Nuclear power unit secondary circuit support system and once-through steam generator nuclear power system

Abstract

The invention relates to the technical field of nuclear power reactors, and discloses a nuclear power unit secondary circuit support system and a once-through steam generator nuclear power system. According to the nuclear power unit secondary loop support system, a plurality of groups of steam generator output pipelines are communicated with a main steam pipeline in parallel; the start-stop reactor main pipe is communicated with the output pipeline of the steam generator through a start-stop branch, a steam-water separator is mounted on the start-stop reactor main pipe in parallel, a steam supply branch is communicated between the start-stop reactor main pipe and the main steam pipeline, the steam supply branch is communicated with a steam exhaust pipeline, and two groups of steam exhaust outlets are formed in the tail end of the steam exhaust pipeline in parallel; and the drainage pipeline is communicated with the liquid phase outlet of the steam-water separator, and two groups of drainage outlets are arranged on the drainage pipeline in parallel. Start-stop steam exhaust of multiple groups of steam generators is treated through the shared start-stop reactor main pipe and the steam-water separator, graded recycling of working media and heat energy in the start-stop process is achieved, vapor-phase media are recycled, and waste of heat energy resources and water resources in the initial stage of start is reduced.

Description

Technical Field

[0001] This invention relates to the field of nuclear power reactor technology, specifically to a secondary loop support system for a nuclear power unit and a DC steam generator nuclear power system. Background Technology

[0002] In high-temperature gas-cooled reactor power generation systems, to improve the power output and economy of a single steam turbine generator unit, a "multiple reactors, one turbine" layout is typically adopted, where multiple reactor modules drive one steam turbine. Direct-current steam generators, which are compatible with this type of reactor, are widely used in these units due to their compact structure and high efficiency.

[0003] Compared to traditional pressurized water reactor units, installing a once-through (DC) steam generator in a multi-reactor unit results in lower outlet steam pressure, temperature, and quality during start-up and shutdown, failing to meet the turbine's steam inlet requirements. Current solutions typically discharge this substandard steam directly into the condenser via a bypass system. This not only leads to significant waste of working fluid and heat but also necessitates starting a high-power electric boiler to heat the feedwater, resulting in extremely poor economic efficiency during start-up and shutdown. Furthermore, when some reactors are already operational, newly started reactors, due to mismatched steam parameters with the main steam header, cannot integrate their generated steam into the main system during power increase and must continuously discharge it into the condenser, causing severe waste. This forces operators to schedule the simultaneous start-up and shutdown of multiple reactors, significantly limiting the flexibility of unit scheduling. Summary of the Invention

[0004] In view of this, the present invention provides a secondary loop support system for nuclear power units and a DC steam generator nuclear power system to solve the problem that in the prior art, nuclear power units with multiple reactors and one unit arrangement using DC steam generators will have a large amount of waste of working fluid and heat during the start-up and shutdown phases.

[0005] In a first aspect, the present invention provides a secondary loop support system for a nuclear power unit, comprising: The main steam pipeline is connected to a steam turbine at its end, and multiple sets of steam generator output pipelines are connected in parallel on the main steam pipeline. The start-stop reactor main pipe is connected to the steam generator output pipeline via a start-stop branch. A steam-water separator is installed in parallel on the start-stop reactor main pipe. The steam phase outlet of the steam-water separator is connected to the start-stop reactor main pipe. A steam supply branch is connected to the main steam pipeline. An exhaust pipeline is connected to the steam supply branch. Two sets of exhaust outlets are connected in parallel at the end of the exhaust pipeline. One set of exhaust outlets is suitable for connection to the condenser. The drain pipe is connected to the liquid phase outlet of the steam-water separator. The drain pipe is provided with two sets of drain outlets in parallel, one of which is adapted to be connected to the condenser.

[0006] The operation of the secondary loop support system of a nuclear power unit can be divided into three stages based on changes in steam parameters. In the initial startup phase, the steam parameters generated by the steam generator are low and cannot directly enter the turbine to perform work. At this time, the steam enters the start-up / shutdown main pipe through the steam generator output line and undergoes vapor-liquid separation in the steam-liquid separator. The separated vapor phase returns to the start-up / shutdown main pipe through the vapor phase outlet, while the liquid phase enters the drain line. During the initial startup phase, when water quality is poor, water is discharged from the system through the drain line. Once the water quality meets standards, water is transported to the condenser through another drain line. In the middle startup phase, as power increases, the steam parameters at the steam generator outlet rise, and the liquid level in the steam-liquid separator gradually decreases, eventually becoming a full steam space. At this point, the steam-liquid separator is shut down, and steam enters the start-up / shutdown main pipe, then enters the exhaust line through the steam supply branch to be discharged into the atmosphere, to other steam-using equipment, or to the condenser. During the later stages of startup, the steam parameters at the steam generator outlet are further improved, allowing steam from the corresponding steam generator output pipeline to be directly fed into the turbine for normal operation via the main steam pipeline. By using a shared start-up / shutdown header and steam-water separator to handle the start-up and shutdown exhaust from multiple steam generators, the system structure is simplified, reducing equipment costs and floor space. Furthermore, it enables the graded recovery and utilization of working fluid and thermal energy during startup and shutdown; the vapor phase is recovered, and the liquid phase, after meeting water quality standards, can be discharged into the condenser, reducing waste of thermal and water resources during the initial startup phase. Simultaneously, the system provides independent start-up and shutdown channels for nuclear power units with multiple steam generators, enabling independent control of the startup and co-operation of individual or multiple reactors, unaffected by other operating reactors. Moreover, the multiple outlet configuration of the exhaust pipeline allows the system to directly discharge steam to the atmosphere to maintain short-term reactor operation in the event of condenser vacuum failure or other fault conditions, avoiding reactor shutdown during condenser vacuum failures, reducing the time spent on start-up and shutdown processes during nuclear power unit maintenance, and significantly improving the overall reliability and operating efficiency of the nuclear power unit.

[0007] In one optional embodiment, the system further includes multiple sets of steam generator water supply lines connected in parallel, wherein the steam generator water supply lines are connected to the inlet end of the steam-water separator via a flushing and recirculation loop.

[0008] Before the steam generator is started, a flushing and recirculation loop is connected between the steam generator feed water pipeline and the inlet of the steam-water separator, so that the feed water can circulate between the steam generator feed water pipeline and the steam-water separator, thereby flushing and heating the steam generator feed water pipeline.

[0009] In one optional embodiment, the steam generator feedwater pipeline is connected to the liquid phase outlet of the steam-water separator via a steam generator wet maintenance circuit.

[0010] After the reactor is shut down, the wet maintenance circuit of the steam generator, which connects the steam generator feedwater line to the liquid phase outlet of the steam-water separator, is used to return the wet heat medium separated by the steam-water separator to the steam generator, thereby achieving wet maintenance of the steam generator.

[0011] In one optional embodiment, a chemical cleaning circuit is connected between the steam generator feedwater pipeline and the start-stop reactor main pipe, and the chemical cleaning circuit is connected upstream of the steam-water separator inlet.

[0012] When chemical cleaning of the steam generator is required, the chemical cleaning solution is introduced into the system through a chemical cleaning loop connected between the steam generator feedwater pipeline and the start-up / shutdown main pipeline. After flowing through the steam generator, the cleaning solution can be returned to the steam generator for processing via the chemical cleaning loop located upstream of the steam-water separator inlet, thus realizing a cleaning cycle.

[0013] In one alternative embodiment, the start-stop reactor header is further connected to a high-pressure steam pipeline, which is adapted to be connected to a high-pressure heater and is located upstream of the steam-water separator inlet.

[0014] During reactor startup, high-parameter steam from upstream of the start-up / shutdown header can be directly introduced to the high-pressure heater as a heating source through a high-pressure steam pipeline connecting the start-up / shutdown header and the high-pressure heater.

[0015] In one optional embodiment, a first desuperheating and pressure-reducing device is installed on the high-pressure steam pipeline. High-parameter steam drawn from the reactor start-up / shutdown header to the high-pressure heater is adjusted by the first desuperheating and pressure-reducing device as it flows through the high-pressure steam pipeline, reducing its pressure and temperature to meet the operating requirements of the high-pressure heater. This prevents damage to the high-pressure heater due to steam overheating and overpressure, ensuring system safety.

[0016] In one optional implementation, the start-up / shutdown main pipe is connected to multiple sets of auxiliary branches, which are adapted to connect to a deaerator or auxiliary steam header. Low-parameter steam from the main pipe can be delivered to the deaerator or auxiliary steam header as needed to provide heating steam for these devices. By utilizing the low-quality steam generated during the initial startup of the steam generator, the steam demand of auxiliary equipment within the nuclear power plant is met, reducing dependence on main steam or external steam sources and further lowering the operating energy consumption of the nuclear power unit.

[0017] In one optional embodiment, a second desuperheating and pressure reducing device is installed on the start-up / shutdown header, between the inlet of the steam-water separator and the vapor phase outlet of the steam-water separator. This ensures that the steam parameters output from the start-up / shutdown header match the steam demand of downstream equipment, maintaining the stable operation of the entire support system.

[0018] In one optional implementation, multiple sets of steam supply branches are installed in parallel. After the unit vacuum is lost, the reactor rapidly reduces its power to maintain low-power operation. The generated steam passes through the main steam pipeline and then through two sets of steam supply branches to enter the corresponding exhaust pipeline, venting the steam to the atmosphere, thereby maintaining the low-power continuous operation of the nuclear reactor in the short term.

[0019] Secondly, the present invention also provides a DC steam generator nuclear power system, including the nuclear power unit secondary loop support system described in the present invention.

[0020] Since the DC steam generator nuclear power system includes the nuclear power unit's secondary loop support system, which has the same technical effect as the nuclear power unit's secondary loop support system, it will not be elaborated here. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the secondary loop support system for nuclear power units provided in an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached diagram: 1. Steam generator output pipeline; 2. Main steam isolation valve of the nuclear island; 3. Auxiliary branch; 4. Main steam isolation valve of the conventional island; 5. Main steam pipeline; 6. Steam turbine; 7. Isolation valve for single-reactor start-up and shutdown; 8. High-temperature main pipe for start-up and shutdown; 9. Second desuperheating and pressure reducing device; 10. Low-temperature main pipe for start-up and shutdown; 11. Bypass valve; 12. Steam supply branch; 13. Exhaust pipeline; 14. Exhaust outlet; 15. Drainage pipeline; 16. First desuperheater. 17. Pressure reducing device; 18. High-pressure steam pipeline; 19. Steam-water separator inlet regulating valve; 20. Steam-water separator outlet isolation valve; 21. Through liquid level regulating valve; 22. Drain outlet; 23. Steam generator feedwater pipeline; 24. Flushing and recirculation loop; 25. Chemical cleaning loop; 26. Steam generator wet maintenance loop; 27. Single reactor feedwater regulating valve; 28. Conventional island main feedwater isolation valve; 29. ​​Nuclear island main feedwater isolation valve. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The following is combined with Figure 1 Embodiments of the present invention are described.

[0026] According to an embodiment of the present invention, in one aspect, a secondary loop support system for a nuclear power generator unit is provided for a nuclear power generator unit with a DC steam generator having multiple nuclear power modules. The secondary loop support system includes a main steam pipeline 5, a reactor start-up / shutdown header, and a drainage pipeline 15.

[0027] The main steam pipeline 5 is connected to a steam turbine 6 at its end. Multiple sets of steam generator output pipelines 1 are connected in parallel to the main steam pipeline 5. The start-up / shutdown main pipe is connected to the steam generator output pipelines 1 via a start-up / shutdown branch. A steam-water separator 19 is installed in parallel on the start-up / shutdown main pipe. The vapor phase outlet of the steam-water separator 19 is connected to the start-up / shutdown main pipe. A steam supply branch 12 connects the start-up / shutdown main pipe to the main steam pipeline 5. An exhaust pipeline 13 is connected to the steam supply branch 12. Two sets of exhaust outlets 14 are connected in parallel at the end of the exhaust pipeline 13. One exhaust outlet 14 is connected to the condenser, and the other exhaust outlet 14 is connected to the atmosphere or other steam-using equipment. In this embodiment, one exhaust outlet 14 is connected to the atmosphere, and the other exhaust outlet 14 is connected to the condenser. The drain pipe 15 is connected to the liquid phase outlet of the steam-water separator 19. The drain pipe 15 is provided with two sets of drain outlets 22 in parallel. One set of drain outlets 22 is suitable for connecting to the condenser, and the other set of drain outlets 22 is connected to the external environment of the system or to the external water system. In this embodiment, one set of drain outlets 22 is connected to the condenser, and the other set of drain outlets 22 is connected to the external environment.

[0028] The operation of the secondary loop support system of a nuclear power unit can be divided into three stages based on changes in steam parameters. In the initial startup phase, the steam parameters generated by the steam generator are low and cannot directly enter the turbine 6 to perform work. At this time, the steam enters the start-up / shutdown main pipe through the steam generator output pipe 1 and undergoes vapor-liquid separation in the steam-liquid separator 19. The separated vapor phase returns to the start-up / shutdown main pipe through the vapor phase outlet, while the liquid phase enters the drain pipe 15. During the initial startup phase, when the water quality is poor, water is discharged from the system through the drain pipe 15. Once the water quality meets the standards, the water is transported to the condenser through another drain pipe 15. In the middle startup phase, as the power increases, the steam parameters at the steam generator outlet rise, and the liquid level in the steam-liquid separator 19 gradually decreases, eventually becoming a full steam space. At this point, the steam-liquid separator 19 is shut down, and the steam enters the start-up / shutdown main pipe, then enters the exhaust pipe 13 through the steam supply branch 12 for discharge to the atmosphere, to other steam-using equipment, or to the condenser. During the later stages of startup, the steam parameters at the steam generator outlet are further improved, allowing the steam in the corresponding steam generator output pipeline 1 to directly enter the steam turbine 6 through the main steam pipeline 5 for normal operation.

[0029] By using a shared start-up / shutdown header and steam-water separator 19 to handle the start-up and shutdown exhaust steam from multiple steam generators, the system structure is simplified, reducing equipment costs and floor space. Furthermore, it enables the graded recovery and utilization of working fluid and thermal energy during start-up and shutdown. The vapor phase is recovered, and the liquid phase, after meeting water quality standards, can also be discharged into the condenser, reducing waste of thermal and water resources during the initial startup phase. Simultaneously, the system provides independent start-up and shutdown channels for nuclear power units with multiple steam generators, allowing independent control of the start-up and steam co-operation of individual or multiple reactors, unaffected by other operating reactor groups. Moreover, the multi-outlet configuration of the exhaust pipeline allows the system to directly discharge steam to the atmosphere to maintain short-term reactor operation in the event of condenser vacuum failure or other fault conditions. This avoids reactor shutdown during condenser vacuum failures, reduces the time spent on start-up and shutdown processes during nuclear power unit maintenance, and significantly improves the overall reliability and operating efficiency of the nuclear power unit.

[0030] In one embodiment, the system further includes multiple sets of steam generator water supply lines 23 arranged in parallel, and the steam generator water supply lines 23 are connected to the inlet end of the steam-water separator 19 via a flushing and recirculation loop 24.

[0031] Before the steam generator is started, the flushing and recirculation loop 24 connecting the steam generator water supply line 23 and the inlet end of the steam-water separator 19 is connected to enable the water supply to circulate between the steam generator water supply line 23 and the steam-water separator 19, thereby flushing and heating the steam generator water supply line 23.

[0032] In one embodiment, the steam generator feedwater line 23 is connected to the liquid phase outlet end of the steam-water separator 19 via a steam generator wet maintenance circuit 26.

[0033] After the reactor is shut down, the wet maintenance circuit 26 of the steam generator, which connects the steam generator feedwater line 23 and the liquid phase outlet of the steam-water separator 19, is used to return the wet heat medium separated by the steam-water separator 19 to the steam generator, thereby achieving wet maintenance of the steam generator by filling it with water.

[0034] In one embodiment, a chemical cleaning circuit is connected between the steam generator feedwater line 23 and the start-up / shutdown reactor main pipe, and the chemical cleaning circuit is connected upstream of the inlet of the steam-water separator 19.

[0035] When chemical cleaning of the steam generator is required, the chemical cleaning solution is introduced into the system through the chemical cleaning loop connected between the steam generator feedwater pipeline 23 and the start-up / shutdown main pipe. After the cleaning solution flows through the steam generator, it can return to the steam generator for processing through the chemical cleaning loop located upstream of the steam-water separator 19 inlet, thus realizing the cleaning cycle.

[0036] In one embodiment, a high-pressure steam pipeline 17 is also connected to the start-up / shutdown main pipe. The high-pressure steam pipeline 17 is adapted to be connected to the high-pressure heater and is located upstream of the inlet of the steam-water separator 19.

[0037] During reactor startup, high-parameter steam from upstream of the start-up / shutdown header can be directly introduced to the high-pressure heater as a heating source through the high-pressure steam pipeline 17 connecting the start-up / shutdown header and the high-pressure heater.

[0038] Furthermore, a first desuperheating and pressure reducing device 16 is installed on the high-pressure steam pipeline 17. The high-parameter steam leading from the reactor start-up / shutdown header to the high-pressure heater is adjusted by the first desuperheating and pressure reducing device 16 as it flows through the high-pressure steam pipeline 17, reducing its pressure and temperature to meet the operating requirements of the high-pressure heater. This prevents damage to the high-pressure heater due to steam overheating and overpressure, ensuring system safety.

[0039] In one embodiment, the start-up / shutdown main pipe is connected to multiple sets of auxiliary branches 3, which are adapted to connect to the deaerator or auxiliary steam header. Low-parameter steam from the main pipe can be delivered to the deaerator or auxiliary steam header as needed to provide heating steam for these devices. By utilizing the low-quality steam generated during the initial startup of the steam generator, the steam demand of auxiliary equipment within the nuclear power plant is met, reducing dependence on main steam or external steam sources and further lowering the operating energy consumption of the nuclear power unit.

[0040] In one embodiment, a second desuperheating and pressure reducing device 9 is installed on the start-up / shutdown header. This device 9 is positioned between the inlet of the steam-water separator 19 and the vapor phase outlet of the steam-water separator 19. This ensures that the steam parameters output from the start-up / shutdown header match the steam demand of downstream equipment, maintaining the stable operation of the entire support system.

[0041] In one embodiment, multiple sets of steam supply branches 12 are installed in parallel. After the unit vacuum is lost, the reactor quickly reduces its power to maintain low-power operation. The generated steam passes through the main steam pipeline 5 and then through the two sets of steam supply branches 12 to enter the corresponding exhaust pipeline 13, thus venting the steam to the atmosphere and maintaining the low-power continuous operation of the nuclear reactor in the short term.

[0042] To achieve on / off control of the pipeline, valve structures are installed in each branch, loop, and pipeline. The following section combines... Figure 1 Provide a detailed description.

[0043] On the steam generator output line 1 at the outlet of each steam generator, a main steam isolation valve 2 with redundant actuation mechanism is installed on the nuclear island side, and a main steam isolation valve 4 is installed on the conventional island. A branch line is led out from the steam generator output line 1 between the two electric valves, the main steam isolation valve 2 on the nuclear island and the main steam isolation valve 4 on the conventional island, as a start-up and shutdown branch line, which leads to the unit's start-up and shutdown reactor system.

[0044] Steam output from the steam generator passes through the single-reactor start-stop isolation valve 7 on the start-stop branch and enters the start-stop main pipe shared by multiple nuclear power units. A second desuperheating and pressure-reducing device 9 is installed on the start-stop main pipe. Upstream of the second desuperheating and pressure-reducing device 9 is the high-temperature start-stop main pipe 8, and downstream is the low-temperature start-stop main pipe 10. After passing through the second desuperheating and pressure-reducing device 9, the high-temperature steam's pressure and temperature are reduced, and it enters the shared low-temperature start-stop main pipe 10. Finally, it can be discharged to the three shared exhaust pipes 13. Each exhaust pipe 13 is equipped with a bypass valve 11, and each bypass valve 11 is connected to two exhaust outlets 14 downstream. Steam either goes to the condenser through one of the exhaust outlets 14 to continue water-steam circulation or to the atmosphere.

[0045] Steam enters the branch pipe at the inlet end of the steam-water separator 19 from the high-temperature header 8 of the start-up / shutdown reactor. After being depressurized by the steam-water separator inlet regulating valve 18, it enters the steam-water separator 19 shared by the unit. Steam and water are separated in the steam-water separator 19. The water medium can enter the condenser or be discharged after passing through the liquid level regulating valve on the drain pipe 15. The steam medium goes to the low-temperature header 10 of the start-up / shutdown reactor through the steam-water separator 19 isolation valve on the branch pipe on the steam phase outlet side of the steam-water separator 19.

[0046] A high-pressure steam pipeline 17 is installed on the high-temperature main pipe 8 of the reactor start-up and shutdown system. Steam passes through the first desuperheating and pressure reducing device 16 on the high-pressure steam pipeline 17 and then goes to the high-pressure heater for utilization of high-quality steam. The low-temperature main pipe 10 of the reactor start-up and shutdown system is equipped with multiple sets of auxiliary branches 3. Steam passes through the regulating valves on the auxiliary branches 3 to the deaerator or to the auxiliary steam header for utilization of low-quality steam.

[0047] On the feedwater side of the steam generator, the feedwater pump collects the feedwater into the feedwater header. Downstream are multiple sets of parallel steam generator feedwater lines 23. Each steam generator feedwater line 23 is equipped with a single-reactor feedwater regulating valve 27, a conventional island main feedwater isolation valve 28, and a nuclear island main feedwater isolation valve 29, ultimately returning to the steam generator inlet of the single reactor. Upstream of the conventional island main feedwater isolation valve 28, there are a flushing recirculation loop, a steam generator wet maintenance loop 26, and a chemical cleaning loop 25.

[0048] By closing the main steam isolation valve 2 of the nuclear island, the main steam isolation valve 4 of the conventional island, and the single-reactor start-up / shutdown isolation valve 7 on the positive steam side of each reactor, and closing the main feedwater isolation valve 28 of the conventional island and the main feedwater isolation valve 29 of the nuclear island on the feedwater side, isolation between the single reactor and the steam-water circuit and the start-up / shutdown reactor can be achieved. Both systems ensure two isolation valves connected in series, achieving reliable isolation and meeting maintenance requirements.

[0049] During reactor startup, in the initial stage, when steam parameters are relatively low, the subcooled water from the reactor outlet passes through the main steam isolation valve 2 of the nuclear island, the single-reactor start-up / shutdown isolation valve 7, the high-temperature start-up / shutdown header 8, and the steam-water separator inlet regulating valve 18 to reduce pressure and expand capacity before entering the steam-water separator 19. At this time, the water entering the steam-water separator 19 is divided into steam and water phases. The steam medium passes through the steam-water separator outlet isolation valve 20 to the low-temperature start-up / shutdown header 10, and then enters the condenser through a bypass valve to achieve medium recovery. When the water medium is of poor quality in the early stage, it is discharged after passing through the level regulating valve 21. When the water quality is qualified, it is switched to the condenser.

[0050] At this time, the steam generator outlet pressure is maintained by the steam-water separator inlet regulating valve 18 to maintain the design pressure, which is generally around 13.9 MPa. The bypass valve 11 maintains the pressure of the steam phase outlet of the steam-water separator 19, which is generally around 2.5 MPa. The liquid level regulating valve maintains the liquid level of the steam-water separator 19.

[0051] During the mid-start-up phase, as the power increases, the steam parameters at the steam generator outlet rise, and the liquid level in the steam-water separator 19 gradually decreases, eventually becoming a full steam space. At this point, the steam-water separator inlet regulating valve 18 and the steam-water separator outlet isolation valve 20 are closed, and the steam-water separator 19 is shut off. After the steam enters the high-temperature header 8 of the start-up / shutdown reactor, it passes through the desuperheating and pressure-reducing device and directly enters the low-temperature header 10 of the start-up / shutdown reactor, and then is discharged to the bypass valve.

[0052] At this time, the steam generator outlet pressure is maintained at the design pressure by the second desuperheating and pressure reducing device 9, which is generally around 13.9 MPa. The second desuperheating and pressure reducing device 9 and the bypass valve 11 together maintain the pressure and temperature of the start-up and shutdown low temperature header 10, which is generally 2.5 MPa and 250°C.

[0053] During the later stages of startup, the steam parameters at the steam generator outlet are further improved, allowing steam to be fed into the main steam pipeline 5. The main steam isolation valve 4 of the conventional island is gradually opened, and the isolation valves 7 for starting and stopping individual reactors are controlled to be closed, so that the steam from each individual reactor can be fed into the main steam pipeline. This operation can be performed on an individual reactor-by-reactor basis.

[0054] At this time, the steam generator outlet pressure is maintained at the design pressure by the second desuperheating and pressure reducing device 9, which is consistent with the main steam pipeline 5, and is regulated by the single-unit feedwater regulating valve 27.

[0055] Finally, the single-reactor power continues to increase, while the outlet temperature and pressure remain unchanged. As the single-reactor feedwater regulating valve 27 is opened, the flow rate is gradually increased, eventually achieving full-power operation of the single-reactor.

[0056] The shutdown process is the reverse of the startup process, and will not be described in detail here.

[0057] This system can simultaneously start up to one reactor and up to half of the reactors. Due to the flow channel design, there is no steam overlap between the start-up and operating reactors. The unit can operate at full power or be shut down, offering overall operational flexibility. In related technologies, multi-module units experience low steam parameters during startup, preventing steam from entering the turbine (6) for work and forcing it to enter the condenser, resulting in significant waste. Simultaneously, feedwater requires heating by an electric boiler, leading to substantial power consumption and poor overall economic efficiency. This system, after collecting steam from the start-up reactor, uses the high-temperature header (8) to collect high-parameter steam, which is then supplied to the high-pressure heater via the first desuperheating and pressure-reducing device (16). The low-parameter steam header (10) collects low-parameter steam, which is then supplied to the deaerator and auxiliary steam header via regulating valves. This system utilizes the deaerator and high-pressure heater nodes to achieve full-process feedwater heating during startup, eliminating the need for continuous heating by an electric boiler and significantly improving the unit's economic efficiency.

[0058] After the unit loses vacuum, the reactor quickly reduces power to maintain low-power operation. The generated steam is discharged to the atmosphere via the main steam pipeline 5 and controlled by two bypass valves 11 connected to the main steam header. At the same time, the feedwater is heated by the deaerator and high-pressure heater mentioned above, and with a certain amount of makeup water, the reactor can operate at low power without vacuum for a short period of time. This buys time for troubleshooting, avoids unnecessary large-scale reactor shutdowns, and improves the reliability of unit operation.

[0059] There are three bypass valves 11, each with a capacity of 50% of the total unit capacity. Generally, two bypass valves 11 are connected online to the main steam pipeline 5 to respond to transient operating conditions of the unit; one bypass valve 11 is connected online to the start-up and shutdown cryogenic header 10 to meet the unit's start-up and shutdown requirements.

[0060] The flushing recirculation loop enables the recirculation of feedwater for flushing and warming before a single reactor startup. The steam generator wet maintenance loop 26 enables wet maintenance circulation of the steam generator after a single reactor shutdown. If a planned shutdown of the operating reactor is required, the steam generator undergoing maintenance must stop circulation, and the start-up / shutdown system must be rewarmed. The chemical cleaning loop 25, in conjunction with external modules, provides chemical cleaning circulation for the steam generator after unit shutdown. Steam generator cleaning is generally performed after all reactors have been shut down. If necessary, this system can provide cleaning loops for several steam generators while some reactors are operating. If a planned shutdown of the operating reactor is required, cleaning must be stopped, and the start-up / shutdown system must be flushed and rewarmed.

[0061] The following describes the operation of the nuclear power unit secondary loop support system provided by this invention after the unit loses vacuum, based on actual operating data. After the unit loses vacuum, the condenser and turbine become unusable. The unit removes reactor heat through atmospheric emissions, and the reactor rapidly reduces its power output. During this period, demineralized water needs to be continuously supplied to the secondary loop. When the steam temperature at the steam generator outlet drops to a certain level, the system switches from the main steam header to reactor start-up / shutdown mode for partial working fluid recovery. For ease of understanding, the reactor full power (100% RFP) will be taken as 250 MW in the following text.

[0062] When a DC steam generator nuclear power system equipped with a secondary loop support system for a nuclear power unit is operating normally, its rated nuclear power is 250MW, main steam pressure is 11PMa, main steam temperature is 520℃, reactor power reduction rate is 5%RFP / min, steam generator temperature drop limit is 5℃ / h, steam-water separator operating pressure is 5MPa, and deaerator pressure is 0.6MPa.

[0063] After a unit loses vacuum, the condenser and turbine become unusable. The unit removes reactor heat through atmospheric venting, and the reactor rapidly reduces its power output. During this period, demineralized water needs to be continuously supplied to the secondary loop. Once the steam generator outlet temperature drops to a certain level, steam is switched from the main steam line to the reactor start-up / shutdown header for partial working fluid recovery. Related technologies using direct-current steam generator nuclear power systems require a large amount of demineralized water after a unit loses vacuum. The nuclear power unit secondary loop support system provided in this application can significantly reduce the amount of demineralized water consumed after a unit loses vacuum. Specifically: When the vacuum is lost, the high vacuum trigger of the condenser immediately shuts down the turbine 6 and activates the bypass valve protection. The main control valve at the inlet of the turbine 6 is closed, and the valve on the exhaust outlet downstream of the bypass valve 11 leading to the condenser side is closed.

[0064] After turbine 6 is shut down, the pressure in the main steam pipeline increases. At this time, steam is supplied to the exhaust pipeline 13 through the steam supply branch 12 connected to the main steam pipeline 5, and finally discharged through the exhaust outlet 14 connected to the atmosphere. At this time, the feedwater flow rate of a single reactor is 341 t / h, which is supplied to the condenser by the demineralized water makeup water tank.

[0065] After turbine 6 is shut down, the extraction valve on the extraction steam pipeline that preheats the feedwater supplied to the steam generator from turbine 6 is closed, and the start-up / shutdown cryogenic header supplies heating steam to the deaerator to maintain the feedwater temperature at 160°C.

[0066] During the reduction of the reactor's operating power from 100% RFP to 30% RFP, the reactor power is automatically reduced to 30% RFP at a rate of 5% RFP / min. This is an open-loop discharge process. A small amount of steam from the steam generator outlet is used to provide heating steam for the deaerator via the start-up / shutdown header; the remaining steam is directed to the steam supply branch and discharged to the atmosphere through the exhaust pipe. During this phase, the steam generator outlet pressure and temperature remain unchanged; only the feedwater and helium flow rates decrease. This phase lasts 14 minutes, and the cumulative makeup water volume during this phase, including closed-loop water makeup, is 43 tons. During this period, two feedwater pumps are shut down, while one feedwater pump remains operational. The closed-loop water system maintains its temperature through a continuous makeup water supply and discharge process. A single reactor requires 13 tons of closed-loop water makeup water per hour.

[0067] During the reduction of the nuclear reactor's operating power from 30% RFP to 20% RFP, the steam generator outlet temperature is cooled at a rate of 28°C / h until it reaches 336°C, while still operating in an open-loop manner. This phase is expected to last 8.39 hours, with a cumulative makeup water volume of 752 tons, including closed-loop makeup water.

[0068] During the period when the operating power of the nuclear reactor is reduced from 20%RFP to 13%RFP, the steam enters the two-phase flow stage. The steam from the outlet of the steam generator is cut into the start-up / shutdown steam-water separator. After depressurization, wet steam appears in the steam-water separator at 5MPa. The water output from the water side of the steam-water separator is recycled. Part of the steam output from the steam side is discharged to the atmosphere through the exhaust pipe after passing through the bypass valve 11, carrying away heat. The other part of the steam is sent to the deaerator through the auxiliary branch to heat the deaerator, which is maintained at 160°C.

[0069] During the period when the reactor's operating power decreases from 13% RFP to 9.4% RFP, the steam-water separator continues to recover steam, and all steam output from the steam side is discharged to the atmosphere through a bypass valve, carrying away heat and eliminating the need for reheating the deaerator. The entire two-phase flow phase is expected to last for 2 hours, during which the cumulative makeup water volume, including closed-loop water makeup, is 126 tons.

[0070] During the period when the operating power of the nuclear reactor decreased from 9.4%RFP to 8%RFP, the reactor reached a low-power stable operating stage of 20MW. During this stage, the pressure of the steam-water separator was gradually reduced until it reached 1.96MPa. All steam was discharged from the steam side, and the recovered water was mixed with demineralized water makeup water before entering the deaerator. The steam generator outlet temperature decreased from 336℃ to 317℃. At this time, the makeup water rate was 40t / h, including 13t / h of closed-loop makeup water.

[0071] If the vacuum problem cannot be resolved during the reduction of the nuclear reactor's operating power from 8%RFP to 1%RFP, and the reactor needs to be shut down, the power will be further reduced to 2.5MW, and the steam-water separator pressure will be further reduced to 0.73MPa. After that, the reactor will be manually shut down normally. This stage is expected to last 4.86 hours, with a cumulative makeup water volume of 136t including closed-loop water makeup.

[0072] Based on the above calculations of the shutdown process, it can be seen that after a single reactor is shut down, during the rapid power reduction process, it can be reduced to 8% power in approximately 11.3 hours, requiring only 950 tons of demineralized water for makeup. For long-term operation, a makeup water rate of 40 tons per hour is sufficient. The system is equipped with a 1400-ton standby demineralized water tank, which can support a single reactor shutdown and maintenance for 24 hours under vacuum conditions.

[0073] Secondly, this invention also provides a direct-current steam generator nuclear power system, including the nuclear power unit secondary loop support system described in this invention. It also includes multiple steam generators, wherein the steam generator output pipeline 1 is connected to the steam outlet of the steam generator output pipeline 1, and the steam generator feedwater pipeline 23 is connected to the feedwater inlet of the steam generator. Because the direct-current steam generator nuclear power system includes the nuclear power unit secondary loop support system, it has the same technical effects as the nuclear power unit secondary loop support system. By using a shared start-up / shutdown mother pipe and steam-water separator 19 to handle the start-up and shutdown exhaust of multiple steam generators, the system structure is simplified, reducing equipment costs and floor space. Furthermore, it achieves graded recovery and utilization of working fluid and thermal energy during start-up and shutdown. The vapor phase medium is recovered, and the liquid phase medium, after meeting water quality standards, can also be discharged into the condenser, reducing the waste of thermal and water resources during the initial startup phase. Simultaneously, the system provides independent start-up and shutdown channels for nuclear power units equipped with multiple steam generators, enabling independent control of the start-up and steam co-operation of single or multiple reactors, without being constrained by other operating reactor groups. Furthermore, the multi-outlet configuration of the exhaust pipeline allows the system to directly discharge steam to the atmosphere in the event of failures such as loss of condenser vacuum, thereby maintaining short-term reactor operation. This avoids reactor shutdown during condenser vacuum failures, reduces the time spent on start-up and shutdown processes during nuclear power unit maintenance, and greatly improves the reliability and operating efficiency of the entire nuclear power unit.

[0074] The DC steam generator nuclear power system provided by this invention includes six nuclear reactors, requiring only two sets of secondary loop support systems for each reactor unit. Considering operational intensity and risk, simultaneous startup of all six reactors is not scheduled. If more than three reactors need to be started, they can be divided into two batches. Considering operational intensity and risk, and the need for a stable backup feedwater heating steam source, simultaneous planned shutdown of all six reactors is generally not performed. Planned shutdown operations for more than three reactors must be divided into two batches. The reactor start-up and shutdown operations of the DC steam generator nuclear power system are conducted according to the aforementioned operating methods of the secondary loop support systems for each reactor unit during reactor start-up and shutdown.

[0075] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A secondary loop support system for a nuclear power unit, characterized in that, include: The main steam pipeline (5) is connected to a steam turbine (6) at its end. Multiple sets of steam generator output pipelines (1) are connected in parallel on the main steam pipeline (5). The start-stop reactor main pipe is connected to the steam generator output pipeline (1) via a start-stop branch. A steam-water separator (19) is installed in parallel on the start-stop reactor main pipe. The steam phase outlet of the steam-water separator (19) is connected to the start-stop reactor main pipe. A steam supply branch (12) is connected between the start-stop reactor main pipe and the main steam pipeline (5). An exhaust pipeline (13) is connected to the steam supply branch (12). Two sets of exhaust outlets (14) are connected in parallel at the end of the exhaust pipeline (13). One set of exhaust outlets (14) is suitable for connection with the condenser. The drain pipe (15) is connected to the liquid phase outlet of the steam-water separator (19). The drain pipe (15) is provided with two sets of drain outlets (22) in parallel, one of which is suitable for connection with the condenser.

2. The nuclear power unit secondary loop support system according to claim 1, characterized in that, It also includes multiple sets of parallel steam generator water supply pipelines (23), and the steam generator water supply pipelines (23) are connected to the inlet end of the steam-water separator (19) via a flushing and recirculation loop (24).

3. The nuclear power unit secondary loop support system according to claim 2, characterized in that, The steam generator water supply line (23) is connected to the liquid phase outlet end of the steam-water separator (19) via a steam generator wet maintenance circuit (26).

4. The nuclear power unit secondary loop support system according to claim 2, characterized in that, A chemical cleaning circuit is connected between the steam generator feedwater pipeline (23) and the start-stop reactor main pipe, and the chemical cleaning circuit is connected upstream of the inlet of the steam-water separator (19).

5. The nuclear power unit secondary loop support system according to any one of claims 1 to 4, characterized in that, The start-stop reactor main pipe is also connected to a high-pressure steam pipeline (17), which is adapted to be connected to a high-pressure heater. The high-pressure steam pipeline (17) is located upstream of the inlet of the steam-water separator (19).

6. The nuclear power unit secondary loop support system according to claim 5, characterized in that, The high-pressure steam pipeline (17) is equipped with a first de-temperature and pressure reducing device (16).

7. The nuclear power unit secondary loop support system according to any one of claims 1 to 4, characterized in that, The start-stop main pipe is connected to multiple sets of auxiliary branches (3), which are suitable for connecting to the deaerator or auxiliary steam header.

8. The nuclear power unit secondary loop support system according to any one of claims 1 to 4, characterized in that, A second desuperheating and pressure reducing device (9) is installed on the start-up and shutdown main pipe. The second desuperheating and pressure reducing device (9) is installed between the inlet of the steam-water separator (19) and the vapor phase outlet of the steam-water separator (19).

9. The nuclear power unit secondary loop support system according to any one of claims 1 to 4, characterized in that, The steam supply branch (12) is installed in parallel with multiple sets.

10. A direct-current steam generator nuclear power system, characterized in that, Includes the nuclear power unit secondary loop support system as described in any one of claims 1 to 9.

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