(238d) Effect of Process Parameters and Characterization of the Properties of Pyrolytic SiC in VHTR Fuel Particles

We investigated the effect of process parameters, such as deposition temperature and gas flow rate, on the properties of pyrolytic SiC coating, which were coated onto spherical particles as simulated nuclear fuel particles by fluidized-bed chemical vapour deposition. A stoichiometric and carbon-free SiC layer was deposited at 1400~1550°C while a small amount of free carbon appeared at 1600°C. The porosity and mean pore size in the SiC layers increased with deposition temperature, especially above 1550°C. The microstructure of the SiC layer deposited at the gas flow rate of 4000 sccm showed high porosity and large pores more than 1 mm in size. The hardness and elastic modulus measured using a nanoindentation method were the highest in the SiC layer deposited at 1500°C. The average fracture strength increased from 410 MPa to 550 MPa by controlling the IPyC/SiC interface and inner surface roughness of the SiC layer through a two-step coating process. The SiC coating process for nuclear fuel particles can be optimized by controlling various parameters such as the deposition temperature, concentration of the source gas, and the gas flow rate.