Tri-isotropic (TRISO) coatings on zirconia surrogate beads are deposited using a fluidized-bed vapor deposition (FB-CVD) method. The silicon carbide layer is particularly important among the coated layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO-coated particles. In this study, we obtain a nearly stoichiometric composition in the SiC layer coated at 1400oC, 1500oC, and 1400oC with 20 vol.% methyltrichlorosilane (MTS), However, the composition of the SiC layer coated at 1300-1350oC shows a difference from the stoichiometric ratio (1:1). The density decreases remarkably with decreasing SiC deposition temperature because of the nanosized pores. The high density of the SiC layer (≥ 3.19 g/cm2) easily obtained at 1500oC and 1400oC with 20 vol.% MTS did not change at an annealing temperature of 1900°C, simulating the reactor operating temperature. The evaluation of the mechanical properties is limited because of the inaccurate values of hardness and Young’s modulus measured by the nano-indentation method.

Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at 1500-1650˚C has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at 1500˚C obtains nearly stoichiometric composition, the composition of the SiC layer coated at 1300-1400˚C shows discrepancy from stoichiometric ratio(1:1). 3-7μm grain size of SiC layer coated at 1500˚C is decreased to sub-micrometer (＜ 1μm) -2μm grain size when coated at 1400˚C, and further decreased to nano grain size when coated at 1300-1350˚C. Moreover, the high density of SiC layer (≥3.19g/cm3) which is easily obtained at 1500˚C coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.