The effect of wall flow velocity on compatibility of high-purity SiC materials with liquid Pb-Li alloy by rotating disc testing for 3000 h up to 900 °C

The lead-lithium (Pb-Li) alloy is considered as a coolant and a tritium breeder for fusion reactor blanket systems. One of the critical requirements in realization of the systems is the compatibility of silicon carbide (SiC) and its composites, as structural and/or functional materials of the blanket, with liquid Pb-Li flow at high temperatures. This study aims to clarify the corrosion process of high-purity SiC materials under flow condition of liquid Pb-Li for 3000 h at 700 and 900 °C, respectively, by using the rotating disc corrosion equipment. Furthermore, the effect of wall flow velocity on the compatibility was specifically evaluated. For that purpose the decrease rate (about 32–37%) of the wall flow velocity on disc type's sample by the dragging effect by fluidic viscosity was first calculated by numerical analysis of the rotating flow condition. The wall flow velocity dependence on the reaction layer's thickness was then evaluated for both high purity SiC and SiC/SiC composites. The test results show that the formation process of the surface reaction layer mainly depends on both the time required for the chemical reaction and the wall flow velocity in the initial stage but the reaction layer thickness tended to approach to the constant regardless of the wall flow velocity with increasing exposed time. In short, no accelerated corrosion was found for about 3000 h. It was also found that there was no significant difference of the temperatures between 700 and 900 °C. Finally the key corrosion mechanism, i.e., the reaction of oxide impurities, e.g., Li₂O, in liquid Pb-Li with the Si-oxide layer over SiC, was identified.