delayed criticality

The point at which the prompt neutrons and delayed neutrons produced by a nuclear…The point at which the prompt neutrons and delayed neutrons produced by a nuclear fission chain reaction, taken together, are just sufficient to sustain the chain reaction (the state of being delayed critical); in this state, changes in reaction power occur slowly, allowing the reaction to be controlled on human timescales, due to the relatively long time delay associated with the emission of the delayed neutrons necessary to maintain the chain reaction.