Uranium Industry Glossary: 70+ Terms Defined A

Reference article · Updated 2026-11-06

Key facts

Uranium oxide concentrate (U3O8) is about 84.8 per cent uranium by mass.
Natural uranium is about 0.711 per cent uranium-235, which is the fissile isotope.
LEU is below 20 per cent uranium-235, HALEU is above 5 and below 20, and HEU is 20 or more.
1 Ci = 3.7e10 Bq; 1 Sv = 100 rem; 1 Gy = 100 rad.

How the glossary is organised

Terms are listed alphabetically in five groups. Definitions are short and general; values such as half-lives are rounded and come from standard nuclear data compilations, and resource terms follow the OECD-NEA and IAEA Red Book. Related background appears on the resources page, the radioactive properties page and the fuel production chain. Sources and methods are on the methodology page.

Uranium industry terms A–C

Activity: The number of nuclear disintegrations per unit time in a radioactive material, measured in becquerels (Bq). See the unit converter.
ALARA: As low as reasonably achievable: the radiation-protection principle of keeping exposures low, taking economic and social factors into account.
Alpha particle: A helium-4 nucleus emitted in some radioactive decays, including those of uranium-238 and radium-226. It is stopped by skin or paper but is hazardous if the emitter is inhaled or ingested.
Assay: In enrichment, the fraction of a material that is uranium-235, for example the tails assay. In geology, a laboratory analysis of ore grade.
Background radiation: Ionising radiation from natural sources such as cosmic rays, terrestrial radionuclides and radon, to which everyone is exposed. See radiation dose and risk.
Becquerel (Bq): The SI unit of activity: one disintegration per second.
Beta particle: An electron or positron emitted in beta decay. It penetrates further than an alpha particle but is stopped by thin metal or plastic.
Burn-up: The amount of energy extracted from nuclear fuel, usually expressed in gigawatt-days per tonne of heavy metal.
By-product uranium: Uranium recovered as a secondary product of mining another metal, as at the Olympic Dam copper-gold mine. See Olympic Dam.
Calcine: Material heated to drive off water and volatile components; in uranium milling, a dried and heated concentrate.
Centrifuge enrichment: A method that separates uranium-235 from uranium-238 hexafluoride in fast-spinning rotors, using the small mass difference. It has largely replaced gaseous diffusion.
Cigar Lake: A high-grade underground uranium mine in the Athabasca Basin, Saskatchewan, Canada. See uranium in Canada.
Conversion: The chemical step that turns uranium oxide concentrate into uranium hexafluoride (UF₆) for enrichment.
Curie (Ci): A legacy unit of activity equal to 3.7 × 10¹⁰ Bq.
Cut-off grade: The minimum ore grade at which material is treated as worth mining or processing under the assumptions of a study.

Uranium industry terms D–H

Daughter product: A nuclide formed by the radioactive decay of another nuclide, also called a decay product.
Decay chain: The sequence of radioactive decays from a parent nuclide to a stable one. The uranium-238 series passes through radium-226 and radon-222 and ends at lead-206. See radioactive properties.
Decommissioning: The administrative and technical actions that take a nuclear or mining facility out of service and prepare it for release from regulatory control. See decommissioning in the USA.
Deconversion: Conversion of depleted uranium hexafluoride to a more stable oxide or metal form for storage, disposal or use.
Depleted uranium (DU): Uranium with a lower proportion of uranium-235 than natural uranium, left over from enrichment. See depleted uranium.
Dose, absorbed: Energy deposited by radiation per unit mass of material, measured in grays (Gy).
Dose, effective: A weighted sum of organ doses that reflects the relative harm of radiation types and organ sensitivity, measured in sieverts (Sv).
Enrichment: Increasing the proportion of uranium-235 above its natural level of about 0.711 per cent. See the SWU calculator.
Feed: The material supplied to an enrichment plant, usually natural uranium hexafluoride.
Fertile material: A nuclide, such as uranium-238 or thorium-232, that can be converted into fissile material by neutron capture.
Fissile: Able to sustain a fission chain reaction with neutrons of any energy, including thermal neutrons. Uranium-235 is the only naturally occurring fissile nuclide in significant amounts.
Fuel assembly: A structured bundle of fuel rods that is loaded into a reactor core as a unit.
Fuel fabrication: The manufacture of fuel pellets and assemblies from enriched uranium oxide.
Gamma ray: High-energy electromagnetic radiation emitted by nuclei. Penetrating, it is attenuated by dense materials.
Gaseous diffusion: An older enrichment method that passes uranium hexafluoride through porous barriers. It uses far more electricity than centrifuges.
Grade: The concentration of uranium in ore, expressed in per cent U or U₃O₈ by weight.
Gray (Gy): The SI unit of absorbed dose, equal to one joule per kilogram. 1 Gy = 100 rad.
HALEU: High-assay low-enriched uranium: enriched to more than 5 per cent but below 20 per cent uranium-235.
Half-life: The time taken for half of the atoms of a radionuclide to decay. It is about 4.47 billion years for uranium-238 and about 704 million years for uranium-235.
Heap leach: A process in which crushed ore is stacked on a pad and irrigated with leaching solution to dissolve uranium.
HEU: Highly enriched uranium: enriched to 20 per cent uranium-235 or more.
Husab: An open-pit uranium mine in the Erongo region of Namibia. See uranium mining in Africa.

Uranium industry terms I–M

In-situ leaching (ISL): Recovery of uranium by pumping a leaching solution through the ore body underground, without conventional excavation, also called in-situ recovery (ISR). See ISL explained.
Inferred resource: A resource estimate with the lowest geological confidence, based on limited sampling. See resources and reserves.
Ionising radiation: Radiation with enough energy to remove electrons from atoms, including alpha, beta, gamma, X-ray and neutron radiation.
Isotope: One of two or more forms of an element with the same number of protons and different numbers of neutrons.
LEU: Low-enriched uranium: enriched to less than 20 per cent uranium-235. Most power reactor fuel is below 5 per cent.
Lixiviant: The solution used to dissolve minerals in leaching; in uranium ISL it is typically groundwater with an oxidant and carbonate or acid.
Milling: Crushing and chemically processing uranium ore to produce a concentrate, usually U₃O₈.
Mine tailings: Fine-grained waste left after minerals are extracted from ore, often stored in impoundments behind dams. See tailings dam safety.
MOX: Mixed-oxide fuel containing plutonium and uranium oxides. See plutonium disposition.

Uranium industry terms N–R

Natural uranium: Uranium as found in nature: about 99.28 per cent uranium-238, about 0.711 per cent uranium-235 and a trace of uranium-234.
Pitchblende: A massive variety of uraninite, the main uranium oxide mineral.
Plutonium-239: A fissile isotope produced in reactors from uranium-238 by neutron capture.
Product: The enriched material that leaves an enrichment plant.
Rad: A legacy unit of absorbed dose; 1 rad = 0.01 Gy.
Radium-226: A radioactive decay product of uranium-238 with a half-life of about 1,600 years; the main long-term hazard of uranium mill tailings.
Radon-222: A radioactive noble gas formed by the decay of radium-226, with a half-life of about 3.8 days. Inhaled radon progeny are a recognised cause of lung cancer.
Reasonably assured resources (RAR): Identified uranium resources with the highest confidence in the Red Book scheme.
Red Book: The common name for the OECD-NEA and IAEA publication on uranium resources, production and demand.
Rem: A legacy unit of effective dose; 1 rem = 0.01 Sv.
Reserve: The economically mineable part of a measured or indicated resource, demonstrated by a study.
Rössing: An open-pit uranium mine in Namibia that began production in 1976. See Rössing.

Uranium industry terms S–Z

Secondary supply: Uranium supply that does not come from newly mined ore, such as stockpiles, recycled material and re-enriched tails.
Sievert (Sv): The SI unit of effective or equivalent dose. 1 Sv = 100 rem.
Spent fuel: Nuclear fuel that has been irradiated in a reactor and removed.
Spot price: The price for uranium delivered in the near term, in contrast with long-term contract prices.
Stockpile: An inventory of uranium or enriched material held by a utility, government or trader.
SWU: Separative work unit: the measure of the effort of enrichment, which depends on the quantities and assays of feed, product and tails.
Tails: The depleted stream that leaves an enrichment plant, with a lower uranium-235 content than the feed.
Thorium-230: A decay product of uranium-238 with a half-life of about 75,000 years, present in uranium tailings.
U₃O₈: Triuranium octoxide, the oxide form in which uranium concentrate is traded, also called yellowcake. About 84.8 per cent of its mass is uranium.
UF₆: Uranium hexafluoride, the compound that is a gas at moderate temperatures and is used as the feed for enrichment.
Unconformity-related deposit: A high-grade uranium deposit near the contact between older basement rocks and overlying sandstone, as in the Athabasca Basin.
Underfeeding: Operating an enrichment plant with less separative work and a lower tails assay than the economic optimum, using more natural uranium.
UO₂: Uranium dioxide, the ceramic compound pressed into pellets for most power reactor fuel.
Uraninite: The main uranium oxide mineral, chemically UO_2+x.
Uranium-235: The fissile isotope of uranium, making up about 0.711 per cent of natural uranium.
Uranium-238: The most abundant uranium isotope, at about 99.28 per cent of natural uranium, with a half-life of about 4.47 billion years.
Yellowcake: Popular name for uranium oxide concentrate produced by milling or ISL plants; see U₃O₈.

Frequently asked questions

What is yellowcake?

Yellowcake is the common name for uranium oxide concentrate, usually U3O8, produced by milling or in-situ leach plants and sold to converters.

What is the difference between LEU, HALEU and HEU?

LEU is enriched to less than 20 per cent uranium-235, HALEU is enriched to more than 5 and less than 20 per cent, and HEU is 20 per cent or more.

What does SWU mean?

SWU is the separative work unit, the measure of the effort of enrichment. It depends on the amounts and uranium-235 assays of feed, product and tails.

What is the difference between becquerel and sievert?

The becquerel measures activity, in disintegrations per second, while the sievert measures effective dose, which reflects biological effect on the body.

What are tailings?

Tailings are the fine-grained waste left after minerals are extracted from ore. Uranium mill tailings contain decay products such as radium-226 and need long-term management.