Interaction of hydrogen with actinide dioxide (011) surfaces

The corrosion and oxidation of actinide metals, leading to the formation of metal-oxide surface layers with the catalytic evolution of hydrogen, impacts the management of nuclear materials. Here, the interaction of hydrogen with actinide dioxide (AnO₂, An = U, Np, or Pu) (011) surfaces by Hubbard corrected density functional theory (PBEsol+U) has been studied, including spin-orbit interactions and non-collinear 3k anti-ferromagnetic behavior. The actinide dioxides crystalize in the fluorite-type structure, and although the (111) surface dominates the crystal morphology, the (011) surface energetics may lead to more significant interaction with hydrogen. The dissociative adsorption of hydrogen on the UO₂ (0.44 eV), NpO₂ (-0.47 eV), and PuO₂ (-1.71 eV) (011) surfaces has been calculated. It is found that hydrogen dissociates on the PuO₂ (011) surface; however, UO₂ (011) and NpO₂ (011) surfaces are relatively inert. Recombination of hydrogen ions is likely to occur on the UO₂ (011) and NpO₂ (011) surfaces, whereas hydroxide formation is shown to occur on the PuO₂ (011) surface, which distorts the surface structure.