Fracture Strength of Silicon Carbide Layers of TRISO Particles Coated at Various Temperatures

TRISO-coated fuel particles for high-temperature gas-cooled reactors consist of UO2 microspheres coated with layers of porous pyrolytic carbon (porous PyC), inner dense PyC (IPyC), silicon carbide (SiC), and outer dense PyC (OPyC). Among the TRISO coating layers, the SiC layer is particularly important because it acts as a diffusion barrier to gaseous/metallic fission products and as a miniaturized pressure vessel of the particle. In order to insure the integrity of the SiC layer after a fabrication and in use, the microstructure, mechanical properties, and chemical composition of the SiC layer should be properly controlled. For a uniform coating of the microspherical particles, the TRISO coating is performed using a fluidized-bed chemical vapor deposition (FBCVD) method. Characteristics of the coating layer depend largely on the FBCVD conditions such as the gas flow rate, concentration of the coating gas, coating temperature, etc. Among the deposition parameters the coating temperature is particularly important for determining the properties of the SiC layer. In this study, we investigated the effect of the coating temperature on the fracture strength of the SiC layer while fixing the other deposition parameters