Stepwise pressure relief device and steam generator secondary-loop heat sink system

Abstract

A stepwise pressure relief device, comprising a steam intake pipeline, a silencing module and a heat recovery module. The steam intake pipeline comprises a first pipeline and at least two discharge pipelines, wherein the first pipeline is in communication with the silencing module and the heat recovery module, and the at least two discharge pipelines are respectively in communication with both the heat recovery module and the atmosphere. The silencing module is in communication with the heat recovery module and the atmosphere, and the heat recovery module is in communication with the atmosphere and users. A steam generator secondary-loop heat sink system, which has a steam delivery and pressure relief pipeline containing a stepwise pressure relief device. By means of the stepwise pressure relief device and the steam generator secondary-loop heat sink system, the economy, and the economy and safety of a power plant can be improved.

Description

A graded pressure relief device and a steam generator secondary circuit heat sink system

[0001] This application claims priority to the Chinese patent application entitled “A Stepped Pressure Relief Device and a Steam Emitter Secondary Circuit Heat Trap System” filed on June 30, 2022, with application number 202210756488.5. Technical Field

[0002] The present invention belongs to the technical field of nuclear plants, and in particular relates to a staged pressure relief device and a steam generator secondary circuit heat sink system. Background Art

[0003] In previous nuclear engineering designs, steam generator secondary heat sink systems primarily relied on active feedwater and steam delivery and discharge systems to address design basis accidents. This placed high demands on the redundancy and reliability of the active feedwater system's pumps and water sources, as well as on turbine bypass measures to ensure they could function as reliable secondary heat sinks and dissipate heat from the reactor coolant system over the long term. Considering the tiering, capacity, redundancy, and diversity of these configurations posed significant challenges in terms of personnel and equipment costs, construction and layout space, and extensive construction, resulting in poor economic efficiency. Furthermore, steam from the steam generator secondary steam delivery and discharge system, while not only used to propel the turbine during normal operation, was also wasted through valves during other startup and shutdown conditions, resulting in significant heat loss. Furthermore, the steam generator secondary pressure relief and discharge devices were not comprehensively considered, resulting in numerous limitations in valve selection, configuration, setting, and discharge piping design. Using the same discharge setting for all valves resulted in high discharge forces and increased vibration, as well as excessive valve redundancy and discharge capacity, hindering plant economics and safety.

[0004] Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention provides a staged pressure relief device and steam generator secondary circuit heat sink system to address secondary circuit heat sinks in design basis accidents. This system also utilizes a defense-in-depth heat sink design to further enhance the reliability of power plant thermal conductivity. Furthermore, the staged pressure relief device ensures more stable steam discharge with minimal vibration, while also recovering high-temperature steam heat for reuse, improving both the economic efficiency and safety of the power plant.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a staged pressure relief device, comprising a steam inlet pipeline, a silencer module and a heat recovery module, the steam inlet pipeline comprising a first pipeline and at least two discharge pipelines, the first pipeline being respectively connected to the silencer module and the heat recovery module, the at least two discharge pipelines being respectively connected to the heat recovery module and respectively connected to the atmosphere, the silencer module being respectively connected to the heat recovery module and the atmosphere, and the heat recovery module being respectively connected to the atmosphere and various users; wherein a regulating valve group and a first isolation valve are provided between the first pipeline and the silencer module and the heat recovery module, a silencer isolation valve is provided between the silencer module and the heat recovery module; a safety valve and a second isolation valve are provided in sequence between the at least two discharge pipelines and the heat recovery module, the safety valve being provided at the inlet of the at least two discharge pipelines, the second isolation valve being provided between the atmospheric section of the at least two discharge pipelines and the heat recovery module, and a heat isolation valve being provided at the connection between the heat recovery module and the atmosphere and various users.

[0007] Furthermore, the regulating valve group includes a third isolation valve and a silencer regulating valve arranged in sequence to achieve the effect of regulating and isolating exhaust steam.

[0008] Furthermore, the second pipeline and the third pipeline are divided into at least two symmetrical rows, which are respectively discharged to the atmosphere or connected to the heat recovery module. The second isolation valve is arranged at the part where the second pipeline and the third pipeline are connected to the heat recovery module.

[0009] Furthermore, the opening setting of the safety valve is higher than the discharge setting of the regulating valve group; the opening setting of the safety valve of at least one of the at least two discharge pipelines is different from the opening setting of the safety valve of at least another of the at least two discharge pipelines.

[0010] Furthermore, the opening set value of the safety valve of the discharge pipeline farther from the first pipeline among the at least two discharge pipelines is higher than or equal to the opening set value of the safety valve of the discharge pipeline closer to the first pipeline among the at least two discharge pipelines, so that the opening set values ​​of all safety valves tend to gradually increase as a whole.

[0011] Furthermore, the discharge height of the safety valve of at least one of the at least two discharge pipelines is arranged at the same or different elevation as the safety valve of at least another of the at least two discharge pipelines, and the discharge diameter of the safety valve of at least one of the at least two discharge pipelines is the same as or different from the discharge diameter of the safety valve of at least another of the at least two discharge pipelines.

[0012] The discharge diameter of the safety valve of the at least two discharge pipelines that is farther away from the first pipeline is greater than or equal to the discharge diameter of the safety valve of the at least two discharge pipelines that is closer to the first pipeline, so that the discharge diameters of all safety valves tend to gradually increase as a whole. Furthermore, the at least two discharge pipelines include a second pipeline and a third pipeline, the second pipeline includes a first connecting section and a first discharge section that are interconnected, wherein the first connecting section is connected to the heat energy recovery module, and the first discharge section is discharged to the atmosphere; the third pipeline includes a second connecting section and a second discharge section that are interconnected, wherein the second connecting section is connected to the heat energy recovery module, and the second discharge section is discharged to the atmosphere, and the second isolation valve is respectively arranged on the first connecting section and the second connecting section.

[0013] The present invention also provides a steam generator secondary circuit heat sink system, comprising: a steam delivery and pressure relief pipeline, which includes a graded pressure relief device; a heat exchange circuit, which includes a steam generator, a steam pipeline, a condensation pipeline, at least one heat exchanger and at least one heat exchange water tank, and the steam generator is connected to the graded pressure relief device; and a water supply pipeline, the water supply pipeline is connected to the steam generator to supply water to the steam generator; wherein the steam pipeline is respectively connected to the steam generator and the heat exchanger, the condensation pipeline is respectively connected to the heat exchanger and the water supply pipeline, and the heat exchanger is located in the heat exchange water tank; a normally open steam isolation valve is provided on the steam pipeline, and at least two first condensation isolation valves connected in parallel and normally closed are provided on the condensation pipeline.

[0014] Furthermore, at least one wide-range liquid level measuring instrument and at least one narrow-range liquid level measuring instrument are provided on the steam generator to monitor the liquid level in the steam generator.

[0015] Furthermore, at least one differential pressure flow measuring instrument is provided between the steam generator and the staged pressure relief device.

[0016] Furthermore, the water supply pipeline includes a main water supply pipeline and a start-stop water supply pipeline, and the main water supply pipeline and the start-stop water supply pipeline are both connected to the steam generator to supply water to the steam generator; the condensation pipeline is respectively connected to the main water supply pipeline and the start-stop water supply pipeline, and a second condensation isolation valve and a third condensation isolation valve are respectively provided at the connection points.

[0017] Furthermore, the main water supply pipeline is sequentially provided with a water flow measuring device, a water supply regulating valve, a water supply isolation valve and a water supply check valve. The water supply flow measuring device is also provided with at least one water supply sensor. The water supply regulating valve and the water supply isolation valve both receive water supply isolation signals and adopt phased isolation according to the hydraulic transient results caused by actual closure.

[0018] Furthermore, the start-stop water supply pipeline is sequentially provided with a start-stop water supply flow measuring device, a start-stop water supply regulating valve, a start-stop water supply isolation valve and a start-stop water supply check valve. The start-stop water supply flow measuring device is also provided with at least one start-stop water supply sensor. The start-stop water supply regulating valve and the start-stop water supply isolation valve both receive water supply isolation signals and adopt staged isolation according to the hydraulic transient results caused by actual closure.

[0019] The present invention achieves this by comprehensively considering the configuration of the steam generator secondary circuit heat sink system, including its grading, capacity, redundancy, and diversity, thereby reducing personnel and equipment costs, conserving construction and layout space, and improving economic efficiency. Furthermore, the use of a staged pressure relief device not only propels the steam turbine during normal operation but also recovers the heat energy of steam discharged through the valve during other start-up and shutdown conditions. Furthermore, the design of valve selection, configuration, setting, and discharge piping improves the economic efficiency and safety of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic diagram of a module of a staged pressure relief device in the present invention;

[0021] FIG2 is a schematic diagram of a module of a steam generator secondary circuit heat sink system according to the present invention.

[0022] Description of reference numerals:

[0023] 10. Staged pressure relief device; 1. Steam inlet pipeline; 2. Silencer module; 3. Heat recovery module; 11. First pipeline; 12. Second pipeline; 13. Third pipeline; 111. Control valve group; 112. First isolation valve; 21. Silencer isolation valve; 31. Thermal isolation valve; 14. Safety valve; 113. Second isolation valve; 114. Silencer control valve; 115. Third isolation valve; 121. First connecting section; 122. First discharge section; 131. Second connecting section; 132. Second discharge section;

[0024] 4. Steam generator; 40. Water supply line; 50. Heat exchange circuit; 60. Steam delivery and pressure relief line; 51. Steam line; 52. Condensate line; 53. Heat exchanger; 54. Heat exchanger tank; 511. Steam isolation valve; 521. First condensate isolation valve; 401. Wide-range liquid level measuring instrument; 402. Narrow-range liquid level measuring instrument; 403. Differential pressure flow measuring instrument; 41. Main water supply line; 42. Start / stop Water supply pipeline; 522, second condensation isolation valve; 523, third condensation isolation valve; 411, water supply flow measuring device; 412, water supply regulating valve; 413, water supply isolation valve; 414, water supply check valve; 415, water supply sensor; 421, start-stop water supply flow measuring device; 422, start-stop water supply regulating valve; 423, start-stop water supply isolation valve; 424, start-stop water supply check valve; 425, start-stop water supply sensor. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] As shown in Figures 1-2, the present invention provides a graded pressure relief device 10, which is arranged on the steam delivery and pressure relief pipeline of the secondary circuit heat sink of the steam generator, and includes a steam inlet pipeline 1 connected to the exhaust pipe on the steam delivery and pressure relief pipeline, a silencer module 2, and a heat recovery module 3. The steam inlet pipeline 1 includes a first pipeline 11, a second pipeline 12, and an optional third pipeline 13. The first pipeline 11 is connected to the silencer module 2 and the heat recovery module 3 respectively, the second pipeline 12 is connected to the heat recovery module 3 and is connected to the atmosphere, the silencer module 2 is connected to the heat recovery module 3 and the atmosphere respectively, and the heat recovery module 3 is connected to the atmosphere and various users respectively. The steam delivery and pressure relief pipeline is a steam pipeline that can both deliver steam to the steam turbine and discharge steam through the pressure relief device under overpressure.

[0027] A regulating valve assembly 111 and a first isolation valve 112 are respectively installed between the first pipeline 11 and the muffler module 2 and the heat recovery module 3. A muffler isolation valve 21 is installed between the muffler module 2 and the heat recovery module 3. A safety valve 14 and a second isolation valve 113 are sequentially installed between the second pipeline 12 and the heat recovery module 3. The safety valve 14 is installed at the inlet of the second pipeline 12, and the second isolation valve 113 is installed between the section of the second pipeline 12 connecting to the atmosphere and the heat recovery module 3. A heat isolation valve 31 is installed at the section connecting the heat recovery module 3 to the atmosphere and various users. Similar to the second pipeline 12, the third pipeline 13 is connected to the heat recovery module 3 and the atmosphere. A safety valve 14 is installed at the inlet of the third pipeline 13, and a second isolation valve 113 is installed between the section of the third pipeline 13 connecting to the atmosphere and the heat recovery module 3. It will be appreciated that in some embodiments, a fourth pipeline, a fifth pipeline, and so on, similar to the second pipeline 12, may be provided. Specifically, these additional pipelines may also be similarly provided with safety valves 14 and second isolation valves 113. Furthermore, the number of pipelines may be adjusted as needed and is not specifically limited. It will also be appreciated that each pipeline in the steam inlet line 1, such as the first pipeline 11, the second pipeline 12, and so on, is connected to the exhaust pipe on the steam supply and pressure relief line. In some embodiments, the second pipeline 12, the third pipeline 13, the fourth pipeline, and so on are successively further from the first pipeline 11. Herein, the second pipeline 12, the third pipeline 13, the fourth pipeline, and so on, may be collectively referred to as "exhaust lines." Herein, "further from the first pipeline 11" refers to the location on the exhaust pipe connected to the steam supply and pressure relief line that is further from the first pipeline 11.

[0028] It can be understood that after the steam in the steam delivery and pressure relief pipeline enters the steam inlet pipeline 1, it passes through the first pipeline 11 and the regulating valve group 111 into the silencer module 2, and is discharged to the atmosphere for pressure relief through the silencer module 2. When the silencer isolation valve 21 is opened, the steam can also enter the heat recovery module 3, and the waste heat of the steam is recovered by the heat recovery module 3.

[0029] It will be appreciated that in the staged pressure relief device 10, the opening setting of the safety valve 14 is higher than the discharge setting of the regulating valve assembly 111. Furthermore, in the staged pressure relief device 10, at least one of the safety valves 14 may have a different discharge pressure setting than at least another safety valve in the staged pressure relief device 10. For example, the two safety valves 14 on the second pipeline 12 and the third pipeline 13 can be designed for different discharge pressure settings and each equipped with a nuclear-grade seismic power supply. When the steam pressure reaches the discharge pressure setting, the steam enters the second pipeline 12 and / or the third pipeline 13 and is discharged into the atmosphere, thereby achieving a staged pressure relief effect. When the second isolation valve 113 is opened, the steam can also enter the heat recovery module 3, where the waste heat of the steam is recovered. In some embodiments, two or more safety valves 14 among all the safety valves in the second pipeline 12, the third pipeline 13, the fourth pipeline, and optionally, further pipelines can be designed for different discharge pressure settings. In some embodiments, the opening setting values ​​of all safety valves gradually increase as they move away from the first pipeline 11. This means that some safety valves may have the same opening setting value, as long as all safety valves have a gradually increasing opening setting value. It is understood that in some embodiments, two or more safety valves 14 among all safety valves in the second pipeline 12, the third pipeline 13, the fourth pipeline, and optionally further pipelines may be located at different elevations. It is understood that in some embodiments, two or more safety valves 14 among all safety valves in the second pipeline 12, the third pipeline 13, the fourth pipeline, and optionally further pipelines may have different discharge diameters. In some embodiments, the discharge diameters of all safety valves gradually increase as they move away from the first pipeline 11. This means that some safety valves may have the same discharge diameter, as long as all safety valves have a gradually increasing discharge diameter.

[0030] Furthermore, the regulating valve group 111 includes a third isolation valve 115 and a silencer regulating valve 114 which are sequentially arranged to achieve the effects of regulating and isolating exhaust steam.

[0031] It can be understood that the third isolation valve 115 can be an electric isolation valve, a pneumatic isolation valve, a pilot quick-opening valve, etc.

[0032] Furthermore, the second pipeline 12 and the optional third pipeline 13 are each divided into at least two symmetrically arranged columns, which are respectively discharged to the atmosphere or connected to the heat recovery module 3. The second isolation valve 113 is disposed in the portion where the second pipeline 12 and the third pipeline 13 connect to the heat recovery module 3. In this specification, the term "at least two columns" means that the second pipeline 12 and the optional further pipelines are connected by at least two pipes, for example, by at least two pipes connected to the atmosphere or by at least two pipes connected to the heat recovery module 3.

[0033] Furthermore, the second pipeline 12 includes a first connecting section 121 and a first discharge section 122 that are connected to each other, wherein the first connecting section 121 is connected to the heat recovery module 3, and the first discharge section 122 is discharged to the atmosphere.

[0034] The third pipeline 13 includes a second connecting section 131 and a second discharge section 132 that are interconnected, wherein the second connecting section 131 is connected to the heat recovery module 3, and the second discharge section 132 is discharged to the atmosphere. The second isolation valve 113 is respectively provided on the first connecting section 121 and the second connecting section 131.

[0035] The present invention also provides a steam generator secondary circuit heat sink system, comprising a water supply pipeline 40, a heat exchange circuit 50, and a steam delivery and pressure relief pipeline 60. The water supply pipeline 40 is connected to the steam generator 4 of the heat exchange circuit 50 to supply water to the steam generator 4. The steam generator 4 is connected to the staged pressure relief device 10 of the steam delivery and pressure relief pipeline 60. The heat exchange circuit 50 includes a steam pipeline 51, a condensation pipeline 52, at least one heat exchanger 53, and at least one heat exchange water tank 54. The steam pipeline 51 is connected to the steam generator 4 and the heat exchanger 53 respectively. The condensation pipeline 52 is connected to the heat exchanger 53 and the water supply pipeline 40 respectively. The heat exchanger 53 is located in the heat exchange water tank 54.

[0036] The steam pipeline 51 is provided with a normally open steam isolation valve 511 , and the condensation pipeline 52 is provided with at least two first condensation isolation valves 521 that are normally closed and connected in parallel.

[0037] It can be understood that in this embodiment, the steam generated by the steam generator 4 is discharged to the steam turbine after pressure relief and heat recovery by the staged pressure relief device to supply steam to the steam turbine.

[0038] Furthermore, at least one wide-range liquid level measuring instrument 401 and at least one narrow-range liquid level measuring instrument 402 are provided on the steam generator 4 to monitor the liquid level in the steam generator 4 .

[0039] Furthermore, at least one differential pressure flow measuring instrument 403 is provided between the steam generator 4 and the staged pressure relief device.

[0040] It can be understood that the flow signal measured by the differential pressure flow measuring instrument 403 can be sent to the power plant reactor protection system to trigger a safety protection signal.

[0041] Furthermore, the water supply pipeline 40 includes a main water supply pipeline 41 and a start-stop water supply pipeline 42 . Both the main water supply pipeline 41 and the start-stop water supply pipeline 42 are connected to the steam generator 4 to supply water to the steam generator 4 .

[0042] Furthermore, the condensation line 52 is connected to the main water supply pipeline 41 and the start-stop water supply pipeline 42 respectively, and a second condensation isolation valve 522 and a third condensation isolation valve 523 are respectively provided at the connection points.

[0043] Furthermore, a water flow measuring device 411 , a water regulating valve 412 , a water isolation valve 413 and a water check valve 414 are sequentially provided on the main water supply pipeline 41 , and at least one water sensor 415 is also provided on the water flow measuring device 411 .

[0044] Furthermore, the start-stop water supply pipeline 42 is sequentially provided with a start-stop water supply flow measuring device 421, a start-stop water supply regulating valve 422, a start-stop water supply isolation valve 423 and a start-stop water supply check valve 424, and the start-stop water supply flow measuring device 421 is also provided with at least one start-stop water supply sensor 425.

[0045] As can be understood, the feedwater flow measurement device 411 is located in the earthquake-resistant plant and is designed as a nuclear-grade earthquake-resistant device. The flow signal measured by the feedwater sensor 415 can be fed into the power plant's reactor protection system to trigger a safety protection signal. The feedwater regulating valve 412 is a pneumatic valve designed to close in case of air failure, enabling both regulation and rapid isolation. The feedwater isolation valve 413 can be either an electric isolation valve or a gas-liquid coupled fast-closing isolation valve. Both the feedwater regulating valve 412 and the feedwater isolation valve 413 receive the feedwater isolation signal and can implement phased isolation based on the hydraulic transients caused by the actual closure. Both the feedwater isolation valve 413 and the feedwater regulating valve 412 receive the feedwater isolation signal and can implement phased isolation based on the hydraulic transients caused by the actual closure. The feedwater isolation valve 413 is positioned as close as possible to the containment penetration, and the feedwater check valve 414 is positioned as close as possible to the steam generator 4 and upstream of the heat exchange circuit 50.

[0046] It can be understood that the start-stop water supply flow measurement device 421 is located in the earthquake-resistant plant and is designed as a nuclear-grade earthquake-resistant equipment. The flow signal measured by the start-stop water supply sensor 425 can be sent to the power plant reactor protection system to trigger the safety protection signal. The start-stop water supply regulating valve 422 is a pneumatic valve and is designed to be closed when air is lost. It can realize both the regulation function and the rapid isolation function. The start-stop water supply isolation valve 423 can be an electric isolation valve or a gas-liquid linkage fast-closing isolation valve. The start-stop water supply regulating valve 422 and the start-stop water supply isolation valve 423 both receive water supply isolation signals. According to the hydraulic transient results caused by the actual closure, staged isolation can be adopted. The start-stop water supply isolation valve 423 and the start-stop water supply regulating valve 422 both receive water supply isolation signals. According to the hydraulic transient results caused by the actual closure, staged isolation can be adopted. The start-stop feedwater isolation valve 423 is arranged as close to the containment penetration as possible, and the start-stop feedwater check valve 424 is arranged as close to the steam generator 4 as possible and is located upstream of the heat exchange circuit 50.

[0047] In this embodiment, during normal operation of the nuclear power plant, water is supplied to the steam generator 4 via the main feedwater supply pipeline 41. After heat exchange on the secondary side of the steam generator 4, the water enters the steam turbine via the steam delivery and pressure relief pipeline 60, serving as a secondary heat sink during normal operation. During startup and shutdown operations, water is supplied to the steam generator 4 via the startup and shutdown feedwater pipeline. After heat exchange on the secondary side of the steam generator 4, when normal steam is discharged to the condenser and is unavailable, the steam is discharged through the staged pressure relief device 10, serving as a secondary heat sink during startup and shutdown operations. A regulating valve on the water supply pipeline 40 is used to adjust the flow rate of water supplied to the steam generator 4.

[0048] When steam is discharged through the staged pressure relief device 10, the staged pressure relief device 10 is mainly used for power plant start-up and shutdown or some situations in which the power plant is in a hot shutdown or hot standby stage for a long time and the steam is non-radioactive. When the steam passes through the regulating valve group 111, it first enters the silencer module 2 for noise reduction treatment, and then the steam is discharged into the heat recovery module 3. It can also be discharged directly to the heat recovery module 3 without noise reduction according to the needs of the heat exchange user. Multiple high-pressure energy storage modules can be set in the heat recovery module 3. Finally, according to the needs of the user, heat is distributed by switching and adjusting the isolation valves and regulating valves on the pipelines leading to each user, and the steam is delivered to each user. Each user can then cool and reduce the pressure of the received steam according to their needs.

[0049] The opening setting of the safety valve 14 in the graded pressure relief device 10 is higher than the discharge setting of the regulating valve group 111, and the opening setting of the safety valve 14 is different and increases step by step. Under different transient conditions, the safety valve 14 will open step by step according to the changes in the system pressure. The maximum opening pressure setting must ensure that the secondary side does not exceed the pressure limit under different accident conditions. At the same time, the discharge line of the safety valve 14 is discharged symmetrically in two columns, which can balance the reaction force of the valve outlet, reduce the load on the main steam pipeline, minimize the vibration when the valve is opened, and different numbers of valves can be put into operation for different accidents to achieve optimized operation. This makes steam discharge more reliable, more stable, and less vibrating.

[0050] The safety valves 14 in the staged pressure relief device 10 have a relatively large discharge capacity. Besides acting as a heat sink to discharge heat, they are primarily used for overpressure protection. Steam is generally discharged directly to the atmosphere through the safety valves 14. Without affecting the aforementioned functions, the discharge of the safety valves 14 can also be discharged to the heat recovery module 3. Furthermore, the discharge ports of different safety valves 14 can be arranged at different heights, and the discharge diameters can be gradually increased to reduce discharge backpressure. This arrangement can avoid the impact and localized pressure surges caused by concentrated discharge in a single area.

[0051] In the event of a design basis accident at a nuclear power plant, the main feedwater supply is first lost due to a loss of external power, for example, and the main feedwater pipeline 41 is isolated. Water is then supplied to the steam generator 4 via the start-stop feedwater pipeline 42. After heat exchange on the secondary side of the steam generator 4, if normal steam is discharged to the condenser and is unavailable, the steam is discharged through the staged pressure relief device 10, serving as a secondary heat sink for defense-in-depth during the plant's shutdown. This avoids the need for a passive heat exchange system, further improving the plant's safety and reliability. When steam is discharged through the staged pressure relief device 10, based on analysis of the actual accident situation, if the steam is not discharged and can remain in the recovery period for a long time, heat recovery can be considered; otherwise, it is discharged directly.

[0052] In the event of a design basis accident at a nuclear power plant, the main feedwater supply is first lost due to a loss of external power, for example, and the main feedwater line 41 is isolated. Water is then supplied to the steam generator 4 via the start-stop feedwater line 42. If the start-stop feedwater supply is lost, the start-stop feedwater line 42 is isolated. The low-flow feedwater signal on the start-stop feedwater line 42 is sent to the reactor protection system, which is used to trigger the closing and opening of valves required for the passive heat exchange circuit to be put into operation. Closure signals are required to be sent to the regulating valve and isolation valve on the main feedwater line 41, the feedwater regulating valve 412 and feedwater isolation valve 413 on the start-stop feedwater line 42, and the main steam isolation valve. Opening signals are required to be sent to the two normally closed first condensation isolation valves 521 installed in parallel on the condensation line 52 in the heat exchange circuit 50, as well as the normally open third condensation isolation valve 523 on the condensation line 52 leading to the start-stop feedwater line 42. These valves and signals are powered by reliable nuclear-grade batteries. Even if a single fault occurs in one of the normally closed electric valves or the closed pneumatic valve, the remaining valve can still isolate the passive heat exchange circuit's operational boundary. After heat exchange circuit 50 is operational, steam from the secondary circuit enters heat exchanger 53 via steam pipeline 51, where it transfers heat to heat exchanger tank 54. The steam is condensed into water, which then flows through condensate line 52 and is supplied to steam generator 4 via start-stop feedwater line 42. If a fault occurs in the start-stop feedwater line 42, that line can be isolated. Water supply to steam generator 4 can then be resumed by opening the second condensate isolation valve 522 on condensate line 52, which connects to the main feedwater line 41, thus forming a passive, closed natural circulation system. Heat exchange circuit 50 serves as a heat sink for the steam generator's secondary circuit under design basis accidents, ensuring the safe operation of the nuclear power plant in the event of an accident.

[0053] During transient conditions or accidents at the nuclear power plant, the regulating valve group 111 in the staged pressure relief device 10 is set to a low opening value. This not only regulates steam discharge capacity and stabilizes the pressures in the primary and secondary circuits, but also serves to achieve defense-in-depth heat removal, preventing the passive heat exchange circuit from being activated. Furthermore, it also provides defense-in-depth overpressure protection, preventing the safety valve 14 from being activated.

[0054] During a nuclear power plant accident, such as a SGTR, when radioactivity is detected and the steam generator 4 has a high water level, the feedwater isolation valve 413 and the start-stop feedwater isolation valve 423 of the faulty steam generator 4 are closed to isolate the steam generator 4. At this pressure, the safety valve 14 and the discharge valve in the staged pressure relief device 10 can be closed, automatically isolating the damaged steam generator 4 and preventing the release of radioactivity. This ensures the safety of personnel, the power plant, and the environment.

[0055] The system's staged pressure relief device 10 optimizes the number of valves that open during transient and accidental conditions, avoiding vibrations caused by simultaneous valve opening for discharge or pressure relief. It also recovers some of the heat from the high-temperature, high-pressure steam. This recovery of high-temperature steam heat for reuse improves both the economic efficiency and safety of the power plant.

[0056] It can be seen from the above embodiments that the advantages of the present invention are:

[0057] (1) A safer and more reliable passive heat exchange circuit that uses density difference and gravity to form a natural circulation is used as a secondary circuit heat sink to deal with design basis accidents. At the same time, when the main water supply pipeline 41 is lost, the start-stop water supply pipeline 42 and the graded pressure relief device 10 are used to conduct heat as a depth defense heat sink for the steam generator secondary circuit, avoiding the passive heat exchange circuit 50 from being put into operation, further improving the safety and reliability of the power plant. It avoids the cumbersome and complex design brought about by the previous use of active systems to deal with design basis accidents, and avoids the huge challenges in improving the economy brought about by the comprehensive consideration of various aspects such as equipment classification, capacity, redundancy, and diversity in the above design, such as personnel and equipment costs, construction and layout space, and a large amount of construction. This set of secondary circuit heat sink system improves the economy and safety of the power plant as a whole.

[0058] (2) A graded pressure relief device 10 is used, which includes at least one regulating valve group 111 that can adjust and isolate the exhaust pressure relief, and at least one safety valve 14 that can directly discharge. The number of valves should be determined based on the discharge volume of the valve and the optimization of the accident analysis. The above discharge valves are designed according to different opening pressure settings. The maximum opening pressure setting of the graded pressure relief device 10 should ensure that the secondary side does not exceed the pressure limit under different accident conditions. At the same time, the discharge pipeline of the safety valve 14 is set to more than two rows and discharged symmetrically, which can balance the reaction force of the valve outlet, reduce the load on the main steam pipeline, minimize the vibration when the valve is opened, and different numbers of valves can be put into operation for different accidents to achieve optimized operation. This makes steam discharge more reliable, more stable, and less vibrating.

[0059] (3) A graded pressure relief device 10 is used, which includes at least one silencer module and at least one heat recovery module. The silencer module 2 can be set up with multiple silencers according to the needs of the power plant, and modules with different silencer capabilities can be set up. This flexible setting can consider different degrees of silencer processing according to the user's on-site needs, optimize the equipment as much as possible according to the user's needs, and is conducive to improving the economy of the power plant. The heat recovery module 3 includes at least one heat storage module. The discharge pipeline discharged into the module is comprehensively considered to set its discharge height at different elevations and set different discharge pipe diameters. The final size determined by simulation calculation not only meets the discharge requirements and heat recovery requirements, but also avoids the problems of excessive impact force and excessive pressure increase caused by concentrated discharge at the same location. The recovered heat can be adjusted and reduced in flow and pressure by regulating the valve group 111 according to the user's needs. If necessary, the user can be isolated by an isolation valve. A cooling device can also be set within the user range. The above configuration allows the steam coming out of the heat recovery module 3 to meet different user needs, including conventional high-temperature and high-pressure steam sterilization and cleaning of oil-containing pipelines in power plants, as well as thermal deoxidation for secondary circuit deaerators in power plants, which can reduce the unavailability period of the secondary circuit, shorten the use time of electric boilers, save energy, etc.

[0060] (4) A graded pressure relief device 10 is used, wherein the third isolation valve 115 and the muffler regulating valve 114 in the regulating valve group 111 that can regulate and isolate the exhaust steam pressure relief can be combined with a variety of valve types according to the actual situation of the power plant. The safety valve 14 can be spring-type or pilot-operated according to the actual situation of the power plant. The graded discharge of these valves can ensure the integrity of the shell side of the steam generator 4, the connected pipelines, and the equipment that performs the safety-related functions of the containment isolation and the steam generator 4 isolation under various operating conditions of the power plant. The regulating valve group 111 that can regulate and isolate the exhaust steam pressure relief can be used for both heat regulation and heat extraction, and can control the stability of the nuclear power primary and secondary circuits. It can also serve as a depth defense measure for secondary circuit overpressure protection and decay heat extraction, further improving the reliability of the power plant.

[0061] (5) The regulating valve of the water supply pipeline 40 has the functions of regulating and isolating the water supply. Therefore, the regulating valve and the isolation valve are equivalent to setting up two nuclear-grade reliable water supply isolation valves. In the event of an SGTR accident, they prevent the steam generator from overflowing and the main steam pipeline from overflowing. They prevent the release of radioactive substances caused by the valve in the staged pressure relief device 10 discharging the water supply and reactor coolant into the atmosphere. At the same time, they serve as a reliable boundary isolation valve for the operation of the passive heat exchange circuit. The main steam isolation valve on the steam pipeline can adopt a gas-liquid linkage isolation valve with two control circuits to achieve reliable steam isolation, and at the same time serve as a reliable boundary isolation valve for the operation of the passive heat exchange circuit. At the same time, the reliable safety valve in the staged pressure relief device 10 on the steam pipeline can be switched to a closed state and maintained closed when overpressure protection is not required, maintaining a closed isolation state. The valve group in the staged pressure relief device 10 that can regulate and isolate the exhaust steam pressure relief adopts the design of an isolation valve plus a regulating valve, which is equivalent to having two isolation measures and maintaining a sealed isolation valve device. The above-mentioned valve in the staged pressure relief device 10 can be used as a reliable boundary isolation valve for the operation of the passive heat exchange circuit.

[0062] The device described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the scope of the technical innovation of the present invention.

Claims

1. A graded pressure relief device, arranged on a steam delivery and pressure relief pipeline, characterized in that: include: Steam inlet pipeline (1), silencer module (2) and heat recovery module (3), The steam inlet pipeline (1) comprises a first pipeline (11) and at least two exhaust pipelines, the first pipeline (11) is respectively connected to the muffler module (2) and the heat recovery module (3), the at least two exhaust pipelines are respectively connected to the heat recovery module (3) and respectively connected to the atmosphere, the muffler module (2) is respectively connected to the heat recovery module (3) and the atmosphere, and the heat recovery module (3) is respectively connected to the atmosphere and each user; Wherein, a regulating valve group (111) and a first isolation valve (112) are provided between the first pipeline (11) and the muffler module (2) and the heat recovery module (3), and a muffler isolation valve (21) is provided between the muffler module (2) and the heat recovery module (3); a safety valve (14) and a second isolation valve (113) are provided in sequence between the at least two discharge pipelines and the heat recovery module (3), the safety valve (14) being provided at the inlet of the at least two discharge pipelines, the second isolation valve (113) being provided between the atmospheric section of the at least two discharge pipelines and the heat recovery module (3), and heat isolation valves (31) being provided at the connection points of the heat recovery module (3) with the atmosphere and each user.

2. A staged pressure relief device according to claim 1, characterized in that: The at least two discharge pipelines are divided into at least two symmetrically arranged rows, which are respectively discharged to the atmosphere or communicated with the heat recovery module (3).

3. A staged pressure relief device according to claim 1, characterized in that: The opening setting value of the safety valve (14) is higher than the discharge setting value of the regulating valve group (111); An opening setting value of a safety valve of at least one of the at least two discharge lines is different from an opening setting value of a safety valve of at least another of the at least two discharge lines.

4. A staged pressure relief device according to claim 3, characterized in that: The opening set value of the safety valve of the discharge pipeline that is farther away from the first pipeline among the at least two discharge pipelines is higher than or equal to the opening set value of the safety valve of the discharge pipeline that is closer to the first pipeline among the at least two discharge pipelines, so that the opening set values ​​of all safety valves tend to gradually increase as a whole.

5. A staged pressure relief device according to claim 3, characterized in that: The discharge height of the safety valve (14) of at least one of the at least two discharge pipelines is arranged at the same or different elevation as that of the safety valve of at least another of the at least two discharge pipelines, and the discharge diameter of the safety valve (14) of at least one of the at least two discharge pipelines is the same or different from the discharge diameter of the safety valve (14) of at least another of the at least two discharge pipelines.

6. A staged pressure relief device according to claim 5, characterized in that: The discharge diameter of the safety valve of the discharge pipeline farther from the first pipeline among the at least two discharge pipelines is greater than or equal to the discharge diameter of the safety valve of the discharge pipeline closer to the first pipeline among the at least two discharge pipelines, so that the discharge diameters of all safety valves tend to gradually increase as a whole.

7. A steam generator secondary circuit heat sink system, characterized in that: include: A steam delivery and pressure relief pipeline (60) comprising a staged pressure relief device (10); a heat exchange circuit (50) comprising a steam generator (4), a steam pipeline (51), a condensation pipeline (52), at least one heat exchanger (53) and at least one heat exchange water tank (54), wherein the steam generator (4) is in communication with the staged pressure relief device (10); and a water supply pipeline (40), the water supply pipeline (40) being in communication with the steam generator (4) to supply water into the steam generator (4); The steam pipeline (51) is connected to the steam generator (4) and the heat exchanger (53), the condensation pipeline (52) is connected to the heat exchanger (53) and the water supply pipeline (40), and the heat exchanger (53) is located in the water exchange tank (54). The steam pipeline (51) is provided with a normally open steam isolation valve (511), and the condensation pipeline (52) is provided with at least two first condensation isolation valves (521) that are normally closed and connected in parallel.

8. A steam generator secondary circuit heat sink system according to claim 7, characterized in that: The water supply pipeline (40) includes a main water supply pipeline (41) and a start-stop water supply pipeline (42), and the main water supply pipeline (41) and the start-stop water supply pipeline (42) are both connected to the steam generator (4) to supply water to the steam generator (4); The condensation pipeline (52) is connected to the main water supply pipeline (41) and the start-stop water supply pipeline (42) respectively, and a second condensation isolation valve (522) and a third condensation isolation valve (523) are respectively provided at the connection points.

9. A steam generator secondary circuit heat sink system according to claim 8, characterized in that: The main water supply pipeline (41) is provided with a water supply regulating valve (412) and a water supply isolating valve (413). Both the water supply regulating valve (412) and the water supply isolating valve (413) receive a water supply isolation signal and adopt staged isolation according to the hydraulic transient result caused by the actual closure.

10. A steam generator secondary circuit heat sink system according to claim 8, It is characterized by: The start-stop water supply pipeline (42) is provided with a start-stop water supply regulating valve (422) and a start-stop water supply isolation valve (423). Both the start-stop water supply regulating valve (422) and the start-stop water supply isolation valve (423) receive water supply isolation signals and adopt staged isolation according to the hydraulic transient results caused by actual shutdown.

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