Assessing the Impact of Improved Thermal Conductivity of UO₂-Mo Fuel Using the ENIGMA Fuel Performance Code

Composite ceramic-metallic (cermet) fuels, such as UO₂-Mo, have gained attention as advanced alternatives to traditional UO₂ fuel, primarily due to their potential to address the issue of poor thermal conductivity in UO₂. This poor thermal conductivity can lead to challenges like elevated fuel temperatures, increased fission gas release (FGR), and heightened clad hoop strain. UO₂-Mo composite fuel offers a potential solution by incorporating molybdenum to significantly enhance thermal conductivity and mitigate these issues.

In this work we develop a new thermal conductivity model for UO₂-Mo fuel and implement it in the ENIGMA fuel performance code to investigate the impact of the increased thermal conductivity on fuel behavior under pressurized water reactor (PWR) operating conditions. We simulate a typical PWR fuel rod, except with UO₂-Mo fuel, under both steady-state irradiation and transient scenarios. Predictions of fuel temperature, FGR, and clad hoop strain are compared against conventional UO₂ fuel, with results indicating significant advantages for UO₂-Mo, including reductions in all three metrics. While not investigating the effects of other differences in material properties and phenomenological behavior of UO₂-Mo fuel (in part due to the lack of irradiation data), the results provide an initial quantification of the benefits of the increased thermal conductivity on UO₂-Mo fuel performance.