Nuclear reactor

Nuclear reactor are a class of devices that initiate and control a self-sustaining series of nuclear fissions. Formerly known as an atomic pile, nuclear reactors are used as power plants for electricity generation, as research tools, as systems for the production of radioactive isotopes, and in nuclear marine propulsion. As of early 2019, the IAEA reports there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world.

Nuclear fission is a process through which a heavy atomic nucleus splits in two smaller fragments. These fragments, in an excited state, emit neurons, photons, and subatomic particles. The emitted neurons cause new fissions, which in turn yield more neutrons, and continue a self-sustaining series of fissions through chain-reactions. The energy released in this process is the basis of a nuclear power system. Uranium-235 and plutonium-239 are the common atomic nuclei used for the fission process. For a nuclear reactor to control the chain reactions, control rods containing neutron poisons and moderators are used to change the portions of neutrons causing more fission.

The process of nuclear fission creates a large amount of heat. This heat is passed to a working fluid (water or gas), which in turn runs through steam turbines. These turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. In many reactors, the water boiled for steam generation is kept separate from the reactor by a different coolant, except in the case of a boiling water reactor, which uses the boiling water as coolant.

Leó Szilárd patented the idea for the nuclear reactor in 1933, a year after the discovery of the neutron by physicist James Chadwick. Leó Szilárd's patent did not include the idea of nuclear fission as a neutron source as the process had yet to be discovered. The discovery of the nuclear chain reaction came from Lise Meitner, Fritz Strassmann and Otto Hahn in 1938 after they bombarded a core of uranium with neutrons and subsequent studies into their method.

The discovery of fission led to Leó Szilárd's letter to Franklin D. Roosevelt in 1939 on the danger of uranium fission leading to the development of a new type of bomb. This led to increased interest and study of the process of nuclear fission, including the Frisch-Peierls memorandum on the amount of uranium needed for a chain reaction. The Frish-Peierls memorandum was part of the MAUD Committee in the United Kingdom, as part of their atomic bomb project, known by the code name Tube Alloys.

In 1942, a team at the University of Chicago lead by Enrico Fermi constructed the Chicago Pile-1, the first artificial nuclear reactor. The Chicago Pile-1 achieved criticality in December 1942. In 1943, the United States Military developed a number of nuclear reactors as part of the Manhattan Project and for their need of plutonium for nuclear weapons. Fermi and Szilárd filed for the patent on nuclear reactors in 1944, but the issuance was delayed due to wartime secrecy.