A nuclear power plant safety system configuration system

Abstract

The application belongs to the technical field of nuclear power plant safety design, and particularly relates to a nuclear power plant safety system configuration system; the system comprises: a passive emergency core cooling system for coping with a design basis accident, a secondary side passive residual heat removal system, and a passive containment cooling system. The configuration of a large number of passive systems fully utilizes the passive characteristics such as natural circulation and gravity, greatly improves the safety and reliability of the nuclear power plant, and through the passive safety system configuration scheme, the active equipment is cancelled, the external power source is cancelled, the safety support system is reduced, the safety class emergency diesel generator set is cancelled, and the like, so that the design, construction, operation and maintenance of the system are simplified, the unit economy is further improved while the safety is ensured.

Description

Technical Field

[0001] This application belongs to the field of nuclear power plant safety design technology, specifically relating to a nuclear power plant safety system configuration scheme. Background Technology

[0002] During the design process of nuclear power plants, the design principle of safety first must be adhered to and ensured. This is to ensure that the reactor can effectively control the reactivity of the core, remove residual heat from the core, and ensure that contained radionuclides are not released to the outside under all circumstances. The safety system is the core system for ensuring reactor safety. The safety system directly determines the nuclear power plant's ability to mitigate accidents and the safety level of the reactor under accident conditions.

[0003] In the design of pressurized water reactor nuclear power plants, as the requirements for nuclear safety continue to increase, the design of safety systems has gradually become more complex than simple ones. Nuclear power plants have adopted the concept of defense in depth and various dedicated safety measures to ensure their safety. Among these, Generation II and improved Generation II nuclear power plants generally employ active safety systems, requiring a large number of pumps, valves, pipes, water tanks, heat exchangers, and other equipment, while also requiring a safety-grade emergency power supply (emergency diesel generator set) system to achieve its safety functions. Another design approach is to use a passive safety concept, utilizing the inherent physical properties of nature to ensure safety: using gravity, natural convection, diffusion, evaporation, and condensation to remove residual heat from the reactor core after an accident. This approach simplifies the system, reduces equipment and components, improving the economics of the nuclear power plant; it also simplifies operation, reduces the possibility of human error, and improves the overall safety of the nuclear power plant in the event of an accident. Summary of the Invention

[0004] The purpose of this application is to provide a nuclear power plant safety system configuration system that solves the problem of complex safety system design, simplifies the configuration of the safety system while balancing economy and safety, and ensures the safety of the nuclear power plant under any circumstances.

[0005] The technical solution to achieve the purpose of this application is as follows:

[0006] This application provides a nuclear power plant safety system configuration system, which includes: a passive emergency core cooling system (ECCS), a secondary passive residual heat removal system (PRS), and a passive containment cooling system (PCS) for responding to design basis accidents.

[0007] The passive emergency core cooling system adopts a fully passive configuration within the containment, including two sub-series. Each sub-series includes a full-pressure makeup water tank, a safety injection tank, an automatic depressurization system (ADS), and an elevated gravity injection tank.

[0008] The inlet pipe of the total pressure water supply tank is led out from the outlet of the main pump and connected to the direct injection (DVI) line. The outlet of the safety injection tank is connected to the direct injection line. The high-level gravity water supply tank is connected to the direct injection line through a pipe. The automatic pressure relief system is set with 4 stages. Stages 1-3 are led out from the top of the pressure stabilizer and connected to the water in the high-level gravity water supply tank through corresponding pipes and stage 1-3 ADS valves. Stage 4 is led out from the hot section and realizes the venting of the containment into the air through stage 4 ADS valves.

[0009] The secondary passive waste heat removal system adopts a steam generator secondary side layout scheme. Each steam generator corresponds to a series of passive waste heat removal systems. Each series includes an emergency waste heat removal cooler and an emergency cooling water tank.

[0010] The passive containment cooling system consists of a PCS heat exchanger inside the containment and a cooling water tank outside the containment, wherein the cooling water tank outside the containment is shared with the PRS water tank.

[0011] Optionally, the full-pressure water supply tank, the safety injection tank, and the elevated gravity water injection tank are all equipped with an outlet isolation valve when connected to the direct injection pipeline.

[0012] Optionally, the passive emergency core cooling system is used to provide emergency cooling, emergency water replenishment, boronizing, and safety injection functions for the core in the event of a design basis accident. When a design basis accident occurs, after the safety injection signal is triggered, the isolation valve of the full-pressure water replenishment tank opens to inject water at a low flow rate under full pressure. When the water level in the full-pressure water replenishment tank is low, the 1st to 3rd stage ADS valves are triggered sequentially to depressurize the system. As the system pressure decreases, the safety injection tank starts operation when the system pressure drops to a certain value to inject water at a high flow rate. In the later stages of the accident, the 4th stage ADS valve opens, and water from the high-level gravity water injection tank is injected into the core. When the water injection in the high-level gravity water injection tank ends, the inlet and outlet nozzles of the pressure vessel and the parts below are immersed in water, and the core heat is carried away through natural circulation.

[0013] Optionally, the secondary passive residual heat removal system serves as a dedicated safety facility to remove residual heat from the reactor core after an accident. When the PRS operation signal is triggered, the PRS isolation valve opens and operates through natural circulation. The steam generated in the steam generator is condensed by the PRS heat exchanger and then reinjected into the steam generator through the feedwater pipeline, thereby removing the reactor core energy through the steam generator.

[0014] Optionally, the passive containment cooling system is one of the dedicated safety facilities for responding to design-based accidents, and it is used to handle the removal of heat from the containment after an accident. When the containment pressure and temperature rise, the PCS system is automatically triggered to operate based on the signal. The water in the PCS heat exchanger is heated by the containment air and enters the cooling water tank under the drive of the density difference. The cold water in the cooling water tank flows into the PCS heat exchanger inside the containment and is heated again, thereby cooling the containment in a natural circulation manner.

[0015] Optionally, the system may also include: a normal residual heat removal system (RNS), a containment spray system (CPS), a start-up feedwater system, and a passive cavity cooling system for accident response and consequence mitigation during normal operation or design extended operating conditions.

[0016] The normal waste heat removal system is combined with the containment spray system to achieve the sharing of pumps and heat exchangers. Its inlets are the high-level gravity water injection tank, the containment pit and the hot section, respectively, and its outlets are the containment spray pipe and the cold section or the direct injection pipeline, respectively.

[0017] The passive reactor cavity cooling system includes the flow channel of the pressure vessel external insulation layer and corresponding pipes, which is used to cool the pressure vessel after a severe accident and ensure that the molten core remains inside the pressure vessel.

[0018] Starting the water supply system includes the water pump, water tank, and necessary pipes and valves.

[0019] Optionally, a normal waste heat removal system and a containment spray system are provided as countermeasures to address extended design conditions, and have the functions of normal waste heat removal, low-pressure safety injection, and containment spraying.

[0020] When performing the normal waste heat removal function, the valves from the heat pipe section to the waste heat removal pump are opened, and the pump and heat exchanger start operating. The coolant in the hot section of the main pipeline is cooled in the heat exchanger and then returned to the cold section or directly injected into the pipeline. When performing the low-pressure safety injection function, the system injects cold water from the high-level gravity injection tank into the reactor coolant system through the pump and then through the direct injection pipeline to achieve low-pressure safety injection. When performing the containment spray function, the pump draws water from the high-level gravity injection tank, and sprays it through the pipeline and valves from the spray head, or draws water from the sump, and after passing through the pump and heat exchanger, sprays it through the pipeline and valves from the spray head.

[0021] Optionally, a passive cavity cooling system, as one of the measures to deal with severe accidents, is used to cool the outer wall of the pressure vessel, thereby retaining the molten material inside the pressure vessel. When the passive cavity cooling system is required to operate, water in the high-level gravity injection tank is injected into the sump through the injection pipe and gradually submerges the vessel. During this process, water in the sump enters the insulation layer through the water outlet of the insulation layer flow channel at the bottom of the insulation layer, and is heated into steam by the outer wall of the pressure vessel in the flow channel and discharged from the outlet of the insulation layer flow channel. After the submersion is completed, the water in the insulation layer flow channel is heated by the outer wall of the pressure vessel and flows back to the sump from the top, achieving cooling of the pressure vessel wall through natural circulation, ensuring that the pressure vessel is not melted through by the core molten material, thereby retaining the molten material in the pressure vessel.

[0022] Optionally, the feedwater system can be started as one of the measures to cope with the extended operating conditions, performing the functions of steam generator feedwater during the start-up and shutdown process of the nuclear power plant and steam generator feedwater after an accident.

[0023] Optionally, the elevated gravity water tank can be located inside or outside the containment. When placed outside the containment, the top of the elevated gravity water tank is connected to the containment via a pressure balance pipe, and the elevated gravity water tank is not connected to the 1-3 stage ADS depressurization system.

[0024] The beneficial technical effects of this application are as follows:

[0025] This application provides a nuclear power plant safety system configuration that employs a fully passive emergency core cooling system, a passive secondary-side residual heat removal system, and a passive containment cooling system to address design-baseline accidents. To handle extended design conditions, it also adds an active start-up feedwater system, a containment spray system, a residual heat removal system, and a passive reactor cavity cooling system. The extensive use of passive systems fully leverages the passive characteristics of natural circulation and gravity, significantly improving the safety and reliability of the nuclear power plant. Furthermore, the passive safety system design simplifies system design, construction, operation, and maintenance by eliminating active equipment, external power sources, safety support systems, and safety-grade emergency diesel generator sets, thereby further improving unit economy while ensuring safety. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the configuration system of a nuclear power plant safety system provided in an embodiment of this application.

[0027] In the picture:

[0028] 1: Containment vessel; 2: Spray head; 3: Cooling water tank; 4: PRS heat exchanger; 5: High-level gravity water injection tank; 6: Total pressure water supply tank; 7: ADS valves of stages 1-3; 8: Safety injection tank; 9: ADS valve of stage 4; 10: Pressure regulator; 11: Steam generator; 12: PCS heat exchanger; 13: PRS isolation valve; 14: Start-up feedwater pump; 15: Start-up feedwater tank; 16: Safety spray system valve; 17: Isolation valve from gravity water injection tank to waste heat discharge pump; 18: Other containment compartments; 19: Direct injection line; 20: Pressure vessel; 21: Insulation layer flow channel; 22: Main pump; 23: Heat exchanger; 25: Pump; 26: Sump filter; 27: Sump. Detailed Implementation

[0029] To enable those skilled in the art to better understand this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only a part of the embodiments of this application, and not all of them. Based on the embodiments described in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] This application provides a nuclear power plant safety system configuration that employs a fully passive emergency core cooling system, a passive secondary-side residual heat removal system, and a passive containment cooling system to address design-baseline accidents. Simultaneously, to address extended design conditions, an active start-up feedwater system, a containment spray system, a residual heat removal system, and a passive reactor cavity cooling system are added. This achieves a "passive + active" safety system configuration scheme, with passive systems as the primary component and active systems as secondary components. The various safety systems cooperate to respond to various accidents in the nuclear power plant and perform safety functions such as post-accident reactive control, residual heat removal, and radioactive containment. This nuclear power plant safety system configuration, by replacing active systems with numerous passive systems, not only improves the inherent safety of the nuclear power plant but also reduces related support systems, improving the economics of construction and operation. It can be widely used in the safety system design of advanced nuclear power plants.

[0031] Based on the above, in order to clearly and in detail illustrate the advantages of this application, the specific embodiments of this application will be described below in conjunction with the accompanying drawings.

[0032] See Figure 1 The figure is a schematic diagram of the configuration system of a nuclear power plant safety system provided in an embodiment of this application.

[0033] This application provides a nuclear power plant safety system configuration system, including: a passive emergency core cooling system (ECCS), a secondary passive residual heat removal system (PRS), and a passive containment cooling system (PCS) for responding to design basis accidents;

[0034] The passive emergency core cooling system adopts a fully passive configuration within containment 1, which includes two sub-series. Each sub-series includes a full-pressure makeup water tank 6, an safety injection tank 8, an automatic depressurization system (ADS), and an elevated gravity injection water tank 5.

[0035] The inlet pipe of the total pressure water supply tank 6 is led out from the outlet of the main pump 22 and the outlet is connected to the direct injection (DVI) line 19. The outlet of the safety injection tank 8 is connected to the direct injection line 19. The high-level gravity water injection tank 5 is connected to the direct injection line 19 through a pipe. The automatic pressure relief system is set with 4 stages. Stages 1-3 are led out from the top of the pressure stabilizer 10 and connected to the water in the high-level gravity water injection tank 5 through corresponding pipes and stage 1-3 ADS valves 7. The fourth stage is led out from the hot section and realizes the venting of the containment 1 into the air through stage 4 ADS valves 9.

[0036] In one example, the high-gravity water tank 5 is located inside or outside the containment 1; when placed outside the containment 1, the top of the high-gravity water tank 5 needs to be connected to the containment 1 through a pressure balance pipe, and the high-gravity water tank 5 is not connected to the 1-3 level ADS depressurization system.

[0037] The secondary passive waste heat removal system adopts a secondary side arrangement of steam generator 11. Each steam generator 11 corresponds to a series of passive waste heat removal systems. Each series includes an emergency waste heat removal cooler 4 and an emergency cooling water tank 3.

[0038] The passive containment cooling system consists of a PCS heat exchanger 12 inside the containment 1 and a cooling water tank 3 outside the containment, wherein the cooling water tank 3 outside the containment is shared with the PRS water tank.

[0039] In one example, the total pressure water supply tank 6, the safety injection tank 8, the high-level gravity water injection tank 5 are all equipped with an outlet isolation valve when connected to the direct injection pipeline 19.

[0040] In some possible implementations of the embodiments of this application, the passive emergency core cooling system is used to provide emergency cooling, emergency water replenishment, boronizing, and safety injection functions for the core in the event of a design basis accident. When a design basis accident occurs, after the safety injection signal is triggered, the isolation valve of the full-pressure water replenishment tank 6 is opened to perform full-pressure low-flow injection. When the water level in the full-pressure water replenishment tank 6 is low, the 1st to 3rd stage ADS valves 7 are triggered sequentially to depressurize the system. As the system pressure decreases, the safety injection tank 8 is put into operation when the system pressure drops to a certain value to perform high-flow injection. In the later stage of the accident, the 4th stage ADS valve 9 is opened, and water in the high-level gravity water injection tank 5 is injected into the core. When the water injection in the high-level gravity water injection tank 5 is completed, the inlet and outlet nozzles and the part below the pressure vessel 20 are immersed in water, and the core heat is carried away by natural circulation.

[0041] In some possible implementations of this application, the secondary passive residual heat removal system serves as a dedicated safety facility, performing the function of removing residual heat from the reactor core after an accident. When the PRS operation signal is triggered, the PRS isolation valve 13 is opened and operates through natural circulation. The steam generated in the steam generator 11 is condensed by the PRS heat exchanger 4 and then reinjected into the steam generator 11 through the feedwater pipeline, thereby achieving the removal of reactor core energy through the steam generator 11.

[0042] In some possible implementations of the embodiments of this application, the passive containment cooling system is one of the dedicated safety facilities for dealing with design-based accidents, and is responsible for the removal of heat from the containment after an accident. When the pressure and temperature of containment 1 rise, the PCS system is automatically triggered to operate according to the signal. The water in the PCS heat exchanger 12 is heated and enters the cooling water tank 3 under the drive of density difference. The cold water in the cooling water tank 3 flows into the PCS heat exchanger 4 inside containment 1 and is heated again, thereby cooling containment 1 in a natural circulation manner.

[0043] In some possible implementations of the embodiments of this application, the system further includes: a normal residual heat removal system (RNS), a containment spray system (CPS), a start-up feedwater system, and a passive reactor cavity cooling system for accident response and consequence mitigation during normal operation or design extended operating conditions;

[0044] The normal waste heat removal system is combined with the containment spray system to achieve the sharing of pumps and heat exchangers. Its inlets are the high-level gravity water injection tank 5, the containment pit 1 and the hot section, respectively, and its outlets are the containment spray pipe and the cold section or the direct injection pipeline 19, respectively.

[0045] The passive reactor cavity cooling system includes the pressure vessel external insulation layer flow channel 21 and corresponding pipes, which are used to cool the pressure vessel 20 after a severe accident, ensuring that the core molten material remains inside the pressure vessel 20.

[0046] Starting the water supply system includes the water pump, water tank, and necessary pipes and valves.

[0047] In one example, the normal residual heat removal system and the containment spray system are used as countermeasures to deal with the extended design conditions, and have the functions of normal residual heat removal, low-pressure safety injection and containment spray.

[0048] When the normal waste heat removal function is performed, the valve from the heat pipe section to the waste heat removal pump is opened, the pump and heat exchanger start to operate, and the coolant in the hot section of the main pipeline is cooled in the heat exchanger 23 and then returned to the cold section (or directly injected into the pipeline 19). When the low-pressure safety injection function is performed, the system injects cold water from the high-level gravity injection tank 5 into the reactor coolant system through the pump 25 and then through the direct injection pipeline 19 to achieve low-pressure safety injection. When the containment spray function is performed, the pump 25 draws water from the high-level gravity injection tank 5, and sprays it through the pipeline and valves from the spray head, or draws water from the pit 27, and after passing through the pump 25 and the heat exchanger 23, sprays it through the pipeline and valves from the spray head.

[0049] In some possible implementations of this application, the passive reactor cavity cooling system, as one of the measures to deal with severe accidents, is used to cool the outer wall of the pressure vessel, thereby achieving the retention of molten material inside the pressure vessel. When the passive reactor cavity cooling system is required to operate, water in the high-level gravity water injection tank 5 is injected into the pit 27 through the injection pipe and gradually submerges the vessel. During this process, water in the pit 27 enters the insulation layer from the water flow holes of the insulation layer flow channel at the bottom of the insulation layer, and is heated into steam by the outer wall 20 of the pressure vessel in the flow channel and discharged from the outlet 21 of the insulation layer flow channel. After the submersion is completed, the water in the insulation layer flow channel is heated by the outer wall of the pressure vessel 20 and flows back to the pit 27 from the upper flow channel 21. The cooling of the wall of the pressure vessel 20 is achieved through natural circulation, ensuring that the pressure vessel 20 is not melted through by the core molten material, thereby retaining the molten material in the pressure vessel 20.

[0050] In one example, the start-up feedwater system is used as one of the design responses to extended operating conditions, performing start-up feedwater functions during the nuclear power plant's reactor start-up and shutdown processes and after an accident.

[0051] The present application has been described in detail above with reference to the accompanying drawings and embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. All content not described in detail in this application can be derived from existing technology.

Claims

1. A nuclear power plant safety system configuration system, characterized in that, The system includes: a passive emergency core cooling system for responding to design-based accidents, a secondary-side passive residual heat removal system, and a passive containment cooling system; The passive emergency core cooling system adopts a fully passive configuration scheme within the containment (1), which includes two sub-series. Each sub-series includes a full-pressure water supply tank (6), a safety injection tank (8), an automatic depressurization system, and a high-level gravity water injection tank (5). The inlet pipe of the total pressure water supply tank (6) is led out from the outlet of the main pump (22) and the outlet is connected to the direct injection line (19). The outlet of the safety injection tank (8) is connected to the direct injection line (19). The high-level gravity water injection tank (5) is connected to the direct injection line (19) through a pipe. The automatic pressure relief system is set with 4 stages. Stages 1-3 are led out from the top of the pressure stabilizer (10) and connected to the water in the high-level gravity water injection tank (5) through pipes and stage 1-3 ADS valves (7). Stage 4 is led out from the hot section and realizes the discharge of air into the containment (1) through stage 4 ADS valves (9). The secondary passive waste heat discharge system adopts a steam generator (11) secondary side layout scheme. Each steam generator (11) corresponds to a series of passive waste heat discharge systems. Each series includes an emergency waste heat discharge cooler and an emergency cooling water tank. The passive containment cooling system includes a PCS heat exchanger (12) inside the containment (1) and a cooling water tank (3) outside the containment, wherein the cooling water tank (3) outside the containment is shared with the PRS water tank; The secondary passive residual heat removal system is a dedicated safety facility that performs the function of removing residual heat from the reactor core after an accident. When the PRS operation signal is triggered, the PRS isolation valve (13) is opened and operates in a natural circulation manner. The steam generated in the steam generator (11) is condensed by the PRS heat exchanger (4) and then injected back into the steam generator (11) through the feedwater pipeline. The core energy is removed through the steam generator (11). The passive containment cooling system is one of the dedicated safety facilities for responding to design basis accidents. When the pressure and temperature of the containment (1) rise, the PCS system is automatically triggered to operate according to the signal. The water in the PCS heat exchanger (12) is heated and enters the cooling water tank (3) under the drive of density difference. The cold water in the cooling water tank (3) flows into the PCS heat exchanger (12) inside the containment (1) and is heated again, thereby cooling the containment (1) in a natural circulation manner.

2. The nuclear power plant safety system configuration system according to claim 1, characterized in that, When the full-pressure water supply tank (6), the safety injection tank (8), the high-level gravity water injection tank (5) are connected to the direct injection pipeline (19), an outlet isolation valve is provided.

3. The nuclear power plant safety system configuration system according to claim 1, characterized in that, The passive emergency core cooling system is used to provide emergency cooling, emergency water replenishment, boronizing, and safety injection functions for the core in the event of a design basis accident. When a design basis accident occurs, after the safety injection signal is triggered, the isolation valve of the full pressure water replenishment tank (6) is opened to inject full pressure at a low flow rate. When the water level in the full pressure water replenishment tank (6) is low, the 1st to 3rd level ADS valves (7) are triggered in sequence to reduce the system pressure. As the system pressure decreases, the safety injection tank (8) is put into operation when the system pressure decreases to a certain value to inject a large flow rate. In the later stage of the accident, the 4th level ADS valve (9) is opened and the water in the high-level gravity water injection tank (5) is injected into the core. When the water injection in the high-level gravity water injection tank (5) ends, the inlet and outlet nozzles and the part below the pressure vessel (20) are immersed in water and the core heat is carried out by natural circulation.

4. The nuclear power plant safety system configuration system according to any one of claims 1-3, characterized in that, The system also includes: a normal residual heat removal system for accident response and consequence mitigation during normal operation or design extended operating conditions, a containment spray system, a start-up feedwater system, and a passive reactor cavity cooling system; The normal waste heat discharge system is combined with the containment spray system to achieve the sharing of pumps and heat exchangers. Their inlets are the high-level gravity water injection tank (5), containment (1) pit and hot section, respectively, and their outlets are the containment spray pipe and cold section or direct injection pipeline (19). The passive reactor cavity cooling system includes the pressure vessel external insulation layer flow channel (21) and corresponding pipes, which are used to cool the pressure vessel (20) after a severe accident to ensure that the core melt remains in the pressure vessel (20); Starting the water supply system includes the water pump, water tank, pipes, and valves.

5. The nuclear power plant safety system configuration system according to claim 4, characterized in that, The normal residual heat removal system and the containment spray system are measures to deal with the extended design conditions, and have the functions of normal residual heat removal, low-pressure safety injection and containment spraying. When the normal waste heat discharge function is performed, the valve from the heat pipe section to the waste heat discharge pump is opened, and the pump (25) and heat exchanger (23) start to run. The coolant in the hot section of the main pipeline is cooled in the heat exchanger (23) and then returned to the cold section or directly injected into the pipeline (19). When the low-pressure safety injection function is performed, the system injects the cold water in the high-level gravity water tank (5) into the reactor coolant system through the pump (25) and then through the direct injection pipeline (19) to achieve low-pressure safety injection. When the containment spray function is performed, the pump (25) draws water from the high-level gravity water tank (5), and sprays it from the spray head through the pipeline and valve, or draws water from the pit (27), and sprays it from the spray head through the pump (25) and heat exchanger (23) through the pipeline and valve.

6. The nuclear power plant safety system configuration system according to claim 4, characterized in that, As one of the measures to deal with severe accidents, the passive cavity cooling system is used to cool the outer wall of the pressure vessel, thereby achieving the retention of molten material inside the pressure vessel. When the passive cavity cooling system is required to operate, the water in the high-level gravity water injection tank (5) is injected into the pit (27) through the injection pipe and gradually submerges the pressure vessel. During this process, the water in the pit (27) enters the insulation layer from the water flow hole at the bottom of the insulation layer and is heated into steam by the outer wall of the pressure vessel (20) in the flow channel. It is discharged from the outlet of the insulation layer flow channel (21). After the submersion is completed, the water in the insulation layer flow channel (21) is heated by the outer wall of the pressure vessel (20) and flows back to the pit (27) from the upper insulation layer flow channel (21). The cooling of the pressure vessel (20) wall is achieved through natural circulation, ensuring that the pressure vessel (20) is not melted through by the core molten material, thereby retaining the molten material inside the pressure vessel (20).

7. The nuclear power plant safety system configuration system according to claim 4, characterized in that, The start-up of the feedwater system is one of the measures to address the extended operating conditions designed for nuclear power plants, and performs the feedwater functions of the steam generator (11) during the start-up and shutdown process of the nuclear power plant and the steam generator (11) after the accident.

8. The nuclear power plant safety system configuration system according to claim 1, characterized in that, The high-level gravity water tank (5) is located inside or outside the containment (1); when placed outside the containment (1), the top of the high-level gravity water tank (5) is connected to the containment (1) through a pressure balance pipe.

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