Thermodynamic investigations of the uranium-molybdenum-oxygen system by a coupling of density functional theory and CALPHAD methodologies

Abstract

This paper examines the development of a consistent thermodynamic model for the uranium (U) – molybdenum (Mo) – oxygen (O) system for incorporation into the Thermodynamics of Advanced Fuels - International Database (TAF-ID). Phase diagram data and thermodynamic properties from the literature are reviewed. Density functional theory ab initio calculations at 0 K are combined with a quasi-harmonic statistical thermodynamic model to calculate thermodynamic functions (e.g.,∆fH298.15Ko, S298.15Ko, and Cp°(T)) of the relevant ternary compounds when little or no thermodynamic literature data are available. A CALPHAD method is employed to derive a model describing the Gibbs energy functions for all the relevant ternary compounds, the liquid phase, and the gas phase of the U-Mo-O system. A consistent thermodynamic model is obtained for the Mo-U-O system with a special emphasis placed on the oxygen rich portion of the ternary (i.e., MoO2-UO2-O). Finally, supporting binary and pseudo binary diagrams (e.g., Mo-O, UO2-MoO3 and UO3-MoO3) are computed and compared to literature data.