Patent ID: 7245688

Claim:
A nuclear reactor plant which includes a nuclear heat source; a housing within which the heat source is housed, an inner surface of the housing being spaced from the heat source such that an annular space is defined between the heat source and the housing; and a cooling system which includes at least two cooling circuits, each of which includes a plurality of coolant chambers arranged around the heat source within the annular space; and pump means configured to pump coolant to and from the coolant chambers, each coolant chamber being defined by a generally vertical tubular wall and a top and closed bottom connected respectively to the tubular wall top and tubular wall bottom, with a coolant inlet pipe which is connected in flow communication with an outlet of the pump entering the coolant chamber through or adjacent the top extending downwardly through the coolant chamber and terminating at a discharge end and an outlet leading from the coolant chamber which is connected in flow communication with an inlet side of the pump, the volumetric capacity of the coolant chambers being sufficiently large such that, when in a passive mode, i.e. in the event of a failure of the pump means, the plant can continue to operate and the temperature of a water coolant in the coolant chambers will remain below boiling point for at least 8 hours.