Evaluation of thermal properties of mixed oxide fuel by molecular dynamics

The molar specific heat and the thermal conductivity of PuO2 and (U,Pu)O2 solid solution were evaluated by a molecular dynamics (MD) technique. The partially ionic model was used. The calculated molar specific heat of PuO2 well agreed with the experimental data. The simulation results for the temperature dependence of thermal conductivity of PuO2, obtained by the Green-Kubo technique, was in good agreement with the experimental data. The Bredig transition did not occur in the MD cell of PuO2 at high temperature. The variation in the calculated lattice parameter of (U,Pu)O2 with PuO2 content closely followed Vegard's law. The calculated specific heat and thermal conductivity of (U0.8,Pu0.2)O2 were in good agreement with the experimental values. From the change in the thermal conductivity of (U,Pu)O2 with Pu content, it was found that the simulated Pu ions mutually act as phonon scattering centers. The simulated (U,Pu)O2 cell showed both the existence of the Bredig transition and a peak in the specific heat in the vicinity of 2350 K, and provided various information on the diffusion coefficients for anions and cations at high temperature. (orig.)