Starting water supply system applied to modular high-temperature gas cooled reactor nuclear power plant

Abstract

The invention relates to the technical field of thermal hydraulic control of a nuclear power plant, and discloses a starting water supply system applied to a modular high-temperature gas cooled reactor nuclear power plant, which comprises a starting water supply deaerator, a starting water supply pump, a water supply pipe network assembly and a distributed control system. The water supply pipe network is physically connected to the downstream of the main feed pump outlet isolation valve. The control system adjusts the deaerator to heat steam and replenish water based on the energy balance principle, so that the feed water temperature tracks the dynamic set value in real time; thermal shock protection logic is integrated, water inlet temperature difference and temperature change rate are limited, and thermal stress damage of equipment is prevented; undisturbed switching logic based on flow conservation and cross amplitude limiting is adopted, and the total flow is maintained to be constant through double-valve cooperative adjustment when switching from starting water supply to main water supply. The problem of feed water temperature matching under asymmetric operation of a multi-module unit is solved, stable switching of water supply modes is achieved, and the standby water supply function under the working condition that main water supply is lost is achieved.

Description

Technical Field

[0001] This invention relates to the field of thermal-hydraulic control technology for nuclear power plants, specifically to a start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant. Background Technology

[0002] Modular high-temperature gas-cooled reactor (HTGR) nuclear power plants typically employ a multi-reactor-one-unit configuration, where multiple nuclear steam supply system modules (NSSS) share a single conventional island turbine generator unit and main feedwater system. While this unique configuration enhances the plant's availability and operational flexibility, it also presents significant challenges to the design and control of auxiliary systems, particularly in the configuration and logic control of the feedwater system. In actual operation, asymmetric conditions frequently arise where the operating states of different reactor modules are inconsistent. For example, one module may be operating at full power while another is in the startup phase after a cold shutdown or in a hot standby phase.

[0003] In existing start-up feedwater system designs, the start-up feedwater pipeline is often directly drawn from the shared main feedwater deaerator or connected via a simple bypass. This strongly coupled design causes the start-up feedwater temperature to be heavily dependent on the real-time status of the main system on the conventional island. When the power plant is operating under asymmetrical conditions, the water temperature in the main deaerator is determined by the high-power modules in operation, maintaining a high-temperature, high-pressure state. At this time, if another module needs to perform a cold start-up or warm-state cleaning, the high-temperature feedwater is directly injected into the low-temperature steam generator, generating enormous transient thermal stress on the thick-walled tube sheet, shell, and heat transfer tube bundle of the steam generator. Conversely, if the main system is under low-load, low-temperature conditions, while the module to be started is in a hot state, the low-temperature feedwater will also cause cold shock. Existing technology lacks a means to independently regulate the feedwater temperature independent of the main system, making it difficult to meet the strict limitations on the thermal shock threshold of steam generator materials. Long-term operation can easily lead to equipment fatigue damage or even structural failure.

[0004] Furthermore, the switching process from the start-up feedwater system to the main feedwater system is the most critical thermal-hydraulic transient process during unit startup. Existing control strategies typically employ a relatively coarse open-loop sequential control or manual adjustment mode, simply opening the main feedwater valve and closing the start-up feedwater valve after the main feedwater pump starts. Because the flow characteristic curves of the start-up feedwater regulating valve and the main feedwater regulating mechanism differ, and the pressure difference between them dynamically changes with operating conditions, this non-coordinated switching operation easily leads to drastic fluctuations in the total flow rate entering the steam generator. For high-temperature gas-cooled reactors using once-through steam generators, the secondary side water volume is small and extremely sensitive to flow rate changes. Flow disturbances can quickly trigger spurious fluctuations in water level (false water level phenomenon), which in turn triggers high / low water level shutdown signals in the reactor protection system, leading to startup failure and severely impacting the unit's economic efficiency and operational stability.

[0005] In summary, existing start-up feedwater systems have significant shortcomings in matching thermal parameters and ensuring smooth switching of multi-module units, and cannot effectively guarantee the structural integrity of critical equipment and the stability of process parameters under complex asymmetric operating conditions. Therefore, there is an urgent need for a start-up feedwater system with independent thermal regulation capabilities and the ability to achieve disturbance-free switching. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a start-up feedwater system for modular high-temperature gas-cooled reactor nuclear power plants. It solves the problems of thermal shock caused by the inability of the start-up feedwater temperature to independently match the thermal state of the equipment under asymmetric operating conditions, as well as the instability of unit operation caused by flow disturbances during the switching process from start-up feedwater to main feedwater.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant. The system is physically independent of the main feedwater system of the nuclear power plant and includes a start-up feedwater deaerator, a start-up feedwater pump, a water supply network assembly, and a distributed control system.

[0008] The start-up feedwater deaerator is equipped with a makeup water inlet and a heating steam inlet for receiving external water and heat sources, heating and deoxygenating the input fluid, and establishing a thermo-mass balance. The suction inlet of the start-up feedwater pump is connected to the liquid outlet of the start-up feedwater deaerator via a pipeline to provide fluid transport power. The water supply network assembly is connected between the discharge outlet of the start-up feedwater pump and the feedwater inlet of at least one steam generator. The distributed control system is signal-connected to the start-up feedwater deaerator, the start-up feedwater pump, and the water supply network assembly for performing logical operations and outputting instructions.

[0009] In terms of connection topology, the physical connection point of the water supply network component is located downstream of the main feedwater pump outlet isolation valve of the main feedwater system and upstream of the feedwater inlet of the steam generator. This connection method allows the start-up feedwater system to form a parallel relationship with the main feedwater system, enabling it to independently supply water to the steam generator, or to supply water in coordination with the main feedwater system during switching.

[0010] Furthermore, to achieve flexible water source allocation, the makeup water inlet of the start-up feedwater deaerator is connected to two independent makeup water pipelines. The first pipeline connects to the condensate water system of the power plant, and is equipped with a condensate water start-up feedwater regulating valve. The second pipeline connects to the demineralized water system of the power plant, and is also equipped with a demineralized water start-up feedwater regulating valve. The heating steam inlet of the start-up feedwater deaerator is connected to the auxiliary steam source (including the auxiliary boiler system and the turbine extraction steam system) via pipelines, and is equipped with a start-up feedwater deaerator heating steam regulating valve. The distributed control system adjusts the opening of the makeup water valve based on the deaerator liquid level signal and adjusts the opening of the heating steam valve based on energy balance requirements.

[0011] Furthermore, to adapt to the multi-reactor structure of modular nuclear power plants, the water supply network assembly includes at least two parallel water supply branches. The first water supply branch connects to the first steam generator, and the second water supply branch connects to the second steam generator. Each branch is equipped with a corresponding start-up feedwater regulating valve. A start-up feedwater pump outlet isolation valve is installed between the outlet of the start-up feedwater pump and the branch point of each water supply branch. In addition, the system also includes a recirculation pipeline connecting the start-up feedwater pump outlet header to the start-up feedwater deaerator. This pipeline is equipped with a recirculation regulating valve to establish an internal closed-loop circulation for fluid preheating or pump protection when no external water supply is being provided.

[0012] In terms of thermal hydraulic regulation and control, the distributed control system integrates a temperature control module, which executes control logic based on energy balance. The system collects fluid temperature, stored water mass, and mass flow rate and specific enthalpy data of each input branch in the start-up feedwater deaerator. Based on the energy balance differential relationship, it calculates the energy input required to maintain the target temperature, and then adjusts the opening of the heating steam regulating valve so that the start-up feedwater temperature tracks the preset dynamic temperature setpoint in real time.

[0013] The dynamic temperature setpoint is automatically selected by the distributed control system according to the current operating conditions: under cold flushing conditions, the setpoint is a gradient temperature rise curve that increases linearly with time; under hot start-up conditions, the setpoint is anchored to the metal wall temperature of the steam generator to be started; under grid connection preparation conditions, the setpoint is anchored to the fluid temperature of the main deaerator in the main feedwater system.

[0014] To prevent equipment damage, the distributed control system integrates a thermal shock protection logic module. This module monitors the start-up feedwater temperature and the metal temperature of the steam generator to be started in real time, calculating the absolute value of the temperature difference between them and the temperature change rate of the steam generator. The system only generates a permission command to open the feedwater regulating valve when the absolute value of the temperature difference is less than a preset safety threshold; when the temperature change rate is detected to exceed the material's allowable limit, the system uses forced logic to reduce the flow rate of heating steam entering the start-up feedwater deaerator or increase the flow rate of cold source makeup water to limit the temperature change rate.

[0015] During system switching, to ensure reactor parameter stability, the distributed control system is equipped with a disturbance-free switching control module. After confirming the establishment of the main feedwater pump outlet pressure, the system enters an overlapping switching cycle. During this period, based on the principle of flow conservation, the system simultaneously adjusts the closing rate of the start-up feedwater regulating valve and the opening rate of the main feedwater system regulating mechanism according to a complementary time function relationship. Through flow feedback correction, the total feedwater flow entering the steam generator is maintained constant at the reactor's required setpoint, achieving a smooth transition from start-up feedwater to main feedwater.

[0016] In addition, the system has a backup response function under abnormal operating conditions. When the main feedwater system loses its flow, the distributed control system forcibly switches the heating steam source to the auxiliary boiler system, and prioritizes opening the start-up feedwater regulating valve to quickly inject water according to the water level status of the steam generator. Then, the control mode is switched to closed-loop control with the steam generator water level as the controlled variable to maintain the secondary side heat dissipation capacity.

[0017] This invention provides a start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant. It offers the following advantages: 1. This invention achieves independent and precise adjustment of the start-up feedwater temperature by setting up a physically independent start-up feedwater deaerator and an integrated energy balance algorithm temperature control module. This technical feature enables the system to automatically generate a dynamic temperature setpoint based on the actual metal wall temperature of the steam generator to be started under asymmetric operation conditions of a modular high-temperature gas-cooled reactor, ensuring that the temperature difference between the injected working fluid and the equipment wall is within a safe threshold. This effectively solves the feedwater matching problem caused by inconsistent thermal states of modules in multi-module units, and prevents thermal stress damage or fatigue failure of the steam generator tube sheet and heat transfer tube bundle caused by drastic temperature differences.

[0018] 2. This invention employs a disturbance-free switching control logic based on the principle of flow conservation and a cross-limiting strategy. During the overlapping switching cycle of transferring water supply from the start-up feedwater pump to the main feedwater pump, the control system synchronously adjusts the opening of the two valves through complementary time functions and corrects deviations in real time using flow feedback. This control method ensures that the total mass flow rate entering the steam generator is always maintained near the reactor's required setpoint, eliminating sudden flow changes and large fluctuations in the steam generator water level caused by conventional switching operations, thereby avoiding unplanned reactor shutdowns due to exceeding thermal parameter limits.

[0019] 3. This invention, by configuring a backup steam source interface connecting to the auxiliary boiler, multiple water supply pipelines, and an integrated abnormal operating condition backup response module, endows the start-up feedwater system with a non-safety-level backup feedwater function in the event of a main feedwater system failure. When a loss of main feedwater flow is detected, the system can automatically switch to the auxiliary heat source and quickly establish a water injection channel to the steam generator, maintaining the secondary side water level to continuously remove residual heat from the reactor core. This design, without adding additional dedicated emergency facilities, utilizes existing start-up facilities to improve the safety and defense-in-depth level of nuclear power plants in response to feedwater failures. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the water supply system for startup of the present invention; Figure 2 This is a flowchart of the start-up water supply system operation control of the present invention. Detailed Implementation

[0021] The technical solutions in 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, and 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.

[0022] See attached document Figure 1 The present invention provides a start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant. This system is physically independent of the main feedwater system of the conventional island and is coupled to the main feedwater pipeline through a valve network.

[0023] A main deaerator 1 is installed on the conventional island side to provide deaerated feedwater during normal power operation. The liquid outlet of the main deaerator 1 is connected via pipelines to the suction inlets of both the No. 1 main feedwater spring 2 and the No. 2 main feedwater spring 3. The outlet of the No. 1 main feedwater spring 2 is connected via pipelines to the No. 1 main feedwater pump outlet isolation valve 18, and the downstream pipeline of this isolation valve is connected to the feedwater inlet of the No. 1 steam generator 5. The outlet of the No. 2 main feedwater pump 3 is connected via pipelines to the No. 2 main feedwater pump outlet isolation valve 19, and the downstream pipeline of this isolation valve is connected to the feedwater inlet of the No. 2 steam generator 4.

[0024] The start-up feedwater system described in this embodiment is equipped with an independent start-up feedwater deaerator 8. As the core heat and mass exchange vessel of this subsystem, the start-up feedwater deaerator 8 has two independent makeup water lines connected to its fluid input end. The first line is a condensate makeup water line, one end of which is connected to the main pipe of the power plant condensate system 7, and the other end is connected to the start-up feedwater deaerator 8. A condensate supply start-up feedwater regulating valve 14 is connected in series on this line. The second line is a demineralized water makeup water line, one end of which is connected to the main pipe of the demineralized water system 9, and the other end is connected to the start-up feedwater deaerator 8. A demineralized water supply start-up feedwater regulating valve 13 is connected in series on this line.

[0025] The start-up feedwater deaerator 8 is equipped with a heating steam input interface for receiving external heat sources to raise the feedwater temperature and perform deaeration. This interface is connected via pipeline to the steam supply header of the auxiliary boiler system 11 or the turbine extraction steam system. A start-up feedwater deaerator heating steam regulating valve 12 is installed on the heating steam supply pipeline to regulate the flow rate of heating steam entering the start-up feedwater deaerator 8.

[0026] The liquid outlet of the start-up feedwater deaerator 8 is connected to the suction inlet of the start-up feedwater pump 10 via a pipeline. The start-up feedwater pump 10 provides circulating head and flow power for the start-up feedwater system. A recirculation pipeline is connected to the outlet header of the start-up feedwater pump 10, and the end of this recirculation pipeline returns to the start-up feedwater deaerator 8. A start-up feedwater pump recirculation regulating valve 20 is installed on the recirculation pipeline to establish a minimum flow protection cycle for the pump and a thermal pre-conditioning cycle within the system when no water is supplied to the steam generator.

[0027] A start-up feedwater pump outlet isolation valve 17 is connected in series downstream of the outlet header of the start-up feedwater pump 10. Downstream of the start-up feedwater pump outlet isolation valve 17, the water supply pipeline is divided into two parallel branches. The first branch is connected to the inlet pipeline of steam generator 5, and its physical connection point is located between the downstream side of the main feedwater pump outlet isolation valve 18 and the feedwater inlet of steam generator 5. A start-up feedwater regulating valve 15 for steam generator 5 is installed on the first branch.

[0028] The second branch line connects to the inlet pipeline of steam generator 4 (No. 2), and its physical connection point is located downstream of the isolation valve 19 at the outlet of the main feedwater pump (No. 2) and between the feedwater inlet of steam generator 4 (No. 2). A start-up feedwater supply regulating valve 16 for steam generator 4 (No. 2) is installed on the second branch line. By controlling the opening and closing states of regulating valves 15 and 16, selective water supply to different steam generator modules can be achieved through the start-up feedwater system.

[0029] Temperature and pressure sensors are installed inside the start-up feedwater deaerator 8 to monitor the thermodynamic state within the vessel. Based on the aforementioned physical connection structure, the energy balance within the start-up feedwater deaerator 8 is determined by the input condensate, demineralized water, heating steam, and output feedwater. This energy balance relationship is defined by the following formula: ; in, This indicates the current water quality stored within the feedwater deaerator 8 at the moment of startup; This indicates the specific heat capacity of water at constant pressure. This indicates the fluid temperature inside the feedwater deaerator 8 when it is started; Represents a time variable; This indicates the mass flow rate of condensate entering through the condensate supply start-up water regulating valve 14; This indicates the specific enthalpy of the condensate entering the container; This indicates the mass flow rate of demineralized water entering through the demineralized water supply regulating valve 13; This indicates the specific enthalpy of the incoming demineralized water; This indicates the mass flow rate of the heating steam entering through the heating steam regulating valve 12 of the feedwater deaerator. This indicates the specific enthalpy of the incoming heating steam; This indicates the start-up feedwater mass flow rate pumped by the start-up feedwater pump 10; This indicates the specific enthalpy of the start-up feedwater extracted.

[0030] In addition, temperature monitoring points are installed on the metal walls of steam generator 5 (No. 1) and steam generator 4 (No. 2) to obtain the real-time metal temperature of the steam generators. A temperature sensor is installed on the outlet header of the feedwater pump 10 to obtain the actual temperature of the supplied fluid. The signal output terminals of these sensors are connected to the power plant's distributed control system (DCS) to support temperature difference calculation and closed-loop control during subsequent operation.

[0031] The start-up feedwater system constructed based on this invention relies on the coordinated control of mass balance and energy balance within the start-up feedwater deaerator 8 for its core thermal-hydraulic regulation process. The start-up feedwater deaerator 8 is not only a deaeration container but also an unsteady-state thermo-mass mixing node, and its control logic includes two coupled subsystems: a water level control loop and a temperature control loop.

[0032] In the water level control loop, the control system receives the liquid level signal from the start-up feedwater deaerator 8 and maintains the water level in the container by adjusting the opening of the condensate supply start-up feedwater regulating valve 14 or the demineralized water supply start-up feedwater regulating valve 13. Within the preset safe operating range, the process follows the law of conservation of mass, i.e., the input condensate mass flow rate... With demineralized water mass flow rate The sum needs to be dynamically matched to the output flow rate drawn by the starting water supply pump 10. And the change in working fluid density caused by temperature changes.

[0033] In the temperature control loop, the system adjusts the opening of the start-up feedwater deaerator heating steam regulating valve 12. This is used to control the input of heating steam, thereby changing the specific enthalpy of the mixed working fluid. The goal of this control logic is to control the fluid temperature within the start-up feedwater deaerator 8. Real-time tracking of preset target temperature curves Target temperature curve It is not a fixed value, but a function that varies with time, calculated based on the current metal wall temperature and allowable heating rate of the connected steam generator module (such as Steam Generator 5 #1 or Steam Generator 4 #2).

[0034] The specific control algorithm employs a feedback control strategy with temperature deviation as input. The control system collects the actual fluid temperature inside the feedwater deaerator 8 in real time during startup. And calculate its relationship with the target temperature. deviation ,Right now Based on this deviation, the controller outputs an opening command for the start-up feedwater deaerator heating steam regulating valve 12. The control law is described by the following formula: ; in, express The opening command for the feedwater deaerator heating steam regulating valve 12 is activated at all times, with a value range standardized to [0,1]. This represents the proportional gain coefficient, used to respond to the current temperature deviation; This represents the integral gain coefficient, used to eliminate steady-state temperature errors; This represents the differential gain coefficient, used to predict temperature change trends and suppress overshoot; Represents the integral variable; This represents the feedforward compensation component, which is based on the current water supply flow rate. and water replenishment temperature The required heat load is calculated in advance to improve the system's response speed to fluctuations in influent flow rate.

[0035] Physically, the opening command of the control valve Converted into actual heating steam mass flow rate This process is constrained by the flow characteristics of the valve and the pressure difference conditions before and after the pipeline network. This flow characteristic relationship is defined by the following formula: ; in, This indicates the actual mass flow rate of heating steam entering the deaerator through the regulating valve. This indicates the rated flow coefficient of the steam regulating valve 12 for starting the feedwater deaerator; The inherent flow characteristic function of the control valve (such as linear or equal percentage characteristic) describes the nonlinear relationship between valve opening and flow area. Indicates the density of the heating steam; This indicates the steam supply header pressure of auxiliary boiler system 11 or turbine extraction steam system; This indicates the operating pressure inside the feedwater deaerator 8 when it is started.

[0036] By combining the above control law formulas and valve characteristic formulas, and substituting them into the energy balance formula, a complete closed-loop control model for the start-up feedwater deaerator's thermal balance is constructed. Based on this model, the system adjusts the auxiliary boiler steam supply pressure... Automatically adjust valve opening in case of fluctuations or sudden changes in water supply flow. Ensure the start-up water supply temperature It can accurately and stably maintain the set value required by the process, thereby providing feedwater to the downstream steam generator that meets the requirements for thermal shock protection.

[0037] During the thermal coupling process between the start-up feedwater system and the steam generator (such as Steam Generator 5 of Unit 1 or Steam Generator 4 of Unit 2), to prevent irreversible thermal stress damage or low-cycle fatigue failure of thick-walled components (such as tube sheets and shells) and heat transfer tube bundles of the steam generator due to excessive temperature differences in the working fluid, a steam generator thermal shock protection logic module is integrated into the control system. This module applies strict boundary constraints to the opening operation of the start-up feedwater regulating valve and the regulation rate of the heating steam through real-time monitoring and calculation.

[0038] The thermal shock protection mechanism first establishes an injection permission interlock logic based on static temperature difference. Before the start-up feedwater pump outlet isolation valve 17 and the corresponding steam generator inlet regulating valve (15 or 16) are opened, the protection logic module collects the instantaneous temperature of the fluid at the start-up feedwater pump 10 outlet in real time. and the critical metal temperature of the steam generator to be started (Typically, the tube sheet temperature or the downflow channel water temperature is used). The control system only generates a command to open the valve when the absolute value of the temperature difference between the two is within the safe threshold allowed by the material fracture mechanics analysis. This static injection constraint relationship is defined by the following formula: ; in, express The logic state of water inlet permission at any given time: 1 indicates that water inlet is allowed, and 0 indicates that water inlet is prohibited and the recirculation mode is forcibly maintained; Indicates the water supply temperature at which the water supply system is started; This indicates the representative metal temperature of the target steam generator; This indicates the preset maximum allowable inlet water temperature difference threshold, which is determined by the thermal shock toughness curve of the steam generator material.

[0039] After the static constraints are met and water begins to flow into the steam generator, the protection mechanism automatically switches to dynamic heating rate limiting mode. During this stage, to prevent excessively large transient temperature gradients inside the steam generator due to rapid fluid temperature changes, the control system limits the rate of change of the opening of the feedwater deaerator heating steam regulating valve 12. The system monitors the heating rate of the steam generator through differential calculations and ensures that it remains below the limit allowed by structural integrity. This dynamic constraint relationship is described by the following equation: ; in, This indicates the rate of change of the steam generator temperature over time. Indicates the sampling period of the control system; This indicates the maximum allowable rate of heating or cooling for the steam generator.

[0040] When the control system detects that the calculated rate of temperature change is close to In such cases, the protection logic takes precedence over the aforementioned temperature control loop, forcibly locking or reducing the opening of the start-up feedwater deaerator heating steam regulating valve 12. In extreme cases, it may even introduce a cold source by increasing the opening of the condensate supply start-up feedwater regulating valve 14 to actively suppress the heating rate, thereby strictly maintaining the thermal stress on the steam generator tube wall within the material safety envelope. This injection permission mechanism based on real-time temperature difference monitoring and the dynamic heating rate limiting mechanism together constitute the thermal safety barrier of the start-up feedwater system.

[0041] After the start-up feedwater system completes the flushing or preheating of the steam generator (e.g., Steam Generator 4, No. 2), and the start-up feedwater temperature and the fluid temperature of the main feedwater system meet the synchronization condition, the control system executes the flow distribution and disturbance-free switching procedure. This procedure aims to smoothly transfer the water supply task of the steam generator from the start-up feedwater pump 10 to the main feedwater pump (e.g., Main Feedwater Pump 3, No. 2). During this process, the fluctuation of the total mass flow rate entering the steam generator must be kept within a minimal range to maintain the stability of the secondary side water level of the steam generator and the balance of reactor thermal power.

[0042] The flow allocation and switching control logic is based on the principles of flow conservation and cross-limiting. At any moment during the switching process... Total instantaneous mass flow rate entering the steam generator The flow rate of the starting water supply branch Flow rate of the main water supply branch These are superimposed. The core objective of the control system is to ensure that this total flow rate always equals the set flow rate required under the current reactor operating conditions. That is, it satisfies the following flow conservation constraints: ; in, express The actual total mass flow rate entering the target steam generator at any given time; express The flow rate supplied at all times by activating the water supply regulating valve (such as valve 16); express The flow rate supplied through the main water supply system at all times; This indicates the feedwater flow rate setpoint required to maintain the current reactor thermal load.

[0043] To achieve this goal, the control system employs a dual-loop coordinated control strategy. First, the system confirms that the main feedwater pump (e.g., main feedwater pump #2, pump #3) has started and that the outlet pressure is [data missing]. Established, and above the internal pressure of the steam generator. Subsequently, the main feedwater pump outlet isolation valve (e.g., valve 19) is opened, entering the overlapping switching period. During the overlapping switching period, the control system generates two complementary action signals, which respectively drive the start feedwater regulating valve (e.g., valve 16) and the main feedwater flow regulating mechanism (main feedwater regulating valve or pump speed controller).

[0044] The flow characteristics of the starting water supply branch are determined by the physical opening of the valve and the pressure difference before and after it, following the orifice plate formula in fluid dynamics: ; Similarly, the flow characteristics of the main water supply branch are described as follows: ; in, , These represent the rated flow coefficients of the starting water supply regulating valve and the main water supply regulating mechanism, respectively. , These represent the opening commands for starting the water supply regulating valve and the main water supply regulating mechanism at time t, respectively, with values ​​ranging from [0,1]. , These represent the inherent flow characteristic functions (such as linear or equal percentage characteristic curves) of the corresponding valves. , Indicates fluid density; This indicates the pressure of the feedwater pump outlet header when starting. This indicates the outlet pressure of the main feedwater pump; This indicates the inlet pressure of the steam generator.

[0045] During the switching cycle Inside, the control system follows a preset time function. Cross-adjustment is performed on the two actuators. It is a normalized time function that monotonically increases from 0 to 1. The logic for generating the opening instruction is as follows: ; ; in, To maintain the opening of the water supply regulating valve before the switchover begins; The target opening degree of the main water supply regulating mechanism after the switchover is completed; This is a real-time correction item based on traffic feedback.

[0046] Due to valve characteristic curve It is typically nonlinear and relies solely on the open-loop. The function cannot guarantee complete flow conservation. Therefore, the control system introduces a flow feedback correction loop. The system collects the total flow measurement and setpoint in real time. The deviation is calculated using the PID algorithm to determine the correction term. The operating rate of the two valves can be dynamically fine-tuned. When the value reaches 1, the water supply regulating valve is fully closed, the main water supply regulating mechanism takes over the entire flow, and the total flow fluctuation is always limited to the allowable dead zone range (e.g., ±2%), thereby achieving a smooth switching.

[0047] See attached document Figure 1 and attached Figure 2This embodiment describes the operation control process for starting the feedwater system when a nuclear power plant is in a multi-module asymmetric operation scenario, i.e., the first nuclear steam supply system (e.g., NSSS module 1) is in power operation while the second nuclear steam supply system (e.g., NSSS module 2) is in cold shutdown and requires cleaning and startup. This process strictly follows three continuous thermal stages: cold flushing, gradient heating, and parameter synchronization.

[0048] At the initial moment of process startup, the control system confirms that the No. 1 main feedwater pump 2 is running, the No. 1 main feedwater pump outlet isolation valve 18 is open, and the main deaerator 1 is maintained in a high-temperature and high-pressure operating state. Simultaneously, it confirms that the No. 2 main feedwater pump 3 is in a stopped or standby state, and the No. 2 main feedwater pump outlet isolation valve 19 is closed, thus physically isolating the No. 2 steam generator 4, which is to be started, from the high-temperature main feedwater system. At this time, the feedwater system is in standby mode, the feedwater pump 10 is stopped, and all regulating valves and isolation valves are in the closed position.

[0049] Phase 1: Establishment and operation of the cold flushing circuit.

[0050] Upon receiving a cold start command, the control system first executes the cold water injection logic. The system opens the condensate supply start-up feedwater regulating valve 14 or the demineralized water supply start-up feedwater regulating valve 13, injecting water into the start-up feedwater deaerator 8 to the specified level. During this stage, the control system forcibly locks the start-up feedwater deaerator heating steam regulating valve 12 to the fully closed state. This ensures that the output fluid is maintained at a low temperature determined by the water source (usually room temperature).

[0051] Subsequently, the system starts the feedwater pump 10, and after confirming the pump outlet pressure is established, opens the feedwater pump outlet isolation valve 17. Immediately afterwards, the control system outputs a command to open the feedwater supply regulating valve 16 to the No. 2 steam generator. Low-temperature flushing water is injected into the No. 2 steam generator 4 via pipeline, flows through the heat transfer tube bundle, and then enters the downstream discharge or purification system. During this process, the system continuously monitors the water quality parameters of the outflowing fluid (such as conductivity, silica content, etc.) until the indicators meet the water quality standards of the secondary side of the steam generator.

[0052] Second stage: hot flushing and gradient temperature control.

[0053] After confirming that the water quality meets the standards, the system enters the gradient temperature rise phase. The control system unlocks the heating steam regulating valve 12 of the start-up feedwater deaerator and activates the temperature rise rate control logic. This logic no longer targets a fixed temperature but generates a dynamic temperature setpoint that increases linearly or quasi-linearly with time. .

[0054] The control system adjusts the opening of valve 12 to introduce heating steam from the auxiliary boiler system 11 or the turbine extraction steam, thereby raising the actual water temperature at the outlet of the start-up feedwater pump 10. The system closely follows the rise of this dynamic setpoint. During this period, the system collects the pipe wall temperature of steam generator #2 (4) in real time and calculates the rate of temperature rise. If the rate of temperature rise is detected to be approaching the material's allowable limit (e.g., ...), the system will take action. (or engineering limit), the control system will automatically reduce the opening of valve 12 or pause the set value through a negative feedback mechanism. As the temperature rises, a hold operation is implemented until the rate of temperature increase returns to a safe range. This process ensures a smooth transition of the steam generator from a cold to a hot state, avoiding severe thermal stress concentration.

[0055] Phase 3: Parameter synchronization and grid connection preparation.

[0056] When steam generator #2 (4) completes its hot flushing and the temperature rises to near its operating point, the system enters the parameter synchronization phase. At this time, the target temperature setpoint of the control system is... The temperature of the fluid inside the main deaerator 1 is automatically switched and anchored. .

[0057] The control system continuously adjusts the steam flow rate entering the start-up feedwater deaerator 8 to eliminate the start-up feedwater temperature. With main feed water temperature The deviation between them. When the absolute value of the temperature difference between the two remains stable within the preset grid connection allowable threshold (e.g., When the temperature remains below a certain level and the duration exceeds the confirmation cycle (e.g., 5 minutes), the system sends a signal indicating that the grid connection conditions are met. At this time, the inlet water temperature of the No. 2 steam generator 4 is fully matched with that of the main system, and the system has the thermal conditions to start the No. 2 main feedwater spring 3 and open the isolation valve 19 to switch the water supply at any time, thus ending the independent operation task of starting the feedwater system.

[0058] See attached document Figure 1 and attached Figure 2 This section describes the direct water inlet startup process when the nuclear steam supply system to be started (e.g., NSSS module #2) is in a hot or warm shutdown state, meaning the steam generator already has a high initial temperature and the secondary water quality is up to standard, and cold flushing is not required. The core of this process is to preheat the internal closed-loop circulation of the feedwater system to eliminate the temperature difference between the working fluid and the high-temperature equipment, thus preventing thermal shock.

[0059] Before issuing the start command, the control system first confirms that module #1 NSSS is in power operation, and that the main deaerator 1 and the main feedwater network are under high temperature and high pressure conditions. Simultaneously, it confirms that main feedwater pump #2 3 is shut down and its outlet isolation valve 19 is closed, and steam generator #2 4 is in a thermal isolation state. At this time, the water stored in feedwater deaerator 8 is typically at room temperature; directly injecting it into steam generator #2 4 would cause severe thermal stress. Therefore, the system executes the following step-by-step control strategy: Phase 1: System self-circulation and preheating.

[0060] The control system first starts the feedwater pump 10, but keeps the feedwater pump outlet isolation valve 17 fully closed, thereby cutting off the water supply to the steam generator. At the same time, the control system fully opens or adjusts the start-up feedwater pump recirculation regulating valve 20 to establish a short-circuit circulation loop between the start-up feedwater deaerator 8, the start-up feedwater pump 10, and the recirculation pipeline.

[0061] After the internal circulation is established, the control system opens the start-up steam regulating valve 12 of the feedwater deaerator, injecting auxiliary steam into the deaerator. At this time, the temperature controller setpoint... Set to track the current average metal temperature or tube sheet temperature of steam generator #2. Heating steam rapidly increases the temperature of the feed water circulating in the short-circuit loop through a mixed heating method. The control system monitors the pump outlet fluid temperature in real time. until it rises and stabilizes at Within the nearby allowable deviation band (e.g.) ), to complete the thermal preparation before water injection.

[0062] Phase 2: Establishment of the second loop and initial flow control.

[0063] When the start-up water supply temperature With steam generator temperature After the thermal matching conditions are met, the control system issues a water inlet command. The system first opens the start-up feedwater outlet isolation valve 17, and then linearly opens the start-up feedwater supply regulating valve 16 to the No. 2 steam generator.

[0064] During this stage, to avoid drastic fluctuations in the steam generator water level (false water level phenomenon) caused by sudden changes in flow rate, the opening of regulating valve 16 is limited by special low-flow control logic. The control system performs PID regulation on valve 16 based on the deviation between the setpoint and actual level of steam generator 4 (No. 2), establishing a stable secondary loop water circulation with a low flow rate. At this time, the feedwater absorbs residual heat from the reactor core or heat transferred from the primary loop and then vaporizes, maintaining the steam generator's hot-state operating level.

[0065] Phase 3: Temperature target redirection and synchronization adjustment.

[0066] After the secondary loop circulation stabilizes, in order to switch to the main feedwater system, the control target for the start-up feedwater temperature needs to shift from matching the equipment temperature to matching the main system fluid temperature. The control system will then set the temperature setpoint. from Smooth transition to feedwater temperature in main deaerator 1 .

[0067] like Higher than the current The control system continues to increase the opening of the heating steam regulating valve 12 to raise the temperature; if Lower than the current (For example, if the main system is under reduced load), the steam opening is reduced or the makeup water flow is increased to lower the temperature. During this adjustment process, the control system continuously monitors the temperature change rate of the steam generator to ensure that the transition process meets the thermal stress constraint.

[0068] Phase 4: Seamless handover execution.

[0069] When the start-up water supply temperature With main feed water temperature When precise synchronization is achieved (temperature difference less than a preset threshold) and the primary loop status of module #2 NSSS meets the power increase requirements, the system starts main feedwater pump #2. After confirming that the main pump outlet pressure meets the grid connection conditions, the control system executes the aforementioned cross-limiting switching logic: gradually opening the isolation valve 19 at the outlet of main feedwater pump #2 and the main regulating mechanism, while simultaneously closing the start-up feedwater regulating valve 16. When valve 16 is completely closed, the system stops starting feedwater pump #10, closes the heating steam regulating valve 12, and starts the feedwater system into standby mode, completing the entire hot start-up task.

[0070] See attached document Figure 1 and attached Figure 2 This section details the technical implementation process of the start-up feedwater system as a non-safety-level backup feedwater measure. This function is mainly applied to situations where the conventional island main feedwater system experiences unexpected failures (such as main feedwater pump tripping, main deaerator failure, or main feedwater pipeline rupture), causing the steam generators (such as No. 1 steam generator 5 and No. 2 steam generator 4) to lose normal feedwater supply, but the reactor has not yet reached the threshold for triggering the emergency shutdown protection system, or abnormal operating conditions where residual heat needs to be removed after reactor shutdown.

[0071] During normal power operation, the power plant's distributed control system (DCS) continuously monitors the operating status signals of No. 1 main feedwater pump 2 and No. 2 main feedwater pump 3, as well as the outlet header flow signal. When the control system detects a fault signal indicating a loss of main feedwater flow, and the duration of this signal exceeds the anti-maloperation judgment time limit (e.g., 2 seconds), the system automatically triggers the backup feedwater activation logic.

[0072] Phase 1: Steam source switching and hot standby activation.

[0073] In the event of a main feedwater system failure and concurrent turbine tripping, the conventional turbine extraction steam pressure will drop rapidly, failing to continue providing heating steam to the deaerator. At this time, the control logic for starting the feedwater system prioritizes the steam source switching operation. The control system, through interlocking logic, forcibly disconnects the pipeline from the turbine extraction system (if any) and sends a steam supply request to the auxiliary boiler system 11. Simultaneously, it adjusts the start-up feedwater deaerator heating steam regulating valve 12 to completely switch the steam source channel to the auxiliary boiler steam supply header.

[0074] By introducing auxiliary steam, the water stored in the feedwater deaerator 8 is rapidly heated or maintained at a preset standby temperature (usually set to the minimum permissible temperature that can mitigate the thermal shock to the high-temperature steam generator, such as 150°C-180°C), ensuring reduced thermal stress during emergency water injection.

[0075] Phase Two: Rapid Start-up and Piping Filling.

[0076] After confirming the availability of auxiliary steam, the control system immediately issues a preemptive start command to start the feedwater pump 10. After the pump starts, the system monitors the pump outlet pressure. Once the pressure exceeds the system back pressure, the start feedwater pump outlet isolation valve 17 is immediately opened.

[0077] At this point, the control system prioritizes water supply based on the liquid level status of each steam generator. If the water level in steam generator #1 (5) drops faster than that in steam generator #2 (4), or approaches the low water level alarm threshold, the control system will prioritize and quickly open the start-up water supply regulating valve 15 to steam generator #1. The initial opening rate of the regulating valve is set to a rapid charging mode to fill the pipeline and establish a flow path to the steam generator in the shortest possible time, preventing the secondary side of the steam generator from drying out.

[0078] Phase 3: Post-accident control based on water level.

[0079] Once the water injection flow rate is established, the control strategy for the water supply system automatically switches from flow / temperature control to steam generator level maintenance control. The control system uses the narrow-range water level signal from the steam generator as the controlled variable and the opening degree of the start-up water supply regulating valve (15 or 16) as the manipulated variable, executing single-impulse or three-impulse PID control.

[0080] The control objective is to maintain the steam generator water level above the minimum safe level that covers the bottom of the heat transfer tube bundle, thus establishing a stable secondary heat sink. At this time, the feedwater flowing through the steam generator absorbs the sensible heat and decay heat transferred from the primary loop and boils. The generated steam is discharged into the condenser or the atmosphere through the main steam bypass discharge system (SDDS), thereby continuously removing the core residual heat.

[0081] Phase 4: Long-term cooling and water replenishment maintenance.

[0082] During periods of abnormal operation, the liquid level in the start-up feedwater deaerator 8 will decrease due to continuous water supply. The control system ensures continuous cold source replenishment by increasing the opening of the condensate supply start-up feedwater regulating valve 14 or the demineralized water supply start-up feedwater regulating valve 13. If the condensate system 7 becomes unavailable due to power failure, the system automatically switches to the demineralized water system 9 or the fire water / emergency water supply interface for gravity replenishment or emergency pump replenishment.

[0083] This standby feedwater status will remain in place until the main feedwater system is cleared and put back into operation, or until the reactor and primary loop systems have cooled to a cold shutdown state and secondary heat dissipation via the steam generator is no longer required. This design enhances the nuclear power plant's defense-in-depth capability in a feedwater loss sequence without requiring additional dedicated safety features.

Claims

1. A start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant, characterized in that, include: Start the feedwater deaerator, which is equipped with a water supply inlet and a heating steam inlet, to heat and deoxygenate the incoming fluid and establish a heat and mass balance; Start the feedwater pump, whose suction inlet is connected to the liquid outlet of the start-up feedwater deaerator via a pipeline to provide power for fluid transport; A water supply network assembly connected between the outlet of the start-up water pump and the water inlet of at least one steam generator; A distributed control system, which is communicatively connected to the start-up feedwater deaerator, start-up feedwater pump, and water supply network components; The physical connection point of the water supply network component is located downstream of the main water supply pump outlet isolation valve of the main water supply system and upstream of the water supply inlet of the steam generator, so that the start-up water supply system can supply water to the steam generator in parallel with the main water supply system.

2. The start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 1, characterized in that, The water supply inlet of the start-up water deaerator is connected to two independent water supply lines: The first line is the condensate water supply pipeline, which connects to the power plant's condensate system. A condensate water supply start-up regulating valve is installed on the pipeline. The second route is the demineralized water supply pipeline, which connects to the power plant's demineralized water system. A demineralized water supply start-up regulating valve is installed on the pipeline. The heating steam inlet of the start-up feedwater deaerator is connected to the auxiliary steam source through a pipeline, and the pipeline is equipped with a start-up feedwater deaerator heating steam regulating valve. The distributed control system is configured to adjust the opening degree of the condensate supply start-up feedwater regulating valve or the demineralized water supply start-up feedwater regulating valve according to the liquid level signal of the start-up feedwater deaerator.

3. The start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 1, characterized in that, The water supply network assembly includes at least two parallel water supply branches and is adapted to a multi-module steam generator architecture. The first water supply branch is connected to the first steam generator, and a regulating valve for starting water supply to the first steam generator is installed on the branch. The second water supply branch is connected to the second steam generator, and a regulating valve for starting the water supply to the second steam generator is installed on the branch. An isolation valve for the outlet of the starting water supply pump is also provided between the outlet of the starting water supply pump and the branch point of the first water supply branch and the second water supply branch.

4. The start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 1, characterized in that, Also includes: The recirculation pipeline has one end connected to the outlet header of the start-up feedwater pump and the other end connected back to the start-up feedwater deaerator. The recirculation pipeline is equipped with a start-up feedwater pump recirculation regulating valve. When the start-up water supply system is in the self-circulation preheating stage of hot start-up, the distributed control system is configured to close the passage from the water supply network component to the steam generator, open the recirculation regulating valve of the start-up water supply pump, and carry out fluid circulation heating in the closed loop formed by the start-up water supply deaerator, the start-up water supply pump and the recirculation pipeline.

5. A start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 2, characterized in that, The distributed control system integrates a temperature control module, which is configured to execute energy balance-based control logic. Collect data on fluid temperature, stored water mass, mass flow rate and specific enthalpy of each input branch in the start-up feedwater deaerator; The energy input required to maintain the target temperature is calculated based on the energy balance differential relationship. Adjust the opening of the heating steam regulating valve of the start-up feedwater deaerator according to the calculation results, so that the start-up feedwater temperature tracks the preset dynamic temperature setting value in real time.

6. The start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 5, characterized in that, The dynamic temperature setpoint is automatically selected by the distributed control system based on the current operating conditions. Under cold rinsing conditions, the dynamic temperature setpoint is a gradient temperature rise curve that increases linearly with time; Under hot start-up conditions, the dynamic temperature setpoint is anchored to the metal wall temperature of the steam generator to be started. During the grid connection and switching preparation, the dynamic temperature setpoint is anchored to the fluid temperature of the main deaerator in the main feedwater system.

7. The start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 1, characterized in that, The distributed control system integrates a thermal shock protection logic module, which is configured as follows: Real-time monitoring of the start-up feedwater temperature and the metal temperature of the steam generator to be started; Calculate the absolute value of the temperature difference between the two and the temperature change rate of the steam generator; A permission command to open the corresponding regulating valve in the water supply network component is generated only when the absolute value of the temperature difference is less than a preset safety threshold. When the temperature change rate exceeds the material's allowable limit, the flow rate of heating steam entering the start-up feedwater deaerator is forcibly reduced or the flow rate of cold source makeup water is increased.

8. A start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 3, characterized in that, The distributed control system is equipped with a disturbance-free switching control module for performing the switching of water supply tasks from the start-up water supply system to the main water supply system. The disturbance-free switching control module is configured as follows: After confirming the establishment of the main feedwater pump outlet pressure, the overlapping switching cycle begins; During the overlapping switching cycle, based on the principle of flow conservation, the closing rate of the regulating valve for starting the feedwater to the first steam generator or the regulating valve for starting the feedwater to the second steam generator, as well as the opening rate of the main feedwater system regulating mechanism, are simultaneously adjusted according to the complementary time function relationship. The total feedwater flow rate into the steam generator is maintained constant at the set value required by the reactor through flow feedback correction.

9. A start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 2, characterized in that, The auxiliary steam source includes an auxiliary boiler system and a steam turbine extraction system; The distributed control system is also equipped with an abnormal operating condition backup response module. When a loss of flow in the main water supply system is detected, the abnormal operating condition backup response module executes the following control logic: The heating steam source for the start-up feedwater deaerator is forcibly switched to the auxiliary boiler system; Based on the rate of water level drop in the steam generator, the corresponding start-up water supply regulating valve is opened first to quickly inject water; Switch the control mode to single-impulse or three-impulse closed-loop control with the steam generator water level as the controlled variable, maintain the steam generator water level and remove the core waste heat.

10. A start-up feedwater system for a modular high-temperature gas-cooled reactor nuclear power plant according to claim 1, characterized in that, It also includes a sensor monitoring network, which includes at least: Temperature and pressure sensors are installed on the start-up water deaerator; A temperature sensor is installed on the outlet header of the start-up water pump; Temperature monitoring points are installed on the metal wall of the steam generator; The distributed control system calculates the temperature difference and temperature rise rate based on the data collected by the sensor monitoring network.

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