First-principles magnetic treatment of the uranium nitride (100) surface and effect on corrosion initiation

Abstract

The magnetic properties of uranium nitride (UN) surfaces are not well understood experimentally or computationally but they have a significant effect on UN performance as a nuclear fuel. We investigated ferromagnetic (FM), antiferromagnetic (AFM), nonmagnetic (NM), and three hybrid magnetic structures of the most stable UN surface (100). To account for electron correlation and metastability, a U-ramp was performed to an effective Hubbard U-term of 2.0 eV. FM was found to be the most energetically favorable magnetic structure. Type 1 AFM slab was optimized to a new magnetic structure consisting of (100) planes with either all spin-up electrons, all spin-down electrons, or half spin-up and half spin-down electrons on uranium atoms. After OH adsorption to simulate corrosion initiation, the AFM, FM, and NM structures yield relatively similar bond lengths but varying bond angles, adsorption energies, and electronic profiles. Partial charge density maps show varying degradation mechanisms across magnetic structures. Electron localization function reveals more charge localized to AFM uranium atoms with spin-down electrons than uranium atoms with spin-up electrons. This leads to different properties depending on if an adsorbate interacts with a spin-up or spin-down terminated AFM surface. This work supports the physical accuracy of future computational studies toward corroborating with experiments and addressing UN fuel corrosion.