Criticality (status)
Criticality is the state of a nuclear chain reacting medium when the chain reaction is just self-sustaining (or critical), that is, when the reactivity is zero. More loosely, the term is used for states in which the reactivity is greater than zero.[1]
Applications
In the context of a nuclear reactor, particularly in a nuclear power plant, criticality refers to the normal operating condition of a reactor, in which nuclear fuel sustains a fission chain reaction. A reactor achieves criticality (and is said to be critical) when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.[2]
The International Atomic Energy Agency also 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. For example, Qinshan 1, China's first domestically designed and constructed nuclear power plant, achieved first criticality on 31 October 1991.[4]
