Enriched uranium

Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written ²³⁵U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (²³⁸U with 99.2732–99.2752% natural abundance), uranium-235 (²³⁵U, 0.7198–0.7210%), and uranium-234 (²³⁴U, 0.0049–0.0059%).^{[1] 235}U is the only nuclide existing in nature (in any appreciable amount) that is fissile with thermal neutrons.^[2]

Enriched uranium is a critical component for both civil nuclear power generation and military nuclear weapons.

Low-enriched uranium (below 20% ²³⁵U) is necessary to operate light water reactors, which make up almost 90% of nuclear electricity generation.^[3]

Highly enriched uranium (above 20% ²³⁵U) is used for the cores of many nuclear weapons, as well as compact reactors for naval propulsion and research, as well as breeder reactors. There are about 2,000 tonnes of highly enriched uranium in the world.^[4]

Enrichment methods were first developed on a large scale by the Manhattan Project. Its gaseous diffusion method was used in the 1940s and 1950s, when the gas centrifuge method was developed in the Soviet Union, and became widespread.^[5]

The ²³⁸U remaining after enrichment is known as depleted uranium (DU), and is considerably less radioactive than natural uranium, though still very dense. Depleted uranium is used as a radiation shielding material and for armor-penetrating weapons.