Mesoscale thermal transport in oxide nuclear fuels

Thermal transport in nuclear fuels is critical from both operational and safety points of view. Uranium dioxide fuel has an inherently low thermal conductivity that degrades further by the fission process and accumulation of defects and damage. In order to predict the effects of the fission process on thermal transport, it is important to have first-principles based models. An Energy Frontier Research Center (EFRC) titled Center for Materials Science of Nuclear Fuel, which combines radiation effects and thermal transport studies, has been established to make progress in that direction. The center combines theory and experiments to make progress towards a predictive understanding of thermal transport in uranium dioxide at the mesoscale. This talk summarizes the structure of this theory-driven program at a high level, and focuses on the mesoscale thermal transport and connection with defects and microstructure modeling, where Purdue participants take the lead. Being mostly an ionic material, thermal transport in uranium dioxide takes place by phonon mechanism over the temperature range of interest for reactor operation. Progress in the modeling phonon transport in uranium dioxide using Boltzmann transport equation will be highlighted, and the connection of this effort to the defect state in the fuel will be emphasized. An important part of this connection has been the incorporation of thermodynamic models of defects in fuel into the thermal transport modeling framework based on Boltzmann transport equation. The parameterization of phonon lifetime in both perfect crystals and crystals with point defects using atomic scale information will be explained. Results to date will also be summarized.