Diffusion of helium in non-stoichiometric uranium dioxide

Diffusion coefficients of helium in solid UO2+x at high temperature and various stoichiometric compositions are evaluated by using molecular dynamics simulations based on a partly-ionic model in conjunction with a polaron ‘Free Hopping Approximation’ proposed earlier. The results are compared with existing experimental and simulation data. A strong dependence of the apparent diffusion activation energy on stoichiometry is found and the mechanisms of He migration in non-stoichiometric solid UO2+x are discussed.