[ree-ak-ter] 
| 1. | a person or thing that reacts or undergoes reaction. |
| 2. | Electricity. a device whose primary purpose is to introduce reactance into a circuit. |
| 3. | Immunology, Veterinary Medicine. a patient or animal that reacts positively towards a foreign material. |
| 4. | Also called atomic pile, chain reactor, chain-reacting pile, nuclear reactor, pile. Physics. an apparatus in which a nuclear-fission chain reaction can be initiated, sustained, and controlled, for generating heat or producing useful radiation. |
| 5. | Chemistry. (esp. in industry) a large container, as a vat, for processes in which the substances involved undergo a chemical reaction. |
| nuclear reactor n. Any of several devices in which a chain reaction is initiated and controlled, with the resulting heat typically used for power generation and the neutrons and fission products used for military, experimental, and medical purposes. Also called atomic reactor. |
nuclear reactor
(click for larger image in new window) 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. Our Living Language : 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. |