New insights into the irradiation stability of the IPyC/SiC interface in TRISO fuel particles using in-situ ion irradiation TEM

Understanding the irradiation behaviour of inner pyrolytic carbon (IPyC) and silicon carbide (SiC) coatings, which serve as fission product barriers in tri-structural isotropic (TRISO) particles, is vital for designing fuel for high-temperature gas-cooled reactors (HTGRs). In this study, a thin lamella containing the IPyC/SiC interface from TRISO particles was irradiated with Xe ions at 1000°C, up to 33.3 dpa, in an in-situ transmission electron microscopy (TEM) system, simulating TRISO operational conditions, to investigate their behaviour under irradiation. Real-time TEM observations revealed that the IPyC/SiC interface remained structurally intact, with no cracking, and energy-dispersive X-ray spectroscopy confirmed the interface’s chemical stability. The PyC exhibited high irradiation sensitivity, including reduced inter-planar spacing, increased texturing, and enhanced structural order. SiC was largely unaffected, aside from void/bubble formation. These findings provide new insights into irradiation-induced evolution at the IPyC/SiC interface and highlight PyC degradation as a critical factor influencing TRISO fuel performance.