Components of nuclear power stations where a controlled, self-maintaining chain reaction of nuclear fission generates nuclear energy, part of which is transformed into electricity through thermal conversion. At the same time, nuclear reactors also produce large amounts of radio nuclides, which collect in the nuclear fuel from where they are removed chemically after a certain time. In research nuclear reactors the resultant heat is simply dissipated and only the high neutron flow is put to use. Depending on the type of neutrons predominantly responsible for splitting the nuclei in the nuclear reactor, one speaks of thermal, epithermal or fast reactors. In addition to this differentiation and the breakdown according to application (research, power or test reactors),

reactors are classified by the nuclear fuel used, by the working principle of the cooling system or medium for dissipating the generated heat (e. g. pressurized water reactors, boiling water reactors or gas-cooled reactors), by the generated temperatures (e.g. high-temperature reactors), by the structure (heterogeneous or homogeneous nuclear reactors) and by the moderator (light-water reactors, heavy-water reactors or graphite reactors). Breeder reactors (breeders) and converters are differentiated by the amount of new fissile material produced.