Destruction and Decay
236U, on absorption of a thermal neutron, does not undergo fission, but becomes 237U, which quickly beta decays to 237Np. However, the neutron capture cross section of 236U is low, and this process does not happen quickly in a thermal reactor. Spent nuclear fuel typically contains about 0.4% U-236. With a much greater cross-section, 237Np may eventually absorb another neutron, becoming 238Np, which quickly beta decays to plutonium-238.
236U and most other actinides are fissionable by fast neutrons in a nuclear bomb or a fast neutron reactor. A small number of fast reactors have been in research use for decades, but widespread use for power production is still in the future.
Uranium-236 alpha decays with a half-life of 23.420 million years to thorium-232. It is longer-lived than any other artificial actinides or fission products produced in the nuclear fuel cycle. (Plutonium-244 which has a half-life of 80 million years is not produced in significant quantity by the nuclear fuel cycle, and the longer-lived U-235, U-238, and thorium-232 occur in nature.)
Read more about this topic: Uranium-236
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