Patent Number: 
Section: claims

1. A passive reactor cavity cooling system, comprising:a reactor cavity formed between a reactor vessel and a containment structure enclosing the reactor vessel; a first cooling system to control external air to sequentially pass through an air falling pipe and an air rising pipe provided in the reactor cavity, so that residual heat of a core transferred to the reactor cavity is discharged to an atmosphere or removed;a second cooling system having a water cooling pipe disposed in an inner space of the containment structure or in a wall of the containment structure to discharge the residual heat of the core transferred to the reactor cavity to outside the atmosphere or removed; anda functional conductor having an insulating property in a normal operation temperature range of a reactor and a heat transfer property in an accident occurrence temperature range of the reactor which is a higher temperature environment than the normal operation temperature range, wherein the air falling pipe and the water cooling pipe are disposed behind the air rising pipe with respect to a direction viewed from the reactor vessel, and the functional conductor is disposed between the air falling pipe and the air rising pipe,wherein the functional conductor comprises:a first plate disposed close to the air rising pipe;a second plate disposed close to the air falling pipe, wherein the first plate and the second plate are disposed to face each other at spaced positions, so that a fluid is filled between the first plate and the second plate;lattices disposed between the first plate and the second plate, and wherein a space to be filled with the fluid is formed by the first plate, the second plate, and the lattices; andwherein the first plate, the second plate, the fluid, and the lattices form a unit structure of the functional conductor, and the functional conductor is formed by an assembly of the unit structures, thereby the plurality of plates is sequentially disposed and spaced apart from one another in a manner of interposing the lattices therebetween, and the fluid is filled between the plurality of plates. 2. The system of claim 1, further comprising a water tank provided outside the containment structure, wherein the water cooling pipe comprises:a water falling part connected to the water tank; and a water rising part extending along an inner space of the air falling pipe or along inside of the wall of the containment structure, wherein the water falling part and the water rising part are connected through the containment structure. 3. The system of claim 1, wherein the first cooling system is formed along an inner circumferential surface of the containment structure and surrounds the reactor vessel at a position spaced apart from the reactor vessel. 4. The system of claim 1, wherein the reactor cavity is cooled by the first cooling system in a normal operation temperature range of the reactor, and wherein the reactor cavity is cooled by the second cooling system when a function of the first cooling system is lost in an accident occurrence temperature range of the reactor. 5. The system of claim 1, further comprising a water tank provided outside the containment structure, wherein the water cooling pipe is connected to a lower portion of the water tank. 6. The system of claim 1, wherein the water cooling pipe extends along an inner space of the air falling pipe through the containment structure or along the inside of the wall of the containment structure. 7. The system of claim 1, wherein the functional conductor has effective thermal conductivity in a range that water passing through the water cooling pipe is maintained in a liquid state in the normal operation temperature range of the reactor, and wherein the functional conductor has effective thermal conductivity in a range that the water passing through the water cooling pipe is boiled in the accident occurrence temperature range of the reactor. 8. The system of claim 1, wherein the fluid suppresses heat transfer between the first plate and the second plate in the normal operation temperature range of the reactor, and heat transfer through radiation is performed from one plate of the first and second plates to another plate of the first and second plates in the accident occurrence temperature range of the reactor. 9. The system of claim 1, wherein each of the first plate and the second plate is provided with a first surface and a second surface opposite to each other on each of the first plate and the second plate, so that heat conduction is performed from one surface of the first and the second surfaces to another surface of the first and second surfaces. 10. The system of claim 9, wherein thermal conductivity from one surface of the first and second surfaces to another surface of the first and second surfaces is 1W/m·K or 5 more. 11. The system of claim 1, wherein a surface of the first plate and a surface of the second plate have emissivity of 0.60 to 0.95. 12. The system of claim 1, wherein the first plate and the second plate are formed of a metal and have a thickness of 0.1 mm to 5 mm. 13. The system of claim 1, wherein the fluid contains at least one selected from a group including air, helium, nitrogen, and water. 14. The system of claim 1, wherein the lattices are formed of ceramic and have thermal conductivity of 0.1 W/m·K to 1.0 W/m·K. 15. The system of claim 1, wherein a length of each of the first plate and the second plate in a vertical direction is greater than a thickness of the lattice, and wherein a thickness ratio of the lattice to the vertical length of each of the first plate and the second plate is 0.2 or less. 16. The system of claim 1, wherein the unit structures are repeatedly arranged in a vertical direction.