Nuclear power pipeline thermal cycle and thermal stratification fluctuation risk assessment method and device

Abstract

The invention discloses a nuclear power pipeline thermal cycle and thermal stratification fluctuation risk assessment method and device. The method comprises the steps of obtaining pipeline size parameters and operation condition parameters; establishing a finite element model based on the pipeline size parameters, and setting calculation conditions and boundary conditions based on the operation condition parameters; based on the finite element model, the calculation condition and the boundary condition, obtaining a cold and hot fluid mixing interface position and a temperature evolution state; determining the risk degree based on the position of the cold and hot fluid mixing interface and the temperature evolution state, and judging whether a mitigation measure needs to be designed or not; if so, designing a mitigation measure based on the risk degree; the degree of risk is re-determined based on the designed mitigation measures. According to the method, through accurate numerical simulation and a dynamic risk assessment mechanism, comprehensive identification and quantitative analysis of thermal cycle and thermal stratification fluctuation risks in a complex pipeline system are realized.

Description

Technical Field

[0001] This application relates to the field of nuclear power technology, and in particular to a method and apparatus for assessing the risk of thermal circulation and thermal stratification fluctuations in nuclear power pipelines. Background Technology

[0002] During the operation of a nuclear power plant, the heat generated by the reactor needs to be transferred through a piping system. The fluid movement within these pipes can become highly complex due to their unique structure, such as the turbulent infiltration-induced thermal circulation phenomenon in the downstream horizontal stagnant branch pipes. This phenomenon is characterized by a reciprocating thermal fluctuation at the interface between hot and cold elements. When this temperature fluctuation is transmitted to the pipe wall, it causes periodic intensification and weakening of thermal stratification, leading to localized fatigue loads at critical locations within the pipes. This exacerbates crack initiation, shortens the lifespan of critical pipes, and poses a potential threat to the operational safety of nuclear power facilities.

[0003] Existing technology CN116066654A discloses a piping system for eliminating thermal fatigue in nuclear power plant pipelines, including a heat pipe device and a temperature measuring device. The heat pipe device is located on the outer periphery of the thermal stratification zone of the pipeline to eliminate the thermal stratification effect; the temperature measuring device is located on the outer periphery of the thermal stratification zone to detect the temperature. Although this solution can reduce the occurrence of thermal stratification, thermal circulation, and thermal oscillation in nuclear power plant pipelines, it still suffers from insufficient accuracy of the temperature measuring device, making it unable to accurately monitor the temperature of the thermal stratification zone and assess the thermal fatigue state of the pipeline.

[0004] Existing technology CN116221525A discloses an axial heat transfer system for mitigating thermal stratification in nuclear power plant pipelines, including a heat pipe device and a temperature measuring device. The heat pipe device extends axially along the lower outer wall of the pipeline to transfer heat to sensitive areas to eliminate or mitigate the thermal stratification effect; the temperature measuring device is located on the outer periphery of the sensitive area to detect the temperature. Although this patent can reduce the occurrence of pipeline thermal stratification, thermal circulation, and thermal oscillation, it still suffers from problems such as unreasonable arrangement of the temperature measuring unit, making it impossible to accurately detect the pipeline temperature and thermal stratification effect.

[0005] The existing technology has the following shortcomings: 1) It cannot specifically assess the risk of thermal cycling, and thus cannot mitigate the impact of the risk based on the specific situation at the interface between hot and cold fluids. For example, when the interface between hot and cold fluids is only at the vertical pipe section and does not reach the horizontal pipe, adding heat pipes or other heat conduction devices may introduce additional heat, which may lead to the risk of thermal cycling. Conversely, when the interface between hot and cold fluids has exceeded the horizontal section, the anti-eddy current device may cause insufficient heat transport, causing fluctuations to reappear at the horizontal pipe, increasing the potential risk of thermal cycling; 2) It cannot mitigate the damage to the pipeline caused by changes in operating conditions. When there are significant changes in operating conditions, such as the start-up and shutdown of the unit, large loads may be generated at weak points. If the changes are frequent, the risk is even greater, and the existing device cannot solve the damage problem caused by such situations; 3) It is difficult to process and install, and subsequent operation and maintenance are also difficult. Summary of the Invention

[0006] The purpose of this application is to solve the aforementioned technical problems.

[0007] To achieve the above objectives, the first aspect of this application proposes a method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines, comprising: Obtain pipeline size parameters and operating condition parameters; A finite element model is established based on the pipe size parameters, and calculation conditions and boundary conditions are set based on the operating condition parameters. Based on the aforementioned finite element model, calculation conditions, and boundary conditions, the location and temperature evolution state of the interface between the hot and cold fluids are obtained. The risk level is determined based on the location of the interface between the hot and cold fluids and the temperature evolution state, and it is determined whether mitigation measures need to be designed. If necessary, mitigation measures shall be designed based on the aforementioned level of risk; The level of risk is reassessed based on the mitigation measures designed for it.

[0008] Furthermore, the step of determining the risk level and judging whether mitigation measures need to be designed based on the location of the hot and cold fluid mixing interface and the temperature evolution state includes assessing the risk level of pipeline damage based on the location of the hot and cold fluid mixing interface and the temperature evolution state, and judging whether mitigation measures need to be designed, wherein different risk levels are associated with different mitigation measures.

[0009] Furthermore, the mitigation measures include adding one or more of the following: adding sleeves, installing heat dissipation fins, adding support beams, adding brackets, and changing the thickness of the insulation layer.

[0010] Furthermore, the step of determining the risk level and deciding whether to design mitigation measures based on the location of the hot and cold fluid mixing interface and the temperature evolution state includes: when the hot and cold fluid mixing interface is located in a vertical pipe, the risk level is determined to be low risk and no mitigation measures are used; when the hot and cold fluid mixing interface is located in the upper region of a bend before entering a horizontal pipe, and the temperature fluctuation exceeds ±10℃, the risk level is determined to be medium risk and a first mitigation measure is used.

[0011] Furthermore, the process of determining the risk level and deciding whether to design mitigation measures based on the location of the hot and cold fluid mixing interface and the temperature evolution state further includes the following: when the hot and cold fluid mixing interface is located in a horizontal pipe and the temperature evolution state is in a quasi-static thermal stratification phenomenon, if a stress assessment of overheating stratification is performed, the risk level is determined to be low risk, and no mitigation measures are used; if no stress assessment of overheating stratification is performed, the risk level is determined to be medium risk, and a first mitigation measure is used; when the hot and cold fluid mixing interface is located in a horizontal pipe and the temperature evolution state is in a thermal cycle or thermal stratification fluctuation phenomenon, the risk level is determined to be high risk; if the maximum height of thermal stratification does not exceed 1 / 2 of the inner diameter of the branch pipe, a second mitigation measure is used; if the maximum height of thermal stratification exceeds 1 / 2 of the inner diameter of the branch pipe, a third mitigation measure is used.

[0012] Furthermore, the process of determining the risk level and deciding whether to design mitigation measures based on the location and temperature evolution of the hot and cold fluid mixing interface further includes the following: when the hot and cold fluid mixing interface is located in a horizontal pipe, and the average temperature of the horizontal pipe is not lower than 90% of the main pipe temperature, and the bottom temperature of the horizontal pipe is not lower than 90% of the main pipe temperature, if there is no internal leakage of cold flow in the valve and frequent changes in operating power, the risk level is determined to be low risk, and no mitigation measures are used; if there is internal leakage of cold flow in the valve or frequent changes in operating power, the risk level is determined to be high risk, and a fourth mitigation measure is used.

[0013] Furthermore, the frequent changes in operating power include: when the main flow rate fluctuation does not exceed 35%, the operating power change frequency is greater than 30 times per day; when the main flow rate fluctuation is between 35% and 75%, the operating power change frequency is greater than 6 times per day; and when the main flow rate fluctuation exceeds 75%, the operating power change frequency is greater than 5 times per week.

[0014] Furthermore, the mitigation measures designed based on the risk level include: the first mitigation measure includes one or more of the following: adding a sleeve to the vertical pipe, installing heat dissipation fins on the sleeve, and reducing the thickness of the insulation layer of the vertical pipe; the second mitigation measure includes one or more of the following: adding a sleeve between the vertical pipe and the horizontal pipe, adding a support beam between the sleeves, and reducing the thickness of the insulation layer between the vertical pipe and the bend; the third mitigation measure includes one or more of the following: adding a sleeve between the vertical pipe and the horizontal pipe, adding a support beam between the sleeves and adding an insulation layer to the support beam, and increasing the thickness of the insulation layer of the horizontal pipe and the bend; the fourth mitigation measure includes one or more of the following: adding a sleeve between the vertical pipe and the horizontal pipe, adding a support beam between the sleeves, and adding a bracket between the sleeve and the room floor slab.

[0015] Furthermore, the risk level redetering based on the design mitigation measures includes modifying the finite element model, calculation conditions, and boundary conditions according to the assessed risk level and the designed mitigation measures, reassessing the risk, and adjusting the parameters of each sub-measure in the mitigation measures according to the reassessed risk level and characteristics, until the assessed risk level no longer requires the use of mitigation measures.

[0016] Furthermore, the pipe size parameters include the main pipe inner diameter, main pipe thickness, branch pipe inner diameter, branch pipe thickness, vertical pipe length, horizontal pipe length, bend radius, insulation layer thickness, the angle between the transition section and the horizontal direction, the bend radius of the transition section, and the straight pipe length of the transition section; the operating condition parameters include the main pipe flow velocity, main pipe temperature, ambient temperature, valve side temperature, horizontal pipe temperature, pipe wall heat transfer coefficient, medium density, and insulation layer thermal conductivity.

[0017] Furthermore, the step of establishing a finite element model based on the pipe size parameters includes establishing a three-dimensional geometric model based on the pipe size parameters. The three-dimensional geometric model includes a solid domain and a fluid domain. The length from the main pipe inlet to the branch pipe inlet is greater than 10 times the inner diameter of the main pipe. The three-dimensional geometric model is divided into finite element meshes. The meshes of the fluid and solid domains are connected by common nodes. The mesh type is a hexahedral or polyhedral mesh.

[0018] Furthermore, the step of obtaining the position and temperature evolution state of the cold and hot fluid mixing interface based on the finite element model, calculation conditions, and boundary conditions includes: performing CFD calculations based on the finite element model, calculation conditions, and boundary conditions; using a large eddy simulation turbulence model to calculate the position of the cold and hot interface after a certain time; with a calculation step size ≤ 0.5s, an iteration count ≥ 30 times, and a total calculation time ≥ 3600s, thereby obtaining the position and temperature evolution state of the cold and hot fluid mixing interface.

[0019] To achieve the above objectives, a second aspect of this application proposes a device for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines, comprising: The acquisition module is used to acquire pipeline size parameters and operating condition parameters; The model establishment and condition setting module is used to establish a finite element model based on the pipeline size parameters and to set calculation conditions and boundary conditions based on the operating condition parameters. The cold-hot interface calculation module is used to obtain the location and temperature evolution state of the cold-hot fluid mixing interface based on the finite element model, calculation conditions and boundary conditions. The risk assessment module is used to determine the risk level and whether mitigation measures need to be designed based on the location of the interface between the hot and cold fluids and the temperature evolution state. The mitigation design module is used to design mitigation measures based on the risk level, if necessary. The risk level reassessment module is used to redetermine the risk level based on the mitigation measures designed.

[0020] To achieve the above objectives, a third aspect of this application proposes a computer-readable storage medium comprising a stored computer program, wherein the computer program can be executed by an electronic device to perform the method for assessing the thermal cycling and thermal stratification fluctuation risk of a nuclear power pipeline.

[0021] To achieve the above objectives, the fourth aspect of this application proposes a computer program product, including a computer program that, when executed by a processor, implements the steps of the method for assessing the thermal cycling and thermal stratification fluctuation risks of a nuclear power pipeline.

[0022] To achieve the above objectives, the fifth aspect of this application proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute the nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method through the computer program.

[0023] By applying the above-described technical solution of the present invention, at least the following technical effects are achieved: 1. This method, through precise numerical simulation and dynamic risk assessment mechanism, enables comprehensive identification and quantitative analysis of the risks of thermal circulation and thermal stratification fluctuations in complex pipeline systems. Combined with designed mitigation measures, it can effectively reduce the risk of damage to pipelines caused by thermal circulation and thermal stratification fluctuations, and significantly improve the safety and service life of nuclear power unit pipeline systems.

[0024] 2. This method, through CFD technology combined with a large eddy simulation turbulence model, accurately predicts the location and dynamic changes of the interface between hot and cold fluids, thus improving the accuracy and reliability of risk assessment.

[0025] 3. This method designs four mitigation measures for different risk characteristics, each of which includes three sub-measures, which can flexibly respond to various situations from low risk to high risk, and improve the effectiveness and pertinence of the mitigation plan.

[0026] 4. This method evaluates the effectiveness of mitigation measures through model improvement and iterative analysis, continuously optimizes design parameters, and ultimately achieves a low-risk state, ensuring the optimal configuration of mitigation measures.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A flowchart of a method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power pipelines according to one embodiment is presented; Figure 2 A flowchart of the risk assessment and mitigation design process in one embodiment is presented; Figure 3 A detailed flowchart of a method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines according to one embodiment is presented; Figure 4 A schematic diagram of the second and third mitigation measures in one embodiment is shown; Figure 5 A schematic diagram of the first mitigation measure in one embodiment is shown; Figure 6 A schematic diagram of a nuclear power pipeline thermal circulation and thermal stratification fluctuation risk assessment device according to an embodiment is provided; Figure 7 A schematic diagram of the structure of a nuclear power plant pipeline thermal circulation and thermal stratification fluctuation risk assessment product of one embodiment is presented; Figure 8 A schematic diagram of the structure of an electronic device according to an embodiment is shown.

[0029] Reference numerals in the attached diagram: 1. Main pipe; 2. Vertical pipe; 3. Bend; 4. Horizontal pipe; 5. Vertical pipe sleeve; 6. Horizontal pipe sleeve; 7. Thermal pad; 8. Thermal support beam; 9. Heat dissipation fin. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0032] Example 1

[0033] According to one aspect of the present invention, a method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power pipelines is proposed.

[0034] like Figure 1 The present invention illustrates a method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines according to an embodiment of the present invention. The process mainly includes the following steps: S1. Obtain pipeline size parameters and operating condition parameters.

[0035] Specifically, in this embodiment, the nuclear power pipeline has a downward horizontal stagnation pipeline structure, including a main pipe 1, a transition section, branch pipes and a shut-off valve, wherein the branch pipes include a vertical pipe 2, a bend 3 and a horizontal pipe 4.

[0036] In a downward horizontal stagnant pipe structure, the inner diameter DR of the main pipe 1 is greater than or equal to the inner diameter D of the branch pipe, and the inner diameter of the transition section is equal to D. The main pipe 1 is connected to the transition section or branch pipe via a tee. The transition section is the connecting section between the main pipe and the branch pipe, including a transition straight pipe and a transition elbow. Its inner diameter is equal to D, and its thickness is equal to the thickness t of the branch pipe. The transition straight pipe starts from the main pipe 1, extends horizontally or at a certain downward angle, and then connects to the vertical pipe 2 of the branch pipe via a transition elbow. The length of the transition section is the distance from the radius of the main pipe 1 to half the arc length of the centerline of the transition elbow, and this length does not exceed 5D. If the transition straight pipe extends vertically downward directly from the main pipe 1, the transition pipe section and the vertical pipe 2 of the branch pipe are merged into a single vertical pipe 2.

[0037] The vertical pipe 2 of the downward-flowing horizontal stagnation pipeline structure is a vertically extending pipe with a length ≤30D. It is welded to the horizontal pipe 4 via a 90° bend 3. The end of the horizontal pipe 4 is connected to a stagnation valve, which is normally closed, and the temperature on its outer side is lower than the fluid temperature of the main pipe 1. The outer walls of the vertical pipe 2, bend 3, and horizontal pipe 4 of the branch pipe are all fitted with a thickness of t. n The insulation layer.

[0038] The risks of thermal circulation and thermal stratification fluctuations are caused by the combined effects of turbulent infiltration and heat dissipation in branch pipes, resulting in thermal stratification in horizontal pipe sections. Furthermore, the interface between hot and cold fluids in the thermal stratification will move back and forth when the heat gain and heat dissipation reach a dynamic equilibrium, causing periodic temperature difference fluctuations at the top and bottom of the pipe wall in the horizontal pipe section, which in turn leads to risks such as fatigue damage to the pipeline.

[0039] Among these, the phenomenon that causes the risk of thermal cycling and thermal stratification fluctuations is the thermal cycling and thermal stratification fluctuation phenomenon. It only triggers when certain conditions are met, resulting in an enhanced interaction between the heat gain from turbulent infiltration and the heat dissipation in the branch pipes. Influencing factors include the main pipe flow velocity, the temperature difference between the main and branch pipes, the ambient temperature, the valve side temperature, the pipe wall heat transfer coefficient, the medium density, and the thermal conductivity of the insulation layer. Specifically, the main pipe flow velocity must be ≥8 m / s, the main pipe fluid temperature ≥200℃, and the branch pipe fluid temperature ≤2 / 3 of the main pipe temperature.

[0040] Furthermore, the pipe size parameters include the inner diameter of the main pipe, the thickness of the main pipe, the inner diameter of the branch pipe, the thickness of the branch pipe, the length of the vertical pipe, the length of the horizontal pipe, the radius of the bend, the thickness of the insulation layer, the angle between the transition section and the horizontal direction, the radius of the bend in the transition section, and the length of the straight pipe in the transition section; the operating condition parameters include the flow velocity of the main pipe, the temperature of the main pipe, the ambient temperature, the valve side temperature, the temperature of the horizontal pipe, the heat transfer coefficient of the pipe wall, the density of the medium, and the thermal conductivity of the insulation layer.

[0041] S2. Establish a finite element model based on the pipe size parameters, and set calculation conditions and boundary conditions based on the operating condition parameters.

[0042] Furthermore, a three-dimensional geometric model is established based on the pipe size parameters. The three-dimensional geometric model includes a solid domain and a fluid domain. The length from the main pipe inlet to the branch pipe inlet is greater than 10 times the inner diameter of the main pipe. The three-dimensional geometric model is divided into finite element meshes. The meshes of the fluid and solid are connected by common nodes. The mesh type is hexahedral or polyhedral mesh.

[0043] Specifically, in this embodiment, the finite element model is first established using software such as Space Claim, based on the pipe dimensions, to create a three-dimensional geometric model. The model includes a solid domain and a fluid domain, with the length from the main pipe inlet to the branch pipe inlet exceeding 10 DR. Then, mesh generation software is used to create a finite element mesh for the geometric model. The fluid and solid meshes share common nodes, and the mesh type is hexahedral or polyhedral. In the calculation and boundary condition setting section, fluid calculation finite element software such as Fluent is used to set the main pipe velocity, main pipe temperature, medium density, and pipe wall heat transfer coefficient. The medium density is not constant but decreases as the medium temperature increases.

[0044] S3. Based on the finite element model, calculation conditions and boundary conditions, the location and temperature evolution state of the interface between the hot and cold fluids are obtained.

[0045] Furthermore, CFD calculations were carried out based on the finite element model, calculation conditions, and boundary conditions. The position of the hot and cold interface after a certain time was calculated using the turbulence model of large eddy simulation. The calculation step size was ≤0.5s, the number of iterations was ≥30, and the total calculation time was ≥3600s, thus obtaining the position of the hot and cold fluid mixing interface and the temperature evolution state.

[0046] Specifically, in this embodiment, the CFD calculation is carried out in fluid calculation finite element software such as Fluent, using a large eddy simulation turbulence model to calculate the position of the hot and cold interface after a certain time. The calculation step size is ≤0.5s, the number of iterations is ≥30, and the total calculation time is ≥3600s.

[0047] S4. Determine the degree of risk based on the location of the interface between the hot and cold fluids and the temperature evolution state, and determine whether mitigation measures need to be designed.

[0048] Furthermore, based on the location of the interface between hot and cold fluids and the temperature evolution state, the risk level of pipeline damage is assessed and it is determined whether mitigation measures need to be designed, with different risk levels associated with different mitigation measures.

[0049] Specifically, in this embodiment, such as Figure 2 As shown, the risk assessment process involves evaluating the degree of pipeline damage risk based on the temperature evolution at the interface between hot and cold fluids and critical locations obtained through CFD calculations. The assessed risk levels are divided into three categories: low risk, medium risk, and high risk. Low risk is considered as no risk whatsoever, requiring no mitigation measures. Medium and high risk levels, however, require targeted design and implementation of mitigation measures.

[0050] Furthermore, when the interface between the hot and cold fluids is located in the vertical pipe, the risk level is determined to be low, and no mitigation measures are used; when the interface between the hot and cold fluids is located in the upper region of the bend before entering the horizontal pipe, and the temperature fluctuation exceeds ±10℃, the risk level is determined to be medium, and the first mitigation measure is used.

[0051] Furthermore, when the interface between the hot and cold fluids is located in a horizontal pipe and the temperature evolution is in a quasi-static thermal stratification state, if a stress assessment for overheating stratification is performed, the risk level is determined to be low, and no mitigation measures are used; if no stress assessment for overheating stratification is performed, the risk level is determined to be medium, and the first mitigation measure is used; when the interface between the hot and cold fluids is located in a horizontal pipe and the temperature evolution is in a thermal cycle or thermal stratification fluctuation state, the risk level is determined to be high. If the maximum height of the thermal stratification does not exceed 1 / 2 of the inner diameter of the branch pipe, the second mitigation measure is used; if the maximum height of the thermal stratification exceeds 1 / 2 of the inner diameter of the branch pipe, the third mitigation measure is used.

[0052] Furthermore, when the interface between the hot and cold fluids is located in a horizontal pipe, and the average temperature of the horizontal pipe is not lower than 90% of the temperature of the main pipe, and the temperature at the bottom of the horizontal pipe is not lower than 90% of the temperature of the main pipe, if there is no internal leakage of cold flow in the valve and frequent changes in operating power, the risk level is determined to be low risk, and no mitigation measures are used; if there is internal leakage of cold flow in the valve or frequent changes in operating power, the risk level is determined to be high risk, and the fourth mitigation measure is used.

[0053] Furthermore, situations involving frequent changes in operating power include: when the main flow rate fluctuation does not exceed 35%, the operating power is changed more than 30 times per day; when the main flow rate fluctuation is between 35% and 75%, the operating power is changed more than 6 times per day; and when the main flow rate fluctuation exceeds 75%, the operating power is changed more than 5 times per week.

[0054] Specifically, in this embodiment, the risk level is assessed based on the location and temperature evolution of the interface between the hot and cold fluids calculated by CFD. A low risk occurs when the interface remains only within the vertical pipe region; a medium risk occurs when the interface enters a bend, but is only located in the upper region of the bend, and the bend itself is within the bend, in which case the first mitigation measure can be adopted. When the interface extends into the horizontal pipe and thermal stratification occurs, it is necessary to distinguish whether there is periodic fluctuation at the interface where the hot and cold fluids mix. If there is no fluctuation, it is a quasi-static thermal stratification phenomenon. In this case, if a stress assessment for thermal stratification was performed during the design process, the risk level is low; if no assessment was performed, the risk level is medium, and the first mitigation measure can be adopted. If thermal cycling or thermal stratification fluctuations exist, the risk level is high. In this case, if the maximum height of the thermal stratification does not exceed 1 / 2D, the second mitigation measure is adopted; if the maximum height of the thermal stratification exceeds 1 / 2D, the third mitigation measure is adopted. When the interface not only reaches the horizontal pipe but also ensures that the fluid in the horizontal pipe is completely at a high temperature, with the bottom temperature not lower than 90% of the main pipe temperature, and if the check valve at the end of the horizontal pipe does not leak cold flow into the horizontal pipe and there are no frequent fluctuations in the main pipe flow rate due to frequent changes in operating power, the risk is assessed as low, and no measures are required. If there is cold flow leakage from the valve or frequent changes in operating power, the risk is assessed as high, and a fourth mitigation measure is required.

[0055] S5. If necessary, design mitigation measures based on the aforementioned risk level.

[0056] Further mitigation measures include adding sleeves, installing heat dissipation fins, adding support beams, adding brackets, and changing one or more of the insulation layer thickness.

[0057] Furthermore, such as Figure 2As shown, mitigation measures designed based on risk levels include: The first mitigation measures include one or more of the following: adding sleeves to the vertical pipes, installing heat dissipation fins on the sleeves, and reducing the thickness of the insulation layer of the vertical pipes. The second mitigation measures include adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and reducing the thickness of the insulation layer between vertical and curved pipes, or one or more of these measures. The third mitigation measures include adding sleeves between vertical and horizontal pipes, adding support beams between sleeves and adding insulation layers to the support beams, and increasing the thickness of insulation layers in horizontal pipes and bends, or one or more of these measures. The fourth mitigation measures include adding one or more of the following: adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and adding brackets between sleeves and the room floor slab.

[0058] Specifically, in this embodiment, the process of designing mitigation measures involves adjusting the device structure based on the risk assessment status and the fundamental structure of the mitigation measures, taking into account the risk characteristics. This process includes two aspects: designing new mitigation measures and adjusting the parameters of existing mitigation measures.

[0059] The basic structure of the mitigation device includes a vertical pipe sleeve 5, a horizontal pipe sleeve 6, a heat-conducting pad 7, and a heat-conducting support beam 8, as well as optional components such as an insulation layer, a support frame, and heat dissipation fins 9. It can be installed without requiring additional disassembly and processing of existing pipelines and is easy to operate and maintain. Based on the assessed risk level and characteristics, there are four mitigation measures, each containing three sub-measures. These sub-measures can be implemented simultaneously or selected based on specific site conditions.

[0060] Vertical pipe sleeve 5 and horizontal pipe sleeve 6 are respectively installed on vertical pipe 2 or horizontal pipe 4, respectively covering the weld between bend 3 and vertical pipe 5 or between bend 3 and horizontal pipe 4. Their length is ≥2D, thickness is 1 / 4t ≤ thickness ≤ 2 / 3t, and material is the same as the branch pipe. Each sleeve is made of two semi-circular components. During installation, the two semi-circles are adjusted to the appropriate position and then welded to form a complete sleeve. The sleeve is connected to the branch pipe by welding.

[0061] The thermally conductive pad 7 is a lightweight, thin-walled metal plate or a thermally conductive filler, located between the sleeve and the branch pipe. The thermally conductive pad 7 has good flexibility and thermal conductivity, and can be tightly attached to both the sleeve and the branch pipe to transfer heat between them.

[0062] The heat-conducting support beam 8 is arranged inside the bend 3 and is welded to the vertical pipe sleeve 5 and horizontal pipe sleeve 6 on the vertical pipe 2 and horizontal pipe 4, respectively. Its cross-section is I-shaped, square, or round, and its material is the same as the sleeve, with a thickness of 1 / 4t ≤ thickness ≤ 1 / 2t. This support beam possesses good structural stability and thermal conductivity, effectively transferring heat between the two sleeves to achieve thermal balance, and structurally balancing the forces between the sleeves, thus increasing pipeline stability.

[0063] The insulation layer material can be selected from rock wool, aluminum silicate wool, glass wool, foam glass, quartz wool or at least one of similar low thermal conductivity materials, located on the outside of the branch pipe, sleeve and thermally conductive support beam, with a thickness ≤6t.

[0064] The support has a T-shaped structure, made of a material similar to the branch pipe. The top is directly welded to the outside of the sleeve, while the bottom is a square steel plate that connects to the embedded plate of the factory floor slab via bolts or welding. This design effectively secures the sleeve and significantly reduces fatigue damage.

[0065] S6. Redetermine the level of risk based on design-based mitigation measures.

[0066] Furthermore, based on the assessed risk level and the designed mitigation measures, the finite element model, calculation conditions, and boundary conditions are modified, the risk is reassessed, and the parameters of each sub-measure in the mitigation measures are adjusted according to the reassessed risk level and characteristics until the assessed risk level no longer requires the use of mitigation measures.

[0067] Specifically, in this embodiment, the improved model and iterative analysis process involves modifying the finite element model and calculations and boundary conditions based on the assessed risk level and designed mitigation measures, then re-performing CFD calculations and reassessing the risk. Based on the reassessed risk type and characteristics, the parameters of each sub-measure in the designed mitigation measures are adjusted until the assessed risk is low, thus completing the improved model and iterative analysis process.

[0068] like Figure 3 The figure shows a detailed flowchart of a nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method according to an embodiment of the present invention.

[0069] Example 2

[0070] The nuclear power pipeline thermal circulation and thermal stratification fluctuation risk assessment method in this embodiment mainly includes the following steps: ①In the input parameter stage, based on the pipeline to be analyzed, determine the pipeline size parameters and operating condition parameters, and store them in data or text format as the basis for the finite element model and calculation conditions.

[0071] ② The process of establishing the finite element model and calculation examples involves establishing a finite element model based on the pipe size parameters, and setting calculation and boundary conditions based on the operating conditions parameters to form a calculation example file.

[0072] ③ In the CFD calculation process, the calculation example in step ② is imported into fluid calculation software such as Fluent, and parameters such as calculation step size and calculation time are set to carry out CFD calculation. The total calculation time is not less than 3600s.

[0073] ④ In the risk assessment stage, based on the calculation results in step ③, the interface between the hot and cold fluids reaches the horizontal pipe, and thermal circulation or thermal stratification fluctuations occur in the horizontal pipe. Therefore, it is assessed as a high-risk state, and mitigation measures need to be designed. Since the calculation results show that the maximum height of the thermal stratification exceeds 1 / 2D of the horizontal pipe, a third mitigation measure is adopted to increase the temperature level of the horizontal pipe, thereby reducing the temperature difference between the top and bottom of the thermal stratification.

[0074] ⑤ The mitigation measures design stage, such as Figure 4 As shown, based on the evaluation results of step ④, mitigation measures are designed. Vertical pipe sleeves 5 and horizontal pipe sleeves 6 are added to both vertical pipe 2 and horizontal pipe 4. The sleeves are 2D in length and 1 / 4t thick. A heat-conducting pad 7 is placed between the sleeves and the branch pipes, and a heat-conducting support beam 8 is installed between the sleeves. An insulation layer is installed on the outside of the heat-conducting support beam 8. Simultaneously, the insulation layer thickness is appropriately increased by 20% based on the original insulation layer at the horizontal pipe 4 and bend 3 locations.

[0075] ⑥ In the model improvement stage, based on the mitigation measures in step ⑤, establish finite element models of vertical pipe sleeve 5, horizontal pipe sleeve 6, heat-conducting pad 7, and heat-conducting support beam 8, improve and adjust the original finite element model, modify the calculation and boundary conditions, and then carry out CFD calculations again.

[0076] ⑦ Based on the new calculation results in step ⑥, reassess the risk. If the interface between hot and cold fluids still reaches the horizontal pipe 4, and the horizontal pipe 4 produces thermal circulation or thermal stratification fluctuations, but the thermal stratification height is greater than before, it is still assessed as high risk, and the parameters of the measures are adjusted based on the original mitigation measures.

[0077] ⑧ The mitigation measures were redesigned, increasing the thickness of the vertical pipe sleeve 5 and the horizontal pipe sleeve 6 to 1 / 2t, and increasing the thickness of the insulation layer on the outside of the heat-conducting support beam 8 by 50%. At the same time, the insulation layer thickness at the positions of the horizontal pipe 4 and the bend 3 was increased to 40% of the original structure.

[0078] ⑨ Repeat step ⑥. When the interface between hot and cold fluids reaches the horizontal pipe and the entire horizontal pipe is at a high temperature, further investigation reveals that there is no internal leakage of cold flow in the valve or frequent changes in operating power. At this point, the risk is assessed as low, and the assessment and design of mitigation measures are completed.

[0079] Example 3

[0080] The nuclear power pipeline thermal circulation and thermal stratification fluctuation risk assessment method in this embodiment mainly includes the following steps: ①In the input parameter stage, based on the pipeline to be analyzed, determine the pipeline size parameters and operating condition parameters, and store them in data or text format as the basis for the finite element model and calculation conditions.

[0081] ② The process of establishing the finite element model and calculation examples involves establishing a finite element model based on the pipe size parameters, and setting calculation and boundary conditions based on the operating conditions parameters to form a calculation example file.

[0082] ③ In the CFD calculation process, the calculation example in step ② is imported into fluid calculation software such as Fluent, and parameters such as calculation step size and calculation time are set to carry out CFD calculation. The total calculation time is not less than 3600s.

[0083] ④ In the risk assessment stage, according to the calculation results in step ③, the interface between the hot and cold fluids is located at the top of the bend and the temperature fluctuates significantly. At this time, it is assessed as a medium-risk state, and a first mitigation measure needs to be added to enhance the heat dissipation of the vertical pipe 2 and the bend 3, thereby reducing the heat transport generated by turbulent infiltration.

[0084] ⑤ The mitigation measures design stage, such as Figure 5 As shown, based on the evaluation results of step ④, mitigation measures are designed by adding a vertical pipe sleeve 5 to the vertical pipe. The vertical pipe sleeve 5 has a length of 3D and a thickness of 1 / 4t. A heat-conducting pad 7 is placed between the vertical pipe sleeve 5 and the branch pipe, and a heat dissipation fin 9 is added to the outside of the vertical pipe sleeve 5. Since the insulation layer at the vertical pipe location is not easy to remove, no mitigation measures are implemented.

[0085] ⑥ In the model improvement stage, based on the mitigation measures in step ⑤, establish finite element models of the sleeve, pad, and heat dissipation fins, improve and adjust the original finite element model, modify the calculation and boundary conditions, and then carry out CFD calculations again.

[0086] ⑦ Based on the new calculation results from step ⑥, reassess the risk. When the interface between hot and cold fluids is located only in the vertical pipe, the risk is assessed as low, thus completing the assessment and design of mitigation measures.

[0087] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0088] Example 4

[0089] According to another aspect of the embodiments of this application, the present invention also provides a device for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power pipelines. For example... Figure 6 As shown, the device includes: Module 601 is used to acquire pipeline size parameters and operating condition parameters; The model establishment and condition setting module 602 is used to establish a finite element model based on the pipe size parameters and set calculation conditions and boundary conditions based on the operating condition parameters. The cold-hot interface calculation module 603 is used to obtain the location and temperature evolution state of the cold-hot fluid mixing interface based on the finite element model, calculation conditions and boundary conditions. The risk assessment module 604 is used to determine the risk level and whether mitigation measures need to be designed based on the location of the interface between the hot and cold fluids and the temperature evolution state. The mitigation design module 605 is used to design mitigation measures based on the risk level if necessary; Risk level reassessment module 606 is used to redetermine the risk level based on the mitigation measures designed.

[0090] As an optional approach, the process of determining the risk level and deciding whether to design mitigation measures based on the location of the hot and cold fluid mixing interface and the temperature evolution state includes assessing the risk level of pipeline damage based on the location of the hot and cold fluid mixing interface and the temperature evolution state, and deciding whether to design mitigation measures, wherein different risk levels are associated with different mitigation measures.

[0091] As an alternative, the mitigation measures include adding a sleeve, installing heat dissipation fins, adding a support beam, adding a bracket, and changing one or more of the insulation layer thickness.

[0092] As an optional approach, the process of determining the risk level and deciding whether to design mitigation measures based on the location of the hot and cold fluid mixing interface and the temperature evolution state includes: when the hot and cold fluid mixing interface is located in a vertical pipe, the risk level is determined to be low risk and no mitigation measures are used; when the hot and cold fluid mixing interface is located in the upper region of a bend before entering a horizontal pipe, and the temperature fluctuation exceeds ±10℃, the risk level is determined to be medium risk and a first mitigation measure is used.

[0093] As an optional approach, the process of determining the risk level and deciding whether to design mitigation measures based on the location of the hot and cold fluid mixing interface and the temperature evolution state further includes the following: when the hot and cold fluid mixing interface is located in a horizontal pipe and the temperature evolution state is in a quasi-static thermal stratification phenomenon, if a stress assessment of overheating stratification is performed, the risk level is determined to be low risk, and no mitigation measures are used; if no stress assessment of overheating stratification is performed, the risk level is determined to be medium risk, and a first mitigation measure is used; when the hot and cold fluid mixing interface is located in a horizontal pipe and the temperature evolution state is in a thermal cycle or thermal stratification fluctuation phenomenon, the risk level is determined to be high risk; if the maximum height of thermal stratification does not exceed 1 / 2 of the inner diameter of the branch pipe, a second mitigation measure is used; if the maximum height of thermal stratification exceeds 1 / 2 of the inner diameter of the branch pipe, a third mitigation measure is used.

[0094] As an optional approach, the process of determining the risk level and deciding whether to design mitigation measures based on the location and temperature evolution of the hot and cold fluid mixing interface further includes the following: when the hot and cold fluid mixing interface is located in a horizontal pipe, and the average temperature of the horizontal pipe is not lower than 90% of the main pipe temperature, and the bottom temperature of the horizontal pipe is not lower than 90% of the main pipe temperature, if there is no internal leakage of cold flow in the valve and frequent changes in operating power, the risk level is determined to be low risk, and no mitigation measures are used; if there is internal leakage of cold flow in the valve or frequent changes in operating power, the risk level is determined to be high risk, and a fourth mitigation measure is used.

[0095] As an optional approach, the frequent changes in operating power include: when the main flow rate fluctuation does not exceed 35%, the operating power change frequency is greater than 30 times per day; when the main flow rate fluctuation is between 35% and 75%, the operating power change frequency is greater than 6 times per day; and when the main flow rate fluctuation exceeds 75%, the operating power change frequency is greater than 5 times per week.

[0096] As an optional solution, the mitigation measures designed based on the risk level include: the first mitigation measure includes one or more of the following: adding sleeves to vertical pipes, installing heat dissipation fins on sleeves, and reducing the thickness of the insulation layer of vertical pipes; the second mitigation measure includes one or more of the following: adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and reducing the thickness of the insulation layer between vertical and curved pipes; the third mitigation measure includes one or more of the following: adding sleeves between vertical and horizontal pipes, adding support beams between sleeves and adding insulation layers to the support beams, and increasing the thickness of the insulation layer of horizontal pipes and curved pipes; the fourth mitigation measure includes one or more of the following: adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and adding supports between sleeves and the room floor slab.

[0097] As an optional approach, the risk assessment based on the design-based mitigation measures includes modifying the finite element model, calculation conditions, and boundary conditions according to the assessed risk level and the designed mitigation measures, reassessing the risk, and adjusting the parameters of each sub-measure in the mitigation measures according to the reassessed risk level and characteristics, until the assessed risk level no longer requires the use of mitigation measures.

[0098] As an optional solution, the pipe size parameters include the inner diameter of the main pipe, the thickness of the main pipe, the inner diameter of the branch pipe, the thickness of the branch pipe, the length of the vertical pipe, the length of the horizontal pipe, the radius of the bend, the thickness of the insulation layer, the angle between the transition section and the horizontal direction, the radius of the bend in the transition section, and the length of the straight pipe in the transition section; the operating condition parameters include the flow velocity of the main pipe, the temperature of the main pipe, the ambient temperature, the temperature on the valve side, the temperature of the horizontal pipe, the heat transfer coefficient of the pipe wall, the density of the medium, and the thermal conductivity of the insulation layer.

[0099] As an optional approach, the establishment of the finite element model based on the pipe size parameters includes: establishing a three-dimensional geometric model based on the pipe size parameters; the three-dimensional geometric model includes a solid domain and a fluid domain; the length from the main pipe inlet to the branch pipe inlet is greater than 10 times the inner diameter of the main pipe; dividing the three-dimensional geometric model into finite element meshes; the meshes of the fluid and solid domains are connected by common nodes; and the mesh type is a hexahedral or polyhedral mesh.

[0100] As an optional approach, obtaining the location and temperature evolution state of the mixing interface of hot and cold fluids based on the finite element model, calculation conditions, and boundary conditions includes: performing CFD calculations based on the finite element model, calculation conditions, and boundary conditions; using a large eddy simulation turbulence model to calculate the location of the hot and cold interface after a certain time; with a calculation step size ≤ 0.5s, an iteration count ≥ 30 times, and a total calculation time ≥ 3600s; thereby obtaining the location and temperature evolution state of the mixing interface of hot and cold fluids.

[0101] In this application embodiment, the terms "module" or "unit" refer to a computer program or part of a computer program that has a predetermined function and works with other related parts to achieve a predetermined goal, and can be implemented wholly or partially using software, hardware (such as processing circuitry or memory), or a combination thereof. Similarly, a processor (or multiple processors or memory) can be used to implement one or more modules or units. Furthermore, each module or unit can be part of an overall module or unit that includes the functionality of that module or unit.

[0102] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0103] Example 5

[0104] According to one aspect of this application, a computer program product is provided, the computer program product comprising a computer program.

[0105] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0106] Figure 7 A schematic block diagram of a computer system architecture for implementing an electronic device according to embodiments of the present application is shown.

[0107] It should be noted that, Figure 7 The computer system 700 of the electronic device shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of this application.

[0108] like Figure 7 As shown, the computer system 700 includes a central processing unit (CPU) 701, which can perform various appropriate actions and processes based on programs stored in read-only memory (ROM) 702 or programs loaded from storage section 708 into random access memory (RAM) 703. The RAM 703 also stores various programs and data required for system operation. The CPU 701, ROM 702, and RAM 703 are interconnected via a bus 704. An input / output interface 705 (I / O interface) is also connected to the bus 704.

[0109] The following components are connected to the input / output interface 705: an input section 706 including a keyboard, mouse, etc.; an output section 707 including a cathode ray tube (CRT), liquid crystal display (LCD), etc., and speakers, etc.; a storage section 708 including a hard disk, etc.; and a communication section 709 including a network interface card such as a local area network card, modem, etc. The communication section 709 performs communication processing via a network such as the Internet. A drive 710 is also connected to the input / output interface 705 as needed. A removable medium 711, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., is installed on the drive 710 as needed so that computer programs read from it can be installed into the storage section 708 as needed.

[0110] Specifically, according to embodiments of this application, the processes described in the various method flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication section 709, and / or installed from removable medium 711. When the computer program is executed by central processing unit 701, it performs various functions defined in the system of this application.

[0111] In such an embodiment, the computer program can be downloaded and installed from a network via the communication section 709, and / or installed from the removable medium 711. When the computer program is executed by the central processing unit 701, it performs various functions provided in the embodiments of this application.

[0112] Example 6

[0113] According to another aspect of the embodiments of this application, an electronic device for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines is also provided. This embodiment uses this electronic device as an example of a terminal device. Figure 8 As shown, the electronic device includes a memory 802 and a processor 804. The memory 802 stores a computer program, and the processor 804 is configured to execute the steps in any of the above method embodiments via the computer program.

[0114] Optionally, in this embodiment, the aforementioned electronic device may be located in at least one of a plurality of network devices in a computer network.

[0115] Optionally, in this embodiment, the processor may be configured to execute the methods in the embodiments of this application via a computer program.

[0116] Alternatively, as those skilled in the art will understand, Figure 8 The structure shown is for illustrative purposes only. Figure 8 This does not limit the structure of the aforementioned electronic devices. For example, the electronic device may also include components that are more... Figure 8 The more or fewer components shown (such as network interfaces, etc.), or having the same Figure 8 The different configurations shown.

[0117] The memory 802 can be used to store software programs and modules, such as the program instructions / modules corresponding to the nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method and apparatus in this embodiment. The processor 804 executes various functional applications and data processing by running the software programs and modules stored in the memory 802, thereby realizing the aforementioned nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method. The memory 802 may include high-speed random access memory, and may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 802 may further include memory remotely located relative to the processor 804, and these remote memories can be connected to the terminal via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof. Specifically, the memory 802 may be used, but is not limited to, to store pipeline size parameters and operating condition parameters. As an example, such as Figure 8 As shown, the memory 802 may include, but is not limited to, the acquisition module 601, model building and condition setting module 602, hot-cold interface calculation module 603, risk level assessment module 604, mitigation measure design module 605, and risk level reassessment module 606 from the aforementioned device. Furthermore, it may include, but is not limited to, other module units from the aforementioned device, which will not be elaborated upon in this example.

[0118] Optionally, the transmission device 806 described above is used to receive or send data via a network. Specific examples of the network described above may include wired networks and wireless networks. In one example, the transmission device 806 includes a Network Interface Controller (NIC), which can be connected to other network devices and a router via a network cable to communicate with the Internet or a local area network. In another example, the transmission device 806 is a Radio Frequency (RF) module, used for wireless communication with the Internet.

[0119] In addition, the aforementioned electronic device also includes: a display 808 for displaying the risk level; and a connection bus 810 for connecting the various module components in the aforementioned electronic device.

[0120] In other embodiments, the aforementioned terminal device or server can be a node in a distributed system, wherein the distributed system can be a blockchain system, which is a distributed system formed by connecting multiple nodes through network communication. The nodes can form a peer-to-peer network, and any form of computing device, such as a server, terminal, or other electronic device, can become a node in the blockchain system by joining this peer-to-peer network.

[0121] According to one aspect of this application, a computer-readable storage medium is provided, wherein a processor of an electronic device reads computer instructions from the computer-readable storage medium, and executes the computer instructions, causing the electronic device to perform the nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method provided in various optional implementations of the above-described nuclear power pipeline thermal cycling and thermal stratification fluctuation risk assessment method.

[0122] Optionally, in this embodiment, the computer-readable storage medium described above may be configured to store methods for performing the embodiments of this application.

[0123] Optionally, in this embodiment, those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing the hardware related to the terminal device. The program can be stored in a computer-readable storage medium, which may include: flash drive, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc.

[0124] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0125] If the integrated units in the above embodiments are implemented as software functional units and sold or used as independent products, they can be stored in the aforementioned computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause one or more electronic devices to execute all or part of the steps of the methods described in the various embodiments of this application.

[0126] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0127] In the several embodiments provided in this application, it should be understood that the disclosed application can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some interfaces; indirect couplings or communication connections between units or modules may be electrical or other forms.

[0128] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0129] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0131] By applying the above-described technical solution of the present invention, at least the following technical effects are achieved: 1. This method, through precise numerical simulation and dynamic risk assessment mechanism, enables comprehensive identification and quantitative analysis of the risks of thermal circulation and thermal stratification fluctuations in complex pipeline systems. Combined with designed mitigation measures, it can effectively reduce the risk of damage to pipelines caused by thermal circulation and thermal stratification fluctuations, and significantly improve the safety and service life of nuclear power unit pipeline systems.

[0132] 2. This method, through CFD technology combined with a large eddy simulation turbulence model, accurately predicts the location and dynamic changes of the interface between hot and cold fluids, thus improving the accuracy and reliability of risk assessment.

[0133] 3. This method designs four mitigation measures for different risk characteristics, each of which includes three sub-measures, which can flexibly respond to various situations from low risk to high risk, and improve the effectiveness and pertinence of the mitigation plan.

[0134] 4. This method evaluates the effectiveness of mitigation measures through model improvement and iterative analysis, continuously optimizes design parameters, and ultimately achieves a low-risk state, ensuring the optimal configuration of mitigation measures.

[0135] The above are merely several specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0136] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0137] It should be noted that, in the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A method for assessing the risk of thermal cycling and thermal stratification fluctuations in nuclear power plant pipelines, characterized in that, include: Obtain pipeline size parameters and operating condition parameters; A finite element model is established based on the pipe size parameters, and calculation conditions and boundary conditions are set based on the operating condition parameters. Based on the aforementioned finite element model, calculation conditions, and boundary conditions, the location and temperature evolution state of the interface between the hot and cold fluids are obtained. The risk level is determined based on the location of the interface between the hot and cold fluids and the temperature evolution state, and it is determined whether mitigation measures need to be designed. If necessary, mitigation measures shall be designed based on the aforementioned level of risk; The level of risk is reassessed based on the mitigation measures designed for it.

2. The evaluation method according to claim 1, characterized in that, The process of determining the risk level and assessing whether mitigation measures are needed based on the location of the cold and hot fluid mixing interface and the temperature evolution state includes, Based on the location of the interface between the hot and cold fluids and the temperature evolution, the risk level of pipeline damage is assessed and it is determined whether mitigation measures need to be designed, with different risk levels associated with different mitigation measures.

3. The evaluation method according to claim 2, characterized in that, The mitigation measures include adding sleeves, installing heat dissipation fins, adding support beams, adding brackets, and changing one or more of the insulation layer thickness.

4. The evaluation method according to claim 3, characterized in that, The process of determining the risk level and assessing whether mitigation measures are needed based on the location of the cold and hot fluid mixing interface and the temperature evolution state includes, When the interface between the hot and cold fluids is located in a vertical pipe, the risk level is determined to be low, and no mitigation measures are used. When the interface between the hot and cold fluids is located in the upper region of the bend before entering the horizontal pipe, and the temperature fluctuation exceeds ±10℃, the risk level is determined to be medium risk, and the first mitigation measure is used.

5. The evaluation method according to claim 4, characterized in that, The process of determining the risk level and judging whether mitigation measures need to be designed based on the location of the interface between the hot and cold fluids and the temperature evolution state also includes, When the interface between the hot and cold fluids is located in a horizontal pipe and the temperature evolution is in a quasi-static thermal stratification state, if a stress assessment of overheating stratification is performed, the risk level is determined to be low and no mitigation measures are used. If a stress assessment for overheating stratification has not been performed, the risk level is determined to be medium risk, and the first mitigation measure is used. When the interface between the hot and cold fluids is located in a horizontal pipe and the temperature evolution is in a state of thermal cycling or thermal stratification fluctuation, the risk level is determined to be high risk. If the maximum height of thermal stratification does not exceed 1 / 2 of the inner diameter of the branch pipe, the second mitigation measure is used; if the maximum height of thermal stratification exceeds 1 / 2 of the inner diameter of the branch pipe, the third mitigation measure is used.

6. The evaluation method according to claim 5, characterized in that, The process of determining the risk level and judging whether mitigation measures need to be designed based on the location of the interface between the hot and cold fluids and the temperature evolution state also includes, When the interface between the hot and cold fluids is located in a horizontal pipe, and the average temperature of the horizontal pipe is not lower than 90% of the temperature of the main pipe, and the temperature at the bottom of the horizontal pipe is not lower than 90% of the temperature of the main pipe, if there is no internal leakage of cold flow in the valve and frequent changes in operating power, the risk level is determined to be low risk and no mitigation measures are used; if there is internal leakage of cold flow in the valve or frequent changes in operating power, the risk level is determined to be high risk and the fourth mitigation measure is used.

7. The evaluation method according to claim 6, characterized in that, The frequent changes in operating power include, When the main flow rate fluctuation does not exceed 35%, the operating power change frequency is greater than 30 times per day; When the main flow rate fluctuates between 35% and 75%, the operating power changes more than 6 times per day. When the main flow rate fluctuates by more than 75%, the operating power changes more than 5 times per week.

8. The evaluation method according to claim 6, characterized in that, The mitigation measures designed based on the aforementioned risk level include, The first mitigation measures include one or more of the following: adding a sleeve to the vertical pipe, installing heat dissipation fins on the sleeve, and reducing the thickness of the insulation layer of the vertical pipe. The second mitigation measures include adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and reducing the thickness of the insulation layer between vertical and curved pipes, or one or more of these measures. The third mitigation measures include adding sleeves between vertical and horizontal pipes, adding support beams between sleeves and adding insulation layers to the support beams, and increasing the thickness of insulation layers in horizontal pipes and bends, or one or more of these measures. The fourth mitigation measure includes one or more of the following: adding sleeves between vertical and horizontal pipes, adding support beams between sleeves, and adding brackets between sleeves and the room floor slab.

9. The evaluation method according to claim 2, characterized in that, The risk assessment based on design-based mitigation measures includes, Based on the assessed risk level and the designed mitigation measures, modify the finite element model, calculation conditions, and boundary conditions, reassess the risk, and adjust the parameters of each sub-measure in the mitigation measures according to the reassessed risk level and characteristics until the assessed risk level no longer requires the use of mitigation measures.

10. The evaluation method according to claim 1, characterized in that, The pipe size parameters include the main pipe inner diameter, main pipe thickness, branch pipe inner diameter, branch pipe thickness, vertical pipe length, horizontal pipe length, bend radius, insulation layer thickness, the angle between the transition section and the horizontal direction, the bend radius of the transition section, and the straight pipe length of the transition section; the operating condition parameters include the main pipe flow velocity, main pipe temperature, ambient temperature, valve side temperature, horizontal pipe temperature, pipe wall heat transfer coefficient, medium density, and insulation layer thermal conductivity.

11. The evaluation method according to claim 1, characterized in that, The finite element model established based on the pipe size parameters includes, A three-dimensional geometric model is established based on the pipe size parameters. The three-dimensional geometric model includes a solid domain and a fluid domain. The length from the main pipe inlet to the branch pipe inlet is greater than 10 times the inner diameter of the main pipe. The three-dimensional geometric model is divided into finite element meshes. The meshes of the fluid and solid are connected by common nodes. The mesh type is hexahedral or polyhedral mesh.

12. The evaluation method according to claim 1, characterized in that, The determination of the location and temperature evolution state of the mixing interface of the hot and cold fluids based on the finite element model, calculation conditions, and boundary conditions includes: Based on the finite element model, calculation conditions, and boundary conditions, CFD calculations were carried out. The position of the hot and cold interface after a certain time was calculated using the turbulence model of large eddy simulation. The calculation step size was ≤0.5s, the number of iterations was ≥30, and the total calculation time was ≥3600s. The position and temperature evolution state of the hot and cold fluid mixing interface were obtained.

13. A device for assessing the risk of thermal circulation and thermal stratification fluctuations in nuclear power plant pipelines, characterized in that, include: The acquisition module is used to acquire pipeline size parameters and operating condition parameters; The model establishment and condition setting module is used to establish a finite element model based on the pipeline size parameters and to set calculation conditions and boundary conditions based on the operating condition parameters. The cold-hot interface calculation module is used to obtain the location and temperature evolution state of the cold-hot fluid mixing interface based on the finite element model, calculation conditions and boundary conditions. The risk assessment module is used to determine the risk level and whether mitigation measures need to be designed based on the location of the interface between the hot and cold fluids and the temperature evolution state. The mitigation design module is used to design mitigation measures based on the risk level, if necessary. The risk level reassessment module is used to redetermine the risk level based on the mitigation measures designed.

14. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein the computer program can be executed by an electronic device to perform the method described in any one of claims 1 to 12.

15. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method described in any one of claims 1 to 12.

16. An electronic device comprising a memory and a processor, characterized in that, The memory stores a computer program, and the processor is configured to execute the method described in any one of claims 1 to 12 through the computer program.

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