Passive residual heat removal system and method for nuclear power plant

Abstract

The invention discloses a passive residual heat removal system and method for a nuclear power plant. The problems that in the prior art, a pure water cooling mode is insufficient in initial heat exchange intensity and limited in long-term operation time, and a pure air cooling mode is poor in heat exchange capacity are solved. The passive residual heat removal system of the nuclear power unit comprises a passive residual heat removal system body, wherein a heat exchanger is used for guiding decay heat of a reactor core into the passive residual heat removal system body; the air guide plate is arranged opposite to the air inlet and used for creating a cold air introduction channel, and an air distribution skirt is arranged on the lower portion of the air guide plate and used for guiding cold air to the heat exchanger; and the sprayer is used for spraying cooling water to the surface of the heat exchanger under a passive condition when an accident occurs. Self-adaptive matching of heat exchange modes driven by decay heat removal requirements in different stages is achieved, and the reliability, safety and long-term operation capacity of a nuclear power unit waste heat removal system are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reactor safety, in particular to a nuclear power device passive residual heat removal system and method. BACKGROUND

[0002] The passive residual heat removal system of the marine nuclear power device is a key system to ensure the safety of the reactor core under accident conditions, which needs to continuously remove the decay heat of the reactor core without relying on external power to prevent the reactor core from melting down. The existing technology mainly relies on natural circulation driven by density difference, and the cooling methods are divided into two types of water cooling and air cooling. For the water cooling system, such as CN201220072123.2, water is used as the cooling medium, and a large amount of initial water needs to be filled in the cooling tank, which occupies the limited space of the ship. The water cooling system needs to invest a large amount of support resources to maintain water quality in the long-term standby state, and long-term immersion can cause corrosion of the heat exchanger, which increases the difficulty of in-service inspection. The air cooling system, such as CN202310753153.2, uses air as the medium, and the heat exchange efficiency is low, and the required heat exchange area is large, which is difficult to meet the heat removal capacity demand of accident cooling under the constraints of limited space and volume.

[0003] CN202310774721.7 gives a hybrid passive cooling system which couples the water cooling system and the air cooling system, but this design scheme has structural defects: the water cooling and the air cooling are physically isolated, which easily leads to pressure imbalance at the condensate collection point and causes parallel operation loop flow oscillation. This hybrid scheme increases the complexity of the passive residual heat removal system, and the physical volume is large, which is difficult to adapt to the compact space constraints of the ship.

[0004] Therefore, it is urgent to develop a passive residual heat removal system with multiple heat exchange mechanisms to complement each other, and systematically improve the reliability, safety and long-term operation capability of the residual heat removal of the reactor core. SUMMARY

[0005] Therefore, the present application aims to provide a nuclear power device passive residual heat removal system and method to solve the problems of insufficient initial heat exchange intensity of the pure water cooling mode, long-term operation limitation of the pure water cooling mode, poor heat exchange capacity of the pure air cooling mode, and structural defects of the hybrid cooling system, and to realize the adaptive matching of the time evolution law of the reactor core decay heat and different heat exchange modes.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: according to the first aspect of the present application, a nuclear power device passive residual heat removal system is provided, comprising:

[0007] A passive residual heat removal system body, a heat exchanger is arranged at the inner bottom of the passive residual heat removal system body, the heat exchanger is used for guiding the decay heat of the reactor core into the passive residual heat removal system body, an air inlet is arranged on the side wall, a discharge outlet is arranged at the top, and a drain outlet is arranged at the lower part;

[0008] An air deflector is arranged directly opposite the air inlet to create a cold air introduction channel. An air distribution skirt is provided at the bottom to rectify the cold air drawn in from the air inlet and guide it from the air distribution skirt to the heat exchanger.

[0009] A sprayer is used to spray cooling water onto the surface of the heat exchanger under passive conditions in the event of an accident.

[0010] Furthermore, the heat exchanger inlet is connected to the steam side of the steam generator via isolation valve two, and the heat exchanger outlet is connected to the feedwater side of the steam generator via isolation valve one.

[0011] Furthermore, the heat exchanger also includes a heat exchanger cooling pipe, through which the medium enters the heat exchanger cooling pipe via the heat exchanger inlet and exits from the heat exchanger outlet.

[0012] Furthermore, the inlet of the sprayer is connected to the outlet of the accumulator tank via a spray pipeline isolation valve, and the inlet of the accumulator tank is connected to the compressed air storage tank via an air tank control valve.

[0013] Furthermore, a drain isolation valve is installed at the drain outlet of the passive waste heat discharge system.

[0014] Furthermore, the top of the passive waste heat removal system is a streamlined dome.

[0015] Furthermore, the passive waste heat removal system body is equipped with a backup water supply pipeline, and the water supply pipeline is equipped with an emergency water supply isolation valve.

[0016] Furthermore, the diameter of the openings on the air distribution skirt gradually decreases from the side closer to the air inlet to the side farther away.

[0017] According to another aspect of the present invention, a method for passively removing residual heat from a nuclear power plant is provided, comprising the following steps:

[0018] In the initial stage of the accident, the spray water from the sprayers and the air from the air distribution skirt worked together to cool the heat exchangers, achieving efficient heat removal during the high-level decay heat stage of the reactor core. As the reactor core decay heat decreased and the water level in the passive residual heat removal system rose and a water seal was established in the air distribution skirt, the system automatically transitioned to an immersion water-cooled heat exchange mode. Relying on the heating of the cooling water and subsequent boiling heat exchange, the system continuously and stably removed heat from the flat zone of the reactor core decay heat. As the cooling water in the passive residual heat removal system was consumed, the water level continued to drop, and the water seal in the air distribution skirt gradually broke down. The system then entered a combined mode of boiling heat exchange outside the heat exchanger tubes and natural air convection heat exchange, and finally transitioned to a pure air cooling stage, releasing the low-level reactor core decay heat into the atmosphere for a long period of time.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. The greatest advantage of this invention lies in its creative solution to the inherent defects of existing single water-cooling, air-cooling, and hybrid cooling modes. The system can automatically and smoothly transition between cooling modes throughout the entire post-accident cycle, based on the intensity variation of core decay heat and the coolant level within the system: from the highly efficient combined cooling of "spray water cooling + air convection" during the initial high-power phase of the accident, to "immersion water cooling" during the stable phase of the decay heat plateau, then to "boiling water cooling + air convection" combined cooling during the continuous decline of decay heat, and finally transitioning to "pure air cooling" during the long-term low-power phase. This adaptive capability ensures that the heat dissipation intensity is always well matched with the decay heat output, greatly improving the reliability and safety of the system throughout the entire accident process.

[0021] 2. By integrating water-cooling and air-cooling heat exchange modes into a single heat exchange unit and its surrounding space, the redundancy, bulkiness, and complex connection problems caused by physical isolation in existing hybrid systems are completely eliminated. Air deflectors and air distribution skirts fit tightly with the heat exchanger body, and the streamlined dome at the top optimizes the airflow path, resulting in an extremely compact system structure that fits the stringent constraints of limited space on ships. This solves the key pain point of existing hybrid systems failing to meet cooling capacity requirements within confined spaces.

[0022] 3. The air distribution skirt adopts a gradient opening design. As the coolant evaporates and the liquid level drops, the distribution skirt is gradually exposed, and its effective airflow cross-sectional area automatically and smoothly increases. This matches the transition requirements from water-cooled to air-cooled, avoiding sudden changes in flow resistance and potential flow instability. The tapered flow channel structure design of the distribution skirt utilizes the Venturi effect to effectively increase the local airflow velocity while increasing the airflow cross-sectional area, significantly improving the heat exchange efficiency during the natural air convection stage and overcoming the weakness of poor heat exchange capacity in pure air-cooled mode.

[0023] 4. A pressurized water tank and sprayers are installed to achieve passive atomization spraying of cooling water using pressure difference. This design can quickly form an efficient water film evaporation and convection heat transfer on the heat exchanger surface in the most critical initial stage of an accident, significantly enhancing the heat dissipation capacity during the high decay heat stage and solving the problem of insufficient heat transfer intensity that may exist in pure water cooling mode, especially in the initial stage of natural circulation establishment.

[0024] 5. Compared to traditional water-cooling systems that require maintaining large water volumes and complex water quality over long periods, the adaptive design of this invention significantly reduces the maintenance and support resources required for long-term standby. Cooling water is primarily used and consumed during emergencies, significantly reducing the risk of corrosion from prolonged heat exchanger immersion and the difficulty of in-service inspection. The integrated design is simpler in structure, has fewer components, and fewer potential failure points than physically isolated hybrid systems, improving the inherent reliability and potential maintainability of the system. Attached Figure Description

[0025] 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:

[0026] Figure 1 This is a schematic diagram of the structure of a passive waste heat removal method and system for a nuclear power plant according to the present invention;

[0027] Figure 2 This is an enlarged schematic diagram of the heat exchanger described in this invention;

[0028] Figure 3 This is a schematic diagram of the airflow direction of the air distribution skirt described in this invention;

[0029] Figure 4 This is a diagram showing the relative positions of the heat exchanger and the sprayer described in this invention.

[0030] Figure 5 This is a schematic diagram of the structure of the passive waste heat removal system body described in this invention.

[0031] Reactor 1; Steam generator 2; Pressurizer 3; Main pump 4; Heat exchanger 5; Heat exchanger inlet 5-1; Heat exchanger outlet 5-2; Heat exchanger cooling pipe 5-3; Sprayer 6; Passive waste heat removal system body 7; Streamlined dome 7-1; Compressed air storage tank 8; Pressurized water tank 9; Air inlet 10; Discharge outlet 11; Air guide plate 12; Air distribution skirt 13; Isolation valve one 14; Isolation valve two 15; Emergency water supply isolation valve 16; Spray pipeline isolation valve 17; Gas tank control valve 18; Drainage isolation valve 19. Detailed Implementation

[0032] 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.

[0033] It should be noted that the descriptions of "left," "right," "left side," "right side," "upper part," "lower part," "top," and "bottom" in this invention are defined based on the orientation or positional relationships shown in the accompanying drawings. They are merely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the described structure must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In the description of this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] Referring to the accompanying drawings, this embodiment provides a passive waste heat removal system for a nuclear power plant, comprising:

[0036] The passive waste heat removal system body 7 has a heat exchanger 5 installed at its bottom, which is used to introduce the decay heat of the reactor 1 into the passive waste heat removal system body 7. An air inlet 10 is provided on the side wall, an exhaust outlet 11 is provided at the top, and a drain outlet is provided at the bottom. The passive waste heat removal system body 7 is generally upright, with an internal cavity for accommodating various equipment, and must meet the requirements of heat resistance and structural strength. The streamlined dome 7-1 at the top of the passive waste heat removal system body 7 facilitates smooth airflow. The smooth transition between the exhaust outlet 11 and the streamlined dome 7-1 further improves airflow smoothness. Utilizing the shape of the passive waste heat removal system body 7 and the arrangement of the exhaust outlet 11 and air inlet 10, combined with the temperature difference, a chimney effect can be created, increasing the fluidity of the gas flow path. After entering through air inlet 10, the gas is redirected by air deflector 12 and then split through lower air distribution skirt 13. This ensures the gas is evenly distributed across the surface of heat exchanger 5, cooling it. The gas then rises and, guided by the streamlined dome 7-1, exits through outlet 11. Combined with the chimney effect created by temperature differences, this rapidly generates a strong gas flow, effectively dissipating heat. During the air cooling stage, the airflow rectified by the tapered flow channel of air distribution skirt 13 forms natural convection heat exchange with the heat exchanger tube bundle. This stage maintains stable natural air circulation through the Venturi and chimney effects, ensuring reliable long-term cooling.

[0037] Specifically, the passive waste heat removal system body 7 has two holes on the outer wall of one side, one at the bottom and one at the top. One end of the pipe through the upper hole is connected to the sprayer 6, and the other end of the pipe passes through the spray pipe isolation valve 17, the pressurized water tank 9, the air tank control valve 18, and the compressed air storage tank 8 in sequence to form the spray pipe. The pipe through the lower hole passes through the emergency water supply isolation valve 16, the fire protection system and the emergency water supply system in sequence to form the water supply pipe, which is put into operation when the passive spray system fails. The pipe through the bottom hole passes through the drainage isolation valve 19 and the drainage system in sequence to form the drainage pipe, which drains the residual water in the heat exchange system and restores the system to its initial state.

[0038] An air deflector 12 is arranged opposite to the air inlet 10, and an air distribution skirt 13 is provided at the bottom to rectify the air introduced by the air inlet 10 and blow it from the air distribution skirt 13 to the heat exchanger 5.

[0039] Sprayer 6 is used to spray water onto the surface of heat exchanger 5 under passive conditions. The main purpose of sprayer 6 is to automatically cool heat exchanger 5 in a passive manner in the event of an accident, so that the heat exchange medium flowing inside heat exchanger 5 can be cooled. The sprayed droplets adhere to the outer wall of heat exchange tubes, and the heat of heat exchange tubes is carried away through the phase change conversion between liquid water and steam.

[0040] In this embodiment, the heat exchanger 5's inlet 5-1 is connected to the steam side of the steam generator 2 via isolation valve 2 15, and the heat exchanger outlet 5-2 is connected to the feedwater side of the steam generator 2 via isolation valve 14. The heat exchanger 5 also includes a heat exchanger cooling pipe 5-3, through which the medium enters the cooling pipe 5-3 via the inlet 5-1 and exits from the outlet 5-2. The specific structure of the heat exchanger 5 is designed to facilitate effective heat exchange in the synergistic heat dissipation mechanism. It should help expand the heat exchange area with the gas and facilitate phase change heat exchange with the sprayed water. A reasonable configuration based on actual conditions is sufficient. The isolation valves 14 and 15 are used to improve the control of the flow rate and on / off state of the heat exchange medium within the pipeline.

[0041] In this embodiment, the inlet end of the sprayer 6 is connected to the outlet end of the pressure storage tank 9 via the spray pipeline isolation valve 17, and the inlet end of the pressure storage tank 9 is connected to the compressed air storage tank 8 via the air tank control valve 18.

[0042] In this embodiment, a drain isolation valve 19 is provided at the drain outlet of the passive waste heat discharge system body 7. The drain isolation valve 19 is used to control the discharge flow rate of water in the passive waste heat discharge system body 7 and whether to drain water.

[0043] In this embodiment, the passive waste heat removal system body 7 is equipped with a backup water supply pipeline, and an emergency water supply isolation valve 16 is installed on the water supply pipeline. The water supply pipeline can be a fire protection system or other types of water supply system, and should be reasonably configured according to actual conditions. It needs to be able to open the emergency water supply isolation valve 16 when the passive drainage system fails, and spray water to the heat exchanger through the relevant pipeline and the sprinkler 6.

[0044] In this embodiment, the air distribution skirt 13 adopts a gradient opening design, with the diameter gradually decreasing from the side closer to the air inlet 10 to the side farther away. This increases the airflow velocity through the Venturi effect, creating a distributed gas flow effect. Combined with the chimney effect, this results in a synergistic effect of higher overall flow velocity, reduced flow resistance, and increased heat dissipation area. In this embodiment, the openings on the air distribution skirt 13 employ a gradient design with larger diameters near the air inlet 10 and smaller diameters further away. This structure enhances the airflow velocity through the Venturi effect, creating a distributed and uniform airflow, and, in conjunction with the chimney effect, achieves increased flow velocity, reduced flow resistance, and optimized heat dissipation efficiency.

[0045] According to a second aspect of the present invention, a method for passively removing residual heat from a nuclear power plant is provided, specifically:

[0046] Under normal reactor shutdown conditions, the system operates in a single air-cooled mode. The specific technical implementation scheme is as follows: Isolation valve 2 15 and isolation valve 1 14 are open, while spray pipeline isolation valve 17, emergency water replenishment isolation valve 16, and drainage isolation valve 19 are closed. In this operating mode, the core decay heat of reactor 1 is absorbed by the main coolant and transported to the primary side of steam generator 2 via the evaporation section. After completing the heat transfer, the coolant returns to the core through the main pump, forming a closed loop. The saturated steam generated on the secondary side of steam generator 2 enters heat exchanger 5 through isolation valve 2 15, transferring heat to the cold air in the passive residual heat removal system body 7. The steam condenses into water, which flows through isolation valve 1 14 and returns to the feedwater inlet of steam generator 2. The cold air enters the passive residual heat removal system body 7 through air inlet 10 and along air guide plate 12, cooling the high-temperature steam in heat exchanger 4. The heated air, after absorbing heat, is discharged from the louvers of exhaust outlet 11, realizing the removal of core decay heat.

[0047] In the event of an accident, such as failure of the main coolant system or loss of external power: Initially, isolation valves 17, 15, and 14 in the spray pipeline open, while emergency water supply isolation valve 16 and drainage isolation valve 19 close. The pressurized water tank 8 automatically depressurizes, driving cooling water towards the spray head 5 under pressure differential. The coolant stored inside is atomized into a high-speed jet by the sprayer 5, cooling the heat exchanger 5. This process rapidly absorbs the high-temperature steam and decay heat within the containment vessel through the flash phase change of the droplets. The sprayed droplets adhere to the heat exchanger tube wall, increasing the heat transfer coefficient between the heat exchanger tube and the air. Simultaneously, the natural air circulation induced by the combined chimney effect further enhances the heat transfer efficiency. As the reactor core decay heat decreases and the non-… The water level in the active residual heat removal system body 7 rises and establishes a water seal on the air distribution skirt 13. The system automatically transitions to a submerged water-cooled heat exchange mode, relying on the heating of the cooling water and subsequent boiling heat exchange to continuously and stably remove heat from the core decay heat plateau region. In the later stages of the accident, the coolant in the passive residual heat removal system body 7 undergoes a phase change. As the air distribution skirt 13 is gradually exposed, isolation valves 14 and 15 open, while spray pipeline isolation valve 17, gas tank control valve 18, and drain isolation valve 19 close. As the cooling medium continues to evaporate and deplete, the system's thermodynamic state transitions from a combined mode of external boiling heat exchange and natural air convection heat exchange to a single gas-phase air-cooled dominant mode, ultimately achieving passive, indefinite-duration continuous heat removal capability. After the accident, drain isolation valve 19 is opened to drain the remaining water in the passive residual heat removal system body 7.

[0048] During operation, the entire system can perform pure air cooling. Through the structural shape of the air distribution skirt 13 and the chimney effect, along with the air guide plate 12 to redirect the gas flow, optimize the gas velocity, improve heat exchange efficiency, and rapidly remove heat, ensuring continuous and effective heat exchange. In the event of an accident, a spray system works in conjunction with airflow for coordinated heat dissipation. The sprayed coolant submerges the air distribution skirt 13 and heat exchanger 5, creating a submerged saturated boiling cooling state. The decay heat then drops to a very low level. As the air distribution skirt 13 is gradually exposed, a mixed evaporation and air-cooling mode of cooling is resumed, gradually transitioning to pure air cooling and entering an infinite heat dissipation phase. This system can introduce different heat exchange methods based on the time-varying trend of decay heat, achieving adaptive matching between decay heat and heat dissipation modes, ensuring the overall stability and reliability of the heat exchange system.

[0049] The sensors, controllers, and control programs mentioned above are all existing technologies and will not be elaborated upon.

[0050] The 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 implementations 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 a nuclear power plant, characterized in that, include: The passive waste heat removal system body (7) has a heat exchanger (5) at its bottom. The heat exchanger (5) is used to introduce the core decay heat of the reactor (1) into the passive waste heat removal system body (7). An air inlet (10) is provided on the side wall, an exhaust outlet (11) is provided at the top, and a drain outlet is provided at the bottom. An air deflector (12) is arranged opposite to the air inlet (10) to create a cold air introduction channel. An air distribution skirt (13) is provided at the bottom to rectify the cold air drawn in by the air inlet (10) and guide it from the air distribution skirt (13) to the heat exchanger (5). A sprayer (6) is used to spray cooling water onto the surface of the heat exchanger (5) under passive conditions.

2. A passive waste heat removal system for a nuclear power plant according to claim 1, characterized in that: The heat exchanger inlet (5-1) of the heat exchanger (5) is connected to the steam side of the steam generator (2) via isolation valve two (15), and the heat exchanger outlet (5-2) is connected to the water supply side of the steam generator (2) via isolation valve one (14).

3. A passive waste heat removal system for a nuclear power plant according to claim 2, characterized in that: The heat exchanger (5) also includes a heat exchanger cooling pipe (5-3). The medium enters the heat exchanger cooling pipe (5-3) through the heat exchanger inlet (5-1) and is discharged from the heat exchanger outlet (5-2).

4. A passive waste heat removal system for a nuclear power plant according to claim 1, 2, or 3, characterized in that: The inlet of the sprayer (6) is connected to the outlet of the pressure tank (9) via the spray pipeline isolation valve (17), and the inlet of the pressure tank (9) is connected to the compressed air storage tank (8) via the air tank control valve (18).

5. A passive waste heat removal system for a nuclear power plant according to claim 1, characterized in that: A drain isolation valve (19) is installed at the drain outlet of the passive waste heat discharge system body (7).

6. A passive waste heat removal system for a nuclear power plant according to claim 1, characterized in that: The top of the passive waste heat removal system body (7) is a streamlined dome (7-1).

7. A passive waste heat removal system for a nuclear power plant according to claim 1, characterized in that: The passive waste heat discharge system body (7) is equipped with a backup water supply pipeline, and an emergency water supply isolation valve (16) is installed on the water supply pipeline.

8. A passive residual heat removal system for a nuclear power plant according to claim 1, 2, 3, 5, 6 or 7, characterized in that: The openings on the air distribution skirt (13) gradually decrease in diameter from the side closer to the air inlet (10) to the side farther away.

9. A method for passively removing residual heat from a nuclear power plant, characterized in that, Includes the following steps: In the early stages of the accident, the spray water from the sprayer (6) and the air from the air distribution skirt (13) work together to cool the heat exchanger (5), achieving efficient heat removal during the high-level decay heat stage of the reactor core. As the core decay heat of the reactor (1) decreases, the water level in the body (7) of the passive residual heat removal system rises and the air distribution skirt (13) water seal is established, the system automatically transitions to the submerged water-cooled heat exchange mode, relying on the cooling water to heat up and absorb heat and boiling heat exchange to continuously and stably remove the core decay heat. As the cooling water in the passive waste heat removal system (7) is consumed, the water level continues to drop and the water seal of the air distribution skirt (13) is gradually broken. The system enters the heat exchanger (5) tube external boiling and natural air convection combined heat exchange mode in sequence, and finally transitions to the pure air cooling stage, releasing the low-level core decay heat into the atmospheric environment for a long time and continuously.

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