Infobox isotope

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isotope_name = Uranium-233
isotope_filename =
alternate_names =
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 =
decay_energy1 =
decay_mode2 =
decay_energy2 =
decay_mode3 =
decay_energy3 =
decay_mode4 =
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.

before=Plutonium-237 (α)
Neptunium-233 (β+)
Protactinium-233 "'(β-)
after=Thorium-229 "'(α)

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