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二氧化钚（PuO2）作为一种重要的核燃料材料，表面特性直接影响放射性元素的稳定性和迁移行为，在能源储存领域收到广泛关注。本文通过第一性原理方法研究水分子在二氧化钚（111）和（110）表面的吸附行为以及氧空位过量电子对这些表面的影响对于改进核燃料储存技术、延长储存寿命和降低潜在风险具有重要的实际意义。我们的模拟表明，PuO2（111）表面比（110）表面表现出更高的稳定性，具有更高的氧空位形成能。在化学计量的PuO2（111）和（110）表面上，水分子的解离吸附构型是最稳定的。利用NEB方法，我们发现在PuO2（111）和（110）表面上，第一个氢原子的解离仅需0.11 eV和0.007 eV的能垒，而第二步的完全解离则需要更高的能垒，分别为0.85 eV和1.02 eV。在还原的PuO2（110）表面存在氧空位的情况下，可以促进水分子解离成位于氧空位上方的羟基和与表面氧原子结合的氢原子，在一定条件下，克服3.31 eV的能垒，二个氢原子即可形成H2，在PuO2（111）过氢表面产生H2能垒下降到1.92 eV。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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