Abstract
The CALPHAD methodology was used to develop a thermodynamic assessment of the U-La-O system. The solid solution and liquid phases are described with the compound energy formalism and the partially ionic two-sublattice liquid model respectively. A density functional theory (DFT) calculation for the lattice stability of the fictive lanthanum oxide fluorite structure compound is used to determine the Gibbs energies for the La containing end-members in the CEF model for U1-yLayO2±x. Experimental thermodynamic and phase equilibria data were then used in optimizations to develop representations of the phases in the system that can be extended to include other actinide and fission products to develop multi-component models. The models that comprise this assessment very well reproduce experimentally determined oxygen potentials and the observed phase relations for the U-La-O system.
