Evaluation of thermal conductivity of hypostoichiometric (U, Pu)O_2-x solid solution by molecular dynamics simulation at temperatures up to 2000 K

The thermal conductivities of hypostoichiometric U_1-yPu_yO_2-x solid solutions have been investigated by the molecular dynamics (MD) simulation between 300 and 2000 K using the Born-Mayer-Huggins interatomic potential with the partially ionic model. In the present equilibrium MD system, the thermal conductivity was calculated by the time-integral of auto-correlation function of energy current based on the Green-Kubo relationship. For stoichiometric U_1-yPu_yO_2.0 crystals (y = 0.0-0.3), the thermal conductivity was almost constant as a function of Pu content y. On the other hand, for hypostoichiometric U_0.8Pu_0.2O_2-x solid solutions (x = 0.0-0.06), the effect of oxygen deficiency x on the thermal conductivity became larger with increasing x, and their thermal conductivities were lower than that of the stoichiometric oxide, while the temperature dependence was weakened. These results were caused by that oxygen vacancies as lattice defects disordered phonon conduction, which was elucidated by the vibration analyses, i.e. the correlation function of energy current and the phonon-level density.