Atomistic calculations of the surface energy as a function of composition and temperature in γ U–Zr to inform fuel performance modeling

Uranium-zirconium alloy fuels are candidates for advanced sodium cooled fast reactors due to their high uranium density, high thermal conductivity, inherent safety and ability to incorporate minor actinides into the fuel. Unlike traditional ceramic UO₂ fuel, U–Zr alloys swell rapidly and substantially, but the actual mechanistic process of swelling, including the rate of swelling, is not well understood. Fuel performance models are being developed to describe the swelling process, but these models currently lack the requisite underlying physics and fundamental property data to be truly predictive. In this work, molecular dynamics simulations are utilized to investigate a number of bulk thermophysical properties in γU-Zr, the void surface energy as a function of temperature and composition, and the void free energy. Finally, the effect of surface energy on fuel swelling behavior is demonstrated via finite element based fuel performance simulations, emphasizing the importance of the inclusion of accurate fundamental material properties.