Effect of Ce doping on UO2 structure and its oxidation behavior

The structure of U1-yCeyO2 was studied in terms of added Ce cation. The oxygen vacancy, the oxidation state of cerium and uranium, and changes in the lattice parameter were investigated. Most Ce ions exist as tetravalent ions, which cause a lattice contraction due to the ionic radius. However, some Ce ions exist as trivalent Ce3+ ions, causing the oxidation of U4+ into higher oxidation states as well as a formation of oxygen vacancy for a charge balance. In addition, the effect of Ce on the oxidation of uranium dioxide was also studied by thermo-gravimetric analysis. The oxidation of Ce doped UO2 proceeds through dominant path given as two step reaction U1-yCeyO2-δ → (U1−yCey4+)4O9 → (U1−yCey4+)3O8. However, for higher Ce content (y = 0.136 to 0.332), an alternative pathway is proposed as (U1−yCey4+)4O9 → (U1−yCey3+)4O9. The increasing Ce content stabilizes the cubic (U1-yCey)4O9 phase, prohibits the formation of a metastable tetragonal (U1-yCey)3O7 phase, and inhibits the formation of (U1-yCey)3O8 proportional to the Ce content.