TRISO fuel particles are often described as the most robust nuclear fuel ever developed. Each particle is roughly the size of a poppy seed: a tiny kernel of uranium (typically uranium oxycarbide) surrounded by concentric layers of porous carbon buffer, dense pyrolytic carbon, silicon carbide, and another layer of pyrolytic carbon. These coatings act as a miniature containment system, retaining fission products even at temperatures exceeding 1,600 degrees Celsius — well above the operating conditions of any reactor that uses them.
TRISO fuel is central to several leading advanced reactor designs. X-energy's Xe-100 pebble-bed reactor packs thousands of TRISO particles into billiard-ball-sized graphite pebbles. Ultra Safe Nuclear Corporation embeds TRISO particles in silicon carbide to create its Fully Ceramic Microencapsulated (FCM) fuel. The U.S. Department of Energy has invested heavily in TRISO fuel qualification, and production facilities like those operated by BWXT in Lynchburg, Virginia are scaling up to supply the growing advanced reactor pipeline.
The inherent safety characteristics of TRISO fuel are a key selling point for advanced reactor licensing. Because the fuel itself serves as a primary containment barrier, reactors using TRISO may qualify for reduced emergency planning zones and simplified safety systems — potentially enabling nuclear deployment in locations previously considered unsuitable. The fuel's ability to survive extreme temperatures supports the passive safety case that is central to many SMR designs. For deeper coverage, see DeepTechIntel's nuclear section.