Pressurized-water reactor emergency core cooling system

An emergency core cooling system for a pressurized-water reactor pressure vessel containing a core and forming a lower plenum having an inlet for receiving pressurized-water coolant for upward flow through said core, and an upper plenum receiving said coolant from said core and having an outlet connection for said coolant, said system having a first means for holding a first supply of emergency water under a first pressure and for connecting this first supply through a check valve to said lower plenum, and a second means for holding a second supply of emergency water under pressure and for connecting this second supply through a second check valve to said upper plenum, said pressure of both said means being lower than the pressure of the pressurized-water coolant when said upward flow is adequate to cool said core, said check valves opening in the event said pressure of said coolant drops below said pressure of said means, so that said supplies flow into said plenum, said second means providing a flow of said second supply into said upper plenum, at a greater rate than the flow rate provided by said first means of said first supply into said lower plenum.