An atomistic study of defect energetics and diffusion with respect to composition and temperature in γU and γU-Mo alloys

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.

Automated summary

This study investigated the properties of point defects in gamma U and gamma U-xMo alloys through molecular dynamics simulations. The results show that vacancy formation energy was higher than self-interstitial formation energy in the evaluated temperature range. In gamma U-xMo, vacancy formation energy decreased with increasing Mo content, while self-interstitial formation energy increased.