What is the Role of Nb on Preferential Hydriding of Double-Phased Uranium, Stabilizing γ-U, or Avoiding Hydrogen Aggregation?

Uranium as the heaviest naturally occurring element plays important roles in nuclear industries. Hydrogen-caused corrosions and irradiation-caused structural damages are two critical degradations that threaten the safe storage and practical applications of uranium. Through alloying with transition metals like Nb, the γ-phase of U can be stabilized at room temperature, which shows better performance against hydrogen-caused corrosions than the ground-state α-U. The underlying mechanisms have not been fully understood yet. To explain the preferential hydriding phenomenon observed on a specially fabricated double-phase U-2.5 wt % Nb alloy, we perform multiscale ab initio calculations and kinetic Monte Carlo (KMC) simulations. We find that because of different diffusion mechanisms, intrinsic α-U and γ-U already show different hydrogen accumulation behaviors. The existence of random Nb atoms further inhibits hydrogen accumulation in γ-U. Our work declares its contribution by pointing out the important role of crystal lattice architectures on hydrogen accumulations in metals.