Atomistic Investigations of Intrinsic and Extrinsic Point Defects in bcc Uranium

Abstract

Metallic alloys of uranium show great potential as transmutation fuels that could be used to burn long-lived and high-heat-producing minor actinides and fission products in nuclear reactors. In fuels, fission and radiation damage result in the production of a large number of intrinsic point defects and extrinsic fission atoms. Radiation damage and diffusion (processes heavily dependent on point defects), as well as fission product behavior, are important to the understanding of the behavior of these metallic fuel alloys. Of the fission products, fission gases Xe, Kr, and the decay product He are of special importance, as they migrate and form bubbles detrimentally affecting fuel properties. In this work, several systems of body-centered-cubic (gamma) U are examined through a semi-empirical interatomic potential based on the modified embedded-atom method. The vacancy formation energy is analyzed as a function of pressure and is used to determine the stable vacancy formation energy at ambient conditions. The vacancy formation energy as a function of temperature is analyzed for high-temperature systems. Interatomic potentials are developed and implemented in the investigation of He, Xe, and Kr point defects in the gamma phase of uranium. For all fission gases studied, the most energetically favorable location is the substitutional position, with helium having the lowest formation energies of the species investigated.