Patent Number: 
Section: claims

1. A water-air combined passive feed water cooling apparatus for a nuclear reactor containment building comprising:a water-cooled heat exchanger connected to the inside of the containment building, the water-cooled heat exchanger configured to cool down main steam of a steam generator;a cooling tank located outside the containment building, the cooling tank comprising the water-cooled heat exchanger therein and configured to store cooling water at a surface level and condense the main steam generated by the steam generator;an evaporative steam pipe connected to the cooling tank and having a bottom end positioned above the surface level of the cooling water, the evaporative steam pipe configured to receive steam of the cooling water generated by the water-cooled heat exchanger in the cooling tank;an air-cooled heat exchanger positioned above the cooling tank and connected to the evaporative steam pipe and configured to cool and condense the steam flowing into the evaporative steam pipe, the air-cooled heat exchanger having an opening portion at a top end of the air-cooled heat exchanger configured to emit non-condensable gas outside of the containment building;a condensed water collecting pipe configured to refill the cooling tank with the steam condensed by the air-cooled heat exchanger, wherein the condensed water collecting pipe has a bottom end positioned below the surface level of the cooling water; andan air induction duct extending vertically along an outside surface of the containment building above the cooling tank, the duct configured to induce an air flow around the air-cooled heat exchanger positioned within the duct. 2. The apparatus of claim 1, wherein the cooling tank is a pressure vessel. 3. The apparatus of claim 1, wherein the air-cooled heat exchanger comprises a radiator receiving steam of cooling water generated in the cooling tank through the evaporative steam pipe and emitting heat outwards. 4. The apparatus of claim 3, wherein the radiator is formed of at least two vertical pipes and at least two horizontal pipes intersecting with one another. 5. The apparatus of claim 3, wherein the radiator comprises at least one pipe having an incline to allow condensed steam to flow toward the condensed water collecting pipe. 6. The apparatus of claim 5, wherein the condensed steam is allowed to flow into the vertical pipes extended from the condensed water collecting pipe due to the incline. 7. The apparatus of claim 6, wherein the condensed water collecting pipe, to prevent a backflow toward the condensed water collecting pipe, has an outlet located below an uppermost location of the water-cooled heat exchanger. 8. The apparatus of claim 1, wherein the air-cooled heat exchanger comprises at least a horizontal heat exchange condensing tube. 9. The apparatus of claim 8, wherein the horizontal heat exchange condensing tube is formed of a heat exchange tube comprising a cooling fin to increase heat emission efficiency. 10. The apparatus of claim 1, wherein the opening portion is a pipe. 11. The apparatus of claim 3, wherein the opening portion is a pipe connected to a top pipe of the radiator. 12. A water-air combined passive feed water cooling system for a nuclear reactor containment building formed of a plurality of passive feed water cooling systems each comprising:a water-cooled heat exchanger located outside the containment building and connected to the inside of the containment building and configured to cool down main steam of a steam generator;a cooling tank located outside the containment building, the cooling tank comprising the water-cooled heat exchanger therein and configured to store cooling water at a surface level and condense the main steam generated by the steam generator;an evaporative steam pipe connected to the cooling tank and having a bottom end positioned above the surface level of the cooling water, the evaporative steam pipe configured to receive steam of the cooling water generated by the water-cooled heat exchanger in the cooling tank;an air-cooled heat exchanger positioned above the cooling tank connected to the evaporative steam pipe and configured to cool and condense the steam flowing into the evaporative steam pipe, the air-cooled heat exchanger having an opening portion at a top end of the air-cooled heat exchanger configured to emit non-condensable gas outside of the containment building;a condensed water collecting pipe configured to refill the cooling tank with the steam condensed by the air-cooled heat exchanger, wherein the condensed water collecting pipe has a bottom end positioned below the surface level of the cooling water;an air induction duct formed of a hollow pipe comprising one air inlet and one air outlet, the duct extending vertically along an outside surface of the containment building above the cooling tank and configured to induce an air flow around the air-cooled heat exchanger positioned within the duct; anda cooling air blower installed inside the air induction duct and configured to forcibly generate the air flow,wherein each quadrant of the containment building is provided with one of the plurality of the passive feed water cooling systems. 13. The system of claim 12, wherein the cooling air blower is located on a top end inside the air induction duct. 14. The system of claim 12, wherein the cooling air blower is located on a bottom end inside the air induction duct. 15. The system of claim 12, wherein the cooling air blower is located in a middle inside the air induction duct. 16. The system of claim 12, wherein the cooling air blower is selectively formed in at least two selected from the top end, the bottom end, and the middle inside the air induction duct. 17. The system of claim 12, wherein the air induction duct is extended in a direction horizontal to a ground surface. 18. The system of claim 12, wherein the cooling air blower comprises:an electric-powered fan generating an air flow; anda driving unit for driving the electric-powered fan. 19. The system of claim 18, wherein the electric-powered fan comprises at least three rotors, andwherein to naturally circulate the air when the driving unit does not operate, the electric-powered fan has a total projected cross-sectional area of the rotors less than about ⅓ of a cross-sectional area of the air induction duct. 20. The system of claim 18, wherein the driving unit is formed of a motor.