U233

Uranium-233 (U-233) is a fissile isotope of uranium with 92 protons and 141 neutrons, giving it a mass of 233 atomic mass units. It is produced primarily in the thorium fuel cycle in nuclear reactors, where thorium-232 captures a neutron to become thorium-233, which beta decays to protactinium-233 and then to uranium-233.

U-233 is an alpha emitter with a long half-life of about 159,200 years. It is readily fissionable by thermal neutrons and releases roughly 200 MeV of energy per fission, comparable to the more common fissile isotopes uranium-235 and plutonium-239. In its natural decay chain, U-233 eventually becomes thorium-229. Its chemical properties are indistinguishable from other uranium isotopes, so it behaves similarly in chemical processes and reactor fuel handling.

Occurrences and handling: U-233 does not occur in usable quantities in nature and is typically produced in reactors or dedicated laboratories. It must be chemically separated and purified for use as fuel. Because it is radioactive, U-233 poses radiological hazards and requires appropriate shielding and safety measures during production, processing, and handling.

Applications and implications: The principal interest in U-233 lies in its potential as a reactor fuel for thorium-based designs, which proponents argue could leverage abundant thorium resources and offer certain waste advantages. It has been studied in experimental reactors and pilot projects, but has not achieved widespread commercial deployment.

Proliferation considerations: U-233 could, in principle, be used to make nuclear weapons. In practice, thorium-fuel cycles often yield impurities such as U-232, a strong gamma emitter, which complicates handling and weaponization and serves as a proliferation deterrent in many contexts.