Criticality (status)


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 is the normal operating condition of a nuclear reactor, in which nuclear fuel sustains a fission chain reaction. A reactor achieves criticality (and is said to be critical) when each fission releases a sufficient number of neutrons to sustain an ongoing series of nuclear reactions.[2]

The International Atomic Energy Agency defines the first criticality date as the date when the reactor is made critical for the first time.[3] This is an important milestone in the construction and commissioning of a nuclear power plant.

See alsoEdit


  1. ^ "Criticality" (PDF). IAEA Safety Glossary. International Atomic Energy Agency. 2007. p. 46. Retrieved 17 February 2014.
  2. ^ "Criticality". Glossary. US Nuclear Regulatory Commission. 11 December 2013. Retrieved 17 February 2014.
  3. ^ "First Criticality Date". Glossary. International Atomic Energy Agency. Retrieved 17 February 2014.