{{Short description|Neutron source used to start nuclear reactors}}
A '''Startupstartup neutron source''' is a [[neutron source]] used for stable and reliable initiation of [[nuclear chain reaction]] in [[nuclear reactor]]s, when they are loaded with fresh [[nuclear fuel]], whose [[neutron flux]] from [[spontaneous fission]] is insufficient for a reliable startup, or after prolonged shutdown periods. Neutron sources ensure a constant minimal population of neutrons in the reactor core, sufficient for a smooth startup. Without them, the reactor could suffer fast power excursions during startup from state with too few self-generated neutrons (new core or after extended shutdown).
The startup sources are typically inserted in regularly spaced positions inside the [[reactor core]], in place of some of the [[fuel rod]]s.
