Patent Number: 
Section: claims

1. A completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant, comprising:a shield building having an outer wall and a through air inlet arranged on an upper part of the outer wall;a water tank arranged at an upper part of the shield building;a cooling water distribution plate arranged above a top of a containment within the shield building;a spray pipe arranged at an inside of the top of the shield building and having a water inlet end and a water outlet end, wherein the water inlet end is connected to a bottom of the water tank and the water outlet end is extended to be above the cooling water distribution plate; andan air deflector arranged between the shield building and the containment and having an upper end connected to an inside of the top of the shield building,wherein a smokestack is arranged on a top of the shield building with a steel-concrete composite structure,wherein the water tank is arranged around the smokestack, andwherein the shield building comprises a double-layer steel-concrete composite structure top which is a double layer structure and is formed on an upper end of a cylindrical steel-concrete composite structure, while a cylindrical steel-concrete air flow passage is formed on the double-layer steel-concrete composite structure top, and the double-layer steel-concrete composite structure top forms the water tank;wherein a ratio of a spacing between the air deflector and an inside of the containment to a spacing between the air deflector channel and an outside of the shield building is in the range of 0.15-1:1. 2. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein the double-layer steel-concrete composite structure top comprises an inner shell which is hemiellipsoid and an outer shell which is hemisphere, an opening is formed as an air flow channel at central portions of the hemiellipsoid of the inner shell and the hemisphere of the outer shell, and a cavity as the water tank is formed by the inner shell, the outer shell and the air flow channel. 3. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein the double-layer steel-concrete composite structure top comprises an inner shell which is hemiellipsoid and an outer shell which is cylinder, an opening is formed as an air flow channel at central portions of the hemiellipsoid of the inner shell and the cylinder of the outer shell, and a cavity as the water tank is formed by the inner shell, the outer shell and the air flow channel. 4. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein the double-layer steel-concrete composite structure top comprises an inner shell which is cone and an outer shell which is cylinder, an opening is formed as an air flow channel at central portions of the cone of the inner shell and the cylinder of the outer shell, and a cavity as the water tank is formed by the inner shell, the outer shell and the air flow channel. 5. The completely passive cooling system for a post-incident reactor core of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein a steel framework of the steel-concrete composite structure at the top of the shield building adopts a mesh arrangement of arched beams. 6. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein the smokestack is arranged on the steel-concrete air flow channel of the shield building, and is higher than the top of the shield building by 0-12 m. 7. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein the air deflector plate is provided with an outer border tilting outwardly by 20-60 degrees on a lower part thereof. 8. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein a lower end of the air deflector is extended to a lower part of an equipment lock gate and a personnel lock gate, a channel is provided at a position corresponding to the equipment lock gate and the personnel lock gate, and the lower end is apart from a floor by 1 m-4 m. 9. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, wherein an axis of the air inlet tilts upwardly by 50-80 degrees from an outside of the shield building. 10. The completely passive cooling system for a reactor core after an accident of a large-scale pressurized water reactor nuclear power plant according to claim 1, further comprising a plurality of through air inlets wherein two to five rows of the air inlets are provided along a circumferential direction of the shield building, a diameter of the air inlets is in range of 7-20 cm, and a center spacing is in range of 12-24 cm.