A reactor safety system combining active and passive functions and its control method

Abstract

The present application discloses a reactor safety system combining active and passive functions and a control method thereof. The reactor safety system includes a safety injection subsystem combining active and passive functions, a containment energy management subsystem, a secondary side heat removal subsystem, and a reactor cavity water injection subsystem; wherein the safety injection subsystem includes two DVI safety injection pipelines and two independently arranged safety injection sub-trains, each DVI safety injection pipeline includes a DVI pipe, which receives the safety injection flow from a safety injection pump in each of the two safety injection sub-trains, and injects the safety injection flow into the reactor through the DVI pipe after being cooled by a series-connected safety injection heat exchanger; the control method includes: for a large breach accident, under a single fault criterion, providing the reactor with the safety injection flow of at least two safety injection boxes and two safety injection pumps, with the safety injection boxes providing a large short-term safety injection flow in the early stage, and the safety injection pumps providing a continuous safety injection flow thereafter; for other accidents, at least one DVI safety injection pipeline is effective.

Description

Technical Field

[0001] The present invention relates to the technical field of pressurized water reactors in nuclear power plants, and in particular to an active and passive combined reactor safety system and a control method thereof. Background Art

[0002] During the design process of a nuclear power plant, the principle of safety first must be upheld to ensure that the reactor can effectively control core reactivity, remove residual heat, and contain radioactivity under all circumstances. The reactor safety system is the core system for ensuring reactor safety. Its configuration directly determines the nuclear power plant's ability to prevent and mitigate accidents, as well as the reactor's safety level under accident conditions.

[0003] In the design of pressurized water reactor (PWR) nuclear power plants, a defense-in-depth approach and various dedicated safety measures are adopted to ensure plant safety. Second-generation and improved-generation PWRs generally employ active reactor safety systems. For example, in some designs, the safety injection subsystem utilizes two sets of main pipes connected in parallel to the reactor coolant system, making it prone to mutual interference between the redundant components of the system. In some designs, the safety injection system requires the coordinated connection of medium-pressure and low-pressure safety injection pumps to perform its injection function, posing the risk of failure of the injection connection function. Furthermore, the reactor safety system configuration of traditional active PWR PWRs is complex, and the excessive number of active devices leads to high operating and maintenance costs and difficult equipment layout. This also places a significant burden on support systems such as power supply, ventilation, and cold chain.

[0004] Subsequent upgraded nuclear power plants have adopted the concept of fully utilizing passive technologies. Key reactor safety systems, such as the core cooling system, containment heat removal system, and residual heat removal system, all employ passive technologies. The application of passive technologies simplifies the design of reactor safety and support systems and reduces operator workload. While passive technologies have gradually been recognized as a means to achieve higher levels of safety and economic efficiency in pressurized water reactor (PWR) nuclear power plants, numerous issues have been identified during subsequent engineering, operational, and technical reviews, exposing some of their shortcomings. For example, the application of passive technologies relies heavily on a deep understanding of key physical phenomena and system performance under various operating conditions, requiring extensive basic research and testing. Passive system performance is constrained by the inherent properties of the physical phenomena, and the natural driving forces and resistances are subject to numerous uncertainties. Failure of the physical processes in a passive system can lead to overall system failure. Due to the nonlinear nature of natural circulation phenomena, passive systems may exhibit instabilities that are not directly observable. Therefore, the passive reactor safety system has problems such as weak driving force, difficult process control, operational uncertainty, unstable flow, and easy interruption of natural circulation capacity. Relying entirely on passive technology to perform the safety functions of nuclear power plants involves certain technical risks and uncertainties. Summary of the Invention

[0005] To address the aforementioned technical issues, this application provides a combined active and passive reactor safety system and its control method. This system addresses the technical issues of existing nuclear reactors, such as the complex configuration, high operating and maintenance costs, and heavy system burden of active reactor safety systems, as well as the high risk of natural circulation interruption in passive reactor safety systems. This application simplifies the reactor safety system configuration, improves the effectiveness and reliability of injection, and shortens the core cooling path after an accident.

[0006] The present application provides a reactor safety system that combines active and passive functions. The reactor safety system includes an active and passive combined injection subsystem, an active and passive combined containment energy management subsystem, an active and passive combined secondary side heat removal subsystem, and an active and passive combined reactor cavity water injection subsystem, providing a combination of active and passive in-depth defense safety measures.

[0007] The injection subsystem includes two DVI injection pipelines and two independently arranged safety injection sub-columns. Each DVI injection pipeline includes a DVI pipe. The DVI pipe is configured to receive the injection flow from a safety injection pump in each of the two safety injection sub-columns, and inject the flow into the reactor through the DVI pipe after cooling through a series-connected safety injection heat exchanger.

[0008] Each safety injection sub-train includes a safety injection tank and two safety injection pumps capable of providing both medium- and low-pressure safety injection. The safety injection tank is connected to the DVI safety injection pipeline downstream of the safety injection heat exchanger. It is used to provide a short-term high flow rate for large and medium-sized breach accidents. The two safety injection pumps are connected in parallel to draw water from the refueling water tank and pump it into two DVI safety injection pipelines.

[0009] In some embodiments, each of the DVI safety injection pipelines is connected in series with one of the safety injection heat exchangers, and is capable of receiving the safety injection flow from one of the safety injection pumps in each of the two safety injection sub-columns, and then merging and cooling through the safety injection heat exchanger before injecting the flow into the reactor through the DVI safety injection pipeline.

[0010] In some embodiments, the reactor safety system also includes an active residual heat removal subsystem, which is arranged in two independent rows, each connected to a loop of the reactor coolant system; wherein each row of the active residual heat removal subsystem includes a residual heat removal heat exchanger and a residual heat removal pump, the residual heat removal pump connects a branch pipe of a loop hot pipe section and the hot side inlet of the residual heat removal heat exchanger, and the hot side outlet of the residual heat removal heat exchanger is connected to a loop cold pipe section through a pipeline branch.

[0011] In some embodiments, the containment energy management subsystem includes a passive containment heat extraction subsystem and an active containment spray subsystem; wherein, the function of the active containment spray subsystem is taken care of by the active residual heat removal subsystem, and the active containment spray subsystem is provided with a spray connecting pipeline downstream of the residual heat removal heat exchanger, and the spray connecting pipeline is connected to the containment spray ring pipe.

[0012] In some embodiments, in each column of the active waste heat removal subsystem, the inlet end branch of the waste heat removal pump is connected to the outlet end of the refueling water tank, and can be switched to take water from the refueling water tank, which is cooled and used for reactor water injection or containment spraying.

[0013] In some embodiments, the reactor safety system also includes an active emergency boration subsystem, which includes an emergency boric acid tank and an emergency boration pump. The emergency boration pumps are connected in parallel to the outlet end of the emergency boric acid tank and the branch pipe of the first-loop cooling pipe section.

[0014] In some embodiments, the secondary side heat removal subsystem includes an active secondary side emergency water supply subsystem, and the active secondary side emergency water supply subsystem includes an emergency water supply tank, the outlet end of the emergency water supply tank is connected to the inlet end of the main water supply pipe of the steam generator in a dual-path parallel output manner, and each path includes two emergency water supply pumps connected in parallel.

[0015] The two emergency water supply pumps on one route are electric emergency water supply pumps, and the two emergency water supply pumps on the other route are pneumatic emergency water supply pumps; or, one of the two emergency water supply pumps on the same route is an electric emergency water supply pump and the other is a pneumatic emergency water supply pump.

[0016] In some embodiments, the secondary side heat removal subsystem further includes a passive steam atmosphere discharge subsystem, which includes a steam release isolation valve, a steam release regulating valve, and a muffler sequentially connected to the steam outlet pipeline of the steam generator.

[0017] In some embodiments, the reactor safety system further includes a cooling water tank located high outside the containment vessel. The secondary heat removal subsystem further includes a passive secondary residual heat removal subsystem, comprising an SG steam condenser disposed in the cooling water tank. The SG steam condenser is connected to a steam generator steam outlet pipeline and a water supply pipeline via an SG steam condenser connecting pipeline.

[0018] In some embodiments, the cooling water tank serves as a medium for heat removal from the passive secondary side waste heat removal subsystem and the passive containment heat removal subsystem.

[0019] In some embodiments, the passive containment heat removal subsystem includes several groups of heat exchange modules, each group of the heat exchange modules includes a PCCS evaporator arranged in the containment, a PCCS condenser arranged in the cooling water tank, and a PCCS connecting pipeline between the two. The PCCS evaporator and the PCCS condenser are connected through the PCCS connecting pipeline to form a loop heat pipe heat removal system.

[0020] In some embodiments, the reactor cavity water injection subsystem includes an in-core retention water pool and an injection pump. The injection pumps are connected in parallel to the outlet end of the refueling water tank and the inlet end of the in-core retention water pool. The outlet end of the in-core retention water pool is connected to the water injection pipeline of the reactor cavity.

[0021] In some embodiments, the outlet branches of the two parallel water injection pumps are connected to the two DVI injection lines and can be switched to inject water into the reactor cavity or directly into the reactor.

[0022] In some embodiments, the containment energy management subsystem further includes a passive hydrogen control subsystem, which includes a number of passive hydrogen recombiners and a hydrogen monitoring unit arranged in the containment, and the hydrogen monitoring unit is used to detect the hydrogen concentration in the containment; the passive hydrogen recombiner is configured to automatically cause the hydrogen in the containment to react with oxygen to generate water.

[0023] In some embodiments of the present application, a control method for a combined active and passive reactor safety system is provided. The control method is applied to any of the above-described reactor safety systems, and the control method includes the following scenarios:

[0024] For large breach accidents, under the single failure criterion, the injection subsystem provides the reactor with effective injection flow from at least two injection tanks and two injection pumps to match the higher injection flow demand under corresponding conditions. In the early stage, the injection tanks provide a large short-term injection flow, and then the injection pumps are started to provide continuous injection flow. For other accidents, at least one DVI injection pipeline is effective, and one injection tank and one injection pump can meet the corresponding injection flow demand.

[0025] In some embodiments, the control method further includes:

[0026] For small and medium-sized rupture accidents: when the pressure on the secondary side of the steam generator increases, the passive steam atmosphere discharge subsystem is started to remove the heat from the core; when the liquid level of any steam generator is too low, the emergency feed water pump of the active secondary side emergency feed water subsystem is triggered to start, so as to inject water from the emergency feed water tank into the steam generator; as the pressure of the primary circuit continues to decrease, the injection pump and the passive steam atmosphere discharge subsystem of the injection subsystem are started to realize the cooling and pressure reduction of the primary circuit; when the pressure of the primary circuit is reduced to the injection pressure of the injection pump, the injection pump injects the boron-containing water in the refueling water tank into the core through the intact DVI injection pipeline.

[0027] And / or, for the steam generator heat transfer tube rupture accident: as the pressure of the primary circuit decreases and the water level of the affected steam generator increases, the passive steam atmospheric discharge subsystem is triggered to start, so as to achieve cooling and pressure reduction of the primary circuit; as the pressure of the primary circuit further decreases, the injection pump of the injection subsystem is started; when the liquid level of any steam generator is too low, the emergency water supply pump of the active secondary side emergency water supply subsystem is triggered to start, so as to inject water from the emergency water supply tank into the steam generator.

[0028] And / or, for a feedwater pipe rupture accident: when the liquid level of any steam generator is too low, the emergency feedwater pump of the active secondary side emergency feedwater subsystem is triggered to start, and the water in the emergency feedwater tank is injected into the steam generator; when the steam generator pressure increases, the passive steam atmosphere discharge subsystem is activated to remove the core heat; after the operator intervenes, the affected steam generator is isolated, and the active emergency boronization subsystem is activated to inject the concentrated boron solution in the emergency boric acid tank into the primary circuit through the emergency boronization pump, while the primary circuit temperature continues to be reduced through the intact steam generator; when the primary circuit temperature drops to the accessible temperature of the active residual heat removal subsystem, the residual heat removal pump is activated, and the residual heat removal heat exchanger is used to perform the long-term core cooling function;

[0029] And / or, for the main steam pipe rupture accident: as the pressure of the primary circuit decreases, the injection pump of the injection subsystem is started to draw water from the refueling water tank, and water is injected into the core through the DVI injection pipeline to ensure the stability of the water loading in the primary circuit; when the operator intervenes, the affected steam generator is isolated, the main steam isolation valve and the feed water isolation valve are closed to limit the release of mass and energy; the primary circuit is cooled by opening the steam release isolation valve corresponding to the intact steam generator; at the same time, the emergency feed water pump of the active secondary side emergency feed water subsystem is started to inject water from the emergency feed water tank into the intact steam generator; during the cooling process, the active emergency boration subsystem is started, and the concentrated boron solution in the emergency boric acid tank is injected into the primary circuit through the emergency boration pump; when the temperature of the primary circuit drops to the accessible temperature of the active residual heat removal subsystem, the residual heat removal pump is started, and the long-term core cooling function is performed through the residual heat removal heat exchanger.

[0030] In some embodiments, the control method further includes:

[0031] In the event of a power outage in the entire plant: the passive steam atmosphere discharge subsystem is activated to remove the core heat; when the liquid level of any steam generator is too low, the steam-driven emergency feed water pump of the active secondary side emergency feed water subsystem is triggered to start, and the water in the emergency feed water tank is injected into the steam generator; if the active secondary side emergency feed water subsystem is unavailable, the low liquid level signal of the steam generator triggers the activation of the passive secondary side residual heat removal subsystem, and the steam generator is cooled by the SG steam condenser arranged in the cooling water tank, and the core decay heat is transferred to the cooling water tank by relying on the natural circulation of the secondary circuit and discharged to the final heat sink atmosphere.

[0032] In some embodiments, the control method further includes:

[0033] For severe accidents: start the cavity water injection subsystem, and use the in-core retention water pool to inject water into the reactor cavity to achieve in-core retention of the melt; when the in-core retention water pool is at low liquid level, start the water injection pump of the cavity water injection subsystem to draw water from the refueling water tank, replenish water to the in-core retention water pool through the water replenishment pipeline, and inject water into the reactor cavity through the in-core retention water pool to continue to keep the reactor cavity submerged; start the passive containment heat extraction subsystem, and extract the heat in the containment to the cooling water tank through the PCCS evaporator arranged in the containment and the PCCS condenser arranged in the cooling water tank outside the containment; control the hydrogen concentration in the containment through the passive hydrogen recombiner of the passive hydrogen control subsystem, and perform real-time monitoring of the hydrogen concentration in the containment through the hydrogen monitoring unit.

[0034] In the combined active and passive reactor safety system provided by this application, the safety injection subsystem maximizes the advantages of both active and passive reactor safety systems, enabling independent operation of the two safety injection subtrains. This avoids the adverse effects of traditional mother control on the independence of each safety injection subtrain, thereby improving the effectiveness and reliability of safety injection. Furthermore, this application utilizes the safety injection pump to perform active core injection throughout the entire accident process, effectively shortening the emergency core water injection path after an accident, avoiding the risk of failure of the safety injection connection function, simplifying the reactor safety system configuration, and improving the reliability of the safety injection function. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The technical solution of this application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0036] Figure 1 This is a schematic diagram of the reactor safety system structure of one embodiment of the present application.

[0037] The reference numerals are as follows:

[0038] 1-pressure vessel, 2-pressurizer, 3-steam generator, 4-coolant pump, 5-reactor cavity, 6-main pipeline, 7-pressure relief tank, 8-containment, 9-pressurizer safety valve, 101-refueling water tank, 102-injection tank, 103-injection pump, 104-injection heat exchanger, 105-DVI injection pipeline, 106-DVI pipe, 201-waste heat removal pump, 202-waste heat removal heat exchanger, 203-containment spray ring pipe, 204-waste heat removal injection pipeline, 205-spray connection pipeline, 301-emergency boron Acid tank, 302-emergency boration pump, 401-emergency water supply tank, 402-electric emergency water supply pump, 403-pneumatic emergency water supply pump, 501-steam release isolation valve, 502-steam release regulating valve, 503-muffler, 601-cooling water tank, 602-SG steam condenser, 603-SG steam condenser connecting pipeline, 701-PCCS evaporator, 702-PCCS condenser, 703-PCCS connecting pipeline, 801-in-pile retention water pool, 802-water injection pump, 901-passive hydrogen recombiner. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the technical solution of the present invention is further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] See also Figure 1 In some embodiments of the present application, a reactor safety system combining active and passive functions is provided, which adopts active and passive safety measures at the defense-in-depth level. The reactor safety system includes but is not limited to a safety injection subsystem (SIS) combining active and passive functions, a containment energy management subsystem combining active and passive functions, a secondary side heat removal subsystem combining active and passive functions, and a cavity water injection subsystem (CIS) combining active and passive functions.

[0041] The safety injection subsystem includes two DVI safety injection pipelines 105 and two independently arranged safety injection sub-trains. Each DVI safety injection pipeline 105 includes a DVI pipe 106. The DVI pipe 106 is configured to receive the safety injection flow from a safety injection pump 103 in each of the two safety injection sub-trains. After cooling through a series-connected safety injection heat exchanger 104, the water is injected into the reactor through the DVI pipe 106. The safety injection subsystem draws water from the refueling water tank 101 within the containment vessel 8 and injects it directly into the pressure vessel 1 through the DVI safety injection pipelines 105 and the DVI safety injection pipe 106.

[0042] Each safety injection sub-train consists of a safety injection tank 102 and two safety injection pumps 103 capable of handling both medium- and low-pressure safety injection, along with associated pipelines, valves, and instrumentation. The safety injection tank 102 is connected to the DVI safety injection pipeline 105 downstream of the safety injection heat exchanger 104, providing a short-term, high-flow capacity for large and medium-sized breaches. The two safety injection pumps 103 are connected in parallel to the outlet of the refueling water tank 101 and the hot-side inlet of the safety injection heat exchanger 104. The outlet of the safety injection tank 102 and the hot-side outlet of the safety injection heat exchanger 104 are also connected in parallel to the inlet of the DVI safety injection pipeline 105. The DVI safety injection pipeline 105 is connected to the annular descending section of the pressure vessel 1 via a DVI pipe 106. The two safety injection pumps 103 draw water from the refueling water tank 101 in parallel and pump it into the two DVI safety injection pipelines 105. The safety injection sub-train is mainly used to supplement the water volume of the reactor primary circuit in the event of a rupture accident.

[0043] In order to simplify the description and avoid confusion of lines in the drawings, Figure 1 The medium-pressure injection subsystem will be described using only one DVI injection line 105, and one injection pump 103 connected to each DVI injection line 105 in each of the two safety injection subtrains. Each DVI injection line 105 receives flow from one injection pump 103 in each of the two safety injection subtrains and from one injection tank 102 in parallel. Each of the two safety injection subtrains is equipped with two injection pumps, each integrating both medium-pressure and low-pressure injection functions. The outlets of the two injection pumps in each train are connected to the hot-side inlets of the injection heat exchangers 104 on the two DVI injection lines 105. After cooling, the fuel is injected into the reactor's downcomer annulus through the DVI pipe 106. Each DVI injection line can provide at least one continuous injection pump and one short-term injection tank. Under the single failure criterion, in a large breach accident, it can provide the reactor with effective injection flow of at least two injection tanks and two injection pumps, which can match the higher injection flow demand under corresponding conditions; in other accidents, it can provide the injection flow of at least one injection pump and one injection tank.

[0044] Existing safety injection system designs utilize separate medium-pressure and low-pressure safety injection pumps, employing either a "four-series independent safety injection configuration" or a "two-series main pipe-controlled safety injection configuration." The four-series configuration offers lower efficiency and higher costs. The "two-series main pipe-controlled" configuration introduces significant uncertainty in main pipe distribution, often requiring increased equipment capacity. Main pipe failure often presents a safety and reliability shortcoming. Safety injection systems typically utilize a loop injection system, and a loop breach would result in failure of the corresponding safety injection system.

[0045] The active safety injection system for the two safety injection sub-trains in this application utilizes a "single pump" configuration strategy. Its safety injection pump integrates both medium-pressure and low-pressure safety injection functions, effectively reducing the number of safety injection pumps and lowering emergency power requirements. Its two DVI safety injection lines each connect a safety injection tank and a safety injection pump in each of the two safety injection sub-trains. This configuration avoids the complexity of a four-train configuration while also mitigating the risks of parent control in a traditional two-train configuration, maximizing the advantages of both active and passive reactor safety systems.

[0046] The safety injection subsystem of the present application adopts a two-column independent configuration to realize the independent operation of the "two columns" of safety injection sub-columns, avoid the adverse effects of the main control on the independence of each column of safety injection sub-columns, and improve the effectiveness and reliability of the safety injection. In addition, the safety injection subsystem of the present application adopts a "one pump to the end" solution, that is, the safety injection pump 103 performs the active core injection function throughout the entire accident process to realize the connection between the medium-pressure and low-pressure injection stages. There is no need to configure a medium-pressure safety injection pump and a low-pressure safety injection pump separately. Compared with the existing method of using a medium-pressure safety injection pump and a low-pressure safety injection pump for continuous injection, the configuration is simplified and the safety configuration efficiency is improved. Due to the use of a two-column direct injection method, the problem of safety injection failure caused by loop rupture is avoided, and the reliability of the safety injection function is effectively improved.

[0047] Furthermore, the safety injection subsystem of this application utilizes a combination of active and passive methods to achieve emergency water injection into the reactor core after an accident. For design basis accidents that occur more frequently, active systems with stronger driving force and more controllable processes are prioritized, with a limited number of passive measures considered as supplementary. For design expansion conditions that occur less frequently, passive systems with lower operator intervention and longer response times are prioritized. This significantly simplifies the configuration of the reactor safety system and its support systems for design expansion conditions, while also increasing the diversity of different defense-in-depth levels. Compared to traditional active PWR nuclear power plant safety system configurations, this application effectively simplifies the reactor safety system configuration while ensuring redundancy and independence, significantly reducing the number of active devices. Compared to traditional active PWR nuclear power plants, the reactor safety system also significantly reduces its demand for support systems such as power, cooling, and HVAC. Compared to fully passive safety injection subsystems, this application's safety injection function is stable and controllable, with sufficient driving force to ensure core water injection and cooling, and without the risk of natural circulation interruption.

[0048] See also Figure 1In some embodiments, each DVI safety injection pipeline 105 is connected in series with a safety injection heat exchanger 104, and each safety injection heat exchanger 104 can accept the safety injection flow of one safety injection pump 103 in each of the two safety injection sub-trains. The safety injection pump 103 draws water from the refueling water tank 101, and the water is merged and cooled by the safety injection heat exchanger 104 before being injected into the reactor through the DVI safety injection pipeline 105.

[0049] In the reactor safety system combining active and passive functions provided herein, the injection subsystem can pump water from the refueling water tank 101 into the injection heat exchanger 104 connected in series by two DVI injection pipelines 105 via the injection pump 103 for cooling. Under shutdown conditions, if the reactor's active residual heat removal subsystem fails, the injection heat exchanger 104 can remove core decay heat and maintain the temperature of the refueling water tank 101. If the residual heat removal system fails, the core heat can be transferred outside the containment through the injection subsystem alone, without relying on the containment heat removal system. This effectively shortens the core cooling path after an accident.

[0050] See also Figure 1 In some embodiments, the reactor safety system also includes an active residual heat removal subsystem (RHRS), which is arranged in two independent rows, each connected to a loop of the reactor coolant system. Each row of the active residual heat removal subsystem includes a residual heat removal heat exchanger 202, a residual heat removal pump 201, and associated pipelines, valves, and instrumentation. The residual heat removal pump 201 connects a branch pipe from the primary hot pipe section of the main pipeline 6 to the hot side inlet of the residual heat removal heat exchanger 202. The hot side outlet of the residual heat removal heat exchanger 202 is connected to a branch pipe from the primary cold pipe section of the main pipeline 6 via a residual heat removal injection line 204.

[0051] In order to simplify the description and avoid confusion of lines in the drawings, Figure 1 Only one column of active residual heat removal subsystems is taken for illustration. The present application can actively pump the high-temperature coolant of a hot pipe section of a circuit into the hot side inlet of the residual heat removal heat exchanger 202 through the residual heat removal pump 201 of any column of active residual heat removal subsystems, so as to remove the residual heat of the core through the low-temperature medium (equipment cooling water) on the cold side of the residual heat removal heat exchanger 202, and pump the cooled low-temperature coolant into the cold pipe section of a circuit through the residual heat removal injection pipeline 204 through the hot side outlet of the residual heat removal heat exchanger 202, so as to realize the circulation of the coolant in the circuit and ensure the long-term cooling function of the core. Even if one of the columns fails, the configuration scheme of the residual heat removal pump 201 of the reactor safety system of the present application can ensure that at least one residual heat removal pump 201 can remove the residual heat of the core through the corresponding residual heat removal heat exchanger 202.

[0052] See also Figure 1In some embodiments, the containment energy management subsystem includes a passive containment heat removal subsystem (PCCS) and an active containment spray subsystem. The active containment spray subsystem's functionality is concurrently performed by the active residual heat removal subsystem (RHRS). The active containment spray subsystem is provided with a spray connection line 205 downstream of the residual heat removal heat exchanger 202. The spray connection line 205 is connected to a containment spray loop 203. The containment spray loop 203 is located within the containment 8 and primarily performs a spraying operation to reduce the pressure and temperature within the containment 8 during an accident.

[0053] In some embodiments, in each active waste heat removal subsystem, the inlet of the waste heat removal pump 201 is branched and connected to the outlet of the refueling water tank 101. That is, the inlet of the waste heat removal pump 201 is connected to the outlet of the primary heat pipe segment and the outlet of the refueling water tank 101, respectively, and the outlet of the waste heat removal pump 201 is connected to the hot-side inlet of the waste heat removal heat exchanger 202. The waste heat removal pump 201 can be switched to draw water from the refueling water tank 101 and pump it into the waste heat removal heat exchanger 202 for cooling. The cooled water is then pumped into the containment spray loop 203 through the spray connection pipeline 205 to perform the containment spray function. This enables the active waste heat removal subsystem to have a containment spray function, thus realizing active containment spray cooling of the containment energy management subsystem.

[0054] In the event of a primary circuit breach and the complete failure of the injection pump 103, the long-term core cooling function can be maintained by using the charge-discharge mode of any active residual heat removal subsystem. Specifically, by switching the pipeline, the residual heat removal pump 201 of any column can draw water from the refueling water tank 101, pump the water into the residual heat removal heat exchanger 202 for cooling, and then pump the cooled water into the primary circuit cooling pipe section through the corresponding residual heat removal injection pipeline 204, thus achieving long-term core cooling.

[0055] In some existing designs, the containment spray system is configured independently. Using a separate containment spray pump and associated pipelines and valves, water from the refueling water tank is pumped into the containment spray loop to achieve containment spray cooling. Because the containment spray pump is not integrated with the injection system or the waste heat removal system, this design results in complex system configuration and high costs. Furthermore, the excessive number of safety-grade active equipment requires a large capacity of emergency diesel generators.

[0056] This application connects the containment spray loop pipe 203 to the active residual heat removal subsystem via a spray connection line 205. Specifically, the residual heat removal pump 201 in each active residual heat removal subsystem not only performs a primary coolant circulation, but also provides reactor water injection and cooling, as well as containment spray cooling and radioactivity removal in a charge-and-discharge mode. This provides robust safety features and a high level of overall safety.

[0057] See also Figure 1 In some embodiments, the reactor safety system also includes an active emergency boration subsystem (EBS), which includes an emergency boric acid tank 301, an emergency boration pump 302, and related pipelines, valves, and instrumentation. Two emergency boration pumps 302 are connected in parallel, connecting the outlet of the emergency boric acid tank 301 to a branch pipe of the primary cooling section of the main pipeline 6. The active emergency boration subsystem primarily performs emergency boration functions under accident conditions, compensating for positive reactivity introduced by cooling and other factors after an accident, bringing the core to a safe state as quickly as possible, and can serve as a diversified emergency shutdown measure. When an Anticipated Transient Unsuccessful Scramble (ATWS) condition occurs and the control rods are unable to perform the Scramble function, boron injection can be used to achieve an emergency shutdown.

[0058] The two parallel emergency boration pumps 302 in the active emergency boration subsystem can be powered by separate power supply trains, enabling independent operation of the two emergency boration pumps 302 and preventing common-mode failures of the two emergency boration pumps 302 due to power supply problems. The two parallel emergency boration pumps 302 in the active emergency boration subsystem draw concentrated boron solution from the emergency boric acid tank 301 and inject it into different cold pipe sections of the primary circuit through corresponding main pipes.

[0059] During a post-accident shutdown, the emergency boronization pump 302 can be used to inject concentrated boron solution from the emergency boric acid tank 301 into the primary circuit to compensate for the negative reactivity introduced by the primary circuit's water level and cooling, thereby quickly bringing the core to a safe state. Even considering the worst-case scenario of a single failure, the emergency boronization pump 302 configuration scheme of the reactor safety system of this application ensures that at least one emergency boronization pump 302 can perform the concentrated boron solution injection function.

[0060] See also Figure 1 In some embodiments, the secondary heat rejection subsystem includes an active secondary emergency feedwater subsystem (EFWS), which includes an emergency feedwater tank 401, an emergency feedwater pump, and related pipelines, valves, and instrumentation. The outlet of the emergency feedwater tank 401 is connected to the inlet of the main feedwater pipeline of the steam generator 3 in a dual-parallel output configuration, with each output pipeline including two parallel emergency feedwater pumps. In this embodiment, the two parallel emergency feedwater pumps on one output pipeline are electric emergency feedwater pumps 402, and the two parallel emergency feedwater pumps on the other output pipeline are steam-powered emergency feedwater pumps 403.

[0061] Alternatively, in some other embodiments, one of the two emergency water supply pumps connected in parallel on the same output pipeline is an electric emergency water supply pump 402, and the other is a pneumatic emergency water supply pump 403. That is, the two emergency water supply pumps connected in parallel on the same output pipeline can be the same or different.

[0062] The active secondary side emergency water supply subsystem provided in this application has two types of emergency water supply pumps on its two output pipelines, one is an electric pump and the other is a pneumatic pump. The two emergency water supply pumps can be connected to the output pipeline of the emergency water tank in a dual-parallel output manner in different combinations.

[0063] The active secondary side emergency water supply subsystem is used to provide emergency water supply to intact steam generators 3 under accident conditions, remove core decay heat and sensible heat through steam generators 3, and continue until the active residual heat removal subsystem is connected. The two emergency water supply pumps connected in parallel on each output pipeline can be driven by power sources of different columns, respectively, to achieve independent operation of the two emergency water supply pumps connected in parallel on the same output pipeline, and prevent common mode failure of the two emergency water supply pumps due to power source problems. Each output pipeline can supply water to all steam generators 3 through the corresponding branch pipeline. The emergency water supply tank 401 is set outside the containment vessel 8. The two emergency water supply pumps connected in parallel on the same output pipeline draw water from the emergency water supply tank 401 and deliver the water to the main water supply pipeline downstream of the main water supply check valve in the containment vessel 8 near the inlet of the steam generator 3 through the corresponding branch pipeline. A flow regulating valve (not shown in the figure) is provided on the output pipeline of the active secondary side emergency water supply subsystem to control the emergency water supply volume of the corresponding steam generator 3 .

[0064] The active secondary side emergency water supply subsystem provided by this application has a total of four emergency water supply pumps arranged in parallel on the dual output pipelines of the emergency water supply tank 401. The four emergency water supply pumps adopt a diversified combination design of "two electric and two steam" to achieve secondary side emergency water supply. Compared with the traditional electric emergency water supply solution, it effectively reduces the probability of failure of the emergency water supply pump due to common cause failure, significantly improves the accident fault tolerance of the active secondary side emergency water supply subsystem, and also greatly reduces the load demand for safety-grade power supply. In addition, compared with the use of a passive design solution, this application uses the active emergency water supply subsystem and steam generator 3 to cooperate with the design benchmark accident solution, and the forced circulation heat carrying capacity is more stable and sufficient, and there is no risk of functional failure caused by natural circulation interruption.

[0065] See also Figure 1 In some embodiments, the secondary side heat removal subsystem further includes a passive steam atmosphere discharge subsystem (ASDS), which includes a steam release isolation valve 501, a steam release regulating valve 502, and a muffler 503 connected in sequence to the steam outlet pipeline of the steam generator 3.

[0066] Passive steam-to-air venting subsystems are installed for each steam generator 3, one for each bank of steam generators 3. These subsystems are located in a valve station outside the reactor building, with physical isolation between the subsystems in different banks. These subsystems are primarily used to protect the secondary side of steam generator 3 from overpressure following an accident and to rapidly depressurize the primary circuit after a loss of coolant accident (LOCA), ensuring rapid access to the injection subsystem.

[0067] After an accident, when the primary circuit is under high pressure, the passive steam atmosphere discharge subsystem needs to cooperate with the active secondary side emergency water supply subsystem to quickly discharge the residual heat of the core by reducing the opening setting value of the steam release isolation valve 501 and discharging steam into the atmosphere. In this way, when a rupture accident occurs in the primary circuit, the core "rapid cooling" function can be achieved through any column of the passive steam atmosphere discharge subsystem, ensuring the rapid access of the injection subsystem and the effective connection of the injection pump 103.

[0068] The steam release isolation valve 501 is located upstream of the steam release regulating valve 502 in the airflow direction. It has a rapid response capability and serves as a safety barrier at the entrance of the steam atmospheric emission subsystem. It is used to perform secondary side overpressure protection of the steam generator 3 and can also perform post-accident isolation. The steam release regulating valve 502 is installed downstream of the steam release isolation valve 501 and adjusts the discharged steam flow by controlling the valve core opening. The muffler 503 is set at the end of the steam outlet pipeline to reduce the noise generated during steam emission.

[0069] See also Figure 1 In some embodiments, the reactor safety system further includes a cooling water tank 601 located at an elevated position outside the containment vessel 8. The secondary heat removal subsystem further includes a passive secondary residual heat removal subsystem (SPHRS). This passive secondary residual heat removal subsystem includes an SG steam condenser 602 disposed in the cooling water tank 601. The SG steam condenser 602 is connected to the steam outlet pipeline and the feedwater pipeline of the steam generator 3 via an SG steam condenser connecting line 603. Under design expansion conditions that require the active secondary emergency feedwater subsystem to be operational but unavailable, the passive secondary residual heat removal subsystem removes residual heat through a passive circulation system on the secondary side of the steam generator.

[0070] The passive secondary side waste heat removal subsystem is installed in correspondence with the steam generators 3. Each row of steam generators 3 is equipped with a corresponding row of SG steam condensers 602, along with associated pipelines, valves, and instrumentation. All SG steam condensers 602 transfer core decay heat to the final heat sink via a shared cooling water tank 601.

[0071] The SG steam condenser 602 is positioned high relative to the steam generator 3, providing the driving force for natural circulation through the density difference between the rising steam and the descending condensed water. The cooling water tank 601 is positioned high on the outer wall of the reactor building, and the SG steam condenser 602 is completely immersed in the cooling water tank 601. The upstream end of the SG steam condenser connecting pipeline 603 is connected to the steam outlet pipeline of the corresponding steam generator 3, and the downstream end of the SG steam condenser connecting pipeline 603 is connected to the feed water pipeline of the corresponding steam generator 3. Because the SG steam condenser 602 is completely immersed in the cooling water tank 601, the steam discharged from the steam outlet pipeline can exchange heat with the condensed water in the cooling water tank 601 in the SG steam condenser 602. The cooled condensed water then flows back to the feed water pipeline, achieving passive natural circulation.

[0072] Regarding the secondary side heat removal related systems, traditional designs use active emergency water supply systems and other systems to remove reactor heat, while some rely entirely on secondary side passive systems to remove reactor heat. The former has a weak ability to cope with the power outage of the entire plant, and its safety self-sustaining performance is lacking; the latter is prone to causing the secondary side circulating medium to be lost with overpressure discharge when responding to reactive accidents, which can easily introduce a steep edge effect of safety risks. The secondary side heat removal subsystem technology combining active and passive technologies proposed in this application combines the advantages of active and passive processes, has strong safety self-sustaining performance, and can avoid the steep edge effect risk of a single passive process.

[0073] See also Figure 1 In some embodiments, a cooling water tank 601 disposed at a high position outside the containment serves as a medium for heat removal from the passive secondary side residual heat removal subsystem (SPHRS) and the passive containment heat removal subsystem (PCCS).

[0074] See also Figure 1 In some embodiments, the containment energy management subsystem includes a passive containment heat removal subsystem (PCCS). This passive containment heat removal subsystem comprises several sets of heat exchange modules. Each set of heat exchange modules includes a PCCS evaporator 701 located within the containment 8, a PCCS condenser 702 located in a cooling water tank 601 located at a high position outside the containment 8, and associated pipelines, valves, and instrumentation. The PCCS evaporator 701 and PCCS condenser 702 are connected via a PCCS connecting pipeline 703 to form a loop-type heat pipe heat removal system. The passive containment heat removal subsystem is designed to remove heat from the containment 8 under extended operating conditions, control the pressure and temperature of the containment 8, and maintain the integrity of the containment 8.

[0075] The passive containment heat removal subsystem (PCCS) and the passive secondary waste heat removal subsystem (SPHRS) share a cooling water tank 601 located high outside containment 8, eliminating duplication of cooling water tanks. The PCCS evaporator 701 is located high inside containment 8, while the PCCS condenser 702 is immersed in the cooling water tank 601. The upstream end of the PCCS connecting pipeline 703 connects to the gas-phase heat exchange medium outlet of the corresponding PCCS evaporator 701, while the downstream end of the PCCS connecting pipeline 703 connects to the liquid-phase heat exchange medium inlet of the corresponding PCCS evaporator 701, forming a fully enclosed heat pipe loop.

[0076] A heat exchange medium capable of achieving heat transfer through phase change can be provided within the PCCS evaporator 701. Since the PCCS evaporator 701 is positioned high within the containment vessel 8, the PCCS condenser 702 is completely immersed in the cooling water tank 601. After an accident occurs, the liquid heat exchange medium within the PCCS evaporator 701 is heated by the high-temperature air-steam mixture within the containment vessel 8, causing a phase change. After absorbing heat within the containment vessel 8, it is converted into a high-temperature vapor-phase heat exchange medium. The high-temperature vapor-phase heat exchange medium is delivered to the upstream of the PCCS connecting pipeline 703 via the vapor-phase heat exchange medium outlet. This allows the high-temperature vapor-phase heat exchange medium to exchange heat with condensed water in the cooling water tank 601 within the PCCS condenser 702. The liquid-phase heat exchange medium, which is condensed after being cooled by the condensed water, flows back to the liquid-phase heat exchange medium inlet, achieving passive closed self-circulation of the heat exchange medium. Heat within the containment vessel 8 is then transferred to the cooling water tank 601 through heat transfer between the high-temperature air-steam mixture and the heat exchange medium within the pipe.

[0077] In some existing designs, the passive containment heat removal subsystem directly connects the containment to an external water tank via a heat exchanger and related piping. Damage to the heat exchanger or piping within the containment after an accident could cause the containment to bypass, potentially releasing radioactive material from the containment into the external environment. The passive containment heat removal subsystem provided in this application utilizes a "separate heat pipe loop" to completely isolate the containment 8 from the external atmosphere through a fully enclosed heat pipe loop. Even if the PCCS connecting line 703 were to break, this would prevent the containment 8 from being bypassed, effectively preventing the leakage of radioactive material from the containment 8 and providing increased safety.

[0078] In addition, this application rationally configures active and passive systems according to different defense-in-depth levels, primarily using passive systems to address design expansion conditions, including situations where the active system completely fails due to support systems or mechanical issues. This application strengthens the application of passive technology, using a passive secondary side residual heat removal subsystem (SPHRS) to transfer heat from steam generator 3 when emergency feedwater is unavailable, and a passive containment heat removal subsystem (PCCS) to remove heat from the containment when containment spraying is unavailable.

[0079] In some embodiments, the cooling water tank 601 may also provide gravity water replenishment to the spent fuel pool through relevant pipes, valves, etc.

[0080] See also Figure 1 In some embodiments, the reactor cavity injection subsystem (CIS) includes an in-core retention water pool 801, an injection pump 802, and related pipelines, valves, and instruments. Two injection pumps 802 are connected in parallel, connecting the outlet of the refueling water tank 101 and the inlet of the in-core retention water pool 801. The outlet of the in-core retention water pool 801 is connected to the injection pipeline of the reactor cavity 5.

[0081] The two parallel injection pumps 802 in the reactor cavity water injection subsystem utilize a redundant design. They can be powered by different power supply trains, enabling independent operation of the two pumps 802 and preventing common-mode failures of the two pumps 802 due to power supply problems. The two parallel injection pumps 802 draw water from the refueling water tank 101 and pump it into the in-core retention water pool 801 through a combined outlet and a water replenishment pipeline. This enables active and rapid water replenishment of the in-core retention water pool 801, maintaining a high water level in the pool. The water is then forced into the reactor cavity 5 by gravity through the water injection pipeline, achieving passive and rapid water injection into the reactor cavity.

[0082] The reactor cavity water injection subsystem provided in this application utilizes a combination of active and passive methods. In the early stages of an accident, a high-positioned in-core water retention pool 801 utilizes gravity to rapidly fill the reactor cavity 5 through a passive, high-flow cavity water injection method to cool the exterior of the reactor pressure vessel 1. Furthermore, an injection pump 802 can actively replenish water to the in-core water retention pool 801 through relevant pipelines. In the later stages of an accident, injection pump 802 is activated to inject water into the reactor cavity 5 through the injection pipeline. This low-flow active cavity water injection method ensures a balance between evaporation and water injection, helping to reduce the capacity and scale of the active water injection system.

[0083] In other embodiments, the combined outlet of the two parallel water injection pumps 802 is connected to two DVI safety injection lines 105 via a branch connection line (not shown), allowing for switchable injection of water into the reactor cavity 5 or direct injection into the reactor. Specifically, the combined outlet of the two parallel water injection pumps 802 can be configured to connect to the inlet of the in-core retention water pool 801 and the DVI safety injection line 105, respectively. This allows the two parallel water injection pumps 802 to not only provide active water replenishment to the in-core retention water pool 801 but also provide core water injection, enabling emergency core water injection in the event of an emergency where the safety injection subsystem (SIS) is unavailable.

[0084] The core cavity water injection subsystem is primarily used to inject water into the core cavity during severe accident conditions to cool the exterior of the reactor pressure vessel 1. By flooding the core cavity, molten debris and radioactive material are retained within the core. Under design expansion conditions that do not significantly damage the core, and when the safety injection subsystem (SIS) is unable to effectively perform core injection, the core cavity water injection subsystem's water injection pump 802 can also be used to inject boron water from the refueling water tank 101 directly into the core through the DVI safety injection pipeline 105, thereby ensuring core cooling while also providing core water injection.

[0085] See also Figure 1 In some embodiments, the containment energy management subsystem also includes a passive hydrogen control subsystem (PHCS). This passive hydrogen control subsystem comprises several passive hydrogen recombiners 901 disposed within the containment vessel 8 and a hydrogen monitoring unit (not shown). The hydrogen monitoring unit is used to monitor the hydrogen concentration within the containment vessel 8. The passive hydrogen recombiners 901 are configured to automatically react hydrogen and oxygen within the containment vessel 8 to produce water. The passive hydrogen control subsystem is primarily used to control the hydrogen concentration within the containment vessel 8 after an accident to ensure the structural and sealing integrity of the containment vessel 8 and to monitor the hydrogen concentration within the containment vessel 8 after an accident.

[0086] See also Figure 1 In some embodiments, the reactor safety system further includes a pressurizer 2, a pressurizer safety valve 9, and a pressure relief tank 7, which are sequentially connected to the pressure-stabilizing pipeline of the primary-loop heat pipe section. The steam space of the pressurizer 2 is directly connected to the pressure-stabilizing pipeline of the primary-loop heat pipe section. When the primary-loop pressure drops, the electric heater in the pressurizer 2 starts to generate steam to supplement the primary-loop pressure; when the primary-loop pressure is too high, the pressurizer safety valve 9 automatically opens to release part of the steam into the pressure relief tank 7 to prevent the pressure boundary of the primary-loop heat pipe section from rupturing.

[0087] This application also discloses a control method for a reactor safety system that combines active and passive functions. This control method is applicable to any of the above-mentioned reactor safety systems. The control method includes the following scenarios:

[0088] A) During normal operation:

[0089] During normal operation of a nuclear power plant unit, the isolation valves of the passive containment heat removal subsystem (PCCS) remain open to facilitate rapid response to pressure increases in the containment vessel after an accident. Other safety subsystems are in standby mode. Furthermore, the active residual heat removal subsystem (RHRS) can be used to remove decay heat during normal unit shutdown.

[0090] B) For medium to large breach incidents:

[0091] For a large breach accident, under the single failure criterion, the safety injection subsystem (SIS) provides the reactor with effective safety injection flow from at least two safety injection tanks 102 and two safety injection pumps 103 to match the higher safety injection flow demand under corresponding conditions. In the early stage, the safety injection tanks provide a large short-term safety injection flow, and then the safety injection pumps are started and provide continuous safety injection flow. For other accidents, at least one DVI safety injection pipeline is effective, and one safety injection tank and one safety injection pump can meet the corresponding safety injection flow demand.

[0092] In the event of a large-break (LB-LOCA) or medium-break (IB-LOCA) accident at a nuclear power plant, the reactor's primary circuit pressure drops rapidly. After the blowdown phase, the safety injection tank 102 first injects a large flow of water into the core through the DVI safety injection line 105, refilling the downdraft section and lower chamber of the pressure vessel 1. Subsequently, upon receiving the safety injection signal, the safety injection pump 103 automatically activates, draws water from the refueling water tank 101, and injects water into the core through the DVI safety injection line 105, reflooding the core and restoring the water charge. Even considering the worst-case scenario of a single failure, the configuration of the safety injection pumps 103 ensures that at least two pumps can inject water into the reactor pressure vessel 1 through the DVI pipes 106 of the two DVI safety injection lines 105.

[0093] C) For small and medium-sized breach accidents:

[0094] In the event of a direct-injection line closure (DVI-LOCA) or a small-diameter closure (SB-LOCA) at a nuclear power plant, the primary coolant's ability to dissipate heat through the closure is limited, potentially causing a pressure increase on the secondary side of steam generator 3. The steam release isolation valve 501 of the passive steam atmospheric discharge subsystem (ASDS) will initiate an overpressure discharge, dissipating heat from the core. If the liquid level in any steam generator 3 is too low, the emergency feedwater pump of the active secondary emergency feedwater subsystem (EFWS) will be activated to inject water from the emergency feedwater tank 401 into steam generator 3.

[0095] As the primary circuit pressure continues to drop, the SIS injection pump 103 automatically starts upon receiving the injection signal. Simultaneously, the passive steam atmospheric discharge subsystem (ASDS) activates its "rapid cooling" function, lowering the setpoint of the steam release isolation valve 501 to cool and reduce the primary circuit pressure. When the primary circuit pressure rapidly drops to the injection pressure of the SIS pump 103, the pump 103 injects boron-containing water from the refueling water tank 101 into the core via the intact DVI injection line 105. The rupture flow is gradually replenished by the injection flow, maintaining the core submerged. Over a long period of time, core heat can be removed via the SIS heat exchanger 104 through the equipment cooling water.

[0096] D) For the steam generator 3 heat transfer tube rupture accident:

[0097] When a steam generator heat transfer tube rupture (SGTR) occurs in a nuclear power plant, leakage from the primary to the secondary side of the steam generator causes a decrease in primary circuit pressure and water charge. As the primary circuit pressure decreases and the water level in the affected steam generator 3 rises, the passive steam atmospheric drainage subsystem (ASDS)'s "rapid cooling" function is triggered, lowering the setpoint of the steam release isolation valve 501 to reduce the primary circuit temperature and pressure. As the primary circuit pressure drops further, the safety injection pump 103 of the safety injection subsystem (SIS) automatically starts upon receiving the safety injection signal. Continued discharge from the passive steam atmospheric drainage subsystem (ASDS) causes the liquid level in intact steam generators 3 to continue to drop. If the liquid level in any steam generator 3 becomes too low, the emergency feedwater pump of the active secondary emergency feedwater subsystem (EFWS) will start, injecting water from the emergency feedwater tank 401 into the steam generator 3. Due to the high water level in the affected steam generator 3, the corresponding row of the active secondary emergency feedwater subsystem (EFWS) will be isolated from water supply. At this time, the core heat is continuously removed through the passive steam atmospheric discharge subsystem (ASDS), and the injection pump 103 ensures the stability of the core coolant charge.

[0098] After the "rapid cooling" period, the liquid level in the affected steam generator 3 continued to rise. To prevent overflow, the affected steam generator 3 was isolated, the opening setting of the steam release isolation valve 501 corresponding to the affected steam generator 3 was increased, the main steam isolation valve of the affected steam generator 3 was closed, and the feedwater to the affected steam generator 3 was isolated. After the affected steam generator 3 was isolated, the pressures in the primary and secondary circuits gradually reached equilibrium, and the leak eventually ceased.

[0099] E) For water supply pipe rupture accidents:

[0100] If a feedwater line breach (FLB) occurs in a nuclear power plant, the breach causes a rapid drop in the pressure and water level in steam generator 3, triggering main steam isolation and closing the main steam isolation valve. If the liquid level in any steam generator 3 is too low, the emergency feedwater pump of the active secondary emergency feedwater subsystem (EFWS) will be activated, pumping water from the emergency feedwater tank 401 into steam generator 3. This reduction in secondary heat removal capacity will cause the pressure in steam generator 3 to increase, prompting the steam release isolation valve 501 of the passive steam atmospheric discharge subsystem (ASDS) to remove core heat through overpressure discharge.

[0101] After operator intervention, the affected steam generator 3 will be isolated and the isolation valve for injecting water into the affected steam generator 3 via the active secondary side emergency feedwater subsystem (EFWS) will be closed. After the affected steam generator 3 is isolated, the primary circuit will be cooled and depressurized, and boronization will be performed. The active emergency boronization subsystem (EBS) will be activated, and concentrated boron solution from the emergency boric acid tank 301 will be injected into the primary circuit via the emergency boronization pump 302 to compensate for the primary circuit water load and the negative reactivity introduced by the cooling. Simultaneously, the primary circuit temperature will continue to be lowered through the intact steam generator 3. Once the primary circuit temperature drops to a temperature at which the active residual heat removal subsystem (RHRS) can be connected, the residual heat removal pump 201 will be activated, and long-term core cooling will be performed through the residual heat removal heat exchanger 202, which is cooled by equipment cooling water.

[0102] F) For main steam pipe rupture accidents:

[0103] When a main steam line breach (MSLB) occurs in a nuclear power plant, the primary circuit is overcooled due to the release of steam from the secondary side of the steam generator, causing coolant contraction and a pressure drop. As the primary circuit pressure decreases, the injection pump 103 of the safety injection subsystem (SIS) automatically starts upon receiving a safety injection signal, draws water from the refueling water tank 101, and injects it into the reactor core through the DVI safety injection pipeline 105, ensuring a stable primary circuit water level.

[0104] After operator intervention, the affected steam generator 3 was isolated, and the main steam isolation valve and feedwater isolation valve were closed to limit mass and energy release. The primary circuit was cooled by opening the steam release isolation valve 501 corresponding to the intact steam generator 3. Simultaneously, the emergency feedwater pump of the active secondary emergency feedwater subsystem (EFWS) was activated, pumping water from the emergency feedwater tank 401 into the intact steam generator 3. During the cooling process, the active emergency boronization subsystem (EBS) was activated, injecting concentrated boron solution from the emergency boric acid tank 301 into the primary circuit via the emergency boronization pump 302 to compensate for the primary circuit water load and the negative reactivity introduced by the cooling. Once the primary circuit temperature dropped to a temperature accessible by the active residual heat removal subsystem (RHRS), the residual heat removal pump 201 was activated, and long-term core cooling was performed via the residual heat removal heat exchanger 202, which was cooled by equipment cooling water.

[0105] G) For power outage in the entire plant:

[0106] In the event of a power outage (SBO) in a nuclear power plant, the reactor coolant system's coolant pump 4 slows down due to the power outage, triggering an emergency shutdown and a turbine trip. Since steam generator 3 cannot effectively remove core heat, the pressure in steam generator 3 increases. The steam release isolation valve 501 of the passive steam atmospheric discharge subsystem (ASDS) removes the core heat through overpressure relief. If the liquid level in any steam generator 3 is too low, the steam-driven emergency feedwater pump 403 of the active secondary emergency feedwater subsystem (EFWS) will activate, pumping water from the emergency feedwater tank 401 into steam generator 3. If the active secondary emergency feedwater subsystem (EFWS) becomes unavailable, the steam generator 3 water level will continue to drop. The low-liquid-level signal from steam generator 3 will automatically trigger the passive secondary residual heat removal subsystem (SPHRS) to automatically activate, cooling steam generator 3 through the SG steam condenser 602. Relying on secondary natural circulation, the core decay heat is transferred to the cooling water tank 601 and discharged to the atmosphere, the final heat sink.

[0107] H) For serious accidents:

[0108] To prevent meltthrough of the pressure vessel 1 after a severe accident at a nuclear power plant, the CIS (Core Injection System) is activated. This passively utilizes water from the in-core retention pool 801 to initially fill and replenish the reactor cavity 5. This provides external cooling for the pressure vessel 1 and allows for melt retention within the reactor. Once the water in the in-core retention pool 801 is depleted, the CIS's injection pump 802 is activated, drawing water from the refueling water tank 101. This water is then replenished via the replenishment pipeline to the in-core retention pool 801. Furthermore, water is injected into the reactor cavity 5 via the in-core retention pool 801 and the injection pipeline to maintain submergence of the reactor cavity 5.

[0109] After a serious accident occurs, the PCCS evaporator 701 of the passive containment heat removal subsystem (PCCS) will remove heat from the containment 8 through heat transfer between the high-temperature air-steam mixture and the heat exchange medium in the pipe. At the same time, the PCCS condenser 702 removes the heat of the heat exchange medium heated to the gas phase in the heat pipe loop to the cooling water tank 601 outside the containment 8, thereby removing heat from the containment 8 in a passive manner for a long period of time, preventing overpressure in the containment 8 and ensuring the integrity of the containment 8.

[0110] In addition, in order to prevent the accumulation of hydrogen in the containment 8 after a serious accident from threatening the integrity of the containment 8, the hydrogen concentration in the containment 8 will be controlled by the passive hydrogen recombiner 901 of the passive hydrogen control subsystem (PHCS) to ensure that the integrity of the structure and seal of the containment 8 is maintained, and real-time monitoring of the hydrogen concentration in the containment 8 will be performed through the hydrogen monitoring unit.

[0111] In summary, this application maximizes the advantages of active reactor safety systems and passive reactor safety systems. For design basis accidents that occur more frequently, priority is given to active systems with stronger driving force and controllable processes, and a small number of passive means are considered as supplements. For design expansion conditions that occur less frequently, priority is given to passive systems with lower operator intervention and longer response times, which greatly simplifies the configuration of reactor safety systems and their supporting systems for design expansion conditions, while increasing the diversity of different defense-in-depth levels.

[0112] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A reactor safety system combining active and passive functions, characterized in that: The reactor safety system includes an active and passive combined injection subsystem, an active and passive combined containment energy management subsystem, an active and passive combined secondary side heat removal subsystem, an active and passive combined reactor cavity water injection subsystem, and an active residual heat removal subsystem; The safety injection subsystem includes two DVI safety injection pipelines and two independently arranged safety injection sub-trains. Each DVI safety injection pipeline includes a DVI pipe. The DVI pipe is configured to receive the safety injection flow from a safety injection pump in each of the two safety injection sub-trains, and then cool it through a series-connected safety injection heat exchanger before injecting it into the reactor through the DVI pipe. Each safety injection sub-train includes a safety injection tank and two safety injection pumps that provide both medium-pressure and low-pressure safety injection. The safety injection tank is branched onto the DVI safety injection pipeline downstream of the safety injection heat exchanger and is used to provide a short-term, high-flow rate for large / medium-sized breach accidents. The two safety injection pumps draw water from the refueling water tank in parallel and pump it to two DVI safety injection pipelines, respectively. Each DVI safety injection pipeline receives water from one safety injection pump and one safety injection tank in each of the two safety injection sub-trains in parallel. The active residual heat removal subsystem is arranged in two independent rows, each connected to a loop of the reactor coolant system; wherein each row of the active residual heat removal subsystem includes a residual heat removal heat exchanger and a residual heat removal pump, wherein the residual heat removal pump is connected to the branch pipe of the primary loop hot pipe section and the hot side inlet of the residual heat removal heat exchanger, and the hot side outlet of the residual heat removal heat exchanger is connected to the branch pipe of the primary loop cold pipe section via a residual heat removal injection pipeline; The waste heat removal pump of any column of the active waste heat removal subsystem actively pumps the high-temperature coolant of the primary hot pipe section into the hot side inlet of the waste heat removal heat exchanger, so as to carry out the core waste heat through the low-temperature medium on the cold side of the waste heat removal heat exchanger, and pumps the cooled low-temperature coolant into the primary cold pipe section through the waste heat removal injection pipeline through the hot side outlet of the waste heat removal heat exchanger, thereby realizing the circulation of the coolant in the primary circuit and ensuring the long-term cooling function of the core.

2. The active and passive combined reactor safety system according to claim 1, characterized in that: Each of the DVI safety injection pipelines is connected in series with one of the safety injection heat exchangers, and is capable of receiving the safety injection flow from one of the safety injection pumps in each of the two safety injection sub-trains, merging the flow and cooling it through the safety injection heat exchanger before injecting it into the reactor through the DVI safety injection pipeline.

3. The active and passive combined reactor safety system according to claim 1, characterized in that: The containment energy management subsystem includes a passive containment heat removal subsystem and an active containment spray subsystem; Among them, the function of the active containment spray subsystem is taken care of by the active waste heat removal subsystem. The active containment spray subsystem is provided with a spray connecting pipeline downstream of the waste heat removal heat exchanger, and the spray connecting pipeline is connected to the containment spray ring pipe.

4. The active and passive combined reactor safety system according to any one of claims 1 to 3, characterized in that: In each row of the active waste heat removal subsystem, the inlet end branch of the waste heat removal pump is connected to the outlet end of the refueling water tank, and can be switched to take water from the refueling water tank, which is cooled and used for reactor water injection or containment spraying.

5. The active and passive combined reactor safety system according to claim 1, characterized in that: The reactor safety system also includes an active emergency boration subsystem, which includes an emergency boric acid tank and an emergency boration pump. The emergency boration pumps are connected in parallel to the outlet end of the emergency boric acid tank and the primary cooling pipe section.

6. The active and passive combined reactor safety system according to claim 1, characterized in that: The secondary side heat removal subsystem includes an active secondary side emergency water supply subsystem, which includes an emergency water supply tank. The outlet end of the emergency water supply tank is connected to the inlet end of the main water supply pipe of the steam generator in a dual-path parallel output mode, and each path includes two emergency water supply pumps connected in parallel. The two emergency water supply pumps on one route are electric emergency water supply pumps, and the two emergency water supply pumps on the other route are pneumatic emergency water supply pumps; or, one of the two emergency water supply pumps on the same route is an electric emergency water supply pump and the other is a pneumatic emergency water supply pump.

7. The active and passive combined reactor safety system according to claim 1, characterized in that: The secondary side heat removal subsystem further includes a passive steam atmosphere discharge subsystem, which includes a steam release isolation valve, a steam release regulating valve, and a muffler that are sequentially connected to the steam outlet pipeline of the steam generator.

8. The active and passive combined reactor safety system according to claim 3, characterized in that: The reactor safety system also includes a cooling water tank arranged at a high position outside the containment vessel; The secondary side heat removal subsystem also includes a passive secondary side waste heat removal subsystem, which includes an SG steam condenser arranged in the cooling water tank, and the SG steam condenser is connected to the steam outlet pipeline and the water supply pipeline of the steam generator through the SG steam condenser connecting pipeline.

9. The active and passive combined reactor safety system according to claim 8, characterized in that: The cooling water tank serves as a medium for heat extraction from the passive secondary side waste heat removal subsystem and the passive containment heat extraction subsystem.

10. The active and passive combined reactor safety system according to claim 9, characterized in that: The passive containment heat removal subsystem includes several groups of heat exchange modules, each group of which includes a PCCS evaporator arranged in the containment and a PCCS condenser arranged in the cooling water tank. The PCCS evaporator and the PCCS condenser are connected by a PCCS connecting pipeline to form a loop heat pipe heat removal system.

11. The active and passive combined reactor safety system according to claim 1, characterized in that: The reactor cavity water injection subsystem includes an in-core retention water pool and an injection pump. The injection pumps are connected in parallel to the outlet end of the refueling water tank and the inlet end of the in-core retention water pool. The outlet end of the in-core retention water pool is connected to the reactor cavity water injection pipeline.

12. The active and passive combined reactor safety system according to claim 11, characterized in that: The outlet branches of the two parallel water injection pumps are connected to the two DVI injection pipelines, and can be switched to inject water into the reactor cavity or directly into the reactor.

13. The active and passive combined reactor safety system according to claim 1, characterized in that: The containment energy management subsystem also includes a passive hydrogen control subsystem, which includes several passive hydrogen recombiners and hydrogen monitoring units arranged in the containment. The hydrogen monitoring unit is used to detect the hydrogen concentration in the containment; the passive hydrogen recombiners are configured to automatically cause the hydrogen in the containment to react with oxygen to generate water.

14. A control method for a reactor safety system combining active and passive functions, characterized in that: The control method is applied to the reactor safety system according to any one of claims 1 to 13, and the control method includes the following scenarios: For large breach accidents, under the single failure criterion, the injection subsystem provides the reactor with effective injection flow from at least two injection tanks and two injection pumps to match the injection flow demand under corresponding conditions. In the early stage, the injection tanks provide a short-term injection flow, and then the injection pumps are started to provide continuous injection flow. For other accidents, at least one DVI injection pipeline is effective, and one injection tank and one injection pump can meet the corresponding injection flow demand.

15. The control method of the active and passive combined reactor safety system according to claim 14, characterized in that: The control method further includes: For small and medium-sized breach accidents: when the secondary side pressure of the steam generator increases, the passive steam atmosphere discharge subsystem is activated to remove the core heat; when the liquid level of any steam generator is too low, the emergency feed water pump of the active secondary side emergency feed water subsystem is triggered to start, so as to inject water from the emergency feed water tank into the steam generator; as the primary circuit pressure continues to decrease, the injection pump and the passive steam atmosphere discharge subsystem of the injection subsystem are activated to achieve the cooling and pressure reduction of the primary circuit; when the primary circuit pressure drops to the injection pressure of the injection pump, the injection pump injects the boron-containing water in the refueling water tank into the core through the intact DVI injection pipeline; And / or, for a steam generator heat transfer tube rupture accident: as the primary circuit pressure decreases and the water level of the affected steam generator increases, the passive steam atmospheric discharge subsystem is triggered to start, so as to reduce the temperature and pressure of the primary circuit; as the primary circuit pressure further decreases, the injection pump of the injection subsystem is started; when the liquid level of any steam generator is too low, the emergency water feed pump of the active secondary side emergency water feed subsystem is triggered to start, so as to inject water from the emergency water feed tank into the steam generator; And / or, for a feedwater pipe rupture accident: when the liquid level of any steam generator is too low, the emergency feedwater pump of the active secondary side emergency feedwater subsystem is triggered to start, and the water in the emergency feedwater tank is injected into the steam generator; when the pressure of the steam generator increases, the passive steam atmosphere discharge subsystem is activated to remove the heat from the core; after the intervention, the affected steam generator is isolated, the active emergency boration subsystem is activated, and the concentrated boron solution in the emergency boric acid tank is injected into the primary circuit through the emergency boration pump, while the temperature of the primary circuit continues to be reduced through the intact steam generator; when the temperature of the primary circuit drops to the accessible temperature of the active residual heat removal subsystem, the residual heat removal pump is activated, and the long-term core cooling function is performed through the residual heat removal heat exchanger; And / or, for the main steam pipe rupture accident: as the pressure of the primary circuit decreases, the injection pump of the injection subsystem is started to draw water from the refueling water tank, and water is injected into the core through the DVI injection pipeline to ensure the stability of the water loading in the primary circuit; after intervention, the affected steam generator is isolated, the main steam isolation valve and the feed water isolation valve are closed to limit the release of mass and energy; the primary circuit is cooled by opening the steam release isolation valve corresponding to the intact steam generator; at the same time, the emergency feed water pump of the active secondary side emergency feed water subsystem is started to inject water from the emergency feed water tank into the intact steam generator; during the cooling process, the active emergency boration subsystem is started, and the concentrated boron solution in the emergency boric acid tank is injected into the primary circuit through the emergency boration pump; when the temperature of the primary circuit drops to the accessible temperature of the active residual heat removal subsystem, the residual heat removal pump is started, and the long-term core cooling function is performed through the residual heat removal heat exchanger.

16. The control method of the active and passive combined reactor safety system according to claim 14, characterized in that: The control method further includes: In the event of a power outage in the entire plant: the passive steam atmosphere discharge subsystem is activated to remove the core heat; when the liquid level of any steam generator is too low, the steam-driven emergency feed water pump of the active secondary side emergency feed water subsystem is triggered to start, and the water in the emergency feed water tank is injected into the steam generator; if the active secondary side emergency feed water subsystem is unavailable, the low liquid level signal of the steam generator triggers the activation of the passive secondary side residual heat removal subsystem, and the steam generator is cooled by the SG steam condenser arranged in the cooling water tank, and the core decay heat is transferred to the cooling water tank by relying on the natural circulation of the secondary circuit and discharged to the final heat sink atmosphere.

17. The control method of the active and passive combined reactor safety system according to claim 14, characterized in that: The control method further includes: For severe accidents: start the cavity water injection subsystem, and use the in-core retention water pool to inject water into the reactor cavity to achieve in-core retention of the melt; when the in-core retention water pool is at low liquid level, start the water injection pump of the cavity water injection subsystem to draw water from the refueling water tank, replenish water to the in-core retention water pool through the water replenishment pipeline, and inject water into the reactor cavity through the in-core retention water pool to continue to keep the reactor cavity submerged; start the passive containment heat extraction subsystem, and extract the heat in the containment to the cooling water tank through the PCCS evaporator arranged in the containment and the PCCS condenser arranged in the cooling water tank outside the containment; control the hydrogen concentration in the containment through the passive hydrogen recombiner of the passive hydrogen control subsystem, and perform real-time monitoring of the hydrogen concentration in the containment through the hydrogen monitoring unit.

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