Editing Nuclear reactor (section)

===Current technologies===
{{unreferenced section|date=June 2015}}
[[File:Diablo canyon nuclear power plant.jpg|thumb|[[Diablo Canyon Power Plant|Diablo Canyon]] – a PWR]]
* [[Pressurized water reactor]]s (PWR) [moderator: high-pressure water; coolant: high-pressure water]

:: These reactors use a pressure vessel to contain the nuclear fuel, control rods, moderator, and coolant. The hot radioactive water that leaves the pressure vessel is looped through a steam generator, which in turn heats a secondary (nonradioactive) loop of water to steam that can run turbines. They represent the majority (around 80%) of current reactors. This is a [[thermal neutron]] reactor design, the newest of which are the Russian [[VVER-1200]], Japanese [[Advanced Pressurized Water Reactor]], American [[AP1000]], Chinese [[Hualong One|Hualong Pressurized Reactor]] and the Franco-German [[European Pressurized Reactor]]. All the [[United States Naval reactor]]s are of this type.
* [[Boiling water reactor]]s (BWR) [moderator: low-pressure water; coolant: low-pressure water]

:: A BWR is like a PWR without the steam generator. The lower pressure of its cooling water allows it to boil inside the pressure vessel, producing the steam that runs the turbines. Unlike a PWR, there is no primary and secondary loop. The [[thermal efficiency]] of these reactors can be higher, and they can be simpler, and even potentially more stable and safe. This is a thermal-neutron reactor design, the newest of which are the [[Advanced Boiling Water Reactor]] and the [[Economic Simplified Boiling Water Reactor]].
[[File:CANDU at Qinshan.jpg|thumb|The [[CANDU]] [[Qinshan Nuclear Power Plant]]]]
* [[Pressurised heavy water reactor|Pressurized Heavy Water Reactor]] (PHWR) [moderator: high-pressure heavy water; coolant: high-pressure heavy water]

:: A Canadian design (known as [[CANDU]]), very similar to PWRs but using [[heavy water]]. While heavy water is significantly more expensive than ordinary water, it has greater [[neutron economy]] (creates a higher number of thermal neutrons), allowing the reactor to operate without [[Isotope separation|fuel enrichment facilities]]. Instead of using a single large pressure vessel as in a PWR, the fuel is contained in hundreds of pressure tubes. These reactors are fueled with natural [[uranium]] and are thermal-neutron reactor designs. PHWRs can be refueled while at full power, ([[online refueling]]) which makes them very efficient in their use of uranium (it allows for precise flux control in the core). CANDU PHWRs have been built in Canada, [[Argentina]], China, [[India]], [[Pakistan]], [[Romania]], and [[South Korea]]. India also operates a number of PHWRs, often termed 'CANDU derivatives', built after the Government of Canada halted nuclear dealings with India following the 1974 [[Smiling Buddha]] nuclear weapon test.
:[[File:Elektrownia Ignalina.jpg|thumb|The [[Ignalina Nuclear Power Plant]] – a RBMK type (closed 2009)]]
* Reaktor Bolshoy Moschnosti Kanalniy (High Power Channel Reactor) ([[RBMK]]) (also known as a Light-Water Graphite-moderated Reactor—LWGR) [moderator: graphite; coolant: high-pressure water]

:: A Soviet design, RBMKs are in some respects similar to CANDU in that they can be refueled during power operation and employ a pressure tube design instead of a PWR-style pressure vessel. However, unlike CANDU they are unstable and large, making [[containment building]]s for them expensive. A series of critical safety flaws have also been identified with the RBMK design, though some of these were corrected following the [[Chernobyl disaster]]. Their main attraction is their use of light water and unenriched uranium. As of 2024, 7 remain open, mostly due to safety improvements and help from international safety agencies such as the U.S. Department of Energy. Despite these safety improvements, RBMK reactors are still considered one of the most dangerous reactor designs in use. RBMK reactors were deployed only in the former [[Soviet Union]].
[[File:Sizewell A.jpg|thumb|The [[Magnox]] [[Sizewell A]] nuclear power station]]
[[File:Torness Nuclear Power Station, Scotland.JPG|thumb|The [[Torness nuclear power station]] – an AGR]]
* [[Gas-cooled reactor]] (GCR) and [[advanced gas-cooled reactor]] (AGR) [moderator: graphite; coolant: carbon dioxide]

:: These designs have a high thermal efficiency compared with PWRs due to higher operating temperatures. There are a number of operating reactors of this design, mostly in the United Kingdom, where the concept was developed. Older designs (i.e. [[Magnox]] stations) are either shut down or will be in the near future. However, the AGRs have an anticipated life of a further 10 to 20&nbsp;years. This is a thermal-neutron reactor design. Decommissioning costs can be high due to the large volume of the reactor core.
* [[Breeder reactor|Liquid metal]] [[Fast breeder reactor#Fast breeder reactor|fast-breeder reactor]] (LMFBR) [moderator: none; coolant: liquid metal]
[[File:Topaz nuclear reactor.jpg|thumb|right|Scaled-down model of [[TOPAZ nuclear reactor]]]]

:: This totally unmoderated reactor design produces more fuel than it consumes. They are said to "breed" fuel, because they produce fissionable fuel during operation because of [[neutron capture]]. These reactors can function much like a PWR in terms of efficiency, and do not require much high-pressure containment, as the liquid metal does not need to be kept at high pressure, even at very high temperatures. These reactors are [[fast neutron]], not thermal neutron designs. These reactors come in two types:

[[File:Superphénix.jpg|thumb|The [[Superphénix]], closed in 1998, was one of the few FBRs.]]

:::[[Lead-cooled fast reactor|Lead-cooled]]
:::: Using lead as the liquid metal provides excellent radiation shielding, and allows for operation at very high temperatures. Also, lead is (mostly) transparent to neutrons, so fewer neutrons are lost in the coolant, and the coolant does not become radioactive. Unlike sodium, lead is mostly inert, so there is less risk of explosion or accident, but such large quantities of lead may be problematic from toxicology and disposal points of view. Often a reactor of this type would use a [[lead-bismuth eutectic]] mixture. In this case, the bismuth would present some minor radiation problems, as it is not quite as transparent to neutrons, and can be transmuted to a radioactive isotope more readily than lead. The Russian [[Alfa class submarine]] uses a lead-bismuth-cooled fast reactor as its main power plant.
::: [[Sodium-cooled fast reactor|Sodium-cooled]]
:::: Most LMFBRs are of this type. The [[TOPAZ nuclear reactor|TOPAZ]], [[BN-350]] and [[BN-600]] in USSR; [[Superphénix]] in France; and [[Enrico Fermi Nuclear Generating Station|Fermi-I]] in the United States were reactors of this type. The sodium is relatively easy to obtain and work with, and it also manages to actually prevent corrosion on the various reactor parts immersed in it. However, sodium explodes violently when exposed to water, so care must be taken, but such explosions would not be more violent than (for example) a leak of superheated fluid from a pressurized-water reactor. The [[Monju Nuclear Power Plant|Monju reactor]] in Japan suffered a sodium leak in 1995 and could not be [[Monju Nuclear Power Plant#2010 Restart|restarted]] until May 2010. The [[EBR-I]], the first reactor to have a core meltdown, in 1955, was also a sodium-cooled reactor. 
* [[Pebble-bed reactor]]s (PBR) [moderator: graphite; coolant: helium]
:: These use fuel molded into ceramic balls, and then circulate gas through the balls. The result is an efficient, low-maintenance, very safe reactor with inexpensive, standardized fuel. The prototypes were the [[AVR reactor|AVR]] and the [[THTR-300]] in Germany, which produced up to 308MW of electricity between 1985 and 1989 until it was shut down after experiencing a series of incidents and technical difficulties. The [[HTR-10]] is operating in China, where the [[HTR-PM]] is being developed. The HTR-PM is expected to be the first generation IV reactor to enter operation.<ref name="WNN2018">{{cite news|url=https://www.neimagazine.com/features/featurehtr-pm-making-dreams-come-true-7009889/|title=HTR-PM: Making dreams come true|work=Nuclear Engineering International|access-date=12 December 2019|archive-date=28 March 2022|archive-url=https://web.archive.org/web/20220328064002/https://www.neimagazine.com/features/featurehtr-pm-making-dreams-come-true-7009889/|url-status=dead}}</ref>
* [[Molten-salt reactor]]s (MSR) [moderator: graphite, or none for fast spectrum MSRs; coolant: molten salt mixture]
::These dissolve the fuels in [[fluoride]] or [[chloride]] salts, or use such salts for coolant. MSRs potentially have many safety features, including the absence of high pressures or highly flammable components in the core. They were initially designed for aircraft propulsion due to their high efficiency and high power density. One prototype, the [[Molten-Salt Reactor Experiment]], was built to confirm the feasibility of the [[Liquid fluoride thorium reactor]], a thermal spectrum reactor which would breed fissile uranium-233 fuel from thorium.
* [[Aqueous homogeneous reactor]] (AHR) [moderator: high-pressure light or heavy water; coolant: high-pressure light or heavy water]

:: These reactors use as fuel soluble nuclear salts (usually [[uranium sulfate]] or [[uranium nitrate]]) dissolved in water and mixed with the coolant and the moderator. As of April 2006, only five AHRs were in operation.<ref>{{cite web|url=https://nucleus.iaea.org/RRDB/RR/ReactorSearch.aspx|title=RRDB Search|website=nucleus.iaea.org|access-date=6 January 2019|archive-date=12 May 2019|archive-url=https://web.archive.org/web/20190512142147/https://nucleus.iaea.org/RRDB/RR/ReactorSearch.aspx|url-status=live}}</ref>