Uranium233

Uranium-233 (U-233) is a fissile isotope of uranium that does not occur in meaningful quantities in nature. It is produced in nuclear reactors or accelerator-driven systems by irradiating thorium-232 with neutrons. Th-232 captures a neutron to become Th-233, which beta decays to protactinium-233 and then to U-233.

The short-lived intermediates Th-233 (t1/2 about 22 minutes) and Pa-233 (t1/2 about 27 days) decay to U-233, which has a long half-life of about 159,200 years. U-233 is fissile with thermal neutrons and has a fission cross section comparable to that of other common fissile materials, making it attractive for certain reactor designs.

It has been studied as a fuel in thorium-based nuclear fuel cycles, including molten salt reactors and some light- and heavy-water reactor concepts. The thorium cycle uses abundant Th-232 to breed U-233, which then sustains fission and energy production. Despite research interest, widespread commercial use has been limited by proliferation concerns, economics, and the availability of uranium-based fuels.

Handling and use of U-233 are constrained by safety and regulatory considerations. It is highly radioactive and chemically reactive; production often yields trace U-232, whose decay products emit strong gamma radiation. This gamma hazard complicates processing, shielding, and safeguards, influencing licensing, transport, and potential weaponization risks despite U-233's proliferation-resistant aspects when heavily contaminated with U-232.

See also: Thorium fuel cycle, Thorium, Nuclear fuel cycle.