Computational Modeling of Cation Diffusion in Isolated Nanocrystals of Mixed Uranium, Plutonium and Thorium Dioxides

A classical molecular dynamics simulation of cation diffusion in isolated crystals (UxPuyTh1−x−y)O2 bounded by a free surface was performed. It was shown that in the bulk of the same model crystallite, the diffusion coefficients of cations of all types were practically identical. At the same time, the cation diffusion coefficients changed with the melting temperature of nanocrystals, which increased with increasing thorium content. At a given temperature, the diffusion coefficients were the higher, the lower were the melting points of the (UxPuyTh1−x−y)O2 crystallites. The temperature dependences of the diffusion coefficients in crystallites of different compositions converged when using coordinates normalized to the melting points.