What are the fission properties of uranium isotopes?

Uranium isotopes exhibit distinct nuclear properties, particularly regarding whether they can undergo fission to sustain a chain reaction. Uranium-235 is fissile in response to thermal neutrons, making it crucial for nuclear reactors and weapons. In contrast, uranium-238 is non-fissile with thermal neutrons but is fertile and fissionable by fast neutrons. Additionally, uranium-233 is a fissile isotope bred from thorium-232.

What we know

• Uranium-235 is the only isotope existing in nature to any appreciable extent that is fissile in response to thermal neutrons. [2, 4]
• Uranium-238 cannot sustain a chain reaction in a thermal-neutron reactor because inelastic scattering reduces neutron energy below the fast fission range. [3]
• Uranium-233 usually fissions on neutron absorption and is produced via the neutron irradiation of thorium-232. [5]
• Most neutron absorptions by uranium-235 induce fission, while a minority of about 15 percent result in the formation of uranium-236. [4]

Where to go next

• how it workedWhy is uranium-235 fissile while uranium-238 is not?
• what caused itHow does the thorium fuel cycle produce uranium-233?
• the bigger pictureWhat is natural uranium isotopic composition?
• a case in pointHow does uranium enrichment increase uranium-235 proportions?
• compared withHow do capture-to-fission ratios compare between uranium-233 and uranium-235?
• an unexpected connectionHow does uranium-238 decay contribute to Earth's heat and geoneutrinos?Although uranium-238 cannot sustain a thermal fission chain reaction, its radioactive decay is responsible for about 40 percent of the internal heat of the Earth and produces detectable geoneutrinos.

Sources

• [1]isotope of uranium (Wikidata Q1369686) · CC0 1.0
• [2]Isotopes of uranium · CC BY-SA 4.0
• [3]Uranium-238 · CC BY-SA 4.0
• [4]Uranium-235 · CC BY-SA 4.0
• [5]Uranium-233 · CC BY-SA 4.0