The latter usually involves used "recycled" MOX fuel which entered the reactor containing significant amounts of plutonium. Pu that it cannot be used in current reactors operating with a thermal neutron spectrum. Pu, which determines the "grade" of produced plutonium, ranging from weapons grade, through reactor grade, to plutonium so high in 240 Depending on burnup and neutron temperature, different shares of the 239 U is unavoidable wherever it is exposed to neutron radiation. In a typical nuclear reactor, up to one-third of the generated power comes from the fission of 239Pu, which is not supplied as a fuel to the reactor, but rather, produced from 238U. In a fission nuclear reactor, uranium-238 can be used to generate plutonium-239, which itself can be used in a nuclear weapon or as a nuclear-reactor fuel supply. Reprocessed uranium is also mainly 238U, with about as much uranium-235 as natural uranium, a comparable proportion of uranium-236, and much smaller amounts of other isotopes of uranium such as uranium-234, uranium-233, and uranium-232. The decay of 238U to daughter isotopes is extensively used in radiometric dating, particularly for material older than ~ 1 million years.ĭepleted uranium has an even higher concentration of the 238U isotope, and even low-enriched uranium (LEU), while having a higher proportion of the uranium-235 isotope (in comparison to depleted uranium), is still mostly 238U. The 238U decay chain contributes 6 electron anti-neutrinos per 238U nucleus (1 per beta decay), resulting in a large detectable geoneutrino signal when decays occur within the Earth. ĭue to its natural abundance and half-life relative to other radioactive elements, 238U produces ~40% of the radioactive heat produced within the Earth. Doppler broadening of 238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control.Īround 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41 ×10 17 seconds (4.468 ×10 9 years, or 4.468 billion years). 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. However, it is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. Uranium-238 ( 238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%.
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