background = #fc6
isotope_name = Uranium-234
halflife =246,000 years
decay_product = Thorium-230
parent = Plutonium-238
parent_decay = a
parent2 = Protactinium-234
parent2_mass = 234
parent2_symbol = Pa
parent2_decay = b-
parent3 = Neptunium-234
parent3_mass = 234
parent3_symbol = Np
parent3_decay = b+
decay_mode1 =Alpha decay
decay_energy4 = Uranium-234 is an isotope of Uranium. In
natural uraniumand uranium ore, 234U occurs as an indirect decay productof 238U, but it makes up only 0.0055% of the raw uranium because its half-lifeof just 246,000 years is only about 1/18,000 as long as the half-life of 238U.
Large-scale extraction of 234U from natural uranium would only be feasible by
isotope separationsimilar to that used for uranium enrichment, and there is no industrial demand for isolating U-234. Pure samples of U-234 can be extracted (by ion exchange) from pure plutonium-238which has been aged to allow some of it to decay to 234U. Enriched uraniumcontains more U-234 than natural uranium as a side-effect of enrichment for U-235, which concentrates lighter isotopes even more. The increased level of U-234 in enriched natural uranium is acceptable in current nuclear reactorsbut re-enriched reprocessed uraniummay contain higher levels which are undesirable.
234U has a
neutron absorption cross sectionof 100 barns for thermal neutrons, and 700 barns for resonance integral, an average over neutrons of various intermediate energies. Hence, in a thermal reactor, it is converted to fissile235U at a faster rate than the much larger amount of 238U (with an absorption cross section of 2.7) is converted to 239Pu. Thus spent nuclear fuelshould contain only some of the 234U that was in the fresh fuel. Depleted uraniumcontains much less U-234 (around 0.001% [ [http://www.who.int/mediacentre/factsheets/fs257/en/ WHO | Depleted uranium] ] ) which makes the radioactivity of depleted uranium about one-half of that of natural uranium, since natural uranium has an "equilibrium" concentration of 234U, and therefore an equal number of decays of 238U and 234U will occur. Depleted uranium also contains less U-235, but in spite of its half-life which is shorter than U-238's, the concentration of U-235 in natural uranium is low enough so that the U-235 depletion does not result in a significant reduction in radioactivity.
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