Insight into impurities in α-U and hydrogen trapping at impurities from first-principles

First-principles calculations were performed to investigate the physical properties including structural stability, electronic structures and hydrogen trapping characteristics of various impurities in α-U. The impurities were selected based on relevant literature including 14 metallic elements (Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo) and 13 non-metallic elements (H, He, B, C, N, O, F, Ne, Si, Cl, Ar, Kr, Xe). Three interstitial sites and one substitutional site were taken into consideration. It is found that non-metallic impurities including H, C, N and O preferentially occupy interstitial sites, whereas other non-metallic impurities tend to occupy substitutional sites, and all the metallic impurities favor substitutional positions. The incorporation of impurities in α-U is governed by atomic sizes and electron hybridizations. Compared with non-metallic impurities, metallic impurities in α-U exhibit a higher propensity to act as hydrogen traps, particularly Cr, Mn, Fe, Co, Ni, and Cu. These results provide theoretical insights into the microstructure evolution of uranium and the underlying mechanisms controlling the complex failure behaviors of metallic nuclear materials, such as corrosion, swelling, and irradiation damage.