Supercritical fission situation

In addition to the product nuclides, neutrons are produced in the fission reactions of This makes it possible to produce a self-sustaining fission process—a chain reaction (see Fig. 21.12). For the fission process to be self-sustaining, at least one neutron from each fission event must go on to split another nucleus. If, on the average, less than one neutron causes another fission event, the process dies out the reaction is said to be subcritical. If exactly one neutron from each fission event causes another fission event, the process sustains itself at the same level and is said to be critical. If more than one neutron from each fission event causes another fission event, the process rapidly escalates and the heat buildup causes a violent explosion. This situation is described as supercritical. 

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