nuclear reactor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several devices in which nuclear fission initiates a controlled chain reaction, producing heat energy typically used for power generation, and neutrons and fission products often used for military, experimental, and medical purposes.

from the GNU version of the Collaborative International Dictionary of English.

• noun (phys.) Any of several devices that maintain and control a sustained nuclear fission chain reaction, for the production of energy, heat, or artificial elements, or for research purposes. The main fuel sustaining the reaction and consumed by the process is typically uranium or plutonium.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics Any device in which a controlled chain reaction is maintained for the purpose of creating heat (for power generation) or for creating neutrons and other fission products for experimental, medical or other purposes.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (physics) any of several kinds of apparatus that maintain and control a nuclear reaction for the production of energy or artificial elements