Oxide growth and corrosion resistance of Si-containing SiC fuel matrices fabricated by reaction sintering for high-power nuclear reactors

To assess the potential risk of fuel matrix degradation, this study examines the oxidation behavior of the reaction-sintered SiC containing residual Si (Si-RS-SiC) during air-ingress accidents. Si-RS-SiC samples were subjected to oxidation tests in air and under 1 ppm O₂ flow using thermogravimetric analysis (TGA). The morphology and thickness of the silicon oxide layer were investigated using scanning electron microscopy with energy-dispersive X-ray spectroscopy. The Si-RS-SiC exhibited exceptional resistance to air oxidation up to 1400°C, forming a uniform oxide layer of 20 μm thickness with a pure Si layer (2 μm thick) between SiO₂ and SiC at this temperature. At lower temperatures, the Si-RS-SiC formed oxide layers with irregular thickness, which became thicker and more uniform as the temperature increased. Additionally, TGA tests in 1 ppm O₂ showed that the passive/active transition behavior of Si-RS-SiC shifts in a preferable direction compared to previously reported Si-less RS-SiC, indicating that the presence of residual Si significantly enhances the corrosion resistance.