Interaction of hydrogen with actinide dioxide (011) surfaces

Area of Science:

• Nuclear materials science
• Surface chemistry
• Computational materials science

Background:

• Actinide metal corrosion and oxidation produce surface oxides, influencing nuclear material management.
• Hydrogen interaction with actinide oxides is critical for understanding material degradation and safety.
• The (011) surface of actinide dioxides may exhibit unique reactivity compared to the more common (111) surface.

Purpose of the Study:

• To investigate the interaction of hydrogen with actinide dioxide (AnO2, An = U, Np, Pu) (011) surfaces.
• To determine the adsorption energies and reaction pathways for hydrogen on UO2, NpO2, and PuO2 (011) surfaces.
• To understand the implications of these interactions for nuclear material safety and management.

Main Methods:

• Utilized Hubbard-corrected density functional theory (PBEsol+U) for calculations.
• Included spin-orbit interactions and non-collinear antiferromagnetic (3k) behavior.
• Calculated dissociative adsorption energies of hydrogen on UO2, NpO2, and PuO2 (011) surfaces.

Main Results:

• Calculated hydrogen dissociative adsorption energies: UO2 (0.44 eV), NpO2 (-0.47 eV), PuO2 (-1.71 eV).
• Observed significant hydrogen dissociation and hydroxide formation on the PuO2 (011) surface, leading to surface distortion.
• Found UO2 (011) and NpO2 (011) surfaces to be relatively inert, favoring hydrogen ion recombination.

Conclusions:

• The reactivity of actinide dioxide (011) surfaces towards hydrogen varies significantly among uranium, neptunium, and plutonium.
• PuO2 (011) surfaces are chemically active, promoting hydrogen dissociation and hydroxide formation, impacting material stability.
• UO2 (011) and NpO2 (011) surfaces exhibit limited reactivity, suggesting hydrogen recombination as the dominant process.