Fission gas-induced transport degradation in δ-UZr₂: Insights from first-principles modeling

The thermophysical and electronic effects of Xenon and Krypton incorporation in the δ-phase of U-10Zr metallic nuclear fuel were analyzed using Density Functional Theory and Boltzmann transport formalism. Fission gas atoms were modelled in both substitutional and interstitial configurations, and their influence on structural integrity, transport coefficients, and electronic structure was systematically evaluated. Vacancy formation energies indicate a thermodynamic preference for uranium-site substitution, whereas incorporation energies highlight an inclination for interstitial accommodation, with dumbbell configurations producing the most pronounced lattice distortion. Transport properties—including relaxation time, thermal and electrical conductivity—were significantly degraded in interstitial configurations due to enhanced scattering and suppression of the density of states near the Fermi level. Partial density-of-states analysis confirmed the central role of U-5f orbitals in governing electronic behavior. These findings provide the first configuration-resolved insight into how fission gases perturb δ-UZr 2 transport, advancing phase-specific understanding of metallic fuel degradation under irradiation.