A novel empirical potential for high-temperature molecular dynamics simulation of ThO2 and MOX nuclear fuel crystals

Using a global optimization method, the parameters of a pair potential of the interaction of thorium and oxygen ions in ThO2 are fitted, which are compatible with the potential set MOX-07 previously proposed for UO2 and PuO2 crystals. The potential is expressed in the form U(R) = exp(X–Y•R) eV, and the optimal parameter values are X = 8.073687, Y = 3.349 A−1. Using these parameter values, the potential reproduces the lattice constant of the ThO2 crystal in the entire temperature range up to melting, and quantitatively describes the high-temperature peak in the heat capacity that is associated with the superionic transition.