nuclear reactor

American  

[noo-klee-er ree-ak-ter, nyoo-] / ˈnu kli ər riˈæk tər, ˈnju- /

noun

Physics.

1. an apparatus in which a nuclear-fission chain reaction can be initiated, sustained, and controlled, for generating heat or producing useful radiation.

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nuclear reactor British  

noun

1. Sometimes shortened to: reactor.  Former name: atomic pile.  a device in which a nuclear reaction is maintained and controlled for the production of nuclear energy See also fission reactor fusion reactor

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nuclear reactor Scientific  

1. A device used to generate power, in which nuclear fission takes place as a controlled chain reaction, producing heat energy that is generally used to drive turbines and provide electric power. Nuclear reactors are used as a source of power in large power grids and in submarines.

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nuclear reactor Cultural  

1. A device in which the energy released by the fission of nuclei of uranium or another element is used to produce steam to run an electrical generator or other device.

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Pronunciation

See nuclear ( def. ).

Closer Look

A nuclear reactor uses a nuclear fission chain reaction to produce energy. The cylindrical core of a reactor consists of fuel rods containing pellets of fissionable material, usually uranium 235 or plutonium 239. These unstable isotopes readily split apart into smaller nuclei (in the fission reaction) when they absorb a neutron; they release large quantities of energy upon splitting, along with more neutrons that may be absorbed by the nuclei of other isotopes, causing a chain reaction. The neutrons are expelled from the fission reaction at very high speeds, and are not likely to be absorbed at such speeds. Moderators such as heavy water are therefore needed to slow the neutrons to a speed at which they are readily absorbed. The fuel rods contain enough fissionable material arranged in close enough proximity to start a self-sustaining chain reaction. To regulate the speed of the reaction, the fuel rods are interspersed with control rods made of a material (usually boron or cadmium) that absorbs some of the neutrons given off by the fuel. The deeper the control rods are inserted into the reactor core, the more the reaction is slowed down. If the control rods are fully inserted, the reaction stops. The chain reaction releases enormous amounts of heat, which is transferred through a closed loop of radioactive water to a separate, nonradioactive water system, creating pressurized steam. The steam drives turbines to turn electrical generators.

Etymology

Origin of nuclear reactor

First recorded in 1940–45

Example Sentences

See Examples For:

nuclear reactor

A massive influx of jellyfish has led to the partial shutdown of a nuclear reactor in northern France.

From BBC ● Aug. 27, 2026

Now, Double Chooz has added another first to its scientific record by detecting the faint neutrino glow that continues after a nuclear reactor goes dark.

From Science Daily ● Aug. 14, 2026

“Any time you’re putting a nuclear reactor in a hole, it’s kind of scary,” he said in his office, surrounded by Kansas City Royals memorabilia.

From The Wall Street Journal ● Jul. 28, 2026

The Port of Long Beach this week signed an agreement with federal regulators to explore the construction of a small nuclear reactor to power the energy-hungry port.

From The Wall Street Journal ● Jul. 23, 2026

It can take up to twenty-four hours for a properly functioning nuclear reactor to reach cold shutdown—the point at which the temperature of the core dips below boiling.

From "Meltdown" by Deirdre Langeland

Related Words

• reactor