- noun a device which creates heat and energy by starting and controlling atomic fission
- A device which utilizes controlled nuclear fusion or fission to generate energy. A fission reactor, for instance, has the following key components: a fissionable fuel, such as uranium-235, a moderator, such as heavy water, shielding, such as that provided by thick concrete, control rods, such as those made with boron, and a coolant such as water. The heat produced by the nuclear reactions can be utilized to generate electricity. Also called atomic reactor, or reactor (2). Deprecated terms for this concept include nuclear pile, atomic pile, and pile (2).