Editing Breeder reactor (section)

=== 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>