Review: Oxidation of SIC/SIC composites in low oxidising and high temperature environment

Due to their thermal, mechanical, and nuclear properties, silicon carbide fiber-reinforced, silicon carbide matrix (SiCf/SiCm) composites are promising candidate materials for fuel assembly in gas-cooled fast reactors (GFR), but their long term oxidation resistance must be evaluated under GFR relevant environments: high temperature, impure helium, yearlong in-core exposure. Experience from other high temperature applications shows that in an inert atmosphere SiC fibers may undergo a thermal decomposition. On the other hand at high P(O-2), SiC based elements form surface silica that provides an outstanding corrosion resistance. However, oxidative volatilization of silica occurs at intermediate P(O-2) and SiC suffers from active oxidation. Finally, the carbon layer at the fiber/matrix interface is highly sensitive to oxidation. The overall SiCf/SiCm behaviour is complex because it may involve degradation of several components and coupled interactions as well. A comprehensive R&D program is required to design a candidate composite material and to determine suitable environmental conditions. Fundamental as well as technical knowledge would be the basis of models for life time prediction.