Why Advanced Nuclear Reactors Need HALEU

Published: July 2026

Advanced nuclear reactors are being designed to do more than produce electricity from large, conventional nuclear plants. Many are intended to be smaller, more flexible, more fuel efficient and capable of producing high-temperature heat for industrial uses, hydrogen production and remote power applications. To achieve those goals, many advanced reactor designs require high-assay low-enriched uranium, or HALEU, a nuclear fuel material enriched to contain more uranium-235 than today’s standard commercial reactor fuel. The U.S. Nuclear Regulatory Commission defines HALEU as uranium enriched between 5% and 20% uranium-235, compared with conventional low-enriched uranium fuel, which is typically enriched to 3% to 5%.

The main reason advanced reactors need HALEU is energy density. A higher concentration of uranium-235 allows more fission energy to be packed into a smaller amount of fuel. That matters because many advanced reactors are designed with compact cores, smaller footprints and longer operating cycles than conventional light-water reactors. The NRC notes that HALEU fuel may allow advanced non-light-water reactors to use smaller reactor cores, extend core life, improve fuel efficiency and reduce fuel waste compared with currently operating reactors. The Department of Energy similarly says most advanced reactor designs require HALEU to achieve smaller designs, longer operating cycles and increased efficiencies over current technologies.

HALEU also enables reactor designs that use fuel forms other than the familiar uranium oxide pellets used in today’s large light-water reactors. Several advanced reactor developers are designing systems around TRISO fuel, molten salt fuel or metallic fuel forms. The NRC identifies HALEU as a proposed fuel for many advanced non-light-water reactors and notes that developers have proposed using HALEU in molten salt reactors and TRISO fuel. These fuel forms can support different reactor physics, higher operating temperatures and specialized performance characteristics that are difficult to achieve with traditional 3% to 5% enriched fuel.

See also: Energy.gov: HALEU Availability Program

For small modular reactors and microreactors, HALEU can be especially important because size and refueling interval are central to the value proposition. A microreactor intended for a remote site, military installation, mine, data center or industrial facility may need to operate for years without frequent refueling. Higher-assay fuel helps extend the time between refueling outages and supports compact designs that can be manufactured, transported or deployed more easily than a large conventional nuclear plant. DOE states that gaps in HALEU supply could delay the deployment of advanced reactors, underscoring that fuel availability is not a secondary issue but a core deployment requirement.

HALEU also matters because advanced reactors are expected to contribute to future clean-energy systems. Idaho National Laboratory’s HALEU requirements report was prepared to estimate potential HALEU needs for commercial advanced reactors as part of DOE planning for the HALEU Availability Program. The study modeled a net-zero emissions scenario in which nuclear capacity expands significantly by 2050, then assessed how different mixes of conventional and advanced reactors could affect demand for HALEU. While exact demand depends on which reactor technologies are built, the analysis reinforces a central point: advanced reactor deployment and HALEU supply planning are directly linked.

The challenge is that HALEU is not yet broadly available from domestic commercial suppliers at the scale needed for a large advanced reactor market. DOE states that HALEU is not currently available from domestic suppliers and that supply gaps could delay advanced reactor deployment. To address this, DOE established the HALEU Availability Program under the Energy Act of 2020 to support access to HALEU for civilian domestic research, development, demonstration and commercial use. The program is intended to acquire HALEU through purchase agreements with domestic industry partners and produce limited initial amounts from DOE-owned assets, helping stimulate private investment in the nuclear fuel supply chain.

In short, advanced reactors need HALEU because their benefits depend on a different fuel architecture than the one used by most existing nuclear power plants. HALEU supports smaller cores, longer lifetimes, higher fuel utilization and specialized fuel forms that enable many next-generation reactor designs. Without reliable HALEU supply, advanced reactors may remain technically promising but commercially constrained. With adequate HALEU production, deconversion, fabrication and transportation capacity, the United States can better support the demonstration and deployment of advanced nuclear technologies.