Ultra-high temperature microstructural changes of SiC layers in TRISO particles

The SiC layer is the critical layer in the tristructural-isotropic (TRISO) fuel particle with the ability to sustain internal pressure and retain fission products. Further research into the failure mechanisms and tolerance limits of SiC layers at ultra-high temperatures is required. The microstructural evolution of the SiC layer in TRISO particles heat-treated at1800 similar to 2500 degrees C in argon atmosphere is the focus of this paper. The results show that SiC decomposition and phase transition occur at temperatures above 2200 degrees C, causing TRISO particles to fail. At 2200 degrees C, significant decomposition of the SiC layer occurred, resulting in an increase in carbon content on the surface and the appearance of pores. The decomposition reaction of SiC became more complicated at higher temperatures, and the carbon with the graphene structure remained after decomposition. At temperatures above 2300 degrees C, the SiC phase changed from 3C to 6H, with an abnormal increase in grain size. This study establishes a database for the performance of SiC layers under operation or accident conditions and serves as a reference for future applications of TRISO particles in novel ultra-high temperature reactors.