Reactor shutdown device

A first storage vessel sealed with liquid neutron absorber and inert gases and disposed between fuel assemblies in parallel with the axis and a second storage vessel sealed with neutron absorbers and inert gases and disposed above the first storage vessel at the outside of the reactor core region are in communication with each other. During usual operation, highly pressurized coolants intrude into a lower chamber and the inert gases in the first and the second storage vessel are compressed, to keep the balance with the coolants. When the reactor core can not be cooled due to some or other reasons, the pressure of the coolants is lowered and the internal gases are expanded. As a result, most of the neutron absorbers enter to the first storage vessel, and upon occurrence of a reactor accident, a great amount of neutron absorbers are automatically enter into the reactor core. Further, if the temperature inside of the reactor cores should elevate and the temperature of coolants should abnormally elevate, the internal gases are expanded and the neutron absorbers are flown out to the first storage vessel. Thus, reactor scram and the power suppression, upon occurrence of accidents, can be conducted reliably. (N.H.)