钚氧化物中氢行为的第一性原理研究

通过第一性原理计算和原子级热力学方法，系统研究H、H₂在PuO₂和α-Pu₂O₃中的吸附、扩散和溶解行为.研究发现：氢的上述行为均是吸热过程，但在α-Pu₂O₃与PuO₂中有显著不同：在α-Pu₂O₃中H可自发聚合成H₂，但在PuO₂中H难再聚合；在α-Pu₂O₃中H、H₂均能扩散，通常H会聚合成H₂再扩散，在PuO₂中H₂解离后才能扩散，且PuO₂中H沿高势能面的扩散比α-Pu₂O₃中H₂扩散更容易；在氢压、温度驱动下，氢在α-Pu₂O₃中存在H₂溶解到H+H₂混合溶解机制的转变，平衡气压P_H2远小于H在PuO₂中溶解的情况.基于此，给出PuO₂和α-Pu₂O₃中氢行为的微观图像和PuO₂的阻氢微观机制：PuO₂表面限制H₂解离、渗透，PuO₂块体限制H的溶解，但不阻止H扩散.结合钚氧化层表面氢行为研究获得了钚氢化孕育期的微观机制，为孕育期全过程理论建模提供依据.

First-principles Study of Hydrogen Behaviors in Plutonium Oxides

In-depth investigation of hydrogen behaviors in Pu-oxide overlayers (mainly PuO₂ and α-Pu₂O₃) is critical for modeling complex induction period of Pu hydriding. Within DFT+U and DFT-D3 schemes, systematic first-principles calculations and ab initio thermodynamic evaluations reveal that hydrogen absorption, dissolution behaviors, and diffusion mechanism in PuO₂ are quite different from those in α-Pu₂O₃, among which highly endothermic absorption and dissolution of hydrogen are primary hydrogen resistance mechanism of PuO₂. Since its difficult recombination, atomic H is preferred existence state in PuO₂, but H will recombine spontaneously in α-Pu₂O₃. In PuO₂, H diffusion is always clinging to O anions, whereas in α-Pu₂O₃, H₂ prefers to migrate along O vacancies with higher barriers. Based on a series of theoretical studies, we conclude that the main interactions between hydrogen and Pu-oxide overlayers are not involved with chemical reactions and intact PuO₂ can effectively inhibit hydrogen permeation.The hydrogen dissolution in α-Pu₂O₃ can be reasonably described by an ideal solid solution model.