Anti-freezing passive residual heat removal system and use method

Abstract

The invention provides an anti-freezing passive residual heat removal system and a use method, and belongs to the nuclear safety passive field. The problems that a traditional waste heat removal system depends on a large-volume water tank, is insufficient in heat dissipation continuity and is difficult to adapt to extremely cold climate are solved. Comprising a steam generator, a cooling water tank, a water cooling loop, an air cooling loop and a spraying system, the air cooling loop comprises a pressure difference transmitter, a series heat exchanger and an air cooling heat exchanger, the series heat exchanger is arranged in the cooling water tank, and an outlet of the series heat exchanger is communicated with an inlet of the air cooling heat exchanger through an air outlet pipeline; an outlet of the air-cooled heat exchanger communicates with an inlet of the series heat exchanger through a backflow pipeline. A series heat exchanger inlet header is arranged on the backflow pipeline, a series heat exchanger outlet header is arranged on the air outlet pipeline, one end of the pressure difference transmitter is connected with an outlet of the series heat exchanger outlet header, and the other end of the pressure difference transmitter is connected with an inlet of the series heat exchanger inlet header. And a rotary-vane vacuum pump is arranged at the outlet end of the air-cooled heat exchanger.

Description

Technical Field

[0001] This invention belongs to the field of passive nuclear safety technology, and in particular relates to a passive residual heat removal system for preventing freezing and its usage method. Background Technology

[0002] Passive natural circulation heat removal systems achieve heat transfer based on the principle of natural circulation and have significant application value in various industrial fields such as nuclear energy safety and industrial waste heat utilization. These systems drive the circulation of cooling media through physical effects such as natural convection and gravity, achieving continuous heat removal without relying on an external power source. This provides a reliable heat removal path for critical equipment. In the field of nuclear energy applications, passive waste heat removal systems are of particular significance in ensuring reactor safety and preventing radioactive release. Taking China's independently developed third-generation nuclear power technology, "Hualong One," as an example, its safety system design... The design embodies an advanced passive safety concept. Its passive residual heat removal system, installed on the secondary side of the steam generator, can automatically start operating under accident conditions. Through mechanisms such as gravity diversion and natural circulation, the residual heat from the reactor core is transferred to a water tank located at an elevated position. Finally, the heat is discharged into the atmosphere through the evaporation of water, effectively improving the nuclear power plant's ability to cope with extreme accidents. It provides an important reference for the application of passive safety technology in a wider range of scenarios. Especially in special applications such as marine nuclear power platforms, the passive residual heat removal system is regarded as a key technical means to ensure nuclear safety due to its characteristics of not being easily affected by external power.

[0003] Most existing passive waste heat removal systems continue the technical approach of using large water tanks as the final heat sink, relying on the sensible heat absorption and latent heat of phase change of the water to achieve heat transfer. However, this design has obvious limitations under extreme accident conditions. When the water stored in the tank is consumed by continuous evaporation, the system will lose its ability to continuously remove heat. This defect is particularly evident in special application scenarios such as marine nuclear power platforms. Since the platform is far from shore support, it is difficult to replenish the cooling medium, making it difficult to achieve the goal of truly long-term passive heat removal safety. In addition, when the large water tank design of land-based nuclear power plants is directly applied to marine platforms where space and load-bearing capacity are strictly limited, there are problems such as crowded equipment layout, increased platform center of gravity, and structural reinforcement costs, which significantly increase the difficulty and cost of engineering implementation.

[0004] For nuclear energy plants operating in high-latitude regions, the low-temperature environment creates favorable conditions for air cooling. Theoretically, an air-cooled waste heat removal system can utilize low-temperature air to achieve near-perpetual heat removal, overcoming the problem of water tank capacity limitations. However, after the reactor is shut down, the decay heat power decreases exponentially over time, requiring the system to have the ability to quickly remove a large amount of waste heat in the initial stage of operation. However, the heat exchange efficiency of air is much lower than that of water, making it difficult to meet the initial high-power heat removal requirements. Furthermore, extreme low-temperature environments can easily cause the internal medium of the system to freeze, resulting in flow channel blockage or equipment damage, seriously affecting the reliability of the system. Summary of the Invention

[0005] In view of this, the present invention aims to propose a passive waste heat removal system and its usage method to solve the problems of traditional waste heat removal systems that rely on large-capacity water tanks, have insufficient heat dissipation continuity, and are difficult to adapt to extremely cold climates.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a passive waste heat removal system for freeze protection, comprising a steam generator, a cooling water tank, a water-cooled circuit, an air-cooled circuit, and a spray system. The water-cooled circuit includes a system isolation valve, a water-cooled heat exchanger inlet manifold, a water-cooled heat exchanger, a water-cooled heat exchanger outlet manifold, and a condensate isolation valve connected sequentially by pipes. The inlet of the system isolation valve is connected to the outlet of the steam generator, and the outlet of the condensate isolation valve is connected to the return end of the steam generator. The water-cooled heat exchanger is disposed inside the cooling water tank. The air-cooled circuit includes a differential pressure transmitter, a series heat exchanger, and an air-cooled heat exchanger. The series heat exchanger is disposed inside the cooling water tank, and the outlet of the series heat exchanger is connected to the inlet of the air-cooled heat exchanger via an outlet pipe. The outlet of the air-cooled heat exchanger is connected to the inlet of the series heat exchanger via a return pipe; the return pipe is equipped with the inlet header of the series heat exchanger, and the outlet pipe is equipped with the outlet header of the series heat exchanger; one end of the differential pressure transmitter is connected to the outlet of the outlet header of the series heat exchanger, and the other end is connected to the inlet of the inlet header of the series heat exchanger; the spray system includes a spray pipe, a spray device, a wind duct, a spray water collection device, and a spray return pipe; one end of the spray pipe is connected to the top of the cooling water tank, and the other end is equipped with a spray device and extends into the wind duct; the spray water collection device is located at the bottom of the wind duct; one end of the spray return pipe is connected to the spray water collection device, and the other end is connected to the cooling water tank; a rotary vane vacuum pump is installed at the outlet end of the air-cooled heat exchanger.

[0007] Furthermore, a water-cooled heat exchanger flow equalization plate is provided inside the inlet header of the water-cooled heat exchanger.

[0008] Furthermore, an electric pump is installed on the water-cooling circuit.

[0009] Furthermore, a flow equalization plate for the series heat exchanger is provided inside the inlet header of the series heat exchanger.

[0010] Furthermore, the air-cooled heat exchanger adopts an annular finned tube structure, with the tube bundles arranged in a triangular pattern and independent control valves installed on both sides of the tube bundles.

[0011] Furthermore, the water-cooled heat exchanger is a shell-and-tube heat exchanger.

[0012] Furthermore, an electromagnetic level gauge is installed inside the cooling water tank.

[0013] Furthermore, the air-cooled heat exchanger is positioned above the cooling water tank, and the water-cooled heat exchanger is positioned above the steam generator.

[0014] Furthermore, a shut-off valve is installed on the spray return pipe.

[0015] A method of using a passive waste heat removal system for frost prevention includes the following steps: S1: Under cold conditions, water is added to the air-cooled system until the water level covers the outlet end of the outlet header of the series heat exchanger. Water replenishment is completed when the reading of the differential pressure transmitter returns to zero. The pressure of the air-cooled system is reduced by a rotary vane vacuum pump. S2: Open the system isolation valve and condensate isolation valve. The core residual heat is discharged into the steam generator. The generated steam enters the water-cooled heat exchanger. The steam transfers heat to the cooling water tank through the water-cooled heat exchanger and then condenses into condensate, which flows back to the steam generator through the pipeline. S3: After the water in the cooling water tank is heated, the heat in the cooling water tank is removed through the series heat exchanger. After the water in the air-cooled system pipeline is heated, it boils. The steam enters the air-cooled heat exchanger for cooling and then flows back to the series heat exchanger. S4: When the cooling water in the cooling water tank is heated to boiling, the generated steam enters the spray pipe and is sprayed out through the spray device to spray the air-cooled heat exchanger. The spray water is cooled in the air duct and collected by the spray water collection device, and then flows back to the cooling water tank through the spray return pipe to complete the passive waste heat discharge.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention, by setting up a heat dissipation structure that combines water-cooled and air-cooled circuits, enables the system to quickly remove a large amount of decay heat during initial operation by utilizing the high-efficiency heat exchange characteristics of the water-cooled heat exchanger. This effectively overcomes the problem of insufficient heat removal capacity of a purely air-cooled system in the early stages of an accident. When the cooling water tank temperature rises, the system can automatically switch to the air-cooled circuit for continuous heat removal, using air cooling to achieve long-term operation of the system. This addresses the dual needs of high-power heat removal in the early stages of an accident and long-term continuous operation. Furthermore, by using water level coverage of the outlet end of the series heat exchanger outlet header and a rotary vane vacuum pump to maintain the system pressure at a low pressure, the system avoids frost formation and medium freezing in extreme cold weather, significantly improving the system's adaptability to cold conditions and solving the low-temperature operation problem faced by nuclear power plants in high-latitude regions. 2. The passive waste heat removal system of the present invention uses the atmosphere as the final heat sink, which fundamentally avoids the risk of heat removal interruption caused by the depletion of water due to water evaporation in the traditional water tank solution. The spray water collection device in the spray system leads the collected spray water back to the cooling water tank through the spray return pipe, thereby reducing the loss of cooling medium. The cooling water tank no longer needs to be replenished frequently, so that the system can still maintain long-term stable operation under the condition of limited external supply. It is particularly suitable for the safety requirements of continuous heat removal in special application scenarios such as offshore platforms. 3. This invention adopts a compact modular design, which greatly reduces the dependence on large-capacity water tanks through the cooperation of multi-stage heat exchangers. The series heat exchangers are set inside the cooling water tank and, together with the spray system, form a multi-stage synergistic heat dissipation mechanism. This structural design not only improves the system's heat dissipation efficiency, but also significantly reduces the dependence on large-capacity water tanks, effectively alleviating the pressure on the offshore platform in terms of spatial layout and structural load-bearing capacity. Furthermore, the passive operation mode of natural circulation reduces the demand for external power, thereby improving the system's economy and inherent safety. 4. This invention monitors temperature by installing thermocouples in water-cooled heat exchangers, series heat exchangers, and air-cooled heat exchangers, as well as at the inlet and outlet headers of water-cooled heat exchangers. This is combined with electromagnetic level gauges and differential pressure transmitters to capture the changing trends of system operating parameters in real time, facilitating timely understanding of the system's operating status, providing data support for operating condition adjustments, and further ensuring stable system operation. 5. This invention uses a rotary vane vacuum pump to control the pressure of the air-cooled circuit system under negative pressure, which significantly reduces the boiling point of the cooling medium in the circuit, allowing the medium to boil violently even at low water temperatures. The vacuum negative pressure environment enhances the phase change heat transfer process, enabling the series heat exchangers to establish a stable steam flow more quickly. This greatly improves the thermal response speed and heat exchange efficiency of the air-cooled circuit during startup and low-load operation, and enhances the system's ability to cope with changing operating conditions. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the structure of a passive waste heat removal system for frost prevention according to the present invention.

[0018] In the picture: 1. Steam generator; 2. System isolation valve; 3. Inlet manifold of water-cooled heat exchanger; 4. Flow equalization plate of water-cooled heat exchanger; 5. Water-cooled heat exchanger; 6. Cooling water tank; 7. Electromagnetic level gauge; 8. Spraying device; 9. Air duct; 10. Air-cooled heat exchanger; 11. Rotary vane vacuum pump; 12. Spray water collection device; 13. Shut-off valve; 14. Inlet manifold of series heat exchanger; 15. Flow equalization plate of series heat exchanger; 16. Series heat exchanger; 17. Electric pump; 18. Condensate isolation valve; 19. Outlet manifold of water-cooled heat exchanger; 20. Outlet manifold of series heat exchanger; 21. Differential pressure transmitter. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0020] Detailed Implementation Method 1: See Figure 1This embodiment describes a passive waste heat removal system for freeze protection, comprising a steam generator 1, a cooling water tank 6, a water-cooled circuit, an air-cooled circuit, and a spray system. The water-cooled circuit includes a system isolation valve 2, a water-cooled heat exchanger inlet manifold 3, a water-cooled heat exchanger 5, a water-cooled heat exchanger outlet manifold 19, and a condensate isolation valve 18, all connected sequentially by pipes. The inlet of the system isolation valve 2 is connected to the outlet of the steam generator 1, and the outlet of the condensate isolation valve 18 is connected to the return end of the steam generator 1. The water-cooled heat exchanger 5 is housed within the cooling water tank 6. The steam generator 1 is used to transfer heat from the reactor core into the water-cooled circuit. The system isolation valve 2 and the condensate isolation valve 18... The valve 18 is used to control the start and stop of the system. The inlet header 3 of the water-cooled heat exchanger is used to distribute the steam generated by the steam generator 1 to the water-cooled heat exchanger 5. The outlet header 19 of the water-cooled heat exchanger is used to collect the condensate generated by the water-cooled heat exchanger 5 and return it to the steam generator 1 through the return pipe. The water-cooled heat exchanger 5 is used to transfer the heat of the steam to the water in the cooling water tank 6. The heat generated by the reactor core enters the steam generator 1 and heats the steam generator 1, which generates steam. The steam flows through the pipe to the water-cooled heat exchanger 5 located in the cooling water tank 6. After the steam encounters the cold water and condenses into condensate, it flows back to the steam generator 1 through the pipe, realizing primary heat exchange. The air-cooled circuit includes a differential pressure transmitter 21, a series heat exchanger 16, and an air-cooled heat exchanger 10. The series heat exchanger 16 is installed inside the cooling water tank 6. The outlet of the series heat exchanger 16 is connected to the inlet of the air-cooled heat exchanger 10 via an exhaust pipe. The outlet of the air-cooled heat exchanger 10 is connected to the inlet of the series heat exchanger 16 via a return pipe. The series heat exchanger 16 is used to transfer heat from the cooling water tank 6 to the air-cooled circuit. The steam from the series heat exchanger 16 enters the air-cooled heat exchanger 10 for condensation. The differential pressure transmitter 21 is used to measure the pressure difference between the exhaust pipe and the return pipe of the air-cooled circuit. The return pipe is provided with the inlet of the series heat exchanger. The header 14 has a series heat exchanger outlet header 20 installed on the air outlet pipe. One end of the differential pressure transmitter 21 is connected to the outlet of the series heat exchanger outlet header 20, and the other end is connected to the inlet of the series heat exchanger inlet header 14. When the water in the cooling water tank 6 is heated, the series heat exchanger 16 installed in the cooling water tank 6 absorbs the heat in the cooling water tank 6, and the water level in the series heat exchanger 16 gradually rises. After heating, the hot water flows into the air-cooled heat exchanger 10 through the series heat exchanger outlet header 20 under the action of buoyancy. After the hot water in the air-cooled heat exchanger 10 is cooled, it flows back to the series heat exchanger 16 through the series heat exchanger inlet header 14 under the action of gravity, thus realizing two-stage heat exchange.The spray system includes a spray pipe, a spray device 8, a duct 9, a spray water collection device 12, and a spray return pipe. One end of the spray pipe is connected to the top of the cooling water tank 6, and the other end is equipped with the spray device 8 and extends into the duct 9. The spray water collection device 12 is located at the bottom of the duct 9. One end of the spray return pipe is connected to the spray water collection device 12, and the other end is connected to the cooling water tank 6. The duct 9 provides a stable air passage for the air-cooled heat exchanger 10 and the spray device 8, utilizing natural air convection to improve heat dissipation efficiency. The spray device 8 uses spiral spray nozzles. The shut-off valve 13 is used to control the opening and closing of the spray return pipe. When the water temperature in the cooling water tank 6 is too high and boils, the generated steam is sprayed out through the spray device 8 on the spray pipe into the duct 9 and forms a liquid film on the surface of the air-cooled heat exchanger 9. The steam ejected from the spray device 8 drives the airflow in the duct 9 through the chimney effect. The steam condenses into droplets and forms a liquid film on the surface of the air-cooled heat exchanger 10. This liquid film, with its much higher thermal conductivity than air, fills the thermal resistance gap between the air and the wall, and simultaneously generates micro-convection with the airflow, significantly reducing the contact thermal resistance between the wall and the fluid, thus enhancing convective heat transfer. Furthermore, although the liquid film does not reach its boiling point, water molecules on its surface diffuse into the air and evaporate through molecular thermal motion, further increasing the heat transfer per unit area and improving thermal conductivity through a large amount of latent heat of vaporization. A rotary vane vacuum pump 11 is installed at the outlet of the air-cooled heat exchanger 10. This pump reduces the pressure in the air-cooling circuit, thereby lowering the freezing point of the water and preventing the water in the pipes of the air-cooling circuit from freezing due to low temperatures.

[0021] This invention addresses the waste heat removal requirements of nuclear power plants by designing a cascaded heat transfer architecture consisting of a water-cooled circuit, an air-cooled circuit, and a spray system. Through deep integration of multi-circuit collaboration, passive drive, and efficient heat exchange, it solves problems such as reliance on large-capacity water tanks, insufficient heat dissipation continuity, and limited environmental adaptability in traditional waste heat removal systems. A vacuum environment is established using a rotary vane vacuum pump 11, lowering the boiling point of water and ensuring the water level covers the outlet end of the series heat exchanger header, thus solving the problems of system frosting and medium freezing in extreme cold weather. Furthermore, the steam generator 1 transfers core waste heat to the water-cooled reflux, and gravity drives the natural circulation of condensate. The water-cooled heat exchanger 5 introduces heat into the cooling water tank 6, initially completing heat transfer. The series heat exchanger 16 installed in the cooling water tank 6 then introduces heat into the air-cooled circuit. Once the water in the cooling water tank 6 is heated to boiling, it enters the spray system, where it further absorbs waste heat, thus achieving continuous operation of the waste heat removal system.

[0022] The inlet manifold 3 of the water-cooled heat exchanger is equipped with a water-cooled heat exchanger flow equalization plate 4, which can ensure that steam enters the water-cooled heat exchanger 5 evenly.

[0023] An electric pump 17 is installed on the water cooling circuit. The electric pump 17 is used to increase the flow rate of the water cooling circuit, thereby enhancing the heat exchange efficiency.

[0024] The inlet header 14 of the series heat exchanger is provided with a flow equalization plate 15 for the series heat exchanger, which is used to ensure that water flows into the series heat exchanger 16 evenly.

[0025] The air-cooled heat exchanger 10 adopts an annular finned tube structure, with the tube bundle arranged in a triangular pattern. Independent control valves are set on both sides of the tube bundle, which can adjust the number of heat exchange tubes and thus the heat exchange capacity of the air-cooled system by opening and closing the valves on both sides of the heat exchange tubes of the air-cooled heat exchanger 10. The air-cooled heat exchanger 10 is arranged at an angle of 3° to 5°, and the condensate is guided to flow in a specific direction by gravity, so as to avoid the problem of increased flow resistance or local heat exchange failure caused by the condensate stagnation in the tubes of the air-cooled heat exchanger 10.

[0026] The water-cooled heat exchanger 5 is a shell-and-tube heat exchanger. After steam enters the water-cooled heat exchanger 5, it is cooled by exchanging heat with the water in the cooling water tank 6. The condensed water is left in the steam generator 1 under the action of gravity, thus establishing a natural circulation.

[0027] An electromagnetic level gauge 7 is installed inside the cooling water tank 6. The electromagnetic level gauge 7 is vertically installed inside the cooling water tank 6 and is used to measure the liquid level in the cooling water tank 6.

[0028] The air-cooled heat exchanger 10 is positioned higher than the cooling water tank 6. It utilizes gravity and density difference to drive the air-cooled circuit to achieve natural circulation. The water in the series heat exchangers 16 in the cooling water tank 6 is heated and boils, causing its density to decrease. It rises to the air-cooled heat exchanger 10, condenses, and increases in density before flowing back by gravity. At the same time, this height difference ensures that the condensate can flow back to the cooling water tank 6 when the system is shut down, preventing the air-cooled heat exchanger 10 from freezing and cracking in extremely cold environments. The water-cooled heat exchanger 5 is positioned higher than the steam generator 1 to establish a natural circulation driving force for the water-cooled circuit. The steam generated by the steam generator 1 rises to the water-cooled heat exchanger 5 due to the density difference and condenses. The condensate can then flow back to the steam generator 1 by gravity, thereby achieving continuous passive heat discharge without relying on external power.

[0029] A shut-off valve 13 is provided on the spray return pipe. The shut-off valve 13 is used to control the opening and closing of the spray return pipe, so that the system can close the spray return pipe when maintenance is required or when spray return is not needed.

[0030] A method of using a passive waste heat removal system for frost prevention includes the following steps: S1: Under cold conditions, add water to the air-cooled system until the water level can cover the outlet end of the outlet header 20 of the series heat exchanger. Observe the reading of the differential pressure transmitter 21. When the reading of the differential pressure transmitter 21 returns to zero, the water replenishment is completed. Reduce the pressure of the air-cooled system by the rotary vane vacuum pump 11 to 0.02MPa. S2: Open system isolation valve 2 and condensate isolation valve 18. After the waste heat discharge system is put into operation, the first-stage heat exchange is carried out. The core waste heat is discharged into the steam generator 1. The generated steam enters the water-cooled heat exchanger 5. The steam transfers heat to the cooling water tank 6 through the water-cooled heat exchanger 5 and then condenses into condensate. The condensate flows back to the steam generator 1 through the pipeline, completing the first-stage heat exchange. At the same time, the heat is transferred to the cooling water tank 6. S3: After the water in the cooling water tank 6 is heated, it undergoes secondary heat exchange. The heat in the cooling water tank 6 is removed through the series heat exchanger 16. After the water in the air-cooled system pipeline is heated, it boils due to the low system pressure. The steam enters the air-cooled heat exchanger 10 for cooling and then flows back to the series heat exchanger 16 to complete the secondary heat exchange. S4: When the cooling water in the cooling water tank 6 is heated to boiling, it undergoes three-stage heat exchange. The generated steam enters the spray pipe and is sprayed out through the spray device 8 to spray the air-cooled heat exchanger 10. The spray water is cooled in the air duct 9 and collected through the spray water collection device 12. It then flows back to the cooling water tank 6 through the spray return pipe, thus completing the passive waste heat discharge.

[0031] Detailed Implementation Method 2: See Figure 1This embodiment describes a passive waste heat removal system for freeze protection. Under normal operating conditions, the air-cooled circuit is full of water. The system isolation valve 2 and condensate isolation valve 18 are opened, and the system is put into operation. The steam generator 1 transfers the core waste heat to the cooling water tank 6 through the water-cooled circuit. As the cooling water tank 6 continuously absorbs heat, the cooling water boils and generates steam. The steam enters the air duct 9 through the spray pipe, is cooled by the air, and condenses into droplets that fall onto the air-cooled heat exchanger 10, forming a liquid film. This creates an enhanced heat transfer path between the heat exchange tubes and the air in the air-cooled heat exchanger 10. The liquid film rapidly absorbs heat from the heat exchange tubes through thermal conduction. On one hand, it forms convective heat transfer with the flowing air in the air duct 9, transferring sensible heat. On the other hand, upon reaching the boiling point, it releases a large amount of latent heat through evaporation. Its transfer efficiency is far higher than simple air convection. As the liquid film flows along the heat exchange tubes, the interface is continuously renewed, avoiding localized heat transfer. Overheated, unevaporated droplets are returned to the cooling water tank 6 via the spray water collection device 12, completing the circulation. This process transforms the single gas-solid heat exchange into a coupled mechanism of heat conduction, convection, and phase change, which not only expands the heat exchange area but also reduces thermal resistance through phase change enhancement and boundary layer disturbance. The heat from the series heat exchanger 16 is efficiently removed through the air-cooled heat exchanger 10, which, together with the water-cooled and air-cooled loops, enhances the continuity and efficiency of the system's passive heat dissipation. Unboiled condensate is collected by the spray water collection device 12 and flows back to the cooling water tank 6 via the check valve 13. In addition, the cooling water in the air-cooled loop is heated in the series heat exchanger 16 and then flows into the air-cooled heat exchanger 10. After being cooled, it flows back to the series heat exchanger 16 via the series heat exchanger inlet header 14. Since the air-cooled loop is a closed loop, the pressure of the cooling water gradually increases after heating, making the cooling water's heat exchange capacity stronger, thereby enhancing the heat exchange capacity of the air-cooled loop.

[0032] Detailed implementation method 3: See Figure 1 This embodiment describes a passive waste heat removal system for frost protection. Under extreme operating conditions, it is necessary to quickly remove the heat from the steam generator 1. This can be achieved by turning on the electric pump 17 after the system is put into operation to increase the flow rate in the water-cooling circuit, thereby enhancing the heat exchange efficiency. Other embodiments are the same as under normal operating conditions.

[0033] Detailed implementation method 4: See Figure 1 This embodiment describes a passive waste heat removal system for preventing freezing. When the waste heat removal system is used in the reactor primary loop, the high-temperature and high-pressure subcooled water generated in the reactor primary loop flows into the water-cooled heat exchanger 5 by natural circulation. In the water-cooled heat exchanger 5, the subcooled water transfers heat to the water in the cooling water tank 6 through a one-phase phase heat transfer method. After its own temperature decreases, it flows back to the reactor primary loop. During this process, the water-cooled loop is always a single-phase liquid flow, which is different from the two-phase flow of vapor and liquid on the secondary side under normal operating conditions. Other conditions are the same as normal operating conditions.

[0034] The specific embodiments of the present invention disclosed above are merely illustrative of the invention. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A passive waste heat removal system for frost prevention, characterized in that: The system includes a steam generator (1), a cooling water tank (6), a water-cooled circuit, an air-cooled circuit, and a spray system. The water-cooled circuit includes a system isolation valve (2), a water-cooled heat exchanger inlet manifold (3), a water-cooled heat exchanger (5), a water-cooled heat exchanger outlet manifold (19), and a condensate isolation valve (18) connected in sequence by pipes. The inlet of the system isolation valve (2) is connected to the outlet of the steam generator (1), and the outlet of the condensate isolation valve (18) is connected to the return end of the steam generator (1). The water-cooled heat exchanger (5) is located inside the cooling water tank (6). The air-cooled circuit includes a differential pressure transmitter (21), a series heat exchanger (16), and an air-cooled heat exchanger (10). The series heat exchanger (16) is located inside the cooling water tank (6), and the outlet of the series heat exchanger (16) is connected to the inlet of the air-cooled heat exchanger (10) through an outlet pipe. The outlet of the air-cooled heat exchanger (10) is connected to the outlet of the air-cooled heat exchanger (10) through an outlet pipe. The return pipe is connected to the inlet of the series heat exchanger (16); the return pipe is provided with the inlet header (14) of the series heat exchanger, and the outlet pipe is provided with the outlet header (20) of the series heat exchanger. One end of the differential pressure transmitter (21) is connected to the outlet of the outlet header (20) of the series heat exchanger, and the other end is connected to the inlet of the inlet header (14) of the series heat exchanger. The spray system includes a spray pipe, a spray device (8), a wind duct (9), a spray water collection device (12) and a spray return pipe. One end of the spray pipe is connected to the top of the cooling water tank (6), and the other end is provided with the spray device (8) and extends into the wind duct (9). The spray water collection device (12) is located at the bottom of the wind duct (9). One end of the spray return pipe is connected to the spray water collection device (12), and the other end is connected to the cooling water tank (6). A rotary vane vacuum pump (11) is provided at the outlet end of the air-cooled heat exchanger (10).

2. The antifreeze passive waste heat removal system according to claim 1, characterized in that: The inlet header (3) of the water-cooled heat exchanger is equipped with a water-cooled heat exchanger flow equalization plate (4).

3. The antifreeze passive waste heat removal system according to claim 1, characterized in that: An electric pump (17) is installed on the water cooling circuit.

4. The antifreeze passive waste heat removal system according to claim 1, characterized in that: The inlet header (14) of the series heat exchanger is provided with a flow equalization plate (15).

5. The antifreeze passive waste heat removal system according to claim 1, characterized in that: The air-cooled heat exchanger (10) adopts an annular finned tube structure, with the tube bundle arranged in a triangular pattern and independent control valves set on both sides of the tube bundle.

6. The antifreeze passive waste heat removal system according to claim 1, characterized in that: The water-cooled heat exchanger (5) is a shell-and-tube heat exchanger.

7. The antifreeze passive waste heat removal system according to claim 1, characterized in that: An electromagnetic level gauge (7) is installed inside the cooling water tank (6).

8. The antifreeze passive waste heat removal system according to claim 1, characterized in that: The air-cooled heat exchanger (10) is positioned above the cooling water tank (6), and the water-cooled heat exchanger (5) is positioned above the steam generator (1).

9. The antifreeze passive waste heat removal system according to claim 1, characterized in that: A shut-off valve (13) is installed on the spray return pipe.

10. A method of using the antifreeze passive waste heat removal system as described in claim 1, characterized in that, Includes the following steps: S1: Under cold conditions, water is added to the air-cooled system until the water level can cover the outlet end of the outlet header (20) of the series heat exchanger. Water replenishment is completed when the reading of the differential pressure transmitter (21) returns to zero. The pressure of the air-cooled system is reduced by the rotary vane vacuum pump (11). S2: Open the system isolation valve (2) and the condensate isolation valve (18), and the core waste heat is discharged into the steam generator (1). The generated steam enters the water-cooled heat exchanger (5). The steam transfers heat through the water-cooled heat exchanger (5) into the cooling water tank (6) and condenses into condensate, which flows back to the steam generator (1) through the pipeline. S3: After the water in the cooling water tank (6) is heated, the heat in the cooling water tank (6) is taken away through the series heat exchanger (16). After the water in the air-cooled system pipeline is heated, it boils. The steam enters the air-cooled heat exchanger (10) for cooling and then flows back to the series heat exchanger (16). S4: When the cooling water in the cooling water tank (6) is heated to boiling, the generated steam enters the spray pipe and is sprayed out through the spray device (8) to spray the air-cooled heat exchanger (10). The spray water is cooled in the air duct (9) and collected by the spray water collection device (12), and flows back to the cooling water tank (6) through the spray return pipe to complete the passive waste heat discharge.

Images