Engineering Oxidation-Resistant Uranium Mononitride Surfaces via Thermodynamically Stable (111) Facets.

Area of Science:

• Materials Science
• Nuclear Engineering
• Computational Chemistry

Background:

• Uranium mononitride (UN) is a promising nuclear fuel due to its advantageous properties.
• Rapid oxidation of UN in hydrothermal accident scenarios limits its deployment.
• Current mitigation strategies negatively impact UN's performance.

Purpose of the Study:

• Investigate the facet-dependent oxidation resistance of UN.
• Identify intrinsic solutions for enhancing UN's stability.
• Establish design principles for oxidation-resistant UN fuel.

Main Methods:

• First-principles calculations.
• Hubbard-corrected density-functional theory (DFT+U).
• Analysis of surface energy and oxygen adsorption on UN facets.

Main Results:

• The N-terminated (111) UN surface is thermodynamically dominant with low surface energy (0.36 J/m²).
• Oxygen adsorption is thermodynamically forbidden on the (111) facet (+0.68 eV), unlike the (100) facet (-1.57 eV).
• Surface reconstruction on the (111) facet strengthens U-N bonds and creates a U⁵⁺-like electronic state, conferring inertness.

Conclusions:

• Facet-dependent oxidation resistance is an intrinsic property of UN.
• The (111) facet offers superior oxidation resistance compared to the (100) facet.
• Engineering a strong ⟨111⟩ texture is crucial for developing high-performance, oxidation-resistant UN nuclear fuel.