Flange surface liquid level control method, system and primary circuit control system

Abstract

This invention discloses a flange face liquid level control method, system, and primary loop control system. The control method includes: a flange face liquid level control method for pressure vessels, comprising the following steps: after switching to the flange face liquid level control logic, monitoring whether the current liquid level of the pressure vessel flange face is within the normal range; when the current liquid level of the flange face is within the normal range, obtaining the required opening value of the low-pressure discharge flow regulating valve; based on the required opening value and combined with the current opening value of the low-pressure discharge flow regulating valve, obtaining the control result; the control result includes the opening change value and the rate of change value from the current opening value to the required opening value; and adjusting the low-pressure discharge flow regulating valve according to the control result. This method can automatically control the liquid level of the pressure vessel flange face within the normal range, eliminating the burden of manual control.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power, and in particular to a flange surface liquid level control method, system and a primary loop control system. Background Art

[0002] During the overhaul of a nuclear power plant, the pressure vessel in the primary circuit system needs to be opened for inspection, and when the cover is opened, the flange surface liquid level of the pressure vessel needs to be within the normal range. It can be understood that there is a flange in the pressure vessel, and the flange has a certain thickness. Since the liquid level of the pressure vessel is within the flange thickness range, it is called the flange surface liquid level; when the liquid level of the pressure vessel is within the flange thickness range and within the preset range, it means that the flange surface liquid level of the pressure vessel is within the normal range.

[0003] Generally, it takes dozens of hours to open the pressure vessel cover. In addition, when the unit is running or the pressure vessel cover is closed, the water level in the pressure vessel also needs to be maintained within the liquid level range, which also takes dozens of hours. In the related technology, during this period, a master operator will be responsible for tracking the liquid level of the pressure vessel and manually adjusting it. Since the water level changes all the time, it is impossible to distract the operator from other work, which brings a great burden to the operator and is not conducive to the smooth progress of other work.

[0004] Therefore, how to achieve automatic control of the flange surface liquid level of the pressure vessel within the normal range has become the current research goal. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a flange surface liquid level control method, system and a primary loop control system.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a flange surface liquid level control method for a pressure vessel, comprising the following steps:

[0007] S1: After switching to the flange surface liquid level control logic, monitor whether the current liquid level of the flange surface of the pressure vessel is within a normal range;

[0008] S2: when the current liquid level on the flange surface is within a normal range, obtaining a required opening value of the low-pressure discharge flow regulating valve;

[0009] S3: according to the required opening value, combined with the current opening value of the low-pressure discharge flow control valve, a control result is obtained; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value;

[0010] S4: According to the control result, the low-pressure discharge flow regulating valve is adjusted.

[0011] Preferably, the step of obtaining the required opening value of the low-pressure discharge flow regulating valve includes:

[0012] S21: Obtaining a first flow difference between the charging flow rate change rate and the discharging flow rate change rate;

[0013] S22: collecting the current liquid level of the flange surface, and converting the current liquid level of the flange surface and the set liquid level of the flange surface to obtain a second flow difference;

[0014] S23: Obtaining a first opening value that the low-pressure discharge flow regulating valve needs to reach according to the first flow difference and the second flow difference, and setting the first opening value as the required opening value.

[0015] Preferably, the step of obtaining the required opening value of the low-pressure discharge flow regulating valve includes:

[0016] S24: After receiving the automatic tracking command, the current opening value is acquired, and the current opening value is set as the final required opening value.

[0017] Preferably, it also includes:

[0018] When the current liquid level of the flange surface reaches a first preset interval, determining that the current liquid level of the flange surface is in an abnormal range, and setting the maximum opening value as the final required opening value;

[0019] And / or, when the current liquid level of the flange surface reaches a second preset interval, it is determined that the current liquid level of the flange surface is in an abnormal range, and the minimum opening value is set as the final required opening value.

[0020] Preferably, in collecting the current liquid level of the flange surface of the pressure vessel, at least three liquid levels of the flange surfaces of the pressure vessel are collected, and the second largest value among the at least three flange surface liquid levels is used as the final current liquid level of the flange surface.

[0021] The present invention also constructs a flange surface liquid level control system for a pressure vessel, comprising:

[0022] The OAF function control device is used to monitor whether the current liquid level of the flange surface of the pressure vessel is within a normal range after switching to the flange surface liquid level control logic;

[0023] A first computing device, used for obtaining a required opening value of the low-pressure discharge flow regulating valve when the current liquid level on the flange surface is within a normal range;

[0024] A second computing device is used to obtain a control result according to the required opening value and the current opening value of the low-pressure discharge flow control valve; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value;

[0025] The regulating device is used to regulate the low-pressure discharge flow regulating valve according to the control result.

[0026] Preferably, the first computing device comprises:

[0027] A flow rate change rate feedforward device, used to obtain a first flow difference between an upper charging flow rate change rate and a lower discharging flow rate change rate;

[0028] A liquid level closed-loop control device, used for collecting the current liquid level of the flange surface, and converting the current liquid level of the flange surface and the set liquid level of the flange surface to obtain a second flow difference;

[0029] The flange surface liquid level PID control device is used to obtain the first opening value that the low-pressure discharge flow regulating valve needs to reach according to the first flow difference and the second flow difference, and set the first opening value as the required opening value.

[0030] Preferably, the flange surface liquid level PID control device is further used to obtain the current opening value after receiving the automatic tracking command, and set the current opening value as the final required opening value.

[0031] Preferably, the liquid level closed-loop control device comprises at least three liquid level gauges and a third calculation unit;

[0032] The at least three liquid level gauges are respectively used to collect the liquid levels of the flange surfaces of the pressure vessels;

[0033] The third calculation unit is used to take the second largest value among the at least three flange surface liquid levels as the final current liquid level of the flange surface.

[0034] The present invention also constructs a single-loop control system, including a single-phase pressure control system, a PZR water level control system, and a loop water level control system, characterized in that it also includes the above-mentioned flange surface liquid level control system for the pressure vessel and a switching system for switching to one of the single-phase pressure control system, the PZR water level control system, the loop water level control system and the flange surface liquid level control system.

[0035] The implementation of the present invention has the following beneficial effects: the liquid level on the flange surface of the pressure vessel can be automatically controlled within a normal range, the burden of human control is eliminated, other work is facilitated, and errors caused by human factors can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0037] Figure 1is a flowchart of a method for controlling a flange surface liquid level of a pressure vessel according to some embodiments of the present invention;

[0038] Figure 2 is a control logic diagram of a primary loop system of the present invention in some embodiments. DETAILED DESCRIPTION

[0039] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0040] It should be noted that the flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0041] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0042] See also Figure 1 and Figure 2 The present invention constructs a flange surface liquid level control method for a pressure vessel, which can be applied to a nuclear power plant to automatically control the liquid level of a pressure vessel in a primary circuit system.

[0043] In some embodiments, the flange surface liquid level control method comprises the following steps:

[0044] S1: After switching to the flange surface liquid level control logic, monitor whether the current liquid level of the flange surface of the pressure vessel is within the normal range;

[0045] S2: When the current liquid level on the flange surface is within a normal range, obtaining the required opening value of the low-pressure discharge flow regulating valve 11;

[0046] S3: according to the required opening value, combined with the current opening value of the low-pressure discharge flow control valve 11, a control result is obtained; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value;

[0047] S4: According to the control result, the low-pressure discharge flow regulating valve 11 is adjusted.

[0048] It can be understood that the pressure vessel can generally flow the liquid in the pressure vessel to the RIS / RHR system (cooling normal shutdown system) through the downflow loop, and then the RIS / RHR system will lead the liquid to the control box of the RCV system (chemical volume system); and the RCV system can rely on the charging pump to pump the liquid back into the pressure vessel along the charging loop.

[0049] The RCV system is provided with a low-pressure discharge flow regulating valve 11, which is used to control the flow of liquid from the RIS / RHR system to the control tank. By controlling the opening value of the low-pressure discharge flow regulating valve 11, the discharge flow of the pressure vessel is controlled, thereby realizing the change of the liquid level of the pressure vessel.

[0050] In step S1, in a primary loop system, the low-pressure discharge flow regulating valve 11 can control not only the pressure vessel liquid level, but also the one-way pressure, the pressurizer liquid level and the loop water level. A switching system can be set up so that the operator can select the control object corresponding to the low-pressure discharge flow regulating valve 11. After the operator chooses to switch to the flange surface liquid level control logic, the flange surface liquid level control method can be executed.

[0051] At the same time, the flange surface liquid level control method also monitors the current liquid level of the flange surface of the pressure vessel to determine whether the current liquid level of the flange surface is within the normal range, and adds two OAF functions (auxiliary control functions) triggered when the liquid level is too high or too low, which are used to have corresponding auxiliary control functions to adjust and control when the current liquid level of the flange surface of the pressure vessel exceeds the normal range, so as to avoid more serious consequences caused by the operator's untimely response. The normal range is set by relevant personnel according to the actual working conditions. When the current liquid level of the flange surface is within the normal range, step S2 can be continued. When the current liquid level of the flange surface is within the abnormal range, the opening of the low-pressure discharge flow regulating valve 11 is opened to the maximum or minimum according to the current liquid level.

[0052] In some embodiments, when the current liquid level of the flange surface reaches the first preset interval, it is determined that the current liquid level of the flange surface is in an abnormal range, the maximum opening value is set as the final required opening value, and step S3 is executed.

[0053] Optionally, by arranging one or more liquid level gauges on the inner wall of the pressure vessel near its opening, when the liquid level gauge detects that the current liquid level on the flange surface of the pressure vessel is too high, the low-pressure discharge flow regulating valve 11 is fully opened to reduce the liquid level on the flange surface of the pressure vessel as quickly as possible to prevent liquid from overflowing from the pressure vessel. In some embodiments, the maximum opening value is 100%.

[0054] In some embodiments, when the current liquid level of the flange surface reaches the second preset interval, it is determined that the current liquid level of the flange surface is in an abnormal range, the minimum opening value is set as the final required opening value, and step S3 is executed.

[0055] Optionally, by arranging one or more liquid level gauges on the inner wall of the pressure vessel near its bottom, when the liquid level gauge detects that the current liquid level on the flange surface of the pressure vessel is too low, the low-pressure discharge flow regulating valve 11 is completely closed to raise the liquid level on the flange surface of the pressure vessel as quickly as possible and keep the liquid level on the flange surface at an appropriate position. In some embodiments, the minimum opening value is 0%.

[0056] Preferably, an alarm signal is issued when the OAF function is triggered, and more preferably, a pre-alarm can be set based on the alarm.

[0057] In some embodiments, a liquid level below 6.79 m (the second preset interval) is used as a low threshold alarm for the liquid level on the flange surface of the pressure vessel; and a liquid level above 7.08 m (the first preset interval) is used as a high threshold alarm for the liquid level on the flange surface of the pressure vessel.

[0058] See also Figure 2 In step S2, the required opening value of the low-pressure discharge flow regulating valve 11 is obtained, including:

[0059] S20: Determine whether an automatic tracking command is received; if no automatic tracking command is received, execute step S21; if an automatic tracking command is received, execute step S24;

[0060] It can be understood that the automatic tracking command is automatically triggered and sent when the first computing device used to collect the charging flow change rate, the discharging flow change rate and the current liquid level of the flange surface fails, or when switching to manual control of the low-pressure discharging flow regulating valve 11.

[0061] S21: when no automatic tracking command is received, obtaining a first flow difference between a charging flow change rate and a discharging flow change rate;

[0062] In some embodiments, step S21 includes: collecting the charging flow rate change rate and the discharge flow rate change rate, and subtracting the charging flow rate change rate from the discharge flow rate change rate to obtain a first flow difference. It can be understood that the purpose of obtaining the first flow difference is to achieve open-loop regulation and adjust the valve response rate according to the current situation.

[0063] S22: collecting the current liquid level of the flange surface, and converting the current liquid level of the flange surface and the set liquid level of the flange surface to obtain a second flow difference;

[0064] In some embodiments, step S22 includes: collecting the current liquid level of the flange surface, and subtracting the current liquid level of the flange surface from the preset flange surface set liquid level to obtain a liquid level deviation value; and then converting the liquid level deviation value into a second flow difference value. It can be understood that the purpose of obtaining the liquid level deviation value is to achieve closed-loop regulation so that the measured water level reaches the set water level requirement.

[0065] Preferably, multiple water level measurement MNs (liquid level gauges) can be set at the flange surface liquid level position of the pressure vessel, and the second largest value among the collected liquid level values ​​is taken as the current liquid level value of the flange surface to improve the accuracy of liquid level acquisition and avoid single failure. In some implementations, three water level measurement MNs are set, and the water level measurement MNs are all narrow-range liquid level gauges.

[0066] The flange surface setting liquid level can be preset by relevant personnel. In some embodiments, the flange surface setting liquid level can be the liquid level at the center line of the flange surface perpendicular to the axial direction. In some embodiments, the intermediate value between 6.79m and 7.08m is used as the flange surface setting liquid level.

[0067] S23: Obtaining a first opening value that the low-pressure discharge flow regulating valve 11 needs to reach according to the first flow difference and the second flow difference, and setting the first opening value as the required opening value.

[0068] In some embodiments, step S23 includes: summing the first flow difference and the second flow difference to obtain a desired flow value; calculating the desired flow value using a PID {Proportional, Integral, Differential} control algorithm to obtain a first opening value, and setting the first opening value as the desired opening value.

[0069] It can be understood that based on the first flow difference and the second flow difference, the flow difference between the current liquid level on the flange surface in the pressure vessel and the set liquid level, as well as the flow difference between filling into the pressure vessel and discharging from the pressure vessel can be known. From this, it can be calculated how much the flow of the low-pressure discharge flow regulating valve 11 needs to increase / decrease in order to make the current liquid level on the flange surface in the pressure vessel reach the set liquid level, and based on the amount of flow that needs to be increased / decreased (required flow value), the opening value (first opening value) that the regulating valve needs to increase / decrease can be calculated.

[0070] S24: After receiving the automatic tracking command, the current opening value is obtained, and the current opening value is set as the final required opening value.

[0071] It can be understood that when the current liquid level on the flange surface is within the normal range, steps S21 to S23 are generally performed. When the first computing device for collecting the rate of change of the upper filling flow, the rate of change of the lower discharge flow and the current liquid level on the flange surface fails, the current opening value of the low-pressure lower discharge flow regulating valve 11 is used as the final required opening value, in order to maintain the status quo and avoid secondary errors. In other embodiments, according to actual working conditions, step S24 can also be performed when switching to manual control of the low-pressure lower discharge flow regulating valve 11, which is manually controlled by relevant personnel without the need for automatic control intervention.

[0072] In step S3, when the current liquid level on the flange surface of the pressure vessel is within a normal range, the first opening value can be used as the final required opening value, and the first control result can be obtained by subtracting the required opening value from the current opening value.

[0073] When the current liquid level on the flange surface of the pressure vessel is in an abnormal range and reaches the first preset interval, the maximum opening value is used as the final required opening value to obtain a second control result.

[0074] When the current liquid level on the flange surface of the pressure vessel is in an abnormal range and reaches a second preset interval, the minimum opening value is used as the final required opening value to obtain a second control result.

[0075] In step S4, the control result includes the opening change value and the change rate value adjusted from the current opening value to the required opening value. According to different control results, the low-pressure discharge flow control valve 11 is adjusted. It can be understood that the larger the difference between the current opening value and the required opening value, the greater the flow deviation between the current liquid level of the pressure vessel and the set liquid level. At this time, it is necessary to speed up the adjustment speed to approach the set liquid level as soon as possible to ensure the safe operation of the primary circuit system; and the smaller the difference between the current opening value and the required opening value, the smaller the flow deviation between the current liquid level of the pressure vessel and the set liquid level. At this time, the adjustment speed can be relatively slowed down.

[0076] In summary, in the flange surface liquid level control method, after switching to the flange surface liquid level control logic, and when the current liquid level of the flange surface is within the normal range and no automatic tracking command is received, the flow difference between the filling flow rate change rate and the discharge flow rate change rate, and the liquid level deviation between the current liquid level of the flange surface of the pressure vessel and the set liquid level are obtained, and the control result for adjusting the low-pressure discharge flow regulating valve 11 is calculated, and the low-pressure discharge flow regulating valve 11 is adjusted according to the control result, so as to realize the automatic control of the flange surface liquid level of the pressure vessel within the normal range, eliminate the burden of human control, facilitate the development of other work, and reduce the error caused by human factors. It can be understood that the normal range is set by relevant personnel according to the actual working conditions.

[0077] The present invention also constructs a flange surface liquid level control system 1, which, in some embodiments, includes:

[0078] The OAF function control device is used to monitor whether the current liquid level of the flange surface of the pressure vessel is within the normal range after switching to the flange surface liquid level control logic;

[0079] The first computing device is used to obtain the required opening value of the low-pressure discharge flow regulating valve 11 when the current liquid level on the flange surface is within a normal range;

[0080] The second computing device is used to obtain a control result according to the required opening value and the current opening value of the low-pressure discharge flow control valve 11; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value;

[0081] The regulating device is used to adjust the low-pressure discharge flow regulating valve 11 according to the control result.

[0082] In some embodiments, the first computing device includes:

[0083] A judging device, used for judging whether an automatic tracking command is received;

[0084] A flow change rate feedforward device is used to obtain a first flow difference between the upper filling flow change rate and the lower discharge flow change rate; in some embodiments, the flow change rate feedforward device is used to collect the upper filling flow change rate and the lower discharge flow change rate, and subtract the upper filling flow change rate from the lower discharge flow change rate to obtain the first flow difference.

[0085] The liquid level closed-loop control device is used to collect the current liquid level of the flange surface, and convert it into a second flow difference value based on the current liquid level of the flange surface and the set liquid level of the flange surface; in some embodiments, the liquid level closed-loop control device is used to collect the current liquid level of the flange surface, and subtract the current liquid level of the flange surface from the preset set liquid level of the flange surface to obtain a liquid level deviation value; and then convert the liquid level deviation value into a second flow difference value.

[0086] The flange surface liquid level PID control device is used to obtain the first opening value that the low-pressure discharge flow regulating valve 11 needs to reach according to the first flow difference and the second flow difference, and set the first opening value as the required opening value. In some embodiments, the flange surface liquid level PID control device is used to sum the first flow difference and the second flow difference to obtain the required flow value; calculate the required flow value using the PID control algorithm to obtain the first opening value, and set the first opening value as the required opening value.

[0087] The flange surface liquid level PID control device is also used to obtain the current opening value after receiving the automatic tracking command, and set the current opening value as the final required opening value.

[0088] In some embodiments, the OAF function control device includes a first execution unit;

[0089] The first execution unit is used to determine that the current liquid level of the flange surface is in an abnormal range when the current liquid level of the flange surface reaches a first preset threshold value, and set the maximum opening value as the final required opening value.

[0090] In some embodiments, the OAF function control device includes a second execution unit:

[0091] The second execution unit is used to determine that the current liquid level of the flange surface is in an abnormal range when the current liquid level of the flange surface reaches a second preset threshold value, and set the minimum opening value as the final required opening value.

[0092] In some embodiments, the liquid level closed-loop control device includes at least three liquid level gauges and a third computing unit;

[0093] At least three liquid level gauges are used to collect the liquid levels on the flange surfaces of the pressure vessel respectively;

[0094] The third calculation unit is used to take the second largest value among the at least three flange surface liquid levels as the final current flange surface liquid level.

[0095] See also Figure 2 The present invention also constructs a single-loop control system, which in some embodiments includes a single-phase pressure control system 2, a PZR (stabilizer) water level control system 3, a loop water level control system 4, the above-mentioned flange surface liquid level control system 1, and a switching system for switching to one of the single-phase pressure control system 2, the PZR water level control system 3, the loop water level control system 4 and the flange surface liquid level control system 1.

[0096] In some embodiments, the switching system includes a first switching valve 51 for switching to a single-phase pressure control system 2 and a PZR water level control system 3 or a loop water level control system 4 and a flange surface liquid level control system 1, a second switching valve 52 for switching to a single-phase pressure control system 2 or a PZR water level control system 3, and a third valve 53 for switching to a loop water level control system 4 or a flange surface liquid level control system 1.

[0097] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for controlling the liquid level on the flange surface of a pressure vessel, characterized in that: The following steps are involved: S1: After switching to the flange surface liquid level control logic, monitor whether the current liquid level of the flange surface of the pressure vessel is within a normal range; S2: when the current liquid level on the flange surface is within a normal range, obtaining a required opening value of the low-pressure discharge flow regulating valve; S3: according to the required opening value, combined with the current opening value of the low-pressure discharge flow control valve, a control result is obtained; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value; S4: adjusting the low-pressure discharge flow regulating valve according to the control result; Wherein, the step of obtaining the required opening value of the low-pressure discharge flow regulating valve includes: S21: Obtaining a first flow difference between the charging flow rate change rate and the discharging flow rate change rate; S22: collecting the current liquid level of the flange surface, and converting the current liquid level of the flange surface and the set liquid level of the flange surface to obtain a second flow difference; S23: obtaining a first opening value that the low-pressure discharge flow regulating valve needs to reach according to the first flow difference and the second flow difference, and setting the first opening value as the required opening value; In step S4, the change rate value increases as the opening change value increases, and relatively decreases as the opening change value decreases.

2. The flange surface liquid level control method for a pressure vessel according to claim 1, characterized in that: The step of obtaining the required opening value of the low-pressure discharge flow regulating valve comprises: S24: After receiving the automatic tracking command, the current opening value is acquired, and the current opening value is set as the final required opening value.

3. The flange surface liquid level control method for a pressure vessel according to claim 1, characterized in that: Also includes: When the current liquid level of the flange surface reaches a first preset interval, determining that the current liquid level of the flange surface is in an abnormal range, and setting the maximum opening value as the final required opening value; And / or, when the current liquid level of the flange surface reaches a second preset interval, it is determined that the current liquid level of the flange surface is in an abnormal range, and the minimum opening value is set as the final required opening value.

4. The flange surface liquid level control method for a pressure vessel according to claim 1, characterized in that: In collecting the current liquid level of the flange surface of the pressure vessel, at least three liquid levels of the flange surfaces of the pressure vessel are collected, and the second largest value of the at least three flange surface liquid levels is used as the final current liquid level of the flange surface.

5. A flange surface liquid level control system for a pressure vessel, characterized in that: include: The OAF function control device is used to monitor whether the current liquid level of the flange surface of the pressure vessel is within a normal range after switching to the flange surface liquid level control logic; A first computing device, used for obtaining a required opening value of the low-pressure discharge flow regulating valve when the current liquid level on the flange surface is within a normal range; A second computing device is used to obtain a control result according to the required opening value and the current opening value of the low-pressure discharge flow control valve; the control result includes an opening change value and a change rate value adjusted from the current opening value to the required opening value; A regulating device, used for regulating the low-pressure discharge flow regulating valve according to the control result; wherein the change rate value increases as the opening change value increases, and decreases relatively as the opening change value decreases; Wherein, the first computing device comprises: A flow rate change rate feedforward device, used to obtain a first flow difference between an upper charging flow rate change rate and a lower discharging flow rate change rate; A liquid level closed-loop control device, used for collecting the current liquid level of the flange surface, and converting the current liquid level of the flange surface and the set liquid level of the flange surface to obtain a second flow difference; The flange surface liquid level PID control device is used to obtain the first opening value that the low-pressure discharge flow regulating valve needs to reach according to the first flow difference and the second flow difference, and set the first opening value as the required opening value.

6. The flange surface liquid level control system for a pressure vessel according to claim 5, characterized in that: The flange surface liquid level PID control device is also used to obtain the current opening value after receiving the automatic tracking command, and set the current opening value as the final required opening value.

7. The flange surface liquid level control system for a pressure vessel according to claim 5, characterized in that: The liquid level closed-loop control device comprises at least three liquid level gauges and a third calculation unit; The at least three liquid level gauges are respectively used to collect the liquid levels of the flange surfaces of the pressure vessels; The third calculation unit is used to take the second largest value among the at least three flange surface liquid levels as the final current liquid level of the flange surface.

8. A primary circuit control system, comprising a single-phase pressure control system, a PZR water level control system, and a loop water level control system, characterized in that: It also includes a flange surface liquid level control system for a pressure vessel as described in any one of claims 5 to 7 and a switching system for switching to one of the single-phase pressure control system, the PZR water level control system, the loop water level control system and the flange surface liquid level control system.

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