Fissiele

Fissile, also referred to as fissile material in nuclear science, describes nuclides that can undergo fission and sustain a chain reaction when absorbing a neutron, especially a slow or thermal neutron. Fissile isotopes release multiple neutrons per fission, enabling a self-sustaining process under appropriate conditions such as a moderated reactor core or a critical assembly.

Common fissile isotopes include Uranium-235, Uranium-233, and Plutonium-239, along with Plutonium-241. U-235 occurs naturally in uranium ore at about 0.7% abundance, while U-233 is bred from thorium; Pu-239 and Pu-241 are produced in reactors from U-238. Fissile materials differ from fertile materials; fertile like U-238 or Th-232 require conversion in a reactor to become fissile.

To use fissile material in reactors or weapons, the isotope concentration is controlled. Natural uranium can be used after enrichment to increase U-235; low-enriched uranium (<5% U-235) is common for commercial reactors, while highly enriched uranium (>20% U-235, including weapons-grade levels) is subject to strict controls.

In nuclear power, fissile fuel forms a core where moderated neutrons maintain the chain reaction; safety concerns include criticality risks and radiological hazards. Handling and transport require licensed facilities and safeguards; international regimes such as the IAEA regulate nonproliferation and verification.

Fissile materials are central to energy production and national security, and ongoing research aims to improve reactor safety, fuel economics, and proliferation resistance.