Uranium-233

Infobox isotope


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isotope_name = Uranium-233
isotope_filename =
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mass_number =233
symbol =U
num_neutrons =
num_protons =
abundance =
halflife = 160,000 years
error_halflife =
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 =
spin =
excess_energy =
error1 =
binding_energy =
error2 =
decay_mode1 =
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decay_energy4 =

Uranium-233 is a fissile artificial isotope of Uranium, which has been used in a few 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, plutonium-239, and plutonium-241, and is still relatively small at all neutron energies.

Breeding uranium-233 from thorium feedstock is the long-term strategy of the nuclear power program of India, which has substantial thorium reserves. Breeding can be done in either fast reactors or thermal reactors, unlike uranium-based fuel cycles which require the superior neutron economy of a fast reactor in order to "breed", that is to produce more fissile material than is consumed. Outside of India, interest in the thorium-based fuel cycle is not great, although the world's reserves of thorium are three times those of uranium. It is also possible to use uranium-233 as the fission fuel of a nuclear weapon, although this has been done only occasionally. The United States first tested U-233 as part of a bomb core in Operation Teapot in 1955. [http://nuclearweaponarchive.org/Usa/Tests/Teapot.html] 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 (6x10E-9 versus 3x10E-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, that makes uranium-233 very dangerous to work on, and quite easy to detect.

Production of ²³³U (through the irridiation of Thorium-233) 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-) 232UThe 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) 224Rn (α, 55s, 0.54 MeV) 216Po (α, 0.15s) 212Pb (β-, 10.64h) 212Bi (α, 61s, 0.78MeV) 208Tl (β-, 3m, 2.6 MeV) 208PbThis 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 remote manipulation for fuel fabrication.

The decay chain of ²³³U itself is in the neptunium series. The radioisotope bismuth-213 is a decay product of uranium-233. 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.

Isotope|element=Uranium
lighter=Uranium-232
heavier=Uranium-234
before=Plutonium-237 (α)
Neptunium-233 (β+)
Protactinium-233 "'(β-)
after=Thorium-229 "'(α)