First-principles study of surface properties of crystalline and amorphous uranium aluminides

Abstract

Surface energy is a crucial material property required for the modeling of fission gas bubble behavior in nuclear materials. However, there is no information available regarding the surface properties of uranium aluminides. In this work we systematically investigate the surface properties of uranium aluminides (UAl3 and UAl4) by first-principles density functional theory (DFT) calculations. A total of 13 surface orientations with a maximum Miller index (MMI) up to 3 are studied for cubic UAl3, while 19 surfaces with a MMI of 2 for orthorhombic UAl4. Using the surface energies predicted by DFT, the surface properties of equilibrium single crystal UAl3 and UAl4, including surface area weighted surface energy, dominant surface orientations and surface anisotropy, are obtained from Wulff construction. To understand gas bubble behaviors in amorphous uranium aluminides under irradiation, we study the surface properties of amorphous UAl3 and UAl4. Compared to the crystalline phases, the amorphous phases are found to have lower surface energies due to the reduced number of breaking U-Al bonds close to the surface. The currently obtained surface properties of UAl3 and UAl4 can be used for the future modeling of gas bubble behaviors in both crystalline and amorphous uranium aluminide fuels.