A method and system for compensating coolant flow rate in a primary circuit of a nuclear power unit

Abstract

The present invention relates to a method for compensating the flow rate of a primary circuit coolant of a nuclear power unit, the method comprising the steps of: presetting a number of power platforms from 0% to 100% power, including at least a 0% power platform and a main line power platform; selecting a 0% power platform; obtaining the flow rate percentage of the unit at the 0% power platform, and correcting the flow rate algorithm so that the measured flow rate percentage difference is less than the error range; after reaching the preset accuracy, gradually increasing the power, and repeating the above process until the preset accuracy is reached at the main line power of the unit, and if the accuracy has been reached at the main line power, the compensation process is directly completed. The method of the present invention can compensate the flow rate at any time according to the temperature change when the unit increases the power, so that the detected value of the flow rate is always close to the real flow rate value, and avoid the unit operation failure caused by the flow value detection error.

Description

Technical Field

[0001] The invention belongs to the technical field of instrumentation and control, and in particular relates to a method and system for compensating coolant flow in a primary circuit of a nuclear power unit. Background Art

[0002] During the power generation process, a nuclear power unit first needs to convert nuclear energy into thermal energy, that is, to heat the water in the primary circuit, and then transfer the heat of the primary circuit coolant to the secondary circuit through the steam generator. The secondary circuit generates steam, which drives the steam turbine to rotate, and then the generator generates electricity. The following description takes the AP1000 nuclear power unit as an example.

[0003] For the primary coolant, its flow rate represents the cooling capacity of the primary coolant system for the core. When the flow rate is lower than the set value, it means that the cooling capacity is insufficient and the nuclear energy cannot be fully converted into thermal energy, resulting in energy accumulation, which may lead to adverse conditions such as deviation from nucleate boiling, seriously threatening nuclear safety. Therefore, once the primary coolant flow rate is low, measures should be taken immediately, such as water replenishment or reactor shutdown. Accurate monitoring of the changes in the primary coolant becomes crucial.

[0004] In order to avoid leakage of primary coolant, elbow flowmeters are often used as flow measurement elements. The measurement principle is based on the differential pressure on both sides of the pipe wall when the fluid passes through the elbow to calculate the flow rate. For example, each loop of the AP1000 nuclear power unit has four differential pressure flowmeters to measure the fluid differential pressure. Since the temperature of the nuclear power unit changes greatly during the power increase process, the density of the coolant (such as water) will change, so that the differential pressure cannot accurately reflect the flow rate, and the measurement results will be biased, causing the power plant personnel to have a biased judgment on the unit operation status. Once the set value is exceeded, the reactor will be triggered to shut down, causing economic losses. Although the flow measured by the differential pressure is biased at this time, the actual flow rate can meet the reactor requirements, so it is necessary to try to avoid excessive fluctuations in the flow measurement results.

[0005] Therefore, a method is needed to provide compensation for the calculation of the primary coolant flow rate of a nuclear power unit, eliminate the influence of fluid density changes on the measurement results during the power increase of the nuclear power unit, and help power plant operators accurately monitor the changing trend of the primary coolant flow rate. Summary of the invention

[0006] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the objects of the present invention is to at least solve one or more of the above-mentioned problems in the prior art. In other words, one of the objects of the present invention is to provide a method and system for primary-circuit coolant flow compensation of a nuclear power unit that meets one or more of the above-mentioned requirements.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] A method for compensating coolant flow in a primary circuit of a nuclear power unit, the method comprising the steps of:

[0009] S1. Preset several power platforms from 0% to 100% power, and the several power platforms at least include a 0% power platform and a main line power platform;

[0010] S2, select 0% power platform;

[0011] S3, obtaining the flow percentage currently measured by the unit;

[0012] S4, determine whether the difference between the currently measured flow percentage and 100% is less than the error range, and determine whether the current power platform is the main line power platform of the unit. If it is less than the error range and is the main line power platform, then complete the compensation, otherwise go to step S5;

[0013] S5, recalculating the flow percentage according to the flow percentage until the difference between the currently measured flow percentage and 100% is less than the error range;

[0014] S6. Select a higher power platform and return to step S3.

[0015] As a preferred solution, when the 0% power platform is selected, step S5 specifically includes:

[0016] S501, collecting the average differential pressure of the differential pressure flowmeter as a differential pressure value;

[0017] S502, obtaining a zero flow differential pressure value under the current power platform;

[0018] S503, subtracting the differential pressure value from the zero flow differential pressure value to obtain a differential pressure deviation value;

[0019] S504, dividing 10000 by the differential pressure deviation value to obtain a zero power compensation parameter;

[0020] S505, calculating the flow percentage with zero power compensation parameter;

[0021] S506: Determine whether the difference between the currently measured flow percentage and 100% is less than the error range; if not, return to step S501.

[0022] As a further preferred solution, when a non-0% power platform is selected, step S5 specifically includes:

[0023] S511, collecting the average differential pressure of the differential pressure flowmeter as the differential pressure value, and obtaining the current unit power;

[0024] S512, obtaining the zero flow differential pressure value under the current power platform;

[0025] S513, subtracting the differential pressure value from the zero flow differential pressure value to obtain a differential pressure deviation value;

[0026] S514, dividing 10000 by the differential pressure deviation value to obtain the current power compensation parameter;

[0027] S515, subtracting the current power compensation parameter from the 0 power compensation parameter to obtain a compensation calculation intercept;

[0028] S516, dividing the compensation calculation intercept by the current unit power to obtain a compensation calculation slope;

[0029] S517, calculating the flow percentage according to the zero power compensation parameter and the compensation calculation slope;

[0030] S518: Determine whether the difference between the currently measured flow percentage and 100% is less than the error range; if not, return to step S511.

[0031] As a further preferred solution, the flow percentage calculation method of step S505 and step S517 is specifically as follows:

[0032] ;

[0033] ;

[0034] in FLOW ( CF ) is the corrected flow rate, C2 is the zero flow differential pressure value, ΔP is the differential pressure value, C0 is the 0 power compensation parameter, C1 is the compensation calculation slope, q ΔT is the current unit power.

[0035] As a further preferred solution, the differential pressure value is obtained by collecting the differential pressure average value of the differential pressure flowmeter at 1 Hz for 10 minutes.

[0036] As a further preferred solution, the zero flow differential pressure value is calculated based on the differential pressure of the hot section pipeline height, the coolant density and the coolant density in the current working condition. The calculation method is:

[0037] ;

[0038] Where C2 is the zero flow differential pressure value, z is the hot section pipeline height differential pressure, r 0 is the coolant density, r is the density of the coolant under current working conditions.

[0039] On the other hand, the present invention also provides a system for compensating the coolant flow rate of a primary circuit of a nuclear power unit, using any of the above methods, characterized in that:

[0040] The system includes an acquisition module, a compensation calculation module and a flow compensation module;

[0041] The acquisition module is used to collect the indicated differential pressure values ​​of the units under several power platforms;

[0042] The compensation calculation module is used to determine whether the difference between the currently measured flow percentage and 100% is less than the error range, and to correct the flow algorithm of the flow calculation module;

[0043] The flow calculation module is used to calculate the current flow percentage.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The method and system of the present invention can compensate the flow rate at any time according to the temperature change when the unit is increased in power, so that the detected value of the flow rate is always close to the real flow rate value, avoiding the unit operation failure caused by the flow value detection error. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flow chart of a method for compensating coolant flow in a primary circuit of a nuclear power unit according to an embodiment of the present invention;

[0047] Figure 2 is a flow chart of step S5 at a 0% power platform in an embodiment of the present invention;

[0048] Figure 3 It is a flowchart of step S5 in other power platforms of an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to more clearly illustrate the embodiments of the present invention, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings and other implementation methods can be obtained based on these accompanying drawings without creative work.

[0050] Example:

[0051] The present invention is a method for compensating the flow rate of a primary circuit coolant of a nuclear power unit. The normalization method is used to collect the differential pressure results measured under each power platform in the following manner, and the average value in the collection time period is calculated. The difference between the current measured flow value and the actual flow value is calculated in combination with the density of the coolant under different working conditions and the current unit power situation, and the difference is written into the instrumentation and control system as the compensation amount to be applied for flow value detection, thereby ensuring that the measured flow value always matches the actual value. When the actual flow value is insufficient, the reactor shutdown is correctly triggered, rather than the reactor shutdown caused by the inaccurate flow error reflected by the differential pressure.

[0052] S1. Set a 0% power platform, and set a main line power platform according to the main line power of the unit, and set several power platforms in sequence between 0% power and main line power. The setting of the power platform is determined according to the actual situation of the unit. For example, if the main line power of the AP1000 nuclear power unit is 100%, the 0% power platform, 75% power platform, 90% power platform and 100% power platform are set;

[0053] S2. Select the 0% power platform.

[0054] S3. Obtain the flow percentage currently measured by the unit.

[0055] S4. Determine whether the difference between the currently measured flow percentage and 100% is less than the error range, and determine whether the current power platform is the main line power platform of the unit; if the difference between the currently measured flow percentage and 100% is less than the error range, and the current power platform is the main line power platform of the unit, then the unit has completed compensation, risen to the main line power platform and maintained the accuracy of flow measurement. Otherwise, the flow algorithm is corrected according to the flow percentage until the difference between the currently measured flow percentage and 100% is less than the error range. In order to save power increase time, step S4 only forces flow compensation during the power increase process, and when the power platform rises to the main line power platform, if the current flow measurement value has met the accuracy requirements of the acceptance criteria, there is no need to compensate the flow measurement value, thereby reducing the compensation process and saving power increase time.

[0056] S5. Compensate the flow algorithm to correct the current measured flow percentage. The compensation process ends when the current measured flow meets the acceptance criteria, that is, the current measured flow reaches the preset accuracy range. Specifically, the preset accuracy range is set to the acceptance criteria of 99.5%-100.5%.

[0057] S6. Select a higher power platform and return to step S3 to start flow calculation to compensate for the next power platform.

[0058] Specifically, the specific implementation of step S5 varies according to the current power platform. When the current power platform is the 0% power platform, S5 specifically includes the following steps S501-S506:

[0059] S501, collect the average differential pressure of the differential pressure flowmeter as the representative differential pressure value, the representative differential pressure value ΔP is the differential pressure value measured by the flowmeter. The representative differential pressure value is preferably to collect the differential pressure of the differential pressure flowmeter at 1HZ for 10 minutes, and take the average value of all differential pressures to obtain

[0060] S502, obtaining the zero flow differential pressure value C2 of the unit under the current power platform. The zero flow differential pressure value C2 is calculated by the formula. Specifically, the calculation method can be: , where C2 is the zero flow differential pressure value, z is the differential pressure caused by the height difference between the highest and lowest points of the hot section pipeline. In the AP1000 nuclear power unit, ring 1 is 51.1inH2O and ring 2 is 53.8inH2O. The average value is used for calculation. r 0 is the density of the coolant fluid in a closed environment. The primary coolant of the AP1000 nuclear power unit is water. r 0=62.3lbm / ft3. r It is the density of the coolant fluid under the current operating conditions. The coolant in the primary circuit of the AP1000 nuclear power unit is water. The density can be found from the pressure and temperature conditions according to the "Thermodynamic Properties of Water and Water Vapor" or calculated by chemical samplers. However, there are actually a small amount of chemicals such as boric acid in the primary circuit, which have little effect on the density.

[0061] The above C2 value is related to the positions of the two pressure tappings of the differential pressure flowmeter in the pipeline. Since the fluid density changes due to temperature, the value of C2 is also a variable. However, on the same power platform, since the working conditions remain unchanged, a constant can be used in the calculation process. In addition, it is a negative value due to the density difference of the sensing line at zero flow.

[0062] S503, subtracting the representative differential pressure value from the zero flow differential pressure value to obtain a differential pressure deviation value;

[0063] S504, dividing 10000 by the differential pressure deviation value to obtain a zero power compensation parameter;

[0064] S505, calculating the flow percentage using the zero power compensation parameter;

[0065] The new flow percentage is calculated as follows:

[0066] ;

[0067] in , C2 is the zero flow differential pressure value, ΔP is the differential pressure value, C0 is the 0 power compensation parameter, C1 is the compensation calculation slope, q ΔT is the current unit power. When the power is at 0%, C1 and q ΔT The multiplication value is 0, so only C0 is needed. Since C0 and C1 are constants at each power platform, the expression of the k coefficient is a linear function related to the current power situation. In fact, it can be further fitted into a quadratic function or a higher-order function expression, and the calculation result will be more accurate. However, in general, a linear function can meet the requirements. In order to reduce the amount of calculation, it is sufficient to fit it into a linear function.

[0068] S506: Determine whether the difference between the current measured flow percentage and 100% meets the accuracy requirement. If not, return to step S501. Specifically, the preset accuracy range is set to the acceptance criteria of 99.5%-100.5%. The next step is not entered until the flow percentage measured under the current power platform meets the acceptance criteria.

[0069] When the current power platform is not a 0% power platform, S5 specifically includes the following steps S511-S518:

[0070] S511, collect the average differential pressure of the differential pressure flowmeter as the differential pressure value ΔP, and obtain the current unit power q ΔT ;

[0071] S512, obtaining a zero flow differential pressure value C2 under the current power platform;

[0072] S513, subtracting the differential pressure value ΔP from the zero flow differential pressure value C2 to obtain a differential pressure deviation value;

[0073] S514, dividing 10000 by the differential pressure deviation value to obtain the current power compensation parameter;

[0074] S515, subtracting the current power compensation parameter from the 0 power compensation parameter to obtain a compensation calculation intercept;

[0075] S516, dividing the compensation calculation intercept by the current unit power to obtain the compensation calculation slope C1;

[0076] S517, calculating the flow percentage according to the zero power compensation parameter C0 and the compensation calculation slope C1;

[0077] The new flow percentage is calculated using the same formula as S505:

[0078] .

[0079] S518, determine whether the currently measured flow percentage meets the accuracy requirement. If not, return to step S511 to continue compensation. The preset accuracy requirement is also set as the flow percentage should eventually be within the acceptance criteria range of 99.5%-100.5%.

[0080] At each power platform, the current power platform compensation is completed through step S5 so that the flow measurement value of the unit is consistent with the actual value at each platform, and the power platform is gradually increased to the main line in this process. Due to the change in fluid density, both parameters C0 and C1 need to be corrected at regular intervals, and each correction can ensure the accuracy of a certain range of subsequent temperature changes, thereby ensuring that the flow measurement value after increasing to the unit main line power platform is also consistent with the actual flow value.

[0081] On the other hand, this embodiment also provides a system for compensating the coolant flow rate of a primary circuit of a nuclear power unit, applying the above method, the system includes a collection module, a compensation calculation module and a flow compensation module;

[0082] The acquisition module is used to collect the indicated differential pressure values ​​of the units under several power platforms;

[0083] The compensation calculation module is used to execute the above steps S4-S5, to determine whether the current flow measurement value reaches the preset accuracy range, and to correct the flow measurement value;

[0084] The flow compensation module is used to apply the correction results of the compensation calculation module to the instrumentation and control system, and to correct the flow calculation algorithm currently used by the unit so that it can measure the correct flow value.

[0085] It should be noted that the above embodiments are only detailed descriptions of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, there will be changes in the specific implementation methods based on the ideas provided by the present invention, and these changes should also be regarded as the scope of protection of the present invention.

Claims

1. A method for compensating the primary circuit coolant flow of a nuclear power unit, characterized in that: The method comprises the steps of: S1. Preset a number of power platforms from 0% to 100% power, wherein the power platforms at least include a 0% power platform and a main line power platform; S2, select 0% power platform; S3, obtaining the flow percentage currently measured by the unit; S4, judging whether the difference between the currently measured flow percentage and 100% is less than the error range, and judging whether the current power platform is the main line power platform of the unit, if it is less than the error range and is the main line power platform, then completing the compensation, otherwise entering step S5; S5, recalculating the flow percentage according to the flow percentage until the difference between the currently measured flow percentage and 100% is less than an error range; S6, select a higher power platform and return to step S3; When the 0% power platform is selected, step S5 specifically includes: S501, collecting the average differential pressure of the differential pressure flowmeter as a differential pressure value; S502, obtaining a zero flow differential pressure value under the current power platform; S503, subtracting the differential pressure value from the zero flow differential pressure value to obtain a differential pressure deviation value; S504, dividing 10000 by the differential pressure deviation value to obtain a zero power compensation parameter; S505, calculating the flow percentage with zero power compensation parameter; S506, determine whether the difference between the currently measured flow percentage and 100% is less than the error range, if not, return to step S501; when a non-0% power platform is selected, step S5 specifically includes: S511, collecting the average differential pressure of the differential pressure flowmeter as the differential pressure value, and obtaining the current unit power; S512, obtaining the zero flow differential pressure value under the current power platform; S513, subtracting the differential pressure value from the zero flow differential pressure value to obtain a differential pressure deviation value; S514, dividing 10000 by the differential pressure deviation value to obtain the current power compensation parameter; S515, subtracting the current power compensation parameter from the 0 power compensation parameter to obtain a compensation calculation intercept; S516, dividing the compensation calculation intercept by the current unit power to obtain a compensation calculation slope; S517, calculating the flow percentage according to the zero power compensation parameter and the compensation calculation slope; S518, determine whether the difference between the currently measured flow percentage and 100% is less than the error range, if not, return to step S511; the flow percentage calculation method of step S505 and step S517 is specifically as follows: k=(C0-C1*q Δt ÷100%); Where FLOW(CF) is the corrected flow rate, C2 is the zero flow differential pressure value, ΔP is the differential pressure value, C0 is the zero power compensation parameter, C1 is the compensation calculation slope, q ΔT is the current unit power.

2. A method for compensating the primary circuit coolant flow of a nuclear power unit according to claim 1, characterized in that: The differential pressure value is obtained by continuously collecting the differential pressure of the differential pressure flowmeter at 1 Hz for 10 minutes.

3. A method for compensating the primary circuit coolant flow of a nuclear power unit according to claim 1, characterized in that: The zero flow differential pressure value is calculated based on the differential pressure of the hot section pipeline height, the coolant density and the coolant density in the current working condition. The calculation method is: Wherein C2 is the zero flow differential pressure value, z is the hot section pipeline height differential pressure, ρ0 is the coolant density, and ρ is the density of the coolant under the current working condition.

4. A system for compensating the primary circuit coolant flow of a nuclear power unit, using the method according to any one of claims 1 to 3, characterized in that: The system includes an acquisition module, a compensation calculation module and a flow compensation module; The acquisition module is used to collect the indicated differential pressure values ​​of the units under the several power platforms; The compensation calculation module is used to determine whether the difference between the currently measured flow percentage and 100% is less than the error range, and to correct the flow algorithm of the flow calculation module; The flow calculation module is used to calculate the current flow percentage; The flow compensation module is used to apply the correction result of the compensation calculation module to the instrumentation and control system, and to correct the flow calculation algorithm currently used by the unit so that the unit can measure the correct flow value.

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