What Is HALEU Fuel and Why Does It Matter?

Published: July 2026
Updated: September 2026

As the United States pursues a new generation of nuclear energy technologies, one term appears repeatedly in discussions about advanced reactors: HALEU, or High-Assay Low-Enriched Uranium. While advanced reactor developers have made significant progress in reactor design, one of the industry’s greatest challenges remains securing an adequate fuel supply. Today, the availability of HALEU is increasingly viewed as a critical factor that will determine how quickly advanced nuclear technologies can be deployed at commercial scale.

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High-Assay Low-Enriched Uranium (HALEU) is uranium enriched to contain more than 5% but less than 20% uranium-235 (U-235), the fissile isotope that enables nuclear fission. By comparison, today’s commercial nuclear power plants typically operate using low-enriched uranium (LEU) fuel containing approximately 3%–5% U-235.

HALEU occupies a middle ground between conventional reactor fuel and highly enriched uranium (HEU), which contains 20% or more U-235. According to the U.S. Department of Energy (DOE), HALEU is expected to be the fuel of choice for most advanced reactor designs currently under development in the United States. These reactors include small modular reactors (SMRs), microreactors, sodium-cooled fast reactors, molten salt reactors, and high-temperature gas-cooled reactors.

Because HALEU contains a higher concentration of U-235, reactors can generate more energy from a smaller volume of fuel. This enables:

• Smaller reactor cores
• Longer operating periods between refueling
• Improved fuel utilization
• Increased thermal efficiency
• More flexible reactor designs

Sources:

• DOE: What Is HALEU?
• DOE HALEU FAQ
• Nuclear Regulatory Commission HALEU Overview

HALEU is attracting growing interest because it has emerged as one of the most significant bottlenecks facing advanced nuclear deployment.

Over the past decade, dozens of companies have launched efforts to commercialize advanced reactors. Developers including TerraPower, X-energy, Kairos Power, Oklo, and others have announced reactor projects intended to support electric grids, industrial facilities, military installations, data centers, and remote communities. However, many of these designs cannot operate using conventional nuclear fuel.

The DOE estimates that U.S. demand for HALEU could reach approximately 50 metric tons annually by 2035, with demand continuing to grow as additional reactors enter service. Yet domestic production remains extremely limited. For years, Russia was effectively the world’s only commercial-scale supplier of HALEU, creating significant geopolitical and energy security concerns. Following restrictions on Russian uranium imports and broader efforts to strengthen domestic supply chains, building a U.S.-based HALEU industry has become a national priority.

Interest has also increased because advanced nuclear energy is increasingly viewed as a solution to growing electricity demand. Artificial intelligence infrastructure, hyperscale data centers, domestic manufacturing, electrification, and industrial decarbonization initiatives are all expected to place additional pressure on the electric grid. Advanced reactors offer the potential for reliable, carbon-free baseload power that can complement renewable energy resources.

Without sufficient HALEU, many advanced reactor projects could face delays regardless of how quickly reactor technology itself advances.

Sources:

• DOE: What Is HALEU?
• DOE HALEU Availability Program
• World Nuclear Association: HALEU

Producing HALEU requires more than uranium enrichment alone. A complete fuel supply chain contains several interconnected steps:

Natural uranium is extracted from mines and processed into uranium concentrates, often called “yellowcake.”

The uranium concentrate is converted into uranium hexafluoride (UF₆), a gaseous form required for enrichment.

Specialized enrichment facilities increase the concentration of U-235 from its natural level of approximately 0.7% to the 5%–20% range required for HALEU.

Following enrichment, UF₆ must be converted into metal, oxide, or other forms suitable for reactor fuel manufacturing. Deconversion is currently one of the most significant gaps in the U.S. HALEU supply chain.

The enriched material is manufactured into reactor-specific fuel forms, including metallic fuel, TRISO particles, fuel pellets, or molten salt fuel compounds.

Specialized transportation casks, safeguards programs, and regulatory approvals are required to move HALEU safely through the fuel cycle.

Today, each of these segments faces constraints. While the United States has begun rebuilding domestic enrichment capabilities, enrichment alone does not create reactor-ready fuel. Additional investments are required across conversion, deconversion, fuel fabrication, transportation infrastructure, and regulatory support systems.

The DOE has acknowledged this challenge by creating the HALEU Availability Program, issuing contracts for deconversion services, supporting transportation package development, and funding technologies designed to strengthen the domestic fuel cycle.

Sources:

• DOE HALEU Availability Program
• DOE HALEU Technologies Program
• World Nuclear News: DOE Awards Contracts to Spur HALEU Supply Chain

The future of advanced nuclear energy depends on more than reactor innovation. It also depends on fuel.

HALEU has become one of the most important enabling technologies in the nuclear sector because it allows advanced reactors to achieve the performance, efficiency, and flexibility needed for next-generation energy applications. Yet the fuel supply chain remains in its early stages.

Over the coming decade, success will depend on creating a complete domestic ecosystem that includes uranium feedstock, enrichment, deconversion, fabrication, transportation, and regulatory infrastructure. If those investments are made, HALEU can help unlock the widespread deployment of advanced reactors and support America’s goals for energy security, economic growth, and reliable carbon-free power generation.

• DOE HALEU Frequently Asked Questions
• DOE HALEU Availability Program
• DOE HALEU Technologies Program
• Nuclear Regulatory Commission HALEU Overview