A comprehensive understanding of uranium oxidation under H2O-O2 mixtures: Polaron mediated cyclic reaction of H2O

The complex oxidation susceptibility of uranium under the H2O-O2 mixed gases remains a challenging task. Based on the systematical DFT+U first-principles calculations and the ab initio atomistic thermodynamic method, we have proposed a series of physical mechanisms to clarify the reaction behaviors of UO2 and H2O-O2 mixtures, namely, the polaron mediated further oxidation of UO2, the O2-participated hydroxylation process and the consequent overall cyclic reaction of H2O on UO2 surface, and the critical threshold of partial pressure of O2 to postpone the U+H2O reaction. The complex phenomena observed in various experiments have been self-consistently interpreted in detail.