Airborne effluent sampling system optimization method for uranium conversion facility

Abstract

The invention relates to an airborne effluent sampling system optimization method for a uranium transformation facility, which comprises the following steps of: constructing a geometric model by using SOLI DWORKS and Gambit modeling software on the basis of the structural characteristics of a typical exhaust funnel in a uranium transformation process, generating a grid model through grid division, and importing the grid model into CFD software to calculate an airflow velocity field and aerosol concentration distribution. An existing sampling position is analyzed through performance indexes, a plurality of candidate sampling positions are screened based on the mixing uniformity of the flow field, and a final sampling position is further determined through a field test. According to the method, a gas-solid two-phase flow model, a grid encryption technology and post-processing analysis are adopted, field test verification of tracer gas and aerosol is combined, the design of a sampling system is optimized, and the monitoring efficiency is improved. The optimized system reduces deviation caused by non-uniformity of sampling points, ensures that the sampling points can truly reflect flow field characteristics in the exhaust funnel, meets the ISO 2889-2010 standard requirements, and is suitable for environment monitoring scenes of various nuclear facilities.

Description

Technical Field

[0001] The invention relates to the field of nuclear facility environmental impact assessment, and in particular to an optimization method for an airborne effluent sampling system of a uranium conversion facility. Background Art

[0002] Airborne radioactive effluents from nuclear facilities are usually discharged into the atmosphere through chimneys after being filtered or adsorbed. To ensure that emissions meet management limit requirements and detect abnormal conditions in a timely manner, continuous sampling and online monitoring of gaseous effluents in chimneys are required. However, since the distribution of radioactive materials in the pipeline or chimney flow field may be uneven and deposition losses may occur in the sampling pipeline, the representativeness of sampling monitoring is crucial to the accuracy of measurement data and subsequent environmental and radiation safety assessments.

[0004] Environmental monitoring data from existing nuclear bases in my country show that some radionuclide concentration data deviate from the concentration field data measured in the exhaust chimney. The reason for this is that the sampling port locations of most old nuclear facilities are designed based on the "2 / 8 principle" in the old standard, and have not been optimized according to the latest ANSI / HPS N13.1-2011 and ISO 2889-2010 standards. Since the sampling ports are located in the non-uniform area of ​​the flow field, the representativeness and uniformity of the monitoring data are poor, and the actual radionuclide environmental emission level cannot be accurately reflected. Therefore, optimizing the design of the sampling system of the exhaust chimney of nuclear facilities and improving the accuracy and representativeness of sampling monitoring have become issues that need to be urgently addressed.

[0005] In view of the above problems, the present invention is proposed. Summary of the invention

[0006] The invention discloses an optimization method for an airborne effluent sampling system for a uranium conversion facility, aiming to solve the technical problems existing in the prior art.

[0007] The present invention provides a method for optimizing an airborne effluent sampling system for a uranium conversion facility, comprising:

[0008] Based on the structural characteristics of a typical exhaust chimney in the uranium conversion process, the geometric model of the exhaust chimney was constructed using SOLIDWORKS and Gambit modeling software.

[0009] Meshing the geometric model to generate a mesh model containing multiple mesh partitions;

[0010] Import the grid model into computational fluid dynamics (CFD) software, set material properties, boundary conditions, initial conditions, and select the gas-solid two-phase flow model to calculate the airflow velocity field, aerosol and gas concentration distribution of the exhaust pipe;

[0011] Mark the existing sampling position as the first sampling position, calculate and analyze the cross-sectional performance index of the first sampling position, and compare it with the preset index requirements to evaluate whether it meets the preset index requirements; at the same time, analyze whether the first sampling position is located in the gas mixing uniform area;

[0012] Evaluate the mixing uniformity of the flow field inside the exhaust pipe, and select multiple cross-sections with uniform mixing as multiple second sampling positions; calculate and analyze the performance indicators of multiple second sampling positions, and compare them with the preset indicator requirements, and select multiple third sampling positions that meet the preset indicator requirements as recommended new sampling positions;

[0013] Determine whether the third sampling position meets the preset index requirements through on-site tests;

[0014] Based on the field test results, the third sampling position that meets the preset index requirements is determined as the final sampling position, completing the optimization of the sampling system.

[0015] As a preferred technical solution, the mixing uniformity of the flow field inside the exhaust pipe is evaluated, including:

[0016] The air streamline diagram inside the exhaust pipe and the velocity cloud diagram of the radial section are generated by post-processing software to observe the distribution law of gas flow velocity, and to identify the pipeline position where the gas flow velocity gradually reaches stability and the velocity distribution begins to tend to be uniform, and select it as the second sampling position.

[0017] As a preferred technical solution, before generating the air streamline diagram inside the exhaust pipe and the velocity cloud diagram of the radial section by the post-processing software, it also includes:

[0018] CFD-POST and other post-processing software are used to analyze the internal flow field of the exhaust pipe.

[0019] As the preferred technical solution, the preset indicator requirements include:

[0020] Cyclone angle index: The average cyclone angle of the entire cross section should be ≤20°;

[0021] Speed ​​uniformity index: the speed variation coefficient within the 2 / 3 area of ​​the cross section center should be ≤20%;

[0022] Tracer gas concentration distribution index: the relative deviation between the maximum tracer gas concentration and the average concentration of the entire cross section should be ≤30%; the coefficient of variation of the tracer gas concentration within the 2 / 3 area of ​​the cross section center should be ≤20%;

[0023] Aerosol concentration distribution index: The coefficient of variation of aerosol concentration within the 2 / 3 area of ​​the center of the cross section should be ≤20%.

[0024] As a preferred technical solution, the gas-solid two-phase flow model is selected based on the sparseness of the gas-solid two phases.

[0025] As a preferred technical solution, when the volume fraction of the aerosol discrete phase in the gas-solid two-phase flow model is less than 10%, a discrete phase (DPM) model is used for solution.

[0026] As a preferred technical solution, the initial conditions include initial air flow velocity, pressure and concentration distribution state.

[0027] As a preferred technical solution, the initial air flow velocity is obtained by calculation based on the flow rate and the pipe interface of the exhaust pipe.

[0028] As a preferred technical solution, whether the third sampling position meets the preset index requirements is determined through field tests, including:

[0029] Adopt SF 6 As tracer gas, a polydisperse aerosol generator was used to generate tracer particles including 10 μm aerosol particles. During the facility maintenance, the tracer gas and tracer particles were injected into the inlet of the exhaust chimney for field testing.

[0030] As a preferred technical solution, it also includes:

[0031] The cyclone angle, wind speed, tracer gas concentration and tracer particle concentration on the section where the third sampling position is located are measured and compared with the preset index requirements.

[0032] The technical solution adopted by the present invention can achieve at least one of the following beneficial effects:

[0033] 1. The present invention combines CFD numerical simulation and field test methods, based on the calculation and analysis of the airflow velocity field and aerosol concentration distribution, accurately selects the pipeline section with uniform gas mixing as the sampling position, ensuring that the final sampling point can represent the real flow field characteristics in the exhaust pipe. By meeting the performance index requirements of the ISO 2889-2010 standard, the representativeness and accuracy of the airborne effluent sampling data are effectively improved, providing a more reliable scientific basis for environmental monitoring and safety assessment of uranium conversion facilities.

[0034] 2. The present invention reduces the deviation caused by the non-uniformity of the sampling points by selecting the sampling positions with higher mixing uniformity in the exhaust pipe, and optimizes the design of the sampling system. The streamline diagram and velocity cloud diagram generated by the grid encryption technology and post-processing software can quickly and accurately locate the area with stable and uniform flow velocity, thereby greatly improving the operating efficiency of the sampling system and reducing the errors and uncertainties that may occur during the monitoring process.

[0035] 3. The present invention adopts a flexible numerical simulation and experimental verification process, which can adapt to the flow field characteristics of exhaust chimneys with different structures. The comprehensive analysis method based on multiple performance indicators can not only scientifically evaluate the existing sampling locations, but also be used for the optimization design and transformation of new sampling locations. Through comprehensive field test verification of tracer gas and aerosol particles, the present invention further ensures the reliability and feasibility of the optimization results, and is suitable for airborne effluent monitoring scenarios in various nuclear facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, which constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions explain the present invention and do not constitute improper limitations on the present invention. In the drawings:

[0037] Figure 1 The present invention is a schematic diagram of a process flow of a method for optimizing an airborne effluent sampling system for a uranium conversion facility. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. In the description of the present invention, it should be noted that the term "or" is usually used in the sense of including "and / or", unless the content clearly indicates otherwise.

[0039] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or a magnetic connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0040] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] To solve the problems existing in the prior art, an embodiment of the present invention provides an optimization method for an airborne effluent sampling system of a uranium conversion facility, such as Figure 1 As shown, including:

[0042] Modeling step S1: Based on the structural characteristics of a typical exhaust chimney in the uranium conversion process, a geometric model of the exhaust chimney is constructed using SOLIDWORKS and Gambit modeling software. The model includes geometric parameters such as the pipe shape, pipe length, and pipe diameter of the exhaust chimney to truly reflect the physical structure of the exhaust chimney;

[0043] Meshing step S2: Meshing the above geometric model to generate a mesh model containing multiple mesh partitions. During the meshing process, encryption is performed on the area close to the pipe wall and the pipe bend (such areas have large velocity gradients and complex flow field changes), so as to achieve a reasonable mesh layout, improve the solution efficiency while ensuring the calculation accuracy;

[0044] Calculation and solution step S3: import the above-mentioned grid model into computational fluid dynamics (CFD) software, the grid model is used to divide the calculation domain to ensure the calculation accuracy and efficiency; set material properties, boundary conditions, initial conditions, and select a suitable gas-solid two-phase flow model to calculate the airflow velocity field in the exhaust pipe and the concentration distribution of aerosols and gases, and provide data support for the analysis of flow field characteristics and pollutant migration laws in the exhaust pipe; preferably, the material properties include the physical properties of the continuous phase of air and the discrete phase of aerosols in the pipeline, such as density, viscosity and diffusion coefficient; preferably, the boundary conditions include the flow velocity, pressure and concentration distribution at the exhaust pipe inlet, and the flow constraints at the outlet and wall; preferably, the initial conditions include the initial airflow velocity, pressure and concentration distribution state;

[0045] Comparison step S4: marking the existing sampling position as the first sampling position, calculating and analyzing the performance index of the cross section where the first sampling position (the existing sampling position) is located, setting the requirements in the ISO 2889-2010 standard as the preset index requirements, comparing the above calculation and analysis results with the preset index requirements to evaluate whether they meet the standard requirements; at the same time, analyzing whether the first sampling position (the existing sampling position) is located in the gas "uniform mixing" area;

[0046] Preferably, the performance indicators are based on ISO 2889-2010 standard, including the following criteria:

[0047] Cyclone angle index: The average cyclone angle of the entire cross section (the angle between the airflow direction and the central axis of the pipeline) should be ≤20°;

[0048] Speed ​​uniformity index: the speed variation coefficient within the 2 / 3 area of ​​the cross section center should be ≤20%;

[0049] Tracer gas concentration distribution index: the relative deviation between the maximum tracer gas concentration and the average concentration of the entire cross section should be ≤30%; the coefficient of variation of the tracer gas concentration within the 2 / 3 area of ​​the cross section center should be ≤20%;

[0050] Aerosol concentration distribution index: The coefficient of variation of aerosol concentration within the 2 / 3 area of ​​the cross section center should be ≤20%;

[0051] Preselecting a new sampling position step S5: Evaluate the mixing uniformity of the flow field inside the exhaust pipe, and select a section with uniform mixing as a preselected representative sampling position, i.e., the second sampling position; analyze and calculate various performance indicators of these sections, and compare them with the preset indicator requirements (ISO 2889-2010 requirements), and determine the section that meets the standard requirements as the recommended new sampling position, i.e., the third sampling position;

[0052] Step S51: using post-processing software such as CFD-POST to analyze the flow field inside the exhaust pipe in detail; generating an air streamline diagram and a velocity cloud diagram of a radial section inside the exhaust pipe through the post-processing software to observe the distribution law of the gas flow velocity; based on the analysis results, identifying the pipe positions where the gas flow velocity gradually reaches stability and the velocity distribution begins to tend to be uniform, and using these positions as potential pre-selected representative sampling positions, i.e., the second sampling positions;

[0053] Step S52: further calculate and evaluate various performance indicators on the pre-selected cross section, including velocity distribution uniformity, gas concentration distribution uniformity and other related parameters, to ensure that they meet the "mixing uniformity" judgment criteria in the ISO 2889-2010 standard; finally, the cross-sectional position that meets all standard requirements is recommended as a new representative sampling point, i.e., the third sampling position, to provide a scientific basis for the optimization of the sampling system;

[0054] Determination step S6: through field tests, determine whether the third sampling position (pre-selected new sampling position) meets the sampling conditions;

[0055] Step S61: Using SF 6 Conduct field tests as tracer gas, using a polydisperse aerosol generator to generate tracer particles including 10 μm aerosol particles, and inject the tracer gas and tracer particles into the inlet of the exhaust chimney during facility maintenance;

[0056] Step S62: measuring the cyclone angle, wind speed, tracer gas concentration, and tracer particle concentration on the cross section where the third sampling positions (pre-selected sampling positions) are located, and comparing them with the index requirements in ISO 2889-2010 to verify the performance index;

[0057] Determine the sampling position step S7: determine the section that meets the standard requirements as the optimized final sampling position, and formulate a sampling system modification plan based on it.

[0058] The embodiment of the present invention is based on computational fluid dynamics (CFD) simulation and field test methods. By constructing a geometric model of a typical exhaust chimney in a uranium conversion process, flow field simulation and analysis are performed to evaluate the mixing uniformity of the gas in the exhaust chimney, thereby optimizing the sampling position. First, the airflow velocity field and the concentration field of aerosols and tracer gases in the exhaust chimney are simulated using CFD software, and the cross-section with stable gas velocity and uniform distribution is identified through post-processing analysis; secondly, according to the judgment criteria of the ISO 2889-2010 standard, the performance indicators such as velocity uniformity and concentration uniformity of the selected cross-section are quantitatively calculated and evaluated; finally, the performance of the pre-selected sampling position is verified through field tests, and the optimized sampling position that meets the standard requirements is finally determined by combining the measurement of polydisperse aerosols and tracer gas concentrations. Through the above design, the embodiment of the present invention combines CFD numerical simulation with field tests to form a closed-loop optimization process from simulation analysis to actual verification, thereby improving the scientificity and accuracy of sampling position optimization; through multiple indicators such as cyclone angle, velocity uniformity, tracer gas concentration distribution and aerosol concentration distribution, the mixing uniformity of the sampling section is systematically evaluated to ensure that the selected position meets international standard requirements; for complex flow field changes near the pipe wall area and the pipe bend, local grid encryption processing is used to improve the calculation accuracy and solution efficiency, providing technical support for accurate analysis of gas flow field characteristics; by generating air streamline diagrams and radial section velocity cloud diagrams, the airflow velocity and distribution law are intuitively analyzed, and a pre-selected sampling position determination method based on velocity stability and distribution uniformity is proposed; by using field test methods of tracer gas (SF6) and aerosol particles, key parameters such as airflow velocity and concentration are accurately measured to fully verify the reliability and compliance of the pre-selected position.

[0059] In some preferred embodiments, in the calculation and solution step S3, the initial air flow velocity is obtained by calculation according to the flow rate and the pipe interface of the exhaust chimney.

[0060] In some preferred implementation schemes, in the calculation and solution step S3, the initial conditions also include an initial temperature, and the initial temperature is set according to actual working conditions.

[0061] In some preferred embodiments, in the calculation and solution step S3, the gas-solid two-phase flow model is selected based on the rarefaction of the gas-solid two-phase. Preferably, when the volume fraction of the aerosol discrete phase is less than 10%, the discrete phase (DPM) model should be used for solution.

[0062] In some preferred implementation schemes, in the calculation and solution step S3, the inlet adopts a velocity inlet boundary; the outlet adopts a pressure outlet boundary; and the wall adopts a no-slip boundary.

[0063] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for optimizing an airborne effluent sampling system for a uranium conversion facility, characterized in that: include: Based on the structural characteristics of a typical exhaust chimney in the uranium conversion process, a geometric model of the exhaust chimney was constructed using SOLIDWORKS and Gambit modeling software; Meshing the geometric model to generate a mesh model including a plurality of mesh partitions; The grid model is imported into computational fluid dynamics (CFD) software, and material properties, boundary conditions, initial conditions, and a gas-solid two-phase flow model are set to calculate the airflow velocity field, aerosol and gas concentration distribution of the exhaust pipe; Mark the existing sampling position as the first sampling position, calculate and analyze the cross-sectional performance index of the first sampling position, and compare it with the preset index requirements to evaluate whether it meets the preset index requirements; at the same time, analyze whether the first sampling position is located in the gas mixing uniform area; Evaluate the mixing uniformity of the flow field inside the exhaust pipe, and select multiple cross-sections with uniform mixing as multiple second sampling positions; calculate and analyze the performance indicators of the multiple second sampling positions, and compare them with the preset indicator requirements, and select multiple third sampling positions that meet the preset indicator requirements as recommended new sampling positions; Determine whether the third sampling position meets the preset index requirements through field tests; According to the field test results, the third sampling position that meets the preset index requirements is determined as the final sampling position, and the optimization of the sampling system is completed.

2. The method for optimizing an airborne effluent sampling system according to claim 1, characterized in that: The mixing uniformity evaluation of the flow field inside the exhaust pipe includes: The air streamline diagram inside the exhaust pipe and the velocity cloud diagram of the radial section are generated by post-processing software to observe the distribution pattern of the gas flow rate, and the pipeline position where the gas flow rate gradually reaches stability and the velocity distribution begins to tend to be uniform is identified and selected as the second sampling position.

3. The method for optimizing an airborne effluent sampling system according to claim 2, wherein: Before generating the air streamline diagram inside the exhaust pipe and the velocity cloud diagram of the radial section by the post-processing software, the method further includes: The internal flow field of the exhaust pipe is analyzed using post-processing software such as CFD-POST.

4. The method for optimizing an airborne effluent sampling system according to claim 3, wherein: The preset indicator requirements include: Cyclone angle index: The average cyclone angle of the entire cross section should be ≤20°; Speed ​​uniformity index: the speed variation coefficient within the 2 / 3 area of ​​the cross section center should be ≤20%; Tracer gas concentration distribution index: the relative deviation between the maximum tracer gas concentration and the average concentration of the entire cross section should be ≤30%; the coefficient of variation of the tracer gas concentration within the 2 / 3 area of ​​the cross section center should be ≤20%; Aerosol concentration distribution index: The coefficient of variation of aerosol concentration within the 2 / 3 area of ​​the center of the cross section should be ≤20%.

5. The method for optimizing an airborne effluent sampling system according to claim 1, wherein: The gas-solid two-phase flow model is selected based on the rarefaction degree of the gas-solid two-phase.

6. The method for optimizing an airborne effluent sampling system according to claim 5, characterized in that: When the volume fraction of the aerosol discrete phase of the gas-solid two-phase flow model is less than 10%, a discrete phase (DPM) model is used for solving the problem.

7. The method for optimizing an airborne effluent sampling system according to claim 1, wherein: The initial conditions include initial air flow velocity, pressure and concentration distribution state.

8. The method for optimizing an airborne effluent sampling system according to claim 7, wherein: The initial air flow velocity is obtained by calculation according to the flow rate and the pipe interface of the exhaust pipe.

9. The method for optimizing an airborne effluent sampling system according to claim 1, wherein: The determining whether the third sampling position meets the preset index requirement through field testing includes: The field test was conducted by using SF6 as the tracer gas and a polydisperse aerosol generator to generate tracer particles including 10 μm aerosol particles, and injecting the tracer gas and tracer particles into the inlet of the exhaust chimney during facility maintenance.

10. The method for optimizing an airborne effluent sampling system according to claim 9, wherein: Also includes: The cyclone angle, wind speed, tracer gas concentration, and tracer particle concentration on the cross section where the third sampling position is located are measured and compared with the preset index requirements.

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