The influence of SiC particle size and volume fraction on the thermal conductivity of spark plasma sintered UO2–SiC composites

This study examines the influence of Silicon Carbide (SiC) particle addition on thermal conductivity of UO2–SiC composite pellets. UO2 powder and β-SiC particles of different sizes and of different volume fractions were mechanically mixed and sintered at 1350–1450 °C for 5 min by Spark Plasma Sintering (SPS). The particle size (0.6–55 μm diameter) and volume fraction (5–20%) of SiC were systematically varied to investigate their influence on the resulting UO2–SiC composite pellet microstructure and the thermal properties. It was found that SiC particle size less than 16.9 μm with larger volume fraction is more effective for improving the thermal conductivity of the fuel pellets. Scanning Electron Microscopy examination revealed micro-cracking and interfacial debonding in the composites containing larger size SiC particles (16.9 and 55 μm) which resulted in reduced thermal conductivity. For the UO2–SiC composite pellets containing 1 μm diameter SiC particles, the thermal conductivity increased almost linearly with volume fraction of particles. However, the addition of a larger volume fraction of SiC reduces the amount of heavy metal in the composite pellet and therefore a higher U-235 enrichment is necessary to compensate for the heavy metal loss. The experimental thermal conductivity values of the UO2–SiC composite pellets are in good agreement with the theoretical values based on the available model in the literature.