Supercriticality

Supercriticality refers to a state in which a nuclear reaction is self-sustaining due to the production of a sufficient number of neutrons. This state is achieved when the neutron multiplication factor (k) is greater than one.

Overview

In a nuclear reactor, supercriticality is the condition that allows a chain reaction to continue indefinitely. This is achieved when the number of neutrons produced in one generation of fission is greater than the number absorbed or lost. This state is crucial for the operation of nuclear reactors and the detonation of nuclear weapons.

Supercriticality in Nuclear Reactors

In a nuclear reactor, the state of supercriticality is carefully controlled to maintain a steady rate of fission reactions. This is achieved by adjusting the position of control rods, which absorb neutrons and thus reduce the neutron multiplication factor. If the reactor becomes subcritical, the chain reaction will die out; if it becomes prompt supercritical, it can lead to a rapid increase in power and potential reactor damage.

Supercriticality in Nuclear Weapons

In a nuclear weapon, the assembly must become supercritical in a very short time to achieve a successful detonation. This is typically achieved by using conventional explosives to compress a subcritical mass of fissile material into a supercritical state.

Safety Considerations

The state of supercriticality must be carefully controlled to prevent accidents. In a nuclear reactor, this is achieved through the use of control rods and safety systems designed to shut down the reactor if it becomes prompt supercritical. In the handling and storage of fissile materials, care must be taken to prevent the formation of a critical mass.

See Also

• Criticality (nuclear engineering)
• Nuclear chain reaction
• Nuclear fission
• Nuclear reactor physics