TRISObeschichteten

TRISObeschichteten (TRISO-coated particles) are micro-scale nuclear fuel particles designed with a tristructural isotropic coating around a fuel kernel. The coating provides containment and structural stability under high-temperature irradiation, enabling robust performance in certain reactor concepts.

The coating comprises three isotropic layers: an inner pyrolytic carbon layer (IPyC), a silicon carbide (SiC) layer, and an outer pyrolytic carbon layer (OPyC). A fuel kernel, typically uranium oxycarbide (UCO) or uranium oxide, is embedded inside the IPyC layer. The SiC layer acts as the primary fission-product barrier and provides most of the mechanical strength and diffusion resistance, while the PyC layers accommodate thermal expansion and offer additional buffering against cracking.

Manufacture is performed by sequential deposition of the layers, commonly via chemical vapor deposition in a fluidized-bed reactor. Kernels are coated in steps with strict quality controls to minimize defects, which can compromise fission-product retention. The coating thickness, uniformity, and integrity are critical to performance under irradiation and during high-temperature transients.

Applications include high-temperature gas-cooled reactors, such as pebble-bed and prismatic-core designs, where TRISO fuel enables high burnups, excellent fission-product retention, and passive safety features. TRISO-coated fuel has also been studied for research reactors and potential advanced fuel cycles.

Challenges include production cost, scale-up of manufacturing, defect control, and long-term performance under irradiation and extreme transients. Nevertheless, TRISO-coated fuels remain a leading option for accident-tolerant, high-temperature nuclear fuel research and prospective Gen IV HTGR deployments.