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The half-life of 238 U is about 190 times as long as that of 236 U; therefore, 236 U should have about 190 times as much specific activity. That is, in reprocessed uranium with 0.5% 236 U, the 236 U and 238 U will produce about the same level of radioactivity. (235 U contributes only a few percent.)
Uranium-236 has a half-life of about 23 million years; and is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in the reprocessed uranium made from spent nuclear fuel.
The half-life of uranium-236 is too short for it to be primordial, though it has been identified as an extinct progenitor of its alpha decay daughter, thorium-232. [67] Uranium-236 occurs in spent nuclear fuel when neutron capture on 235 U does not induce fission, or as a decay product of plutonium-240.
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods include jumping up and down make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds.
Some of the excited 236 U nuclei undergo fission, but some decay to the ground state of 236 U by emitting gamma radiation. Further neutron capture creates 237 U; which, with a half-life of 7 days, decays to 237 Np. Since nearly all neptunium is produced in this way or consists of isotopes that decay quickly, one gets nearly pure 237 Np.
A further 10 nuclides, platinum-190, samarium-147, lanthanum-138, rubidium-87, rhenium-187, lutetium-176, thorium-232, uranium-238, potassium-40, and uranium-235 have half-lives between 7.0 × 10 8 and 4.83 × 10 11 years, which means they have experienced at least 0.5% depletion since the formation of the Solar System about 4.6 × 10 9 years ...
Reprocessed uranium will contain 236 U, which is not found in nature; this is one isotope that can be used as a fingerprint for spent reactor fuel. If using a thorium fuel to produce fissile 233 U, the SNF (Spent Nuclear Fuel) will have 233 U , with a half-life of 159,200 years (unless this uranium is removed from the spent fuel by a chemical ...
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] U-233 is produced from thorium-232 by neutron capture. [19]