Effects of water vapor on the oxidation and the fracture strength of SiC layer in TRISO fuel particles

Steam oxidation of silicon carbide (SiC) layer in nuclear fuel particles were performed in flowing argon–water vapor mixture with a total pressure of 1 bar at 1173–1673 K. Both the phase composition and the microstructure of the oxide scale on the SiC layer varied with the oxidation temperature. Reaction rates of water vapor with the SiC layer were determined by measuring the oxide scale thickness. It was found that the oxidation of SiC layer follows the parabolic law. The activation energy was calculated to be 103 ± 11 kJ/mol. It is proposed that the rate determine step of the oxidation is the diffusion of water vapor molecules in the oxide scale. The fracture strength of SiC shell after steam oxidation was evaluated using a crush test. The fracture strength decreased with the increase of the oxidation temperature due to the thinning of the SiC layer.