Theoretical study on the hydrogen capture and damage mechanisms of PuO2 nanograin boundary

Abstract

The hydriding corrosion is harmful to the long-term storage of plutonium (Pu). Since the defect-free PuO2 overlayer has been proved to resistance hydrogen attack, Pu hydriding is mainly related to such penetrating defects as the grain boundaries (GBs) of PuO2. We perform comprehensive DFT+U-D3 calculation and tensile-test simulation to investigate the incorporation and dissolution behaviors of H in PuO2 GB, and the induced hydrogen damage. The exothermic incorporation and dissolution of H confirm the capture effect of PuO2 GB, which are contrary to endothermic behaviors of H in PuO2 bulk. The predicted saturation solubility of H demonstrates that GB is the active site that promotes H dissolution, which is one of the important factors to Pu hydriding. The dissolved H can further weaken the Pu–O bonds in GB and facilitate the intergranular fracture of PuO2 overlayer. Our study provides key mechanistic insights towards interpreting of Pu hydriding corrosion, which is critical for predictive modeling of the induction time.