High-Assay Low-Enriched Uranium


Developing a U.S. Fuel Source for Advanced Reactors

When uranium is extracted from the earth, more than 99 percent of the atoms are U238, while the fissionable isotope U235 represents less than one percent.  To fuel one of today’s commercial nuclear reactors, the uranium must be enriched so that the U235 concentration, or “assay,” is raised to between 4-5 percent.  This is called low-enriched uranium (LEU).

Many of the reactor designs being prepared for future deployment will need a higher assay uranium fuel to operate.  High-assay low-enriched uranium (HALEU) has a U235 assay above 5 percent but below 20 percent.  This is still far below the assay required to make weapons or to power U.S. submarines and aircraft carriers.

HALEU fuel has many advantages that improve reactor performance.  Because the U235 is more concentrated, the fuel assemblies and reactors can be smaller, which is one reason why many small modular reactor (SMR) designs will run on HALEU.  The reactors do not need to be refueled as often, and they can achieve higher “burnup” rates, which means less fuel will be required and less waste will be produced.

HALEU Fuel Fabrication

Once uranium has been enriched to a level necessary for HALEU fuel, it will need to be fabricated into fuel forms for loading into a reactor. To that end, Centrus is working under a contract with X-energy, a pioneering reactor and fuel company, to pursue the development of a fuel fabrication facility that would produce X-energy’s uranium oxycarbide (UCO) tristructural isotropic (TRISO) fuel forms using HALEU. This unique HALEU fuel could power a variety of advanced reactors under development around the world, ensuring a U.S. source of supply for this emerging industry.