page_title: Uranium-233
section_title: Fissile material
hierarchical_section_title: Uranium-233 / Fissile material
caption_attribution_description: English: A top down view of the Molten Salt Reactor Experiment.
context_page_description: 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. 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, to maintain the neutron economy.
  ²³³U usually fissions on neutron absorption, but sometimes retains the neutron, becoming uranium-234. The capture-to-fission ratio of uranium-233 is smaller than those of the other two major fissile fuels, uranium-235 and plutonium-239.
context_section_description: In 1946, the public first became informed of uranium-233 bred from thorium as "a third available source of nuclear energy and atom bombs" (in addition to uranium-235 and plutonium-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.
caption: Molten-Salt Reactor Experiment
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