Oxidation of metal oxides and minerals is a surface-mediated process that is important to mitigate corrosion, promote surface activation or passivation, understand weathering and transformations in the geological record, and minimize transport and bioavailability of toxic pollutants. For UO2, mitigation of oxidation is also important to prevent failure in nuclear fuel rods and long-term storage of radioactive waste. In UO2, it was recently determined by a combination of X-ray scattering, spectroscopy, and density functional theory (DFT) that during the initial oxidation of the (111) surface, oxygen interstitials self-organize into a nanoscopic lattice with 3-layer periodicity. (Stubbs et al., PRL 114, 246103 (2015)). We use DFT and ab initio thermodynamics to show how the nature of the UO2(111) and (100) surfaces – orientation, stoichiometry, structure, and redox state – is determined by temperature and the chemical potentials of O2 and H2O in the environment. These factors, as well as the nature of the electron transfer process between uranium and oxygen, influence the self-organization of oxygen interstitials into nanoscopic subsurface arrays with structures distinctly different from classical diffusion model predictions and bulk uranium oxide structures.

Ab initio thermodynamics of how the oxidation of uranium dioxide’s surface, subsurface, and bulk is determined by the chemical potentials of oxygen and water in the environment

251st National Meeting (2016)

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