Nuclear power plant tracer gas diffusion ventilation simulation method
Through the CFD numerical simulation method, the grid optimization and tracer gas safety threshold problems of the ventilation system of the nuclear power plant main control room were solved, and the efficient design and safety monitoring of the ventilation system of the nuclear power plant main control room were achieved, which reduced the simulation error and modeling difficulty and ensured the safety of personnel.
Patent Information
- Application Number
- CN202510967343.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-14
- Publication Date
- 2025-10-28
AI Technical Summary
Existing technologies lack grid optimization methods for complex ventilation systems in the main control room of a nuclear power plant. This ignores the safety threshold of toxic tracer gases and the gravitational effect of high-density tracer gases, resulting in large simulation errors and making it difficult to monitor gas diffusion balance and safety thresholds in real time.
A numerical simulation method based on CFD was adopted. By establishing a simplified model and performing mesh division, combining the component transport model and the standard k-ε turbulence model, defining boundary conditions and solver types, and using FLUENT software for simulation, ventilation parameters and gravity effects were considered, and the gas concentration distribution was dynamically monitored to obtain the diffusion equilibrium time and safety assessment.
It enables rapid and accurate simulation of tracer gas diffusion in the main control room of a nuclear power plant, optimizes the ventilation system, monitors gas concentration in real time, identifies ventilation dead zones, ensures personnel safety, and reduces modeling difficulty and calculation errors.
Smart Images
Figure CN120850872A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of nuclear power plant safety monitoring technology, specifically a nuclear power plant tracer gas diffusion ventilation simulation method based on computational fluid dynamics (CFD) for assessing the ventilation efficiency of the main control room of a nuclear power plant and the risk of personnel exposure. Background Technology
[0002] Tracer gases are an effective method for evaluating ventilation systems and are widely used in buildings and underground mines. Tracer gases must be able to mix thoroughly with air, pose low risk, and be cost-effective. Commonly used tracer gases include SF6, N2O, CO2, and Ne. In most cases, the tracer gas method is used to monitor the gas diffusion balance in specific areas of buildings. However, diffusion experiments are expensive, require significant investment, and the data may contain errors, with various uncontrollable conditions. The rapid development of computer technology has revolutionized research methods and promoted the advancement of computer numerical simulation of gas diffusion models. Numerical simulation of tracer gases in three-dimensional space is complex, necessitating the development of software based on mathematical models for rapid and accurate simulation results. Many diffusion simulation software programs have been developed, mainly categorized into diffusion model simulation and numerical simulation based on their simulation methods.
[0003] Diffusion simulation software is primarily based on specific diffusion models, such as Gaussian models, box models, and shallow diffusion models. Users program the software according to the expressions and calculation processes of these models, input the data into a computer, and establish a user interface. However, this type of software is specific to certain research objects and must assume similar distributions of velocity and concentration, as well as that the gas diffuses under ideal conditions of steady, uniform turbulence. For gas diffusion under other conditions, especially complex diffusion, the simulation results in significant calculation errors compared to theoretical values, thus exhibiting certain limitations.
[0004] Traditional tracer gas experiments (such as SF6 and iodomethane) suffer from high costs, toxicity risks, and large data errors. Especially in confined spaces like nuclear power plant control rooms, it is difficult to monitor the diffusion balance and safety thresholds of toxic gases in real time. Fluid dynamics simulation software using numerical simulation methods can more accurately describe the physical phenomena of fluids in atmospheric turbulent motion, has broad applicability, and is particularly reliable in simulating non-uniform and stable flow fields and complex processes with obstacles or significant terrain changes. Existing CFD simulation methods do not address the following issues: lack of mesh optimization methods for the complex ventilation systems of nuclear power plant control rooms; inadequate consideration of safety thresholds for toxic tracer gases; and neglect of the gravitational effects of high-density tracer gases. Summary of the Invention
[0005] To address the problems existing in the prior art, the present invention aims to provide a numerical simulation method for investigating the diffusion ventilation phenomenon of tracer gases in nuclear power plants. This method is applicable to observing the diffusion ventilation phenomenon of tracer gases in nuclear power plants, and is an effective method for evaluating the ventilation safety of the main control room of a nuclear power plant in the event of an accident.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant includes the following steps:
[0008] Step 1: The overall model suitable for observing the diffusion and ventilation of tracer gases includes the main control room, walls, doors, fresh air ducts and recirculation ducts. The simplified models established for the overall model include the simplified geometric model of the main control room, the simplified geometric model of the walls, the simplified geometric model of the fresh air ducts and the simplified geometric model of the recirculation ducts.
[0009] Step 2: Divide the simplified model established in Step 1 into a computational grid, and adjust the grid distribution and refine the grid at the locations where the tracer gas is ventilated to obtain the computational grid of the simplified model.
[0010] Step 3: Perform numerical simulation of tracer gas diffusion ventilation in nuclear power plants. The specific settings of this numerical simulation method are as follows: define the solver type, establish the component transport model and the standard k-ε turbulence model, define the physical properties of various tracer gas materials, define the boundary conditions, combine the algorithm provided by FLUENT software and select the interpolation method to complete the solution method settings, adjust the sub-relaxation factor and adaptive time step to complete the solution settings. After using the adaptive time step, when the difference between the air and tracer gas flow velocities is too large, the calculation time will differ by a factor of one hundred. In order to accelerate the calculation convergence and shorten the solution time, the initial field settings were performed.
[0011] During the numerical simulation, ventilation parameters, including fresh air volume, supply air volume, and return air volume, need to be considered when defining boundary conditions. A component transport model is used to simulate the diffusion of tracer gases, and the flow equation is solved in combination with the standard k-ε turbulence model. The gas concentration distribution is dynamically monitored. When the rate of change of the diffusion concentration of the tracer gas with time no longer changes, the diffusion equilibrium of the tracer gas is determined, the diffusion equilibrium time is obtained, the simulated diffusion equilibrium concentration is compared with the occupational exposure concentration limit of toxic tracer gases, and a safety assessment report is output.
[0012] Preferably, in step 1, the simplified geometric model of the fresh air duct and the simplified geometric model of the circulating air duct are horizontal pipe structures to ensure the practicality and universality of the models.
[0013] Preferably, in step 1, the simplified geometric model of the fresh air duct and the simplified geometric model of the circulating air duct are connected to each other and located on top of the simplified geometric model of the main control room. An air and tracer gas mixing inlet is set at the connection inlet with the simplified geometric model of the main control room, which significantly improves the calculation efficiency and optimizes the model structure.
[0014] Preferably, in the mesh generation described in step 2, Fluent is used to generate an unstructured mesh with a mesh count of one million or more, and the mesh quality meets the computational requirements to prevent gas backflow during the calculation.
[0015] Preferably, in step 1, a 3D model including rooms, doors and windows, fresh air ducts and recirculation ducts is built using 3D software based on the nuclear power plant design drawings, simplifying non-critical equipment such as tables and chairs, while retaining details such as door gaps and pipe interfaces; in step 2, the inlet and outlet areas, ventilation areas, and duct interfaces of the fresh air ducts and recirculation ducts are densified with mesh to optimize computing resources and improve computing precision.
[0016] Preferably, in step 3, the solver type is defined as a pressure-based solver, the time type as transient calculation, the gravity parameter is set to simulate the sinking phenomenon of heavy gas, and the gravity in the y-axis direction is set to -9.81 m·s. -2 This aligns with actual phenomena.
[0017] Preferably, in step 3, the standard k-ε turbulence model adopts a Realizable k-ε turbulence model that can simulate complex flows such as jets, separated flows, and swirling flows, and uses a component transport model to ensure that the tracer gas and air are mixed and enter at different rates.
[0018] Preferably, in step 3, the component transport mixture is set to air and tracer gas, and the components are specified by mole fraction; this facilitates gas unit conversion and reduces errors.
[0019] Preferably, in step 3, the inlet is set as a velocity inlet, the circulating air duct is set as an inlet fan, the fresh air duct is set as an exhaust fan, and the remaining boundaries are set as boundary conditions of an insulated wall. This ensures gas exchange and ventilation to simulate the actual conditions of a nuclear power plant.
[0020] Preferably, in step 3, the path and concentration changes of gas diffusion with airflow are calculated, the tracer gas concentration in each area is displayed in real time, the characteristics of tracer gas diffusion are analyzed, ventilation dead zones are marked based on simulation results, and duct modification schemes are proposed.
[0021] Compared with the prior art, the beneficial effects of the present invention are:
[0022] 1. This invention overcomes the challenges of high experimental costs, difficulty in obtaining diffusion results, and challenges in ensuring personnel safety in traditional experiments. It enables the prediction of tracer gas diffusion and ventilation phenomena through numerical simulation calculations even when experiments are inconvenient. This significantly improves the design and safety monitoring efficiency of the ventilation system in the main control room of nuclear power plants, allowing for real-time monitoring of gas concentration distribution and automatic comparison with safety limits. It can quickly identify ventilation dead zones, optimize airflow organization, and ensure personnel safety during nuclear power plant accidents.
[0023] 2. The present invention connects the simplified geometric models of the fresh air duct and the circulating air duct to each other and places them on top of the simplified geometric model of the main control room. An air and tracer gas mixing inlet is set at the connection inlet of the simplified geometric model of the main control room. This can greatly reduce the modeling difficulty, and the mesh generated by using the simplified model has high accuracy and good effect. Attached Figure Description
[0024] Figure 1 This is a flowchart of the numerical simulation method of the present invention.
[0025] Figure 2 This is a simplified model diagram of the overall circuit.
[0026] Figure 3 This is a grid division diagram at the inlet where air and tracer gas mix.
[0027] Figure 4 It is a cloud map of the diffusion equilibrium distribution of tracer gas. Detailed Implementation
[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0029] This invention provides a method for simulating tracer gas diffusion ventilation in nuclear power plants. Figure 1 As shown, the specific steps include:
[0030] Step 1: For the tracer gas diffusion ventilation phenomenon in the main control room of a nuclear power plant, a simplified overall model is designed and established. This model includes the main control room, walls, doors, fresh air ducts, and recirculation ducts. A 1:1 scale model is used, with appropriate simplification of non-critical equipment such as tables and chairs, while retaining details such as door gaps and pipe interfaces. Structural components affecting tracer gas diffusion ventilation are preserved, including the routing of the fresh air and recirculation ducts at the top and the spatial connectivity of the personnel activity area. The simplified overall model diagram of the tracer gas diffusion ventilation phenomenon in a nuclear power plant is shown below. Figure 2 As shown.
[0031] The simplified geometric models of the fresh air duct and the recirculation duct are horizontal pipe structures, and the simplified models are interconnected and located on top of the simplified geometric model of the main control room. To increase the ease of calculation and reduce calculation errors, the distance between the simplified geometric models of the fresh air duct and the recirculation duct and the top of the simplified geometric model of the main control room is set to 0.
[0032] The simplified geometric models of each fresh air duct and each circulating air duct are connected at a 90° angle to each other, forming a T-shaped connection.
[0033] The simplified geometric models of the fresh air duct and the recirculation duct are connected to the simplified geometric model of the main control room at the entrance where an air and tracer gas mixing inlet is located. The simplified geometric model of the main control room contains five interconnected rooms of different sizes, with simplified door geometry; the interconnected area of the rooms is approximately the size of a normal door.
[0034] Step 2: Divide the simplified model established in Step 1 into a computational grid, and adjust the grid distribution and refine the grid at the locations where the tracer gas is ventilated to obtain the computational grid of the simplified model.
[0035] The simplified overall loop model was meshed using ICEM CFD software. Considering the diffusion and ventilation phenomena of tracer gases in nuclear power plants, the air-trace gas mixing inlet is relatively small compared to the overall model. To ensure computational quality and speed, the O-Block function of the O-type mesh cutting method was used to refine the mesh at the air-trace gas mixing inlet. Simultaneously, the mesh distribution at the connections of the fresh air duct, recirculation duct, and main control room was adjusted to make the mesh denser at the interfaces. The mesh generation diagram for the air-trace gas mixing inlet is shown below. Figure 3 As shown, this meshing method can accurately capture the diffusion distribution signal of tracer gas at the interface; by adjusting the mesh, the orthogonality quality reaches above 0.6, which improves the calculation accuracy of numerical simulation of tracer gas diffusion ventilation phenomena in nuclear power plants.
[0036] Step 3: Perform numerical simulation of tracer gas diffusion ventilation in nuclear power plants. The specific steps of this numerical simulation are as follows: define the solver type, establish a component transport model and a standard k-ε turbulence model, define the components of the mixed gas, define the boundary conditions, combine the algorithm provided by FLUENT software and select the interpolation method to complete the solution method settings, adjust the sub-relaxation factor and adaptive time step to complete the solution settings. After using the adaptive time step, when the flow velocities of air and tracer gas differ too much, the calculation time will differ by a factor of one hundred. In order to accelerate the calculation convergence and shorten the solution time, the initial field settings were performed.
[0037] The solver type is pressure-based, the time type is transient calculation, and gravity parameters are set to simulate the sinking phenomenon of heavy gases. The gravity in the y-axis is set to -9.81 m·s.-2 .
[0038] The standard k-ε turbulence model employs a Realizable k-ε turbulence model capable of simulating complex flows such as jets, separated flows, and swirling flows. A component transport model is used to ensure that the tracer gas and air are mixed at different rates. The component transport mixture is set as air and tracer gas; the proportion of the gas in the air is calculated based on the concentration of the tracer gas, and finally, the components are specified in mole fraction.
[0039] During the numerical simulation, ventilation parameters, including fresh air volume, supply air volume, and return air volume, need to be considered when defining boundary conditions. A component transport model is used to simulate the diffusion of tracer gases, and the flow equation is solved in combination with the standard k-ε turbulence model. The gas concentration distribution is dynamically monitored. When the rate of change of the diffusion concentration of the tracer gas with time no longer changes, the diffusion equilibrium of the tracer gas is determined, the diffusion equilibrium time is obtained, the simulated diffusion equilibrium concentration is compared with the occupational exposure concentration limit of toxic tracer gases, and a safety assessment report is output.
[0040] Set the inlet as the velocity inlet, the circulating air duct as the inlet fan, the fresh air duct as the exhaust fan, and the remaining boundaries as the boundary conditions of the insulated wall.
[0041] The system calculates the path and concentration changes of the gas as it diffuses with the airflow, displays the real-time concentration of the tracer gas in each area, analyzes the characteristics of the tracer gas diffusion pattern, and generates a tracer gas diffusion equilibrium distribution cloud map, as shown below. Figure 4 As shown, from Figure 4 The results show that after the tracer gas has fully diffused within the nuclear power plant, the gas concentration distribution in each area is uniform, indicating that a diffusion equilibrium has been reached. Based on the simulation results, ventilation dead zones are marked, and duct modification schemes are proposed.
Claims
1. A method for simulating the diffusion ventilation of tracer gases in a nuclear power plant, characterized in that: Includes the following steps: Step 1: To observe the diffusion and ventilation phenomenon of tracer gas in the main control room of a nuclear power plant, an overall model suitable for observing the diffusion and ventilation phenomenon of tracer gas is established. The overall model includes the main control room, walls, doors, fresh air ducts and recirculation ducts. The simplified models established for the overall model include the geometrically simplified model of the main control room, the geometrically simplified model of the walls, the geometrically simplified model of the fresh air ducts and the geometrically simplified model of the recirculation ducts. Step 2: Divide the simplified model established in Step 1 into a computational grid, and adjust the grid distribution and refine the grid at the locations where the tracer gas is ventilated to obtain the computational grid of the simplified model. Step 3: Perform numerical simulation of tracer gas diffusion ventilation in nuclear power plants. The specific steps of this numerical simulation method are as follows: define the solver type, establish the component transport model and the standard k-ε turbulence model, define the components of the mixed gas, define the boundary conditions, combine the algorithm provided by FLUENT software and select the interpolation method to complete the solution method settings, adjust the sub-relaxation factor and adaptive time step to complete the solution settings, and after using the adaptive time step, perform initial field settings in order to accelerate the calculation convergence and shorten the solution time. During the numerical simulation, ventilation parameters, including fresh air volume, supply air volume, and return air volume, need to be considered when defining boundary conditions. A component transport model is used to simulate the diffusion of tracer gases, and the flow equation is solved in combination with the standard k-ε turbulence model. The gas concentration distribution is dynamically monitored. When the rate of change of the diffusion concentration of the tracer gas with time no longer changes, the diffusion equilibrium of the tracer gas is determined, the diffusion equilibrium time is obtained, the simulated diffusion equilibrium concentration is compared with the occupational exposure concentration limit of toxic tracer gases, and a safety assessment report is output.
2. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 1, the simplified geometric models of the fresh air duct and the circulating air duct are horizontal pipe structures.
3. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 1, the simplified geometric model of the fresh air duct and the simplified geometric model of the circulating air duct are connected to each other and located on top of the simplified geometric model of the main control room. An air and tracer gas mixing inlet is set at the connection inlet of the simplified geometric model of the main control room.
4. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 2, the mesh generation process requires the use of Fluent to generate an unstructured mesh with a mesh count of one million or more. The mesh quality must meet the computational requirements to prevent gas backflow during the calculation.
5. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 1, based on the nuclear power plant design drawings, a 3D model including rooms, doors and windows, fresh air ducts and recirculation ducts is built using 3D software. Non-critical equipment is simplified while retaining details of door gaps and pipe interfaces. In step 2, the inlet and outlet areas, ventilation opening areas and duct interfaces of the fresh air ducts and recirculation ducts are densified with mesh.
6. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 3, the solver type is defined as a pressure-based solver, the time type is defined as transient calculation, gravity parameters are set to simulate the sinking phenomenon of heavy gas, and the gravity in the y-axis is set to -9.81 m·s. -2 ; In step 3, the standard k-ε turbulence model adopts the Realizable k-ε turbulence model, which can simulate complex flows such as jets, separated flows, and swirling flows. The component transport model is used to ensure that the tracer gas and air are mixed and enter at different rates.
7. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 3, the component transport gas mixture is set to air and tracer gas, with the components specified by mole fraction; In step 3, the inlet is set as the velocity inlet, the circulating air duct is set as the inlet fan, the fresh air duct is set as the exhaust fan, and the remaining boundaries are set as the boundary conditions of the insulated wall.
8. The method for numerical simulation of tracer gas diffusion ventilation in a nuclear power plant according to claim 1, characterized in that: In step 3, the path and concentration changes of gas diffusion with airflow are calculated, the tracer gas concentration in each area is displayed in real time, the characteristics of tracer gas diffusion are analyzed, ventilation dead zones are marked based on simulation results, and duct renovation schemes are proposed.