Device and method for monitoring and calibrating gas emission of fresh air system of nuclear power station

Abstract

The invention discloses a device and method for monitoring and calibrating the gas emission of a fresh air system of a nuclear power plant, and the device comprises an end cover which is provided with a mounting hole and an avoiding hole; the multiple splicing pipe joints are linearly spliced, the end cover is connected with the splicing pipe joint close to the end in a sealed mode, and the interior of each splicing pipe joint is used for containing a pressure taking pipe of a pitot tube and a signal line of a platinum resistance thermometer. The pitot tube is located in the splicing pipe joint, and the measuring end of the pitot tube extends into the chimney pipe through the receding hole of the end cover. The measuring end of the platinum resistance thermometer is positioned in the chimney pipe; the transmitter assembly is connected with the pitot tube and the platinum resistance thermometer and displays related data in the parameter display center. The flange positioning structure is fixedly connected to the detection port and provides a sliding supporting foundation of the splicing pipe joint, and the device can perform field calibration and verification on the thermal mass flow meter under the actual operation condition, so that the traceability, reliability and measurement accuracy of gaseous effluent discharge flow data of a fresh air system of a nuclear power station are ensured.

Description

Technical Field

[0001] This invention relates to the field of thermal mass flow meter calibration technology, specifically to an apparatus and method for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system. Background Technology

[0002] Currently, domestic nuclear power plants commonly use thermal mass flow meters (TMFs) to monitor the gas emission flow of fresh air systems. In actual operation, the accuracy and stability of these instruments are easily affected by factors such as changes in gas composition, temperature fluctuations, and flow conditions, thus requiring regular calibration.

[0003] Current calibration methods typically involve removing the thermal mass flow meter installed inside the pipeline and sending it to a qualified laboratory for offline calibration to determine its metrological characteristics. However, factors such as the uniformity and stability of the flow field inside the pipeline, as well as the pipeline structure and instrument installation location, can significantly affect the flow measurement results. These non-ideal factors related to field operating conditions are often difficult to eliminate or quantify through calibration under laboratory conditions, leading to deviations between calibration results and actual operating conditions, thus affecting the reliability and accuracy of flow monitoring data.

[0004] Currently, the metrological characteristics of thermal mass flow meters are mainly determined through offline laboratory calibration. Factors such as the uniformity and stability of the flow field within the pipeline, as well as the pipeline layout and instrument installation location, significantly affect the accuracy of flow measurement results. Deviations caused by these non-ideal factors are difficult to eliminate or quantify through laboratory calibration, ultimately leading to flow data monitored by thermal mass flow meters potentially failing to meet the requirements of the energy industry standard NB / T 20374 "Sampling of Airborne Radioactive Materials from Nuclear Power Plant Chimneys," which stipulates that the flow measurement and recording system should be able to measure the mass or volumetric flow rate of the effluent, and the deviation from the measured value using the reference method should be within ±10%.

[0005] Furthermore, the complex inlet conditions of the main discharge pipeline and the significant differences in gas flow parameters across multiple branches result in a non-uniform flow field, making it difficult for conventional flow measurement equipment to perform online total flow measurement. The narrow external space of the pipeline places high demands on the size, compactness, and flexibility of the flow measurement device, rendering conventional measurement equipment unsuitable.

[0006] Therefore, how to provide a traceable on-site device and calibration method for monitoring and calibrating gas emissions from nuclear power plant fresh air systems is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a traceable on-site device and calibration method for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system. It is used for measuring the total gaseous emission flow rate and calibrating the TMF (Total Flow Rate) of the fresh air system in a nuclear power plant. It is easy to install, highly flexible, and can be detected and traced online, providing accurate calibration data for the TMF.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a device for monitoring and calibrating gas emissions in a nuclear power plant's fresh air system, which is slidably installed at the detection port of a chimney pipe, characterized in that it includes: an end cap, wherein the end cap is provided with an installation hole and a clearance hole; The splicing pipe section has multiple sections that are linearly spliced ​​together. The end cap is sealed to the splicing pipe section near the end. The interior of the splicing pipe section is used to accommodate the pressure tap of the Pitot tube and the signal line of the platinum resistance thermometer. Pitot tube, the Pitot tube being located inside the spliced ​​pipe joint and the measuring end extending into the interior of the chimney pipe through the clearance hole of the end cap; A platinum resistance thermometer, wherein the platinum resistance thermometer is fixedly connected to the mounting hole, and the measuring end of the platinum resistance thermometer is located inside the chimney tube; A transmitter assembly connected to the Pitot tube and the platinum resistance thermometer; The parameter display center is electrically connected to the transmitter assembly. The parameter display center receives the total pressure signal, static pressure signal and temperature signal fed back by the transmitter assembly, and displays the total pressure data and differential pressure data of the Pitot tube and the temperature data of the platinum resistance thermometer. A flange positioning structure is fixedly connected to the detection port and provides a sliding support base for the splicing pipe joint.

[0009] The beneficial technical effects of this invention are as follows: This device is used for online on-site calibration of thermal mass flow meters (TMF). The splicing pipe joints are suitable for installation in complex and narrow environments. The number of sections can be increased according to the site environment and measurement depth to improve installation flexibility. The flange positioning structure provides a support foundation for the installation and sliding of the measuring device. The insertion position of the measuring device can be adjusted as needed. The Pitot tube is used to measure total pressure and differential pressure data, and the platinum resistance thermometer is used to measure temperature. The measurement data is displayed intuitively using the parameter display center, which facilitates the calculation of the working density of the fluid (using REFPROP 10.0 thermophysical parameter calculation software, after inputting the fluid type, temperature and pressure parameters, the density value of the fluid under the corresponding working conditions can be automatically output). Combined with the Pitot tube velocity calculation formula, the local velocity of each measuring point can be obtained. Then, the total flow rate can be calculated according to the velocity-area method, thereby realizing the on-site calibration of thermal mass flow meters (TMF). Preferably, it further includes a clamping member, which is detachably connected to the outside of the end cap. The clamping member is used to clamp the Pitot tube, and a conical sealing gasket is provided between the Pitot tube and the clamping member.

[0010] The resulting technical effect is that the clamping element is used to hold the tube body on which the Pitot tube is installed, while the conical sealing gasket provides a sealing condition to prevent gas leakage.

[0011] Preferably, an O-ring is provided between the contact surface of the clamping member and the end cap.

[0012] The resulting technical effect is that all relevant gaps need to be sealed to prevent leakage, which could affect the flow field distribution and cause measurement deviations.

[0013] Preferably, adjacent splicing pipe sections are connected by threads, and sealing gaskets are provided on the mating surfaces of adjacent splicing pipe sections.

[0014] The resulting technical effect is that modular splicing has the advantage of flexible assembly, adaptability to narrow environments, and the ability to flexibly add sections according to the measurement depth, effectively covering the full cross-sectional measurement range of square pipes with a length and width of approximately 2 m.

[0015] Preferably, the axial length of the splicing pipe section is 50cm to 60cm, and the number of splicing pipe sections is determined according to the diameter of the chimney pipe and the position of the Pitot tube measuring end extending into the chimney pipe.

[0016] The resulting technical advantages are: the short-section segmented installation offers high flexibility and convenient layout. Specifically, it can be made of aluminum alloy with a sleeve wall thickness of 20 mm, providing sufficient strength to withstand deformation caused by gravity, ensuring that the Pitot tube measuring head is aligned with the main direction, and providing accurate and reliable measurement data.

[0017] Preferably, the transmitter assembly includes a temperature transmitter, a differential pressure transmitter, and a pressure transmitter. The temperature transmitter is connected to the platinum resistance thermometer via a signal line and is used to receive and convert temperature measurement signals. The differential pressure transmitter is connected to the total pressure port and static pressure port of the Pitot tube via a gas line and receives and converts the pressure difference measurement signals between the total pressure port and the static pressure port. The pressure transmitter is connected to the total pressure port of the Pitot tube via a gas line and receives and converts the pressure measurement signals from the total pressure port. The temperature transmitter, differential pressure transmitter, and pressure transmitter are each electrically connected to the parameter display center.

[0018] The resulting technical effect is that the transmitter acquires relevant parameter signals and feeds them back to the parameter display center for intuitive display, which facilitates subsequent calculation and verification.

[0019] Preferably, the flange positioning structure includes a mounting sleeve, an auxiliary pipe, and a tightening bolt. The mounting sleeve is fixedly connected to the inspection port of the chimney pipe. The auxiliary pipe is connected to the inner side of the mounting sleeve and fixed in position on the mounting sleeve by the tightening bolt. The auxiliary pipe is slidably connected to the spliced ​​pipe section and provides support and sliding guidance for the spliced ​​pipe section.

[0020] The resulting technical effect is that the flange positioning structure provides sliding support and guidance for the splicing pipe section, and can be advanced to the required depth according to measurement needs, enabling multi-point measurement at different depths inside the chimney pipe.

[0021] Preferably, the inner wall of the auxiliary pipe is provided with a plurality of sealing rings corresponding to its axial direction, and the plurality of sealing rings slide to seal the outer wall of the spliced ​​pipe section.

[0022] The resulting technical effect is that all relevant gaps need to be sealed to prevent leakage from affecting the test results.

[0023] This invention also discloses a method for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system, using the aforementioned apparatus, comprising the following steps: Step 1: Use a rangefinder to measure the inner cross-sectional area of ​​the chimney pipe, and determine the measurement location in the area where the TMF is installed on the chimney pipe. Set up multiple detection ports around the measurement location on the chimney pipe. Step 2: Calibrate the accuracy of the Pitot tube. The L-type standard Pitot tube is pre-calibrated with a Laser Doppler Velocity (LDV) instrument, achieving a measurement accuracy of 0.3%. It can be indirectly traced back to the (0.2~30) m / s air velocity reference device of the National Institute of Metrology, China. Its measurement data has extremely high accuracy and reliability, laying a good foundation for the online experiment of this calibration device. After calibration, the calibration device is installed and sealed at the detection port. Multiple calibration devices are used to carry out multi-point measurements within the measurement section. The flow characteristics in the pipeline are evaluated through temperature uniformity and flow field stability analysis. Step 3: Calculate the average flow velocity in the core area based on the multi-point velocity measurement results of the calibration device, complete the volumetric flow rate integration, and compare and analyze the measured standard flow rate with the output results of the TMF being calibrated to obtain its indication error and calibration coefficient.

[0024] The beneficial technical effects of this invention are: multiple calibration devices are arranged at multiple measurement points on the measurement section, the average flow velocity in the core area is calculated based on the multi-point velocity measurement results, the volumetric flow rate is integrated, and the measured standard flow rate is compared and analyzed with the output result of the TMF being calibrated, thereby obtaining its indication error and calibration coefficient.

[0025] Preferably, in step two, the calibration device simultaneously evaluates the flow field and temperature field at the measurement point. By combining the Pitot tube and the platinum resistance thermometer, flow velocity, temperature, and pressure parameter data are collected simultaneously within the measurement section. After unified collection, the data is used to analyze the uniformity of fluid flow and temperature distribution characteristics within the pipeline. By weighted calculation of the test results from multiple measurement points, the overall flow integral of the measurement section within the pipeline is accurately obtained.

[0026] The resulting technical effects are: this invention can simultaneously measure the flow field and temperature field, accurately analyze the flow uniformity and temperature distribution characteristics, and then perform weighted calculations on the measurement points, improving the accuracy of the overall flow integral. It can significantly reduce measurement uncertainties caused by flow field fluctuations, ensuring that the velocity-area method meets accuracy standards under actual operating conditions. Attached Figure Description

[0027] Figure 1 This is a structural diagram of a traceable on-site device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system, according to the present invention. Figure 2 for Figure 1 Enlarged view of point A; Figure 3 for Figure 1 Enlarged view of point B; Figure 4 for Figure 1 Enlarged view of point C; Figure 5 The distribution of measurement points for chimney ducts and the location of measurement points determined using the logarithmic-linear method.

[0028] 1 End cap, 2 Splicing pipe joint, 3 Pitot tube, 4 Platinum resistance thermometer, 5 Transmitter assembly, 51 Temperature transmitter, 52 Differential pressure transmitter, 53 Pressure transmitter, 6 Flange positioning structure, 61 Mounting sleeve, 62 Auxiliary pipe, 63 Tightening bolt, 7 Clamping parts, 8 Conical sealing gasket, 9 O-ring seal, 10 Sealing gasket, 11 Sealing ring. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] See the appendix of this invention. Figures 1 to 5 According to an embodiment of the present invention, a device for monitoring and calibrating gas emissions of a nuclear power plant’s fresh air system is slidably installed at the detection port of a chimney pipe, comprising: an end cap 1, the end cap 1 having an installation hole and a clearance hole; The splicing pipe section 2 consists of multiple parallel splicing pipe sections. In this case, 5 splicing pipe sections 2 are installed. The end cap 1 is sealed to the splicing pipe section 2 closest to the end, and the splicing pipe section at the far end needs to be sealed with a plug (the plug needs to avoid the passage of signal lines and gas lines). Pitot tube 3: This device uses an L-shaped standard Pitot tube, which can achieve a measurement accuracy of 0.3%. The Pitot tube 3 is located inside the splicing pipe section 2 and the measuring end extends into the inside of the chimney pipe through the clearance hole of the end cover 1. Platinum resistance thermometer 4 is fixedly connected to the mounting hole. The measuring end of the platinum resistance thermometer 4 is located inside the chimney tube, enabling simultaneous measurement of the flow field and temperature field. Transmitter assembly 5, which is connected to Pitot tube 3 and platinum resistance thermometer 4, is used to provide feedback on relevant detection signals. The parameter display center is electrically connected to the transmitter assembly 5. The parameter display center receives the total pressure signal, static pressure signal and temperature signal fed back by the transmitter assembly 5, and displays the total pressure data, differential pressure data and temperature data of the Pitot tube and the platinum resistance thermometer. Flange positioning structure 6 is fixedly connected to the detection port and provides a sliding support base for the spliced ​​pipe section 2. The measurement depth can be flexibly adjusted according to measurement needs. The flange positioning structure provides guidance and support for the inserted spliced ​​pipe section. Because the dimensions of the openings and pre-drilled threads on the walls of nuclear power plant chimneys are not consistent (or their known dimensions deviate from the actual dimensions), the flange positioning structure can adapt to different detection port diameters and installation conditions within a wider range, enhancing the versatility of this calibration device.

[0031] In other embodiments, a clamping member 7 is also included. The clamping member 7 is detachably connected to the outside of the end cap 1. The clamping member 7 is used to clamp the Pitot tube 3. A conical sealing gasket 8 is provided between the Pitot tube 3 and the clamping member 7 to seal the relevant gaps.

[0032] In some other embodiments, an O-ring 9 is provided between the contact surface of the clamping member 7 and the end cap 1.

[0033] In some other specific embodiments, adjacent splicing pipe sections 2 are connected by threads, and sealing gaskets 10 are provided on the mating surfaces of adjacent splicing pipe sections 2 to prevent gas from leaking out of the chimney pipe and thus affecting the test results.

[0034] In other embodiments, the axial length of the splicing pipe section 2 is 510 mm, the inner diameter is 50 mm, and the outer diameter is 90 mm. Adjacent splicing pipe sections are connected by a 30 mm long thread, allowing for segmented assembly within an operating space less than 1 m wide. The number of sections in the splicing pipe section 2 is determined based on the diameter of the chimney pipe and the position of the Pitot tube measuring end within the chimney pipe. The segmented design of the splicing pipe section aims to achieve complete measurement of large-section pipes in field environments with limited operating space. The external space of a nuclear power plant chimney is typically less than 1 m. If a single integral sleeve structure is used, it will be impossible to complete the installation operation perpendicular to the chimney wall in such a narrow space. This invention, through the threaded sequential connection design of multiple splicing pipe sections, allows the measuring personnel to install section by section within a limited space. After most of the length of the previous pipe section extends into the chimney, the next pipe section is connected sequentially, thereby achieving segmented extension and filling. This structure not only effectively covers the full cross-sectional measurement points of a 2 m wide square chimney but also ensures the operability and safety of the device during installation and disassembly.

[0035] The specific locations of the L-type standard Pitot tube and thermometer are determined according to the logarithmic linear method recommended in ISO 3966, and their distribution is as follows: Figure 5 As shown, by adjusting the insertion depth of the sleeve, the L-shaped standard Pitot tube and the thermometer can be precisely controlled to reach each designated measurement position.

[0036] In other embodiments, the transmitter assembly 5 includes a temperature transmitter 51, a differential pressure transmitter 52, and a pressure transmitter 53. The temperature transmitter 51 is connected to the platinum resistance thermometer 4 via a signal line and is used to receive and convert temperature measurement signals. The differential pressure transmitter 52 is connected to the total pressure port and static pressure port of the Pitot tube 3 via a gas line and receives and converts the pressure difference measurement signals between the total pressure port and the static pressure port. The pressure transmitter 53 is connected to the total pressure port of the Pitot tube 3 via a gas line and receives and converts the pressure measurement signals from the total pressure port. The temperature transmitter 51, differential pressure transmitter 52, and pressure transmitter 53 are respectively electrically connected to the parameter display center.

[0037] In some other embodiments, the flange positioning structure 6 includes a mounting sleeve 61, an auxiliary pipe 62, and a tightening bolt 63. The mounting sleeve 61 is fixedly connected to the inspection port of the chimney pipe. The auxiliary pipe 62 is connected to the inner side of the mounting sleeve 61 and is fixed in position on the mounting sleeve 61 by the tightening bolt 63. The auxiliary pipe 62 is slidably connected to the splicing pipe section 2 and provides support and sliding guidance for the splicing pipe section 2.

[0038] The calibration device extends into the chimney duct via an auxiliary pipe, and is externally positioned and axially constrained by a flange positioning device, allowing the device to move only in the axial direction. This precisely controls the insertion depth and measurement position of the L-shaped standard Pitot tube and thermometer within the duct. The Pitot tube pressure tap and thermometer signal lines are led out from the end of the spliced ​​pipe section and connected to external measuring instruments to achieve synchronous acquisition and transmission of flow velocity and temperature signals.

[0039] No fixed connectors are needed between the splicing pipe section and the auxiliary pipe. Once the splicing pipe section reaches the designated position, its position will not change without human intervention. It can be positioned by relying on the frictional resistance between the outer wall of the splicing pipe section and the sealing ring. In addition, there is no axial force acting on the splicing pipe section inside the chimney, which can ensure the stable position of the measuring point.

[0040] In other embodiments, the inner wall of the auxiliary pipe 62 is provided with a plurality of sealing rings 11 corresponding to its axial direction, specifically using USH shaft sealing rings. The plurality of sealing rings 11 slide to seal the outer wall of the splicing pipe section 2 and provide a multi-level sealing effect.

[0041] This invention provides a traceable on-site calibration device for measuring and calibrating the total gaseous discharge flow rate of a nuclear power plant's fresh air system. This device enables on-site calibration and verification of thermal mass flow meters under actual operating conditions, reducing errors caused by differences between laboratory offline calibration and on-site operating conditions. It overcomes the non-uniformity of the flow field in the total discharge duct and measurement deviations caused by asynchronous temperature and pressure measurements, achieving accurate acquisition of the flow velocity distribution across the chimney duct cross-section and calculation of the total flow rate. It provides a small, compact, and flexible measuring device suitable for on-site operation in confined spaces.

[0042] Ultimately, it is essential to ensure the traceability, reliability, and measurement accuracy of the gaseous effluent flow data from the nuclear power plant's fresh air system.

[0043] This invention also discloses a method for monitoring and calibrating gas emissions in a nuclear power plant's fresh air system. The method uses the velocity-area method to measure the gas emission flow rate in the pipeline on-site. The velocity-area method is a flow rate measurement method based on the basic principles of fluid mechanics. Its basic principle is to select several measuring points on a cross-section of the pipeline where the flow field is fully developed, measure the local flow velocity at each measuring point using a velocity measuring device, and obtain the volumetric flow rate of the cross-section by numerical integration based on the distribution of measuring points and the flow field characteristics, as shown in equation (1). This method can be used as a primary standard to quantify gas flow rate. (1) in, q v Volumetric flow rate, The cross-sectional area of ​​the pipe. The average flow velocity across the cross section is given.

[0044] The L-shaped Pitot tube is a gas flow velocity measuring device based on Bernoulli's principle. Its structure consists of two open ends: one end is parallel to the gas flow direction and is used to measure the total pressure (the sum of static and dynamic pressure), while the other end is perpendicular to the flow direction and is used to measure the static pressure. By measuring the total pressure... With static pressure The difference yields the dynamic pressure. And calculate the local velocity according to Bernoulli's equation. : (2) in, This represents the gas density.

[0045] The data measurement using the above-described apparatus includes the following steps: Step 1: Use a rangefinder to measure the inner cross-sectional area of ​​the chimney pipe, and determine the measurement location in the area where the TMF is installed on the chimney pipe. Set up multiple detection ports around the measurement location on the chimney pipe. Step 2: Calibrate the accuracy of the Pitot tube and complete the installation and sealing of the calibration device at the detection port. Use multiple calibration devices to conduct multi-point measurements within the measurement section, and evaluate the flow characteristics in the pipeline through temperature uniformity and flow field stability analysis. Step 3: Calculate the average flow velocity in the core area based on the multi-point velocity measurement results of the calibration device, complete the volumetric flow rate integration, and compare and analyze the measured standard flow rate with the output results of the TMF being calibrated to obtain its indication error and calibration coefficient.

[0046] In step two, the calibration device simultaneously evaluates the flow field and temperature field at the measurement point. Through the combined arrangement of Pitot tubes and platinum resistance thermometers, flow velocity, temperature, and pressure parameter data are collected simultaneously within the measurement section. After unified collection, the data is used to analyze the uniformity of fluid flow and temperature distribution characteristics within the pipeline. By weighting the test results of multiple measurement points, the overall flow integral of the measurement section within the pipeline is accurately obtained.

[0047] Before calibrating the Pitot tube, the inner cross-sectional area of ​​the pipe is measured, and the outer width of the rectangular pipe is measured using a laser rangefinder and an ultrasonic thickness gauge, respectively. W o, outer high H The cross-sectional area inside the pipe is calculated by taking o and wall thickness e, and then using formula (3).

[0048] (3) In addition to cross-sectional area, the average flow velocity in the core region v coreThis is also a key parameter affecting the accuracy of standard flow measurement. To reasonably characterize the flow characteristics of the core area, a multi-point velocity measurement method is used to obtain the velocity distribution during calibration. In the flow measurement pipe section of Unit X, in addition to the thermal flow meter measurement interface, multiple DN100 detection ports are also provided on both sides of the pipe wall to meet the implementation requirements of the velocity-area method. By inserting L-shaped standard Pitot tubes and platinum resistance thermometers into each detection port, the simultaneous measurement of flow velocity and temperature at multiple points within the measurement cross-section is achieved, thereby more accurately characterizing the volumetric flow rate through the cross-section. The layout of the measurement points is determined according to the logarithmic linear method recommended in ISO 3966 standard.

[0049] The uniformity of density distribution across the measurement cross section is characterized by temperature uniformity. During calibration, the temperature uniformity Δ of the measurement cross section is determined according to JJF 1101-2019, "Calibration Specification for Temperature and Humidity Parameters of Environmental Testing Equipment". t u Temperature uniformity can be measured using the highest measured temperature in each group of measurements. t imax Difference from the lowest temperature t imin The arithmetic mean is given in equation (4).

[0050] (4) The platinum resistance thermometer and the Pitot tube probe are fixed together to the end cap and can move between measurement points with the end cap. While performing differential pressure measurements, it can simultaneously read temperature readings and calculate temperature uniformity.

[0051] The flow velocity at the measurement point is calculated based on data collected by the Pitot tube. After the Pitot tube is inserted into the flow field, the differential pressure value Δ can be obtained from the total pressure orifice at the tip of the measuring head in the flow direction and the static pressure orifices evenly distributed on the circumference of the measuring head. p Combined with fluid density ρ Pitot tube calibration coefficient α and compression correction factor (1- ε The flow velocity of the fluid can be calculated, as shown in equation (5).

[0052] (5) At the calibrated flow point, the air velocity in the ventilation duct is much less than Mach 0.2, and the compression correction factor is almost equal to 1. The Pitot tube velocity calculation can be further simplified to Equation (6).

[0053] (6) Fluid density can be calculated according to JJG 518-2023 "Pituto" calibration factor. α The flow velocity at the measured location can be calculated by calibrating a standard Pitot tube in a wind tunnel using a laser Doppler current meter and combining the differential pressure value measured by the Pitot tube.

[0054] Flow stability characterizes the fluctuation of flow rate across the measurement cross-section. All measurement points were... n =10 repeated measurements, taking the velocity measurement results at one point within the core area. v i-core The relative standard deviation is the stability of the flow point. S q See equation (7) below, where This is the mean of repeated measurements.

[0055] (6) The maximum value of the stability results at each measurement point under the same flow rate is taken as the flow rate stability of the standard device at that flow rate point.

[0056] The apparatus and methods disclosed in the embodiments are described simply because they correspond to the methods disclosed in the embodiments. For relevant details, please refer to the method section.

[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system, slidably installed at the detection port of a chimney pipe, characterized in that... include: End cap (1), the end cap (1) is provided with mounting holes and clearance holes; The splicing pipe section (2) has multiple sections that are spliced ​​linearly, and the end cap (1) is sealed to the splicing pipe section (2) near the end. Pitot tube (3), the Pitot tube (3) is located inside the splicing pipe joint (2) and the measuring end extends into the inside of the chimney pipe through the clearance hole of the end cap (1); A platinum resistance thermometer (4) is fixedly connected to the mounting hole, and the measuring end of the platinum resistance thermometer (4) is located inside the chimney tube. Transmitter assembly (5), which is connected to the Pitot tube (3) and the platinum resistance thermometer (4); The parameter display center is electrically connected to the transmitter assembly (5). The parameter display center receives the total pressure signal, static pressure signal and temperature signal fed back by the transmitter assembly (5), and displays the total pressure data, differential pressure data and temperature data of the Pitot tube and the platinum resistance thermometer. Flange positioning structure (6) is fixedly connected to the detection port and provides a sliding support base for the splicing pipe section (2).

2. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 1, characterized in that, It also includes a clamping member (7), which is detachably connected to the outside of the end cap (1). The clamping member (7) is used to clamp the Pitot tube (3), and a conical sealing gasket (8) is provided between the Pitot tube (3) and the clamping member (7).

3. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 2, characterized in that, An O-ring (9) is provided between the contact surface of the clamping member (7) and the end cap (1).

4. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 1, characterized in that, The adjacent splicing pipe sections (2) are connected by threads, and sealing gaskets (10) are provided on the mating surfaces of the adjacent splicing pipe sections (2).

5. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 1, characterized in that, The axial length of the splicing pipe section (2) is 50cm~60cm, and the number of sections of the splicing pipe section (2) is determined according to the diameter of the chimney pipe and the position of the Pitot tube measuring end extending into the chimney pipe.

6. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 1, characterized in that, The transmitter assembly (5) includes a temperature transmitter (51), a differential pressure transmitter (52), and a pressure transmitter (53). The temperature transmitter (51) is connected to the platinum resistance thermometer (4) via a signal line and is used to receive and convert temperature measurement signals. The differential pressure transmitter (52) is connected to the total pressure port and static pressure port of the Pitot tube (3) via a gas line and receives and converts the pressure difference measurement signal between the total pressure port and the static pressure port. The pressure transmitter (53) is connected to the total pressure port of the Pitot tube (3) via a gas line and receives and converts the pressure measurement signal from the total pressure port. The temperature transmitter (51), differential pressure transmitter (52), and pressure transmitter (53) are respectively electrically connected to the parameter display center.

7. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 1, characterized in that, The flange positioning structure (6) includes a mounting sleeve (61), an auxiliary pipe (62), and a tightening bolt (63). The mounting sleeve (61) is fixedly connected to the inspection port of the chimney pipe. The auxiliary pipe (62) is connected to the inner side of the mounting sleeve (61) and fixed in position on the mounting sleeve (61) by the tightening bolt (63). The auxiliary pipe (62) is slidably connected to the splicing pipe section (2) and provides support and sliding guidance for the splicing pipe section (2).

8. The device for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 7, characterized in that, The inner wall of the auxiliary pipe (62) is provided with a plurality of sealing rings (11) fixedly in axial direction, and the plurality of sealing rings (11) slide to seal the outer wall of the spliced ​​pipe section (2).

9. A method for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system, using the apparatus described in any one of claims 1-8, characterized in that... Includes the following steps: Step 1: Use a rangefinder to measure the inner cross-sectional area of ​​the chimney pipe, and determine the measurement location in the area where the TMF is installed on the chimney pipe. Set up multiple detection ports around the measurement location on the chimney pipe. Step 2: Calibrate the accuracy of the Pitot tube and complete the installation and sealing of the calibration device at the detection port. Use multiple calibration devices to conduct multi-point measurements within the measurement section, and evaluate the flow characteristics in the pipeline through temperature uniformity and flow field stability analysis. Step 3: Calculate the average flow velocity in the core area based on the multi-point velocity measurement results of the calibration device, complete the volumetric flow rate integration based on the velocity-area method, and compare and analyze the measured standard flow rate with the output results of the TMF being calibrated to obtain its indication error and calibration coefficient.

10. A method for monitoring and calibrating gas emissions from a nuclear power plant's fresh air system according to claim 9, characterized in that, In step two, the calibration device simultaneously evaluates the flow field and temperature field at the measurement point. Through the combined arrangement of Pitot tubes and platinum resistance thermometers, flow velocity, temperature, and pressure parameter data are collected simultaneously within the measurement section. After unified collection, the data is used to analyze the uniformity of fluid flow and temperature distribution characteristics within the pipeline. By weighting the test results of multiple measurement points, the overall flow integral of the measurement section within the pipeline is accurately obtained.

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