System and method for removing residual heat of integrated nuclear reactor

Abstract

The present invention relates to a system and a method for removing residual heat of an integrated nuclear reactor, capable of removing residual heat of the integrated nuclear reactor by constantly maintaining a water level of an ultimate heat sink tank (hereinafter, referred to as an "UHS tank") to be passive without external power even in case that water of the UHS tank is completely depleted when an accident exceeding a design standard of the integrated nuclear reactor occurs.

Description

Integrated reactor residual heat removal system and residual heat removal method

[0001] The present invention relates to an integrated reactor residual heat removal system and a residual heat removal method that can maintain the water level of a water tank even when a design basis exceeding accident occurs in an integrated reactor in which the reactor vessel and the containment vessel are designed as one unit, at which point the water in the water tank that exchanges heat with the heat exchanger inside the containment vessel is completely depleted.

[0002] A passive decay heat removal system for a nuclear power plant that can continuously generate and supply electricity required for the operation of a cooling pump during an abnormal state of the reactor by a supercritical pressure fluid cycle that cools the reactor coolant is described in Korean Patent Publication No. 10-2238185.

[0003] The passive decay heat removal system of a nuclear power plant is equipped with a stationary cooling pump installed in a reactor coolant pipe that circulates the reactor coolant that cools the reactor, a stationary cooling heat exchanger installed between the reactor and the stationary cooling pump for heat exchange between the reactor coolant and the supercritical pressure fluid circulated through the supercritical pressure fluid pipe, and a turbine generator connected to the stationary cooling heat exchanger that generates electricity using the high-temperature gaseous supercritical pressure fluid that has passed through the stationary cooling heat exchanger and supplies it to the stationary cooling pump.

[0004] The passive decay heat removal system of a nuclear power plant includes an external heat exchanger mounted on a supercritical pressure fluid duct so that the supercritical pressure fluid passing through the turbine generator can be cooled and sent to a stationary cooling heat exchanger, and a pump disposed between the external heat exchanger and the stationary cooling heat exchanger to send the supercritical pressure fluid cooled through the external heat exchanger to the stationary cooling heat exchanger to circulate the supercritical pressure fluid cycle.

[0005] The turbine generator connected to the stationary cooling pump via an electric line is configured to supply electricity required for the operation of the stationary cooling pump to the stationary cooling pump via an electric line when the reactor is in an abnormal state.

[0006] A method and device for emergency core cooling using a reactor protection vessel and a compression tank are described in Korean Patent Publication No. 10-0419194.

[0007] The emergency core cooling method of an integral reactor is to install a small reactor protection vessel designed for high temperature and high pressure outside the reactor vessel, and to block the amount of coolant released from the reactor vessel by utilizing the phenomenon of pressure increase due to evaporation of the coolant released in the event of a loss of coolant accident, and to have a step of passively supplying coolant into the reactor vessel in the event of a loss of coolant accident by using a compressed tank containing emergency core coolant so that the coolant is filled up to the top of the steam generator.

[0008] The emergency core cooling method consists of cooling the primary system using a passive residual heat removal system including a steam generator installed inside the reactor vessel and a heat exchanger installed outside, and removing the decay heat generated in the core by allowing natural circulation within the reactor vessel (primary system) when a sufficient primary system water level is secured through continuous safety injection using a compression tank, and replenishing the small amount of coolant loss in the primary system that may occur due to the difference in the cooling rate of the primary system through the passive residual heat removal system and the cooling rate of the reactor protection vessel due to external natural convection after pressure equalization using the remaining coolant in the compression tank.

[0009] The emergency core cooling system of an integral reactor is configured by installing a reactor protection vessel surrounding the outer surface of the reactor vessel, and then installing a compression tank storing coolant for emergency core cooling at the upper part of the reactor vessel so that in the event of a loss of coolant accident, the coolant is injected up to the upper part of the steam generator within the reactor vessel due to the pressure difference. After pressure equalization, the small amount of coolant loss in the primary system that may occur due to the difference in cooling rates of the primary system through the passive residual heat removal system and the reactor protection vessel due to external natural convection is piped so that the residual coolant in the compression tank is injected.

[0010] The passive residual heat removal system, which includes a steam generator installed inside the reactor vessel and a heat exchanger installed outside the reactor protection vessel to remove decay heat generated in the core during long-term cooling, is configured to be connected with pipes to allow circulation.

[0011] [Prior Art Literature]

[0012] [Patent Document]

[0013] (Patent Document 1) Korean Patent Publication No. 10-2238185

[0014] (Patent Document 2) Korean Patent Publication No. 10-0419194

[0015] Since the Fukushima nuclear accident, the design concept of a passive safety system driven by natural forces such as gravity and density differences has been actively introduced even in the event of a long-term power loss or extreme disaster.

[0016] In the case of an integral reactor design in which the reactor vessel and containment vessel are designed as one unit, in order to eliminate a large-scale loss-of-coolant accident, a method of installing a heat exchanger inside the containment vessel to release residual heat to the outside can be applied instead of eliminating the large coolant pipe.

[0017] Therefore, the heat exchanger receives water from an external cooling water tank, exchanges heat, and then comes into contact with the atmosphere, releasing the vapor through evaporation. However, because the water in the cooling water tank cannot be increased indefinitely, once the tank is completely depleted, the removal of residual heat within the containment vessel becomes entirely dependent on the ambient temperature.

[0018] The present invention aims to maintain the water level of a cooling water tank even when the water in the cooling water tank is completely depleted to remove residual heat from an integral reactor, i.e., when an accident occurs that exceeds the design standard.

[0019] When the water source for filling the cooling water tank is an outdoor tank of a power plant or an additional water source such as fire water, the cooling water tank is installed above ground like an outdoor tank, so a pump is required to supply the water source to the top of the cooling water tank.

[0020] Accordingly, the present invention aims to secure a safe shutdown time for a nuclear power plant by delaying the time leading to a major accident by passively filling a cooling water tank with water without external power using a turbine-driven pump.

[0021] The integrated reactor residual heat removal system of the present invention comprises a containment vessel, an ultimate heat sink (UHS) tank, an outdoor tank, a turbine, and a turbine drive pump.

[0022] The containment vessel of the present invention is equipped with a reactor vessel and a heat exchanger capable of discharging residual heat to the outside, and when a water level gauge installed in the UHS tank detects that the water in the UHS tank is depleted below a specific water level, a control operation signal is transmitted through a signal transmission line to a pressure relief valve of the containment vessel and a water isolation valve that isolates an outdoor tank through a water level transmitter of the water level gauge, thereby controlling valve operation.

[0023] The pressure reducing valve of the containment vessel of the present invention automatically opens when a signal is received through a level transmitter of a level gauge of a UHS tank or when a pressure exceeding a preset set point of the containment vessel occurs.

[0024] When the pressure reducing valve of the containment vessel of the present invention is opened, the thermal energy of the high-temperature, high-pressure steam inside the containment vessel is supplied to the turbine, and the thermal energy that drives the turbine is converted into mechanical kinetic energy to operate the turbine-driven pump.

[0025] The present invention is configured such that water, which is cooling water, is supplied from an outdoor tank through an outdoor supply line, passes through a water fill isolation valve, and is supplied into the UHS tank through a water fill supply line by operation of the turbine-driven pump.

[0026] The cooling water supplied through the supply line from the UHS tank of the present invention is converted into high-temperature steam through heat exchange in a heat exchanger (HX) inside a containment vessel (CV), and is returned to the UHS tank through a steam line, where it comes into contact with the atmosphere, and the steam with heat is released into the atmosphere (open to evaporation).

[0027] Condensate from the turbine of the present invention passes through a check valve along a condensate line and is re-supplied into the containment vessel (CV), and the check valve is configured to prevent the condensate from flowing back from the turbine.

[0028] A method for removing residual heat using an integrated reactor residual heat removal system of the present invention includes, when the integrated reactor is in normal operation, performing a step (S1) of exchanging heat between a heat exchanger (HX) in a containment vessel (CV) and a UHS tank water source, and performing a step (S2) of exchanging heat between the UHS tank water source and the atmosphere.

[0029] When the integrated reactor of the present invention detects the occurrence of a design basis exceeding accident, which is ① when a specific water level is reached due to evaporation of the water source inside the UHS tank, the UHS LT (level transmitter) signal operates, or ② when the design exceeding pressure of the containment vessel (CV) occurs (S3), the reactor automatically performs the step (S4) of opening the pressure reducing valve (PRV) and the water filling isolation valve of the containment vessel (CV).

[0030] A step (S5) is performed in which high-temperature, high-pressure steam within a containment vessel (CV) of the present invention is supplied to a turbine, and steam thermal energy is converted into mechanical kinetic energy to drive a turbine-driven pump, and a step (S6) is performed in which water from an outdoor tank is supplied to a UHS tank, and the process returns to the normal operation step (S1).

[0031] An over-design accident may occur in which water, the coolant used as the ultimate heat sink (UHS) to cool the reaction heat in an integral reactor, is lost.

[0032] In the event of a nuclear power plant accident, it is possible to secure a source of cooling water from yard tanks such as a fire water tank, demineralized water tank, and raw water tank located within the power plant. Therefore, it is possible to secure a safe shutdown time for the nuclear power plant by passively supplying water to the ultimate heat sink tank without an external power source, thereby mitigating the occurrence of an accident exceeding the design standard and delaying the time leading to a severe accident.

[0033] Figure 1 shows a configuration diagram of a residual heat removal system of a nuclear reactor according to the present invention.

[0034] Figure 2 is an operation flow chart of a residual heat removal method of a residual heat removal system of a nuclear reactor according to the present invention.

[0035] The present invention relates to a residual heat removal system and a residual heat removal method for an integral reactor, which can remove residual heat from an integral reactor by passively maintaining the water level of an ultimate heat sink tank (hereinafter referred to as a “UHS tank”) constant without external power even when the water in the UHS tank is completely depleted in the event of an accident exceeding the design basis of an integral reactor.

[0036] The residual heat removal system of the integral reactor of the present invention includes an integral reactor having a pressure relief valve (PRV) in a containment vessel (CV), an ultimate heat rejection source (UHS) tank having a level transmitter (LT) for detecting a water level for passive heat exchange with the integral reactor, an outdoor tank (yard tank) for supplying cooling water to the UHS tank, and a turbine-driven pump for supplying cooling water stored in the outdoor tank to the UHS tank by driving using steam by the containment vessel pressure relief valve.

[0037] Hereinafter, the integrated reactor residual heat removal system and residual heat removal method according to the present invention will be described in more detail with reference to the attached drawings.

[0038] The source of the additional water added to the UHS tank is the yard tank of the power plant or an additional water source such as fire fighting water.

[0039] Since the UHS tank is located at ground level, which is the same height as or higher than the outdoor tank, a pump is required to supply water to the top of the UHS tank.

[0040] Therefore, the present invention uses a turbine-driven pump to passively fill water into a UHS tank without external power.

[0041] Figure 1 shows a configuration diagram of a residual heat removal system of a nuclear reactor according to the present invention.

[0042] The main components of the residual heat removal system of the nuclear reactor include a containment vessel (CV) (100), an UHS tank (200), an outdoor tank (300), a turbine (400), and a turbine driving pump (500).

[0043] Inside the containment vessel (CV) (100), there is a reactor vessel (RV) (110) and a heat exchanger (HX) (120) that can discharge residual heat to the outside.

[0044] Cooling water supplied from the UHS tank (200) through the supply line (220) is converted into high-temperature steam through heat exchange in the heat exchanger (HX) (120) inside the containment vessel (CV) (100) and is returned to the UHS tank (200) through the steam line (230) and is configured to come into contact with the atmosphere.

[0045] The heat accumulated in the UHS tank (200) evaporates the water inside the UHS tank (water evaporation), and the water vapor with heat is released into the atmosphere (open to evaporation).

[0046] The water level meter installed in the UHS tank (200) is configured to control valve operation by transmitting a control operation signal through the signal transmission lines (211, 212, 213) to the pressure relief valve (PRV) (140) of the containment vessel (CV) and the water make-up isolation valve (510) that isolates the yard tank (300) when the water level transmitter (LT) (210) of the water level meter detects that the water in the UHS tank is depleted below a specific water level.

[0047] The pressure reducing valve (140) of the containment vessel (CV) (100) automatically opens when a signal is received through the level transmitter (LT) (210) of the level gauge of the UHS tank or when the pressure exceeds a preset set point of the containment vessel (CV) (100).

[0048] When the pressure reducing valve (140) of the containment vessel (CV) (100) is opened, the thermal energy of the high temperature and high pressure steam inside the containment vessel (CV) (100) is supplied to the turbine (TB, 400), and the thermal energy that drives the turbine is converted into mechanical kinetic energy to operate the turbine driven pump (500).

[0049] When pressure exceeding the design pressure of the containment vessel (CV) (100) occurs, the pressure reducing valve (140) receives a signal through the level transmitter (LT) (210) and operates the water isolation valve (510) through the signal transmission line (213).

[0050] That is, the make-up isolation valve (510) automatically opens when a signal is received through the level transmitter (LT) (210) of the UHS tank (200) or when a pressure exceeding the design pressure of the containment vessel (CV) occurs and the pressure reducing valve (140) operates.

[0051] Normally, water is filled up to the front end of the water isolation valve (510) due to the water head difference.

[0052] Since the UHS tank is located at ground level (600) like an outdoor tank (yard tank), a pump is required to supply water to the top of the UHS tank.

[0053] The thermal energy of high-temperature, high-pressure steam within the containment vessel (CV) (100) is supplied to a turbine (400), and the thermal energy driving the turbine can be converted into mechanical kinetic energy to operate a turbine-driven pump (500).

[0054] It is possible to supply water to the top of the UHS tank using a turbine-driven pump.

[0055] A drive pump is required to circulate water to supply water from an outdoor tank (300) installed at ground level (600) to a UHS tank (200) to cool a containment vessel (CV) (100) installed underground.

[0056] Since the water in the UHS tank (200) cannot be increased indefinitely, it is possible to resupply water to the UHS tank (200) by driving the turbine with the high-temperature, high-pressure steam of the turbine and using a turbine-driven pump (500) driven by the turbine.

[0057] By the operation of the turbine drive pump (500), water as cooling water is supplied from the outdoor tank (300) through the outdoor supply line (310), passes through the water fill isolation valve (510), and is supplied into the UHS tank (200) through the water fill supply line (520).

[0058] Condensate from the turbine (400) passes through a check valve (130) along a condensate line (410) and is re-supplied into the containment vessel (CV) (100), and the check valve (130) prevents the condensate from the turbine (400) from flowing back.

[0059] Figure 2 is an operation flow chart of a residual heat removal method of a residual heat removal system of a nuclear reactor according to the present invention.

[0060] When the integral reactor is operating normally, the heat exchange process is carried out in the next step.

[0061] A step (S1) of performing heat exchange between a heat exchanger (HX) in a containment vessel (CV) and a UHS tank water source is performed,

[0062] A step (S2) of heat exchange between the UHS tank water source and the atmosphere is performed.

[0063] When the integrated reactor detects an occurrence of an accident exceeding the design criteria, such as ① when a certain level is reached due to evaporation of the water source inside the UHS tank, the UHS LT (level transmitter) signal is activated, or ② when a stage (S3) in which the design pressure of the containment vessel (CV) exceeds the design pressure occurs, the containment vessel (CV) pressure relief valve (PRV) and the water fill isolation valve are automatically opened (S4).

[0064] A step (S5) is performed in which high-temperature, high-pressure steam inside a containment vessel (CV) is supplied to a turbine, and the steam thermal energy is converted into mechanical kinetic energy to drive a turbine-driven pump.

[0065] The step (S6) is performed in which water from the outdoor tank (or other external devices and equipment) is supplied to the UHS tank, and the normal operation step (S1) is returned.

[0066] The present invention enables securing a UHS tank water source from an outdoor tank located within a power plant, such as a fire water tank, a pure water tank, or a raw water tank, in the event of a design standard exceeding accident in which the water source of the UHS tank is lost.

[0067] By supplying water to the UHS tank passively without an external power source, it is possible to mitigate the occurrence of design-exceeding accidents, delay the time leading to a major accident, and secure the safe shutdown time of the nuclear power plant.

[0068] Although the present invention has been described in detail through representative examples above, those skilled in the art to which the present invention pertains will understand that various modifications can be made to the above-described embodiments without departing from the scope of the present invention.

[0069] Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by all changes or modifications derived from the claims and equivalent concepts as well as the claims described below.

[0070] [Explanation of symbols]

[0071] 100: Containment Vessel (CV)

[0072] 110: Reactor Vessel (RV)

[0073] 120: Heat exchanger (HX)

[0074] 130: Check valve

[0075] 200: UHS (ultimate heat sink) tank

[0076] 210: Water Level Transmitter (LT)

[0077] 300: Outdoor tank

[0078] 400: Turbine

[0079] 500: Turbine-driven pump

[0080] 510: Appendix isolation valve

[0081] 600: Ground level

Claims

1. The integrated reactor residual heat removal system is composed of a containment vessel (CV) (100), an ultimate heat sink (UHS) tank (200), an outdoor tank (300), a turbine (400), and a turbine drive pump (500). Inside the containment vessel (CV) (100), a reactor vessel (RV) (110) and a heat exchanger (HX) (120) capable of discharging residual heat to the outside are provided. When the water level meter installed in the UHS tank (200) detects that the water in the UHS tank is depleted below a specific water level, the water level transmitter (LT) (210) of the water level meter transmits a control operation signal to the pressure reducing valve (PRV) (140) of the containment vessel (CV) and the water isolation valve (510) that isolates the outdoor tank (300) through the signal transmission line (211, 212, 213) to control the valve operation. The pressure reducing valve (140) of the containment vessel (CV) (100) automatically opens when a signal is received through the level transmitter (LT) (210) of the level gauge of the UHS tank or when the pressure exceeds the preset set point of the containment vessel (CV) (100). When the pressure reducing valve (140) of the containment vessel (CV) (100) is opened, the heat energy of the high temperature and high pressure steam inside the containment vessel (CV) (100) is supplied to the turbine (TB, 400), and the heat energy that drives the turbine is converted into mechanical kinetic energy to operate the turbine drive pump (500). An integrated reactor residual heat removal system characterized in that water as cooling water is supplied from an outdoor tank (300) through an outdoor supply line (310) through a water fill isolation valve (510) and into the UHS tank (200) through a water fill supply line (520) by the operation of a turbine drive pump (500).

2. In paragraph 1, An integrated reactor residual heat removal system characterized in that the cooling water supplied from the UHS tank (200) through the supply line (220) is converted into high-temperature steam through heat exchange in a heat exchanger (HX) (120) inside the containment vessel (CV) (100), is returned to the UHS tank (200) through the steam line (230), and comes into contact with the atmosphere, so that the steam with heat is released into the atmosphere (open to evaporation).

3. In paragraph 1, An integrated reactor residual heat removal system characterized in that condensate from a turbine (400) passes through a check valve (130) along a condensate line (410) and is resupplied into the containment vessel (CV) (100), and the check valve (130) prevents the condensate from the turbine (400) from flowing back.

4. A method for removing residual heat using an integrated reactor residual heat removal system according to any one of paragraphs 1 to 3, When the integral reactor is in normal operation, a step (S1) of heat exchange is performed between the heat exchanger (HX) in the containment vessel (CV) and the UHS tank water source. Performing a heat exchange step (S2) between the UHS tank water source and the atmosphere, When the integral reactor detects ① the occurrence of a design basis exceedance accident, which is the stage (S3) where the design pressure of the containment vessel (CV) exceeds the specified level due to evaporation of the water source inside the UHS tank, the UHS LT (level transmitter) signal operates, or ② Perform a step (S4) of automatically opening the pressure reducing valve (PRV) and the water isolation valve of the containment vessel (CV), A step (S5) is performed in which high-temperature, high-pressure steam inside a containment vessel (CV) is supplied to a turbine, and the steam heat energy is converted into mechanical kinetic energy to drive a turbine-driven pump. A method for removing residual heat using an integrated reactor residual heat removal system characterized in that the step (S6) of supplying water from an outdoor tank to a UHS tank is performed and the step (S1) of returning to the normal operation step is performed.

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