Revisiting the diffusion mechanism of helium in UO2: A DFT+ U study

The understanding of migration properties of helium atoms after their generation through alpha-decay of actinides in spent nuclear fuels is important for the safety of nuclear fuel storage and disposal. The diffusion of helium in UO2 is revisited by using the DFT+U simulation methodology employing the Uramping method to address the issue of metastable energy states. A novel diffusion mechanism by helium interstitials, the asymmetric hop mechanism, is reported and compared to other diffusion mechanisms including an oxygen vacancy mediated mechanism and available experimental diffusion data. The new mechanism is shown to be the dominant one over a wide temperature range. (C)' 2017 Elsevier B.V. All rights reserved.