Editing Breeder reactor (section)

==Design==
{|class="wikitable sortable" style="text-align:center; margin-left:10px" align="right" border="1"
|+Fission probabilities of selected actinides, thermal vs. fast neutrons.<ref>{{cite web |title=Plentiful Energy: The Story of the Integral Fast Reactor |url=https://gsdm.u-tokyo.ac.jp/file/140528gps_chang.pdf |page=21 |access-date=2 March 2015 |url-status=live |archive-url=https://web.archive.org/web/20141027012652/http://gsdm.u-tokyo.ac.jp/file/140528gps_chang.pdf |archive-date=27 October 2014}}</ref><ref>{{cite web |title=Cross Section Table |url=https://wwwndc.jaea.go.jp/CN14/index.html}}</ref>
The percentages of thermal and fast fission indicate the fraction of nuclei fissioned when hit by a respective neutron. The remainder undergoes neutron capture.
|-
!Isotope !! Thermal fission<br>cross section !! Thermal<br>fission<br>% !! Fast fission<br>cross section !! Fast<br>fission<br>%
|-
|{{sort|710|Th-232}} || 53.71 microbarn || 1 n || 79.94 millibarn || 3 n
|-
|{{sort|720|U-232}} || 76.52 [[barn (unit)|barn]] || 59 || 2.063 barn || 95
|-
|{{sort|730|U-233}} || 531.3 barn || 89 || 1.908 barn || 93
|-
|{{sort|740|U-235}} || 585.1 barn || 81 || 1.218 barn || 80
|-
|{{sort|750|U-238}} || 16.8 microbarn || 1 n || 306.4 millibarn || 11
|-
|{{sort|760|Np-237}} || 20.19 millibarn || 3 n || 1.336 barn || 27
|-
|{{sort|770|Pu-238}} || 17.77 barn || 7 || 1.968 barn || 70
|-
|{{sort|780|Pu-239}} || 747.4 barn || 63 || 1.802 barn || 85
|-
|{{sort|790|Pu-240}} || 36.21 millibarn || 1 n || 1.328 barn || 55
|-
|{{sort|800|Pu-241}} || 1012 barn || 75 || 1.626 barn || 87
|-
|{{sort|810|Pu-242}} || 2.436 millibarn || 1 n || 1.151 barn || 53
|-
|{{sort|820|Am-241}} || 3.122 barn || 1 n || 1.395 barn || 21
|-
|{{sort|830|Am-242m}} || 6401 barn || 75 || 1.834 barn || 94
|-
|{{sort|840|Am-243}} || 81.58 millibarn || 1 n || 1.081 barn || 23
|-
|{{sort|850|Cm-242}} || 4.665 barn || 1 n || 1.775 barn || 10
|-
|{{sort|860|Cm-243}} || 587.4 barn || 78 || 2.432 barn || 94
|-
|{{sort|870|Cm-244}} || 1.022 barn || 4 n || 1.733 barn || 33
|-
|colspan=5|n=non-fissile
|}

=== Conversion ratio ===
One measure of a reactor's performance is the "conversion ratio", defined as the ratio of new fissile atoms produced to fissile atoms consumed. All proposed nuclear reactors except specially designed and operated actinide burners<ref name="Hoffman">{{cite web |title=Preliminary Core Design Studies for the Advanced Burner Reactor over a Wide Range of Conversion Ratios |id=ANL-AFCI-177 |website=Argonne National Laboratory |author=E. A. Hoffman |author2=W. S. Yang |author3=R. N. Hill |url=https://publications.anl.gov/anlpubs/2008/05/61507.pdf}}</ref> experience some degree of conversion. As long as there is any amount of a fertile material within the [[neutron flux]] of the reactor, some new fissile material is always created. When the conversion ratio is greater than 1, it is often called the "breeding ratio".

For example, commonly used light water reactors have a conversion ratio of approximately 0.6. [[Pressurized heavy-water reactor|Pressurized heavy-water reactors]] running on natural uranium have a conversion ratio of 0.8.<ref>{{cite web |last=Kadak |first=Prof. Andrew C. |title=Lecture 4, Fuel Depletion & Related Effects |work=Operational Reactor Safety 22.091/22.903 |publisher=Hemisphere, as referenced by MIT |page=Table 6–1, "Average Conversion or Breeding Ratios for Reference Reactor Systems" |url=http://www.learningace.com/doc/3103775/a22b70ccd4d6c2b95d5cc687c2e09c06/mit22_091s08_lec04 |access-date=24 December 2012 |url-status=dead |archive-url=https://web.archive.org/web/20151017114605/http://www.learningace.com/doc/3103775/a22b70ccd4d6c2b95d5cc687c2e09c06/mit22_091s08_lec04 |archive-date=17 October 2015}}</ref> In a breeder reactor, the conversion ratio is higher than 1. "Break-even" is achieved when the conversion ratio reaches 1.0 and the reactor produces as much fissile material as it uses.

=== Doubling time ===
The [[doubling time]] is the amount of time it would take for a breeder reactor to produce enough new fissile material to replace the original fuel and additionally produce an equivalent amount of fuel for another nuclear reactor. This was considered an important measure of breeder performance in early years, when uranium was thought to be scarce. However, since uranium is more abundant than thought in the early days of nuclear reactor development, and given the amount of plutonium available in spent reactor fuel, doubling time has become a less important metric in modern breeder-reactor design.<ref>{{cite web |title=Who is afraid of breeders? |publisher=Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India |first1=Placid |last1=Rodriguez |first2=S. M. |last2=Lee |url=http://www.iisc.ernet.in/currsci/nov251998/articles13.htm |access-date=24 December 2012 |url-status=live |archive-url=https://web.archive.org/web/20130326060136/http://www.iisc.ernet.in/currsci/nov251998/articles13.htm |archive-date=26 March 2013}}</ref><ref>{{cite news |title=Fast breeder reactor: Is advanced fuel necessary? |author=R. Prasad |location=Chennai, India |work=[[The Hindu]] |date=10 October 2002 |url=http://www.hindu.com/thehindu/seta/2002/10/10/stories/2002101000030200.htm |url-status=dead |archive-url=https://web.archive.org/web/20031205071218/http://www.hindu.com/thehindu/seta/2002/10/10/stories/2002101000030200.htm |archive-date=5 December 2003}}</ref>

=== Burnup ===
"[[Burnup]]" is a measure of how much energy has been extracted from a given mass of heavy metal in fuel, often expressed (for power reactors) in terms of gigawatt-days per ton of heavy metal. Burnup is an important factor in determining the types and abundances of isotopes produced by a fission reactor. Breeder reactors by design have high burnup compared to a conventional reactor, as breeder reactors produce more of their waste in the form of fission products, while most or all of the actinides are meant to be fissioned and destroyed.<ref>{{cite web |title=Fast Reactor Systems and Innovative Fuels for Minor Actinides Homogeneous Recycling |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/45/089/45089649.pdf |url-status=live |archive-url=https://web.archive.org/web/20161013023325/https://www.iaea.org/NuclearPower/Downloadable/Meetings/2013/2013-03-04-03-07-CF-NPTD/T8.3/T8.3.calabrese.pdf |archive-date=13 October 2016}}</ref>

In the past, breeder-reactor development focused on reactors with low breeding ratios, from 1.01 for the [[Shippingport Reactor]]<ref>Adams, R. (1995). [http://www.atomicinsights.com/oct95/LWBR_oct95.html Light Water Breeder Reactor] ({{Webarchive|url=https://web.archive.org/web/20070915175600/http://www.atomicinsights.com/oct95/LWBR_oct95.html |date=15 September 2007}}), ''Atomic Energy Insights'' '''1'''.</ref><ref>Kasten, P. R. (1998) [http://www.princeton.edu/~globsec/publications/pdf/7_3kasten.pdf Review of the Radkowsky Thorium Reactor Concept] ({{webarchive|url=https://web.archive.org/web/20090225154333/http://www.princeton.edu/~globsec/publications/pdf/7_3kasten.pdf |date=25 February 2009}}). ''Science & Global Security'' '''7''', 237–269.</ref> running on thorium fuel and cooled by conventional light water to over 1.2 for the Soviet [[BN-350 reactor|BN-350]] liquid-metal-cooled reactor.<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fasbre.html Fast Breeder Reactors] ({{Webarchive|url=https://web.archive.org/web/20060911211311/http://hyperphysics.phy-astr.gsu.edu/HBASE//nucene/fasbre.html |date=11 September 2006}}), Department of Physics & Astronomy, [[Georgia State University]]. Retrieved 16 October 2007.</ref> Theoretical models of breeders with liquid sodium coolant flowing through tubes inside fuel elements ("tube-in-shell" construction) suggest breeding ratios of at least 1.8 are possible on an industrial scale.<ref>Hiraoka, T., Sako, K., Takano, H., Ishii, T., and Sato, M. (1991). [http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5560940 A high-breeding fast reactor with fission product gas purge/tube-in-shell metallic fuel assemblies] ({{Webarchive|url=https://web.archive.org/web/20070929120507/http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5560940 |date=29 September 2007}}). ''Nuclear Technology'' '''93''', 305–329.</ref> The Soviet BR-1 test reactor achieved a breeding ratio of 2.5 under non-commercial conditions.<ref name="Korobeinikov_2014"/>

=== Reprocessing ===
Fission of the nuclear fuel in any reactor unavoidably produces neutron-absorbing [[fission products]]. The fertile material from a breeder reactor then needs to be [[nuclear reprocessing|reprocessed]] to remove those [[neutron poison]]s. This step is required to fully utilize the ability to breed as much or more fuel than is consumed. All reprocessing can present a [[nuclear proliferation|proliferation]] concern, since it can extract weapons-usable material from spent fuel.<ref name="Bari">{{cite web |title=Proliferation Risk Reduction Study ofAlternative Spent Fuel Processing |work=BNL-90264-2009-CP |publisher=Brookhaven National Laboratory |author=R. Bari |year=2009 |display-authors=etal |url=http://www.bnl.gov/isd/documents/70289.pdf |access-date=16 December 2012 |url-status=live |archive-url=https://web.archive.org/web/20130921054853/http://www.bnl.gov/isd/documents/70289.pdf |archive-date=21 September 2013}}</ref> The most common reprocessing technique, [[PUREX]], presents a particular concern since it was expressly designed to separate plutonium. Early proposals for the breeder-reactor fuel cycle posed an even greater proliferation concern because they would use PUREX to separate plutonium in a highly attractive isotopic form for use in nuclear weapons.<ref name="Bathke1">{{cite web |title=An Assessment of the Proliferation Resistance of Materials in Advanced Fuel Cycles |publisher=Department of Energy |author=C.G. Bathke |year=2008 |display-authors=etal |url=http://www.ne.doe.gov/peis/references/RM874_Bathkeetal_2008.pdf |access-date=16 December 2012 |url-status=dead |archive-url=https://web.archive.org/web/20090604220247/http://www.ne.doe.gov/peis/references/RM874_Bathkeetal_2008.pdf |archive-date=4 June 2009}}</ref><ref>{{cite web |title=An Assessment of the Proliferation Resistance of Materials in Advanced Nuclear Fuel Cycles |year=2008 |url=http://www.armscontrolcenter.com/resources/BathkeProlifResistSlidesApril08.pdf |access-date=16 December 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130921054802/http://www.armscontrolcenter.com/resources/BathkeProlifResistSlidesApril08.pdf |archive-date=21 September 2013}}</ref>

Several countries are developing reprocessing methods that do not separate the plutonium from the other actinides. For instance, the non-water-based [[pyrometallurgical]] electrowinning process, when used to reprocess fuel from an [[integral fast reactor]], leaves large amounts of radioactive actinides in the reactor fuel.<ref name="Argonne" /> More conventional water-based reprocessing systems include SANEX, UNEX, DIAMEX, COEX, and TRUEX, and proposals to combine PUREX with those and other co-processes. All these systems have moderately better proliferation resistance than PUREX, though their adoption rate is low.<ref>{{cite web |title=A New Reprocessing System Composed of PUREX and TRUEX Processes For Total Separation of Long-lived Radionuclides |first1=M. |last1=Ozawa |first2=Y. |last2=Sano |first3=K. |last3=Nomura |first4=Y. |last4=Koma |first5=M. |last5=Takanashi |url=https://www.oecd-nea.org/pt/docs/iem/mol98/session2/SIIpaper1.pdf |access-date=20 September 2013 |url-status=live |archive-url=https://web.archive.org/web/20130921054156/http://www.oecd-nea.org/pt/docs/iem/mol98/session2/SIIpaper1.pdf |archive-date=21 September 2013}}</ref><ref>{{cite web |title=Nuclear Fuel Reprocessing |first1=Michael F. |last1=Simpson |first2=Jack D. |last2=Law |publisher=Idaho National Laboratory |date=February 2010 |url=http://www.inl.gov/technicalpublications/Documents/4460757.pdf |access-date=20 September 2013 |url-status=live |archive-url=https://web.archive.org/web/20130921054442/http://www.inl.gov/technicalpublications/Documents/4460757.pdf |archive-date=21 September 2013}}</ref><ref>{{cite web |title=Proliferation Risk Reduction Study of Alternative Spent Fuel Processing |url=https://www.bnl.gov/isd/documents/70289.pdf |access-date=1 January 2017 |url-status=live |archive-url=https://web.archive.org/web/20170101161936/https://www.bnl.gov/isd/documents/70289.pdf |archive-date=1 January 2017}}</ref>

In the thorium cycle, thorium-232 breeds by converting first to protactinium-233, which then decays to uranium-233. If the protactinium remains in the reactor, small amounts of uranium-232 are also produced, which has the strong gamma emitter [[isotopes of thallium|thallium-208]] in its decay chain. Similar to uranium-fueled designs, the longer the fuel and fertile material remain in the reactor, the more of these undesirable elements build up. In the envisioned commercial [[thorium-based nuclear power|thorium reactors]], high levels of uranium-232 would be allowed to accumulate, leading to extremely high gamma-radiation doses from any uranium derived from thorium. These gamma rays complicate the safe handling of a weapon and the design of its electronics; this explains why uranium-233 has never been pursued for weapons beyond proof-of-concept demonstrations.<ref>{{cite web |title=U-232 and the Proliferation-Resistance of U-233 in Spent Fuel |work=0892-9882/01 |publisher=Science & Global Security, Volume 9 pp 1–32 |author=Kang and Von Hippel |year=2001 |url=http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf |access-date=18 December 2012 |url-status=dead |archive-url=https://web.archive.org/web/20150330020952/http://www.princeton.edu/sgs/publications/sgs/pdf/9_1kang.pdf |archive-date=30 March 2015}}</ref>

While the thorium cycle may be proliferation-resistant with regard to uranium-233 extraction from fuel (because of the presence of uranium-232), it poses a proliferation risk from an alternate route of uranium-233 extraction, which involves chemically extracting protactinium-233 and allowing it to decay to pure uranium-233 outside of the reactor. This process is an obvious chemical operation which is not required for normal operation of these reactor designs, but it could feasibly happen beyond the oversight of organizations such as the International Atomic Energy Agency (IAEA), and thus must be safeguarded against.<ref>{{cite web |title=Thorium: Proliferation warnings on nuclear 'wonder-fuel' |year=2012 |url=https://phys.org/news/2012-12-thorium-proliferation-nuclear-wonder-fuel.html |access-date=22 September 2017 |url-status=live |archive-url=https://web.archive.org/web/20170923050943/https://phys.org/news/2012-12-thorium-proliferation-nuclear-wonder-fuel.html |archive-date=23 September 2017}}</ref>