Editing Nuclear reactor (section)

====By coolant====
[[File:RIAN archive 450312 Treatment of interior part of reactor frame.jpg|thumb|Treatment of the interior part of a [[VVER|VVER-1000]] reactor frame at [[Atommash]] ]]
[[File:Thermal reactor diagram.png|thumb|In thermal nuclear reactors (LWRs in specific), the coolant acts as a moderator that must slow the neutrons before they can be efficiently absorbed by the fuel.]]
* 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.<ref name="IAEA_reactors_stats" />
** [[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 reactor]]s 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 <sup>235</sup>U, 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.<ref name="nuclear_energy">{{cite web |last1=Lipper |first1=Ilan |first2=Jon |last2=Stone |url=http://www.umich.edu/~gs265/society/nuclear.htm |title=Nuclear Energy and Society |publisher=University of Michigan |access-date=3 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090401172451/http://www.umich.edu/~gs265/society/nuclear.htm |archive-date=1 April 2009 }}</ref> During normal operation, pressure is controlled by the amount of steam flowing from the reactor pressure vessel to the turbine.
** [[Supercritical water reactor]] (SCWR)
*** SCWRs are a [[Generation IV reactor]] concept where the reactor is operated at supercritical pressures and water is heated to a supercritical fluid, which never undergoes a transition to steam yet behaves like saturated steam, to power a [[Steam generator (boiler)|steam generator]].
** [[Reduced moderation water reactor]] [RMWR] which use more highly enriched fuel with the fuel elements set closer together to allow a faster neutron spectrum sometimes called an [[Epithermal neutron]] Spectrum.
** Pool-type reactor can refer to unpressurized water cooled [[open pool reactor]]s,<ref>{{cite web |title=Pool Reactors 1: An Introduction – ANS / Nuclear Newswire |url=https://www.ans.org/news/article-2066/pool-reactors-1-an-introduction/ |url-status=live |archive-url=https://web.archive.org/web/20211106161715/https://www.ans.org/news/article-2066/pool-reactors-1-an-introduction/ |archive-date=6 November 2021 |access-date=6 November 2021}}</ref> but not to be confused with [[pool type LMFBR]]s which are sodium cooled
** Some reactors have been cooled by [[heavy water]] which also served as a moderator. Examples include:
***Early [[CANDU]] reactors (later ones use heavy water moderator but light water coolant)
***[[DIDO (nuclear reactor)|DIDO]] class research reactors 
* [[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 (element)|mercury]].
** [[Sodium-cooled fast reactor]]
** [[Lead-cooled fast reactor]]
* [[Gas cooled reactor]]s 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, and Japanese plants. [[Nitrogen]]<ref>{{cite journal |title=Emergency and Back-Up Cooling of Nuclear Fuel and Reactors and Fire-Extinguishing, Explosion Prevention Using Liquid Nitrogen. |journal=USPTO Patent Applications |date=2018-05-24 |volume=Document number 20180144836 }}</ref> and helium have also been used, helium being considered particularly suitable for high temperature designs. Use 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 reactor]]s (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. Other eutectic salt combinations used include [[Zirconium tetrafluoride|"ZrF<sub>4</sub>"]] with [[Sodium Fluoride|"NaF"]] and [[Lithium chloride|"LiCl"]] with [[Beryllium chloride|"BeCl<sub>2</sub>"]].
* [[Organic nuclear reactor]]s use organic fluids such as biphenyl and terphenyl as coolant rather than water.