Fissiel

Fissiel is the term used in some languages for fissile material, a substance that can sustain a nuclear chain reaction. Fissile materials have a high probability of fission when struck by neutrons, including slow (thermal) neutrons, such that the neutrons released by one fission event can trigger further fissions in nearby nuclei. This self-sustaining property distinguishes fissile materials from many other fissionable substances that may fission but do not maintain a continuous chain reaction under ordinary conditions.

Common fissile isotopes include uranium-235, plutonium-239, and uranium-233. Uranium ore contains only a small percentage of U-235, and enrichment processes increase its share to levels suitable for use as reactor fuel or weapons material. Plutonium-239 is produced in reactors from uranium-238. Some materials, such as U-238, are fertile rather than fissile themselves; they can be converted into fissile isotopes (for example Pu-239) in a reactor.

Fissile materials are used primarily in nuclear reactors for power generation and in some research facilities, as well as historically in nuclear weapons. Their handling, transport, and use are tightly regulated due to proliferation and safety concerns. International controls, such as those administered by the IAEA and governed by nonproliferation agreements, aim to secure fissile materials, prevent unauthorized access, and minimize risks of accidents or misuse.

In summary, fissiel denotes fissile materials capable of sustaining a chain reaction, central to both civilian nuclear energy and broader security considerations, with strict regulatory and safety frameworks surrounding their production and use.