Reference Work Entry

Environmental Geology

Part of the series Encyclopedia of Earth Science pp 440-448

Nuclear energy

  • Pekka Silvennoinen

Fission nuclear energy is released from the splitting of a fissionable nucleus struck by a neutron. In nuclear reactor applications, relevant neutron energies lie around or below 10 MeV (1eV=1.60210 × 10−19 Joule) and thus only certain isotopes of thorium, uranium and plutonium are fissionable in the practical sense. Nuclei which can undergo fission when absorbing an arbitrarily slow, or low-energy neutron are called fissile. Nuclear fuel is always designed to contain at least one of the fissile isotopes U233, U235, Pu239 and Pu241. Of these, U235 is the only one that occurs in any separable quantity in nature (Zweifel, 1973).

Besides yielding fission product nuclei, emitting gamma radiation and releasing energy, additional neutrons are emitted from fission. These emitted secondary neutrons can be utilized to induce further fission reactions. Hence a chain reaction can be perpetuated. When nuclear reactors operate at a steady fission rate they are referred to as being cri ...

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