Microstructural evolution and thermal conductivity degradation of TRISO particle coatings under ion irradiation

This study presents a comprehensive investigation into the microstructural and thermal conductivity degradation of coatings in TRISO particles, a highly robust nuclear fuel form, under room-temperature 540 keV He ion irradiation. Detailed Raman spectroscopy and transmission electron microscopy studies unveil the structural evolution of pyrolytic carbon (PyC) and silicon carbide (SiC) coatings, and thermal conductivities are quantified using spatial-domain thermoreflectance technique. The results reveal that the PyC coating exhibits a distinct core-shell architecture. Upon irradiation, the shell region transitions from a medium to a low texture while maintaining partial order. In contrast, the low-texture core region undergoes complete amorphization at the highest dose. Correspondingly, the thermal conductivity of PyC decreases from approximately 10 to 3 W m −1 K −1 . SiC exhibits complete amorphization within the peak damage region, with its thermal conductivity decreasing from 113 W m −1 K −1 by over 99% toward the amorphous limit. Lattice dynamics simulations reveal that the thermal degradation of PyC is governed by its mixed nanocrystalline-amorphous structure. The irradiation-sensitive crystalline phase drives the rapid initial degradation of conductivity, whereas the amorphous phase provides irradiation tolerance. These findings offer key insights into the thermal properties of carbon materials in extreme environment and guide the optimization of advanced nuclear fuel designs.