A passive waste heat removal system for nuclear power plants

Abstract

This utility model relates to the field of nuclear power plant safety and energy conservation technology, and in particular to a passive residual heat removal system for nuclear power plants, including a core cooling loop, a containment cooling loop, and a switching device. The core cooling loop includes a main heat exchanger forming a natural circulation path, a riser section, at least two air coolers, and a downcomer section. The main heat exchanger is located inside the pressure vessel within the containment, and the air coolers are located outside the containment. The containment cooling loop includes connecting pipes and an in-containment heat exchanger located within the containment. The switching device connects the containment cooling loop and at least one air cooler in the core cooling loop, allowing the containment cooling loop and the core cooling loop to selectively connect to the shared air cooler. The passive residual heat removal system for nuclear power plants provided by this utility model integrates the core cooling loop and the containment cooling loop through a shared air cooler, optimizing equipment costs, improving heat removal continuity, and system response efficiency.

Description

Technical Field

[0001] This utility model relates to the field of nuclear power plant safety and energy-saving technology, and in particular to a passive waste heat removal system for nuclear power plants. Background Technology

[0002] In pressurized water reactor (PWR) nuclear power plant design, passive residual heat removal systems rely on natural forces to drive the cooling cycle, which can improve system reliability. Traditional solutions require separate systems for core residual heat removal and containment heat removal. The core cooling system necessitates a high-level, large-capacity heat exchanger tank to maintain natural circulation, resulting in high construction costs and limited layout. More importantly, the core cooling system may trigger reactor recriticality risks due to excessively rapid cooling rates during the initial commissioning phase. Furthermore, separate systems cannot share heat sink resources, leading to equipment redundancy and reduced economic efficiency. Utility Model Content

[0003] This invention provides a passive residual heat removal system for nuclear power plants. By sharing an air cooler, the core cooling circuit and containment cooling circuit are integrated, which optimizes equipment costs, improves heat removal continuity and system response efficiency. By setting up a switching device, the risk of reactor re-criticality may be caused by excessively rapid cooling rate in the early stage of core cooling system commissioning.

[0004] This utility model provides a passive waste heat removal system for nuclear power plants, comprising:

[0005] The core cooling loop includes a main heat exchanger forming a natural circulation path, a riser section, at least two air coolers, and a downcomer section; the main heat exchanger is located inside the pressure vessel within the containment and is used for core heat dissipation within the pressure vessel, while the air coolers are located outside the containment and dissipate heat through natural air convection.

[0006] The containment cooling circuit includes connecting pipes and an in-containment heat exchanger disposed within the containment.

[0007] A switching device connects at least one of the air coolers in the containment cooling circuit and the core cooling circuit, wherein the containment cooling circuit and the core cooling circuit are selectively connected to the shared air cooler via the switching device.

[0008] In one embodiment of the present invention, the switching device includes a three-way ball valve, which is connected to the outlet of the shell heat exchanger, the outlet of the main heat exchanger, and the inlet of the air cooler.

[0009] In one embodiment of the present invention, the core cooling circuit further includes a first makeup water tank and a first isolation valve disposed on the downcomer section;

[0010] The first water supply tank is connected to the downcomer section between the air cooler outlet and the first isolation valve.

[0011] In one embodiment of this utility model, the inner diameter of the connecting pipe between the first water replenishment tank and the downcomer section is less than a preset threshold.

[0012] In one embodiment of the present invention, an air-cooled tower is also included, wherein the air cooler is disposed inside the air-cooled tower and located at the bottom of the air-cooled tower.

[0013] In one embodiment of the present invention, the containment cooling circuit further includes:

[0014] Two isolation valves are located outside the containment and are normally closed; when the containment cooling requirement is triggered, the isolation valves open to connect the circuit.

[0015] In one embodiment of the present invention, in the core cooling circuit, the rising pipe section connects the outlet of the main heat exchanger and the inlet of the air cooler;

[0016] The downcomer section connects the air cooler outlet to the main heat exchanger inlet; after absorbing heat in the main heat exchanger, the cooling water is driven by the density difference to flow along the upcomer section to the air cooler.

[0017] In one embodiment of the present invention, the first water replenishment tank is configured to replenish cooling water to the core cooling circuit by gravity under accident conditions.

[0018] In one embodiment of this utility model, the air cooler is placed at the bottom of the air-cooling tower; the air-cooling tower drives air to enter from the bottom of the tower and exit from the top of the tower through the internal air density difference.

[0019] In one embodiment of the present invention, the in-shell heat exchanger is a group of heat exchangers arranged in parallel and distributed in different areas within the containment.

[0020] In one embodiment of the present invention, the number of air coolers shared by the safety cooling circuit and the core cooling circuit is less than the total number of air coolers in the core cooling circuit.

[0021] The beneficial effects of this invention are as follows: This invention proposes a passive residual heat removal system for nuclear power plants. This system dynamically connects the core cooling circuit and the containment cooling circuit to the same air cooler via a switching device. It utilizes natural air convection as the final heat sink, thus eliminating dependence on coolant capacity and makeup water systems to a certain extent, achieving long-term continuous heat removal and reducing reliance on makeup water. The high-velocity airflow established within the air cooler during core cooling circuit operation provides pre-driving force for the containment cooling circuit, significantly accelerating its natural circulation establishment process. This integrated system reduces the number of devices and construction costs while solving the problems of low heat sink resource utilization, uncontrolled cooling in the early stages of an accident, and limited long-term heat removal capacity in traditional discrete systems. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] In the attached diagram:

[0024] Figure 1 This is a passive waste heat removal system prior to the improvement of this utility model;

[0025] Figure 2 This is a containment heat removal system prior to the improvement of this utility model;

[0026] Figure 3 This is a passive waste heat removal system for nuclear power plants provided in one embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of one state of the connection channel of the three-way ball valve provided in one embodiment of the present utility model;

[0028] Figure 5 This is a schematic diagram of another state of the three-way ball valve connection channel provided in one embodiment of the present invention;

[0029] The attached diagram is labeled as follows: Main steam pipe A1, main feedwater pipe A2, emergency cooling water tank A3, waste heat discharge heat exchanger A4, makeup water tank A5, atmosphere A6, steam generator A7, and hot water exchange tank A8.

[0030] Containment 10, Air cooler 1, Air cooling tower 11, Core cooling circuit 2, Main heat exchanger 21, Rising section 22, Downcomer section 23, Containment cooling circuit 3, Isolation valve 31, In-containment heat exchanger 32, Switching device 4, Three-way ball valve 41, First makeup water tank 24, First isolation valve 25, Core 26, M inside the containment, N outside the containment. Detailed Implementation

[0031] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0032] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the present invention.

[0034] like Figure 1-2 As shown, in the design of nuclear power plants, a passive residual heat removal system is used to remove residual heat from reactor core 26, improving the safety and economy of the plant. Similarly, the design of nuclear power plants considers using a passive heat removal system to remove heat from containment 10. However, for passive equipment, to meet the capacity to remove residual heat from reactor core 26, the passive heat removal system needs to be equipped with large-volume heat exchangers and heat traps, which will be detrimental to improving the plant's economics. Therefore, it is necessary to design a residual heat removal system that functionally meets the heat removal capacity while also improving economic efficiency.

[0035] like Figure 1-2As shown, for example, in a certain third-generation reactor type, the passive core residual heat removal system is connected to the main steam pipe A1 and the main feedwater pipe A2, and consists of an emergency cooling water tank A3, a residual heat removal heat exchanger A4, and connecting pipes. The passive containment heat removal system consists of several sets of residual heat removal heat exchangers A4 installed inside the containment 10, and a heat exchange water tank A5 installed at a high position outside the containment 10 as a heat sink, and the heat exchange water tank A5 is connected to the atmosphere A6. Therefore, the external environment of the containment 10 is used as the final long-term heat sink.

[0036] The above case presents the following problems: First, both the passive core residual heat removal system and the passive containment heat removal system require a large-capacity heat exchanger tank A5, which must be placed at a high position to ensure the normal operation of the natural circulation system; Second, traditional core cooling systems may pose a potential risk of reactor re-criticality due to excessively rapid cooling rates during the initial commissioning phase, which is detrimental to reactor safety; Third, the heat exchanger tank A5 has a limited capacity, and water replenishment is required in the later stages of an accident, thus necessitating a water replenishment system and reducing the economic efficiency of the power plant.

[0037] like Figure 3-5 As shown, this utility model provides a passive residual heat removal system for a nuclear power plant, including a core cooling circuit 2, a containment cooling circuit 3, and a switching device 4;

[0038] The core cooling circuit 2 includes a main heat exchanger 21 forming a closed natural circulation path, a riser section 22, at least two air coolers 1, and a downcomer section 23; the air coolers 1 are located outside the containment 10 and dissipate heat through natural air convection; the main heat exchanger 21 is located inside the pressure vessel within the containment 10 and is used for heat dissipation of the core 26 within the pressure vessel; the containment cooling circuit 3 includes a connecting pipe 31 and an in-containment heat exchanger 32 located inside the containment 10; the switching device 4 connects the containment cooling circuit 3 with at least one of the air coolers 1 in the core cooling circuit 2, and the containment cooling circuit 3 and the core cooling circuit 2 are selectively connected to the shared air cooler 1 through the switching device 4.

[0039] It should be noted that the air cooler 1 is located outside the containment 10, and its function is to remove heat through natural air convection, serving as a heat sink for the system. The air cooler 1 can adopt a finned tube type, plate-fin type, or other structural forms, utilizing increased heat exchange area to enhance the heat dissipation effect of natural air convection. The core cooling circuit 2 forms a closed natural circulation path consisting of the main heat exchanger 21, the riser section 22, the air cooler 1, and the downcomer section 23. The main heat exchanger 21 is located in the pressure vessel inside the containment 10, directly contacting the core 26 or absorbing residual heat generated by the core 26 through the cooling medium within the pressure vessel. 1. U-tube heat exchangers, spiral tube heat exchangers, and other structures can be adopted to adapt to the spatial layout within the pressure vessel. The rising pipe section 22 and the descending pipe section 23 serve as working fluid flow channels. The rising pipe section 22 can be a single large-diameter pipe or multiple parallel small-diameter pipes, and the descending pipe section 23 is similar. The working fluid absorbs heat and rises in temperature and density at the main heat exchanger 21, and releases heat and cools in temperature and density at the air cooler 1, forming a natural circulation to continuously remove residual heat from the reactor core 26. The containment cooling circuit 3 includes connecting pipes 31 and an in-containment heat exchanger 32. The in-containment heat exchanger 32 is located inside the containment 10 and is used to absorb heat within the containment 10. (Heat generated by steam, high-temperature air, etc. due to core 26 leakage or other reasons), the in-containment heat exchanger 32 can adopt a coil heat exchanger, a spray heat exchanger (heat exchange is achieved through spraying the working fluid to contact the gas inside the containment 10), etc. The connecting pipe 31 serves as the path for the working fluid flow and can be a metal pipe or a corrosion-resistant composite material pipe to adapt to the environment inside the containment 10; the switching device 4 is configured to selectively connect the containment cooling circuit 3 to the core cooling circuit 2, so that the two circuits can share at least one air cooler 1. The switching device 4 includes a first valve and a second valve, the first valve being located between the in-containment heat exchanger 32 and the core cooling circuit 2. The inlet connecting pipe of the air cooler 1 in the core cooling circuit 2 is connected to the air cooler 1; the second valve is set on the connecting pipe between the main heat exchanger 21 and the air cooler 1; the first valve and the second valve can be electric valves, pneumatic valves, or the switching device can be a three-way ball valve, etc. The opening and closing of the valve realizes the connection or disconnection between the containment cooling circuit 3 and the air cooler 1 of the core cooling circuit 2, and its function is to control the connection timing of the two circuits; wherein, after the core cooling circuit 2 is put into operation, the switching device 4 connects the containment cooling circuit 3, so that the heat absorbed by the heat exchanger 32 in the containment 10 is discharged through the connecting pipe 31 and the air cooler 1.

[0040] The principle behind this system's solution to the technical problems of traditional solutions lies in sharing the air cooler 1, a heat sink, between the core cooling loop 2 and the containment cooling loop 3. This eliminates the need for separate high-level, large-capacity heat exchange tanks for each system, reducing the need for large equipment, lowering construction costs, and alleviating layout constraints. Furthermore, the shared air cooler 1 between the two loops enables the sharing of heat sink resources, reducing equipment redundancy and improving system economy. Specifically, it addresses the high construction costs and layout constraints caused by the separate setup of the core 26 residual heat removal and containment 10 heat extraction systems in traditional solutions; the risk of reactor re-criticality due to excessively rapid cooling rates in the initial operation of the core 26 cooling system; and the equipment redundancy and reduced economy caused by the inability of separate systems to share heat sink resources. This solution simplifies the overall structure of the passive residual heat removal system, reduces construction and maintenance costs, and lessens spatial layout restrictions. By controlling the timing of the containment cooling loop 3's connection, it avoids excessive initial cooling of the core 26, improving reactor operational safety. Through the sharing of heat sink resources, it reduces the number of devices, improving system economy and resource utilization.

[0041] As an optional embodiment of this case, the switching device 4 includes a three-way ball valve 41, which is connected to the outlet of the shell heat exchanger 32, the outlet of the main heat exchanger 21 and the inlet of the air cooler 1 respectively; the three-way ball valve 41 includes a first flow channel, a second flow channel and a third flow channel, the first flow channel is connected to the outlet of the shell heat exchanger 32, the second flow channel is connected to the outlet of the main heat exchanger 21 and the third flow channel is connected to the inlet of the air cooler 1. More specifically, the three-way ball valve 41 includes a valve body, a ball, a valve seat, a valve stem, a sealing assembly, and an operating mechanism; the valve body has three interconnected fluid interfaces forming a T-shaped or L-shaped channel layout, and the valve body adopts a three-section split structure; the ball is rotatably disposed inside the valve body, and the ball has a through fluid channel, which is T-shaped or L-shaped; the valve seat is fixed inside the valve body and fits against the surface of the ball to form a spherical seal; one end of the valve stem is fixedly connected to the ball, and the other end extends out of the valve body and is connected to the operating mechanism; the sealing assembly includes a stuffing box disposed between the valve stem and the valve body and a sealing gasket disposed at the valve body interface; the operating mechanism drives the valve stem to rotate the ball 90° to realize the switching or opening / closing of the fluid channel, and the three fluid interfaces are respectively the interfaces of the first flow channel, the second flow channel, and the third flow channel.

[0042] As an optional embodiment of this case, the switching device 4 includes a three-way ball valve 41, which is configured to connect the inlet of the heat exchanger 32 inside the containment to the outlet of the air cooler 1 and connect the outlet of the heat exchanger 32 inside the containment to the inlet of the air cooler 1 when the cooling demand of the containment 10 is triggered.

[0043] It should be noted that the switching device 4 includes a three-way ball valve 41. As the core component for realizing loop switching, the three-way ball valve 41 can change the internal flow channel connection state through electric drive. The three-way ball valve 41 is, for example, a pneumatic three-way ball valve, an electromagnetically controlled three-way valve, etc. These devices can all drive the valve core to switch the flow channel through mechanical or electromagnetic force. The switching device 4 is configured to connect the inlet of the heat exchanger 32 inside the containment 10 to the outlet of the air cooler 1 when the cooling demand of the containment 10 is triggered (for example, when the temperature or pressure inside the containment 10 reaches a preset threshold), and at the same time connect the outlet of the heat exchanger 32 inside the containment 10 to the inlet of the air cooler 1, so that the containment cooling circuit 3 is connected to the core cooling circuit 2 and shares the air cooler 1. The principle behind this setup is to utilize the switching function of the three-way structure to achieve selective connection between the two loops without the need for an additional independent heat sink. This solves the economic problem caused by equipment redundancy in traditional discrete systems. At the same time, by controlling the access timing through clear trigger conditions, it avoids interference with the initial operation of the core cooling loop 2, thereby simplifying the system piping layout, reducing equipment costs, ensuring that the containment 10 cooling is started on demand, and improving the overall coordination and reliability of the system.

[0044] As an optional embodiment of this case, the core cooling circuit 2 further includes a first makeup water tank 24 and a first isolation valve 25 disposed on the downcomer section 23, wherein the first makeup water tank 24 is connected to the downcomer section 23 between the outlet of the air cooler 1 and the first isolation valve 25.

[0045] It should be noted that the core cooling loop 2 also includes a first makeup water tank 24, which is used to replenish the cooling medium lost in the loop due to evaporation, leakage, etc., and maintain the stability of the total amount of working medium in the loop. Alternative implementations include expansion tanks with pressure stabilization functions, closed-loop liquid replenishment tanks, etc., which can all achieve the liquid replenishment function by storing a certain amount of spare working medium. The first makeup water tank 24 is connected to the downcomer section 23 between the outlet of the air cooler 1 and the first isolation valve 25. This connection position allows the working medium in the makeup water tank to flow naturally into the downcomer section 23 under the action of gravity or loop pressure difference, replenishing the working medium in a timely manner, thereby reducing the system's space height requirements, reducing the construction cost of large water tanks, ensuring sufficient working medium in the loop to maintain the continuity of natural circulation, and improving the system's economy and layout flexibility; it solves the problems of high construction cost and limited layout caused by traditional high-level water tanks.

[0046] As an optional embodiment of this case, the inner diameter of the connecting pipe of the first water replenishment tank 24 is less than a preset threshold, which is used to maintain single-phase natural circulation under accident conditions, such as the preset threshold of the inner diameter of the connecting pipe of the first water replenishment tank 24 being 50mm.

[0047] It should be noted that this pipe diameter setting is used to limit the working fluid exchange rate between the makeup water tank and the main circuit, preventing a large amount of working fluid from flowing into or out of the main circuit in a short period of time. Alternative preset thresholds include, but are not limited to, 40mm and 30mm, which can be determined based on the circuit flow rate and working fluid characteristics. This structure is used to maintain single-phase natural circulation under emergency conditions. For example, when the inner diameter of the connecting pipe is no greater than 50mm, it can effectively control the amount of working fluid exchanged between the makeup water tank and the main circuit, preventing the stability of the natural circulation from being disrupted by phase changes (such as flash evaporation or condensation) caused by violent working fluid flow. This solves the problem of circulation instability caused by working fluid phase changes in traditional systems.

[0048] As an optional embodiment of this case, the air cooler 1 is disposed inside the air-cooled tower 11 and located at the bottom of the air-cooled tower 11, the air-cooled tower 11 having a hyperbolic profile to optimize the natural air convection path.

[0049] It should be noted that the air cooler 1 is placed at the bottom of the air-cooled tower 11. This arrangement allows the air cooler 1 to directly utilize the air convection channel formed by the air-cooled tower 11 to enhance heat dissipation. As a structure that accommodates and guides airflow, the air-cooled tower 11 has a hyperbolic profile that can reduce airflow resistance and accelerate natural air convection by optimizing the change in the cross-section of the airflow channel from the air inlet to the outlet. Alternative implementations include parabolic profiles, streamlined conical profiles, etc. These profile designs can guide the orderly flow of air through smoothly transitioned geometric shapes. This structural arrangement of the air-cooled tower 11 is used to optimize the natural air convection path, so that after the cold air enters from the bottom of the tower, it rises along the tower body under the action of thermal buoyancy and carries away the heat released by the air cooler 1. The principle behind this setup is to enhance the intensity and stability of natural air convection by utilizing the specially contoured air-cooled tower 11, thereby solving the problem that the traditional air cooler 1 has limited heat dissipation efficiency when relying solely on the surrounding ambient air. This improves the heat dissipation capacity of the air cooler 1, ensuring the heat dissipation effect when the core cooling circuit 2 and the containment cooling circuit 3 share the heat sink. At the same time, the integrated design of the air-cooled tower 11 reduces the system's footprint and improves the rationality of the overall layout.

[0050] As an optional embodiment of this case, when the switching device 4 switches, it immediately connects the in-shell heat exchanger 32 to the corresponding air cooler 1 when the main heat exchanger 21 is shut down and the air cooler 1 is closed; when the core cooling circuit 2 is put into operation, the predetermined flow rate airflow established in the air cooler 1 promotes the natural circulation of the containment cooling circuit 3.

[0051] It should be noted that when the core cooling circuit 2 is put into operation, the surrounding air is heated through the heat release process of the working fluid in the air cooler 1. This causes the air to generate natural convection due to density differences, forming an airflow with a predetermined velocity. This predetermined velocity can be controlled by the heat exchange area, fin structure, or profile design of the air cooler 11. The principle is to utilize the airflow established after the core cooling circuit 2 is started to provide additional convective power for the containment cooling circuit 3, solving the problem of insufficient natural circulation driving force when the containment cooling circuit 3 is started alone. This ensures that the containment cooling circuit 3 can quickly establish an effective circulation after being connected, improving the timeliness and efficiency of heat removal from the containment 10. Simultaneously, there is no need to set up an additional airflow driving device for the containment cooling circuit 3, reducing equipment redundancy and improving system economy.

[0052] As an optional embodiment of this case, the containment cooling circuit 3 further includes two isolation valves 31 located outside the containment 10 and in a normally closed state; when the switching device 4 is triggered, the isolation valves 31 are opened to connect the circuit.

[0053] It should be noted that the containment cooling circuit 3 also includes two isolation valves 31. These isolation valves 31, acting as components to block or connect the circuit, are located outside the containment 10 to prevent the high-temperature, high-pressure environment inside the containment 10 from affecting valve performance. Being normally closed, they prevent accidental connection between the containment cooling circuit 3 and the core cooling circuit 2 in a non-triggered state, thus avoiding working fluid leakage or circuit interference. When the switching device 4 is triggered—that is, when the containment 10 requires cooling—the switching device 4 sends a signal to control the isolation valves 31 to open, creating a connected flow path between the containment cooling circuit 3 and the core cooling circuit 2. The principle of this setup is to achieve reliable isolation of the containment cooling circuit 3 through the normally closed isolation valves 31, and to establish a circuit only when needed through the linkage of the switching device 4. This solves the problem of unreliable circuit isolation in traditional systems leading to malfunctions or working fluid loss, thereby improving the safety and reliability of system operation. It ensures that the containment cooling circuit 3 is only put into operation when necessary, avoiding interference with the normal operation of the core cooling circuit 2. Furthermore, the external valves facilitate maintenance, reducing system maintenance costs.

[0054] As an optional embodiment of this case, in the core cooling circuit 2: the rising pipe section 22 connects the outlet of the main heat exchanger 21 to the inlet of the air cooler 1; the falling pipe section 23 connects the outlet of the air cooler 1 to the inlet of the main heat exchanger 21; after absorbing heat in the main heat exchanger 21, the cooling water flows to the air cooler 1 along the rising pipe section 22 driven by the density difference.

[0055] It should be noted that in the core cooling loop 2, the rising pipe section 22 connects the outlet of the main heat exchanger 21 to the inlet of the air cooler 1. This connection can be made of flange or welded connection. The rising pipe section 22 can be made of high-temperature alloy pipe, seamless steel pipe, or other materials. Its direction can be vertical or inclined depending on the spatial layout. The falling pipe section 23 connects the outlet of the air cooler 1 to the inlet of the main heat exchanger 21. The connection can also be made of flange or welded connection. The falling pipe section 23 can be made of the same or compatible material as the rising pipe section 22. Its direction can be vertical or stepped to adapt to the layout requirements. The cooling water exchanges heat with the core 26 in the main heat exchanger 21 and absorbs heat, resulting in a decrease in its density. Under the buoyancy generated by the density difference, it flows naturally along the rising pipe section 22 to the air cooler 1. After heat dissipation, its density increases, and it flows back to the main heat exchanger 21 along the falling pipe section 23, forming a continuous natural circulation. The principle of this setup is to use the driving force generated by the density difference after the working fluid absorbs heat to achieve circulation without external power. This solves the problem of reduced reliability caused by the reliance on pumps and other active equipment in traditional systems, thereby eliminating the risk of failure of active components, improving the reliability of core 26 cooling, simplifying the system structure and reducing operating energy consumption. At the same time, the flexible pipe connection and routing design can adapt to different spatial layout requirements.

[0056] As an optional embodiment of this case, the first water replenishment tank 24 is configured to replenish cooling water to the core cooling circuit 2 by gravity under accident conditions.

[0057] It should be noted that the first makeup water tank 24 is configured to replenish cooling water to the core cooling circuit 2 by gravity during accident conditions. The installation position of the first makeup water tank 24 is higher than its connection point with the downcomer section 23, forming a certain liquid level difference to provide gravity driving force. The shape of the makeup water tank can be cylindrical, square, etc., and the material can be corrosion-resistant metal or composite material to adapt to the cooling water quality. The principle of this configuration is to use gravitational potential energy to make the cooling water in the makeup water tank automatically flow in when the working fluid in the circuit is insufficient, without the need for additional pump equipment to provide power. This solves the reliability risks caused by relying on active equipment for liquid replenishment in traditional systems and the problem of excessive cost of high-level large-volume water tanks. This ensures timely replenishment of the working fluid during accident conditions, maintains the continuity of the natural circulation of the core cooling circuit 2, avoids the use of active components, improves the safety and economy of the system, and simplifies the structural design of the liquid replenishment system.

[0058] As an optional embodiment of this case, the air cooler 1 is placed at the lower part of the air cooling tower 11; the air cooling tower 11 drives air to enter from the bottom of the tower and exit from the top of the tower through the internal air density difference.

[0059] It should be noted that the air cooler 1 is placed at the bottom of the air-cooled tower 11. This arrangement allows the air cooler 1 to directly contact the cold air entering from the bottom of the tower, improving heat exchange efficiency. The air cooler 1 can be installed in the bottom of the air-cooled tower 11 by means of suspension, bracket fixing, etc., and its arrangement can be a single row or a combination of multiple rows. The air-cooled tower 11 creates an air density difference through the temperature difference between the internal air and the external environment, driving the cold air to enter from the bottom of the tower and absorb the heat released by the air cooler 1. The heated air flows upward due to the decrease in density and is discharged from the top of the tower, forming a continuous natural convection. The principle of this setup is to enhance the heat dissipation effect of the air cooler 1 by utilizing the cold air environment and density difference driven airflow at the bottom of the air-cooled tower 11. This solves the problem of unstable heat dissipation efficiency caused by the traditional air cooler 1 being exposed to the external environment, thereby improving the heat dissipation capacity and stability of the air cooler 1. This ensures that it can meet the heat dissipation requirements of the core cooling loop 2 and the containment cooling loop 3 as a shared heat sink. At the same time, the natural convection design of the air-cooled tower 11 eliminates the need for active equipment such as fans, reducing energy consumption and failure risk, and improving the overall reliability of the system.

[0060] As an optional embodiment of this case, the three-way ball valve 41 is configured such that: when the containment cooling circuit is in operation, the flow path between the main heat exchanger 21 and the target shared air cooler 1 in the core cooling circuit is first cut off, and then at least one of the multiple air coolers 1 (i.e. the target shared air cooler) is connected to the containment cooling circuit 3; when the containment cooling circuit is out of operation, the flow path between it and the shared air cooler 1 is first cut off, and then the connection between the main heat exchanger 21 and the shared air cooler 1 in the core cooling circuit is restored.

[0061] As an optional embodiment of this case, the in-shell heat exchanger 32 is a group of heat exchangers arranged in parallel and distributed in different areas within the containment 10.

[0062] It should be noted that the heat exchanger 32 inside the containment 10 is a group of heat exchangers arranged in parallel. Each group of heat exchangers is connected by parallel pipelines to form an independent heat exchange unit. Alternative implementation methods include a hybrid heat exchanger group combining series and parallel connections, a modular and detachable heat exchanger group, etc. These arrangements can all achieve synchronous heat exchange in multiple areas. The heat exchanger groups are distributed in different areas inside the containment 10, such as the top space of the containment 10, near the side walls, and the bottom area, to cover various locations inside the containment 10 where heat may accumulate. The principle of this setup is to expand the heat exchange area by arranging multiple sets in parallel and to achieve uniform heat absorption throughout the containment 10 by utilizing a dispersed distribution. The parallel structure ensures that the remaining sets can still work normally when a single set of heat exchangers fails. This solves the problems of limited heat absorption range and easy local heat accumulation of traditional single or centralized in-shell heat exchangers 32. As a result, it improves the uniformity and efficiency of heat removal within the containment 10, enhances the redundancy and reliability of the system, adapts to the complex heat distribution within the containment 10, and ensures that the pressure and temperature of the containment 10 are effectively controlled. At the same time, the modular inter-set design facilitates maintenance and replacement, reducing system operation and maintenance costs.

[0063] As an optional embodiment of this case, the number of air coolers 1 shared by the containment cooling circuit 3 and the core cooling circuit 2 is less than the total number of air coolers 1 in the core cooling circuit 2. Since the containment cooling circuit 3 generally does not need to share all the air coolers 1 with the core cooling circuit 2, the number of air coolers 1 shared by the containment cooling circuit 3 and the core cooling circuit 2 is less than the total number of air coolers 1 in the core cooling circuit 2. This avoids waste caused by installing too many conversion devices 4. On the other hand, it also avoids transferring all the air coolers 1 in the core cooling circuit 2 to the containment cooling circuit 3, which would reduce the cooling efficiency of the core cooling circuit 2 and the overall cooling efficiency of the passive residual heat removal system of the nuclear power plant.

[0064] This patent uses a pressurized water reactor as an example to propose a specific technical solution. A schematic diagram of the device can be found here. Figure 3The waste heat removal system of the nuclear power plant in this case includes a core 26 cooling section and a containment 10 cooling section. Regarding the core 26 cooling section, the main heat exchanger 21 absorbs heat from the pressure vessel, causing the cooling water to heat up and its density to decrease. Driven by buoyancy, the cooling water flows upward along the riser section 22 to the air cooler 1. After being cooled by air in the air cooler 1, the cooling water flows back to the main heat exchanger 21 by gravity along the downcomer section 23. The air cooler 1 is located at the lower part of the air-cooled tower 11. The ambient air is driven to enter from the lower part of the air-cooled tower 11 and exit from the upper part of the air-cooled tower 11 by the lifting force generated by the density difference within the air-cooled tower 11. Regarding the cooling section of containment 10, when the containment cooling circuit 3 is activated, the flow path between the main heat exchanger 21 in the core cooling circuit 2 and a portion of the air coolers 1 (i.e., the shared air cooler) is first cut off via a three-way ball valve 41. Then, the two isolation valves 31 of the containment cooling circuit 3 are opened, and the shared air cooler 1 is connected to the containment cooling circuit 3 via an electric three-way ball valve 41. Under the influence of density difference, the cooling water in the heat exchanger 32 inside the containment absorbs heat from the containment 10 and flows into the shared air cooler 1 through a connecting pipe. In the air cooler 1, it exchanges heat with the air through the pipe wall and cools down. The cooled water returns to the heat exchanger 32 inside the containment, thus achieving unlimited heat dissipation capacity. When the cooling requirement of containment 10 is relieved, the isolation valve 31 is first closed, and then the connection between the containment cooling circuit 3 and the shared air cooler 1 is cut off via an electric three-way ball valve 41, restoring the flow path between the core cooling circuit and the shared air cooler 1.

[0065] This project primarily achieves the following technical effects: First, it simplifies the containment heat removal system and the core residual heat removal system. Both containment 10 heat removal and core 26 residual heat removal utilize air as the final heat sink, allowing for unlimited heat removal from containment 10 and core 26, simplifying system design and improving plant safety and economy. Second, the residual heat removal system operates the core 26 residual heat removal section and the containment 10 heat removal section as needed. After the core 26 residual heat removal section is operational, it ensures a high upward airflow velocity within the air-cooled tower 11, enabling rapid establishment of natural circulation when the containment 10 heat removal section is operational, resulting in high system stability. Third, the connecting pipe of the first makeup water tank 24 uses a small inner diameter pipe, which can handle breach-type accidents and ensures that the passive residual heat removal system of the nuclear power plant operates as a single-phase natural circulation, improving plant safety. In this case, the use of a three-way ball valve 41 allows the same air-cooled system to be used for both heat removal from the containment 10 and residual heat removal from the core 26, simplifying system configuration and improving the economic efficiency of the power plant. The first makeup water tank 24 is located between the air cooler 1 and the descending section of the isolation valve 31, ensuring that the natural circulation direction is positive and improving the safety of the power plant.

[0066] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A nuclear power plant passive residual heat removal system, characterized by, include: The core cooling loop includes a main heat exchanger forming a natural circulation path, a riser section, at least two air coolers, and a downcomer section; the main heat exchanger is located inside the pressure vessel within the containment and is used for core heat dissipation within the pressure vessel, while the air coolers are located outside the containment and dissipate heat through natural air convection. The containment cooling circuit includes connecting pipes and an in-containment heat exchanger disposed within the containment. A switching device connects at least one of the air coolers in the containment cooling circuit and the core cooling circuit, wherein the containment cooling circuit and the core cooling circuit are selectively connected to the shared air cooler via the switching device.

2. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, The switching device includes a three-way ball valve, which is connected to the outlet of the shell heat exchanger, the outlet of the main heat exchanger, and the inlet of the air cooler.

3. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, The core cooling circuit also includes a first makeup water tank and a first isolation valve disposed on the downcomer section; The first water supply tank is connected to the downcomer section between the air cooler outlet and the first isolation valve.

4. The nuclear power plant passive residual heat removal system in accordance with claim 3, characterized by, The inner diameter of the connecting pipe between the first water replenishment tank and the downcomer section is less than a preset threshold.

5. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, It also includes an air-cooled tower, wherein the air cooler is disposed inside the air-cooled tower and located at the bottom of the air-cooled tower.

6. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, The containment cooling circuit also includes: Two isolation valves are located outside the containment and are normally closed; when the containment cooling requirement is triggered, the isolation valves open to connect the circuit.

7. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, In the core cooling circuit: The riser section connects the outlet of the main heat exchanger to the inlet of the air cooler. The downcomer section connects the air cooler outlet to the main heat exchanger inlet; After absorbing heat in the main heat exchanger, the cooling water is driven by the density difference to flow along the riser section to the air cooler.

8. The nuclear power plant passive residual heat removal system in accordance with claim 3, characterized by, The first water replenishment tank is configured to replenish the core cooling circuit with cooling water by gravity during accident conditions.

9. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, The air cooler is located at the bottom of the air cooling tower; The air-cooled tower uses the internal air density difference to drive air to enter from the bottom of the tower and exit from the top.

10. The nuclear power plant passive residual heat removal system in accordance with claim 1, characterized by, The number of air coolers shared by the containment cooling circuit and the core cooling circuit is less than the total number of air coolers in the core cooling circuit.

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