High-enriched uranium (HEU) is uranium that has a high percentage of the isotope Uranium-235. While natural uranium contains about 0.7% of this isotope, HEU typically contains 20% or more, with some forms exceeding 90%. This increased concentration makes HEU suitable for use in certain types of nuclear reactors and in the production of nuclear weapons. The use of HEU raises concerns about nuclear proliferation, as it can be diverted for military purposes. Efforts are ongoing globally to reduce the stockpiles of HEU and promote the use of low-enriched uranium (LEU) in civilian nuclear applications to enhance safety and security.