Mechanical behavior of SiC/SiC composites after exposure in high temperature liquid sodium for Sodium Fast Reactors applications.

Abstract SiC/SiC composites have aroused interest for various nuclear applications. For example, the use of SiC/SiC components in Sodium-cooled Fast Reactors in replacement of steel wrapper tubes should improve the safety. However, the chemical compatibility between the liquid sodium and SiC or SiC/SiC composites and its effect on their mechanical properties remain unknown. Corrosion tests were conducted on both CVD SiC and both undamaged and pre-damaged SiC/SiC in liquid sodium at 823 K up to 2000 h in two different sodium batches, a purified and an oxygen-rich. No strong corrosion of the CVD SiC and no degradation of the mechanical properties of SiC/SiC composites were observed in both conditions, even with mechanical pre-damaging prior to immersion. A strong increase of ultimate tensile strength was highlighted after exposure, only for the undamaged samples. This phenomenon is attributed to the healing by liquid sodium of the microcracks generated during the manufacturing process.