Emergency core cooling system

Abstract

An emergency core cooling system, comprising a first line (1) and a second line (2), wherein the first line (1) comprises a first safety injection pump (101), a second safety injection pump (102), a first emergency core water-injection line, and a first connecting line (15) for conveying an emergency coolant to a second nozzle (209) of a reactor pressure vessel; and the second line (2) comprises a third safety injection pump (201), a fourth safety injection pump (202), a second emergency core water-injection line, and a second connecting line (25) for conveying the emergency coolant to a first nozzle (109). The system can effectively shorten an emergency core water-injection path after an accident, improve the reliability of an emergency core injection function, and reduce the probability of reactor core damage caused by a loss-of-coolant accident, and the system can also reduce the production cost, and facilitate a balanced design with both system safety and economy.

Description

Emergency core cooling system Technical Field

[0001] The present application relates to the field of nuclear power technology, and more specifically, to an emergency core cooling system. Background Art

[0002] Loss of coolant accident (LOCA) is a typical design basis accident condition that must be considered in nuclear power plant design. After a LOCA occurs, ensuring emergency core cooling is a primary objective of accident management. Failure to promptly provide emergency cooling water to the core will result in an inability to effectively cool the reactor core due to the loss of emergency coolant, ultimately leading to damage to the core fuel cladding and the uncontrolled release of radioactive materials. Therefore, to address this LOCA accident condition, pressurized water reactor nuclear power plants are equipped with emergency core cooling systems that can perform emergency core injection after a LOCA accident.

[0003] The emergency core cooling system is a critical safety system in nuclear power plants. Its configuration must meet independence requirements and the single failure criterion. Independence requires that appropriate measures, such as physical isolation, electrical isolation, functional independence, and independent communication (data transmission), be used to prevent interference between systems or between redundant components of the same system. The single failure criterion requires that, in the event of a LOCA accident, the emergency core cooling system be in its most unfavorable permissible configuration, meaning that a failure of any device in the emergency core cooling system renders it unusable.

[0004] In existing nuclear power plant emergency core cooling system designs, system independence requirements and single failure criteria are generally achieved through redundant configuration and physical isolation. Redundant configuration involves configuring "N+1" emergency core cooling system trains. "N" represents the number of trains that can fail due to LOCA initiating events, single failures, and system online maintenance, and "1" represents the remaining train that is operational. Independence design is a further optimization of redundant design. This involves preventing mutual interference between emergency core cooling system trains through appropriate measures, such as physical isolation, electrical isolation, functional independence, and independent communication (data transmission). For example, as shown in Figure 2, prior art 1 constructs an emergency core cooling system consisting of three systems: high-pressure safety injection (HSI), medium-pressure safety injection (MPSI), and low-pressure safety injection (LPSI). The HSI is equipped with three high-pressure safety injection pumps (HHSI), the MPSI is primarily equipped with three medium-pressure safety injection containers (ACCs), and the LPSI is equipped with two low-pressure safety injection pumps (LHSIs). As another example, as shown in Figure 3, prior art 2 constructs an emergency core cooling system consisting of three independent and redundant trains. Each system consists of a low-pressure safety injection (LHSI), a medium-pressure safety injection (MHSI), and a safety injection box system. For example, as shown in Figure 4, a conventional three-configuration emergency core cooling system includes two independent HHSI pumps, two ACC pumps, and two LHSI pumps, each of which injects water into the core via two DVI pumps. As another example, as shown in Figure 5, a conventional four-configuration emergency core cooling system consists of four strictly physically separated independent pipelines, each corresponding to a loop of the reactor coolant system. Each column is located in a separate safety compartment and includes an injection box, an MHSI pump, and an LHSI pump (which also serves as a waste heat removal pump).

[0005] Among them, Existing Technology 1 does not meet the independence requirements between safety systems. Three HHSI pumps and two LHSIs are connected in parallel to the RCP system using a mother pipe connection. This mother pipe connection causes interconnectedness between the ECCS trains. During a LOCA accident, some of the emergency coolant effectively injected into the train escapes through the breach, affecting the effective flow rate for emergency core injection. Existing Technology 2 and Existing Technology 4 both have excessive redundancy, increasing the number of trains in the system configuration itself. This also requires a corresponding number of trains for supporting systems (such as emergency diesel engines, cold chain systems, and HVAC systems). This increases the size of the safety plant, leaving room for economic optimization. Existing Technology 3 fails to meet the single failure criterion. This system configuration only has one HHSI and LHSI per train. Considering a DVI pipeline rupture between the check valve and the RPV, according to the single failure criterion, if another HHSI and LHSI train fails, the emergency core injection function will be lost, making it unable to respond to a DVI pipeline rupture. Summary of the Invention

[0006] The technical problem to be solved by the present application is to provide an improved emergency core cooling system in view of the above-mentioned defects of the prior art.

[0007] The technical solution adopted by the embodiment of the present application to solve the technical problem is to construct an emergency core cooling system, including:

[0008] a first pipeline, comprising a first safety injection pump, a second safety injection pump, a first emergency core water injection pipeline, and a first connecting pipeline for conveying emergency coolant to a second interface of the reactor pressure vessel, wherein an input end of the first emergency core water injection pipeline is connected to a replacement material water tank in the containment vessel, and an output end is connected to the first interface of the reactor pressure vessel; the first safety injection pump is disposed on the first emergency core water injection pipeline; an input end of the first connecting pipeline is connected to the replacement material water tank in the containment vessel, and an output end is connected to the second interface; and the second safety injection pump is disposed on the first connecting pipeline;

[0009] The second pipeline includes a third injection pump, a fourth injection pump, a second emergency core water injection pipeline and a second connecting pipeline for conveying emergency coolant to the first interface, the input end of the second emergency core water injection pipeline is connected to the replacement material water tank in the containment vessel, and the output end is connected to the second interface, the third injection pump is arranged on the second emergency core water injection pipeline, the input end of the second connecting pipeline is connected to the replacement material water tank in the containment vessel, and the output end is connected to the first interface, and the fourth injection pump is arranged on the second connecting pipeline.

[0010] In some embodiments, the first pipeline further includes a first injection tank, which is disposed downstream of the first injection pump, and the second pipeline further includes a second injection tank, which is disposed downstream of the third injection pump.

[0011] In some embodiments, the first pipeline further includes a first injection heat exchanger, and the second pipeline further includes a second injection heat exchanger, the first injection heat exchanger is disposed downstream of the first injection pump, and the second injection heat exchanger is disposed downstream of the third injection pump;

[0012] The output end of the first connecting pipe is connected to the pipe between the second injection heat exchanger and the third injection pump, and the output end of the second connecting pipe is connected to the pipe between the first injection heat exchanger and the first injection pump.

[0013] In some embodiments, the first emergency core water injection pipeline includes a first cold segment located outside the containment boundary and a first output segment located inside the containment boundary, the two ends of the first cold segment being respectively connected to the replacement water tank in the containment and the input end of the first output segment, the output end of the first output segment being connected to the first interface, the first injection pump being disposed on the first cold segment, and the first injection tank being connected to the first output segment;

[0014] The second pipeline includes a second cold section located outside the containment boundary and a second output section located inside the containment boundary. The two ends of the second cold section are respectively connected to the replacement material water tank in the containment and the input end of the second output section. The output end of the second output section is connected to the second interface. The third injection pump is arranged on the second cold section, and the second injection tank is connected to the second output section.

[0015] In some embodiments, the first pipeline further comprises a first hot segment pipeline, the input end of the first hot segment pipeline is connected to the output end of the first cold segment pipeline, and the output end of the first hot segment pipeline is connected to one of the reactor loop hot segments;

[0016] The second pipeline further includes a second hot segment pipeline, the input end of the second hot segment pipeline is connected to the output end of the second cold segment pipe section, and the output end of the second hot segment pipeline is connected to another reactor loop hot segment.

[0017] In some embodiments, the first pipeline also includes a third connecting pipe whose two ends are respectively connected to the first injection tank and the first output pipe section, and a check valve and an electric control valve are provided on the third connecting pipe; the second pipeline also includes a fourth connecting pipe whose two ends are respectively connected to the second injection tank and the second output pipe section, and a check valve and an electric control valve are provided on the fourth connecting pipe.

[0018] In some embodiments, the first pipeline further includes a first water intake pipe section located within the containment boundary, and both ends of the first water intake pipe section are respectively connected to the replacement water tank in the containment and the input end of the first cold section pipe section;

[0019] The second pipeline also includes a second water intake pipe section located within the containment boundary, and both ends of the second water intake pipe section are respectively connected to the replacement material water tank in the containment and the input end of the second cold section pipe section.

[0020] In some embodiments, the input end of the first connecting pipe is connected to the output end of the first water intake pipe section, and is connected to the replacement water tank in the containment shell through the first water intake pipe section;

[0021] The input end of the second connecting pipe is connected to the output end of the second water intake pipe section, and is connected to the replacement material water tank in the containment shell through the second water intake pipe section.

[0022] In some embodiments, a pit filter is provided between the first water intake pipe section and the second water intake pipe section and the replacement material water tank in the containment.

[0023] In some embodiments, both ends of the first cold section pipe segment and the second cold section pipe segment are provided with electric control valves, and both the first output pipe segment and the second output pipe segment are provided with three check valves.

[0024] In some embodiments, the first hot section pipeline and the second hot section pipeline are partially located outside the containment boundary and partially located inside the containment boundary, and are respectively provided with an electric control valve and three check valves. The electric control valves on the first hot section pipeline and the second hot section pipeline are all arranged outside the containment boundary, and the three check valves on the first hot section pipeline and the second hot section pipeline are all arranged inside the containment boundary.

[0025] In some embodiments, the output ends of the first injection pump, the second injection pump, the third injection pump, and the fourth injection pump are all provided with check valves.

[0026] In some embodiments, the first injection pump, the second injection pump, the third injection pump, and the fourth injection pump are all medium-pressure injection pumps.

[0027] The implementation of the embodiments of the present invention has at least the following beneficial effects:

[0028] The present invention provides two pipelines, and two injection pumps are connected in parallel on each pipeline. At the same time, one of the two injection pumps is configured to be connected to the other pipeline, so that the four injection pumps can independently pump emergency coolant to the reactor pressure vessel through the DVI pipeline. For a large breach accident, at least two injection pumps can simultaneously inject coolant into the core. For a small breach accident in which the breach diameter is smaller than the inner diameter of the DVI pipeline, at least one injection pump can inject coolant into the core. This meets the requirements for the amount of coolant required for the reactor under different accident conditions, and there is no need to switch the injection pumps according to different situations during the injection process. This effectively shortens the emergency core water injection process after the accident, reduces the operation steps, avoids the possibility of operation errors, and improves the reliability of the emergency core injection function.

[0029] At the same time, in response to various reactor coolant system pipeline rupture accidents, and considering the most unfavorable single failure situation, there are corresponding injection pumps to pump emergency coolant into the reactor, reducing the probability of damage to the core caused by the rupture accident. At the same time, the system structure is simple, and the HVAC, electrical, and instrumentation and control systems corresponding to the two independent safety injection columns are also relatively few, which reasonably reduces redundancy, reduces the number of injection pumps and supporting systems, and the scale of the plant that accommodates these systems and equipment, greatly reducing the system construction cost, which is conducive to the balanced design of system safety and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0031] FIG1 is a schematic structural diagram of an emergency core cooling system according to an embodiment of the present invention;

[0032] FIG2 is a schematic structural diagram of an emergency core cooling system of a prior art;

[0033] FIG3 is a schematic structural diagram of an emergency core cooling system of the prior art II;

[0034] FIG4 is a schematic structural diagram of an emergency core cooling system of the prior art three;

[0035] FIG5 is a schematic structural diagram of an emergency core cooling system of prior art four. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, purposes and effects of the present application, the specific embodiments of the present application are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings and are constructed and operated in specific directions. They are only for the convenience of describing the technical solution and do not indicate that the devices or components referred to must have specific directions. Therefore, they should not be understood as limitations on the present application.

[0037] It should also be noted that, unless otherwise clearly specified and limited, terms such as "installed", "connected", "connected", "fixed", and "set" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intervening elements. The terms "first", "second", and "third" are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second", and "third" can explicitly or implicitly include one or more of the features. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0038] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0039] Figure 1 shows an emergency core cooling system constructed according to the present invention. This system is used to promptly inject emergency coolant (in this embodiment, cooling water) into the reactor in the event of a loss-of-coolant accident (LOCA) caused by a reactor breach, thereby preventing damage to the core fuel cladding and the uncontrolled release of radioactive materials. The emergency core cooling system includes a first pipeline 1 and a second pipeline 2.

[0040] The first pipeline 1 includes a first safety injection pump 101, a second safety injection pump 102, a first emergency core water injection pipeline, and a first connecting pipeline 15. The second pipeline 2 includes a third safety injection pump 201, a fourth safety injection pump 202, a second emergency core water injection pipeline, and a second connecting pipeline 25. The input ends of the first and second emergency core water injection pipelines are both connected to the containment refueling water tank 001. Water in the containment refueling water tank 001 serves as emergency coolant, which is injected into the core in the event of a loss of emergency coolant accident. The output ends of the first and second emergency core water injection pipelines are each connected to the reactor pressure vessel to inject emergency coolant into the reactor pressure vessel. The configuration of the first and second emergency core water injection pipelines allows them to independently perform water injection operations, meeting independence requirements. Specifically, the output end of the first emergency core water injection pipe is connected to the first interface 109 of the reactor pressure vessel, and the output end of the second emergency core water injection pipe is connected to the second interface 209 of the reactor pressure vessel.

[0041] The first injection pump 101 is installed on the first emergency core water injection pipeline and is used to pump cooling water from the replacement water tank 001 in the containment vessel through the first emergency core water injection pipeline to the first port 109. The input end of the first connecting pipeline 15 is connected to the replacement water tank 001 in the containment vessel, and the output end is connected to the second port 209. The second injection pump 102 is installed on the first connecting pipeline 15 and is used to pump emergency coolant to the second port 209 using the power of the first pipeline 1. This prevents the emergency core cooling system from being unable to inject emergency coolant into the reactor if, for example, the second pipeline 2 loses power and the first emergency core water injection pipeline ruptures.

[0042] The third injection pump 201 is installed on the second emergency core water injection pipeline and is used to pump cooling water from the replacement water tank 001 in the containment vessel through the second emergency core water injection pipeline to the second port 209. The input end of the second connecting pipeline 25 is connected to the replacement water tank 001 in the containment vessel, and the output end is connected to the first port 109. The fourth injection pump 202 is installed on the second connecting pipeline 25 and is used to pump emergency coolant to the first port 109 using the power of the second pipeline 2. This prevents the emergency core cooling system from being unable to inject emergency coolant into the reactor if, for example, the first pipeline 1 loses power and the second emergency core water injection pipeline ruptures.

[0043] The present invention arranges two safety injection pumps in parallel on each pipeline. As a result, when a major rupture accident occurs on the main pipeline of the reactor coolant system, even if, according to the single failure criterion, under the most unfavorable operating conditions, one of the pipelines fails (for example, the second pipeline 2 loses its power source, and the third safety injection pump 201 and the fourth safety injection pump 202 cannot operate), at this time, two safety injection pumps (the first safety injection pump 101 and the second safety injection pump 102) on one pipeline (the first pipeline 1) can still inject water into the core at the same time, ensuring that the water injection flow rate meets the water demand for the major rupture accident of the main pipeline.

[0044] In the event of a small breach (e.g., a breach in second pipeline 2) with a diameter smaller than the DVI pipeline's inner diameter, the pressure drop is relatively slow, and the amount of water required is relatively small. In this case, only one injection pump needs to be operational to compensate for the primary coolant loss during the accident. Therefore, even under the single failure criterion, if one of the injection pumps (e.g., second injection pump 102) on the unbroken pipeline (first pipeline 1) fails and becomes inoperable under the worst-case operating conditions, the remaining injection pump (first injection pump 101) can still independently perform water injection operations.

[0045] That is, the present application uses two pipelines, with two parallel injection pumps set on each pipeline. No matter what kind of accident conditions occur, only one startup is required to meet the needs of handling all accident conditions. There is no need to switch different injection pumps for different accident conditions. The accident handling response can be completed by starting the injection pump once, avoiding the risk of injection flow interruption caused by the switching process of the injection pump, reducing the operating steps, and avoiding the possibility of operational errors.

[0046] At the same time, the emergency core injection system constructed in this application does not require the installation of different types of injection pumps (such as high-pressure, medium-pressure, and low-pressure injection pumps). Only one type of injection pump is required to handle all accident conditions, reducing the number of injection pumps and the installation of other supporting systems (such as HVAC, electrical, instrumentation, plant, power source equipment, etc.). The system configuration is simpler, the cost is lower, and the economy is higher. In this embodiment, all equipment on the first pipeline 1 is powered by a common emergency diesel engine. All equipment on the second pipeline 2 is also powered by a common emergency diesel engine to ensure the independence of the two pipelines. It should be understood that "loss of power source" in this embodiment means that the emergency diesel engine shared by the pipeline is unable to supply power to the pipeline.

[0047] It should be understood that the first pipeline 1 and the second pipeline 2 can be directly connected to the descending section of the reactor pressure vessel through the first interface 109 and the second interface 209 respectively, so that the emergency coolant is pumped to the descending section of the reactor pressure vessel, thereby achieving the effect of rapid emergency injection.

[0048] In some embodiments, the first, second, third, and fourth injection pumps 101, 102, 201, and 202 are all medium-pressure injection pumps. The choice of these medium-pressure injection pumps, combined with the configuration of two pipelines, each with two injection pumps, enables the emergency core cooling system to cope with a variety of accidents, including large and small breaches. For example, in a large breach, all four injection pumps can be activated simultaneously to increase overall flow. In a small breach, where high flow is not required, only one or two injection pumps can be used.

[0049] It's important to understand that existing injection pumps are categorized as high-pressure, medium-pressure, and low-pressure. The higher the applicable pressure of an injection pump, the lower its pumping flow rate. In a large breach accident, the primary circuit's back pressure drops rapidly due to the large breach, meeting the startup requirements of the medium-pressure injection pump. In this case, simply connecting multiple injection pumps in parallel can meet the flow requirements. In a small breach accident, due to the smaller breach, the back pressure drops more slowly, and the initial startup requirements of the medium-pressure injection pump (i.e., within its head range) may not be met. In this case, the injection pump can be paired with a medium-pressure rapid cooling valve on the secondary side of the steam generator. This valve can be used to rapidly depressurize the reactor, rapidly reducing the primary circuit back pressure to meet the startup requirements of the medium-pressure injection pump.

[0050] In some embodiments, the first pipeline 1 also includes a first injection tank 104, and the second pipeline 2 also includes a second injection tank 204, both of which are used to passively inject emergency coolant into the reactor as a passive supplementary injection function. No matter what kind of rupture accident occurs, as long as the pressure of one circuit drops below the target pressure, water can be injected into it.

[0051] Specifically, the first safety injection tank 104 is disposed on the first emergency core water injection pipeline and downstream of the first safety injection pump 101. The second safety injection tank 204 is disposed on the second emergency core water injection pipeline and downstream of the third safety injection pump 201 to facilitate faster injection of emergency coolant into the reactor.

[0052] It should be understood that the first injection tank 104 and the second injection tank 204 both contain boron water, and rely on compressed nitrogen gas coverage to provide rapid injection, which can be achieved using existing technology.

[0053] In some embodiments, the first pipeline 1 also includes a first injection heat exchanger 103, and the second pipeline 2 also includes a second injection heat exchanger 203. Both are used to exchange heat with the water pumped by each injection pump, reduce the temperature of the cooling water, improve the cooling effect, and thereby shorten the path for the core heat to be discharged outside the containment.

[0054] Specifically, the first injection heat exchanger 103 is disposed downstream of the first injection pump 101 , and the second injection heat exchanger 203 is disposed downstream of the third injection pump 201 .

[0055] In this embodiment, the output end of the first connecting pipe 15 is connected to the pipe between the second injection heat exchanger 203 and the third injection pump 201, so that the cooling water pumped by the second injection pump 102 can be heat exchanged and cooled in the second injection heat exchanger 203. The output end of the second connecting pipe 25 is connected to the pipe between the first injection heat exchanger 103 and the first injection pump 101, so that the cooling water pumped by the fourth injection pump 202 can be heat exchanged and cooled in the first injection heat exchanger 103.

[0056] In some embodiments, the first emergency core water injection pipeline includes a first cold segment 11 and a first output segment 13. The first cold segment 11 is located outside the containment boundary, with its input end connected to the refueling water tank 001 within the containment, and its output end connected to the input end of the first output segment 13. The first output segment 13 is located within the containment boundary, with its output end connected to the first interface 109. The first injection pump 101 and the first injection heat exchanger 103 are both disposed on the first cold segment 11, and the first injection tank 104 is connected to the first output segment 13.

[0057] The second emergency core water injection pipeline includes a second cold segment 21 and a second output segment 23. The second cold segment 21 is located outside the containment boundary, with its input end connected to the refueling water tank 001 within the containment, and its output end connected to the input end of the second output segment 23. The second output segment 23 is located within the containment boundary, with its output end connected to the second port 209. The third injection pump 201 and the second injection heat exchanger 203 are both located on the second cold segment 21, and the second injection tank 204 is connected to the second output segment 23.

[0058] It should be understood that, since the in-containment replacement water tank 001 is disposed within the containment, the first emergency core water injection pipeline further includes a first water intake pipe section 12, whose input end is connected to the in-containment replacement water tank 001 and whose output end is connected to the input end of the first cold segment pipe section 11. The second emergency core water injection pipeline further includes a second water intake pipe section 22, whose input end is connected to the in-containment replacement water tank 001 and whose output end is connected to the input end of the second cold segment pipe section 21.

[0059] In some other optional embodiments, the first emergency core water injection pipeline and the second emergency core water injection pipeline can also share a water intake pipe section, and the output end of the water intake pipe section can be connected to the input end of the first cold section pipe section 11 and the second cold section pipe section 21 respectively, so as to reduce the number of penetrations on the containment.

[0060] In some embodiments, a pit filter is further provided between the first water intake pipe section 12 and the second water intake pipe section 22 and the replacement material water tank 001 in the containment to filter out impurities in the cooling water.

[0061] In some embodiments, the input and output ends of the first cold segment pipe section 11 are respectively provided with electrically controlled valves, namely, a first electrically controlled valve 108 and a second electrically controlled valve 110. The input and output ends of the second cold segment pipe section 21 are also respectively provided with electrically controlled valves, namely, a third electrically controlled valve 208 and a fourth electrically controlled valve 210.

[0062] In some embodiments, the first output pipe section 13 is provided with three check valves, namely a first check valve 105, a second check valve 106, and a third check valve 107. The second output pipe section 23 is also provided with three check valves, namely a fourth check valve 205, a fifth check valve 206, and a sixth check valve 207.

[0063] It should be understood that since the equipment structures connected to the first and second output pipe sections 13 and 23 serve as the pressure boundary of the reactor, at least two check valves are required in the portions of the first and second output pipe sections 13 and 23 closest to the first and second interfaces 109 and 209, respectively. The containment vessel serves as another pressure boundary of the reactor, so a check valve and an electrically controlled valve are also required inside and outside the containment vessel. Therefore, three check valves are installed in each of the first and second output pipe sections 13 and 23, and an electrically controlled valve is installed at the output ends of the first and second cold-leg pipe sections 11 and 21, respectively.

[0064] In some embodiments, the input end of the first connecting pipe 15 is connected to the output end of the first water intake pipe section 12, and the first connecting pipe 15 is connected to the refueling water tank 001 in the containment vessel via the first water intake pipe section 12. The input end of the second connecting pipe 25 is connected to the output end of the second water intake pipe section 22, and the second connecting pipe 25 is connected to the refueling water tank 001 in the containment vessel via the second water intake pipe section 22. By sharing the first and second water intake pipe sections 12 and 22 to draw water from the refueling water tank 001 in the containment vessel, the number of through-holes provided in the containment vessel boundary can be reduced, reducing the risk of containment leakage or bypass, while also reducing the number and total length of pipes, thereby improving the economic efficiency of the emergency core cooling system.

[0065] In this embodiment, the output end of the first connecting pipe 15 is connected to the first cold segment 11 between the first electrically controlled valve 108 and the first injection pump 101, and further connected to the output end of the first water intake segment 12. The output end of the second connecting pipe 25 is connected to the second cold segment 21 between the third electrically controlled valve 208 and the third injection pump 201, and further connected to the output end of the second water intake segment 22. This can reduce the number of electrically controlled valves installed at the containment boundary, further improving the economic performance of the emergency core cooling system.

[0066] In some other optional embodiments, the output end of the first water intake pipe section 12 (the output end of the second water intake pipe section 22) can also be connected to the input end of the first cold section pipe section 11 (the second cold section pipe section 21) and the input end of the first connecting pipe 15 (the second connecting pipe 25) through a three-way valve or other connecting valve to achieve communication between the three pipes, and an electric-controlled valve is respectively provided at the input end of the first cold section pipe section 11 (the second cold section pipe section 21) and the input end of the first connecting pipe 15 (the second connecting pipe 25).

[0067] In some other optional embodiments, the output end of the first water intake pipe section 12 (the output end of the second water intake pipe section 22) can also be connected to the input end of the first connecting pipe 15 (the second connecting pipe 25), and the input end of the first cold section pipe section 11 (the second cold section pipe section 21) is connected to the first connecting pipe 15 (the second connecting pipe 25) upstream of the second injection pump 102 (the fourth injection pump 202), and is connected to the output end of the first water intake pipe section 12 (the output end of the second water intake pipe section 22) through part of the first connecting pipe 15 (the second connecting pipe 25).

[0068] In some other optional embodiments, four water intake pipe sections can also be set up, and their input ends are respectively connected to the replacement material water tank 001 in the containment shell, and their output ends are respectively connected to the input end of the first connecting pipe 15, the input end of the second connecting pipe 25, the input end of the first cold section pipe section 11 and the input end of the second cold section pipe section 21.

[0069] In some embodiments, the first pipeline 1 further includes a first hot section pipeline 14, the input end of the first hot section pipeline 14 being connected to the first cold section pipeline segment 11, and the output end being connected to one of the reactor loop hot sections. The second pipeline 2 further includes a second hot section pipeline 24, the input end of the second hot section pipeline 24 being connected to the second cold section pipeline segment 21, and the output end being connected to another reactor loop hot section. The first hot section pipeline 14 and the second hot section pipeline 24 are used to inject emergency coolant into the hot section when a breach occurs in the reactor loop hot section. The provision of two independent geothermal section pipelines not only satisfies the principle of independence, but also meets the single failure criterion, ensuring that if one fails, the other can still be put into use.

[0070] It should be understood that there are three hot sections in the reactor loop, and they are interconnected, so the output ends of the first hot section pipe 14 and the second hot section pipe 24 can be connected to any two different reactor loop hot sections.

[0071] In some embodiments, the first hot section pipeline 14 and the second hot section pipeline 24 are respectively located partially outside the containment boundary and partially inside the containment boundary. The portion of the pipeline located outside the containment boundary is also equipped with an electrically controlled valve, while the portion of the pipeline located inside the containment boundary is also equipped with three check valves to protect the two pressure boundaries. This is not further described here.

[0072] In this embodiment, the input end of the first hot section pipe 14 is connected to the pipe between the first injection heat exchanger 103 and the second electric control valve 110, and the input end of the second hot section pipe 24 is connected to the pipe between the second injection heat exchanger 203 and the fourth electric control valve 210.

[0073] It should be understood that the output ends of the first hot section pipeline 14 and the second hot section pipeline 24 can share a nozzle with the residual heat removal system and connect to the reactor loop hot section. This reduces the number of openings on the reactor's main equipment and reduces the probability of rupture accidents in the reactor coolant system's main pipeline.

[0074] In some embodiments, the first pipeline 1 further includes a third connecting pipe 16, whose ends are respectively connected to the first injection tank 104 and the first output pipe section 13, for outputting the emergency coolant in the first injection tank 104 to the reactor pressure vessel through the first output pipe section 13. The second pipeline 2 further includes a fourth connecting pipe 26, whose ends are respectively connected to the second injection tank 204 and the second output pipe section 23, for outputting the emergency coolant in the second injection tank 204 to the reactor pressure vessel through the second output pipe section 23.

[0075] Specifically, the third connecting pipe 16 is further provided with a fifth electrically controlled valve 113 and a seventh check valve 114, wherein the fifth electrically controlled valve 113 is located upstream of the seventh check valve 114. The fourth connecting pipe 26 is further provided with a sixth electrically controlled valve 213 and an eighth check valve 214, wherein the sixth electrically controlled valve 213 is located upstream of the eighth check valve 214.

[0076] In some embodiments, the output end of the first injection pump 101 is provided with a ninth check valve 111, the output end of the second injection pump 102 is provided with a tenth check valve 112, the output end of the third injection pump 201 is provided with an eleventh check valve 211, and the output end of the fourth injection pump 202 is provided with a twelfth check valve 212 to prevent backflow of the emergency coolant.

[0077] In this embodiment, the output end of the first connecting pipe 15 is connected to the pipe between the eleventh check valve 211 and the second injection heat exchanger 203, and the output end of the second connecting pipe 25 is connected to the pipe between the ninth check valve 111 and the first injection heat exchanger 103.

[0078] The following further explains the emergency core cooling system by looking at its different responses under different states of the nuclear power unit:

[0079] During normal operation of the unit, to ensure timely response in the event of an accident, the emergency core cooling system is always in standby mode. At this time, the valves (except the check valve) on the two main pipelines, the third connecting pipeline 16, and the fourth connecting pipeline 26 are all open, the valves on the first hot section pipeline 14 and the second hot section pipeline 24 are all closed, and the first injection pump 101, the second injection pump 102, the third injection pump 201, and the fourth injection pump 202 are all in shutdown standby mode.

[0080] In the event of a large LB-LOCA or medium LOCA with a large rupture, the primary circuit depressurizes quickly due to the large rupture, and the back pressure quickly drops below the applicable pressure of each medium-pressure injection pump. The emergency core injection signal triggers the start of the four injection pumps (simultaneously, when the primary circuit pressure drops below the nitrogen pressure of the two injection tanks, the two passive injection tanks also inject emergency coolant into the core), injecting cooling water into the core, achieving core reflooding and restoring the core water charge.

[0081] At this time, considering the most unfavorable single failure, if one of the pipelines (such as the first pipeline 1) is unusable, the emergency core cooling system can still inject emergency coolant into the core through the two injection pumps in the other intact pipeline (the second pipeline 2).

[0082] In the event of a direct-injection-outlet-of-pressure-vessel-break accident (DVI-LOCA), i.e., a rupture in either the first or second output pipe section 13 , 23 , one of the pipelines (e.g., first pipeline 1) becomes unusable. The emergency core cooling system can only inject emergency coolant into the core through the two safety injection pumps in the other pipeline (second pipeline 2). When the backpressure drops below the rated pressure of the two medium-pressure safety injection pumps, an emergency core injection signal triggers the two safety injection pumps to start (during this process, when the primary circuit pressure drops below the nitrogen pressure in the second safety injection tank 204, the pumps also begin injecting emergency coolant into the core). Cooling water is then injected into the core, reflooding the core and restoring the core water level.

[0083] Considering the worst-case scenario of a single failure, such as a power failure in line 2 (e.g., emergency diesel engine failure), the two injection pumps in line 2 would be unable to start. In this case, the emergency diesel engine in line 1 could supply power to the second injection pump 102 in line 1, which would then connect to the second emergency core water injection pipe via the first connecting pipe 15, thereby injecting cooling water into the core.

[0084] It should be understood that during this process, if such a breach accident occurs and such a single failure occurs, resulting in only one injection pump being available, but the reactor back pressure is high and the starting pressure of the injection pump cannot be reached, the medium-pressure rapid cooling valve on the secondary side of the steam generator can be used to quickly reduce the primary circuit pressure.

[0085] A pipeline rupture in the residual heat removal system occurs during the residual heat removal mode. At this point, one of the two residual heat removal systems with the rupture is isolated, leaving only the other in operation. Considering the single failure criterion, the operating residual heat removal system fails and shuts down. At this point, water can be injected into the primary circuit through the emergency core cooling system, while the pressurizer (PZR) safety valve is opened. Water is then drained into the containment refueling water tank through the pressure relief tank and the return water line connected to the pressure relief tank, thereby achieving the primary circuit's charge-discharge function. The heat from the core will be discharged into the containment refueling water tank. The heat in the containment refueling water tank will eventually be removed through heat exchange cooling by the first and second injection heat exchangers 103 and 203, replacing the residual heat removal system for heat removal, thereby shortening the path for the core heat to be discharged outside the containment.

[0086] It can be understood that the above embodiments only express some implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, all of which fall within the scope of protection of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should fall within the scope of coverage of the claims of the present invention.

Claims

1. An emergency core cooling system, characterized in that: include: A first pipeline (1) includes a first injection pump (101), a second injection pump (102), a first emergency core water injection pipeline, and a first connecting pipeline (15) for conveying emergency coolant to a second interface (209) of the reactor pressure vessel, wherein an input end of the first emergency core water injection pipeline is connected to a replacement water tank (001) in the containment vessel, and an output end is connected to the first interface (109) of the reactor pressure vessel, the first injection pump (101) is arranged on the first emergency core water injection pipeline, the input end of the first connecting pipeline (15) is connected to the replacement water tank (001) in the containment vessel, and the output end is connected to the second interface (209), and the second injection pump (102) is arranged on the first connecting pipeline (15); The second pipeline (2) comprises a third injection pump (201), a fourth injection pump (202), a second emergency core water injection pipeline, and a second connecting pipeline (25) for conveying emergency coolant to the first interface (109), wherein the input end of the second emergency core water injection pipeline is connected to the replacement water tank (001) in the containment, and the output end is connected to the second interface (209), the third injection pump (201) is arranged on the second emergency core water injection pipeline, the input end of the second connecting pipeline (25) is connected to the replacement water tank (001) in the containment, and the output end is connected to the first interface (109), and the fourth injection pump (202) is arranged on the second connecting pipeline (25).

2. The emergency core cooling system according to claim 1, characterized in that: The first pipeline (1) further comprises a first injection tank (104), which is arranged downstream of the first injection pump (101); the second pipeline (2) further comprises a second injection tank (204), which is arranged downstream of the third injection pump (201).

3. The emergency core cooling system according to claim 1, characterized in that: The first pipeline (1) further includes a first injection heat exchanger (103), and the second pipeline (2) further includes a second injection heat exchanger (203), the first injection heat exchanger (103) being arranged downstream of the first injection pump (101), and the second injection heat exchanger (203) being arranged downstream of the third injection pump (201); The output end of the first connecting pipe (15) is connected to the pipe between the second injection heat exchanger (203) and the third injection pump (201), and the output end of the second connecting pipe (25) is connected to the pipe between the first injection heat exchanger (103) and the first injection pump (101).

4. The emergency core cooling system according to claim 2, characterized in that: The first emergency core water injection pipeline comprises a first cold section pipe section (11) located outside the containment boundary and a first output pipe section (13) located inside the containment boundary, the two ends of the first cold section pipe section (11) are respectively connected to the replacement water tank (001) in the containment and the input end of the first output pipe section (13), the output end of the first output pipe section (13) is connected to the first interface (109), the first injection pump (101) is arranged on the first cold section pipe section (11), and the first injection tank (104) is connected to the first output pipe section (13); The second pipeline (2) comprises a second cold section pipe section (21) located outside the containment boundary and a second output pipe section (23) located inside the containment boundary, the two ends of the second cold section pipe section (21) being respectively connected to the replacement material water tank (001) in the containment and the input end of the second output pipe section (23), the output end of the second output pipe section (23) being connected to the second interface (209), the third injection pump (201) being arranged on the second cold section pipe section (21), and the second injection tank (204) being connected to the second output pipe section (23).

5. The emergency core cooling system according to claim 4, characterized in that: The first pipeline (1) further comprises a first hot section pipeline (14), the input end of the first hot section pipeline (14) being connected to the output end of the first cold section pipeline (11), and the output end of the first hot section pipeline (14) being connected to one of the reactor loop hot sections; The second pipeline (2) further comprises a second hot section pipeline (24), the input end of the second hot section pipeline (24) being connected to the output end of the second cold section pipeline (21), and the output end of the second hot section pipeline (24) being connected to another reactor loop hot section.

6. The emergency core cooling system according to claim 4, characterized in that: The first pipeline (1) further includes a third connecting pipeline (16) whose two ends are respectively connected to the first injection box (104) and the first output pipe section (13), and a check valve and an electric control valve are provided on the third connecting pipeline (16); the second pipeline (2) further includes a fourth connecting pipeline (26) whose two ends are respectively connected to the second injection box (204) and the second output pipe section (23), and a check valve and an electric control valve are provided on the fourth connecting pipeline (26).

7. The emergency core cooling system according to claim 4, characterized in that: The first pipeline (1) further comprises a first water intake pipe section (12) located within the containment boundary, wherein both ends of the first water intake pipe section (12) are respectively connected to the replacement water tank (001) within the containment and the input end of the first cold section pipe section (11); The second pipeline (2) further comprises a second water intake pipe section (22) located within the containment boundary, and both ends of the second water intake pipe section (22) are respectively connected to the replacement water tank (001) in the containment and the input end of the second cold section pipe section (21).

8. The emergency core cooling system according to claim 7, characterized in that: The input end of the first connecting pipe (15) is connected to the output end of the first water intake pipe section (12), and is connected to the replacement water tank (001) in the containment shell through the first water intake pipe section (12); The input end of the second connecting pipe (25) is connected to the output end of the second water intake pipe section (22), and is connected to the replacement water tank (001) in the containment shell through the second water intake pipe section (22).

9. The emergency core cooling system according to claim 7, characterized in that: A pit filter is provided between the first water intake pipe section (12) and the second water intake pipe section (22) and the replacement material water tank (001) in the containment.

10. The emergency core cooling system according to claim 4, characterized in that: Both ends of the first cold section pipe section (11) and the second cold section pipe section (21) are provided with electric control valves, and the first output pipe section (13) and the second output pipe section (23) are provided with three check valves.

11. The emergency core cooling system according to claim 5, characterized in that: The first hot section pipeline (14) and the second hot section pipeline (24) are partially located outside the containment boundary and partially located inside the containment boundary, and are respectively provided with an electric control valve and three check valves. The electric control valves on the first hot section pipeline (14) and the second hot section pipeline (24) are all arranged outside the containment boundary, and the three check valves on the first hot section pipeline (14) and the second hot section pipeline (24) are all arranged inside the containment boundary.

12. The emergency core cooling system according to claim 1, characterized in that: The output ends of the first injection pump (101), the second injection pump (102), the third injection pump (201), and the fourth injection pump (202) are all provided with check valves.

13. The emergency core cooling system according to claim 1, characterized in that: The first injection pump (101), the second injection pump (102), the third injection pump (201), and the fourth injection pump (202) are all medium-pressure injection pumps.

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