Computational study of tetravalent uranium and plutonium lattice diffusion in zircon

Empirical potentials have been established for zircon (ZrSiO4), uranium dioxide (UO2) and plutonium dioxide (PuO2) with the pair interactions UO and PuO being transferable to zircon. The quality of the potentials obtained is tested by calculating different physical properties of these oxides and comparing to the experimental values. The transferability to zircon of the two body short range interactions, UO and PuO, is tested by calculating the cell volume variation of orthosilicates ASiO4 (A=Zr, U, Pu) with respect to the contained A4+ ionic radius. Using the established force field and applying static transition state theory, we calculate the activation energies for lattice diffusion of uranium and plutonium in zircon. The corresponding diffusion coefficients are estimated and compared to recent experimental data.