Diffusion in hypo-stoichiometric uranium mononitride

Uranium nitride is a nuclear fuel of interest as it offers enhanced accident tolerance, owing to its intrinsic properties. Before UN can be deployed commercially it is essential to understand its properties and how they evolve during operation. Therefore, molecular dynamics has been employed to study the thermal expansion and diffusivity of the intrinsic species in UN and how these change with stoichiometry. The introduction of hypostoichiometry as either nitrogen antisites or nitrogen vacancy defects is predicted to lead to an increase in nitrogen diffusivity and a concomitant decrease in the activation energy. The activation energies predicted for nitrogen diffusion in hypostoichiometry samples containing antisite defects are shown to offer a very close agreement with experimental observations.