An atomistic study of defect energetics and diffusion with respect to composition and temperature in gamma U and gamma U-Mo alloys
G Park and B Beeler and MA Okuniewski, JOURNAL OF NUCLEAR MATERIALS, 552, 152970 (2021).
Uranium-molybdenum (U-Mo) alloys are promising candidates for high- performance research and test reactors, as well as fast reactors. The metastable gamma phase, which shows acceptable irradiation performance, is retained by alloying U with Mo with specific quenching conditions. Point defects contribute to the atomic diffusion process, defect clustering, creep, irradiation hardening, and swelling of nuclear fuels, all of which play a role in fuel performance. In this work, properties of point defects in gamma U and gamma U-xMo ( x = 7, 10, 12 wt. % ) were investigated. Vacancy and self-interstitial formation energies in gamma U and gamma U-xMo were calculated with molecular dynamics (MD) simulations using an embedded atom method interatomic potential for the U-Mo system. Formation energies of point defects were calculated in the temperature range between 400 K and 1200 K. The vacancy formation energy was higher than the self-interstitial formation energy in both gamma U and gamma U-xMo in the evaluated temperature range, which supports the previous results obtained via first-principles calculations and MD simulations. In gamma U-xMo, the vacancy formation energy decreased with increasing Mo content, whereas the self-interstitial formation energy increased with increasing Mo content in the temperature range of 400 K to 1200 K. The self-diffusion and interdiffusion coefficients were also determined in gamma U-xMo as a function of temperature. Diffusion of U and Mo atoms in gamma U-xMo were negligible below 800 K. The self- diffusion and interdiffusion coefficients decreased with increasing Mo concentration, which qualitatively agreed with the previous experimental observations. Point defect formation energies, self-diffusion coefficients, and interdiffusion coefficients in gamma U-xMo calculated in the present work can be used as input parameters in mesoscale and engineering scale fuel performance modeling. (C) 2021 Elsevier B.V. All rights reserved.
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