Weapons-grade plutonium is made specifically for military purposes. This special reactor only needs weeks or months to produce weapons-grade plutonium.ДЄlthough the two kinds are created by different means, both come from spent, or used, uranium fuel in reactors. weapons-grade plutonium, containing at least 90 percent Pu-239, which is extracted from spent fuel thatвЂ™s been transferred to a special plutonium production reactor.reactor-grade plutonium, containing between 55 and 70 percent Pu-239, which is extracted from spent fuel that has been irradiated, or exposed to radiation, for years in a nuclear reactor and.But uranium can also be used to produce plutonium, an element that is not naturally occurring and is much more powerful than uranium.Дepending on the level of the isotope Pu-239 contained, plutonium can be differentiated into Producing HEU is one way to create a nuclear weapon. That means warheads can be smaller and lighter, enabling missiles to cover greater distances and aircraft to deliver more weapons.Д«ut there is more than one path to the bomb. The more enriched the uranium is, the less of it is needed for a weapon. highly enriched uranium (HEU), which has 20 percent or more U-235 and is mainly used for military purposes: to develop nuclear weapons and in a few other specialized applications such as the reactors on nuclear-powered submarines.ДЄny level of HEU can be used for a weapon, but HEU enriched to at least 90 percent, sometimes called weapons-grade uranium, is the most common.low-enriched uranium (LEU), which has less than 20 percent U-235 and is often used for nuclear power or in non-power reactors, which produce materials for medical use, scientific research, and other purposes and.Uranium can be enriched to various levels, which fall into two categories: Each round of rotation in a centrifuge lowers the proportion of U-238 and increases that of U-235 in the sample. After uranium is converted into gas, it is fed into centrifuges, which rotate at high speeds, to separate the slightly heavier U-238 from U-235. Uranium enrichment most commonly occurs in gas centrifuges. In most cases, nuclear energy production begins with uranium enrichment. So countries with nuclear ambitions-peaceful or not-need to first increase the proportion of U-235 in their uranium samples through a process called enrichment. U-235 is especially important because it easily undergoes fission (unlike U-238) and is extremely rare, accounting for less than 1 percent of the worldвЂ™s natural uranium. In nature, uranium is a mix of mostly two isotopes: uranium-235 (U-235) and uranium-238 (U-238). (Unlike uranium, plutonium isnвЂ™t found in nature-weвЂ™ll return to this issue later.) Fission occurs easily in only a few isotopes, or forms of elements, typically uranium and plutonium.

Nuclear fission occurs when neutrons bombard atomic nuclei and split them, releasing massive amounts of energy.

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