View source for Uranium-233

{{Short description|Fissile isotope of uranium}}
{{other uses|U-233 (disambiguation)}}
{{Use dmy dates|date=February 2020}}
{{Infobox isotope
|image = FLiBe-Solid.gif
|image_caption = An [[ampoule]] containing solidified pieces of a<br />[[FLiBe]] and [[uranium tetrafluoride|uranium-233 tetrafluoride]] mixture
|mass_number =233
|symbol =U
|num_neutrons = 141
|num_protons = 92
|halflife = 160,000 years<ref>{{cite web |title=Uranium-233 at the Hanford Nuclear Site |date=December 2002 |publisher=Washington State Department of Health, Division of Environmental Health, Office of Radiation Protection |url=http://www.doh.wa.gov/portals/1/Documents/Pubs/320-086_u233han_fs.pdf}}</ref>
|decay_product = Thorium-229
|decay_mass = 229
|decay_symbol =Th
|parent = Plutonium-237
|parent_mass = 237
|parent_symbol =Pu
|parent_decay = a
|parent2 = Neptunium-233
|parent2_mass = 233
|parent2_symbol = Np
|parent2_decay = b+
|parent3 = Protactinium-233
|parent3_mass = 233
|parent3_symbol = Pa
|parent3_decay = b-
|mass = 233.039
}}

'''Uranium-233''' ('''{{SimpleNuclide|Uranium|233}}''' or '''U-233''') is a [[fissile]] [[isotope of uranium]] that is bred from [[thorium-232]] as part of the [[thorium fuel cycle]]. Uranium-233 was investigated for use in [[nuclear weapon]]s and as a [[Nuclear fuel|reactor fuel]].<ref name="Forsburg 1999" /> It has been used successfully in experimental [[nuclear reactor]]s and has been proposed for much wider use as a [[nuclear fuel]]. It has a [[half-life]] of 160,000 years.

Uranium-233 is produced by the [[neutron]] [[irradiation]] of thorium-232. When thorium-232 absorbs a neutron, it becomes [[thorium-233]], which has a half-life of only 22&nbsp;minutes. Thorium-233 decays into [[protactinium]]-233 through [[beta decay]]. Protactinium-233 has a half-life of 27&nbsp;days and beta decays into uranium-233; some proposed [[molten salt reactor]] designs attempt to physically isolate the protactinium from further neutron capture before beta decay can occur, to maintain the [[neutron economy]] (if it misses the <sup>233</sup>U window, the next fissile target is <sup>235</sup>U, meaning a total of 4 neutrons needed to trigger fission).

<sup>233</sup>U usually fissions on [[neutron absorption]], but sometimes retains the neutron, becoming [[uranium-234]]. For both thermal neutrons and fast neutrons, the capture-to-fission ratio of uranium-233 is smaller than those of the other two major fissile fuels, [[uranium-235]] and [[plutonium-239]].<ref name=power-ratio>{{cite web |url=https://www.nuclear-power.com/nuclear-power/fission/capture-to-fission-ratio/ |title=Capture-to-fission Ratio |website=nuclear-power.com |access-date=June 26, 2024}}</ref>

==Fissile material==
[[File:MoltenSaltReactor.jpg|thumb|right|[[Molten-Salt Reactor Experiment]]]]
[[File:Shippingport Reactor.jpg|thumb|right|[[Shippingport Atomic Power Station]]]]
[[File:Thtr300 kuehlturm.jpg|thumb|right|German [[THTR-300]]]]

In 1946, the public first became informed of uranium-233 bred from thorium as "a third available source of nuclear energy and atom bombs" (in addition to [[uranium-235]] and [[plutonium-239]]), following a [[United Nations]] report and a speech by [[Glenn T. Seaborg]].<ref>{{cite news |title=Atomic Energy 'Secret' Put into Language That Public Can Understand |url=https://news.google.com/newspapers?id=4jgbAAAAIBAJ&pg=1842%2C3115323 |newspaper=[[Pittsburgh Press]] |date=29 September 1946 |access-date=18 October 2011|agency=[[United Press International|United Press]]}}</ref><ref>{{cite news |title=Third Nuclear Source Bared |agency=[[United Press International|United Press]] |url=https://news.google.com/newspapers?id=ckxBAAAAIBAJ&pg=6357%2C2252004 |newspaper=[[The Tuscaloosa News]] |date=21 October 1946 |access-date=18 October 2011}}</ref>

The United States produced, over the course of the [[Cold War]], approximately 2 metric tons of uranium-233, in varying levels of chemical and isotopic purity.<ref name="Forsburg 1999">{{cite journal |author1=C. W. Forsburg |author2=L. C. Lewis |title=Uses For Uranium-233: What Should Be Kept for Future Needs? |publisher=Oak Ridge National Laboratory |journal=Ornl-6952 |date=24 September 1999 |url=http://moltensalt.org/references/static/downloads/pdf/ORNL-6952.pdf}}</ref> These were produced at the [[Hanford Site]] and [[Savannah River Site]] in reactors that were designed for the production of plutonium-239.<ref name="Orth 1978">{{cite journal |author=Orth, D. A. |title=Savannah River Plant Thorium Processing Experience |date=1 June 1978 |journal=Nuclear Technology |volume=43 |pages=63–74 |doi=10.13182/NT79-A16175 |url=http://www.osti.gov/bridge/product.biblio.jsp?osti_id=6570656|url-access=subscription }}</ref>

==Nuclear fuel==
Uranium-233 has been used as a fuel in several different reactor types, and is proposed as a fuel for several new designs ([[Thorium fuel cycle|see thorium fuel cycle]]), all of which breed it from thorium. Uranium-233 can be bred in either [[fast reactor]]s or [[thermal reactor]]s, unlike the [[uranium-238]]-based [[nuclear fuel cycle|fuel cycles]] which require the superior [[neutron economy]] of a [[fast reactor]] in order to breed plutonium, that is, to produce more fissile material than is consumed.

The long-term strategy of the [[Nuclear power in India|nuclear power program of India]], which has substantial thorium reserves, is to move to a nuclear program breeding uranium-233 from thorium feedstock.

=== Energy released ===
The fission of one atom of uranium-233 generates 197.9 [[Electronvolt|MeV]] = 3.171·10<sup>−11</sup> J &nbsp;(i.e. 19.09&nbsp;TJ/[[mole (unit)|mol]] = 81.95 TJ/kg = 22764 MWh/kg that is 1.8 million times more than the same mass of diesel).<ref>{{cite web|url=http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html|title=Nuclear fission 4.7.1|website=kayelaby.npl.co.uk|access-date=21 April 2018}}</ref>
{| class="wikitable" style="text-align:center"
! Source !! Average energy<br />released (MeV)
|-
|colspan="2" style="background:#88F; color:#FFF;"|'''Instantaneously released energy'''
|-
|Kinetic energy of fission fragments||style="background:#DFD;" style="text-align:center"| 168.2
|-
|Kinetic energy of prompt neutrons||style="background:#DFD;" style="text-align:center"| {{0|00}}4.8
|-
|Energy carried by prompt γ-rays||style="background:#DFD;" style="text-align:center"| {{0|00}}7.7
|-
|colspan="2" style="background:#88F; color:#FFF;"|'''Energy from decaying fission products'''
|-
|Energy of β<sup>−</sup> particles||style="background:#DFD;" style="text-align:center"| {{0|00}}5.2
|-
|''Energy of anti-neutrinos''|| style="color:#AAA;" style="text-align:center"| ''{{0|00}}6.9''
|-
|Energy of delayed γ-rays ||style="background:#DFD;" style="text-align:center"| {{0|00}}5.0
|-
|style="background:#F44;color:#FFF;"|'''Sum''' ''(excluding escaping anti-neutrinos)''||style="background:#F44;color:#FFF;" style="text-align:center"| '''191.0'''
|-
|Energy released when those prompt neutrons which don't (re)produce fission are captured||style="background:#DFD;" style="text-align:center"| {{0|00}}9.1
|-
|style="background:#777;color:#FFF;"|'''Energy converted into heat in an operating thermal nuclear reactor'''||style="background:#777;color:#FFF;" style="text-align:center"| '''200.1'''
|}

==Weapon material==
[[File:Operation Teapot - MET (Military Effects Test).jpg|thumb|right|The first detonation of a nuclear bomb that included U-233, on 15 April 1955]]

As a potential weapon material, pure uranium-233 is more similar to plutonium-239 than uranium-235 in terms of source (bred vs natural), half-life and [[critical mass]] (both 4–5&nbsp;kg in beryllium-reflected sphere).<ref>{{cite book |title=Nuclear proliferation factbook |publisher=Committee on Governmental Affairs. Subcommittee on Energy, N. Proliferation., United States. Congress. House. Committee on Foreign Affairs. Subcommittee on International Economic Policy and Trade., United States. Congress. House. Committee on Foreign Affairs. Subcommittee on Arms Control, I. Security |date=1985 |page=295 |url=https://babel.hathitrust.org/cgi/pt?id=pst.000013383251&view=1up&seq=304 |access-date=29 November 2019}}</ref> Unlike reactor-bred plutonium, it has a very low [[spontaneous fission]] rate, which combined with its low critical mass made it initially attractive for compact [[Gun-type fission weapon|gun-type weapons]], such as small-diameter [[Nuclear artillery|artillery shells]].<ref name="hansen">{{cite book|last=Hansen|first=Chuck|year=2007|title=Swords of Armageddon: US Nuclear Weapons Development since 1945, Version 2|publisher=Chuckelea Publications|pages=I-262, I-270}}</ref>

A declassified 1966 memo from the US nuclear program stated that uranium-233 has been shown to be highly satisfactory as a weapons material, though it was only superior to plutonium in rare circumstances. It was claimed that if the existing weapons were based on uranium-233 instead of plutonium-239, [[Lawrence Livermore National Laboratory|Livermore]] would not be interested in switching to plutonium.<ref name="LRL Memo">{{cite journal |last1=Woods |first1=W. K. |title=LRL interest in U-233 |journal=United States |date=10 February 1966 |volume=DUN-677 |doi=10.2172/79078 |osti=79078 |url=https://digital.library.unt.edu/ark:/67531/metadc720752/}}</ref>

The co-presence of [[uranium-232]]<ref name="Intro to WMD">{{cite book |title= Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological |last= Langford |first= R. Everett |year= 2004 |publisher= [[John Wiley & Sons]] |location= [[Hoboken, New Jersey]] |isbn=0471465607 |page=85}} "The US tested a few uranium-233 bombs, but the presence of uranium-232 in the uranium-233 was a problem; the uranium-232 is a copious alpha emitter and tended to 'poison' the uranium-233 bomb by knocking stray neutrons from impurities in the bomb material, leading to possible pre-detonation. Separation of the uranium-232 from the uranium-233 proved to be very difficult and not practical. The uranium-233 bomb was never deployed since plutonium-239 was becoming plentiful."</ref> can complicate the manufacture and use of uranium-233, though the Livermore memo indicates a likelihood that this complication can be worked around.<ref name="LRL Memo" />

While it is thus possible to use uranium-233 as the fissile material of a [[nuclear weapon]], speculation<ref>{{cite book |title=High Energy Materials: Propellants, Explosives and Pyrotechnics |last=Agrawal |first=Jai Prakash |year=2010 |publisher=[[Wiley-VCH]] |isbn=978-3-527-32610-5 |pages=56–57 |url=https://books.google.com/books?id=rqZROysoS7QC&q=U233&pg=PA56 |access-date=19 March 2012}} states briefly that U233 is "thought to be a component of [[India and weapons of mass destruction|India's weapon program]] because of the availability of Thorium in abundance in India", and could be elsewhere as well.</ref> aside, there is scant publicly available information on this isotope actually having been weaponized:
* The United States detonated an experimental device in the 1955 [[Operation Teapot]] "MET" test which used a plutonium/<sup>233</sup>U [[Pit (nuclear weapon)#Composite cores and uranium pits|composite pit]]; its design was based on the plutonium/<sup>235</sup>U pit from the TX-7E, a prototype [[Mark 7 nuclear bomb]] design used in the 1951 [[Operation Buster-Jangle]] "Easy" test. Although not an outright [[Fizzle (nuclear test)|fizzle]], MET's actual yield of 22 [[kiloton]]s was sufficiently below the predicted 33 kt that the information gathered was of limited value.<ref>{{cite web
 | url= http://nuclearweaponarchive.org/Usa/Tests/Teapot.html
 | title= Operation Teapot
 | date= 15 October 1997 | work= Nuclear Weapon Archive
 | access-date= 9 December 2008}}</ref><ref>{{cite web
 | url= http://nuclearweaponarchive.org/Usa/Tests/Busterj.html
 | title= Operation Buster-Jangle
 | date= 15 October 1997 | work= Nuclear Weapon Archive
 | access-date= 18 March 2012}}</ref>
* The [[Soviet Union]] detonated its first [[hydrogen bomb]] the same year, the [[RDS-37]], which contained a fissile core of <sup>235</sup>U and <sup>233</sup>U.<ref>{{cite web|author=Stephen F. Ashley|title=Thorium and its role in the nuclear fuel cycle|url=http://www.nato-pa.int/shortcut.asp?FILE=3171|access-date=16 April 2014}} PDF page 8, citing: D. Holloway, "Soviet Thermonuclear Development", [[International Security]] 4:3 (1979–80) 192–197.</ref>
* In 1998, as part of its [[Pokhran-II]] tests, India detonated an experimental <sup>233</sup>U device of [[Nuclear weapon yield|low-yield]] (0.2 kt) called Shakti V.<ref>{{cite news |title=Forces gung-ho on N-arsenal |author=Rajat Pandit |url=http://epaper.timesofindia.com/Repository/ml.asp?Ref=VE9JTS8yMDA5LzA4LzI4I0FyMDE1MDA |archive-url=https://web.archive.org/web/20130521000616/http://epaper.timesofindia.com/Repository/ml.asp?Ref=VE9JTS8yMDA5LzA4LzI4I0FyMDE1MDA |url-status=dead |archive-date=21 May 2013 |newspaper=[[The Times of India]] |date=28 August 2009 |access-date=20 July 2012}}</ref><ref>{{cite web |url=http://nuclearweaponarchive.org/India/IndiaShakti.html |title=India's Nuclear Weapons Program – Operation Shakti: 1998 |date=30 March 2001 |access-date=21 July 2012}}</ref>

The [[B Reactor]] and others at the [[Hanford Site]] optimized for the production of [[weapons-grade]] material have been used to manufacture <sup>233</sup>U.<ref>{{cite web|url=http://www.hanfordchallenge.org/cmsAdmin/uploads/Historical_use_of_thorium_at_Hanford.pdf|title=Historical use of thorium at Hanford|website=hanfordchallenge.org|access-date=21 April 2018|archive-url=https://web.archive.org/web/20130512230612/http://www.hanfordchallenge.org/cmsAdmin/uploads/Historical_use_of_thorium_at_Hanford.pdf|archive-date=12 May 2013|url-status=dead}}</ref><ref>{{cite web|url=http://www.hanfordchallenge.org/cmsAdmin/uploads/Chronology_of_thorium_to_U-233_FOIA_Docs.pdf|title=Chronology of Important FOIA Documents: Hanford's Semi-Secret Thorium to U-233 Production Campaign|website=hanfordchallenge.org|access-date=21 April 2018|archive-url=https://web.archive.org/web/20121015222625/http://www.hanfordchallenge.org/cmsAdmin/uploads/Chronology_of_thorium_to_U-233_FOIA_Docs.pdf|archive-date=15 October 2012|url-status=dead}}</ref><ref>{{cite web|url=http://www.radioactivist.org/Q%20&%20A%20from%20GAP.pdf|title=Questions and Answers on Uranium-233 at Hanford|website=radioactivist.org|access-date=21 April 2018}}</ref><ref>{{cite web|url=http://www.clarku.edu/mtafund/prodlib/gap/round1/2001-12-19.pdf|title=Hanford Radioactivity in Salmon Spawning Grounds|website=clarku.edu|access-date=21 April 2018}}</ref>

Overall the United States is thought to have produced two tons of <sup>233</sup>U, of various levels of purity, some with <sup>232</sup>U impurity content as low as 6&nbsp;ppm.<ref name="Alvarez Managing">{{cite web |author=Robert Alvarez |title=Managing the Uranium-233 Stockpile of the United States |publisher=Science and Global Security |url=http://scienceandglobalsecurity.org/archive/sgs21alvarez.pdf}}</ref>

===<sup>232</sup>U impurity===
Production of <sup>233</sup>U (through the irradiation of [[thorium-232]]) invariably produces small amounts of [[uranium-232]] as an impurity, because of parasitic (n,2n) reactions on uranium-233 itself, or on [[protactinium-233]], or on thorium-232:
:<sup>232</sup>Th (n,γ) → <sup>233</sup>Th (β<sup>−</sup>) → <sup>233</sup>Pa (β<sup>−</sup>) → <sup>233</sup>U (n,2n) → <sup>232</sup>U
:<sup>232</sup>Th (n,γ) → <sup>233</sup>Th (β<sup>−</sup>) → <sup>233</sup>Pa (n,2n) → <sup>232</sup>Pa (β<sup>−</sup>)→ <sup>232</sup>U
:<sup>232</sup>Th (n,2n) → <sup>231</sup>Th (β<sup>−</sup>) → <sup>231</sup>Pa (n,γ) → <sup>232</sup>Pa (β<sup>−</sup>) → <sup>232</sup>U

Another channel involves neutron capture reaction on small amounts of [[thorium-230]], which is a tiny fraction of natural thorium present due to the decay of [[uranium-238]]:
:<sup>230</sup>Th (n,γ) → <sup>231</sup>Th (β<sup>−</sup>) → <sup>231</sup>Pa (n,γ) → <sup>232</sup>Pa (β<sup>−</sup>) → <sup>232</sup>U

The [[decay chain]] of <sup>232</sup>U quickly yields strong [[gamma radiation]] emitters. [[Thallium-208]] is the strongest of these, at 2.6&nbsp;MeV:
: <sup>232</sup>U (α, 68.9 y)
: <sup>228</sup>Th (α, 1.9 y)
: <sup>224</sup>Ra (α, 5.44 MeV, 3.6 d, with a γ of 0.24 MeV)
: <sup>220</sup>Rn (α, 6.29 MeV, 56 s, with a γ of 0.54 MeV)
: <sup>216</sup>Po (α, 0.15 s)
: <sup>212</sup>Pb (β<sup>−</sup>, 10.64 h)
: <sup>212</sup>Bi (α, 61 min, 0.78 MeV)
: <sup>208</sup>Tl (β<sup>−</sup>, 1.8 MeV, 3 min, with a γ of 2.6 MeV)
: <sup>208</sup>Pb (stable)
This makes manual handling in a [[glove box]] with only light shielding (as commonly done with [[plutonium]]) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from its decay products) and instead requiring complex [[remote manipulation]] for fuel fabrication.

The hazards are significant even at 5 [[parts per million]]. [[Implosion nuclear weapon]]s require <sup>232</sup>U levels below 50&nbsp;ppm (above which the <sup>233</sup>U is considered "low grade"; [[cf.]] "Standard weapon grade plutonium requires a [[Plutonium-240|<sup>240</sup>Pu]] content of no more than 6.5%." which is 65,000&nbsp;ppm, and the analogous [[Plutonium-238|<sup>238</sup>Pu]] was produced in levels of 0.5% (5,000&nbsp;ppm) or less). [[Gun-type fission weapon]]s additionally need low levels (1&nbsp;ppm range) of light impurities, to keep the neutron generation low.<ref name="Intro to WMD" /><ref>[http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html Nuclear Materials] FAQ</ref>

The production of "clean" <sup>233</sup>U, low in <sup>232</sup>U, requires a few factors: 1) obtaining a relatively pure <sup>232</sup>Th source, low in <sup>230</sup>Th (which also transmutes to <sup>232</sup>U), 2) moderating the incident neutrons to have an energy not higher that 6&nbsp;MeV (too-high energy neutrons cause the <sup>232</sup>Th (n,2n) → <sup>231</sup>Th reaction) and 3) removing the thorium sample from neutron flux before the <sup>233</sup>U concentration builds up to a too high level, in order to avoid fissioning the <sup>233</sup>U itself (which would produce energetic neutrons).<ref name="Alvarez Managing"/><ref>{{cite patent |country=US |number=4393510 |status=patent}}</ref>

The [[Molten-Salt Reactor Experiment]] (MSRE) used <sup>233</sup>U, bred in [[light water reactor]]s such as [[Indian Point Energy Center]], that was about 220&nbsp;ppm <sup>232</sup>U.<ref>{{cite web |author=SA LFTR Energy (Pty.) Ltd. |title=The Superior Design Advantages over All Other Nuclear Reactor Designs of the Liquid Fluoride Thorium Reactor (LFTR), with an Emphasis on Its Anti-Proliferation Features |publisher=The South Africa Independent LFTR Power Producer Project |url=http://twugbcn.files.wordpress.com/2010/10/lftr-and-anti-proliferation.pdf |page=10}}</ref>

== Further information ==
Thorium, from which <sup>233</sup>U is bred, is roughly three to four times more abundant in the Earth's crust than uranium.<ref>
{{cite web
|url = http://www.webelements.com/periodicity/abundance_crust/
|title = Abundance in Earth's Crust: periodicity
|publisher = WebElements.com
|access-date = 12 April 2014
|url-status = dead
|archive-url = https://web.archive.org/web/20080523082920/http://www.webelements.com/periodicity/abundance_crust/
|archive-date = 23 May 2008
|df = dmy-all
}}</ref><ref>
{{cite web
|url = http://education.jlab.org/itselemental/index.html
|title = It's Elemental&nbsp;— The Periodic Table of Elements
|publisher = Jefferson Lab
|access-date = 14 April 2007 |archive-url= https://web.archive.org/web/20070429032414/http://education.jlab.org/itselemental/index.html |archive-date= 29 April 2007 |url-status= live}}</ref>
The decay chain of <sup>233</sup>U itself is part of the [[neptunium series]], the decay chain of its grandparent <sup>237</sup>Np.

Uses for uranium-233 include the production of the medical isotopes [[actinium-225]] and [[bismuth-213]] which are among its daughters, low-mass nuclear reactors for space travel applications, use as an [[isotopic tracer]], nuclear weapons research, and reactor fuel research including the [[thorium fuel cycle]].<ref name="Forsburg 1999" />

The [[radioisotope]] [[bismuth]]-213 is a decay product of uranium-233; it has promise for the treatment of certain types of [[cancer]], including [[acute myeloid leukemia]] and cancers of the [[pancreas]], [[kidney]]s and other [[organ (anatomy)|organs]].

==See also==
* [[Breeder reactor]]
* [[Liquid fluoride thorium reactor]]

== Notes ==
{{reflist}}

{{Isotope sequence
|element=uranium
|lighter=[[uranium-232]]
|heavier=[[uranium-234]]
|before=[[plutonium-237]] '''([[alpha decay|α]])'''<br />[[neptunium-233]] '''([[positron emission|β<sup>+</sup>]])'''<br />[[protactinium-233]] '''([[beta decay|β<sup>−</sup>]])'''<nowiki/>
|after=[[thorium-229]] '''(α)'''<nowiki/>
}}

{{Isotopes of uranium}}

[[Category:Actinides]]
[[Category:Isotopes of uranium]]
[[Category:Fissile materials]]
[[Category:Special nuclear materials]]