Editing Breeder reactor (section)

== Types ==
[[File:Sasahara.svg|thumb|375px|Production of heavy transuranic actinides in current thermal-neutron fission reactors through neutron capture and decays. Starting at uranium-238, isotopes of plutonium, americium, and curium are all produced. In a fast neutron-breeder reactor, all these isotopes may be burned as fuel.]]

Many types of breeder reactor are possible:

A "breeder" is simply a [[nuclear reactor]] designed for very high [[neutron economy]] with an associated conversion rate higher than 1.0. In principle, almost any reactor design could be tweaked to become a breeder. For example, the [[light-water reactor]], a heavily moderated thermal design, evolved into the [[Reduced moderation water reactor|RMWR]] concept, using light water in a low-density [[supercritical fluid|supercritical]] form to increase the neutron economy enough to allow breeding.

Aside from water-cooled, there are many other types of breeder reactor currently envisioned as possible. These include [[Molten-salt reactor|molten-salt cooled]], [[gas-cooled fast reactor|gas cooled]], and [[liquid metal cooled reactor|liquid-metal cooled]] designs in many variations. Almost any of these basic design types may be fueled by [[uranium]], [[plutonium]], many minor [[Actinide|actinides]], or [[thorium]], and they may be designed for many different goals, such as creating more fissile fuel, long-term steady-state operation, or active burning of [[Radioactive waste|nuclear wastes]].

Extant reactor designs are sometimes divided into two broad categories based upon their neutron spectrum, which generally separates those designed to use primarily uranium and [[Transuranium element|transuranics]] from those designed to use thorium and avoid transuranics. These designs are:
* '''Fast breeder reactors''' (FBRs) which use [[Neutron temperature|'fast' (i.e. unmoderated) neutrons]] to breed fissile plutonium (and possibly higher transuranics) from fertile [[uranium-238]]. The fast spectrum is flexible enough that it can also breed fissile [[uranium-233]] from thorium, if desired.
* '''Thermal breeder reactors''' which use 'thermal-spectrum' or 'slow' (i.e. [[Neutron moderator|moderated]]) neutrons to breed fissile [[Thorium fuel cycle|uranium-233 from thorium]]. Due to the behavior of the various nuclear fuels, a thermal breeder is thought commercially feasible only with thorium fuel, which avoids the buildup of the heavier transuranics.

===Fast breeder reactor===
[[File:LMFBR schematics2.svg|thumb|right|upright=1.6|Schematic diagram showing the difference between the Loop and Pool types of LMFBR]]

All current{{When|date=May 2025}} large-scale FBR [[Nuclear power plant|power stations]] were [[liquid metal cooled reactor|liquid metal fast breeder reactors]] (LMFBR) cooled by liquid [[sodium]]. These have been of one of two designs:{{r|Waltar|page=43}}
*''Loop'' type, in which the primary coolant is circulated through primary heat exchangers outside the reactor tank (but inside the [[biological shield]] due to radioactive {{chem2|^{24}Na|link=sodium-24}} in the primary coolant)[[File:ANLWFuelConditioningFacility.jpg|thumb|upright=1.5|[[Experimental Breeder Reactor II]], which served as the prototype for the Integral Fast Reactor]]
*''Pool'' type, in which the primary heat exchangers and pumps are immersed in the reactor tank

There are only two commercially operating breeder reactors {{as of|lc=yes|2017}}: the [[BN-600 reactor]], at 560 MWe, and the [[BN-800 reactor]], at 880 MWe. Both are Russian sodium-cooled reactors. The designs use liquid metal as the primary coolant, to transfer heat from the core to steam used to power the electricity generating turbines. FBRs have been built cooled by liquid metals other than sodium—some early FBRs used [[mercury (element)|mercury]]; other experimental reactors have used a [[Sodium–potassium alloy|sodium-potassium alloy]]. Both have the advantage that they are liquids at room temperature, which is convenient for experimental rigs but less important for pilot or full-scale power stations.

Three of the proposed [[generation IV reactor]] types are FBRs:<ref>{{cite web |date=December 2002 |title=A Technology Roadmap for Generation IV Nuclear Energy Systems |url=https://www.gen-4.org/gif/upload/docs/application/pdf/2013-09/genivroadmap2002.pdf |url-status=live |archive-url=https://web.archive.org/web/20150701185916/https://www.gen-4.org/gif/upload/docs/application/pdf/2013-09/genivroadmap2002.pdf |archive-date=1 July 2015 |access-date=1 July 2015 |website=Generation IV International Forum |id=GIF-002-00}}</ref>
*[[Gas-cooled fast reactor]] cooled by [[helium]].
*[[Sodium-cooled fast reactor]] based on the existing LMFBR and [[integral fast reactor]] designs.
*[[Lead-cooled fast reactor]] based on Soviet naval propulsion units.

FBRs usually use a [[MOX fuel|mixed oxide fuel]] core of up to 20% [[Plutonium(IV) oxide|plutonium dioxide]] ({{chem2|PuO2}}) and at least 80% [[uranium dioxide]] ({{chem2|UO2}}). Another fuel option is [[nuclear fuel#Metal fuel|metal alloys]], typically a blend of uranium, plutonium, and [[zirconium]] (used because it is "transparent" to neutrons). [[Enriched uranium]] can be used on its own.

Many designs surround the [[Nuclear reactor core|reactor core]] in a blanket of tubes that contain non-fissile uranium-238, which, by capturing fast neutrons from the reaction in the core, converts to fissile [[plutonium-239]] (as is some of the uranium in the core), which is then reprocessed and used as nuclear fuel. Other FBR designs rely on the geometry of the fuel (which also contains uranium-238), arranged to attain sufficient fast neutron capture. The plutonium-239 (or the fissile uranium-235) [[Nuclear cross section|fissile cross-section]] is much smaller in a fast spectrum than in a thermal spectrum, as is the ratio between the <sup>239</sup>Pu/<sup>235</sup>U fission cross-section and the <sup>238</sup>U absorption cross-section. This increases the concentration of <sup>239</sup>Pu/<sup>235</sup>U needed to sustain a [[nuclear chain reaction|chain reaction]], as well as the ratio of breeding to fission.<ref name="Hoffman" />
On the other hand, a fast reactor needs no moderator to [[thermalisation|slow down the neutrons]] at all, taking advantage of the fast neutrons producing a greater number of neutrons per fission than slow neutrons. For this reason ordinary liquid [[water]], being a moderator and [[neutron absorber]], is an undesirable primary coolant for fast reactors. Because large amounts of water in the core are required to cool the reactor, the yield of neutrons and therefore breeding of <sup>239</sup>Pu are strongly affected. Theoretical work has been done on [[reduced moderation water reactor]]s, which may have a sufficiently fast spectrum to provide a breeding ratio slightly over 1. This would likely result in an unacceptable power derating and high costs in a liquid-water-cooled reactor, but the supercritical water coolant of the [[supercritical water reactor]] (SCWR) has sufficient heat capacity to allow adequate cooling with less water, making a fast-spectrum water-cooled reactor a practical possibility.<ref name="Superfast">{{cite conference |last=T. Nakatsuka |display-authors=etal |title=Current Status of Research and Development of Supercritical Water-Cooled Fast Reactor (Super Fast Reactor) in Japan |work=Presented at IAEA Technical Committee Meeting on SCWRs in Pisa, 5–8 July 2010}}</ref>

The type of coolants, temperatures, and fast neutron spectrum puts the fuel cladding material (normally [[Austenitic stainless steel|austenitic stainless]] or ferritic-martensitic steels) under extreme conditions. The understanding of the radiation damage, coolant interactions, stresses, and temperatures are necessary for the safe operation of any reactor core. All materials used to date in sodium-cooled fast reactors have known limits.<ref>{{cite journal |last1=Davis |first1=Thomas P. |date=2018 |title=Review of the iron-based materials applicable for the fuel and core of future Sodium Fast Reactors (SFR) |url=http://www.onr.org.uk/documents/2018/onr-rrr-088.pdf |url-status=live |journal=Office for Nuclear Regulation |archive-url=https://web.archive.org/web/20190103055935/http://www.onr.org.uk/documents/2018/onr-rrr-088.pdf |archive-date=3 January 2019 |access-date=2 January 2019}}</ref> [[Oxide dispersion-strengthened alloy]] steel is viewed as the long-term radiation resistant fuel-cladding material that can overcome the shortcomings of today's material choices.

====Integral fast reactor====

One design of fast neutron reactor, specifically conceived to address the waste disposal and plutonium issues, was the [[integral fast reactor]] (IFR, also known as an integral fast breeder reactor, although the original reactor was designed to not breed a net surplus of fissile material).<ref name="ANL">{{cite web |title=The Integral Fast Reactor |url=http://www.ne.anl.gov/About/reactors/integral-fast-reactor.shtml |url-status=live |archive-url=https://web.archive.org/web/20130917072504/http://www.ne.anl.gov/About/reactors/integral-fast-reactor.shtml |archive-date=17 September 2013 |access-date=20 May 2013 |work=Reactors Designed by Argonne National Laboratory |publisher=Argonne National Laboratory}}</ref><ref>{{cite web |title=National Policy Analysis #378: Integral Fast Reactors: Source of Safe, Abundant, Non-Polluting Power – December 2001 |url=http://www.nationalcenter.org/NPA378.html |url-status=dead |archive-url=https://web.archive.org/web/20160125131513/http://www.nationalcenter.org/NPA378.html |archive-date=25 January 2016 |access-date=13 October 2007}}</ref>

To solve the waste disposal problem, the IFR had an on-site [[electrowinning]] fuel-reprocessing unit that recycled the uranium and all the transuranics (not just plutonium) via [[electroplating]], leaving just short-[[half-life]] [[fission product]]s in the waste. Some of these fission products could later be separated for industrial or medical uses and the rest sent to a waste repository. The IFR pyroprocessing system uses molten [[cadmium]] cathodes and electrorefiners to reprocess metallic fuel directly on-site at the reactor.<ref>Hannum, W.H., Marsh, G.E., and Stanford, G.S. (2004). [http://www.gemarsh.com/wp-content/uploads/Purex&Pyro%20P&S%20Jul04.pdf PUREX and PYRO are not the same] {{Webarchive|url=https://web.archive.org/web/20220123061354/https://www.gemarsh.com/wp-content/uploads/Purex%26Pyro%20P%26S%20Jul04.pdf|date=23 January 2022}}. Physics and Society, July 2004.</ref> Such systems co-mingle all the minor actinides with both uranium and plutonium. The systems are compact and self-contained, so that no plutonium-containing material needs to be transported away from the site of the breeder reactor. Breeder reactors incorporating such technology would most likely be designed with breeding ratios very close to 1.00, so that after an initial loading of enriched uranium and/or plutonium fuel, the reactor would then be refueled only with small deliveries of [[natural uranium]]. A quantity of natural uranium equivalent to a block about the size of a milk crate delivered once per month would be all the fuel such a 1&nbsp;gigawatt reactor would need.<ref>[[University of Washington]] (2004). [http://www.evworld.com/library/energy_numbers.pdf Energy Numbers: Energy in natural processes and human consumption, some numbers] {{Webarchive|url=https://web.archive.org/web/20120915012242/http://www.evworld.com/library/energy_numbers.pdf|date=15 September 2012}}. Retrieved 16 October 2007.</ref> Such self-contained breeders are currently envisioned as the final self-contained and self-supporting ultimate goal of nuclear reactor designers.<ref name="Argonne" /><ref name="Hoffman" /> The project was canceled in 1994 by [[United States Secretary of Energy]] [[Hazel R. O'Leary|Hazel O'Leary]].<ref>{{cite web |last=Kirsch |first=Steve |title=The Integral Fast Reactor (IFR) project: Congress Q&A |url=http://www.skirsch.com/politics/ifr/QAcongressKirsch.htm |url-status=live |archive-url=https://web.archive.org/web/20121216121538/http://skirsch.com/politics/ifr/QAcongressKirsch.htm |archive-date=16 December 2012 |access-date=25 December 2012}}</ref><ref>{{cite web |last=Stanford |first=George S. |title=Comments on the Misguided Termination of the IFR Project |url=http://www.skirsch.com/politics/ifr/O%27Leary%20Problems.pdf |url-status=live |archive-url=https://web.archive.org/web/20121215072610/http://skirsch.com/politics/ifr/O%27Leary%20Problems.pdf |archive-date=15 December 2012 |access-date=25 December 2012}}</ref>

====Other fast reactors====
[[File:MSRE Core.JPG|right|thumb|The graphite core of the [[Molten Salt Reactor Experiment]]]]

The first fast reactor built and operated was the Los Alamos Plutonium Fast Reactor ("[[Clementine (nuclear reactor)|Clementine]]") in Los Alamos, NM.<ref name=":1">{{Cite journal |last1=Patenaude |first1=Hannah K. |last2=Freibert |first2=Franz J. |date=2023-07-03 |title=Oh, My Darling Clementine: A Detailed History and Data Repository of the Los Alamos Plutonium Fast Reactor |journal=Nuclear Technology |language=en |volume=209 |issue=7 |pages=963–1007 |doi=10.1080/00295450.2023.2176686 |issn=0029-5450|doi-access=free |bibcode=2023NucTe.209..963P }}</ref> Clementine was fueled by Ga-stabilized delta-phase Pu and cooled with mercury. It contained a 'window' of Th-232 in anticipation of breeding experiments, but no reports were made available regarding this feature.

Another proposed fast reactor is a fast [[molten salt reactor]], in which the molten salt's moderating properties are insignificant. This is typically achieved by replacing the light metal fluorides (e.g. LiF, {{chem2|BeF2}}) in the salt carrier with heavier metal chlorides (e.g., KCl, RbCl, {{chem2|ZrCl4}}).

Several prototype FBRs have been built, ranging in electrical output from a few light bulbs' equivalent ([[Experimental Breeder Reactor I|EBR-I]], 1951) to over 1,000&nbsp;[[MWe]]. As of 2006, the technology is not economically competitive to thermal reactor technology, but [[nuclear power in India|India]], Japan, China, South Korea, and Russia are all committing substantial research funds to further development of fast breeder reactors, anticipating that rising uranium prices will change this in the long term. Germany, in contrast, abandoned the technology due to safety concerns. The [[SNR-300]] fast breeder reactor was finished after 19 years despite cost overruns summing up to a total of {{Euro}}3.6&nbsp;billion, only to then be abandoned.<ref>Werner Meyer-Larsen: ''Der Koloß von Kalkar''. [[Der Spiegel]] 43/1981 vom 19 October 1981, S. 42–55. [[{{citation |title=Der Koloß von Kalkar |work=[[Der Spiegel]] |series=13 September}}]] (German)</ref>

===Thermal breeder reactor===
[[File:Shippingport Reactor.jpg|thumb|The Shippingport Reactor, used as a prototype light water breeder for five years beginning in August 1977]]

The [[advanced heavy-water reactor]] is one of the few proposed large-scale uses of thorium.<ref>{{cite web |title=Thorium |url=http://www.world-nuclear.org/info/inf62.html#b |url-status=live |archive-url=https://web.archive.org/web/20120419180325/http://www.world-nuclear.org/info/inf62.html#b |archive-date=19 April 2012 |access-date=14 June 2012}}</ref> India is developing this technology, motivated by substantial thorium reserves; almost a third of the world's thorium reserves are in India, which lacks significant uranium reserves.

The third and final core of the [[Shippingport Atomic Power Station]] 60&nbsp;MWe reactor was a light water thorium breeder, which began operating in 1977.<ref>{{cite web |title=Shippingport Atomic Power Station: A National Historic Mechanical Engineering Landmark |url=https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engineering%20history/landmarks/47-shippingport-nuclear-power-station.pdf |url-status=live |archive-url=https://web.archive.org/web/20071129121016/http://files.asme.org/ASMEORG/Communities/History/Landmarks/5643.pdf |archive-date=29 November 2007}}</ref> It used pellets made of [[thorium dioxide]] and uranium-233 oxide; initially, the U-233 content of the pellets was 5–6% in the seed region, 1.5–3% in the blanket region, and none in the reflector region. It operated at 236&nbsp;MWt, generating 60&nbsp;MWe, and ultimately produced over 2.1 billion kilowatt hours of electricity. After five years, the core was removed and found to contain nearly 1.4% more fissile material than when it was installed, demonstrating that breeding from thorium had occurred.<ref>{{cite web |last=Adams |first=Rod |date=October 1, 1995 |title=Light Water Breeder Reactor: Adapting A Proven System |url=https://atomicinsights.com/light-water-breeder-reactor-adapting-proven-system/ |url-status=live |archive-url=https://web.archive.org/web/20121028194257/http://atomicinsights.com/1995/10/light-water-breeder-reactor-adapting-proven-system.html |archive-date=28 October 2012 |access-date=2 October 2012}}</ref><ref>[http://www.world-nuclear.org/info/inf62.html Thorium] {{Webarchive|url=https://web.archive.org/web/20120419180325/http://www.world-nuclear.org/info/inf62.html|date=19 April 2012}} information from the [[World Nuclear Association]]</ref>

A [[liquid fluoride thorium reactor]] is also planned as a thorium thermal breeder. Liquid-fluoride reactors may have attractive features, such as inherent safety, no need to manufacture fuel rods, and possibly simpler reprocessing of the liquid fuel. This concept was first investigated at the [[Oak Ridge National Laboratory]] [[Molten-Salt Reactor Experiment]] in the 1960s. From 2012 it became the subject of renewed interest worldwide.<ref>{{cite news |last=Stenger |first=Victor |author-link=Victor J Stenger |date=12 January 2012 |title=LFTR: A Long-Term Energy Solution? |url=http://www.huffingtonpost.com/victor-stenger/lftr-a-longterm-energy-so_b_1192584.html |url-status=live |archive-url=https://web.archive.org/web/20161222022144/http://www.huffingtonpost.com/victor-stenger/lftr-a-longterm-energy-so_b_1192584.html |archive-date=22 December 2016 |access-date=30 September 2012 |work=Huffington Post}}</ref>