NUCLEAR POWER PLANT HAVING IMPROVED COOLING PERFORMANCE AND METHOD FOR OPERATING SAME

The present invention relates to a nuclear power plant having improved cooling performance and a method for operating the same. The nuclear power plant having improved cooling performance according to the present invention comprises: a reactor vessel including a reactor core; a hot-leg and a cold-leg extending from the reactor vessel; a hybrid safety injection tank which contains coolant, is connected to the cold-leg and the reactor vessel, and is positioned higher than the reactor core; a coolant tank connected to the reactor vessel and positioned higher than the reactor core; and a pressure reducing valve connected to the hot-leg.

TECHNICAL FIELD

The present invention relates to a nuclear power plant with improved cooling performance and a method of operating the same.

BACKGROUND ART

An active emergency core cooling system of the nuclear power plant is configured to have a pump (high pressure injection pump, low pressure injection pump, etc.), accumulator (safety injection tank, etc.) and a coolant tank. When a normal heat removal through steam generators and turbines is not available, the active emergency core cooling system injects directly emergency coolant into the reactor coolant system (hot-leg or cold-leg, reactor vessel) to cool the reactor core.

A safety injection tank employs a safety injection tank containing a pressurized gas. When the pressure of the reactor vessel becomes lower than the pressure of the safety injection tank, the safety injection tank supplies the coolant therein to the nuclear reactor. However, when the pressure of the reactor vessel and/or the reactor coolant system is higher than the pressure of the safety injection tank, there is a problem that the coolant of the safety injection tank may not be supplied to the reactor vessel and/or the reactor coolant system.

Further, the pump of the active emergency core cooling system supplies the coolant of the coolant tank to the reactor vessel using the driving force from a motor. Thus, there is a problem that the pump cannot be used when there is no power (AC power).

DISCLOSURE

Technical Problem

A purpose of the present invention is therefore to provide a nuclear power plant with improved cooling performance and a method of operating the same.

Technical Solution

In one aspect, there is proposed a nuclear power plant with improved cooling performance, the plant comprising: a reactor vessel containing a reactor core; a hot-leg and a cold-leg extending from the nuclear reactor; a hybrid safety injection tank for containing coolant therein, wherein the hybrid safety injection tank is connected to the cold-leg and the nuclear reactor, and the hybrid safety injection tank is located above the nuclear reactor; a coolant tank connected to the reactor vessel and positioned above the nuclear reactor; and a pressure-reducing valve connected to the high-temperature pipe.

In one embodiment, the nuclear power plant further comprises a regulating valve located between the hybrid safety injection tank and the low-temperature pipe.

In one embodiment, the reactor vessel further comprises a downcomer, wherein the coolant of the hybrid safety injection tank is supplied to the downcomer.

In one embodiment, the coolant of the hybrid safety injection tank is supplied to a lateral face of the nuclear reactor.

In one embodiment, the nuclear power plant further comprises: a steam generator connected to the high-temperature pipe and the low-temperature pipe; a pressurizer connected to the high-temperature pipe; and a pressure relief valve connected to the pressurizer, wherein the hybrid safety injection tank is not affected by a pressure change resulting from operation of the pressure relief valve.

In one embodiment, the coolant of the hybrid safety injection tank is pressurized by pressurized gas, wherein the coolant of the coolant tank is supplied to a lateral face of the nuclear reactor.

In one embodiment, the nuclear power plant further comprises a safety injection tank containing a coolant and connected to the reactor vessel and positioned above the nuclear reactor, wherein the safety injection tank is pressurized by a pressurizing gas.

In one embodiment, the nuclear power plant further comprises a heat-exchanger to condense vapor inside a reactor building, wherein condensed water produced in the heat exchanger is supplied to the coolant tank.

In another aspect, there is proposed a nuclear power plant with improved cooling performance, the plant comprising: a reactor vessel containing a reactor core; a hot-leg and a cold-leg extending from the nuclear reactor; a hybrid safety injection tank for containing coolant therein, wherein the hybrid safety injection tank is connected to the cold-leg and the nuclear reactor, and the hybrid safety injection tank is located above the nuclear reactor; a coolant tank connected to the reactor vessel and positioned above the nuclear reactor; a pressurizer connected to the high-temperature pipe; and a pressure-reducing valve connected to the high-temperature pipe, wherein when the hybrid safety injection tank communicates with the low-temperature pipe, the hybrid safety injection tank supplies the coolant to the reactor vessel due to a water head differential, wherein the coolant supply from the hybrid safety injection tank is not affected by a pressure change of the pressurizer.

In still another aspect, there is proposed a method for operating a nuclear power plant with improved cooling performance, wherein the plant comprises: a reactor vessel containing a reactor core; a hot-leg and a cold-leg extending from the nuclear reactor; a hybrid safety injection tank for containing coolant therein, wherein the hybrid safety injection tank is connected to the cold-leg and the nuclear reactor, and the hybrid safety injection tank is located above the nuclear reactor; a coolant tank connected to the reactor vessel and positioned above the nuclear reactor; and a pressure-reducing valve connected to the high-temperature pipe, wherein the method comprises:

equalizing a pressure of the reactor vessel with a pressure of the hybrid safety injection tank in an emergency event, thereby to supply the coolant of the hybrid safety injection tank to the reactor vessel using a water head differential; and reducing the pressure of the reactor vessel to an atmospheric pressure by opening the pressure-reducing valve, thereby to supply the coolant of the coolant tank to the reactor vessel using a water head differential.

In one embodiment, the nuclear power plant further comprises a regulating valve located between the hybrid safety injection tank and the low-temperature pipe, wherein the pressure of the hybrid safety injection tank and the reactor vessel is equalized to each other by opening the regulating valve.

In one embodiment, the nuclear power plant further comprises: a steam generator connected to the high-temperature pipe and the low-temperature pipe; a pressurizer connected to the high-temperature pipe; and a pressure relief valve connected to the pressurizer, wherein the hybrid safety injection tank is not affected by a pressure change resulting from operation of the pressure relief valve.

In one embodiment, the method further comprises, after supplying the coolant of the hybrid safety injection tank to the nuclear reactor, lowering a pressure of the high-pressure pipe by opening the pressure relief valve.

Advantageous Effects

In accordance with the present invention, the nuclear power plant with improved cooling performance and the method of operating the same may be realized.

MODE FOR INVENTION

The present invention will now be described in more detail with reference to the drawings.

The accompanying drawings are merely illustrative examples for the purpose of more specifically describing the technical idea of the present invention, and thus the idea of the present invention is not limited to the accompanying drawings. Further, the accompanying drawings may be exaggerated in size and spacing in order to describe the relationship between components.

FIG. 1shows a nuclear power plant according to one embodiment of the present invention.

The nuclear power plant1comprises a reactor vessel10, a hybrid safety injection tank20, a safety injection tank25, a steam generator30, a pressurizer40, a coolant tank50and a heat-exchanger80. In addition, the nuclear power plant1comprises cold-leg61, hot-leg62, various pipes63to67, and various valves71to76.

The reactor vessel10comprises a reactor core11, a downcomer12, and coolant injection portions13and14. The coolant injection portions13and14are located on the side wall of the reactor vessel10and communicate with the downcomer12.

In a normal operation mode, heated pressurized coolant(coolant water) produced in the reactor vessel10is discharged to the high-temperature pipe62and then is heat-exchanged in the steam generator30to generate steam, and then returned to the reactor vessel10through the cold-leg61.

The pressurizer40is connected to the high-temperature pipe62via a pipe65and controls the system pressure during a nuclear power plant operation. The space within the pressurizer40may be divided into a lower space41and an upper space42. The lower space41may contain coolant and the upper space42may contain steam. A pressure relief valve73is located above the pressurizer40. When the reactor coolant system is pressurized above the operation pressure, the pressure-relief valve73is automatically opened to prevent damage to the coolant system. Opening the pressure relief valve73may allow fluid to be released to the outside such that the pressure of the coolant system is lowered.

The high-temperature pipe62is connected to a pressure-reducing valve74. When the pressure-reducing valve74is opened, the pressure of the high-temperature pipe62is reduced.

The hybrid safety injection tank20is located above the reactor vessel10. The top of the hybrid safety injection tank20is connected to the cold-leg61through a pipe64. The bottom of the hybrid safety injection tank20is connected to the coolant injection portion13through a pipe63.

The lower space21of the hybrid safety injection tank20is filled with coolant and its upper space22is filled with pressurizing gas. The pressure of the pressurizing gas in the hybrid safety injection tank20may be in a range of 40 to 100 atm. The pressurizing gas may be nitrogen gas and the coolant may contain boric acid.

A check valve71is located on the pipe63between the hybrid safety injection tank20and the reactor vessel10. The flow of coolant from the reactor vessel10to the hybrid safety injection tank20is limited by the check valve71.

On the pipe64connecting the hybrid safety injection tank20and the cold-leg61, an adjustment valve72is located. The regulating valve72remains closed during a normal operation. At this time, when the pressure of the reactor vessel10is lower than the pressure of the hybrid safety injection tank20, the coolant of the hybrid safety injection tank20is supplied to the reactor vessel10.

The safety injection tank25is located above the reactor vessel10. The bottom of the safety injection tank25is connected to the coolant injection portion13through a pipe67.

The lower space26of the safety injection tank25is filled with coolant and its upper space27is filled with pressurizing gas. The pressure of the pressurizing gas in the safety injection tank25may be in a range of 40 to 100 atm. The pressurizing gas may be nitrogen gas and the coolant may contain boric acid.

The check valve76is located on the pipe67between the safety injection tank25and the reactor vessel10. The coolant flow in the direction from the reactor vessel10to the safety injection tank25is limited by the check valve76.

The coolant tank50is at atmospheric pressure and is located higher than the reactor vessel10. The coolant tank50is connected to the reactor vessel10through a pipe66. Specifically, the coolant in the tank50is supplied to the downcomer12through the coolant injection portion14of the reactor vessel10. A check valve75is provided on the pipe66connecting the reactor vessel10and the coolant tank50to prevent coolant flow in the direction of the coolant tank50from the reactor vessel10. The coolant injection portions13and14connected to the hybrid safety injection tank20and the coolant tank50may be the same injection portion or individual injection portions.

The heat-exchanger80is located above the reactor vessel10and condenses the vapor generated in the reactor building. The heat-exchanger80may be installed on the inner wall of a reactor building or may discharge the heat outside the reactor building.

The coolant, which is condensed and generated in the heat-exchanger80, is fed to the coolant tank50.

Hereinafter, an operation method of a nuclear power plant according to one embodiment of the present invention will be described with reference toFIG. 2toFIG. 4.

Due to an accident, a situation occurs in which the coolant of the hybrid safety injection tank20, safety injection tank25, and coolant tank50must be supplied to the reactor vessel10in the state where the reactor vessel10maintains the high pressure.

According to the present invention, in this case, the method first opens the regulating valve72as shown inFIG. 2. When the regulating valve72is opened, the cold-leg61and the hybrid safety injection tank20are communicated with each other such that the hybrid safety injection tank20is further pressurized. Thus, the cold-leg61and the hybrid safety injection tank20have the same pressure. Further, the reactor vessel10is thus at the same pressure as that of the hybrid safety injection tank20.

When the reactor vessel10and the hybrid safety injection tank20are at the same pressure, the coolant of the hybrid safety injection tank20is supplied to the reactor vessel10due to the water head differential. The coolant of the hybrid safety injection tank20is supplied to the downcomer12through the coolant injection portion13provided on the side wall of the reactor vessel10.

The regulating valve72may be opened by manipulation of operator or by automatic operation. For this purpose, a battery may be installed and used if necessary.

As described above, in accordance with the present invention, the hybrid safety injection tank20is connected to the cold-leg61. When the hybrid safety injection tank20is connected to the pressurizer40, the pressure of the hybrid safety injection tank20may be reduced in an emergency event by opening the pressure-relief valve73. This problem does not occur when the hybrid safety injection tank20is connected to the cold-leg61in accordance with the present invention. That is, the hybrid safety injection tank20according to the present invention is not affected by the operation of the pressure relief valve73at the emergency injection timing.

Further, even when the hybrid safety injection tank20is connected to the high-temperature pipe62, the pressure of the hybrid safety injection tank20may be reduced in an emergency event by opening the pressure-relief valve73. However, since the pressure change of the cold-leg61due to the operation of the pressure-relief valve73is not large, the pipe61can supply coolant efficiently in an emergency event.

In the nuclear power plant, only one pressurizer40is installed, whereas each of the cold-leg61, the high-temperature pipe62and the hybrid safety injection tank20may be provided in a plural manner. Thus, connecting a plurality of hybrid safety injection tanks20to a single pressurizer40results in a long and complicated pipe structure. According to the present invention, each hybrid safety injection tank20is connected to an adjacent cold-leg61, the pipe is short and simple, and the shapes of the pipes may be the same.

As described above, after the supply of the coolant of the hybrid safety injection tank20, and when further cooling is required, the coolant of the coolant tank50is supplied to the reactor vessel10.

Next, as shown inFIG. 3, when the pressure of the reactor vessel10is lowered to be lower than the pressurizing gas of the safety injection tank25, the check valve76is opened. Accordingly, the coolant of the safety injection tank25is supplied to the reactor vessel10. In another embodiment, pressure reduction of the reactor vessel10through the opening of the pressure relief valve73may be required to provide the coolant of the safety injection tank25.

Then, the method opens the pressure relief valve73and the pressure-reducing valve74as shown inFIG. 4to supply the coolant of the coolant tank50. The opening order of the pressure relief valve73and the pressure-reducing valve74is not limited to a specific order. In one example, and the opening operations thereof may occur simultaneously.

The opening of the pressure relief valve73and the pressure-reducing valve74may be accomplished by manipulation of operator or by automatic operation. For this purpose, a battery may be installed and used if necessary.

By opening the pressure relief valve73and the pressure-reducing valve74, the pressure of the pressurizer40and the high-temperature pipe62becomes close to the atmospheric pressure so that the pressure of the reactor vessel10becomes close to the atmospheric pressure. The pressure-reducing valve74is characterized by a larger effective releasing area than those of the pressure relief valve73and pressurizer connection pipe65. Thus, the operation of the pressure-reducing valve74causes a rapid pressure drop in the reactor vessel10. The pressure-reducing valve74may be installed on at least one high-temperature pipe.

In this situation, the coolant of the coolant tank50is supplied to the reactor vessel10due to the water head differential. In an emergency event, the temperature of the upper portion of the reactor vessel10is the highest. According to the present invention, the coolant is supplied through the side portion of the reactor vessel10to increase the reactor core cooling capacity.

The discharged steam through the leakage points of the cold-leg61and the hot-leg62, and the valves73and74condenses on the cold surface of the heat-exchanger80. The condensed condensate is collected in the coolant tank50. The heat-exchanger80discharges the heat inside the reactor building out of the building, thereby reducing the temperature and pressure inside the reactor building.

Since the coolant supply from the coolant tank50as described above is performed without the operation of pump, the coolant may be supplied when the power (AC power) is interrupted.

The embodiments as described above are illustrative of the present invention, and the present invention is not limited thereto. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.