Atomistic simulation of vacancies in uranium-zirconium alloys
Carroll, David Evan
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Metallic alloy fuels were often used in the infancy of nuclear power, but since the industry began focusing on oxide fuels, there hasn’t been a lot of research done on metallic alloy fuels using current research capabilities. In this thesis, uranium-zirconium alloy has been selected for closer examination as zirconium is one of the cheapest of the potential alloying metals, such as molybdenum and niobium. The work will look at the vacancy formation energy of pure uranium, then alloys containing 10%, 20%, and 30% zirconium by atomic percent at temperatures ranging from 100 K to 1400 K, going in steps of 100 K. The simulations will be run using LAMMPS with a MEAM interatomic potential. It also analyzes the results and structure of these simulations using Wigner-Seitz Defect Analysis, Short Range Order Parameter, Common Neighbor Analysis, and the Radial Distribution Function. The results show that the interatomic potential used gives accurate vacancy formation energies for pure uranium, 10% zirconium, and 20% zirconium, usually around 1 – 2 eV. The structure for these metals also maintains the BCC phase. 30% zirconium, however, tends to give negative vacancy formation energies and has difficulty maintaining its phase, due to the creation of vacancy-interstitial pairs. In the end, the U-20Zr alloy is recommended for use in advanced reactors due to wanting as much of zirconium’s thermal properties as possible while still keeping the structure intact.