Atomic scale origin of hydrogen induced pitting corrosion in metallic uranium: first principles study of hydrogen behavior at uranium grain boundaries

Metal uranium hydrogenation corrosion has a point like distribution characteristic and occurs preferentially at grain boundaries. To explore the intrinsic mechanism of hydrogen's special behavior at metal uranium grain boundaries, a first principles method based on density functional theory was used to systematically study the solution, segregation, and diffusion behavior of hydrogen at uranium grain boundaries, as well as the influence of hydrogen on grain boundary strength. The calculation analysis shows that the larger the grain boundary energy, the smaller the overall solution energy of hydrogen atoms at the grain boundary, the smaller the segregation energy, and the stronger the capture ability. The grain boundary structure has a significant impact on the dissolution and segregation of hydrogen atoms. Hydrogen atoms tend to diffuse horizontally within the grain boundary region, making it difficult to diffuse from the grain boundary region to the interior of the grain. The 6d orbitals of uranium atoms and the 1s orbitals of hydrogen atoms on grain boundaries undergo orbital hybridization, and the charge transfer between hydrogen and uranium atoms can reflect the strength of their interaction. The solution of hydrogen atoms at grain boundaries reduces their strength and makes them more prone to embrittlement. The weakening effect of hydrogen atoms on the strength of uranium uranium bonds is the fundamental reason for the embrittlement of grain boundaries caused by hydrogen atoms. This article reveals the behavior of hydrogen at uranium grain boundaries from a microscopic mechanism perspective, providing theoretical support for understanding the hydrogenation corrosion characteristics and corrosion resistance methods of metallic uranium.