Numerical investigation of the thermal conductivity of UO2 – Mo microplate fuel pellets to realize enhanced heat transfer in the fuel radial direction

Abstract

• Thermal conductivity of radially arranged UO 2 –3 vol% Mo microplate pellets increased. • Effective thermal conductivity increased by 53% at 1000 °C. • Central pellet temperature decreased by 149 °C under LHGR of 200 W/cm. • Recommend arranging Mo microplates parallel to the main heat transfer flow. The thermal performance of composite UO 2 fuel pellets, as a potential candidate for accident-tolerant fuels, is being attempted to be actively enhanced by employing high conductivity materials as additives. Herein, we numerically investigated the thermal performance of UO 2 – 3 vol% Mo microplate fuel pellets with microsized Mo plates to enhance the corresponding thermal conductivity in the fuel radial direction. UO 2 – 3 vol% Mo microplate fuel pellets were successfully fabricated through the conventional sintering process, and the characteristics of the thermal conductivities were investigated in terms of the shape factor of the Mo microplate, amount of Mo content, and arrangement (such as the spacing and angle) of the Mo microplates in the UO 2 fuel pellets. The results demonstrated that the arrangement of the Mo microplates parallel to the main heat transfer flow direction could further enhance the thermal conductivity. The numerical results pertaining to the calculation based on the microplate arrangement exhibited a reasonable agreement with the measured values, and the thermal conductivity was noted to be enhanced by 47% at 1000 °C compared to that of UO 2 . Moreover, the UO 2 – 3 vol% Mo microplate fuel pellets with enhanced thermal conductivities could reduce the maximum pellet temperature by 149 °C compared to that of the UO 2 pellet under a linear heat generation rate of 200 W/cm.