Uranium-233

For other uses, see U-233 (disambiguation).

Uranium-233 Full table
General
Name, symbol	Uranium-233,233U
Neutrons	141
Protons	92
Nuclide data
Half-life	160,000 years
Parent isotopes	237Pu (α) 233Np (β+) 233Pa (β−)
Decay products	229Th

Uranium-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; however, it was never deployed in nuclear weapons or used commercially as a nuclear fuel. 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 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 minutes. Thorium-233 decays into protactinium-233 through beta decay. Protactinium-233 has a half-life of 27 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.

²³³U usually fissions on neutron absorption but sometimes retains the neutron, becoming uranium-234, although the proportion of nonfissions is smaller than for the other common fission fuels, uranium-235 and plutonium-239, as well as plutonium-241. It is slightly smaller at all neutron energies.

Fissile material

Ampoule containing solid chunks of FLiBe with uranium-233 tetrafluoride

Molten-Salt Reactor Experiment

Shippingport Atomic Power Station

German THTR-300

In 1946 the public first became informed of U-233 bred from Thorium as "a third available source of nuclear energy and atom bombs" (in addition to U-235 and Pu-239), following a United Nations report and a speech by Glenn T. Seaborg.

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. These were produced at the Hanford Site and Savannah River Site in reactors that were designed for the production of plutonium-239. Historical production costs, estimated from the costs of plutonium production, were $2-4 million / kg. There are few reactors remaining in the world with significant capabilities to produce more uranium-233.

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 breed the Uranium-233 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.

Flibe Energy, a US company founded by former NASA engineer Kirk Sorensen, has announced that it intends to develop small modular Uranium-233 reactors based on liquid fluoride thorium reactor (LFTR) technology, initially for military applications.

Energy released

The fission of one atom of U-233 generates 197.9 MeV = 3.171 × 10⁻¹¹ J, i.e. 19.09 TJ/mol = 81.95 TJ/kg.

Source	Average energy released (MeV)
Instantaneously released energy
Kinetic energy of fission fragments	168.2
Kinetic energy of prompt neutrons	4.9
Energy carried by prompt γ-rays	7.7
Energy from decaying fission products
Energy of β−-particles	5.2
Energy of anti-neutrinos	6.9
Energy of delayed γ-rays	5.0
Sum	197.9
Energy released when those prompt neutrons which don't (re)produce fission are captured	9.1
Energy converted into heat in an operating thermal nuclear reactor	200.1

Weapon material

The first detonation of a nuclear bomb including U-233, on 15 April 1955.

While it is possible to use uranium-233 as the fission fuel of a nuclear weapon, this has been done only occasionally in experimental devices. The United States first tested U-233 along with plutonium as part of a bomb core in Operation Teapot in 1955. Although not an outright fizzle, this experimental plutonium/U-233 device based on the plutonium/U-235 Buster Easy design was a failure, yielding only 22 kt against a predicted yield of 33 kt.

As a weapon material, uranium-233 compares roughly to plutonium-239: its radioactivity is only one seventh (159,200 years half-life versus 24,100 years), but its bare critical mass is 60% higher (16 kg versus 10 kg), and its spontaneous fission rate is twenty times higher (6×10E−9 versus 3×10E−10) — but since the radioactivity is lower, the neutron density is only three times higher. A nuclear explosive device based on uranium-233 is therefore more of a technical challenge than with plutonium, but the technological level involved is roughly the same. The main difference is the co-presence of uranium-232 which makes uranium-233 very dangerous to work on, and quite easy to detect.

U-232 impurity

Production of ²³³U (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:

²³²Th (n,γ) ²³³Th (β−) ²³³Pa (β−) ²³³U (n,2n) ²³²U

²³²Th (n,γ) ²³³Th (β−) ²³³Pa (n,2n) ²³²Pa (β−) ²³²U

The decay chain of ²³²U quickly yields strong gamma radiation emitters:

²³²U (α, 72 years)

²²⁸Th (α, 1.9 year)

²²⁴Ra (α, 3.6 day, 0.24 MeV)

²²⁰Rn (α, 55 s, 0.54 MeV)

²¹⁶Po (α, 0.15 s)

²¹²Pb (β−, 10.64 h)

²¹²Bi (α, 61 s, 0.78 MeV)

²⁰⁸Tl (β−, 3 m, 2.6 MeV)

²⁰⁸Pb (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 thorium-228, radium-224, radon-220, and polonium) and instead requiring complex remote manipulation for fuel fabrication.

Further information

Thorium, from which U-233 is bred, is roughly three times more common than uranium.

The decay chain of ²³³U itself is in the neptunium series.

Uses for uranium-233 include the production of medical isotopes actinium-225 and bismuth-213, low-mass nuclear reactors for space travel applications, use as an isotopic tracer, use in nuclear weapons research, and reactor fuel research including the thorium fuel cycle.

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, kidneys and other organs.

Notes

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)