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minor actinide production in U-Pu cycle

The production of minor actinides mainly occurs from sequential radiative neutron capture and beta decay starting at 239Pu. For thermal neutrons, the ratio of capture to fission cross sections of Pu fissile isotopes reaches 1:3, and the branching to heavier Pu isotope and heavier element production cannot be neglected.

After the decay of short lived fission products, if one can separate U and Pu from irradiated fuel, the main fraction of the remaining activity will come from the so-called minor actinides, i.e. Np, Am and Cm isotopes.

The figure shows how Am and Cm isotopes are produced in the U-Pu fuel cycle. Most of these nuclides are precursors of long alpha decay chains, and their half lives range from 10 to 10,000 years, that means a high activity for thousands of years.

Due to the limited volume of these waste products, the possibility of deep storage is under study. An alternative solution should be to burn them up by fast neutron induced fission, to turn the long lived alpha activity of the minor actinides to short lived beta activity of fission fragments.