Abstract: An emergency core cooling system for a pressurized-water reactor provides one supply of emergency water under pressure for injecting into the reactor's pressure vessel's lower plenum through a check valve, and a separate supply of emergency water under pressure for injecting into the vessel's upper plenum through a second check valve, the pressure on both supplies of emergency water being lower than the pressure of the reactor's coolant under normal reactor operating conditions. Because each plenum is separately supplied with emergency water when required, the pressures and flow rates can be designed for core cooling efficiency in the event of an accident.