铀氢化反应过程中氢扩散行为的第一性原理研究

First-principles studies on hydrogen diffusion behavior in uranium-hydrogen reaction

铀氢化反应动力学及产物形式受氢在铀氧化物及氢化物中的固溶、扩散等过程控制.本文利用第一性原理计算方法,研究氢在UO2、α-UH3、β-UH3、PdHx等介质中的固溶、扩散行为,从微观角度解释氢化反应各个阶段氢化反应速率的主要特征,并对α/β相生成的条件作一番探讨.研究表明,UO2中较高的氢扩散势垒导致氢扩散到达氧化物-金属界面非常困难,这是氢化反应起始阶段存在孕育期的主要原因;与此相反,β-UH3的氢具有非常低的溶解能和扩散势垒,且实际状态下β-UH3的表面积非常大,对氢化反应具有显著的促进作用;PdHx具有和α-UH3相近且均略高于β-UH3的溶解能和扩散势垒,这使得氢在其中的扩散速率较低,是Pd膜覆盖下铀氢化主要产物为α-UH3的主要原因.

The kinetics of uranium-hydrogen reaction and the product phases are dominated by the dissolution and diffusion behaviors of hydrogen in related mediums.To interpret the characteristics of U-H 2 reaction rate,as well as the formation conditions ofα/βhydrides,hydrogen dissolution and diffusion in UO2,α-UH3,β-UH3 and PdH x are investigated with ab initio calculations.The results show that the difficulties for H atoms to reach the oxide-metal interface due to the high diffusion barrier result in the induction period,whereas the lower energy of dissolution and diffusion barrier of H atoms inβ-UH3 with large specific area accelerate the U-H2 reaction.The dissolution energy and diffusion capability of H in PdH x are similar to those inα-UH3,which makesα-UH3 the main product of U-H2 reaction with the surface covered by Pd.