First-principles study of the surface properties of U-Mo system

Abstract

U-Mo alloys are promising fuels for future high-performance research reactors with low enriched uranium. Surface properties, such as surface energy, are important inputs for mesoscale simulations (e.g., phase field method) of fission gas bubble behaviors in irradiated nuclear fuels. The lack of surface energies of U-Mo alloys prevents an accurate modeling of the morphology of gas bubbles and gas bubble-induced fuel swelling. To this end, we study the surface properties of U-Mo system, including bcc Mo, α-U, γ-U, and γ U-Mo alloys. All surfaces up to a maximum Miller index of three and two are calculated for cubic Mo and γ-U and non-cubic α-U, respectively. The equilibrium crystal shapes of bcc Mo, α-U and γ-U are constructed using the calculated surface energies. The dominant surface orientations and the area fraction of each facet are determined from the constructed equilibrium crystal shape. The disordered γ U-Mo alloys are simulated using the Special Quasirandom Structure method. The (1 1 0) and (1 0 0) surface energies of γ U-7Mo and U-10Mo alloys are predicted to lie between those of γ-U and bcc Mo, following a linear combination of the two constituents’ surface energies. To better compare with future measurements of surface energies, the area fraction weighted surface energies of α-U, γ-U and γ U-7Mo and U-10Mo alloys are also predicted.