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 primarily of three isotopes: uranium-238 (238U, 99.2732–99.2752% natural abundance), uranium-235 (235U, 0.7198–0.7210%), and uranium-234 (234U, 0.0049–0.0059%). 235U is the only primordial nuclide present in nature in appreciable quantities that is fissile with thermal neutrons. Enriched uranium is used in both civil nuclear power generation and military nuclear weapons. Low-enriched uranium (LEU), containing less than 20% 235U, is used as fuel in light-water reactors, which make up most nuclear power reactors worldwide. Highly enriched uranium (HEU), containing 20% or more 235U, has been used in nuclear weapons, naval propulsion reactors, some research reactors, and certain specialized reactor designs. There are about 2,000 tonnes of highly enriched uranium in the world. Large-scale enrichment was first developed during the Manhattan Project, which used gaseous diffusion and electromagnetic isotope separation to produce enriched uranium. Historically, gaseous diffusion and the gas centrifuge are the two enrichment methods that have operated on a commercial scale, but gaseous diffusion is now obsolete and has been replaced by centrifuge technology in commercial use. Laser isotope separation has also been developed as a possible third-generation enrichment technology; Global Laser Enrichment has applied to license a laser-based uranium enrichment facility in the United States, but centrifugation remains the enrichment process used commercially. 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 in armor-penetrating weapons.