Combined ab-initio and empirical model for irradiated metal alloys with a focus on uranium alloy fuel thermal conductivity

Abstract

In this work, we developed a model framework of thermal conductivity of irradiated metal and metal alloys based on density functional theory calculations and experimental data. The model incorporates the contributions of point defects (vacancies and transmutation products), grain boundaries, and noble gas bubbles (inter- and intra-granular) resulting from irradiation into the overall thermal conductivity. The model is demonstrated on U-Mo alloys and displays semi-quantitative agreement with experimental data, with a root-mean-square error of about 1 W/m-K (≈9% error versus experiment) over the typical operating temperature and burn-up range for U-Mo alloys. This work provides insight into the relationships of the thermal conductivity changes resulting from the different irradiation-induced changes in microstructure over a wide range of temperatures, and shows that scattering of electrons from point defects produces the majority of the thermal conductivity reduction of U-Mo alloys under irradiation. Specifically, the effect of point defects decreases the thermal conductivity by about 20% when burn-up >20% (e.g., 50% burn-up), while grain boundary and gas bubble formation contribute only about another 10% reduction at 50% burn-up. The ability of our model to individually quantify the effect of different irradiation-related defects on the thermal conductivity as a function of temperature, composition, and irradiation conditions offers both a powerful tool for quantitative semi-empirical modeling of thermal conductivity in irradiated metals and materials design insight for the control of thermal conductivity in metal alloys in applications experiencing irradiation, such as next-generation nuclear reactors.