The concentration of U235, expressed by percentage of weight in uranium, in a given quantity of uranium ore, uranium hexafluoride or uranium metal. An assay of 3 to 5 percent U235 is required for most nuclear power plants.


The step in the nuclear fuel cycle that increases the concentration of U235 relative to U238 in order to make uranium usable as a fuel for nuclear power reactors.


Natural uranium in the form of UF6 suitable for enrichment.

Gas Centrifuge

A uranium enrichment process in which the rotor of the centrifuge machine, containing uranium hexa-fluoride gas, spins at high speed inside a vacuum casing. Centrifugal force concentrates the heavier U238 molecules at the outer wall and the lighter U235 molecules toward the rotor center. Gas circulation flow is created to carry enriched product and tails to opposite ends of the machine.

Gaseous Diffusion

A uranium enrichment process using uranium hexafluoride, which is heated to a gas and passed repeatedly through porous barriers to separate U235 and U238 isotopes. Centrus used the gaseous diffusion process at the Paducah Gaseous Diffusion Plant in Kentucky.


Highly enriched uranium. Uranium enriched to an assay of 20 percent or more. For military application, this enrichment level may exceed 90 percent.


One or more nuclides of the same element having the same atomic number but a different mass number. Although they have the same number of protons, they have a different number of neutrons.


Low-enriched uranium. Uranium enriched to an assay of less than 20 percent. LEU typically has a 3 to 5 percent assay when used as fuel for nuclear reactors.

Natural Uranium

Uranium, as found in nature, has a concentration level of 0.7 percent U235.

Nuclear Fuel Cycle

The multiple steps that convert uranium ore, as it is extracted from the earth, to nuclear fuel for power plants. Uranium enrichment is an intermediate step in the fuel cycle.

Separative Work Unit (SWU)

A measure of the effort expended in a uranium enrichment plant to separate uranium of a given U235 content into two components, one having a higher percentage of U235 and the other a lower concentration.


Uranium hexafluoride that contains a lower concentration of the U235 isotope as a result of the enrichment process. Also known as depleted uranium.


The fissionable isotope found in natural uranium.


The typically non-fissionable isotope that makes up most of natural uranium.


Uranium hexafluoride. A chemical comĀ¬pound containing uranium and fluorine that is solid when stored, and that is gasified for use in the enrichment process.


A fairly abundant metallic element. Approximately 993 of every 1,000 uranium atoms are U238. Almost all of the remaining atoms are U235, which can be made to split, or fission, and generate heat energy.