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• nuclear fission
  nuclear fission

  noun

  fission.
• fission, nuclear
  fission, nuclear

  A nuclear reaction in which a single large nucleus splits into two or more smaller nuclei. In some cases, for example with uranium, energy is released in this process.

nuclear fission

American  

[noo-klee-er fish-uhn] / ˈnu kli ər ˈfɪʃ ən /

noun

1. fission.

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nuclear fission British  

noun

1. Sometimes shortened to: fission.  the splitting of an atomic nucleus into approximately equal parts, either spontaneously or as a result of the impact of a particle usually with an associated release of energy Compare nuclear fusion

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fission, nuclear Cultural  

1. A nuclear reaction in which a single large nucleus splits into two or more smaller nuclei. In some cases, for example with uranium, energy is released in this process.

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Pronunciation

See nuclear ( def. ).

Discover More

The fission of uranium 235, an isotope of uranium, supplies energy for nuclear reactors and atomic bombs (see also atomic bomb).

Etymology

Origin of nuclear fission

First recorded in 1885–90

Example Sentences

The fusion process creates energy by joining atoms together, while nuclear fission creates energy when atoms are split apart.

From The Wall Street Journal • Dec. 10, 2025

It is produced by nuclear fission for use in medical gauges and devices, but can also be a byproduct of nuclear reactors and weapons testing, the agency said.

From Los Angeles Times • Aug. 19, 2025

Like all nuclear fission plants, they are controversial.

From BBC • Feb. 26, 2025

Sam Altman, who also chairs Oklo, a nuclear fission microreactor start-up that’s set to go public this year, is backing the power source to satisfy the world’s growing energy needs, including from A.I.

From New York Times • Mar. 21, 2024

It can only be found in environments where nuclear fission is occurring—in nuclear weapons and nuclear power plants.

From "Meltdown" by Deirdre Langeland