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Plutonium dioxide, as one of the primary materials for nuclear fuel, serves as a critical component in fast neutron reactor fuel and mixed oxide (MOX) fuel due to its distinctive physical and chemical properties. This significantly enhances the utilization efficiency of uranium and diminishes the demand for natural uranium resources. Moreover, plutonium dioxide constitutes an essential component of spent nuclear fuel. However, during long-term storage, oxygen vacancies on its surface can facilitate hydrogen release under the influence of water molecules, thereby posing potential risks to nuclear safety. Consequently, gaining a profound understanding of the interaction mechanism between water molecules and the plutonium dioxide surface is of paramount importance. Such insights provide valuable theoretical guidance for ensuring the safe storage of spent nuclear fuel.Based on the first-principles calculations, this study investigated the adsorption behavior of H2O molecules on the PuO2 (111) and (110) surfaces, as well as the effects of oxygen vacancies and excess electrons on these surfaces. The simulation results revealed that the PuO2 (111) surface demonstrated greater stability compared to the (110) surface, indicating PuO2 (110) is more prone to oxygen vacancies. For the adsorption of water molecules on PuO2 (111) and (110) surfaces, the plutonium atom vertex site was identified as the sole stable adsorption site, with one hydrogen atom of the water molecule preferentially bonding to a surface oxygen atom. Due to the higher reactivity of the PuO2 (110) surface compared to the stoichiometric PuO2 (111) surface, water molecules exhibited molecular adsorption configurations on the latter, while dissociative adsorption configurations were favored on the former. Using the CI-NEB method, it was determined that the energy barriers for the dissociation of the first hydrogen atom on stoichiometric PuO2 (111) and (110) surfaces were 0.11 eV and 0.008 eV, respectively. In contrast, the energy barriers for complete dissociation were significantly higher, at 0.85 eV and 1.02 eV, respectively. For reduced PuO2 (111) surfaces containing surface oxygen vacancies, the energy barriers for H2 production via water decomposition was calculated to be 3.31 eV respectively. On the over-hydrogenated PuO2 (111) surface, the energy barrier for H2 production decreased markedly to 1.92 eV, providing theoretical insights into the mechanism of hydrogen release during nuclear fuel storage.
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Keywords:
- Plutonium dioxide /
- First-principles method /
- Water molecular /
- Oxygen vacancy /
- Adsorption behavior
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