CONTAINMENT HEAT REMOVAL SYSTEM

A gravity driven cooling system pool (34) is disposed at an elevated location with respect to the locations of nuclear fuel rods in a pressure vessel (12) in a containment (14). In the event of a loss of coolant in the pressure vessel, steam pressure is initially reduced by venting (20) the steam into the containment or a closed suppression pool (28) containing a quantity of water (24) under a large air space (26). The suppression pool condenses sufficient steam to lower the steam pressure in the pressure vessel so that water can flow by gravity from gravity driven cooling system pool to flood the fuel rods in the pressure vessel. An isolation condenser (40) is submerged in a large supply of water (50) elevated with respect to pressure vessel. Steam is admitted to the isolation condenser, or heat exchanger, where it is cooled by boiling the water surrounding it. This steam is vented to the atmosphere. A depressurization valve (32) vents steam from the pressure vessel into the containment to aid pressure reduction, and thus to aid the gravity flow of coolant. Later, as the pressure in the pressure vessel is reduced by heat removal in the isolation condenser, steam in the containment is permitted to flow from the containment, through the depressurization valve (32) and thence to the isolation condenser, or heat exchanger.