Enriched uranium
Enriched uranium has a higher share of uranium-235 than natural uranium. What enriched uranium is, enrichment levels from LEU to HALEU, and how it is made.
Enriched uranium is uranium in which the proportion of the fissile isotope uranium-235 has been increased above its natural level of about 0.7 percent. Most commercial power reactors need uranium-235 at 3 to 5 percent to sustain a chain reaction, so enrichment is what makes uranium usable as reactor fuel.
Enrichment levels
Enrichment level defines how the material is used and how tightly it is controlled.
- Low-enriched uranium (LEU), at 3 to 5 percent uranium-235, fuels most commercial power reactors.
- [High-assay low-enriched uranium (HALEU)](/learn/haleu), above 5 percent and below 20 percent, is needed by many advanced and small modular reactor designs.
- Highly enriched uranium (HEU), at 20 percent or more, is not used in commercial power reactors and is subject to strict non-proliferation controls. Weapons-grade material is enriched to about 90 percent.
How enriched uranium is made
Natural uranium is first converted into uranium hexafluoride (UF₆), a gas at moderate heat. Gas centrifuges then separate the slightly lighter uranium-235 from uranium-238, producing an enriched stream and a depleted uranium stream called the tails. The effort required is measured in separative work units (SWU). The enriched UF₆ is then converted to uranium dioxide powder and fabricated into fuel pellets.
Enriched uranium in the market
Enriched uranium is a downstream product, not the traded commodity. Uranium is bought and sold as yellowcake (U₃O₈) at the front of the fuel cycle, and utilities buy enrichment as a separate service applied to uranium they already own. Utilities can also buy enriched uranium product directly, which bundles the uranium, conversion, and enrichment into one purchase.
FAQ
Enriched uranium is uranium in which the share of the fissile isotope uranium-235 has been raised above its natural level of about 0.7 percent. Most power reactors use low-enriched uranium at 3 to 5 percent uranium-235. Enrichment is performed on uranium hexafluoride gas, usually in gas centrifuges.
Low-enriched uranium fuels most commercial nuclear power reactors. High-assay low-enriched uranium, between 5 and 20 percent, is used by many advanced and small modular reactor designs and by some research reactors. Highly enriched uranium is restricted to research, naval, and defense uses under strict controls.
Natural uranium contains about 0.7 percent uranium-235, with nearly all the rest being uranium-238. Enriched uranium has had its uranium-235 share increased, typically to 3 to 5 percent for power reactors. Natural uranium is traded as yellowcake (U₃O₈), while enriched uranium is produced later in the fuel cycle.