Method and system for measuring target-condition volume flow rate of gaseous effluent of nuclear power station

Abstract

The invention discloses a method and a system for measuring target-condition volume flow of gaseous effluent of a nuclear power station. The method comprises the following steps: S1, acquiring the working condition volume flow rate of the gaseous effluent; s2, measuring the temperature of the gaseous effluent at the drain opening of the chimney as the working condition temperature; and S3, according to the working condition volume flow and the working condition temperature, the standard condition volume flow of the gaseous effluent is obtained through calculation. According to the technical scheme, the standard condition volume flow of the gaseous effluent can be accurately measured, an existing flowmeter does not need to be replaced, a hole does not need to be newly formed, the influence on the chimney structure is avoided, high-altitude operation is not needed, the method is simple and reliable, cost and implementation difficulty are greatly reduced, and the nuclear power station environment monitoring level is improved.

Description

Technical Field

[0001] This invention relates to the field of radiation monitoring and environmental safety technology in nuclear power plants, and in particular to a method and system for measuring the standard volumetric flow rate of gaseous effluents from nuclear power plants. Background Technology

[0002] Nuclear power plants generate gaseous radioactive effluents during operation, which are released into the atmosphere through chimneys. To ensure environmental safety and public health, nuclear power plants must accurately monitor and calculate the radioactive emissions of these gaseous effluents. According to the "Technical Specification for Radioactive Monitoring of Nuclear Power Plant Effluents (Trial)" (Document No. 44 of 2020 issued by the State Nuclear Safety Administration), the gas flow rate, temperature, and humidity in the chimney and sampling pipes should be continuously measured to determine the standard volume of the effluent (gas volume at 0°C and one standard atmosphere). Currently, nuclear power plant gaseous effluent monitoring systems typically employ two main measurement methods: 1. Gaseous effluent sampling system measurement: using a thermal mass flow meter to directly measure the standard volumetric flow rate. 2. Gaseous effluent emission system measurement: using a differential pressure flow meter based on the Pitot tube principle to measure the operating volumetric flow rate (gas volume under actual operating conditions). The calculation of total radioactive emissions requires multiplying the concentration of radioactive material measured by sampling by the emission volume. However, the sampling measurement uses the standard volume, while the emission measurement uses the operating volume. The inconsistency between the two standards leads to systematic biases in the calculation results, and the existing methods cannot meet the regulatory requirements.

[0003] The existing solution could replace the existing Pitot tube flowmeter with a thermal mass flowmeter (which can directly output standard flow rate), but it has the following problems: the existing Pitot tube flowmeter is nuclear-grade equipment, and replacement would be costly; the replacement process is complex, requiring downtime for modifications, which would affect the normal operation of the nuclear power plant; the procurement cycle for nuclear-grade equipment is long; and a new safety assessment and verification is required after replacement, which is time-consuming and risky. To achieve standard flow rate measurement using existing equipment, theoretically, temperature and pressure measurements would need to be added at the chimney operating condition volumetric flow rate measurement point (e.g., at elevation +55 meters). However, this presents the following problems: the chimney is a fiberglass structure that has been in use for many years, making it unsuitable to add new openings at elevation +55 meters, posing a structural safety risk; elevation +55 meters is a high-altitude work area, making installation and maintenance difficult and posing a high safety risk; this area also presents radiation risks, requiring special protection for operators, increasing operational difficulty and cost.

[0004] In summary, existing technologies have failed to provide an effective solution for accurately measuring the standard volumetric flow rate of gaseous effluent from nuclear power plants without replacing nuclear-grade equipment or increasing the risks of high-altitude operations. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant.

[0006] The technical solution adopted by this invention to solve its technical problem is: to construct a method for measuring the standard condition volumetric flow rate of gaseous effluent from a nuclear power plant, wherein the gaseous effluent is discharged through a chimney, and the method includes: S1. Obtain the operating volumetric flow rate of the gaseous effluent; S2. Measure the temperature of the gaseous effluent at the chimney's drain outlet as the operating temperature; S3. Calculate the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate and the operating condition temperature.

[0007] Furthermore, the operating volumetric flow rate is measured and calculated using a Pitot tube flow meter.

[0008] Furthermore, the chimney's drain outlet is located at an elevation of 23.2 meters above the chimney and in the area connecting the horizontal and vertical sections of the chimney, or it is located below the chimney's discharge outlet.

[0009] Furthermore, the operating temperature is obtained by installing a PT100 temperature sensor at the drain outlet of the chimney.

[0010] Furthermore, step S2 also includes: determining whether the operating temperature is valid; if invalid, updating the operating temperature to the previous valid operating temperature value or a preset safety value.

[0011] Furthermore, the standard volumetric flow rate is calculated based on the following formula: Among them, V N T is the standard volumetric flow rate. N T represents the standard temperature, and T represents the operating temperature.

[0012] Furthermore, in step S3, the standard condition volumetric flow rate is calculated and displayed using two units.

[0013] This invention also constructs a measurement system for the standard condition volumetric flow rate of gaseous effluent from a nuclear power plant, wherein the gaseous effluent is discharged through a chimney, and the system includes: The data acquisition module is used to acquire the working volumetric flow rate of the gaseous effluent; The signal acquisition module is used to acquire the operating temperature, which is obtained by measuring the temperature of the gaseous effluent at the chimney's drain outlet. The logic calculation module is used to calculate the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate and the operating condition temperature.

[0014] Furthermore, the system also includes: The data display module is used to display the operating condition volumetric flow rate, the standard condition volumetric flow rate, and / or the operating condition temperature.

[0015] Furthermore, the system is a non-core DCS system.

[0016] Implementing this invention has the following beneficial effects: by measuring the temperature of the chimney effluent as the operating temperature to calculate the standard volumetric flow rate, the standard volumetric flow rate of gaseous effluent from nuclear power plants can be accurately measured, meeting regulatory requirements. It does not require replacing existing flow meters, drilling new holes, or shutting down for improvements, thus avoiding power generation losses caused by shutdowns, significantly reducing costs and operational risks, and thereby improving the environmental monitoring level of nuclear power plants. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a flowchart of a method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant, according to one embodiment of the present invention. Figure 2 This is a schematic diagram of the installation of the CPR1000 nuclear power plant chimney in one embodiment of the present invention. Detailed Implementation

[0018] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] The embodiments of the present invention are applicable to CPR1000 reactor type nuclear power plants.

[0020] Figure 1 This is a flowchart of a method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant, according to one embodiment of the present invention. The gaseous effluent is discharged through a chimney, and this embodiment includes the following steps: S1. Obtain the operating volumetric flow rate of the gaseous effluent; In this step, the operating volumetric flow rate is the gas volumetric flow rate measured under the current actual temperature and pressure conditions, and the unit is usually m³ / h.

[0021] In an optional embodiment, the operating volumetric flow rate can be measured and calculated using a Pitot tube flow meter. Specifically, a Pitot tube flow meter is installed in the nuclear power plant chimney. The Pitot tube flow meter can calculate the flow velocity by measuring the difference between the total pressure and the static pressure, and then calculate the operating volumetric flow rate by combining the chimney cross-sectional area and unit time.

[0022] S2. Measure the temperature of the gaseous effluent at the chimney's drain outlet as the operating temperature; In this step, the operating temperature refers to the temperature of the gaseous effluent under actual operating conditions. Nuclear power plant chimneys are pre-installed with drain outlets, also known as blowdown vents. Through actual measurements and simulations, the temperature at the drain outlet meets the error limit requirements, and this temperature is measured as the operating temperature. In some optional embodiments, the operating temperature is measured by installing a PT100 temperature sensor at the chimney drain outlet. Specifically, considering factors such as measurement accuracy and cost, the blind flange of the drain outlet can be replaced, and a single-pole, four-wire PT100 temperature sensor can be installed to measure the temperature. Understandably, other tools can be adaptively selected to measure the temperature. To prevent probe breakage, a protective sleeve can be welded to the mounting flange to ensure full contact between the measuring element and the gaseous effluent.

[0023] In some alternative embodiments, the chimney's drain outlet is located at an elevation of 23.2 meters above the chimney and in the area connecting the horizontal and vertical sections of the chimney, or it is located below the chimney's discharge outlet.

[0024] Specifically, based on measured and simulation data, the temperature difference between the chimney outlet and the temperature at the operating condition measurement point is within the error limit. In the CPR1000 nuclear power plant, the operating condition measurement point is set at an elevation of ±55 meters on the chimney, where instruments are installed to measure the operating condition volumetric flow rate, such as... Figure 2 The diagram shows the chimney installation. The drain outlet 100 is located at an elevation of ±23.2 meters on the chimney, in the connection area between the horizontal and vertical sections. Through synchronous temperature measurements, the maximum temperature deviation between the gas at an elevation of ±55 meters and ±23.2 meters on the chimney is 0.6℃. Simulation verification, considering various extreme conditions, shows that the maximum temperature deviation between the two locations is 2.95℃. Table 1 below shows the temperature simulation test results under various extreme conditions.

[0025] Table 1 Based on a maximum deviation of 2.95℃, the calculated error for standard volumetric flow rate is approximately 0.9%. Adding the sensor accuracies (1% for the 485 sensor, 0.25% for the transmitter, and 0.2% for the temperature sensor), the overall error is approximately 1.38%, corresponding to a flow rate error of 0.28 m / s. At a normal wind speed of 15 m / s, the indicated deviation is 1.84%, far below the 10% error limit required by the National Nuclear Safety Administration document

[2020] No. 44. Understandably, chimney drain outlets are typically located at lower chimney elevations. Through actual measurements and simulations, the gas temperature at the drain outlet is within the error limit, thus the application is acceptable.

[0026] By measuring and calculating the temperature of the gaseous effluent at the chimney outlet, the operating temperature can be used as the reference temperature. Under the premise of meeting error limits, it eliminates the need to drill new holes at high altitudes (e.g., 55 meters) for temperature measurement, avoiding impact on the chimney structure, reducing safety risks associated with high-altitude operations, and lowering economic and time costs associated with construction. The chimney outlet was originally sealed with a blind flange; implementing this invention only requires replacing the flange, simplifying construction. Furthermore, installing a temperature sensor at the outlet facilitates routine maintenance without requiring special protection.

[0027] S3. Calculate the standard condition volumetric flow rate based on the operating condition volumetric flow rate and operating temperature.

[0028] In some alternative embodiments, the standard volumetric flow rate is calculated based on the following formula: Among them, V N For standard volumetric flow rate, T N T represents the standard temperature, and T represents the operating temperature.

[0029] Specifically, according to the ideal gas law and the law of conservation of mass, the standard volumetric flow rate and the operating volumetric flow rate of the gaseous effluent from the chimney have the following relationship: Among them, V N This is the standard volumetric flow rate. This refers to the volumetric flow rate under operating conditions. For operating pressure, P N For standard pressure (101.325 kPa), T N T represents the standard temperature (273.15K) and T represents the operating temperature.

[0030] Because nuclear power plant chimneys are open-air vents, the operating pressure P and the standard atmospheric pressure P N The difference is minimal. In actual measurements conducted at a nuclear power plant, due to the chimney effect, the static pressure at the operating condition pressure measurement point is slightly lower than the standard atmospheric pressure. Table 2 below shows the measured static pressure data at the operating condition pressure measurement point, with a maximum deviation of -122 Pa. The resulting error in calculating the standard condition volumetric flow rate is approximately 0.12%, which meets the limit requirements. Therefore, this error can be ignored, and the formula simplifies to: .

[0031] Table 2 Based on this simplified formula, by substituting the operating condition volumetric flow rate in step S1 into the variable V in the formula, and by substituting the operating condition temperature in step S2 into the variable T in the formula, the standard condition volumetric flow rate V can be obtained. NThis formula can convert the operating volumetric flow rate into the required standard volumetric flow rate without replacing the existing nuclear-grade flow meter at the operating measurement point in the chimney, reducing costs and avoiding downtime for modifications, thus avoiding losses caused by downtime.

[0032] In some optional embodiments, step S2 further includes: determining whether the operating temperature is valid; if invalid, updating the operating temperature to the previous valid operating temperature value or a preset safety value. Specifically, instrument malfunctions or disconnections can cause abnormal operating temperatures. A signal acquisition card with signal anomaly detection function can be used to determine whether the temperature exceeds the normal range. The operating temperature is collected according to business needs at a set period (e.g., every 500ms), and the operating temperature of each period is recorded and saved. If the current operating temperature is determined to be invalid, it is updated to the valid operating temperature value of the previous period or a preset temperature safety value to ensure continuous availability of calculations. The anomaly can also be recorded for subsequent fault analysis, such as triggering an alarm and notifying maintenance personnel when it occurs frequently or continuously.

[0033] In some optional embodiments, in step S3, the standard condition volumetric flow rate can be calculated and displayed using two generator sets. Specifically, the standard condition volumetric flow rate is calculated and displayed by the generator sets. The temperature signal under the same operating condition from step S2 is sent to the common generator set and then to the two generator sets respectively. The primary generator set calculates, outputs, and displays the flow rate. If the primary generator set crashes or makes a calculation error due to hardware failure, software deadlock, or other reasons, the system immediately switches to the standby generator set for calculation and display. This redundancy design ensures service continuity and improves reliability and availability.

[0034] The standard-condition volumetric flow rate measurement system for gaseous effluent from a nuclear power plant of the present invention can be used to perform the standard-condition volumetric flow rate measurement method for gaseous effluent from a nuclear power plant as described in the above embodiments. The gaseous effluent is discharged through a chimney. The standard-condition volumetric flow rate measurement system for gaseous effluent from a nuclear power plant in this embodiment includes: The data acquisition module is used to acquire the working volumetric flow rate of the gaseous effluent; Specifically, the data acquisition module can obtain the chimney's operating volume flow rate data in real time through inter-station communication.

[0035] The signal acquisition module is used to acquire the operating temperature, which is obtained by measuring the temperature of the gaseous outflow at the chimney's drain outlet. Specifically, the signal acquisition module collects operating temperature data in real time. The operating temperature is measured by a temperature sensor installed at the chimney's drain outlet and connected to the signal acquisition module via hardwire.

[0036] The logic calculation module is used to calculate the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate and operating temperature.

[0037] Specifically, the logic calculation module calculates the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate data of the gaseous effluent acquired by the data acquisition module and the operating condition temperature data of the gaseous effluent acquired by the signal acquisition module, using the following formula: Among them, V N For standard volumetric flow rate, T N Here, T represents the standard temperature, and T represents the operating temperature. This formula is derived based on the ideal gas law and the law of conservation of mass.

[0038] In some optional embodiments, the measurement system for the standard volumetric flow rate of gaseous effluent from a nuclear power plant also includes a data display module for displaying the operating volumetric flow rate, standard volumetric flow rate, and / or operating temperature. Specifically, the original operating volumetric flow rate, standard volumetric flow rate, and / or operating temperature are displayed on a single interface. Simultaneous display of multiple data points allows for a clear visual representation of differences. The system can manually or automatically determine the accuracy of the calculated data based on predefined rules. For example, it can monitor the data based on the principle that the operating volumetric flow rate data is typically larger than the standard volumetric flow rate data and issue alarms. Preferably, operating temperature data is received by two units, with the primary unit performing the calculation and display. If the primary unit crashes or makes a calculation error due to hardware failure, software deadlock, or other reasons, the system immediately switches to the standby unit for calculation and display. This redundancy design ensures business continuity and improves reliability and availability.

[0039] In some alternative embodiments, the measurement system for the standard volumetric flow rate of gaseous effluent from a nuclear power plant is a non-nuclear-grade DCS system. Specifically, in a nuclear power plant, if nuclear-grade equipment retrofitting is involved, the required costs are high, and the safety assessment takes a long time. Using a non-nuclear-grade DCS system as the measurement system can further save economic and time costs and reduce implementation risks while achieving the measurement function.

[0040] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for measuring the standard-condition volumetric flow rate of gaseous effluent from a nuclear power plant, characterized in that, The gaseous effluent is discharged through a chimney, the method comprising: S1. Obtain the operating volumetric flow rate of the gaseous effluent; S2. Measure the temperature of the gaseous effluent at the chimney's drain outlet as the operating temperature; S3. Calculate the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate and the operating condition temperature.

2. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 1, characterized in that, The volumetric flow rate under the specified operating conditions is measured and calculated using a Pitot tube flow meter.

3. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 1, characterized in that, The chimney's drain outlet is located at an elevation of 23.2 meters above the chimney and in the area connecting the horizontal and vertical sections of the chimney, or it is located below the chimney's discharge outlet.

4. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 3, characterized in that, The operating temperature is measured by installing a PT100 temperature sensor at the chimney's drain outlet.

5. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 3, characterized in that, Step S2 further includes: determining whether the operating temperature is valid; if invalid, updating the operating temperature to the previous valid operating temperature value or a preset safety value.

6. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 3, characterized in that, The standard volumetric flow rate is calculated based on the following formula: Among them, V N T is the standard volumetric flow rate. N T represents the standard temperature, and T represents the operating temperature.

7. The method for measuring the standard volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 3, characterized in that, In step S3, the standard condition volumetric flow rate is calculated and displayed using two units.

8. A measurement system for the standard condition volumetric flow rate of gaseous effluent from a nuclear power plant, characterized in that, The gaseous effluent is discharged through a chimney, and the system includes: The data acquisition module is used to acquire the working volumetric flow rate of the gaseous effluent; The signal acquisition module is used to acquire the operating temperature, which is obtained by measuring the temperature of the gaseous effluent at the chimney's drain outlet. The logic calculation module is used to calculate the standard volumetric flow rate of the gaseous effluent based on the operating condition volumetric flow rate and the operating condition temperature.

9. The measurement system for standard condition volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 8, characterized in that, The system also includes: The data display module is used to display the operating condition volumetric flow rate, the standard condition volumetric flow rate, and / or the operating condition temperature.

10. The measurement system for standard condition volumetric flow rate of gaseous effluent from a nuclear power plant according to claim 8, characterized in that, The system is a non-core DCS system.

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