Uranium-233

Uranium-233, 233U

An ampoule containing solidified pieces of a
FLiBe and uranium-233 tetrafluoride mixture

General
Symbol| 233U
Names| uranium-233, U-233
Protons| 92
Neutrons| 141
Nuclide data
Half-life| 159,200 years[1]
Parent isotopes| 237Pu (α)
233Np (β+)
233Pa (β−)
Decay products| 229Th
Isotope mass| 233.03963[2] u
Decay modes
Decay mode| Decay energy (MeV)
Alpha| 4.909[3]
Isotopes of Chemistry:uranium
Complete table of nuclides

Uranium-233 (The element Chemistry:Uranium does not exist. 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 weapons and as a reactor fuel.[4] It has been used successfully in experimental nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 159,200 years to alpha decay and is a part of the neptunium decay chain.

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 about 22 minutes. Thorium-233 decays into protactinium-233 through beta decay. Protactinium-233 has a longer half-life of about 27 days to further decay 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 233U window, the next fissile target is 235U, meaning a total of 4 neutrons needed to trigger fission).

233U 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.[5]

## Contents

* 1 History
* 2 Nuclear fuel
* 2.1 Energy released
* 3 Weapon material
* 4 Further information
* 5 See also
* 6 Notes

## History

Molten-Salt Reactor Experiment Shippingport Atomic Power Station 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.[6][7]

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.[4] These were produced at the Hanford Site and Savannah River Site in reactors that were designed for the production of plutonium-239.[8]

## 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 (see thorium fuel cycle), all of which breed it from thorium. Uranium-233 can be bred in either fast reactors or thermal reactors, unlike the uranium-238-based 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 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 MeV = 3.171·10−11 J  (i.e. 19.09 TJ/mol = 81.95 TJ/kg = 22764 MWh/kg that is 1.8 million times more than the same mass of diesel).[9]

Source | Average energy
released (MeV)

|

Instantaneously released energy
Kinetic energy of fission fragments | 168.2
Kinetic energy of prompt neutrons | 004.8
Energy carried by prompt γ-rays | 007.7
Energy from decaying fission products
Energy of β− particles | 005.2
Energy of anti-neutrinos | 006.9
Energy of delayed γ-rays | 005.0
Sum (excluding escaping anti-neutrinos) | 191.0
Energy released when those prompt neutrons which don't (re)produce fission are captured | 009.1
Energy converted into heat in an operating thermal nuclear reactor | 200.1

## Weapon material

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 kg in beryllium-reflected sphere).[10] 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 weapons, such as small-diameter artillery shells.[11]

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, Livermore would not be interested in switching to plutonium.[12]

The co-presence of uranium-232[13] can complicate the manufacture and use of uranium-233, though the Livermore memo indicates a likelihood that this complication can be worked around.[12]

Chuck Hansen wrote in Swords of Armageddon that 233U was evaluated by the United States for its ability to substitute for supergrade plutonium in nuclear weapons. As it was deemed equivalent to plutonium rather than superior to it, military interest in 233U-based weapons waned in the late 1960s. However, several 233U-based nuclear weapons were tested by the US between 1955 and 1968.[14] The Rocky Flats Plant, which refined fissile materials for weapons production, was refining 233U until the early 1980s.[15]

While it is thus possible to use uranium-233 as the fissile material of a nuclear weapon, speculation[16] 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/233U composite pit; its design was based on the plutonium/235U 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, MET's actual yield of 22 kilotons was sufficiently below the predicted 33 kt that the information gathered was of limited value.[17]Cite error: Closing `</ref>` missing for `<ref>` tag
* In 1998, as part of its Pokhran-II tests, India detonated an experimental 233U device of low-yield (0.2 kt) called Shakti V.[18][19]

The B Reactor and others at the Hanford Site optimized for the production of weapons-grade material have been used to manufacture 233U.[20][21][22][23] The United States Atomic Energy Commission used the weapons production reactors at Hanford to breed significant quantities of 233U from thorium for use in both nuclear weapons and for civilian research.[24] Overall the United States is thought to have produced two tons of 233U, of various levels of purity, some with 232U impurity content as low as 6 ppm.[15]

The hazards are significant even at 5 parts per million. Implosion nuclear weapons require 232U levels below 50 ppm (above which the 233U is considered "low grade"; cf. "Standard weapon grade plutonium requires a 240Pu content of no more than 6.5%." which is 65,000 ppm, and the analogous 238Pu was produced in levels of 0.5% (5,000 ppm) or less). Gun-type fission weapons additionally need low levels (1 ppm range) of light impurities, to keep the neutron generation low.[13][25]

The production of "clean" 233U, low in 232U, requires a few factors: 1) obtaining a relatively pure 232Th source, low in 230Th (which also transmutes to 232U), 2) moderating the incident neutrons to have an energy not higher that 6 MeV (too-high energy neutrons cause the 232Th (n,2n) → 231Th reaction) and 3) removing the thorium sample from neutron flux before the 233U concentration builds up to a too high level, in order to avoid fissioning the 233U itself (which would produce energetic neutrons).[15][26] The Molten-Salt Reactor Experiment (MSRE) used 233U that contained 222 ppm 232U.[27]

## Further information

Thorium, from which 233U is bred, is roughly three to four times more abundant in the Earth's crust than uranium.[28][29] The decay chain of 233U itself is part of the neptunium series, the decay chain of its grandparent 237Np.

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.[4] The isotope bismuth-213 has promise for the treatment of certain types of cancer, including acute myeloid leukemia and cancers of the pancreas, kidneys and other organs. However, producing the medical isotopes from 233U practically requires separating the long-lived intermediate thorium-229; the stock of that isotope is very limited and there are no plans to increase it.

## See also

* Breeder reactor
* Liquid fluoride thorium reactor

## Notes

1. ↑ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties". Chinese Physics C 45 (3). doi:10.1088/1674-1137/abddae. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf.
2. ↑ Template:AME2020 II
3. ↑ National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/.
4. ↑ 4.0 4.1 4.2 C. W. Forsberg; L. C. Lewis (24 September 1999). "Uses For Uranium-233: What Should Be Kept for Future Needs?". Ornl-6952 (Oak Ridge National Laboratory). http://moltensalt.org/references/static/downloads/pdf/ORNL-6952.pdf.
5. ↑ "Capture-to-fission Ratio". https://www.nuclear-power.com/nuclear-power/fission/capture-to-fission-ratio/.
6. ↑ "Atomic Energy 'Secret' Put into Language That Public Can Understand". Pittsburgh Press. United Press. 29 September 1946. https://news.google.com/newspapers?id=4jgbAAAAIBAJ&pg=1842,3115323.
7. ↑ "Third Nuclear Source Bared". The Tuscaloosa News. United Press. 21 October 1946. https://news.google.com/newspapers?id=ckxBAAAAIBAJ&pg=6357,2252004.
8. ↑ Orth, D. A. (1 June 1978). "Savannah River Plant Thorium Processing Experience". Nuclear Technology 43: 63–74. doi:10.13182/NT79-A16175. http://www.osti.gov/bridge/product.biblio.jsp?osti_id=6570656.
9. ↑ "Nuclear fission 4.7.1". http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html.
10. ↑ Nuclear proliferation factbook. 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. 1985. p. 295. https://babel.hathitrust.org/cgi/pt?id=pst.000013383251&view=1up&seq=304. Retrieved 29 November 2019.
11. ↑ Hansen, Chuck (2007). Swords of Armageddon: US Nuclear Weapons Development since 1945, Version 2. Chuckelea Publications. pp. I-262, I-270.
12. ↑ 12.0 12.1 Woods, W. K. (10 February 1966). "LRL interest in U-233". United States DUN-677. doi:10.2172/79078. https://digital.library.unt.edu/ark:/67531/metadc720752/.
13. ↑ 13.0 13.1 Langford, R. Everett (2004). Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological. Hoboken, New Jersey: John Wiley & Sons. p. 85. ISBN 0471465607. "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."
14. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `SwordsV1`
15. ↑ 15.0 15.1 15.2 Robert Alvarez. "Managing the Uranium-233 Stockpile of the United States". Science and Global Security. http://scienceandglobalsecurity.org/archive/sgs21alvarez.pdf.
16. ↑ Agrawal, Jai Prakash (2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. pp. 56–57. ISBN 978-3-527-32610-5. https://books.google.com/books?id=rqZROysoS7QC&q=U233&pg=PA56. Retrieved 19 March 2012. states briefly that U233 is "thought to be a component of India's weapon program because of the availability of Thorium in abundance in India", and could be elsewhere as well.
17. ↑ "Operation Teapot". Nuclear Weapon Archive. 15 October 1997. http://nuclearweaponarchive.org/Usa/Tests/Teapot.html.
18. ↑ Rajat Pandit (28 August 2009). "Forces gung-ho on N-arsenal". The Times of India. http://epaper.timesofindia.com/Repository/ml.asp?Ref=VE9JTS8yMDA5LzA4LzI4I0FyMDE1MDA.
19. ↑ "India's Nuclear Weapons Program – Operation Shakti: 1998". 30 March 2001. http://nuclearweaponarchive.org/India/IndiaShakti.html.
20. ↑ "Historical use of thorium at Hanford". http://www.hanfordchallenge.org/cmsAdmin/uploads/Historical_use_of_thorium_at_Hanford.pdf.
21. ↑ "Chronology of Important FOIA Documents: Hanford's Semi-Secret Thorium to U-233 Production Campaign". http://www.hanfordchallenge.org/cmsAdmin/uploads/Chronology_of_thorium_to_U-233_FOIA_Docs.pdf.
22. ↑ "Questions and Answers on Uranium-233 at Hanford". http://www.radioactivist.org/Q & A from GAP.pdf.
23. ↑ "Hanford Radioactivity in Salmon Spawning Grounds". http://www.clarku.edu/mtafund/prodlib/gap/round1/2001-12-19.pdf.
24. ↑ Moment, R.; Gibbs, F.; Freiboth, C. (1999-04-01). ﻿History of Uranium-233 Processing at the Rocky Flats Plant﻿ (Report). ICF Kaiser. https://sgp.fas.org/othergov/doe/lanl/osti/769018.pdf. Retrieved 2025-02-11.
25. ↑ Sublette, Carey. "Section 6.0 Nuclear Materials". https://nuclearweaponarchive.org/Nwfaq/Nfaq6.html.
26. ↑ US patent 4393510
27. ↑ Chandler, J. M.; Bolt, S. E. (1970). "Uranium-233-Bearing Salt Preparation for the Molten Salt Reactor Experiment". Nuclear Applications and Technology 9 (6): 807-813. doi:10.13182/NT70-A28712.
28. ↑ "Abundance in Earth's Crust: periodicity". WebElements.com. http://www.webelements.com/periodicity/abundance_crust/.
29. ↑ "It's Elemental — The Periodic Table of Elements". Jefferson Lab. http://education.jlab.org/itselemental/index.html.

Lighter:
uranium-232 | Uranium-233 is an
isotope of uranium | Heavier:
uranium-234

|
|

Decay product of:
plutonium-237 (α)
neptunium-233 (β+)
protactinium-233 (β−) | Decay chain
of uranium-233  | Decays to:
thorium-229 (α)

* v
* t
* e

Main isotopes of uranium

* 232U
* 233U
* 234U
* 235U
* 236U
* 238U

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