Fission product generation and fuel structure

Heavy nuclides are unstable they can be disintegrated not only by a or P decay or, in some cases, by spontaneous fission, but also by neutron-induced fission. The fission cross sections, however, of the various nuclides show great differences. Among the naturally occurring fissile nuclides is the only one that can be used in thermal reactors in addition, the artificially produced nuclides Pu and Pu show fission cross sections and halflives which make them appropriate for use as nuclear fuels. In the currently operating light water reactors, which are exclusively based on uranium as the starting element, only the fissile nuclides 2 Pu and 2 Pu are of real interest. 

Neutron-induced nuclear fission can be described by the general equation (according to Lieser, 1991) 

Upon neutron capture in the target nucleus A, a highly excited compound nucleus is generated which decays within about 10 s, forming the two fragments B and D. About 10 s later, the prompt fission neutrons n are emitted in the thermal 

The energy released in the thermal fission amounts to about 200 MeV, consisting of the following individual contributions 

Since the neutrinos escape quantitatively from the reactor, the fission energy which is available for production of utilizable energy amounts to 189 MeV per fission 

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