ATOMIC SIMULATIONS OF VOIDS IN U-10wt%Mo FUEL

Abstract

During neutron irradiation of U-Mo alloys, a phenomenon of fcc ordering of cavities is produced, coherent with the bcc structure of its matrix. In the U-10wt %Mo alloy, the cavities have a diameter of about 30 Å and a superlattice parameter of approximately 120 Å. Many works in the literature implicitly link the overpressurization of the cavities with fission gases (Xe,Kr) as being responsible for the interaction that leads to this ordering. However, recent observations indicate that, in the early burnup stages of the fuel, the cavities that make up this superlattice are practically empty. In this work, we perform molecular dynamics simulations aimed at studying the morphology of an empty cavity (void) and characterizing its mutual interaction with distance and ordering. The cavities are found to be faceted and can only interact at very close distances, of a few atomic planes.