The reactor core generates heat in a number of ways: Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring or instrumentation detects unsafe conditions. To control such a nuclear chain reaction, control rods containing neutron poisons and neutron moderators can change the portion of neutrons that will go on to cause more fission. This is known as a nuclear chain reaction. A portion of these neutrons may be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. The heavy nucleus splits into two or more lighter nuclei, (the fission products), releasing kinetic energy, gamma radiation, and free neutrons. When a large fissile atomic nucleus such as uranium-235, uranium-233, or plutonium-239 absorbs a neutron, it may undergo nuclear fission. In the early era of nuclear reactors (1940s), a reactor was known as a nuclear pile or atomic pile (so-called because the graphite moderator blocks of the first reactor to reach criticality were stacked in a pile). As of 2022, the International Atomic Energy Agency reports there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world.
Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. Nuclear generated steam in principle can be used for industrial process heat or for district heating. These either drive a ship's propellers or turn electrical generators' shafts. Heat from nuclear fission is passed to a working fluid (water or gas), which in turn runs through steam turbines. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Core of CROCUS, a small nuclear reactor used for research at the EPFL in SwitzerlandĪ nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. For nuclear stockpiles, see List of states with nuclear weapons.
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