Method and device for safeguarding the discharge of residual heat from a

Abstract

A method for safeguarding discharge of residual heat from a nuclear power station reactor upon a lowered filling level in a primary circuit of a reactor cooling system, includes initially shutting down the reactor and running through an initial cooling and pressure reduction phase in the primary circuit. Then an aftercooling system is cut in for taking over heat discharge from the primary circuit, when heat discharge is no longer guaranteed by a steam generator plant. Then complete pressure relief and a lowering of the filling level in the cooling system to a mid-loop level of a main coolant conduit take place. A coolant reservoir is present for a required refilling of the primary circuit and aftercooling system. To prevent the aftercooling circuit from running dry if the filling level in the aftercooling circuit is lowered inadmissibly, the reservoir is connected to the suction-side connecting conduit through an additional safety flood conduit having a non-return valve and being opened during the lowering of the filling level, in the case of a pressureless reactor cooling system, when the filling level in the suction conduit falls. The non-return valve opens as a function of a closing force of the non-return valve and coolant flows from the reservoir into the suction conduit. The closing force of the non-return valve is increased with the reactor cooling system evacuated for coolant degassing by actuation of a pilot valve and is thereby adapted to modified pressure conditions in the evacuated cooling system.