Nuclear reactor state where the nuclear chain reaction is exactly self-sustaining
In the operation of a nuclear reactor, criticality is the state in which a nuclear chain reaction is self-sustaining—that is, when reactivity is zero. In supercritical states, reactivity is greater than zero.[1]
^"Criticality"(PDF). IAEA Safety Glossary. International Atomic Energy Agency. 2007. p. 46. Retrieved 17 February 2014.