of U(IV), U(V), and U(VI) valence states at room temperature, whereas UO2 consisting of the only U(IV) oxidation state appeared after annealing with zirconium. In the zirconium sample, its surface was spontaneously oxidized to ZrO2 at room temperature, whereas it was variously changed after heating the UO2 -Zr sample. Furthermore, we observed a molten product composed of -Zr(O), (U,Zr)O-2 , and ZrO2 when a UO2 -Zr sample was fully melted.