page_title: Nuclear reactor
section_title: By coolant
hierarchical_section_title: Nuclear reactor / Reactor types / Classifications / By coolant
caption_attribution_description: English: “Treatment of interior part of reactor frame”. Atommash Volga-Don Association of Enterprises for Nuclear Power Engineering and Industry. Treatment of the interior part of a reactor frame. Русский: «Обработка внутренней части корпуса реактора». Волгодонское производственное объединение атомного энергетического машиностроения "Атоммаш". Обработка внутренней части корпуса реактора. Россия, Волгодонск, Ростовская область
context_page_description: A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a self-sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. As of early 2019, the IAEA reports there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world.
context_section_description: Water cooled reactor. These constitute the great majority of operational nuclear reactors: as of 2014, 93% of the world's nuclear reactors are water cooled, providing about 95% of the world's total nuclear generation capacity.
  Pressurized water reactor (PWR) Pressurized water reactors constitute the large majority of all Western nuclear power plants.
  A primary characteristic of PWRs is a pressurizer, a specialized pressure vessel. Most commercial PWRs and naval reactors use pressurizers. During normal operation, a pressurizer is partially filled with water, and a steam bubble is maintained above it by heating the water with submerged heaters. During normal operation, the pressurizer is connected to the primary reactor pressure vessel (RPV) and the pressurizer "bubble" provides an expansion space for changes in water volume in the reactor. This arrangement also provides a means of pressure control for the reactor by increasing or decreasing the steam pressure in the pressurizer using the pressurizer heaters.
  Pressurized heavy water reactors are a subset of pressurized water reactors, sharing the use of a pressurized, isolated heat transport loop, but using heavy water as coolant and moderator for the greater neutron economies it offers.
  Boiling water reactor (BWR)
  BWRs are characterized by boiling water around the fuel rods in the lower portion of a primary reactor pressure vessel. A boiling water reactor uses ²³⁵U, enriched as uranium dioxide, as its fuel. The fuel is assembled into rods housed in a steel vessel that is submerged in water. The nuclear fission causes the water to boil, generating steam. This steam flows through pipes into turbines. The turbines are driven by the steam, and this process generates electricity. During normal operation, pressure is controlled by the amount of steam flowing from the reactor pressure vessel to the turbine.
  Pool-type reactor
  Liquid metal cooled reactor. Since water is a moderator, it cannot be used as a coolant in a fast reactor. Liquid metal coolants have included sodium, NaK, lead, lead-bismuth eutectic, and in early reactors, mercury.
  Sodium-cooled fast reactor
  Lead-cooled fast reactor
  Gas cooled reactors are cooled by a circulating gas.  In commercial nuclear power plants carbon dioxide has usually been used, for example in current British AGR nuclear power plants and formerly in a number of first generation British, French, Italian, & Japanese plants.   Nitrogen and helium  have also been used, helium being considered particularly suitable for high temperature designs.   Utilization of the heat varies, depending on the reactor.  Commercial nuclear power plants run the gas through a heat exchanger to make steam for a steam turbine.  Some experimental designs run hot enough that the gas can directly power a gas turbine.
  Molten salt reactors (MSRs) are cooled by circulating a molten salt, typically a eutectic mixture of fluoride salts, such as FLiBe. In a typical MSR, the coolant is also used as a matrix in which the fissile material is dissolved.
caption: Treatment of the interior part of a VVER-1000 reactor frame on Atommash.
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