Density Functional Theory-Based Study of UC2 and Cr-Doped UO2

A density functional theory-based study of UC2 and Cr-doped UO2 using the phono3py and VASP computational simulation packages is presented. Furthermore, the temperature-dependent thermal conductivities are compared to the traditional urania fuel. Doping of urania with Cr allows for improved fission gas retention, reducing the fission gas release and lowering the oxidation rate of UO2. The thermal conductivity calculated using the random alloy method with one U atom replaced by Cr in a supercell (CrU31O64) shows a slight decrease; however, this may be compensated for by larger grain sizes in the presence of Cr. The reduction of thermal conductivity for the 0.61 wt.% Cr substation in urania is presented. Investigated here, the UC2 metallic high-temperature fcc phase looks promising due to additional electronic contribution to conductivity. Furthermore, we found that the temperature-dependent phonon-assisted thermal conductivities for UC2 and UO2 are very similar. The elastic properties of UC2 were also evaluated and compared with UO2. The presented analysis provides information for further improvement of the design of nuclear fuels.