Grain Boundary Mechanisms and Regulation in the Hydriding Corrosion of Metallic Uranium

Metallic uranium has important applications in nuclear fuels, nuclear materials, and related engineering fields because of its distinctive nuclear physical properties. However, its high chemical reactivity makes it susceptible to hydriding corrosion in hydrogen-containing environments. The substantial volumetric expansion associated with hydride formation, together with the resulting cracking and pulverization, severely compromises structural integrity and poses significant risks to long-term storage and safe service. Focusing on the role of grain boundaries in the hydriding corrosion of metallic uranium, this review summarizes current understanding of hydrogen ingress through the surface oxide layer, hydrogen segregation and migration at grain boundaries, and the regulation of these processes by elemental segregation. Defects and grain boundaries within the oxide layer can provide preferential pathways for hydrogen transport. In the metallic matrix, local structural distortion, excess free volume, and characteristic electronic structures at grain boundaries promote hydrogen trapping and accumulation, potentially facilitating hydride nucleation and intergranular damage by weakening interfacial cohesion. Metallic solutes affect the hydriding process primarily by modifying phase stability, hydrogen accumulation, and grain boundary cohesion, whereas the effects of non-metallic impurities depend on their states of occurrence, segregation tendencies, and co-segregation interactions with hydrogen. Grain boundary structure and local chemistry therefore jointly govern hydrogen ingress, accumulation, and damage evolution, making them central to understanding and regulating localized hydriding corrosion in metallic uranium.