Abstract: The cavity within a pressure vessel for a gas-cooled nuclear reactor is divided into chambers by an intermediate support floor, with the reactor core thereabove and heat-exchangers therebelow. Separate heat-exchange units are connected to separate circulators which discharge the repressurized primary gas coolant through an annular passageway along the inner surface of the pressure vessel cavity. The heat extraction system includes a separate secondary gas coolant circuit connected to each heat-exchange unit, which coolant may be heated to about 850.degree. C. at which it is suitable to provide process heat. Emergency cooling is effected by a heat dump which is connected into each secondary circuit to promptly provide low-temperature secondary gaseous coolant which then indirectly removes the reactor core heat.