Editing Thorium (section)

===Disadvantages===
The used fuel is difficult and dangerous to reprocess because many of the daughters of <sup>232</sup>Th and <sup>233</sup>U are strong gamma emitters.{{sfn|Greenwood|Earnshaw|1997|p=1259}} All <sup>233</sup>U production methods result in impurities of [[uranium-232|<sup>232</sup>U]], either from parasitic knock-out (n,2n) reactions on <sup>232</sup>Th, <sup>233</sup>Pa, or <sup>233</sup>U that result in the loss of a neutron, or from double neutron capture of <sup>230</sup>Th, an impurity in natural <sup>232</sup>Th:<ref name="Intro2WMD" />
:{{nuclide|Th|230}} + n → {{nuclide|Th|231}} + {{math|γ}} {{overunderset|→|''β''<sup>−</sup>|25.5 h}} {{nuclide|Pa|231}} ( {{overunderset|→|''α''|3.28 × 10{{su|p=4}} y}} {{nuclide|Ac|227}} )
:{{nuclide|Pa|231}} + n → {{nuclide|Pa|232}} + {{math|γ}} {{overunderset|→|''β''<sup>−</sup>|1.3 d}} {{nuclide|U|232}} {{overunderset|→|''α''|69 y}}

<sup>232</sup>U by itself is not particularly harmful, but quickly decays to produce the strong gamma emitter [[Isotopes of thallium|<sup>208</sup>Tl]]. (<sup>232</sup>Th follows the same decay chain, but its much longer half-life means that the quantities of <sup>208</sup>Tl produced are negligible.){{sfn|Stoll|2005|p=30}} These impurities of <sup>232</sup>U make <sup>233</sup>U easy to detect and dangerous to work on, and the impracticality of their separation limits the possibilities of [[nuclear proliferation]] using <sup>233</sup>U as the fissile material.<ref name="Intro2WMD">{{cite book |title= Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological |last= Langford |first= R. E. |year= 2004 |publisher= John Wiley & Sons |isbn=978-0-471-46560-7 |page=85 }}</ref> <sup>233</sup>Pa has a relatively long half-life of 27&nbsp;days and a high [[cross section (physics)|cross section]] for neutron capture. Thus it is a [[neutron poison]]: instead of rapidly decaying to the useful <sup>233</sup>U, a significant amount of <sup>233</sup>Pa converts to <sup>234</sup>U and consumes neutrons, degrading [[neutron economy|the reactor efficiency]]. To avoid this, <sup>233</sup>Pa is extracted from the active zone of thorium [[molten salt reactor]]s during their operation, so that it does not have a chance to capture a neutron and will only decay to <sup>233</sup>U.<ref name="NakajimaGroult2005">{{cite book|last1=Nakajima|first1=Ts.|last2=Groult|first2=H.|title=Fluorinated Materials for Energy Conversion|year=2005|publisher=Elsevier|isbn=978-0-08-044472-7|pages=562–565}}</ref>

The irradiation of <sup>232</sup>Th with neutrons, followed by its processing, need to be mastered before these advantages can be realised, and this requires more advanced technology than the uranium and plutonium fuel cycle;{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}} research continues in this area. Others cite the low commercial viability of the thorium fuel cycle:<ref>{{cite news|url=https://www.theguardian.com/environment/2011/jun/23/thorium-nuclear-uranium|title=Don't believe the spin on thorium being a greener nuclear option|last=Rees|first=E.|year=2011|newspaper=[[The Guardian]]|access-date=29 September 2017|archive-date=27 September 2017|archive-url=https://web.archive.org/web/20170927111531/https://www.theguardian.com/environment/2011/jun/23/thorium-nuclear-uranium|url-status=live}}</ref><ref name="SovacoolValentine2012">{{cite book|last1=Sovacool |first1=B. K. |last2=Valentine |first2=S. V. |title=The National Politics of Nuclear Power: Economics, Security, and Governance|date=2012|publisher=[[Routledge]]|isbn=978-1-136-29437-2|page=226}}</ref><ref>{{cite web |url=http://www.ne.anl.gov/pdfs/NuclearEnergyFAQ.pdf |title=Nuclear Energy FAQs |publisher=[[Argonne National Laboratory]] |year=2014 |access-date=13 January 2018 |archive-date=7 October 2014 |archive-url=https://web.archive.org/web/20141007005609/http://www.ne.anl.gov/pdfs/NuclearEnergyFAQ.pdf |url-status=live }}</ref> the international [[Nuclear Energy Agency]] predicts that the thorium cycle will never be commercially viable while uranium is available in abundance—a situation which may persist "in the coming decades".<ref name="FindlayFindlay2011">{{cite book|last=Findlay |first=T. |author-link=Trevor Findlay |title=Nuclear Energy and Global Governance: Ensuring Safety, Security and Non-proliferation|date=2011|publisher=Routledge|isbn=978-1-136-84993-0|page=9}}</ref> The isotopes produced in the thorium fuel cycle are mostly not transuranic, but some of them are still very dangerous, such as <sup>231</sup>Pa, which has a half-life of 32,760&nbsp;years and is a major contributor to the long-term [[radiotoxic]]ity of spent nuclear fuel.<ref name="NakajimaGroult2005" />