Evaluation of Thermal Conductivity of Hyperstoichiometric UO2+ x by Molecular Dynamics Simulation

The thermal conductivity of UO2+x has been investigated by an equilibrium molecular dynamics (EMD) simulation up to 2000K using the Born–Mayer– Huggins iInteratomic potential with the partially ionic model. In the present EMD system with the Green–Kubo method, the thermal conductivity was determined by the auto-correlation functions of energy and charge currents and the cross-coupling term. The thermal conductivity of UO2+x decreased with an increase of x and temperature. Its temperature dependence was relatively small for large x values, which was attributed to phonon scattering by excess oxygens. In addition, the heat capacity was calculated using the phonon-level density deduced by the velocity auto-correlation function for constituent ions. The phonon velocity was also evaluated by the phonondispersion relationship. Using these thermal properties obtained by EMD calculations, the effect of excess oxygens on the phonon mean free path was discussed.