Finite temperature point defect thermodynamics and lattice response of U-10Zr from ab initio molecular dynamics

Uranium-zirconium alloys are extensively utilised as metallic nuclear fuels because of their high thermal conductivity, irradiation tolerance, and ability to stabilise the high-temperature body-centred cubic (γ) phase. During reactor operation, neutron irradiation generates point defects that significantly affect the thermophysical properties of the fuel. This study employs ab initio molecular dynamics (AIMD) simulations to examine the finite-temperature thermodynamics and lattice response of U-10Zr containing uranium and zirconium vacancies as well as tetrahedral interstitials. Simulations were conducted over the temperature range of 1000 K-1400 K, where the γ phase remains thermodynamically stable. Key properties, including equilibrium lattice parameters, linear thermal expansion coefficients, bulk modulus, molar heat capacity, and defect formation energies, were systematically evaluated. Vacancies function as contraction centres, reducing lattice parameters and equilibrium volumes across all temperatures, whereas interstitials serve as dilation centres, resulting in positive volumetric swelling. Zirconium vacancies cause slightly greater contraction than uranium vacancies, whereas uranium interstitials induce more pronounced lattice dilation compared to zirconium interstitials, reflecting compositional and elastic influences in γ-(U,Zr). Finite-temperature defect formation energies indicate that vacancies are energetically more costly than interstitials and increase monotonically with temperature, while interstitial formation energies remain relatively low and exhibit weak temperature dependence. The notably low uranium interstitial formation energies underscore the unique defect thermodynamics of γ-uranium alloys. These results provide a quantitative, temperature-resolved description of point-defect effects on the thermophysical behavior of U-10Zr, supplying physically consistent data for modelling dimensional stability and irradiation-driven evolution in metallic nuclear fuels.