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A nuclear reactor is a device in which nuclear fission chain reactions are initiated, controlled, and sustained at a steady rate (as opposed to a nuclear explosion, where the chain reaction occurs in a split second). Nuclear reactors provide heat for electricity generation, domestic and industrial heating, desalination, and naval propulsion. They also have many research applications including providing a source of neutrons and creating various radioactive isotopes.
Although the term 'nuclear reactor' includes fusion reactors, this article concentrates on nuclear fission devices.
Nuclear power can also be generated in a radioisotope thermoelectric generator, which produces heat through subcritical (i.e. less than critical mass) radioactive decay rather than fission in a near-critical mass. These generators have been used to power space probes and some lighthouseAn aid for navigation and pilotage at sea, a lighthouse is a tower building or framework sending out light from a system of lamps and lenses or, in older times, from a fire. More primitive navigational aids were once used such as a fire on top of a hill os built by the Soviet UnionThe Union of Soviet Socialist Republics (USSR ( Russian: ; tr. Soyuz Sovetskikh Sotsialisticheskikh Respublik (SSSR) also called the Soviet Union ( ; tr. Sovetsky Soyuz , was a state in much of the northern region of Eurasia that existed from 1922 until 1.
All commercial nuclear reactors produce heat through nuclear fission. In this process, the nucleusIn chemistry and physics, the nucleus atomic nucleus is the collection of protons and neutrons in the center of an atom that carries the bulk of the atom's mass and positive charge. In cell biology, the nucleus cell nucleus is the membrane-bound subcellul of an element such as uraniumUranium is a chemical element in the periodic table that has the symbol U and atomic number 92. A heavy, silvery-white, toxic, metallic , and naturally- radioactive element, uranium belongs to the actinide series and its isotope uranium-235 is used as the splits into two smaller atoms. This occurs naturally in radioactive elements, but it can be induced artificially by making some atoms absorb a slow-moving free neutron. This causes the nucleus to become unstable and makes it split apart very quickly.
The fission process for a uranium atom yields two smaller atoms, one to three fast-moving free neutronsA fast neutron is a free neutron with a kinetic energy level close to 1 M eV (10 TJ/kg, hence a speed of 14,000 km/s. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, and high energy neutrons produced in cosmic showers., and energyThis article is about the scientific concept. Energy use by humans is discussed in other articles''. Energy generally and qualitatively speaking, is the property (or the quantity of the property) of doing things or supplying power. The expressions energy. Uranium fission releases more neutrons than it requires. Therefore, the reaction can become self sustaining. This is called a chain reaction. The newly released fast neutrons must be slowed down (moderated) before they can be absorbed by the next fuel atom. This slowing down process is caused by collisions of the neutrons with atoms of an introduced substance called a moderator.
In the vast majority of the world's nuclear power plants, heat energy generated by fissioning uranium fuel is collected in purified water and is carried away from the reactor's core either as steam in boiling water reactors or as superheated water in pressurized-water reactors.
In a pressurized-water reactor, the high temperature water in the primary cooling loop is used to transfer heat energy to a secondary loop for the creation of steam. In either a boiling-water or pressurized-water installation, steam under high pressure is the medium used to transfer the nuclear reactor's heat energy to a turbine that mechanically turns an electric generator.
Boiling-water and pressurized-water reactors are called light water reactors, because they utilize ordinary water as the moderator. In all light water reactors to date this water is also used to transfer the heat energy from reactor to turbine in the electricity generation process. In other reactor designs the heat energy may be transferred by light water, pressurized heavy water, helium, or another cooling substance.
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