Thermodynamic assessment of the U-Y-O system

A CALPHAD assessment of the U-Y-O system has been developed. To represent the YO2 compound in the compound energy formalism (CEF) for U1−yYyO2±x, the lattice stability was calculated using density functional theory (DFT) while a partially ionic liquid sub-lattice model is used to describe the liquid phase. A Gibbs function for the stoichiometric rhombohedral UY6O12 phase is proposed. Models representing the phases in the U-O and Y-O systems taken from the literature along with the phases that appear in the U-Y-O ternary are combined to form a complete assessment.