HALEU (high-assay low-enriched uranium)
HALEU is uranium enriched to between 5 and 20 percent uranium-235. What HALEU fuel is, which reactors need it, and why HALEU supply is limited.
HALEU, high-assay low-enriched uranium, is uranium enriched to more than 5 percent and less than 20 percent uranium-235. That is above the 3 to 5 percent used in most existing commercial reactors, and below the 20 percent threshold that separates low-enriched from highly enriched uranium.
What HALEU fuel is used for
Many advanced reactor and small modular reactor (SMR) designs are built to run on HALEU fuel. Higher enrichment allows smaller cores, longer periods between refueling, and higher fuel efficiency. HALEU is used in several fuel forms, including metallic fuel and TRISO particle fuel, in which small uranium kernels are coated in layers of carbon and ceramic. As interest in advanced reactors grows as part of the nuclear renaissance, so does projected demand for HALEU.
Why HALEU supply is limited
HALEU requires more enrichment work per kilogram than conventional reactor fuel, and enrichment plants built for low-enriched uranium are licensed only up to about 5 percent. Commercial-scale HALEU production has historically been available only from Russia.
In the United States, the Department of Energy runs a HALEU availability program to build a domestic supply for advanced-reactor developers, and a demonstration cascade in Piketon, Ohio began producing HALEU under a DOE contract in 2023. Building commercial-scale capacity takes years, so HALEU supply is a recognized constraint on advanced-reactor deployment.
HALEU and the uranium market
HALEU is a downstream product, more highly processed than the traded uranium commodity, yellowcake (U₃O₈). Each kilogram of HALEU requires more natural uranium feed than conventional fuel, so advanced-reactor growth adds to demand for U₃O₈ as well as for enrichment. See enriched uranium for the full range of enrichment levels.
FAQ
HALEU, or high-assay low-enriched uranium, is uranium enriched to between 5 and 20 percent uranium-235. It is more enriched than the fuel used in most current power reactors and less enriched than highly enriched uranium. Many advanced and small modular reactor designs are built to use it.
Advanced reactors use HALEU fuel because higher enrichment allows smaller cores, longer operation between refueling, and more energy per unit of fuel. These features suit compact designs such as small modular reactors and microreactors.
Commercial-scale HALEU has historically been produced only in Russia. The U.S. Department of Energy runs a HALEU availability program to develop domestic supply, and a demonstration cascade in Piketon, Ohio began producing HALEU in 2023. New commercial capacity is planned but takes years to build.