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Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235 U) has been increased through the process of isotope separation.Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 U with 99.2732–99.2752% natural abundance), uranium-235 (235 U, 0.7198–0.7210%), and uranium-234 (234 U, 0.0049–0.0059%).
Natural uranium is made weapons-grade through isotopic enrichment. Initially only about 0.7% of it is fissile U-235, with the rest being almost entirely uranium-238 (U-238). They are separated by their differing masses. Highly enriched uranium is considered weapons-grade when it has been enriched to about 90% U-235. [citation needed]
Highly enriched uranium (HEU), which contains an even greater proportion of uranium-235, is sometimes used in the reactors of nuclear submarines, research reactors and nuclear weapons. If at least one neutron from uranium-235 fission strikes another nucleus and causes it to fission, then the chain reaction will continue.
The Megatons to Megawatts Program, also called the United States-Russia Highly Enriched Uranium Purchase Agreement, was an agreement between Russia and the United States whereby Russia converted 500 metric tons of "excess" weapons-grade uranium (enough for 20,000 warheads) into 15,000 metric tons of low enriched uranium, which was purchased by the US for use in its commercial nuclear power plants.
The enriched uranium was used in the Little Boy atomic bomb used in the atomic bombing of Hiroshima. In 1946, the K-25 gaseous diffusion plant became capable of producing highly enriched product. After the war, four more gaseous diffusion plants named K-27, K-29, K-31 and K-33 were added to the site.
The term Strategic Special Nuclear Material (SSNM) refers to Uranium-235 contained in uranium enriched above 20 percent (Highly Enriched Uranium), as well as any concentration of Uranium-233 or Plutonium. [1] The distinction between SNM and SSNM is due to the fact that uranium-235 is typically found mixed with other isotopes such as Uranium-238.
The Siberian Chemical Combine (Russian: Сибирский химический комбинат) was established in 1953 in Tomsk-7 now known as Seversk, in the Tomsk Region as a single complex of the nuclear technological cycle for the creation of nuclear weapons components based on fissile materials (highly enriched uranium and plutonium).
Uranyl nitrate is important for nuclear reprocessing.It is the compound of uranium that results from dissolving the decladded spent nuclear fuel rods or yellowcake in nitric acid, for further separation and preparation of uranium hexafluoride for isotope separation for preparing of enriched uranium.