Patent Number: 
Section: claims

1. A passive residual heat removal system for circulating cooling fluid to a steam generator through a main feedwater line connected to a lower inlet of the steam generator and a main steam line connected to an upper outlet of the steam generator to remove sensible heat in a nuclear reactor coolant system and residual heat in a nuclear reactor core during an accident, the passive residual heat removal system comprising:a makeup facility configured to accommodate excess cooling fluid and supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range,wherein the lower inlet is at a first vertical height, and the upper outlet is at a second vertical height higher than the first vertical height,wherein the makeup facility comprises:a makeup tank vertically located between the first vertical height and the second vertical height to passively accommodate the excess cooling fluid and supply the makeup cooling fluid according to a water level of the cooling fluid in the makeup tank;a first connection line connected to the main steam line and the makeup tank for allowing cooling fluid to flow from the main steam line to the makeup tank; anda second connection line connected to the makeup tank and the main feedwater line for supplying the main feedwater line with cooling fluid supplied from the makeup tank. 2. The passive residual heat removal system of claim 1, wherein an initial water level of the makeup tank is set to either one of a first through a third water level, andthe first water level corresponds to a level at which the cooling fluid is fully filled in the makeup tank to supply the makeup cooling fluid when the water level of the steam generator is lower than the water level of the makeup tank during an accident, andthe second water level corresponds to a level at which cooling fluid is depleted in the makeup tank to accommodate the excess cooling fluid and supply the accommodated cooling fluid as the makeup cooling fluid during an accident, andthe third water level corresponds to a level formed at a height between the first water level and the second water level to accommodate the excess cooling fluid and supply the cooling fluid using initially stored cooling fluid as the makeup cooling fluid. 3. The passive residual heat removal system of claim 1, wherein the first connection line is connected to the main steam line through a steam line of the passive residual heat removal system to receive steam or the cooling fluid from the steam line. 4. The passive residual heat removal system of claim 1, wherein the makeup facility further comprises a circulation line having one end connected to the main steam line and having the other end connected to the makeup tank. 5. The passive residual heat removal system of claim 4, wherein the first connection line is connected to the main steam line at a position closer to the steam generator than to the circulation line, and the circulation line is connected to the main steam line at a position farther from the steam generator than the first connection line. 6. The passive residual heat removal system of claim 4, wherein the makeup facility further comprises a first pressure drop structure configured to locally cause a decrease of pressure based on a principle in which a pressure relatively decreases according to a speed increase of fluid, andthe first pressure drop structure is provided at a connection portion of the circulation line and the main steam line. 7. The passive residual heat removal system of claim 4, wherein the makeup tank, the first connection line and the circulation line are insulated by an insulator to limit the energy loss of steam passing through the makeup tank, the first connection line and the circulation line during the normal operation of a nuclear power plant. 8. The passive residual heat removal system of claim 4, wherein the passive residual heat removal system comprises:a condensation heat exchanger configured to discharge sensible heat in the nuclear reactor coolant system and residual heat in the nuclear reactor core received through the circulation of the cooling fluid to an outside;a feedwater line connected to the condensation heat exchanger and the main feedwater line for supplying the cooling fluid from the condensation heat exchanger to the steam generator;a steam line connected to the main steam line and the condensation heat exchanger for supplying cooling fluid discharged from the steam generator to the condensation heat exchanger; anda vent line connected to the steam line and the main steam line or connected to the steam line and the makeup tank for preventing non-condensable gas from being accumulated in the makeup tank or the steam line by allowing the cooling fluid flowing from the steam line to be supplied to the main steam line or the makeup tank. 9. The passive residual heat removal system of claim 8, wherein the passive residual heat removal system further comprises an inflow structure configured to induce at least part of a flow of steam, andthe inflow structure comprises at least one of:a first inflow structure extended from the first connection line and inserted into the main steam line to allow an inlet of an internal flow path to face steam flowing through the main steam line so as to induce at least part of steam flowing through the steam line to the first connection line; anda second inflow structure extended from the vent line and inserted into the steam line to allow an inlet of an internal flow path to face steam flowing through the steam line so as to induce at least part of steam flowing through the steam line to the vent line. 10. The passive residual heat removal system of claim 8, wherein the steam line is connected to the main steam line at a position closer to the steam generator than to the vent line, and the vent line is connected to the main steam line at a position farther from the steam generator than the steam line. 11. The passive residual heat removal system of claim 8, wherein the passive residual heat removal system further comprises a second pressure drop structure configured to locally cause a decrease of pressure based on a principle in which the pressure relatively decreases according to a speed increase of fluid, andthe second pressure drop structure is provided at an internal flow path of a connection portion of the vent line and the main steam line to cause a local pressure drop. 12. The passive residual heat removal system of claim 8, wherein an isolation valve that is open by related signals during an accident is provided at the feedwater line to initiate the operation of the passive residual heat removal system, andthe isolation valve is provided in duplicate or in parallel or provided along with a check valve for preventing the backflow of feedwater from the main feedwater line, andthe second connection line is connected to the feedwater line at a position between the two isolation valves provided in duplicate or between the isolation valve and the check valve, and connected to the main feedwater line through the feedwater line. 13. The passive residual heat removal system of claim 8, wherein the feedwater line is connected to the makeup tank for supplying cooling fluid discharged from the condensation heat exchanger to the makeup tank, and the second connection line is connected to the main feedwater line for supplying cooling fluid received through the feedwater line to the steam generator, and the feedwater line is connected to the main feedwater line through the makeup tank and the second connection line. 14. The passive residual heat removal system of claim 8, wherein the makeup facility further comprises a flow resistance portion, andthe flow resistance portion comprises at least one of:a first flow resistance portion provided at the first connection line to adjust a flow of cooling fluid introduced from the main steam line to the makeup tank;a second flow resistance portion provided at the second connection line to adjust a flow of makeup cooling fluid supplied from the makeup tank to the main feedwater line; anda third flow resistance portion provided at the feedwater line to adjust a flow of cooling fluid supplied from the condensation heat exchanger to the feedwater line. 15. A nuclear power plant, comprising:a steam generator provided at a boundary between a primary system and a secondary system;a main feedwater line connected to a lower inlet of the steam generator to supply feedwater from a feedwater system to the steam generator during a normal operation;a main steam line connected to an upper outlet of the steam generator to supply steam from the steam generator to a turbine system during a normal operation;a passive residual heat removal system configured to circulate cooling fluid to the steam generator through the main feedwater line and the main steam line to remove sensible heat in a nuclear reactor coolant system and residual heat in a nuclear reactor core during an accident; anda makeup facility configured to accommodate excess cooling fluid and supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range,wherein the lower inlet is at a first vertical height, and the upper outlet is at a second vertical height higher than the first vertical height,wherein the makeup facility comprises:a makeup tank vertically located between the first vertical height and the second vertical height to passively accommodate the excess cooling fluid and supply the makeup cooling fluid according to a water level of the cooling fluid in the makeup tank;a first connection line connected to the main steam line and the makeup tank for allowing cooling fluid to flow from the main steam line to the makeup tank; anda second connection line connected to the makeup tank and the main feedwater line for supplying the main feedwater line with cooling fluid supplied from the makeup tank.