a nuclear reactor in which nuclear fissions are caused by neutrons that are slowed down by a moderator

A nuclear power plant that can use only certain isotopes of uranium and the transuranic elements. Neutrons producing fission are slowed down, or moderate to relatively low energies before creating new fission reactions. Contrast with "fast reactor".

A reactor in which the fission chain reaction is sustained primarily by slow neutrons, and hence requiring a moderator (as distinct from Fast Neutron Reactor).

See nuclear reactor.

A thermal reactor has moderating materials to reduce the speed of neutrons to low velocity thermal neutrons, so that uranium-235 will be more likely to fission when it is struck by the neutrons and fewer neutrons will be captured by uranium-238. Thermal reactors are the most common type of nuclear reactor.