HALEU and TRISO

HALEU, high-assay low-enriched uranium, is uranium-235 concentrated between 5% and 20%, always below the 20% threshold that separates low-enriched uranium from highly enriched, weapons-usable uranium. Advanced reactors need it because shrinking the core or stretching the refueling cycle to several years without reloading requires more fissile atom density than the 3–5% of a PWR provides. TRISO, by contrast, is a way of packaging that fuel: a ceramic sphere under a millimetre across, with a uranium oxide or carbide kernel wrapped in four layers, a porous carbon buffer that holds the fission gases, dense pyrolytic carbon, silicon carbide and another layer of pyrolytic carbon. Each particle is, in effect, a miniature pressure vessel that retains fission products up to above 1,600 °C, well beyond any accident temperature in a light-water reactor.

Demand for HALEU comes from the SMRs and advanced reactors starting construction this decade: TerraPower's Natrium, X-energy's Xe-100, Kairos's Hermes, among others, all designed for that fuel. The problem is that, until recently, the world's only commercial source of HALEU was Russia, through TENEX. The United States began closing that gap with Centrus Energy, which operates a cascade of advanced centrifuges in Piketon, Ohio, under contract with the Department of Energy: in June 2025 it completed delivery of 900 kilograms of HALEU to the agency, fulfilling phase two of that contract, since extended to 2026 with options to continue for up to eight more years.

On the TRISO-particle side, the longtime manufacturer is BWXT, which operates its Lynchburg, Virginia plant and in December 2025 delivered the first full core of TRISO fuel for the Pentagon's Project Pele microreactor: it is the only US company manufacturing production-scale, irradiation-tested uranium oxycarbide TRISO fuel. TRISO-X, X-energy's subsidiary, is building a commercial plant in parallel in Oak Ridge, Tennessee, and in February 2026 received the first Category II license the US Nuclear Regulatory Commission has granted to an advanced fuel fabrication plant, a 40-year permit to operate on a 110-hectare site.

On the enrichment side, Urenco is also advancing on two fronts: in Eunice, New Mexico, it added new cascades in 2025 to produce boosted low-enriched uranium (up to 10%) with first delivery expected in 2026, and in Capenhurst, United Kingdom, it is building, with a £196 million co-investment from the UK government, an advanced fuels facility dedicated to HALEU (5% to 20%), with capacity of up to 10 tonnes a year and start-up targeted for 2031.