Oxidation of uranium dioxide plays a key role in the weathering and release of water soluble U6+ into the environment from natural mineral sources and mines, as well as the corrosion and structural failure of nuclear fuel rods in a plant or in storage facilities. In this work, density-functional theory and ab initio thermodynamics are used to delineate the initial stages of surface and subsurface oxidation of UO2 at the (111) surface as a function of temperature and oxygen pressure. Initially, chemisorption of oxygen on the clean stoichiometric surface forms highly stable triple-bonded hemi-uranyl groups and surface U6+ ions. As the oxygen chemical potential increases above -1.0 eV, subsurface oxidation becomes thermodynamically favored.  The degree of uranium oxidation is determined by quantifying the transfer of electrons from the localized U 5f bands to the delocalized O 2p bands as oxygen atoms occupy octahedral interstitial sites in the UO2 lattice.

DFT investigation of the oxidation of uranium dioxide via the (111) surface

243rd National Meeting (2012)

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