State control method and system for secondary loop water supply system of nuclear power station

Abstract

The invention discloses a state control method and system for a secondary loop water supply system of a nuclear power plant, and the method comprises the steps: when the vacuum of a secondary loop needs to be destroyed for equipment maintenance, carrying out the following steps: mechanically isolating a condenser from a secondary loop thermal-state pipeline connected with the condenser; establishing a deaerator circulating system, namely conveying feed water at an outlet of the deaerator to a feed water inlet header by starting a feed water pump, and returning the feed water to the deaerator through a heating pipeline to form a first circulating channel; feed water for starting an outlet of the feed pump is returned to the deaerator through the high-pressure heater and the main feed pump system to form a second circulation channel. A condenser is mechanically isolated from a secondary loop thermal-state pipeline, a deaerator circulating system comprising a plurality of circulating channels is established, and the temperature of a deaerator is maintained by utilizing conversion from mechanical energy to heat energy when a water supply pump is started to operate, so that stable operation of the secondary loop water supply system in a vacuum breaking state is realized.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and in particular to a state control method and system for a secondary circuit water supply system of a nuclear power plant. Background Art

[0002] The secondary water supply system of a pressurized water reactor nuclear power plant is an important system to ensure the safe operation of the unit. Compared with the traditional CPR unit (Chinese Pressurized water Reactor, the second-generation improved pressurized water reactor nuclear power unit), the Hualong One nuclear power unit has eliminated the redundant operation functions of the turbine bypass system (GCT-a) (exhaust to atmosphere), the turbine bypass system (GCT-c) (exhaust to condenser) and the emergency feed water system (ASG) / start-up feed water system (APD) in terms of function allocation, and separated the operation functions of GCT-a and ASG from the safety functions to meet the requirements of independence of defense in depth.

[0003] In terms of system layout, the secondary feedwater system of Hualong One includes: condensate extraction system (CEX), low-pressure feedwater heater system (ABP), feedwater heater drain recovery system (ACO), feedwater deaerator system (ADG), startup and shutdown feedwater system (AAD), high-pressure feedwater heater system (AHP), etc. Although the overall layout is similar to that of the CPR unit, the layout of the main feedwater flow control system (ARE) is similar to that of the EPR unit. Its characteristic is that the ARE feedwater valve station is set in the plant, about 300m away from the conventional island side inlet manifold. At the same time, compared with the EPR unit, Hualong One lacks the regenerative heat exchanger of the startup feedwater treatment system (ATD) and multi-way startup flushing pipelines.

[0004] Therefore, the secondary circuit water supply system of Hualong One has the following major technical difficulties in actual operation: when the vacuum of the secondary circuit needs to be destroyed for maintenance, the primary circuit needs to be retreated to the designated mode, and after the maintenance is completed, the vacuum needs to be re-established and the secondary circuit water needs to be replaced with oxygen-free water, which takes up critical path time. Summary of the invention

[0005] The main purpose of the present invention is to provide a state control method and system for a secondary loop water supply system of a nuclear power plant to solve the above technical problems.

[0006] In a first aspect, the present invention provides a state control method for a secondary water supply system of a nuclear power plant, which is applied to a secondary water supply system of a nuclear power plant. The state control method for a secondary water supply system of a nuclear power plant comprises: when it is necessary to destroy the vacuum of the secondary water supply system for equipment maintenance, executing the following steps:

[0007] Mechanically isolate the condenser from the hot secondary circuit piping connected to it;

[0008] Establishing a deaerator circulation system, including: starting a feed water pump to deliver feed water from the outlet of the deaerator to a feed water inlet header, and then returning the feed water to the deaerator through a warm pipe line to form a first circulation channel;

[0009] The feed water at the outlet of the startup feed water pump is returned to the deaerator via the high pressure heater and the main feed water pump system to form a second circulation channel;

[0010] In the deaerator circulation system, the temperature of the deaerator is maintained by converting the mechanical energy into thermal energy when the startup water supply pump is running.

[0011] Wherein, the mechanical isolation of the hot secondary circuit pipeline connected to the condenser includes:

[0012] Keep the deaerator water supply isolation valve of the condensate extraction system open, and keep the deaerator water supply regulating valve closed;

[0013] Close all valves that normally exhaust the high-pressure heater to the feedwater deaerator, and cut the drain to the drain discharge system;

[0014] Close the feedwater deaerator valve on the connecting pipeline from the feedwater deaerator to the condenser, and keep the auxiliary steam of the feedwater deaerator online;

[0015] Close the sampling valve at the outlet of the low-pressure heater drain pump to prevent the return water from the heating pipe line from flowing back to the low-pressure feedwater heater system.

[0016] Wherein, after the feed water at the outlet of the startup feed water pump is returned to the deaerator via the high pressure heater and the main feed water pump system to form a second circulation channel, the step of establishing the deaerator circulation system further includes:

[0017] The feed water at the outlet of the deaerator is returned to the deaerator through the start-up feed water pump and the secondary circulation pipeline to form a third circulation channel.

[0018] Wherein, after the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the starting feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes:

[0019] Calculate the total heat dissipation of the deaerator circulation system, wherein the total heat dissipation includes natural heat dissipation of pipelines, exhaust steam loss of the deaerator and condensate supply loss;

[0020] When the heat generated by the startup water supply pump is greater than the total heat dissipation, the deaerator circulation system reaches a dynamic balance at a new temperature and pressure platform by adjusting the exhaust volume of the deaerator exhaust pipeline.

[0021] Wherein, after the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the starting feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes:

[0022] The temperature of the deaerator is maintained within the range of 110-120° C., and the pressure of the deaerator is maintained at a slightly positive pressure state of the saturation pressure corresponding to the temperature.

[0023] Wherein, maintaining the pressure of the deaerator at a slightly positive pressure state corresponding to the saturation pressure at the temperature includes:

[0024] Keep the exhaust pipeline of the deaerator unobstructed;

[0025] The non-condensable gas in the deaerator is discharged in time through the exhaust pipeline, so that the oxygen content in the deaerator is maintained at less than 5 ppb.

[0026] Wherein, after the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the starting feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes:

[0027] The liquid level of the deaerator is dynamically maintained between 150 mm and 800 mm through water supplementation regulation and exhaust steam loss.

[0028] Wherein, dynamically maintaining the liquid level of the deaerator between 150 mm and 800 mm by adjusting the water supply and exhaust steam loss includes:

[0029] When the liquid level of the deaerator is lower than 150mm, water is added to the deaerator through the water supply pipeline at the outlet of the condensate pump, and the internal leakage of the valve is adjusted to meet the water supply demand according to the actual operating conditions of the system;

[0030] When the liquid level of the deaerator is higher than 800 mm, the liquid level of the deaerator is lowered by exhausting steam on the steam side or draining water at the remote end.

[0031] Wherein, after the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the starting feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes:

[0032] The outlet regulating valve of the starting water supply pump is used to control the pressure of the water supply inlet manifold within the range of 2.8-3.2 MPa.g, so that the heating pipeline is maintained under positive pressure conditions to avoid cavitation operation.

[0033] Wherein, before controlling the pressure of the water supply inlet manifold to be within the range of 2.8-3.2 MPa.g by the outlet regulating valve of the starting water supply pump, the method further includes:

[0034] Control the cooling rate of the high-pressure heater, where the feed water temperature rise does not exceed 3°C / min and the temperature drop does not exceed 2°C / min.

[0035] In a second aspect, the present invention further provides a secondary circuit water supply system for a nuclear power plant, comprising:

[0036] Condenser;

[0037] A deaerator, wherein the deaerator is provided with an exhaust line discharged to the atmosphere;

[0038] A starting water supply pump is connected to the deaerator, and the starting water supply pump is used to convert mechanical energy into heat energy during operation to maintain the temperature of the deaerator;

[0039] A water supply inlet manifold connected to the starting water supply pump;

[0040] A high-pressure heater, arranged between the startup water supply pump and the deaerator;

[0041] A main feedwater pump system, arranged between the high-pressure heater and the deaerator;

[0042] an isolation device for mechanically isolating the condenser from the hot pipeline of the secondary circuit; and a deaerator circulation system, comprising:

[0043] A first connecting pipeline for forming a first circulation channel, wherein the first circulation channel transports the feed water at the outlet of the deaerator to the feed water inlet manifold via the startup feed water pump and then returns to the deaerator;

[0044] a second connecting pipeline for forming a second circulation channel, wherein the second circulation channel returns the feed water from the outlet of the startup feed water pump to the deaerator via the high-pressure heater and the main feed water pump system;

[0045] A third connecting pipeline is used to form a third circulation channel, and the third circulation channel returns the feed water at the outlet of the deaerator to the deaerator through the start-up feed water pump and the feed water inlet manifold through the warm pipe line.

[0046] Among them, it also includes:

[0047] A condensate pump, wherein the outlet of the condensate pump is provided with a deaerator water supply pipeline, one end of the deaerator water supply pipeline is connected to the outlet of the condensate pump, and the other end is connected to the deaerator;

[0048] An auxiliary steam pipeline is connected to the deaerator.

[0049] Wherein, the isolation device comprises:

[0050] a deaerator water supply isolation valve and a deaerator water supply regulating valve provided on the condensate extraction system where the condensate pump is located, wherein the deaerator water supply isolation valve is used to maintain the water supply function of the condensate extraction system, and the deaerator water supply regulating valve is used to control the water supply to the deaerator;

[0051] An exhaust valve disposed between the high-pressure heater and the deaerator, the exhaust valve being used to control exhaust from the high-pressure heater to the deaerator;

[0052] A feedwater deaerator valve disposed between the deaerator and the condenser, for controlling the connection between the deaerator and the condenser; and

[0053] The sampling valve and steam trap installed on the low-pressure heater are used for water quality monitoring and maintenance discharge of the low-pressure heater.

[0054] The beneficial technical effects of the present invention are as follows: by mechanically isolating the condenser from the hot pipeline of the secondary circuit and establishing a deaerator circulation system including multiple circulation channels, the temperature of the deaerator is maintained by utilizing the conversion of mechanical energy into thermal energy when the feed water pump is started, thereby achieving stable operation of the secondary circuit water supply system under a vacuum state, avoiding the steps of withdrawing the primary circuit and replacing the secondary circuit water with oxygen-free water in traditional processes, and significantly shortening the maintenance period. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0056] Figure 1 A schematic diagram of the steps of a state control method for a secondary water supply system of a nuclear power plant provided by an embodiment of the present invention;

[0057] Figure 2 A schematic diagram of a sub-step of a state control method for a secondary water supply system of a nuclear power plant provided by an embodiment of the present invention;

[0058] Figure 3 A schematic diagram of another sub-step of the state control method of the secondary water supply system of a nuclear power plant provided by an embodiment of the present invention;

[0059] Figure 4 Schematic diagram of a secondary water supply system for a nuclear power plant provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0062] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0063] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0064] Please also refer to Figure 1-Figure 3 The embodiment of the present invention provides a state control method for a secondary circuit water supply system of a nuclear power plant. When it is necessary to destroy the vacuum of the secondary circuit for equipment maintenance, the following steps are performed:

[0065] S100, mechanically isolate the hot secondary circuit pipeline connected to the condenser;

[0066] Establish a deaerator circulation system, including:

[0067] S201. After the feed water at the outlet of the deaerator is transported to the feed water inlet manifold through the start-up feed water pump, it returns to the deaerator through the (ARE) warm pipe (circulation) pipeline to form a first circulation channel; S202. The feed water at the outlet of the start-up feed water pump is returned to the deaerator through the high-pressure heater and the main feed water pump system to form a second circulation channel; S300. In the deaerator circulation system, the temperature of the deaerator is maintained by utilizing the conversion of mechanical energy into thermal energy when the start-up feed water pump is running.

[0068] In this embodiment, when the unit needs to destroy the vacuum of the secondary circuit to eliminate the equipment fault, the condenser and the hot pipeline of the secondary circuit connected to it need to be mechanically isolated first. This isolation method can prevent high-temperature water from entering the condenser that has lost vacuum, prevent the condenser pressure from rising and causing the low-pressure cylinder bursting film to operate, and prevent the condenser temperature from exceeding the design temperature and causing component damage.

[0069] Then establish the deaerator circulation system. In the deaerator circulation system, first establish the first circulation channel S201: the feed water at the outlet of the deaerator is transported to the feed water inlet manifold through the start-up feed water pump (i.e., AAD pump) and then returns to the deaerator. This circulation channel can ensure the basic circulation function of the deaerator. At the same time, establish the second circulation channel S202: the feed water at the outlet of the start-up feed water pump passes through the high-pressure heater (AHP) 7# heater outlet, AHP6# inlet, main feed water pump (APA) warm pump pipeline, APA pump and then returns to the deaerator. This circulation loop can insulate the high-pressure heater and the main feed water pump system.

[0070] In the established deaerator circulation system, since the starting water pump has a motor power of 1400KW, the electrical energy will be converted into fluid mechanical energy and finally into thermal energy during operation. This heat usually exceeds the total heat loss of the deaerator circulation system, so that the entire deaerator circulation system does not need to open additional auxiliary steam for heating when the heat absorption is sufficient. When the heat generated by the deaerator circulation system is greater than the heat dissipation, the temperature of the deaerator will gradually increase, and the corresponding deaerator saturation pressure will increase accordingly. The amount of steam discharged from the deaerator to the atmosphere will also increase accordingly. Finally, the deaerator circulation system will reach dynamic equilibrium under the new temperature and pressure platform.

[0071] Through the implementation of the above steps, the state control method provided in this embodiment can achieve stable operation of the secondary circuit water supply system when the vacuum is broken. This method effectively solves the problems in the traditional process that when the vacuum is broken, the first circuit needs to retreat to a specified mode, and after the maintenance is completed, the vacuum needs to be re-established and the secondary circuit water needs to be replaced with oxygen-free water. It significantly shortens the maintenance period and provides the necessary conditions for equipment maintenance and defect elimination. Specifically, this method establishes a deaerator circulation system and maintains the deaerator and its subsequent pipelines in a hot circulation state, so that the water quality in the secondary circuit water supply system always remains in an oxygen-free state. This is because:

[0072] The deaerator circulation system operates continuously during the entire overhaul period. By maintaining appropriate temperature and pressure conditions (the deaerator is maintained at a saturation temperature of 110°C), the oxygen dissolved in the water can be continuously removed. Since the condenser has been separated from the hot pipeline by mechanical isolation, the destruction of the condenser vacuum will not affect the water quality in the deaerator circulation system. After the overhaul is completed, since the water quality in the deaerator and its subsequent pipelines always remains in an oxygen-free state, there is no need to re-carry out the time-consuming secondary circuit water oxygen-free water replacement process, and water can be directly supplied to the steam generator (SG) by starting the feed water pump.

[0073] This mode of operation significantly optimizes the maintenance process and can save about 12 hours of secondary circuit water oxygen-free water replacement time each time.

[0074] When the deaerator temperature is lower than 110℃, steam needs to be supplied to the deaerator through the auxiliary steam pipeline. By supplying auxiliary steam to the deaerator, multiple regulating effects can be produced: on the one hand, the heat of the deaerator circulation system can be increased; on the other hand, the supply of steam will promote the deaeration process and help maintain water quality; it can also help regulate system pressure.

[0075] In this embodiment, mechanical isolation is physical isolation, which means isolating the condenser and the hot secondary-circuit pipeline connected thereto by means of a valve.

[0076] In this embodiment, hot pipeline refers to a pipeline system that is in a high temperature state during operation. These pipelines usually transport high temperature media (such as steam or hot water) and maintain a high temperature during operation.

[0077] In one embodiment, S100, mechanically isolating the hot pipeline of the secondary circuit connected to the condenser includes:

[0078] S101. Keep the deaerator water supply isolation valve of the condensate extraction system open, and keep the deaerator water supply regulating valve closed;

[0079] S102. Close all valves that normally exhaust the high-pressure heater to the feedwater deaerator, and cut the drain to the drain discharge system;

[0080] S103, closing the feedwater deaerator valve on the connecting pipeline from the feedwater deaerator to the condenser, and keeping the auxiliary steam of the feedwater deaerator online;

[0081] S104. Close the sampling valve at the outlet of the low-pressure heater drain pump to prevent the return water of the heating pipe line from flowing back to the low-pressure feed water heater system.

[0082] In this embodiment, mechanically isolating the hot secondary pipes connected to the condenser involves valve configuration of multiple systems. The main purpose of this mechanical isolation is to prevent high-temperature water from entering the condenser when the vacuum is broken, thereby preventing equipment damage.

[0083] For the valve configuration of the condensate extraction system, the deaerator water isolation valve of the condensate extraction system needs to be kept open, while the deaerator water regulating valve needs to be kept closed. This configuration can ensure the necessary water supply function while preventing hot water from flowing back to the condensate extraction system. In addition, the steam generator drain needs to be cut to the drain discharge system, and the steam turbine generator set drain needs to be switched from the condensate extraction system to the drain discharge system. Such an isolation configuration forms a complete condensate system isolation chain.

[0084] For the HP heater system, it is necessary to close all valves that normally exhaust the HP heater to the feedwater deaerator and cut the drain to the drain discharge system. This can prevent the high-temperature steam from the deaerator from flowing back to the HP heater drain side and eventually being discharged to the condenser.

[0085] For the feedwater deaerator system, the feedwater deaerator valve on the connecting pipeline from the feedwater deaerator to the condenser needs to be closed, while keeping the auxiliary steam of the feedwater deaerator online. As the key valve for the main isolation of the condenser, the feedwater deaerator valve needs to be kept in a closed state to prevent the hot water of the feedwater deaerator system from entering the condenser.

[0086] Finally, in order to prevent the return water from the warm pipe from flowing back through the low-pressure feedwater heater pipe, the sampling valve of the steam generator needs to be closed. This configuration can prevent the return water from the warm pipe of the main feedwater flow control system to the feedwater deaerator from flowing back to the low-pressure feedwater heater system, avoiding unnecessary heat loss or triggering the water hammer effect caused by hot water vaporization.

[0087] Through the above detailed isolation measures, the following technical effects can be achieved: effectively prevent high-temperature water from entering the condenser that has lost vacuum, avoiding damage to the equipment; maintain the necessary circulation function of the system to ensure the safe operation of the equipment; prevent hot water backflow and cross-flow, reduce system energy loss; avoid water hammer caused by pressure and temperature changes. These isolation measures jointly ensure the safe and stable operation of the secondary circuit water supply system under the condition of breaking vacuum.

[0088] In one embodiment, after the feed water at the outlet of the start-up feed water pump is returned to the deaerator via the high-pressure heater and the main feed water pump system to form a second circulation channel, establishing the deaerator circulation system also includes: S203, returning the feed water at the outlet of the deaerator via the start-up feed water pump to the deaerator through the (small flow and) secondary circulation pipeline to form a third circulation channel.

[0089] In this embodiment, the specific path of the third circulation channel is: deaerator → start water supply pump → water supply inlet manifold → warm pipe pipeline → deaerator. The establishment of the third circulation channel has the following technical effects:

[0090] The entire water supply system after the deaerator forms a complete thermal cycle, ensuring the stable operation of the secondary water supply system under the condition of breaking the vacuum; ensuring the continuous circulation of water in the warm pipe line to prevent precipitation or scaling of water in the pipeline; by increasing the circulation loop, the stability of the deaerator circulation system is improved, so that the entire deaerator circulation system forms a more reliable thermal balance state.

[0091] In the third circulation channel, starting the water supply pump to maintain the startup state has a dual role: on the one hand, as the heat generation source of the entire hot standby system circulation, the pump group self-circulation converts electrical energy into fluid mechanical energy and finally into thermal energy; on the other hand, it can ensure that the temperature of the upper and lower shells of the pump group is uniform, avoiding the temperature difference between the upper and lower parts being greater than 16°C and locking the start-up of the water supply pump group, which would affect the subsequent normal water supply.

[0092] By establishing the third circulation channel, combined with the first circulation channel and the second circulation channel, a complete deaerator circulation system is formed. This multi-channel circulation design can better maintain the stable operation of the secondary circuit water supply system under the vacuum state, creating favorable conditions for equipment maintenance and troubleshooting.

[0093] In one embodiment, S203, after the feed water at the outlet of the deaerator is started by the feed water pump and returned to the deaerator through the secondary circulation pipeline to form a third circulation channel, the state control method also includes: calculating the total heat dissipation of the deaerator circulation system, the total heat dissipation includes the natural heat dissipation of the pipeline, the exhaust steam loss of the deaerator and the condensate supply loss; wherein, when the heat generated by starting the feed water pump is greater than the total heat dissipation, the exhaust volume of the deaerator exhaust pipeline is adjusted to make the deaerator circulation system reach dynamic balance at a new temperature and pressure platform.

[0094] In this embodiment, it is first necessary to calculate the total heat dissipation of the deaerator circulation system, which is mainly composed of three parts: natural heat dissipation of the pipeline, exhaust steam loss of the deaerator, and condensate supply loss. Among them, the natural heat dissipation of the pipeline refers to the natural heat dissipation loss of the hot circulation system pipeline to the environment; the exhaust steam loss of the deaerator refers to the heat discharged by the deaerator to the atmosphere through the exhaust pipeline; the condensate supply loss refers to the heat required to heat the cold water entering the deaerator. These three parts of heat loss can be expressed by the following formula: total heat dissipation = natural heat dissipation of the pipeline + exhaust steam loss of the deaerator + condensate supply loss.

[0095] At the same time, the heat generated by the system mainly comes from the conversion of electrical energy into thermal energy of the fluid when the start-up feedwater pump is running. Since the motor power of the start-up feedwater pump reaches 1400KW, the heat generated by it may have exceeded the total heat dissipation loss of the system. In this case, the entire circulation system is in a state of sufficient heat generation, and there is no need to turn on auxiliary steam for additional heating.

[0096] When the heat generated by starting the feedwater pump is greater than the total heat dissipation of the system, the system will automatically enter a new equilibrium state: the temperature of the deaerator will gradually increase; the corresponding deaerator saturation pressure will increase accordingly; the amount of steam discharged from the deaerator to the atmosphere will increase accordingly; and finally a dynamic equilibrium is reached under the new temperature and pressure platform. In order to maintain this thermal equilibrium state, this embodiment achieves this by adjusting the exhaust line at the top of the deaerator. When the system needs to lower the temperature, the exhaust volume can be appropriately increased; when the temperature needs to be maintained, the exhaust volume can be reduced. This adaptive adjustment method enables the entire system to maintain thermal stability and qualified oxygen content by itself without the need for frequent human intervention.

[0097] Through the implementation of the above heat balance control scheme, it can be ensured that the deaerator circulation system is always in a stable and reliable operating state, providing guarantee for safe operation during equipment maintenance and troubleshooting. This control method based on heat balance not only improves the reliability of system operation, but also reduces the labor cost of operation and maintenance.

[0098] In one embodiment, after S203, the feed water at the outlet of the deaerator is started by the feed water pump and returned to the deaerator through the secondary circulation pipeline to form a third circulation channel, the state control method also includes: S204, maintaining the temperature of the deaerator within the range of 110-120°C, and maintaining the pressure of the deaerator at a slightly positive pressure state of the saturation pressure corresponding to the temperature.

[0099] In this embodiment, the temperature control of the deaerator circulation system needs to be maintained within the range of 110-120°C. Among them, 110°C is the minimum temperature requirement to ensure the deoxygenation effect, and the oxygen dissolved in the water can be effectively removed at this temperature. The upper limit temperature of 120°C takes into account the avoidance of reverse heating of a circuit when supplying water to the steam generator during the upward phase of the unit. Specifically in actual operation, the entire circulation pipeline of the deaerator-main feed water pump-high-pressure heater-main feed water flow control system needs to be maintained within this temperature range.

[0100] Regarding the pressure control requirements, this embodiment requires that the deaerator pressure be maintained at a slightly positive pressure of 43 kPa.g. First, it can prevent the outside air from flowing back into the secondary circuit water supply system; second, the pressure of 43 kPa.g matches the temperature range of 110, which can ensure that the deaerator circulation system operates stably under saturation; finally, this pressure state is conducive to the discharge of non-condensable gas in the deaerator, ensuring the deoxidation effect.

[0101] The two parameters of temperature and pressure are interrelated. In actual operation, when the heat generated by starting the feedwater pump is greater than the heat dissipation of the deaerator circulation system, the deaerator temperature will rise, and the temperature increase will cause the saturation pressure to increase. The pressure increase will increase the amount of steam discharged to the atmosphere. Eventually, the deaerator circulation system will reach a dynamic balance on the new temperature and pressure platform. By strictly controlling these operating parameters, it can be ensured that the deaerator circulation system is always in a stable and reliable operating state, providing a guarantee for safe operation during equipment maintenance and troubleshooting.

[0102] In one embodiment, maintaining the pressure of the deaerator at a slightly positive pressure state of the saturation pressure corresponding to the temperature includes: keeping the exhaust pipeline of the deaerator unobstructed; and timely discharging the non-condensable gas in the deaerator through the exhaust pipeline to maintain the oxygen content in the deaerator at less than 5ppb.

[0103] In this embodiment, in order to maintain the deaerator in an operating state with a saturation temperature of 110°C under a slightly positive pressure of 43 kPa.g, this embodiment adopts the following three measures:

[0104] First, maintain the deaerator pressure in a slightly positive state. When the feedwater pump is started to maintain a closed-loop circulation, the deaerator temperature can be maintained at around 117°C by relying solely on the heat generated by the self-circulation of the pump group, without the need for additional auxiliary steam supply. By adjusting the opening of each control valve in the deaerator circulation system, the deaerator circulation system pressure can be stabilized in a slightly positive state.

[0105] Second, ensure that the pipeline from the top of the deaerator to the atmosphere remains unobstructed. The importance of this measure is reflected in the following aspects: it can timely discharge the non-condensable gas accumulated in the deaerator circulation system; it can balance the pressure of the deaerator circulation system by adjusting the exhaust volume; when the temperature or pressure of the deaerator circulation system increases, it can release excess steam through this pipeline to maintain the dynamic balance of the deaerator circulation system.

[0106] Third, timely discharge of non-condensable gas is achieved to maintain the oxygen content in the deaerator at a level less than 5ppb. This control target is achieved through the following mechanisms: According to Dalton's law of partial pressure and Henry's law, at a given temperature, the content of dissolved gas in the deaerator circulation system is proportional to its partial pressure; by maintaining a slightly positive pressure state in the deaerator circulation system and keeping the top exhaust unobstructed, the partial pressure of oxygen can be continuously reduced; at a saturated temperature of 110°C, the solubility of dissolved oxygen in water is significantly reduced. Combining the above factors, the oxygen content in the deaerator circulation system can be controlled below 5ppb.

[0107] In one embodiment, S203, after the feed water at the outlet of the deaerator is started by the feed water pump and returned to the deaerator through the secondary circulation pipeline to form a third circulation channel, the state control method also includes: dynamically maintaining the liquid level of the deaerator between the high and low liquid levels of 150mm and 800mm through water replenishment adjustment and exhaust steam loss; when the liquid level of the deaerator is lower than 150mm, replenishing water to the deaerator through the water supply pipeline at the outlet of the condensate pump, and adjusting the internal leakage of the valve to meet the water replenishment demand according to the actual operating conditions of the system; when the liquid level of the deaerator is higher than 800mm, lowering the liquid level of the deaerator by exhausting steam on the steam side or draining water remotely.

[0108] In this embodiment, in order to ensure the stability of the deaerator circulation system, stable control of the deaerator liquid level is also an important factor. The low liquid level of 150mm is to ensure that the start-up water pump will not trip due to the low deaerator liquid level; the high liquid level of 800mm takes into account the physical capacity and safety margin of the deaerator. When the deaerator liquid level exceeds this range, corresponding adjustment measures need to be taken.

[0109] Specifically, when the deaerator liquid level drops below 150mm, it is necessary to actively or passively replenish water to the deaerator through the condensate pump outlet water supply line. The main factors causing the deaerator liquid level to drop include: the reduction in water volume caused by the exhaust steam loss of the deaerator (based on operating experience, the exhaust steam loss is converted to the liquid level of about 5mm / h), the loss of sampling water, and abnormal leakage of the system. If these losses are not replenished in time, the stable operation of the deaerator circulation system may be affected. Normal water replenishment requires opening the regulating (throttling) valve and actively supplying water to the deaerator through the water supply pipeline. However, under normal circumstances, the regulating valve will not be very tight, and a small amount of water will be supplied to the deaerator (passively) through the water supply pipeline. Therefore, the internal leakage of the regulating valve can be adjusted according to the operating conditions to meet the water replenishment needs.

[0110] When the deaerator liquid level rises above 800mm, the liquid level can be lowered not only by exhaust steam loss, but also by finding a drainage (pipeline) point at the far end (downstream) of the deaerator.

[0111] In actual operation, in order to ensure the continuity of operation and the stable operation of the system, it is recommended to control the deaerator liquid level in the middle area (about 500mm) during shift change. Especially before the system is shut down, the liquid level should be controlled at a high position as much as possible, which can: avoid the need for frequent water replenishment due to deaerator exhaust steam loss; provide sufficient operating margin for the system; and ensure the stable operation of the system under various working conditions.

[0112] In one embodiment, after the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline to form a third circulation channel by starting the feed water pump, the state control method also includes: controlling the pressure of the feed water inlet manifold within the range of 2.8-3.2MPa.g by starting the outlet regulating valve of the feed water pump, so that the heating pipeline is maintained under positive pressure conditions to avoid cavitation operation.

[0113] In this embodiment, the pressure range can ensure that the heating pipeline is maintained under positive pressure to avoid cavitation, and effectively prevent the hot water in the pipeline from vaporizing due to pressure reduction. Once vaporization occurs in the heating pipeline, it will cause gas-liquid two-phase flow, which may cause severe water hammer effect and damage the equipment and pipelines.

[0114] Secondly, the selection of this pressure range also takes into account the pressure bearing capacity of the system equipment. The pressure of 2.8-3.2MPa.g can meet the operation requirements without causing excessive pressure burden on the equipment. This pressure control strategy has shown good results in actual operation. Even when operating at low power and below platforms, when the water supply flow of the start-up feedwater pump to the steam generator is small (usually less than 100t / h), the system can still maintain stable operation.

[0115] This pressure control method effectively avoids the phenomenon of decompression and vaporization of the upper medium in the heating pipe line from the main feedwater flow control system to the feedwater deaerator during the cooling process, thereby preventing the possible risk of severe vibration and equipment damage. Operators need to regularly monitor the pressure of the feedwater inlet manifold and adjust the opening of the start-up feedwater pump outlet regulating valve in time to ensure that the pressure is always maintained within the target range. This not only ensures the normal operation of the heating pipe line, but also provides an important guarantee for the stability of the entire deaerator circulation system.

[0116] In one embodiment, before starting the outlet regulating valve of the water feed pump to control the pressure of the water feed inlet manifold within the range of 2.8-3.2 MPa.g, it also includes: controlling the cooling rate of the high-pressure heater, wherein the temperature rise of the water feed does not exceed 3°C / min, and the temperature drop does not exceed 2°C / min.

[0117] In this embodiment, controlling the cooling rate of the high-pressure heater is an important measure to protect the safe operation of the equipment. Too fast temperature changes will cause large thermal stress on the heat exchange tubes of the high-pressure heater. Such excessive thermal stress may cause damage to the heat exchange tubes and affect the safe operation of the equipment.

[0118] This embodiment controls the temperature change rate of the high-pressure heater from two aspects: feed water temperature rise and temperature drop. The specific control requirements are: the feed water temperature rise rate does not exceed 3°C / min, and the temperature drop rate does not exceed 2°C / min. The setting of these control parameters takes into account the temperature bearing capacity of the equipment and the safety margin of the system, which can avoid damage to the high-pressure heater heat exchange tube due to excessively rapid temperature changes.

[0119] By strictly implementing the above cooling rate control requirements, thermal stress damage to the equipment caused by rapid temperature changes can be effectively avoided, ensuring the safe and reliable operation of the high-pressure heater during various operating conditions.

[0120] like Figure 4 As shown, corresponding to the above nuclear power plant secondary water supply system, an embodiment of the present invention further provides a nuclear power plant secondary water supply system. The secondary water supply system includes a condenser, a deaerator, a start-up water supply pump, a water supply inlet header, a high-pressure heater, a main water supply pump system, an isolation device and a deaerator circulation system.

[0121] In this embodiment, an exhaust line to the atmosphere is provided at the top of the deaerator. The exhaust line is used to discharge non-condensable gas to ensure the deoxygenation effect. According to Dalton's law of partial pressure and Henry's law, at a given temperature, the content of dissolved gas in the system is proportional to its partial pressure. By maintaining the deaerator in a slightly positive pressure state and keeping the top exhaust unobstructed, the partial pressure of oxygen can be continuously reduced, thereby controlling the oxygen content in the system to a qualified level (usually less than 5 ppb).

[0122] The inlet of the startup water pump is connected to the outlet of the deaerator. The startup water pump has a motor power of 1400KW. When running, the startup water pump can convert electrical energy into fluid mechanical energy, and finally into heat energy to maintain the temperature of the deaerator. This design makes full use of the heat generated by the startup water pump when it is running, reducing the system's dependence on external heat sources.

[0123] The feedwater inlet manifold is connected to the outlet of the start-up feedwater pump. The feedwater inlet manifold serves as the collection point of the system and connects multiple circulation loops. The high-pressure heater is set between the outlet of the start-up feedwater pump and the deaerator, and the main feedwater pump system is set between the high-pressure heater and the deaerator. This arrangement allows the feedwater to be fully heated when passing through the high-pressure heater, thereby improving the thermal efficiency of the system.

[0124] The isolation device is used to mechanically isolate the condenser from the hot pipeline of the secondary circuit. This isolation configuration can effectively prevent high-temperature water from entering the condenser that has lost its vacuum, avoid the low-pressure cylinder bursting membrane caused by the increase of condenser pressure or equipment damage caused by the temperature exceeding the design value.

[0125] The deaerator circulation system is the core part of this embodiment, and includes three circulation channels: the first circulation channel is formed by the first connecting pipeline, and the feed water at the outlet of the deaerator is transported to the feed water inlet manifold after starting the feed water pump and then returned to the deaerator; the second circulation channel is formed by the second connecting pipeline, and the feed water at the outlet of the start-up feed water pump is returned to the deaerator through the high-pressure heater and the main feed water pump system; the third circulation channel is formed by the third connecting pipeline, and the feed water at the outlet of the deaerator is returned to the deaerator through the warm pipe pipeline after starting the feed water pump and the feed water inlet manifold.

[0126] This multi-channel circulation design can better maintain the stable operation of the secondary water supply system under the condition of breaking the vacuum. The coordinated work of the three circulation channels can: ensure that the entire water supply system after the deaerator forms a complete thermal cycle; ensure that the water quality in the warm pipe line continues to circulate and flow, and prevent the water quality in the pipe from precipitating or scaling; at the same time, by increasing the circulation loop, the stability of the system is improved, so that the entire deaerator circulation system forms a more reliable thermal balance state.

[0127] In one embodiment, it also includes: a condensate pump, a deaerator water supply pipeline is provided at the outlet of the condensate pump, one end of the deaerator water supply pipeline is connected to the outlet of the condensate pump, and the other end is connected to the deaerator; an auxiliary steam pipeline, the auxiliary steam pipeline is connected to the deaerator; and a regenerative heat exchanger, the cooling water outlet of the regenerative heat exchanger is connected to the deaerator.

[0128] On the basis of the above-mentioned two-circuit water supply system, this embodiment also includes auxiliary equipment for replenishing and adjusting the water volume of the system. Specifically, the two-circuit water supply system is additionally provided with a condensate pump, an auxiliary steam pipeline and a regenerative heat exchanger. Among them, a deaerator water supply pipeline is provided at the outlet of the condensate pump, one end of which is connected to the outlet of the condensate pump and the other end is connected to the deaerator. This design can timely replenish the water loss of the deaerator caused by exhaust steam and other reasons, and maintain the stability of the deaerator liquid level.

[0129] The auxiliary steam pipeline is connected to the deaerator. In the initial stage of system startup, the deaerator can be heated by auxiliary steam to quickly establish the required temperature and pressure conditions; secondly, when the heat generated by the startup feedwater pump is not enough to maintain the system temperature, auxiliary steam can be used to supplement the heat. Figure 4 CEX is the valve of the condensate pump system.

[0130] In one embodiment, the isolation device includes: a deaerator water supply isolation valve and a deaerator water supply regulating valve arranged on the condensate extraction system where the condensate pump is located, the deaerator water supply isolation valve is used to maintain the water supply function of the condensate extraction system, and the deaerator water supply regulating valve is used to control the water supply to the deaerator; an exhaust valve arranged between the high-pressure heater and the deaerator, and the exhaust valve is used to control the exhaust of the high-pressure heater to the deaerator; a feed water deaerator valve arranged between the deaerator and the condenser, which is used to control the connection between the deaerator and the condenser; and a sampling valve and a steam trap arranged on the low-pressure heater, which are used for water quality monitoring and maintenance discharge of the low-pressure heater.

[0131] In this embodiment, first, a deaerator water supply isolation valve and a deaerator water supply regulating valve are set on the condensate extraction system. The deaerator water supply isolation valve is kept in an open state to maintain the basic water supply function of the condensate extraction system; the deaerator water supply regulating valve is kept in a manually closed state to accurately control the amount of water replenishment to the deaerator. Practical experience shows that the internal leakage of the deaerator water supply regulating valve and the steam loss of the deaerator (about 5mm / h) are basically kept in dynamic balance, and the deaerator liquid level can be maintained at a control value of about 500mm.

[0132] Secondly, exhaust valves are set between the high-pressure heater and the deaerator. These exhaust valves are used to control the exhaust from the high-pressure heater to the deaerator. By closing all the exhaust valves from the high-pressure heater system to the deaerator system, high-temperature steam can be prevented from entering the deaerator through the exhaust system and affecting the stability of the system.

[0133] Third, a feedwater deaerator valve is installed between the deaerator and the condenser. This valve is the key valve for the main isolation of the condenser to ensure that the hot water of the deaerator system does not enter the condenser. At the same time, the deaerator system still needs to maintain the online state of auxiliary steam deaeration.

[0134] Finally, in the low pressure heater (i.e. Figure 4 Sampling valves and steam traps are set on the low pressure heater in the pipeline to prevent the return of hot water in the pipeline by isolating these valves, thereby avoiding unnecessary heat loss or water hammer effect caused by hot water vaporization.

[0135] Through the above detailed isolation measures, the following technical effects can be achieved: effectively prevent high-temperature water from entering the condenser that has lost vacuum, avoiding damage to the equipment; maintain the necessary circulation function of the system to ensure the safe operation of the equipment; prevent hot water backflow and cross-flow, reducing system energy loss; avoid water hammer caused by pressure and temperature changes.

[0136] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A state control method for a secondary circuit water supply system of a nuclear power plant, characterized in that: Applied to the secondary water supply system of a nuclear power plant, the state control method of the secondary water supply system of the nuclear power plant comprises: when it is necessary to destroy the vacuum of the secondary circuit for equipment maintenance, executing the following steps: Mechanically isolate the condenser from the hot secondary circuit piping connected to it; Establishing a deaerator circulation system, including: after the feed water at the outlet of the deaerator is transported to the feed water inlet manifold through the startup feed water pump, it returns to the deaerator through the warm pipe line to form a first circulation channel; the feed water at the outlet of the startup feed water pump is returned to the deaerator through the high-pressure heater and the main feed water pump system to form a second circulation channel; In the deaerator circulation system, the temperature of the deaerator is maintained by converting the mechanical energy into thermal energy when the startup water supply pump is running.

2. The state control method of the secondary circuit water supply system of a nuclear power plant according to claim 1, characterized in that: The mechanical isolation of the hot pipeline of the secondary circuit connected to the condenser includes: Keep the deaerator water supply isolation valve of the condensate extraction system open, and keep the deaerator water supply regulating valve closed; Close all valves that normally exhaust the high-pressure heater to the feedwater deaerator, and cut the drain to the drain discharge system; Close the feedwater deaerator valve on the connecting pipeline from the feedwater deaerator to the condenser, and keep the auxiliary steam of the feedwater deaerator online; Close the sampling valve at the outlet of the low-pressure heater drain pump to prevent the return water from the heating pipe line from flowing back to the low-pressure feedwater heater system.

3. The state control method of the secondary circuit water supply system of a nuclear power plant according to claim 1, characterized in that: After the feed water at the outlet of the startup feed water pump is returned to the deaerator via the high pressure heater and the main feed water pump system to form a second circulation channel, the step of establishing the deaerator circulation system further includes: The feed water at the outlet of the deaerator is returned to the deaerator through the start-up feed water pump and the secondary circulation pipeline to form a third circulation channel.

4. The state control method of the secondary water supply system of a nuclear power plant according to claim 3, characterized in that: After the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the start-up feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes: Calculate the total heat dissipation of the deaerator circulation system, wherein the total heat dissipation includes natural heat dissipation of pipelines, exhaust steam loss of the deaerator and condensate supply loss; When the heat generated by the startup water supply pump is greater than the total heat dissipation, the deaerator circulation system reaches a dynamic balance at a new temperature and pressure platform by adjusting the exhaust volume of the deaerator exhaust pipeline.

5. The state control method of the secondary water supply system of a nuclear power plant according to claim 3, characterized in that: After the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the start-up feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes: The temperature of the deaerator is maintained within the range of 110-120° C., and the pressure of the deaerator is maintained at a slightly positive pressure state of the saturation pressure corresponding to the temperature.

6. The state control method of the secondary water supply system of a nuclear power plant according to claim 5, characterized in that: The method of maintaining the pressure of the deaerator at a slightly positive pressure state corresponding to the saturation pressure at the temperature includes: Keep the exhaust pipeline of the deaerator unobstructed; The non-condensable gas in the deaerator is discharged in time through the exhaust pipeline, so that the oxygen content in the deaerator is maintained at less than 5 ppb.

7. The state control method of the secondary water supply system of a nuclear power plant according to claim 3, characterized in that: After the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the start-up feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes: The liquid level of the deaerator is dynamically maintained between 150 mm and 800 mm through water supplementation regulation and exhaust steam loss.

8. The state control method of the secondary water supply system of a nuclear power plant according to claim 7, characterized in that: The method of dynamically maintaining the liquid level of the deaerator between 150 mm and 800 mm by adjusting the water supply and exhaust steam loss comprises: When the liquid level of the deaerator is lower than 150mm, water is added to the deaerator through the water supply pipeline at the outlet of the condensate pump, and the internal leakage of the valve is adjusted to meet the water supply demand according to the actual operating conditions of the system; When the liquid level of the deaerator is higher than 800 mm, the liquid level of the deaerator is lowered by exhausting steam on the steam side or draining water at the remote end.

9. The state control method of the secondary water supply system of a nuclear power plant according to claim 3, characterized in that: After the feed water at the outlet of the deaerator is returned to the deaerator through the secondary circulation pipeline via the start-up feed water pump to form a third circulation channel, the state control method of the secondary circuit feed water system of the nuclear power plant further includes: The outlet regulating valve of the starting water supply pump is used to control the pressure of the water supply inlet manifold within the range of 2.8-3.2 MPa.g, so that the heating pipeline is maintained under positive pressure conditions to avoid cavitation operation.

10. The state control method of the secondary circuit water supply system of a nuclear power plant according to claim 9, characterized in that: Before controlling the pressure of the water supply inlet manifold to be within the range of 2.8-3.2 MPa.g by the outlet regulating valve of the starting water supply pump, the method further comprises: Control the cooling rate of the high-pressure heater, where the feed water temperature rise does not exceed 3°C / min and the temperature drop does not exceed 2°C / min.

11. A secondary circuit water supply system for a nuclear power plant, characterized in that: include: Condenser; A deaerator, wherein the deaerator is provided with an exhaust line discharged to the atmosphere; A starting water supply pump is connected to the deaerator, and the starting water supply pump is used to convert mechanical energy into heat energy during operation to maintain the temperature of the deaerator; A water supply inlet manifold connected to the starting water supply pump; A high-pressure heater, arranged between the startup water supply pump and the deaerator; A main feedwater pump system, arranged between the high-pressure heater and the deaerator; An isolation device, used for mechanically isolating the condenser from the hot pipeline of the secondary circuit; as well as Deaerator circulation system, including: A first connecting pipeline for forming a first circulation channel, wherein the first circulation channel transports the feed water at the outlet of the deaerator to the feed water inlet manifold via the startup feed water pump and then returns to the deaerator; a second connecting pipeline for forming a second circulation channel, wherein the second circulation channel returns the feed water from the outlet of the startup feed water pump to the deaerator via the high-pressure heater and the main feed water pump system; A third connecting pipeline is used to form a third circulation channel, and the third circulation channel returns the feed water at the outlet of the deaerator to the deaerator through the start-up feed water pump and the feed water inlet manifold through the warm pipe line.

12. The secondary circuit water supply system according to claim 11, characterized in that: Also includes: A condensate pump, wherein the outlet of the condensate pump is provided with a deaerator water supply pipeline, one end of the deaerator water supply pipeline is connected to the outlet of the condensate pump, and the other end is connected to the deaerator; An auxiliary steam pipeline is connected to the deaerator.

13. The secondary circuit water supply system according to claim 11, characterized in that: The isolation device comprises: a deaerator water supply isolation valve and a deaerator water supply regulating valve provided on the condensate extraction system where the condensate pump is located, wherein the deaerator water supply isolation valve is used to maintain the water supply function of the condensate extraction system, and the deaerator water supply regulating valve is used to control the water supply to the deaerator; An exhaust valve disposed between the high-pressure heater and the deaerator, the exhaust valve being used to control exhaust from the high-pressure heater to the deaerator; A feedwater deaerator valve disposed between the deaerator and the condenser, for controlling the connection between the deaerator and the condenser; and The sampling valve and the steam trap arranged on the low-pressure heater are used for water quality monitoring and maintenance discharge of the low-pressure heater.

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