Patent Number: 054992770
Section: claims

1. A liquid metal-cooled nuclear reactor comprising a containment vessel, a reactor vessel surrounded by said containment vessel with an inert gas-filled gap space therebetween, a nuclear fuel core arranged inside said reactor vessel, a heat collector cylinder surrounding said containment vessel with a space therebetween, a silo surrounding said heat collector cylinder, an air inlet duct and an air outlet duct in flow communication with atmospheric air external to said reactor, a cold air downcomer gap in flow communication with said air inlet duct and extending between said heat collector cylinder and said silo, a hot air riser gap in flow communication with said cold air downcomer gap and said air outlet duct and extending between said heat collector cylinder and said containment vessel, an inert gas inlet duct and an inert gas outlet duct in flow communication with said inert gas-filled gap space, an inert gas downcomer duct in flow communication with said inert gas inlet duct and an inert gas riser duct in flow communication with said inert gas outlet duct and with said inert gas downcomer duct, wherein said inert gas downcomer duct and said air outlet duct share a common wall made of heat conductive material for removing heat from said inert gas by heat exchange with atmospheric air, wherein said inert gas downcomer duct and said inert gas riser duct are not annular. 2. The liquid metal-cooled nuclear reactor as defined in claim 1, further comprising thermal insulation applied to at least a portion of the outer surface of said inert gas riser duct. 3. The liquid metal-cooled nuclear reactor as defined in claim 1, further comprising an electromagnetic pump and a heat exchanger arranged inside said reactor vessel, and first, second and third baffles arranged vertically in said insert gas-filled gap space, said first and second baffles, in conjunction with said reactor vessel and said containment vessel, defining a first channel for the flow of inert gas, and said second and third baffles, in conjunction with said reactor vessel and said containment vessel, defining a second channel for the flow of inert gas, said first channel being in flow communication with said inert gas outlet duct and located radially outside said heat exchanger, and said second channel being in flow communication with said inert gas inlet duct and said first channel and located radially outside said electromagnetic pump. 4. The liquid metal-cooled nuclear reactor as defined in claim 1, further comprising a stack which surrounds said air inlet duct, said air outlet duct and said inert gas downcomer duct. 5. The liquid metal-cooled nuclear reactor as defined in claim 4, wherein said inert gas downcomer duct communicates with said inert gas riser duct via a horizontal duct which penetrates said stack. 6. The liquid metal-cooled nuclear reactor as defined in claim 1, wherein said inert gas downcomer duct and said air inlet duct share a common wall. 7. A system for removing heat from a liquid metal-cooled nuclear reactor in which a reactor vessel is surrounded by a containment vessel with a fluid-filled gap space therebetween, comprising: a fluid outlet duct in flow communication with said fluid-filled gap space;  a fluid inlet duct in flow communication with said fluid-filled gap space;  a fluid riser duct in flow communication with said fluid outlet duct;  a fluid downcomer duct in flow communication with said fluid inlet duct and said fluid riser duct; and  air circulation flowpath means in flow communication with atmospheric air external to said reactor, wherein said air circulation flowpath means has a first section in heat exchange relationship with said containment vessel and a second section in heat exchange relationship with said fluid downcomer duct, whereby heat is removed from fluid in said fluid downcomer duct by heat exchange with atmospheric air in said air circulation flowpath means, wherein said fluid gas downcomer duct and said fluid riser duct are not annular. 8. The heat removal system as defined in claim 7, further comprising thermal insulation applied to at least a portion of the outer surface of said inert gas riser duct. 9. The heat removal system as defined in claim 7, further comprising a stack which surrounds said air inlet duct, said air outlet duct and said inert gas downcomer duct. 10. The heat removal system as defined in claim 9, wherein said inert gas downcomer duct communicates with said inert gas riser duct via a horizontal duct which penetrates said stack. 11. The heat removal system as defined in claim 9, wherein said stack is made of thermally insulating material. 12. The heat removal system as defined in claim 7, wherein said fluid is an inert gas. 13. In a liquid metal-cooled nuclear reactor comprising a containment vessel, a reactor vessel surrounded by said containment vessel with an inert gas-filled gap space therebetween, a nuclear fuel core arranged inside said reactor vessel, a heat collector cylinder surrounding said containment vessel with a space therebetween, a silo surrounding said heat collector cylinder, first and second air inlet ducts in flow communication with atmospheric air external to said reactor, first and second air outlet ducts in flow communication with atmospheric air external to said reactor, a cold air downcomer gap in flow communication with said first and second air inlet ducts and extending between said heat collector cylinder and said silo, a hot air riser gap in flow communication with said cold air downcomer gap and said first and second air outlet ducts and extending between said heat collector cylinder and said containment vessel, the improvement comprising first and second inert gas circulation loops in flow communication with said inert gas-filled gap space, said first inert gas circulation loop being in heat exchange relationship with said first air outlet duct and said second inert gas circulation loop being in heat exchange relationship with said second air outlet duct, and first through fourth baffles arranged vertically in said insert gas-filled gap space, said first through fourth baffles, in conjunction with said reactor vessel and said containment vessel, defining first through fourth channels for the flow of inert gas, said first and second channels being in flow communication with respective ends of said first inert gas circulation loop, and said third and fourth channels being in flow communication with respective ends of said second inert gas circulation loop. 14. The liquid metal-cooled nuclear reactor as defined in claim 13, further comprising first and second electromagnetic pumps arranged inside said reactor vessel at generally diametrally opposed first and second azimuthal positions, and first and second heat exchangers arranged inside said reactor vessel at generally diametrally opposed third and fourth azimuthal positions intermediate said first and second azimuthal positions, wherein said first and third channels are located radially outside said first and second heat exchangers respectively, and said second and fourth channels are located radially outside said first and second electromagnetic pumps. 15. The liquid metal-cooled nuclear reactor as defined in claim 13, wherein each of said first through fourth baffles extends from a highest elevation of said fluid-filled gap space to an elevation above a lowest elevation of said fluid-filled space so that inert gas may flow from one of said first through fourth channels to an adjacent one of said first through fourth channels around a bottom of a respective one of said first through fourth baffles therebetween. 16. The liquid metal-cooled nuclear reactor as defined in claim 13, wherein each of said first and second inert gas circulation loops comprises an inert gas inlet duct and an inert gas outlet duct in flow communication with said inert gas-filled gap space, an inert gas downcomer duct in flow communication with said inert gas inlet duct and an inert gas riser duct in flow communication with said inert gas outlet duct and with said inert gas downcomer duct, wherein said inert gas downcomer duct of said first inert gas circulation loop and said first air outlet duct share a common wall made of heat conductive material, and said inert gas downcomer duct of said second inert gas circulation loop and said second air outlet duct share a common wall made of heat conductive material. 17. The liquid metal-cooled nuclear reactor as defined in claim 16, further comprising a first stack which surrounds said first air inlet duct, said first air outlet duct and said inert gas downcomer duct of said first inert gas circulation loop, and a second stack which surrounds said second air inlet duct, said second air outlet duct and said inert gas downcomer duct of said second inert gas circulation loop. 18. The liquid metal-cooled nuclear reactor as defined in claim 17, wherein said inert gas downcomer duct of said first inert gas circulation loop communicates with said inert gas riser duct of said first inert gas circulation loop via a horizontal duct which penetrates said first stack. 19. The liquid metal-cooled nuclear reactor as defined in claim 16, wherein said inert gas downcomer duct of said first inert gas circulation loop and said first air inlet duct share a common wall.