Gas-cooled high temperature nuclear reactors

In a gas-cooled, graphite-moderated high temperature nuclear reactor comprising a pressure vessel, a reactor core comprising fuel elements in said pressure vessel, graphite components in said pressure vessel, and a primary coolant gas circuit including a steam generator and coolant gas blowers, the improvement wherein said steam generator is disposed outside said pressure vessel and said steam generator includes a heat exchanger and means mounting said heat exchanger with at least a portion of said heat exchanger located at a level above the level of said reactor core, said primary coolant gas circuit including flow passage means for conveying the primary coolant gas between the reactor core and the heat exchanger, said flow passage means including a first flow passage located below the lower end of said reactor and below the lower end of said heat exchanger for conveying the hot coolant gases from the lower end of said reactor core to the lower end of said heat exchanger, an upwardly extending second flow passage connected at the lower end thereof to said first flow passage and containing at least a portion of said heat exchanger for conducting the hot coolant gases from said reactor core upwardly over said heat exchanger to the upper end of the passage located above the top of the reactor core with the upper end of the heat exchanger in said second flow passage located above the upper end of the reactor core, an upwardly arranged third flow passage for receiving the coolant gas after its passage through said second flow passage for conveying the coolant gas downwardly to a location below said heat exchanger and below the lower end of said core, and a fourth flow passageway for conveying the coolant gas to below the lower end of said reactor core;

• and a fifth flow passage located around said reactor core and connected at its lower end to said fourth flow passage for conveying the coolant gas upwardly to a location above said reactor core and for introducing the coolant gas into the reactor core for downward flow therethrough, said flow passage means arranged to generate a natural convection flow from said reactor core to said heat exchanger and back to said reactor core and for avoiding the reversal of flow direction and ensuring a sufficient cooling gas flow after reactor core shutdown or failure of the blowers.