Silicon Detected in TRISO Nuclear Fuel Before Reactor Exposure, Study Finds

Researchers at Western University investigating nuclear fuel chemistry have detected small regions of silicon inside tri-structural isotropic (TRISO) fuel kernels before the material ever entered a reactor, according to research reported by TechXplore (https://techxplore.com/news/2026-10-silicon-nuclear-fuel-reactor.html). The discovery establishes a pre-irradiation baseline for nuclear materials research and challenges assumptions that silicon found in used fuel originates solely from outer protective layers during reactor operation.

TRISO fuel particles are engineered to contain radioactive fission products inside robust micro-capsules. Each particle contains a central uranium oxycarbide fuel kernel measuring approximately 300 to 400 micrometers across—roughly the size of a poppy seed—surrounded by four protective layers of carbon and silicon carbide. In reactor designs that use the technology, hundreds of thousands or millions of these individual particles are packed together.

Previously, researchers had identified silicon inside irradiated TRISO fuel that had been subjected to extreme reactor temperatures and radiation. Those observations were widely attributed to silicon migrating inward from the outer silicon-carbide shell under operational stress.

The Western University team, led by Samantha Gateman, the university's NWMO Chair in Radiation Induced Chemistry, alongside postdoctoral researchers Soroosh Hakimian and Shamim Pourrahimi, encountered the pre-existing silicon while conducting microscopic characterization work for future fuel storage and disposal studies.

"We found silicon in the fuel kernel before it had ever been inside a reactor. That means when we see silicon inside irradiated fuel, we can't automatically assume it migrated there from the silicon-carbide coating," Gateman said.

The researchers traced the source to the fuel's manufacturing process. TRISO kernels are produced using sol-gel fabrication, in which uranium-bearing material is shaped into spherical droplets inside a heated silicone-oil bath before undergoing thermal processing and receiving protective coatings. Gateman's team examined both bare, uncoated kernels and fully coated particles, finding silicon present in both states, indicating the element is introduced during kernel formation rather than during the subsequent coating steps.

The study, titled "Origin of Silicon-rich phases in Uranium Oxycarbide (UCO) TRi structural ISOtropic (TRISO) fuel kernels: Fabrication-driven formation and implications for fuel performance," was published in the Journal of Nuclear Materials. While earlier studies suggested silicon-rich phases in irradiated fuel could influence internal gas accumulation and pressure, Gateman noted that establishing pre-existing baselines is essential to measuring how much additional material migrates during active reactor lifecycles.