A method and system for phase-to-phase conversion control of a nuclear power plant pressurizer

Abstract

The application provides a nuclear power plant stabilizer phase conversion control method and system, comprising: obtaining a loop operation parameter, including the charging flow, the discharge flow, the average temperature of the loop coolant and the stabilizer pressure; according to the operation parameter, calculating the stabilizer water compensation value for representing the loop water volume change amount based on a preset loop water compensation model; and automatically controlling the pressure and / or liquid level in the stabilizer phase conversion process according to the compensation value. The application couples the temperature, pressure change rate and flow deviation multi-parameters to calculate and generate a feedforward compensation signal, fundamentally actively offsets the pressure disturbance caused by the thermal expansion and cold contraction of the water body, realizes the smooth and automatic control of the whole phase conversion process, significantly reduces the operator workload and human error risk, and improves the essential safety and intelligent level of the nuclear power unit under the start-up and shutdown conditions.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology, and in particular to a method and system for phase-to-phase switching control of a pressurizer in a nuclear power plant. Background Technology

[0002] The pressurizer is a key piece of equipment in a pressurized water reactor nuclear power unit. Its core function is to buffer pressure fluctuations in the primary loop by maintaining a saturated state of coexistence of steam and liquid phases during normal operation. The pressurizer's phase transitions are crucial operations during unit start-up and shutdown. Single-phase to two-phase transition refers to the process during startup where heating the water inside the pressurizer establishes a steam chamber, changing it from a full-water state to a two-phase state. Two-phase to single-phase transition refers to the process during shutdown where flooding the steam chamber restores it to a full-water state.

[0003] Currently, the pressurizer phase-to-phase switching operation of various pressurized water reactor nuclear power units relies primarily on manual control by operators. Operators must continuously monitor multiple parameters such as pressure, liquid level, and temperature, and coordinate the start-up, shutdown, and adjustment of multiple devices, including charging pumps, heaters, spray valves, and high-pressure relief valves, based on experience. Manual control demands extremely high operator skills, involves a heavy workload, and is prone to causing abnormal fluctuations in primary circuit pressure or liquid level, even exceeding operating limits, due to improper timing or magnitude of operations. Furthermore, during the heating and cavity building process from single-phase to two-phase, improper pressure control strategies can easily lead to temperature oscillations caused by repeated heating and cooling of the water, severely impacting cavity building efficiency and equipment safety. Therefore, how to achieve automated control of the pressurizer phase-to-phase switching process, reduce the risk of human error, and ensure a smooth transition of pressure and liquid level during the switching process is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] This invention provides a method and system for controlling the phase-to-phase switching of a pressurizer in a nuclear power plant, in order to solve the technical problems of relying on manual control for the phase-to-phase switching of the pressurizer in nuclear power units, the easy occurrence of primary loop parameters exceeding limits due to improper operation, and the dynamic disturbance of pressure and liquid level and unstable control caused by the thermal expansion and contraction of water and the adjustment inertia of the control system during the phase-to-phase switching process.

[0005] The nuclear power plant pressurizer phase-to-phase switching control method provided by this invention includes: Obtain primary loop operating parameters, which include at least the charging flow rate, the draining flow rate, the average temperature of the primary loop coolant, and the pressure regulator pressure. Based on the primary loop operating parameters, and using a preset primary loop water compensation model, the voltage regulator water compensation value is calculated. Based on the water compensation value of the pressure regulator, the pressure and / or liquid level during the phase transition process of the pressure regulator are automatically controlled. The phase transition process of the pressure regulator includes the process of the pressure regulator transitioning from a single-phase state to a two-phase state, and the process of the pressure regulator transitioning from a two-phase state to a single-phase state.

[0006] In one embodiment of the present invention, calculating the voltage regulator water compensation value based on a preset primary loop water compensation model includes: Calculate the flow deviation between the charging flow rate and the discharge flow rate; Calculate the rate of temperature change of the average temperature of the primary coolant; Calculate the rate of change of pressure in the voltage regulator; Based on the temperature change rate and the pressure change rate, calculate the density change of the primary loop water body, and calculate the volume change of the primary loop water body based on the density change. The water compensation value of the pressure regulator is calculated based on the volume change and the flow deviation.

[0007] In one embodiment of the present invention, the process of the voltage regulator switching from a single-phase state to a two-phase state includes a first pressure control process, which includes: When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the pressure regulator water compensation value is compared with a first threshold. If the pressure regulator water compensation value is lower than the first threshold, the current opening of the high-pressure relief valve is maintained. If the pressure regulator water compensation value is higher than the first threshold, the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator pressure setting value and the actual pressure value.

[0008] In one embodiment of the present invention, the process of the voltage regulator switching from a single-phase state to a two-phase state further includes an automatic control mode switching process after the establishment of the steam cavity, which includes: Determine whether the preset control mode switching conditions are met. The control mode switching conditions include the increase in the discharge flow exceeding the second threshold, the pressure deviation of the regulator being lower than the third threshold, the internal temperature change rate of the regulator being lower than the fourth threshold, and the actual cold water level of the regulator being lower than the fifth threshold. When the control mode switching conditions are met, a control mode switching command is issued to automatically switch the voltage regulator pressure control mode from single-phase control mode to two-phase control mode. Confirm that the voltage regulator spray valve, each heater, the charging valve, and the high-pressure relief valve are all in automatic control mode; The liquid level setpoint is calculated based on the target liquid level value and the rate of liquid level change, and the liquid level of the pressure regulator is adjusted according to the liquid level setpoint. Confirm that the voltage regulator switching to two-phase control is complete.

[0009] In one embodiment of the present invention, the process of the voltage regulator switching from a two-phase state to a single-phase state includes a water filling process, which includes: Set a target liquid level value and a liquid level change gradient setting value, so that the liquid level setting value changes gradually according to the liquid level change gradient setting value; When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the high pressure relief valve is automatically adjusted according to the liquid level setting value to control the pressure regulator liquid level to rise according to the liquid level change gradient setting value. When the measured liquid level of the pressure regulator is higher than the preset liquid level setting value for completion of filling, the filling of the pressure regulator is confirmed to be complete.

[0010] In one embodiment of the present invention, the process of the voltage regulator switching from a two-phase state to a single-phase state further includes a second pressure control process, which includes: Switch the primary circuit pressure control from the voltage regulator to the high-pressure relief valve; Calculate the rate of change of pressure in the primary loop; The high-pressure relief valve is adjusted in stages based on the primary circuit pressure change rate and the pressure regulator water compensation value.

[0011] In one embodiment of the present invention, adjusting the high-pressure relief valve in stages according to the primary circuit pressure change rate and the pressure regulator water compensation value includes: When the rate of change of the primary circuit pressure is negative and the water compensation value of the pressure regulator is negative, the first control stage is executed, and the high-pressure relief valve is gradually closed. When the water compensation value of the pressure regulator is positive and the primary circuit pressure is lower than the sixth threshold, the second control phase is executed to maintain the current opening of the high-pressure relief valve. When the water compensation value of the pressure regulator is positive and the primary circuit pressure is higher than the seventh threshold, the third control stage is executed, and the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator set value and the actual pressure value.

[0012] In one embodiment of the present invention, the second pressure control process further includes: after completing the phased adjustment, confirming that the two-phase control of the voltage regulator is in tracking mode, confirming that the pressure control setpoint is a predetermined setpoint, confirming that the high-pressure relief valve is in automatic mode, and confirming that all heaters have been shut down.

[0013] In one embodiment of the present invention, during the control of the high-pressure relief valve, if it is detected that the relief flow rate drops to a preset minimum flow rate threshold, the current opening degree of the high-pressure relief valve is maintained.

[0014] This invention also proposes a phase-to-phase switching control system for a nuclear power plant pressurizer, comprising: The parameter acquisition unit is used to acquire primary loop operating parameters, which include at least the charging flow rate, the draining flow rate, the average temperature of the primary loop coolant, and the pressure regulator pressure. The water compensation calculation unit is used to calculate the voltage regulator water compensation value based on the primary loop operating parameters and a preset primary loop water compensation model. The control unit is used to automatically control the pressure and / or liquid level during the phase transition process of the pressure regulator based on the water compensation value of the pressure regulator.

[0015] In one embodiment of the present invention, the water compensation calculation unit includes: The flow deviation calculation module is used to calculate the flow deviation between the charging flow and the discharge flow. The temperature change rate calculation module is used to calculate the temperature change rate of the average temperature of the primary coolant. The pressure change rate calculation module is used to calculate the pressure change rate of the pressure regulator. The volume change calculation module is used to calculate the density change of the primary loop water body based on the temperature change rate and the pressure change rate, and to calculate the volume change of the primary loop water body based on the density change. The compensation value generation module is used to calculate the water compensation value of the pressure regulator based on the volume change and the flow deviation.

[0016] In one embodiment of the present invention, the control unit includes a first control module, the first control module being used for: Compare the water compensation value of the voltage regulator with the first threshold; When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the water compensation value of the pressure regulator is positive and lower than the first threshold, the current opening of the high-pressure relief valve is maintained. When the water compensation value of the pressure regulator is positive and higher than the first threshold, the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator's set value and the actual pressure value.

[0017] In one embodiment of the present invention, the control unit further includes a second control module, the second control module being used for: After the pressure regulator establishes the steam chamber, it is determined whether the preset control mode switching conditions are met. If the conditions are met, a control mode switching command is issued to automatically switch the pressure control mode of the pressure regulator from the single-phase control mode to the two-phase control mode. The control mode switching conditions include the increase in the discharge flow rate exceeding the second threshold, the pressure deviation of the pressure regulator being lower than the third threshold, the internal temperature change rate of the pressure regulator being lower than the fourth threshold, and the actual cold water level of the pressure regulator being lower than the fifth threshold. After switching to the dual-phase control mode, the liquid level setpoint is calculated based on the target liquid level value and the liquid level change rate, and the pressure regulator liquid level is adjusted according to the liquid level setpoint.

[0018] In one embodiment of the present invention, the control unit includes a third control module, the third control module being used for: Set a target liquid level value and a liquid level change gradient setting value, so that the liquid level setting value changes gradually according to the liquid level change gradient setting value; When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the high-pressure relief valve is automatically adjusted according to the liquid level setting value to control the pressure regulator liquid level to rise according to the liquid level change gradient setting value.

[0019] In one embodiment of the present invention, the control unit includes a fourth control module, the fourth control module being used for: Switch the primary circuit pressure control unit from the voltage regulator to the high-pressure relief valve; Calculate the rate of change of pressure in the primary loop; The high-pressure relief valve is adjusted in stages based on the primary circuit pressure change rate and the pressure regulator water compensation value.

[0020] The beneficial effects of this invention are as follows: The nuclear power plant pressurizer phase-to-phase switching control method and system proposed in this invention, by constructing a primary loop water compensation algorithm, couples and calculates multiple parameters such as temperature change rate, pressure change rate, and flow deviation to generate a feedforward compensation signal characterizing the volume change of the primary loop water. This proactively predicts and offsets pressure disturbances caused by thermal expansion and contraction of the water, achieving stable control throughout the entire phase-to-phase switching process. Through a pressure control strategy based on water compensation values, temperature oscillations during the build-up heating process are fundamentally eliminated, ensuring continuous and efficient heating of the pressurizer and significantly shortening the build-up time. Furthermore, the automatic switching technology of the control mode based on multi-parameter comprehensive judgment realizes a transition from single-phase control... The seamless and smooth handover to dual-phase control eliminates the risk of timing errors in manual switching; the water filling process control method, which introduces a water compensation model, actively compensates for the cooling and contraction effect of the water, ensuring that the liquid level rises steadily according to the preset gradient; through pressure step control technology, the critical transition stage after water filling is decomposed into three independent control stages: stop the drop, observation, and recovery, which completely solves the problem of pressure easily exceeding limits and becoming unstable before and after the disappearance of the steam cavity; the method and system of this invention realize the automated control of the entire process of phase switching of the pressurizer, significantly reducing the operator's workload and the risk of human error, and improving the inherent safety, automation level, and intelligence level of nuclear power units under start-up and shutdown conditions. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] In the attached diagram: Figure 1 A schematic diagram of a phase-to-phase switching control method for a nuclear power plant voltage regulator provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating a phase-to-phase switching control method for a nuclear power plant pressurizer provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of a primary loop water change compensation algorithm provided in one embodiment of the present invention; Figure 4 This is a logic diagram of the first pressure control process for a single-phase to two-phase voltage regulator provided in one embodiment of the present invention. Figure 5 This is a control principle diagram of the automatic switching process of the control mode after the voltage regulator establishes the steam cavity in one embodiment of the present invention; Figure 6This is a control principle diagram of the water filling process of a voltage regulator switching from two-phase to single-phase in one embodiment of the present invention; Figure 7 This is a schematic diagram of the pressure step control principle for the second pressure control process of a voltage regulator switching from two-phase to single-phase in one embodiment of the present invention. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0024] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0025] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0026] In pressurized water reactor (PWR) nuclear power units, the pressurizer is a key component of the reactor coolant system, used to achieve stable control of the primary coolant pressure. The pressurizer phase transition is a critical operational stage in the start-up and shutdown process of a PWR nuclear power unit. Phase transitions include the "single-phase to two-phase" process during startup and the "two-phase to single-phase" process during shutdown. In single-phase mode, the entire primary coolant loop is a solid water mass, extremely sensitive to pressure changes. Even minute temperature changes causing thermal expansion and contraction of the water can lead to significant pressure fluctuations, even exceeding pressure-temperature operating limits. In two-phase mode, the pressurizer's pressure-stabilizing function is truly realized, stabilizing and controlling the primary coolant pressure through the buffering effect of the steam chamber.

[0027] Currently, the phase-to-phase switching operation of pressurizers in various types of pressurized water reactor nuclear power units relies primarily on manual control by operators. Taking the single-phase to two-phase conversion process as an example, the operator needs to independently heat the pressurizer, determine the saturation state, adjust the heater power, shut down the heater, monitor the discharge flow and liquid level changes, determine the completion of the steam chamber establishment, and finally switch the pressure control mode—a process involving more than ten steps. Similarly, the two-phase to single-phase conversion process also relies on operators to manually complete a series of delicate operations such as water filling and pressure control mode switching. Manual control demands extremely high skill levels and experience from operators, who must continuously monitor multiple parameters and coordinate the operation of multiple devices, resulting in a heavy workload. Especially during changes in unit status, parameters change rapidly. If the timing or magnitude of the operation is inappropriate, it can easily cause abnormal fluctuations in the primary circuit pressure or liquid level, even exceeding operating limits, triggering protection actions, and endangering unit safety. Furthermore, during the single-phase to two-phase heating cavity building process, if the pressure control strategy is not appropriate, the charged low-temperature coolant may repeatedly enter the pressure regulator, causing the heated water to be repeatedly cooled, resulting in temperature oscillations of "heating-expansion-over-adjustment-cooling-reheating", which seriously affects cavity building efficiency and equipment safety.

[0028] Please see Figures 1 to 7 This invention proposes a phase-to-phase switching control method for pressurizers in nuclear power plants. By constructing a feedforward-feedback composite control system based on a physical model, it fundamentally solves the aforementioned technical challenges. The method mainly includes the following steps: S100. Obtain primary circuit operating parameters, which include at least the charging flow rate, the draining flow rate, the average temperature of the primary circuit coolant, and the pressure regulator pressure.

[0029] S200. Based on the primary loop operating parameters and the preset primary loop water compensation model, calculate the voltage regulator water compensation value.

[0030] S300. Based on the water compensation value of the pressure regulator, automatically control the pressure and / or liquid level during the phase transition process of the pressure regulator. The phase transition process of the pressure regulator includes the process of the pressure regulator transitioning from a single-phase state to a two-phase state and the process of the pressure regulator transitioning from a two-phase state to a single-phase state.

[0031] Please see Figures 1 to 7In the nuclear power plant pressurizer phase-to-phase switching control method of the present invention, firstly, the primary loop operating parameters are obtained through step S100 to provide a data foundation for subsequent calculations and control; in step S200, a primary loop water compensation model based on physical mechanisms is constructed. This model couples and calculates isolated multi-source parameters such as flow rate, temperature, and pressure in traditional control, quantifies the volume change of the primary loop water due to thermal expansion and contraction in real time, and generates a comprehensive pressurizer water compensation value. This compensation value serves as a feedforward quantity, characterizing the trend and magnitude of the current net volume change of the primary loop water; step S300 then fundamentally... This approach changes the traditional control decision-making logic: instead of passively adjusting based solely on pressure or level deviations, it uses the "pressure stabilizer water compensation value" as the core basis for control decisions. Throughout the entire phase transition process, regardless of the sub-stage such as heating cavity construction, mode switching after steam cavity establishment, water filling, or pressure transfer, the control system dynamically selects the most suitable control strategy based on this compensation value. This strategy either actively compensates for the thermal expansion and contraction of the water or maintains the system at its optimal operating point for efficient heating / water filling, thus achieving a fundamental shift from "passive deviation response" to "active feedforward compensation."

[0032] It should be noted that the key challenge in the phase transition of the pressurizer lies in maintaining the stability of the primary loop pressure. During this stage, the allowable range of pressure variation in the primary loop is very small, typically requiring fluctuations of less than 1 MPa. Meanwhile, the temperature of the primary loop coolant is continuously changing (heating during single-phase to two-phase transition, and cooling during two-phase to single-phase transition), resulting in significant thermal expansion and contraction of the water, placing extremely high demands on pressure control. To address this challenge, this invention proposes a primary loop water compensation algorithm. This algorithm provides a physically meaningful feedforward compensation signal to the control system by quantifying the changes in water density and volume caused by temperature variations in real time. This algorithm plays a crucial role in both the single-phase to two-phase and two-phase to single-phase transitions of the pressurizer. Combined with targeted control methods for each stage, it enables the pressurizer to maintain stable and orderly pressure and liquid level control throughout the entire phase transition process, preventing exceedances of operating limits. This invention, through the aforementioned technical solution, achieves automated control of the entire phase-to-phase switching process of the pressurizer, covering all complex operating conditions from single-phase to two-phase and from two-phase to single-phase, forming a complete technical closed loop. This significantly reduces the operator's workload and the possibility of human error, improving the automation and intelligence level of the unit. By introducing a water compensation model, the control system can predict and actively offset water volume disturbances caused by temperature changes, fundamentally suppressing pressure oscillations and ensuring that the main parameters of the primary loop are always stably maintained within operating limits. This significantly improves the inherent safety of the unit under high-risk conditions such as start-up and shutdown. It provides a novel, physics-model-driven intelligent control mode for the primary loop control of nuclear power plants.

[0033] Please see Figures 1 to 7In an optional embodiment of the present invention, in step S100, primary loop operating parameters are obtained by fully reusing and integrating information from existing instrumentation and measurement systems in the nuclear power plant. These primary loop operating parameters include at least the charge flow rate, discharge flow rate, average primary loop coolant temperature, and pressurizer pressure. Specifically, the charge flow rate and discharge flow rate can be obtained in real time by corresponding flow detection devices (such as charge flow rate detection devices and discharge flow rate detection devices) in the RCV system (chemical and volume control system), reflecting the water exchange rate between the primary loop and the chemical and volume control system, and serving as boundary conditions for maintaining the primary loop water balance. The average primary loop coolant temperature is calculated from measurements by multiple temperature detectors arranged on the primary loop main pipeline, typically taking the average of the hot-end and cold-end temperatures of the loop, and is a core parameter characterizing the overall thermal state of the primary loop. The pressurizer pressure is obtained from a pressure transmitter at the top of the pressurizer and is the most directly controlled variable for pressure control. The selection of these parameters constitutes a minimum set of parameters that fully describes the primary loop water mass and energy balance. Temperature is the primary factor causing changes in water density, while pressure is a direct control target and a secondary factor affecting density. The inflow and outflow rates are methods for artificially controlling the water's entry and exit from the primary loop. By continuously and in real-time acquiring these parameters, complete and accurate input information is provided for the subsequent water compensation model, enabling the model to accurately and promptly detect any subtle changes in the primary loop water. This is a prerequisite for achieving high-precision feedforward control.

[0034] Please see Figures 1 to 7In an optional embodiment of the present invention, in step S200, based on the primary loop operating parameters and a preset primary loop water compensation model, the pressure regulator water compensation value is calculated. This step transforms the physical principle into an executable control algorithm. Specifically, calculating the pressure regulator water compensation value based on the preset primary loop water compensation model includes: First, calculating the flow deviation between the charging flow rate and the discharge flow rate. This deviation represents the rate of net inflow or outflow of primary loop water caused by active human intervention, and is an active control quantity for maintaining the balance of primary loop water volume. Second, calculating the temperature change rate of the primary loop coolant average temperature. The temperature change rate is the fundamental driving force for water volume change, directly reflecting whether the system is in a heating expansion process or a cooling contraction process, and the degree of drastic change. Third, calculating the pressure change rate of the pressure regulator. Temperature is the dominant factor affecting water density, but pressure also affects density through the elastic compressibility coefficient of water. Especially in high-pressure systems, introducing the pressure change rate can correct the accuracy of density calculation, making the model more accurate in high-pressure, high-precision applications. Next, based on the temperature change rate and the pressure change rate, the density change of the primary loop water is calculated, and the volume change of the primary loop water is calculated based on the density change. In this step, based on the thermodynamic and physical properties of water, temperature and pressure changes affect density to varying degrees. Combined with the known total volume of the primary loop water (i.e., the primary loop volume), the density change can be accurately converted into the net volume change of the entire primary loop water (primary loop water volume change). This change represents the surplus or deficit of water volume caused solely by changes in physical state (not by artificial replenishment or drainage), a crucial but unmeasurable implicit disturbance. Finally, based on the volume change and the flow deviation, the pressure regulator water compensation value is calculated. It can be understood that in the primary loop water balance, the net artificial injection flow should exactly compensate for the volume contraction caused by changes in physical state, or the net artificial discharge flow should exactly offset the volume expansion caused by changes in physical state; that is, the "flow deviation" and the "water volume change" reach a dynamic balance. Therefore, comparing the two, the difference is the pressure regulator water compensation value. When the compensation value is positive, it means that the net inflow is greater than the water body expansion (or the net outflow is less than the water body contraction), and the system water volume increases netly; when the compensation value is negative, it means that the net outflow is greater than the water body contraction (or the net inflow is less than the water body expansion), and the system water volume decreases netly.

[0035] Please see Figures 1 to 7In a specific embodiment, in the primary loop water compensation algorithm, for example, the charging flow rate can be set as Q1 and the discharge flow rate as Q2, then the flow deviation ΔQ can be expressed as: ΔQ = Q1 - Q2. Let the average temperature of the primary loop coolant be T_avg and the pressure regulator pressure be P. The temperature change rate dT / dt and the pressure change rate dP / dt can be obtained through differential calculation of continuously sampled values. The density ρ of the primary loop water is a function of temperature T and pressure P, i.e., ρ = f(T, P), which can be obtained by interpolation or fitting based on a table of thermodynamic properties of water. The density change Δρ can be expressed as: Δρ = ( ρ / T)·(dT / dt)·Δt + ( ρ / P)·(dP / dt)·Δt, where Δt is the control period. Let the total volume of the primary loop water be V_total, then the volume change ΔV of the primary loop water can be expressed as: ΔV ≈ V_total·(Δρ / ρ_avg), where ρ_avg is the current average density. Finally, the pressure regulator water compensation value C can be expressed as the deviation between the volume change and the flow deviation: C = ΔQ - (ΔV / Δt). When C>0, it indicates that the net inflow rate is greater than the water volume expansion rate, resulting in a net increase in system water volume; when C<0, it indicates that the net outflow rate is greater than the water volume contraction rate, resulting in a net decrease in system water volume. It should be noted that the above formula is only a specific calculation example, and the scope of protection of this invention is not limited to this specific expression. Any method based on the coupling calculation of temperature, pressure change rate, and flow deviation to characterize the volume change of the primary loop water falls within the scope of protection of this invention.

[0036] Please see Figures 1 to 7 In an optional embodiment of the present invention, the present invention, through the calculation in step S200, couples the three parameters of temperature change rate, pressure change rate, and flow deviation within a unified physical model framework to generate a feedforward compensation signal with clear physical meaning, rather than adopting a control approach based solely on a single deviation. The "pressurizer water compensation value" calculated by this model not only reflects the current water imbalance state, but more importantly, by introducing the temperature and pressure change rates, it can predict the trend of water volume changes, enabling the control system to have predictive capabilities and act in advance to offset impending disturbances, transforming passive adjustment into active compensation. This is key to achieving a highly stable phase transition process. The model has strong versatility; its physical principles are applicable to any pressurized water reactor nuclear power unit, requiring only parameter calibration based on the primary loop water load and geometric parameters of the specific unit for application.

[0037] Please see Figures 1 to 7In an optional embodiment of the present invention, in step S300, the pressure and / or liquid level during the phase transition process of the pressurizer are automatically controlled based on the pressurizer water compensation value. The phase transition process includes the process of the pressurizer transitioning from a single-phase state to a two-phase state and the process of the pressurizer transitioning from a two-phase state to a single-phase state. These two processes correspond to the two most critical transitional conditions during nuclear power unit startup and shutdown / steam elimination. While the operational objectives, equipment states, and physical processes differ between the two conditions, they share a core challenge: how to maintain the stability of the primary loop pressure and liquid level during dynamic processes involving drastic changes in temperature, pressure, and phase state. Specifically, the pressurizer transition from a single-phase state to a two-phase state includes a first pressure control process and an automatic control mode switching process after the steam cavity is established. The pressurizer transition from a two-phase state to a single-phase state includes a water filling process and a second pressure control process. All control components work together to achieve smooth automation of the entire phase transition process. The core of this invention lies in unifying the aforementioned control tasks under a decision framework centered on the "pressure stabilizer water compensation value." Whether it is heating and anti-oscillation during cavity construction, mode switching after the steam cavity is established, water filling balance during steam cavity extinguishing, or pressure transfer before the steam cavity disappears, the generation of control commands directly or indirectly depends on the calculation of this water compensation value. This creates a logically self-consistent automated control system, solving the fragmentation problem in the prior art where different operating conditions require different control logics and manual switching is necessary.

[0038] Please see Figures 1 to 7In an optional embodiment of the present invention, the process of the pressurizer transitioning from a single-phase state to a two-phase state includes a first pressure control process, which is the cavity-building process during the startup phase of a nuclear power unit. In this process, the pressurizer starts from a full-water state and heats the internal water using an electric heater. As the temperature rises, the water density decreases and its volume expands, causing a rapid increase in pressure within the entire closed primary loop system. At this point, the control system must precisely adjust the opening of the high-pressure relief valve to discharge an appropriate amount of coolant to make room for the thermal expansion of the water and maintain the pressure near the set value. However, traditional PID control has a serious drawback in this stage: when the pressure rises, the PID controller opens the relief valve wider; if over-adjustment leads to excessive discharge, the pressure drops again, at which point the PID controller issues a command to close the relief valve. This cycle of "high pressure - valve open - low pressure - valve close" causes the low-temperature coolant from the charging pipeline to be repeatedly drawn into the pressure regulator, cooling the water being heated. This results in vicious temperature oscillations of "heating - expansion - over-adjustment - cooling - reheating," severely slowing down the cavity-building efficiency and causing unnecessary thermal fatigue to the equipment. To solve this problem, the pressure control method of this invention automatically controls the pressure and / or liquid level during the phase transition of the pressure regulator based on the pressure regulator's water compensation value, ensuring continuous heating, improving heating efficiency, and shortening the single-phase to two-phase transition time. It should be noted that before executing the above pressure control strategy, the control system must first determine that the pressure regulator is in single-phase control mode and combine this first pressure control process with the overall control sequence of unit startup to ensure that the control link is activated at the correct time.

[0039] Specifically, the process includes the following steps: First, the pressure regulator water compensation value is calculated using a primary loop water compensation model and then assessed. Second, when the pressure regulator water compensation value is negative, the opening of the high-pressure relief valve is reduced. Third, when the pressure regulator water compensation value is positive, it is compared with a preset first threshold. If the pressure regulator water compensation value is lower than the first threshold, the current opening of the high-pressure relief valve is maintained. If the pressure regulator water compensation value is higher than the first threshold, the high-pressure relief valve is automatically adjusted based on the deviation between the pressure regulator's setpoint and the actual pressure value. It should be noted that the first threshold is a positive value used to define the upper limit of the ideal balanced heating window. This threshold can be calibrated based on the total volume of the primary loop water, the current heating power, and the pressure regulator's pressure control accuracy requirements. Specifically, it can be determined through engineering tests or simulations of the cavity construction process, ensuring that the system maintains efficient net heating without causing excessively rapid pressure increases within this threshold range.

[0040] Please see Figures 1 to 7It should be noted that the core of the above control strategy is to use the pressure regulator's water compensation value to determine whether the system is currently in the optimal continuous heating state, and to determine the valve action accordingly. When the compensation value is negative, it means that too much water is discharged (or too little water is added), the system is in a net water loss state, and is about to or is in the process of absorbing low-temperature coolant, which is a precursor to severe oscillation. At this time, the control system takes action, forcibly closing the high-pressure discharge valve to reduce hot water discharge and pull the system back to the track of net water addition and continuous heating. When the compensation value turns positive but the magnitude is still small (below the first threshold), it indicates that the current net flow rate of addition and discharge is just enough to balance the thermal expansion of the water. The water inside the pressure regulator is being continuously net heated, the temperature is rising steadily, and there is no repeated inflow and outflow of cold water. This is the most ideal balanced heating window. At this time, the best strategy of the control system is to lock the current valve opening, allowing the system to operate stably at this efficient point and avoiding any unnecessary adjustment actions that would disrupt this perfect balance. When the compensation value increases positively and exceeds the first threshold, it indicates that the system is receiving too much water, and the pressure is about to rise rapidly. At this point, compensation logic alone is insufficient to maintain pressure. Control is then transferred to the PID controller, which automatically adjusts the valves based on the pressure deviation to precisely control the pressure at the set value. This three-mode control strategy based on compensation values ​​decomposes the complex dynamic balance problem into three clearly defined control regions, adding an intelligent feedforward protection layer to the PID controller. This fundamentally eliminates the problem of repeated heating and cooling of the water caused by PID adjustment inertia, ensuring continuous, stable, and efficient heating of the pressure regulator throughout the build-up process. This significantly shortens the build-up time and completely avoids the thermal shock risk to the primary loop equipment caused by temperature oscillations.

[0041] Please see Figures 1 to 7 In an optional embodiment of the present invention, after the vapor chamber is successfully established by the aforementioned pressure control method, the system needs to automatically and safely switch from single-phase control mode to two-phase control mode. This control step is the second critical step in the transition of the pressure regulator from single-phase to two-phase state. At this time, the physical state and control task of the pressure regulator undergo fundamental changes: a compressible vapor phase space appears inside, enabling it to buffer pressure fluctuations through heating and spraying. The primary loop pressure control mode must smoothly transition from the previous "single-phase pressure control" mode relying on the high-pressure relief valve to the "two-phase pressure control" mode operating the heater and spray valve. Simultaneously, liquid level control is also activated. This is a critical and extremely risky operation; improper switching timing may lead to sudden pressure changes or liquid level loss of control. To solve this problem, the present invention constructs a complete set of multi-parameter automatic judgment and execution logic.

[0042] Specifically, after the pressure regulator transitions from a single-phase to a two-phase state and establishes a steam cavity, a judgment is made as to whether preset control mode switching conditions are met. These conditions include: the increase in discharge flow exceeding a second threshold; the pressure deviation of the pressure regulator being lower than a third threshold; the internal temperature change rate of the pressure regulator being lower than a fourth threshold; and the actual cold water level of the pressure regulator being lower than a fifth threshold. These conditions confirm the stable establishment of the steam cavity from different dimensions: the increase in discharge flow is a direct indication of the formation of the steam cavity and the increase in drainage volume due to water expansion; the pressure deviation being lower than the threshold indicates that the pressure is stable and under control; the temperature change rate being lower than the threshold proves that the steam cavity has reached saturation and the temperature no longer changes drastically; and the cold water level being lower than the threshold is direct geometric evidence that the steam cavity occupies sufficient space. The second threshold indicates that the downward flow rate should increase significantly after the steam chamber is established. The third threshold indicates that the pressure control has become stable. The fourth threshold indicates that the vapor-liquid two phases have reached a saturated equilibrium state. The fifth threshold is the steam chamber volume ratio threshold determined based on the regulator geometry and cold calibration. These thresholds can all be determined through engineering verification based on the specific unit's operating data and design parameters.

[0043] Please see Figures 1 to 7 In an optional embodiment of the present invention, when all the above conditions are met, the system automatically issues a control mode switching command, automatically switching the pressure control mode of the pressure regulator from single-phase control mode to dual-phase control mode. It also confirms that the pressure regulator spray valve and each heater are in the automatic control position, and confirms that the charging valve and high-pressure relief valve are in the automatic control position, ensuring that all relevant actuators are ready to respond to subsequent automatic control commands. After the above confirmation is completed, the control system calculates the liquid level setpoint based on the target liquid level value and the liquid level change rate, and adjusts the pressure regulator liquid level according to the liquid level setpoint. By setting the liquid level change rate, the liquid level can be smoothly transitioned from the current value to the target value, avoiding the impact of abrupt liquid level changes on the system. Finally, the system confirms that the pressure regulator switching to dual-phase control is complete, and the automated control of the entire process from single-phase to dual-phase ends. This automatic switching scheme transforms the complex decision-making process of operators based on experience and multi-source information into an objective, quantifiable, and automatically executable logical program. It eliminates the risk of human error, ensures precise timing and smooth process of control mode switching, and achieves seamless automation from single-phase to two-phase control.

[0044] Please see Figures 1 to 7In an optional embodiment of the present invention, the first control stage of the pressurizer's transition from a two-phase to a single-phase state during the unit shutdown phase, namely the water filling process, is designed with automated control. The task of this process is to inject cooling water into the pressurizer, gradually filling it from a vapor-liquid two-phase state to a water-solid state. This process typically involves two charging pumps operating in parallel to provide sufficient charging flow. The control system sets a target pressurizer level (usually full level) and a level change gradient setpoint, causing the level setpoint to rise gradually and slowly according to this gradient setpoint to prevent pressure surges caused by excessively rapid water filling. During the water filling process, the primary coolant temperature continuously decreases due to the synchronous operation of the Residual Heat Removal System (RRA system). Cooling causes the water density to increase and its volume to shrink, resulting in a continuous decrease in the total volume of the primary coolant. Therefore, if the charging flow is simply maintained greater than the draining flow, the volume shrinkage effect of the water may cause the primary coolant pressure to decrease instead of increase due to water filling, or even result in the charging rate failing to keep up with the shrinkage rate, leading to an abnormal situation where the pressurizer level drops instead of rises. To address this issue, the present invention introduces a water compensation model into the water filling process control, and automatically controls the pressure and / or liquid level during the phase transition process of the pressure regulator based on the water compensation value of the pressure regulator.

[0045] Specifically, the process includes the following steps: After confirming that the charging pump is in dual-pump operation mode (two charging pumps are running), a target liquid level value and a liquid level change gradient setting value are set, so that the liquid level setting value changes gradually according to the liquid level change gradient setting value; when the pressure regulator water compensation value (calculated through step S200) is negative, the opening of the high-pressure relief valve is reduced; when the pressure regulator water compensation value is positive, the high-pressure relief valve is automatically adjusted according to the liquid level setting value to control the pressure regulator liquid level to rise according to the liquid level change gradient setting value; when the pressure regulator liquid level measurement value continues to rise and eventually exceeds the preset water filling completion liquid level setting value, the control system automatically determines that the water filling process is complete and issues a pressure regulator water filling completion signal. The issuance of this signal marks the end of the water filling process control link and provides the start-up enable condition for the subsequent pressure step control link.

[0046] Understandably, a negative compensation value indicates that the net flow rate of the current filling and draining is less than the volume of water shrinkage. The system's water supply is insufficient, and the liquid level may stagnate or even drop. In this case, the control system prioritizes closing the drain valve, forcibly increasing the net filling volume through throttling to counteract the water shrinkage effect. When the compensation value turns positive, it means the net filling flow rate has exceeded the water shrinkage, and the system water volume enters a net growth channel. At this point, the control objective returns to liquid level regulation itself. The PID controller automatically adjusts the valve according to the liquid level setpoint gradient, allowing the liquid level to smoothly follow the set trajectory until the target value is reached, completing the filling process. This control strategy incorporates the physical shrinkage of the water body as a feedforward factor into the flow balance calculation, ensuring that the filling flow rate setting and drain valve adjustment can actively adapt to and compensate for volume changes at any cooling rate. This in principle guarantees the reliability and stability of the filling process, avoiding the risk of liquid level control failure or abnormal pressure drops.

[0047] Please see Figures 1 to 7 In an optional embodiment of the present invention, it should be noted that whether the drain valve needs to be closed due to water shrinkage or the valve is adjusted to regulate the liquid level, the drain flow rate must not be lower than a preset minimum flow threshold. Besides its pressure control function, the drain channel also plays a crucial safety role in cooling the drain orifice plate and the drain heat exchanger. Once the drain valve is completely closed, the drain channel will lose its cooling flow, which may lead to the vaporization of the coolant after the drain orifice plate, or the charging pipeline may be automatically isolated by the safety system due to excessively low flow, triggering pump shutdown protection and causing the water filling operation to fail. Therefore, in this embodiment, based on the water filling process control, a safety protection measure is added: during the control of the high-pressure drain valve, if the drain flow rate is detected to drop to the preset minimum flow threshold, the current opening of the high-pressure drain valve is maintained to prevent the drain valve from closing. The preset minimum flow threshold is determined based on the minimum cooling flow requirements of the drain orifice plate and the drain heat exchanger. It must also be higher than the lower flow limit that triggers the upper charging pipeline isolation protection to ensure that the drain channel maintains sufficient cooling capacity under any adjustment operation and does not trigger safety protection actions. This protection logic locks the valve opening at a safe limit position, thus ensuring equipment safety while pursuing control performance.

[0048] Please see Figures 1 to 7In an optional embodiment of the present invention, the present invention also innovatively designs the second control link, namely the second pressure control process, in the process of the pressurizer transitioning from a two-phase state to a single-phase state. When the pressurizer liquid level measurement value has reached the high set value and the water filling operation is basically completed, the pressurizer is close to full water, the steam chamber is about to be completely submerged, the steam space inside the pressurizer is negligible, and it almost loses its pressure buffering capacity. The entire primary loop system approaches a rigid water body system that is extremely sensitive to pressure. At this time, it has not yet fully switched to normal pressurizer single-phase pressure control, but the conventional method of controlling pressure through heaters and spray valves has completely failed. The pressure control task at this stage needs to be undertaken by the high-pressure relief valve of the RCV system. However, at this time, the pressure control faces dual disturbances from the deviation of the charging / relief flow and the continuous contraction of the primary loop water, making the control extremely difficult. The slightest carelessness may lead to a rapid drop in pressure triggering a low-pressure reactor shutdown, or pressure overshoot due to too abrupt valve closure. To solve this problem, the present invention adopts pressure step control technology. Based on the primary loop water compensation algorithm, the high pressure discharge valve is controlled to maintain the balance between the charging flow, the discharge flow and the water shrinkage, so that the pressure is maintained within the normal range and will not cause overpressure or underpressure. After the pressure regulator is fully charged, it switches to the normal single-phase pressure control stage of the pressure regulator.

[0049] Specifically, from the issuance of the pressurizer filling completion signal to the pressurizer being fully filled, a pressurizer filling and pressure maintenance logic control is employed. Based on the pressurizer water compensation value, the pressure and / or liquid level during the phase transition of the pressurizer are automatically controlled to maintain the pressure within the normal range, ensuring that overpressure or underpressure does not occur, until the pressurizer is fully filled and then switches to the normal pressurizer single-phase pressure control stage. This includes the following steps: First, the transfer of control is completed, switching the primary loop pressure control from the pressurizer to the high-pressure relief valve. The heater and spray valve exit pressure control tasks, and the high-pressure relief valve becomes the sole actuator for pressure control. Next, the primary loop pressure change rate is calculated. The pressure change rate is the most direct indicator for judging the dynamic trend of system pressure and can provide the earliest warning of pressure drops or surges. Then, based on the primary loop pressure change rate and the pressurizer water compensation value calculated through the primary loop water compensation model, the high-pressure relief valve is adjusted in stages. This phased strategy divides a highly unstable continuous dynamic process into several distinct control phases based on different combinations of pressure trends and water balance. Each phase sets a single, clear control objective, thereby simplifying the process and achieving a smooth transition.

[0050] Please see Figures 1 to 7In an optional embodiment of the present invention, the high-pressure relief valve is adjusted in stages according to the primary circuit pressure change rate and the pressure regulator water compensation value, specifically including the following steps: When the primary circuit pressure change rate is negative and the pressure regulator water compensation value is negative, the first control stage is executed, controlling the gradual closing of the high-pressure relief valve. Both indicators being negative simultaneously indicates that the pressure is decreasing (pressure change rate is negative), and the net inflow rate can no longer compensate for the water contraction (compensation value is negative), meaning the system is in a state of accelerated pressure decline. At this time, the control system aims to stop the decline, therefore, decisive measures are immediately taken to gradually close the relief valve and forcibly increase the net inflow rate to prevent the pressure from continuing to drop. When the pressure regulator water compensation value is positive and the primary circuit pressure is below the sixth threshold, the second control stage is executed, controlling the maintenance of the current opening of the high-pressure relief valve. After the valve closing action takes effect, the compensation value will turn positive, indicating that the net flow rate can overcome the water contraction, and the water volume begins to increase netly. However, at this time, the pressure may still be low (below the sixth threshold) and has not yet returned to the normal range. During this observation phase, the control system locks the current valve position and refrains from further adjustment, allowing the system to slowly recover pressure naturally through a thermodynamic process under the positive circulation of net water, avoiding any new disturbances that might result from active intervention. When the pressure regulator's water compensation value is positive and the primary loop pressure is higher than the seventh threshold, the third control phase is executed, automatically adjusting the high-pressure relief valve based on the deviation between the pressure regulator's setpoint and the actual pressure. When the pressure recovers to above the normal high threshold (seventh threshold), it indicates that the pressure has essentially recovered, and the most dangerous phase of the transition period has passed. At this point, control is returned to the PID controller, which performs normal automatic adjustment based on the pressure setpoint, ultimately stabilizing the pressure at the normal single-phase control setpoint. The sixth and seventh thresholds are pressure values ​​close to the normal control range; these thresholds can be determined based on the specific unit's primary loop pressure operating limits and engineering test data.

[0051] The aforementioned pressure-stage control strategy decomposes the dangerous transient process of pressure control after water filling—which is highly prone to overshoot and triggers protective actions—into three logically clear and single-objective automatic control stages. By introducing a combination of pressure change rate and compensation value judgments, the control system can accurately identify the instantaneous state of the system and automatically call the control law that best matches that state. This solves the problem of pressure oscillation or even loss of control caused by excessive adjustment or inappropriate timing in traditional PID control under this condition. It is a key technological breakthrough for achieving full automation of the two-phase to single-phase process and ensuring absolute safety.

[0052] Please see Figures 1 to 7In an optional embodiment of the present invention, after completing the above three stages of adjustment and stabilizing the primary loop pressure within the normal control range, the control system confirms that the original two-phase pressure control of the voltage regulator is in tracking mode and no longer actively intervenes in pressure regulation; confirms that the pressure control setpoint is a predetermined setpoint applicable to the single-phase state of the water entity; confirms that the high-pressure relief valve is in automatic control mode and can normally respond to subsequent control commands; and confirms that all electric heaters have been shut down to avoid the risk of local boiling that may be caused by heating in a full water state. Once all the above confirmations are passed, it signifies that the pressure control transition from two-phase to single-phase of the voltage regulator has been safely completed, and the system officially enters the normal single-phase pressure control stage of the water entity. This confirmation step serves as a safe conclusion to the pressure staged control process, ensuring that all control loops and actuators of the system are in a correct and safe operating state after the transition, providing a guarantee for long-term stable operation.

[0053] Please see Figures 1 to 7 In an optional embodiment of the present invention, a safety baseline is also set for this pressure-stage control process. Similar to the water filling process, during the control of the high-pressure relief valve, if the discharge flow rate is detected to drop to a preset minimum flow threshold, the current opening of the high-pressure relief valve is maintained. The protection principle and purpose here are consistent with the protection in the aforementioned water filling process, aiming to prevent secondary safety problems caused by excessive valve closure leading to flow interruption in the discharge channel at any stage of pressure control, and to ensure that the discharge pipeline and related equipment maintain sufficient cooling flow under any pressure regulation operation.

[0054] Please see Figures 1 to 7 This invention also proposes a nuclear power plant pressurizer phase-to-phase switching control system, corresponding to the above method. This system includes a parameter acquisition unit, a water compensation calculation unit, and a control unit. The parameter acquisition unit interfaces with the field instruments of the nuclear power plant's distributed control system (DCS) to acquire primary loop operating parameters in real time. These primary loop operating parameters include at least the charging flow rate, the draining flow rate, the average temperature of the primary loop coolant, and the pressurizer pressure. The water compensation calculation unit internally loads a preset primary loop water compensation model to calculate the pressurizer water compensation value online in real time based on the primary loop operating parameters. The control unit, as the system's execution center, receives the compensation value output by the water compensation calculation unit and, based on this compensation value and preset control strategy logic for various operating conditions, generates control commands for field equipment such as the high-pressure drain valve, charging valve, heater, and spray valve, thereby achieving fully automatic control of the pressure and / or liquid level during the pressurizer phase-to-phase switching process. The core advantage of this system architecture lies in its modularity and model-driven characteristics. The decoupled design of the water compensation calculation unit and the control unit allows the core algorithm to be independently optimized and upgraded. Changes in the control strategy do not affect the integrity of the physical model, and vice versa. This architecture provides the system with extremely high flexibility and maintainability.

[0055] Please see Figures 1 to 7 In an optional embodiment of the present invention, the water compensation calculation unit includes a flow deviation calculation module, a temperature change rate calculation module, a pressure change rate calculation module, a volume change calculation module, and a compensation value generation module. The flow deviation calculation module receives real-time measurements of the charging flow and the discharging flow, and outputs the flow deviation through a difference operation. The temperature change rate calculation module and the pressure change rate calculation module calculate the rate of change of the average temperature of the primary coolant and the pressure regulator pressure, respectively, based on the time series data. The volume change calculation module is the executor of the physical model. It has a pre-set table of thermodynamic property parameters or fitting functions for the primary water body. It calculates the change in water density under the current conditions based on the temperature change rate and the pressure change rate, and then combines this with the pre-stored total volume constant of the primary water body to accurately calculate the net volume change of the primary water body at the current moment. Finally, the compensation value generation module receives the flow deviation and the volume change, calculates and outputs the final pressure regulator water compensation value through a preset fusion algorithm (such as difference, weighted deviation calculation, etc.). This modular decomposition method clearly defines the functional boundaries of each computational step, facilitating step-by-step debugging, verification, and engineering implementation of the algorithm.

[0056] Please see Figures 1 to 7 In an optional embodiment of the present invention, the internal structure of the control unit is designed in detail. Because the control objectives, actuators, and constraints vary greatly under different operating conditions during phase transitions, the control unit is logically composed of multiple sub-control modules. Each module is configured to be activated at different stages to complete a specific control task. The control unit includes a first control module, a second control module, a third control module, and a fourth control module. Specifically, the first control module executes pressure control during the transition of the pressure regulator from a single-phase state to a two-phase state; the second control module executes the automatic switching process of the control mode after the steam chamber is established; the third control module executes the water filling process control during the transition of the pressure regulator from a two-phase state to a single-phase state; and the fourth control module executes the pressure-stage control after water filling is completed. This multi-module design based on automatic operating condition scheduling decomposes the entire complex control task into a series of relatively simple controllers. Each controller only needs to perform optimally under its own operating condition, thereby greatly reducing the design complexity and debugging difficulty of the entire control system.

[0057] Please see Figures 1 to 7In an optional embodiment of the present invention, the first control module is used to perform three-mode pressure control based on compensation values ​​during the single-phase to two-phase transition process. It is configured to perform the following steps: comparing the regulator water compensation value from the water compensation calculation unit with a first threshold stored internally; when the regulator water compensation value is negative, generating and outputting a control command to gradually reduce the opening of the high-pressure relief valve in predetermined steps; when the regulator water compensation value is positive and lower than the first threshold, generating and outputting a valve position holding command to lock the current opening of the high-pressure relief valve; when the regulator water compensation value is positive and higher than the first threshold, activating its internal PID controller to automatically adjust the opening of the high-pressure relief valve based on the deviation between the regulator pressure setpoint and the actual pressure value.

[0058] Please see Figures 1 to 7 In an optional embodiment of the present invention, the second control module is used to execute the automatic control mode switching process after the gas chamber is established. It is configured to perform the following steps: after the pressure regulator establishes the gas chamber, it determines whether a preset control mode switching condition is met, and if the condition is met, it issues a control mode switching command to automatically switch the pressure regulator's pressure control mode from a single-phase control mode to a two-phase control mode; after switching to the two-phase control mode, it calculates a liquid level setpoint based on the target liquid level value and the liquid level change rate, and adjusts the pressure regulator's liquid level according to the liquid level setpoint. Further, the second control module may include a mode switching module and a liquid level adjustment module. The mode switching module stores preset control mode switching conditions, including multiple thresholds related to the increase in discharge flow, pressure deviation, temperature change rate, and cold water level. After the single-phase to two-phase process is activated, it continuously determines whether all these conditions are met simultaneously. Once met, it issues a control mode switching command, transferring control to the liquid level adjustment module. The liquid level control module stores the target liquid level value and the liquid level change rate limit under this operating condition. It first calculates the required liquid level change trajectory based on the target liquid level and the current liquid level, and generates a dynamic liquid level setpoint by combining the rate limit. Then, it activates its internal PID controller, and automatically adjusts the opening of the high-pressure relief valve or the charging valve according to the deviation between the dynamic liquid level setpoint and the actual liquid level, so that the liquid level smoothly transitions to the target value.

[0059] Please see Figures 1 to 7In an optional embodiment of the present invention, the third control module is configured to perform water filling control for switching from two-phase to single-phase operation. It is configured to perform the following steps: store or receive the input target liquid level value and liquid level change gradient set value, and generate a dynamic liquid level set value that gradually increases with time according to the gradient; when the pressure regulator water compensation value is negative, forcibly output an instruction to close the high-pressure relief valve; when the pressure regulator water compensation value is positive, activate its internal liquid level PID controller, and automatically adjust the high-pressure relief valve according to the deviation between the dynamic liquid level set value and the actual liquid level value, so as to control the pressure regulator liquid level to rise according to the preset liquid level change gradient set value.

[0060] Please see Figures 1 to 7 In an optional embodiment of the present invention, the fourth control module is configured to perform pressure-stage control after water filling is completed. It is configured to perform the following steps: upon activation, a control command is first issued to switch the primary loop pressure control unit from the pressure regulator (heater and spray valve) to the high-pressure relief valve; the primary loop pressure change rate is continuously calculated; then, based on the combined state of the primary loop pressure change rate and the pressure regulator water compensation value, the high-pressure relief valve is automatically adjusted in stages. The specific logic of the staged adjustment includes: when the primary loop pressure change rate is negative and the pressure regulator water compensation value is negative, the first control stage is executed, gradually closing the high-pressure relief valve until the pressure regulator water compensation value turns positive; when the pressure regulator water compensation value is positive and the primary loop pressure is below the sixth threshold, the second control stage is executed, maintaining the current opening of the high-pressure relief valve; when the pressure regulator water compensation value is positive and the primary loop pressure is above the seventh threshold, the third control stage is executed, automatically adjusting the high-pressure relief valve based on the deviation between the pressure regulator setpoint and the actual pressure value. After completing the phased adjustment, the fourth control module also performs a transition completion confirmation: confirming that the voltage regulator's two-phase control is in tracking mode, the pressure control setpoint is the predetermined setpoint, the high-pressure relief valve is in automatic mode, and all heaters have been shut down. Furthermore, the third and fourth control modules integrate minimum flow threshold protection logic to first check whether the adjustment command would cause the relief flow to fall below the safe lower limit. If so, the command is automatically corrected to maintain the current opening degree.

[0061] Please see Figures 1 to 7In an optional embodiment of the present invention, after the nuclear power unit receives the start-up command, the system senses through the parameter acquisition unit that the initial state of the primary loop is a single-phase water body. The water compensation calculation unit then starts running and continuously outputs water compensation values. The first control module in the control unit is activated and executes a three-mode control of "valve closure-holding-PID regulation" based on the compensation value. This precisely adjusts the high-pressure relief valve to ensure that the pressure stabilizes during continuous heating of the pressurizer and avoids temperature oscillations. As the steam chamber is gradually established, the relief flow increases, the pressure stabilizes, the temperature stabilizes, and the water level drops. When these indicators simultaneously reach the preset threshold of the mode switching module of the second control module, the module automatically triggers a switching command and seamlessly transfers control to the liquid level regulation module. The system then enters the normal two-phase pressure and liquid level joint control mode. Thus, the phase transition during the start-up phase is automatically completed. During reactor shutdown, when the two-phase to single-phase transition procedure begins, the third control module in the control unit is activated. Based on the water compensation value and the liquid level gradient setpoint, it precisely regulates the balance of the charging and discharging flow rates, ensuring the pressurizer level rises smoothly to full capacity. After charging is complete, the fourth control module seamlessly takes over, executing pressure-stage control and safely transferring pressure control from the pressurizer to the high-pressure discharge valve. Through three-stage logic, it guides the primary loop pressure to smoothly transition to the normal single-phase control state. The entire process requires no operator intervention; all decisions and operations are completed autonomously by the system.

[0062] In summary, the nuclear power plant pressurizer phase-to-phase switching control method and system of this invention, by introducing a primary loop water compensation algorithm based on a physical model and using it as the core feedforward signal, unifies the control architecture for all operating conditions, including single-phase to two-phase and two-phase to single-phase switching. The method and system of this invention achieve full automation of the phase-to-phase switching process, greatly reducing the risk of human error and operator workload; by transforming "passive deviation feedback" into "active feedforward compensation," it fundamentally solves the inherent technical problems of pressure oscillations, temperature oscillations, and parameter over-limits caused by the thermal expansion and contraction of water during reactor start-up and shutdown, achieving extremely stable control of pressure and liquid level. This significantly improves the inherent safety, automation level, and intelligence level of nuclear power units under start-up and shutdown conditions, providing a solid technical guarantee for the optimization and life extension of the primary loop control of nuclear power plants, and has significant engineering application value and promising prospects for widespread application.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

[0064] Throughout this description, numerous specific details, such as examples of components and / or methods, are provided to provide a complete understanding of embodiments of the invention. However, those skilled in the art will recognize that embodiments of the invention may be practiced without one or more of these specific details or by other devices, systems, components, methods, parts, materials, components, etc. In other instances, well-known structures, materials, or operations have not been specifically shown or described in detail to avoid obscuring aspects of embodiments of the invention.

[0065] Throughout this specification, the terms "an embodiment," "embodiment," or "specific embodiment" refer to a particular feature, structure, or characteristic described in connection with an embodiment that is included in at least one embodiment of the invention, but not necessarily in all embodiments. Therefore, the various representations of the phrases "in one embodiment," "in an embodiment," or "in a specific embodiment" in different places throughout the specification do not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic of any specific embodiment of the invention can be combined with one or more other embodiments in any suitable manner. It should be understood that other variations and modifications of the embodiments of the invention described and illustrated herein may be based on the teachings herein and will be considered part of the spirit and scope of the invention.

[0066] It should also be understood that one or more of the elements shown in the figures may be implemented in a more separate or more integrated manner, or may even be removed because they are inoperable in certain circumstances or provided because they may be useful for a particular application.

[0067] Furthermore, unless otherwise expressly stated, any arrows in the accompanying drawings should be considered illustrative only and not limiting. Additionally, unless otherwise stated, the term "or" as used herein is generally intended to mean "and / or". Where a term is anticipated to provide a separation or combination capability that is unclear, a combination of components or steps will also be considered as indicated.

[0068] As used herein and throughout the claims below, unless otherwise specified, “a” and “the” include the plural references. Similarly, as used herein and throughout the claims below, unless otherwise specified, “in” means “in” and “on”.

[0069] The above description of the embodiments shown in this invention (including the content set forth in the abstract of the specification) is not intended to be an exhaustive enumeration or to limit the invention to the precise forms disclosed herein. Although specific embodiments and examples of the invention have been described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the invention, as will be recognized and understood by those skilled in the art. As indicated, these modifications can be made to the invention in accordance with the above description of the embodiments described herein, and such modifications will be within the spirit and scope of the invention.

[0070] This document has generally described the systems and methods in detail to aid in understanding the invention. Furthermore, various specific details have been set forth to provide a general understanding of embodiments of the invention. However, those skilled in the art will recognize that embodiments of the invention can be practiced without one or more specific details, or using other means, systems, accessories, methods, components, materials, parts, etc. In other instances, well-known structures, materials, and / or operations have not been specifically shown or described in detail to avoid obscuring aspects of embodiments of the invention.

[0071] Therefore, although the invention has been described herein with reference to specific embodiments thereof, freedom of modification, various changes and substitutions are also within the scope of the foregoing disclosure, and it should be understood that in some cases, certain features of the invention may be adopted without departing from the scope and spirit of the invention and without corresponding use of other features. Thus, many modifications can be made to adapt a particular environment or material to the essential scope and spirit of the invention. The invention is not intended to be limited to the specific terminology used in the following claims and / or the specific embodiments disclosed as the best mode for carrying out the invention, but the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Therefore, the scope of the invention will be defined only by the appended claims.

Claims

1. A method for phase-to-phase switching control of a pressurizer in a nuclear power plant, characterized in that, include: Obtain primary loop operating parameters, which include at least the charging flow rate, the draining flow rate, the average temperature of the primary loop coolant, and the pressure regulator pressure. Based on the primary loop operating parameters, and using a preset primary loop water compensation model, the voltage regulator water compensation value is calculated. Based on the water compensation value of the pressure regulator, the pressure and / or liquid level during the phase transition process of the pressure regulator are automatically controlled. The phase transition process of the pressure regulator includes the process of the pressure regulator transitioning from a single-phase state to a two-phase state, and the process of the pressure regulator transitioning from a two-phase state to a single-phase state.

2. The method according to claim 1, characterized in that, The calculation of the voltage regulator water compensation value based on the preset primary loop water compensation model includes: Calculate the flow deviation between the charging flow rate and the discharge flow rate; Calculate the rate of temperature change of the average temperature of the primary coolant; Calculate the rate of change of pressure in the voltage regulator; Based on the temperature change rate and the pressure change rate, calculate the density change of the primary loop water body, and calculate the volume change of the primary loop water body based on the density change. The water compensation value of the pressure regulator is calculated based on the volume change and the flow deviation.

3. The method according to claim 1, characterized in that, The process by which the voltage regulator transitions from a single-phase state to a two-phase state includes a first pressure control process, which includes: When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the pressure regulator water compensation value is compared with a first threshold. If the pressure regulator water compensation value is lower than the first threshold, the current opening of the high-pressure relief valve is maintained. If the pressure regulator water compensation value is higher than the first threshold, the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator pressure setting value and the actual pressure value.

4. The method according to claim 3, characterized in that, The process of the voltage regulator switching from single-phase to two-phase state also includes an automatic control mode switching process after the gas cavity is established, which includes: Determine whether the preset control mode switching conditions are met. The control mode switching conditions include the increase in the discharge flow exceeding the second threshold, the pressure deviation of the regulator being lower than the third threshold, the internal temperature change rate of the regulator being lower than the fourth threshold, and the actual cold water level of the regulator being lower than the fifth threshold. When the control mode switching conditions are met, a control mode switching command is issued to automatically switch the voltage regulator pressure control mode from single-phase control mode to two-phase control mode. Confirm that the voltage regulator spray valve, each heater, the charging valve, and the high-pressure relief valve are all in automatic control mode; The liquid level setpoint is calculated based on the target liquid level value and the rate of liquid level change, and the liquid level of the pressure regulator is adjusted according to the liquid level setpoint. Confirm that the voltage regulator switching to two-phase control is complete.

5. The method according to claim 1, characterized in that, The process by which the voltage regulator transitions from a two-phase state to a single-phase state includes a water filling process, which includes: Set a target liquid level value and a liquid level change gradient setting value, so that the liquid level setting value changes gradually according to the liquid level change gradient setting value; When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the high pressure relief valve is automatically adjusted according to the liquid level setting value to control the pressure regulator liquid level to rise according to the liquid level change gradient setting value. When the measured liquid level of the pressure regulator is higher than the preset liquid level setting value for completion of filling, the filling of the pressure regulator is confirmed to be complete.

6. The method according to claim 1, characterized in that, The process of the voltage regulator switching from a two-phase state to a single-phase state also includes a second pressure control process, which includes: Switch the primary circuit pressure control from the voltage regulator to the high-pressure relief valve; Calculate the rate of change of pressure in the primary loop; The high-pressure relief valve is adjusted in stages based on the primary circuit pressure change rate and the pressure regulator water compensation value.

7. The method according to claim 6, characterized in that, The step of adjusting the high-pressure relief valve in stages based on the primary circuit pressure change rate and the pressure regulator water compensation value includes: When the rate of change of the primary circuit pressure is negative and the water compensation value of the pressure regulator is negative, the first control stage is executed, and the high-pressure relief valve is gradually closed. When the water compensation value of the pressure regulator is positive and the primary circuit pressure is lower than the sixth threshold, the second control phase is executed to maintain the current opening of the high-pressure relief valve. When the water compensation value of the pressure regulator is positive and the primary circuit pressure is higher than the seventh threshold, the third control stage is executed, and the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator set value and the actual pressure value.

8. The method according to claim 7, characterized in that, The second pressure control process also includes: after completing the phased adjustment, confirming that the two-phase control of the voltage regulator is in tracking mode, confirming that the pressure control setpoint is the predetermined setpoint, confirming that the high-pressure relief valve is in automatic mode, and confirming that all heaters have been shut down.

9. The method according to claim 5 or 6, characterized in that, During the control of the high-pressure relief valve, if the discharge flow rate is detected to drop to a preset minimum flow threshold, the current opening degree of the high-pressure relief valve is maintained.

10. A phase-to-phase switching control system for a nuclear power plant pressurizer, characterized in that, include: The parameter acquisition unit is used to acquire primary loop operating parameters, which include at least the charging flow rate, the draining flow rate, the average temperature of the primary loop coolant, and the pressure regulator pressure. The water compensation calculation unit is used to calculate the voltage regulator water compensation value based on the primary loop operating parameters and a preset primary loop water compensation model. The control unit is used to automatically control the pressure and / or liquid level during the phase transition process of the pressure regulator based on the water compensation value of the pressure regulator.

11. The system according to claim 10, characterized in that, The water body compensation calculation unit includes: The flow deviation calculation module is used to calculate the flow deviation between the charging flow and the discharge flow. The temperature change rate calculation module is used to calculate the temperature change rate of the average temperature of the primary coolant. The pressure change rate calculation module is used to calculate the pressure change rate of the pressure regulator. The volume change calculation module is used to calculate the density change of the primary loop water body based on the temperature change rate and the pressure change rate, and to calculate the volume change of the primary loop water body based on the density change. The compensation value generation module is used to calculate the water compensation value of the pressure regulator based on the volume change and the flow deviation.

12. The system according to claim 10, characterized in that, The control unit includes a first control module, which is used for: When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the pressure regulator water compensation value is compared with a first threshold. If the pressure regulator water compensation value is lower than the first threshold, the current opening of the high-pressure relief valve is maintained. If the pressure regulator water compensation value is higher than the first threshold, the high-pressure relief valve is automatically adjusted according to the deviation between the pressure regulator pressure setting value and the actual pressure value.

13. The system according to claim 10, characterized in that, The control unit further includes a second control module, the second control module being used for: After the pressure regulator establishes the steam chamber, it is determined whether the preset control mode switching conditions are met. If the conditions are met, a control mode switching command is issued to automatically switch the pressure control mode of the pressure regulator from the single-phase control mode to the two-phase control mode. The control mode switching conditions include the increase in the discharge flow rate exceeding the second threshold, the pressure deviation of the pressure regulator being lower than the third threshold, the internal temperature change rate of the pressure regulator being lower than the fourth threshold, and the actual cold water level of the pressure regulator being lower than the fifth threshold. After switching to the dual-phase control mode, the liquid level setpoint is calculated based on the target liquid level value and the liquid level change rate, and the pressure regulator liquid level is adjusted according to the liquid level setpoint.

14. The system according to claim 10, characterized in that, The control unit includes a third control module, which is used for: Set a target liquid level value and a liquid level change gradient setting value, so that the liquid level setting value changes gradually according to the liquid level change gradient setting value; When the water compensation value of the pressure regulator is negative, the opening of the high-pressure relief valve is reduced. When the pressure regulator water compensation value is positive, the high-pressure relief valve is automatically adjusted according to the liquid level setting value to control the pressure regulator liquid level to rise according to the liquid level change gradient setting value.

15. The system according to claim 10, characterized in that, The control unit includes a fourth control module, which is used for: Switch the primary circuit pressure control unit from the voltage regulator to the high-pressure relief valve; Calculate the rate of change of pressure in the primary loop; The high-pressure relief valve is adjusted in stages based on the primary circuit pressure change rate and the pressure regulator water compensation value.

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