Research system and research method for water seal evolution of U-shaped pipe section of advanced pressurized water reactor

Abstract

The invention relates to the technical field of reactor thermal hydraulic tests, in particular to an advanced pressurized water reactor U-shaped pipe section water seal evolution research system and method, and the system comprises a main coolant simulation loop, a crevasse simulation assembly and a visual measurement and acquisition system, the method comprises the steps of establishing an initial working condition, simulating an accident process, collecting multi-dimensional data, constructing an evolution model and determining a conversion boundary. According to the method, a dependent relationship between different flow forms and a water seal evolution mechanism, a synergistic action mechanism of driving force and flow resistance in a water seal forming process and correlation characteristics between the flow forms and fluid dynamics are established, and technical support is provided for establishment of a water seal conversion boundary.

Description

Technical Field

[0001] This invention relates to the field of reactor thermal-hydraulic testing technology, specifically to a research system and method for studying the evolution of water seals in U-shaped sections of advanced pressurized water reactors. Background Technology

[0002] For pressurized water reactors with a U-tube transition section, a typical small breach loss-of-coolant accident can be divided into the following stages: venting, natural circulation, loop water seal presence, loop water seal removal, and long-term core cooling.

[0003] Although the water seal phenomenon occurs locally in the primary circuit transition section of the reactor, it represents a crucial intermediate stage in small-break loss-of-coolant accidents in pressurized water reactors. It is closely related to the overall characteristics of the reactor system and is essential for the safety analysis of the reactor cladding peak temperature. While numerous loss-of-coolant accident experiments and numerical simulations based on overall effect test facilities have been conducted both domestically and internationally, identifying the water seal phenomenon during the loss-of-coolant accident process, shortcomings remain:

[0004] Existing tests on water seals mostly focus on typical small-to-medium-sized breakage loss-of-coolant accidents. They determine the removal of the water seal based on the system's macroscopic response parameters, focusing on the reactor system's response characteristics during the loss-of-coolant accident process. The purpose is to verify the engineering design. However, the judgment of water seal removal relies on the system's macroscopic response parameters, which leads to inaccurate judgments.

[0005] The existing fluid behavior studies on the local phenomenon of water seal also use alternative fluid media such as air-water to simply observe the manifold evolution of U-shaped pipe sections. These studies suffer from inaccurate simulations of the water seal phenomenon and insufficient understanding of its underlying mechanisms. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a research system and method for studying the evolution of water seals in U-shaped sections of advanced pressurized water reactors. This method can realistically simulate high-temperature and high-pressure operating conditions and possesses high-precision visualization measurement capabilities, thus meeting the needs of advanced pressurized water reactors for refined analysis of accident processes.

[0007] This invention is achieved through the following technical solution:

[0008] A research system for the evolution of water seals in an advanced pressurized water reactor U-section includes:

[0009] The main coolant simulation loop includes a pressure vessel simulation, an evaporator simulation, and a main pump simulation connected in sequence; wherein, the pressure vessel simulation and the evaporator simulation are connected by a heat pipe section, the evaporator simulation and the main pump simulation are connected by a U-shaped transition section, and the main pump simulation and the pressure vessel simulation are connected by a cold pipe section.

[0010] A break simulation component is installed on the main coolant simulation circuit to simulate a water loss accident.

[0011] A visual measurement and acquisition system is installed in the U-shaped transition section to acquire the fluid flow pattern and thermal-hydraulic parameters during the water seal evolution process.

[0012] Optionally, the breach simulation component includes:

[0013] The rupture simulation pipeline has one end connected to the cold pipe section of the main coolant simulation circuit, and the other end connected to the discharge space.

[0014] A rupture opening device is installed on the rupture simulation pipeline to control the opening of the rupture water loss accident simulation.

[0015] A rupture size adjustment component is installed on the rupture simulation pipeline to adjust the flow area of ​​the rupture simulation pipeline to simulate ruptures of different sizes.

[0016] Optionally, the visualization measurement and acquisition system includes:

[0017] A resistive tomography sensor is arranged on the pipeline of the U-shaped transition section to acquire gas-liquid two-phase distribution data in the cross-section of the pipeline;

[0018] A high-speed camera, positioned outside the U-shaped transition section, is used to capture dynamic images of the fluid flow.

[0019] The data acquisition and processing unit is connected to the resistivity tomography sensor and the high-speed camera, respectively, and is used to synchronously acquire and process the distributed data and dynamic images.

[0020] Furthermore, the system also includes multiple sets of liquid level measuring devices, respectively located at:

[0021] The descending and ascending sections of the pressure vessel simulator are used to measure the water level in the descending and ascending sections of the pressure vessel.

[0022] The rising and falling sections of the evaporator simulator are used to measure the water level in the rising section and the water level in the falling section of the evaporator simulator.

[0023] The descending and ascending sides of the U-shaped transition section are used to measure the water level in the descending section and the water level in the ascending section of the water seal.

[0024] Optionally, the pressure vessel simulator contains a core simulator, which includes an electric heating assembly for heating the fluid in the main coolant simulation loop to generate steam that drives natural circulation.

[0025] A research method for studying the evolution of water seals in U-sections of advanced pressurized water reactors, based on the research system described above, includes the following steps:

[0026] Establish initial operating conditions: Heat and pressurize the fluid in the main coolant simulation loop to reach the preset saturation state, and control the water level in the pressure vessel simulation body to be lower than the centerline height of the heat pipe section;

[0027] Simulated accident process: Activate the breach simulation component to simulate a coolant loss accident, causing the main coolant simulation circuit to enter the natural circulation and water seal formation stage;

[0028] Multidimensional data acquisition: Real-time images of the gas-liquid two-phase fluid flow pattern in the U-shaped transition section are obtained using a visualization measurement and acquisition system, and real-time water level data of each key section in the main coolant simulation loop are collected simultaneously using a liquid level measurement device.

[0029] Construct an evolution model: Based on the real-time water level data, establish the dynamic equilibrium relationship of the main coolant simulation loop, and calculate the total driving force and total resistance of the water seal fluid flow;

[0030] Determine the transition boundary: By comparing the magnitude of the total driving force and the total flow resistance, the water seal state is determined, and the transition boundary conditions for water seal removal are determined based on the determination result.

[0031] Optionally, the dynamic equilibrium relationship of the main coolant simulation loop is as follows: ,in: This refers to the water level in the lower section of the pressure vessel. This refers to the water level in the rising section of the pressure vessel. The water level in the descending section of the evaporator simulator; This refers to the water level in the lowering section of the water seal. The water level in the rising section of the evaporator simulator; This refers to the water level in the rising section of the water seal.

[0032] The total driving force for fluid flow in the U-shaped transition section; This represents the total resistance to fluid flow in the U-shaped transition section.

[0033] Optionally, the rule for determining the water seal status is as follows:

[0034] Real-time monitoring of the numerical changes in the total driving force and the total resistance;

[0035] When the total resistance is greater than the total driving force, it is determined that the main coolant simulation circuit is in a state of natural circulation interruption, and the water seal is maintained;

[0036] When the total driving force is greater than the total resistance, it is determined that the water seal is cleared and the main coolant simulation circuit resumes natural circulation.

[0037] The critical moment when the total driving force changes from less than to greater than the total resistance is determined as the moment when the water seal is cleared.

[0038] Optionally, the determined water seal clearance transition boundary conditions include at least the following parameters: U-shaped transition section inlet steam flow rate and main coolant simulation loop system pressure.

[0039] Furthermore, the method also includes a multi-condition flow pattern identification step:

[0040] By adjusting the rupture size adjustment component, changing the heating power of the electric heating component, and adjusting the installation height of the U-shaped transition section, multiple sets of water seal visualization tests were conducted under different rupture sizes, different steam flow rates, and different U-shaped pipe section heights.

[0041] Based on the images acquired by the visualization measurement and acquisition system, the water seal flow patterns during the entire experimental cycle are identified, and the water seal flow patterns are classified and organized to determine the flow pattern conversion conditions between different flow patterns.

[0042] Furthermore, the method also includes a numerical simulation extension step:

[0043] A CFD model is constructed, and the effectiveness of the CFD model is verified using the real-time water level data and the transformation boundary conditions.

[0044] We used the validated CFD model to conduct water seal removal simulations with a wide parameter range to obtain microscopic parameters of the water seal removal process that cannot be directly measured under experimental conditions.

[0045] Furthermore, the method also includes model correction and prediction steps:

[0046] Based on experimental and simulation data, a dimensionless flow ratio-visualized flow pattern map was established.

[0047] By using graphs to correct the dynamic equilibrium relationship, a predictive model for quantitatively predicting the water seal transition boundary is constructed.

[0048] Compared with the prior art, the present invention has the following features and beneficial effects:

[0049] This invention constructs a closed-loop main coolant simulation loop including a pressure vessel, an evaporator, and a U-shaped transition section. A rupture simulation component, a visualization measurement and acquisition system, and multiple sets of liquid level measurement devices are installed on this loop. Based on this hardware system, this invention utilizes real-time acquired gas-liquid two-phase flow images and water level data to construct a dynamic equilibrium model characterizing the relationship between fluid driving force and flow resistance. Combining computational fluid dynamics simulation and dimensionless flow pattern analysis, the invention establishes the judgment logic for water seal removal.

[0050] This invention addresses the critical need for precise safety analysis of peak fuel cladding temperature during advanced nuclear reactor safety analysis processes. Targeting the key phenomenon of water seals that cause fuel cladding temperature spikes, the research proceeds systematically following the guiding principles of "constructing research methods → understanding process mechanisms → mastering influencing laws / synergistic mechanisms → forming methods and theories," and possesses a clear and well-defined research methodology.

[0051] This invention captures the evolution of the flow morphology during the water sealing process using a high-speed camera and a resistivity tomography sensor. It is a typical study that combines overall and individual experiments, which not only accurately and effectively simulates the water sealing phenomenon during the dehydration process of an advanced nuclear reactor, but also deeply explores the evolution mechanism of this local phenomenon of water sealing.

[0052] This invention grasps the evolution law of the water seal, a key phenomenon in the small-break loss-of-coolant accident process in advanced nuclear reactors, from its formation to its removal. It accurately defines the vapor-liquid flow pattern of the water seal throughout its entire cycle, providing experimental basis for judging the natural circulation operation within the U-shaped tube section during the formation and removal of the water seal.

[0053] This invention establishes the dependency relationship between different flow patterns and water seal evolution mechanisms, the synergistic mechanism of driving force and flow resistance in the water seal formation process, and the correlation characteristics between flow patterns and fluid dynamics, providing technical support for the establishment of water seal transition boundaries. Attached Figure Description

[0054] The accompanying drawings illustrate exemplary embodiments of the present invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, but do not constitute a limitation on the embodiments of the present invention.

[0055] Figure 1 This is a schematic diagram of the structure of a research system for the evolution of water seals in an advanced pressurized water reactor U-shaped tube section according to the present invention.

[0056] Figure 2 This is a schematic flowchart of a research method for the evolution of water seals in an advanced pressurized water reactor U-section, as described in this invention.

[0057] Figure reference numerals: 1-Pressure vessel simulator, 2-Break simulation pipeline, 3-Cold pipe section, 4-Main pump simulator, 5-U-shaped transition section, 6-Evaporator simulator, 7-Heat pipe section, 8-Liquid level measuring device, 9-High-speed camera, 10-Resistive tomography sensor, 11-Data acquisition and processing unit. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0059] It should also be noted that, for ease of description, only the parts relevant to the present invention are shown in the accompanying drawings.

[0060] Where there is no conflict, 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.

[0061] The method provided by this invention for studying the water seal evolution of U-shaped tube sections in advanced pressurized water reactors mainly includes constructing water seal boundary conditions, conducting visualization experiments on the water seal clearance evolution process, and constructing a dynamic model of water seal evolution. Its main features are:

[0062] Based on pressure vessel simulators (including core simulators), evaporator simulators, main pump simulators, heat pipe sections, cold pipe sections, and U-shaped transition sections, the main loop system of an advanced nuclear reactor is simulated, and the boundary conditions for the water seal process are constructed.

[0063] Through visualization experiments, the evolution of coolant flow morphology in the U-shaped pipe section during the water seal stage under small and medium-sized breakage water loss accident conditions is reproduced. The two-phase flow image is analyzed in depth, and the influence of operating parameters such as steam flow rate, breakage size, and U-shaped transition section height on the flow morphology of the water seal process is systematically investigated.

[0064] Combining the results of the visualization experiment, CFD was used to capture the details of the internal flow field distribution, pressure field distribution, temperature field distribution and vapor-liquid interface interaction in the water seal process. The evolution law of the vapor-liquid interface in the water seal process was revealed from the microscopic level. The dependency relationship between different flow patterns and water seal process parameters was constructed, and the synergistic effect mechanism of driving force and flow resistance on the water seal evolution process was revealed, thus providing theoretical guidance for the establishment of a quantitative judgment model for the water seal transition boundary.

[0065] The study focuses on revealing the intrinsic relationship between different flow patterns and the water seal transition boundary, understanding the laws governing the changes in water seal transition boundary conditions, identifying the key dimensionless parameters affecting the water seal transition boundary conditions in this multiphase flow system, and constructing a high-precision water seal prediction model.

[0066] Example 1

[0067] This embodiment provides a research system for the evolution of water seal in an advanced pressurized water reactor U-section. First, a closed-loop piping system simulating a reactor is constructed. Second, an artificial break is introduced into the system to trigger two-phase flow of vapor and liquid and the water seal phenomenon. Finally, intuitive physical images and parameter data are obtained through monitoring methods, thereby enabling the study of the water seal evolution mechanism.

[0068] like Figure 1 As shown, the research system described in this embodiment mainly consists of the following three parts:

[0069] The main coolant simulation circuit includes a pressure vessel simulation 1, an evaporator simulation 6, and a main pump simulation 4 connected in sequence; wherein, the pressure vessel simulation 1 and the evaporator simulation 6 are connected by a heat pipe section 7, the evaporator simulation 6 and the main pump simulation 4 are connected by a U-shaped transition section 5, and the main pump simulation 4 and the pressure vessel simulation 1 are connected by a cold pipe section 3.

[0070] Pressure vessel simulator 1 simulates the functions of the reactor core and pressure vessel. Evaporator simulator 6 simulates the functions of the steam generator. Main pump simulator 4 simulates the functions of the reactor coolant pump.

[0071] The components are connected sequentially via pipes, forming a closed loop: Hot pipe section 7 connects pressure vessel simulator 1 and evaporator simulator 6, simulating the path of high-temperature coolant outflow. U-shaped transition section 5 connects evaporator simulator 6 and main pump simulator 4; its special "U" shape causes liquid to accumulate and form a water seal. Cold pipe section 3 connects main pump simulator 4 and pressure vessel simulator 1, simulating the path of cooled fluid returning to the reactor core.

[0072] A rupture simulation component, installed on the main coolant simulation loop, is used to simulate a loss-of-coolant accident. A loss-of-coolant accident refers to an accident state in which a reactor coolant system pipeline ruptures, leading to coolant loss. By simulating fluid leakage caused by a pipeline rupture, the pressure in the main loop decreases, creating a vapor phase space, thereby creating the thermal-hydraulic boundary conditions required to form a water seal.

[0073] A visual measurement and acquisition system, located in the U-shaped transition section 5, is used to acquire the fluid flow pattern and thermal-hydraulic parameters (such as pressure, temperature, and flow rate) during the water seal evolution process. The fluid flow pattern refers to the distribution structure of the vapor-liquid two-phase fluid within the pipe (such as laminar flow, plug flow, and annular flow). This system allows for direct observation and recording of the dynamic changes in the fluid throughout the entire process of water seal formation, maintenance, and removal.

[0074] Example 2

[0075] This embodiment provides a detailed description of the various components mentioned in Embodiment 1.

[0076] To precisely control the accident process, the breach simulation component includes:

[0077] The rupture simulation pipeline 2 has one end connected to the cold pipe section 3 of the main coolant simulation circuit, and the other end connected to the discharge space.

[0078] A rupture opening device is installed on the rupture simulation pipeline 2 to control the opening of the rupture water loss accident simulation; and to control the start time of the rupture water loss simulation, so as to realize the instantaneous switching from normal operation to accident operation.

[0079] A rupture size adjustment component is installed on the rupture simulation pipeline 2 to adjust the flow area of ​​the rupture simulation pipeline 2 to simulate ruptures of different sizes; the flow area of ​​the pipeline can be changed to simulate rupture accidents with different equivalent diameters.

[0080] To comprehensively capture the fluid behavior within the U-shaped transition section 5, the visualization measurement and acquisition system includes:

[0081] The resistivity tomography sensor 10 (ERT) is arranged on the pipeline of the U-shaped transition section 5 to acquire the vapor-liquid two-phase distribution data in the cross-section of the pipeline; by utilizing the difference in conductivity between the vapor and liquid phases, the phase distribution data in the cross-section of the pipeline is reconstructed, thereby quantitatively acquiring microscopic parameters such as the vapor content of the cross-section.

[0082] A high-speed camera 9 is arranged outside the U-shaped transition section 5 to capture dynamic images of fluid flow; reflecting the topology and evolution of the flow pattern (such as the conversion from stratified flow to slug flow).

[0083] The data acquisition and processing unit 11 is connected to the resistivity tomography sensor 10 and the high-speed camera 9, respectively, and is used to synchronously acquire and process the distributed data and dynamic images.

[0084] To establish a mechanical equilibrium model for the evolution of the water seal, this embodiment sets up multiple sets of liquid level measuring devices 8 in the key vertical pipe sections of the system, including:

[0085] The descending and ascending sections of the pressure vessel simulator 1 are used to measure the water level in the descending section and the water level in the ascending section of the pressure vessel.

[0086] The rising section and the falling section of the evaporator simulator 6 are used to measure the water level in the rising section and the water level in the falling section of the evaporator simulator 6.

[0087] The descending and ascending sides of the U-shaped transition section 5 are used to measure the water level of the descending section and the water level of the ascending section of the water seal.

[0088] To simulate a real reactor driving mechanism, the pressure vessel simulator 1 contains a core simulator, which includes an electric heating component for heating the fluid in the main coolant simulation loop to generate steam that drives natural circulation.

[0089] Example 3

[0090] This embodiment provides a research method for the evolution of water seals in advanced pressurized water reactor U-sections based on the system described in Embodiment 1 or Embodiment 2, such as... Figure 2 As shown, the specific steps include:

[0091] Establish initial operating conditions: Heat and pressurize the fluid in the main coolant simulation loop to reach the preset saturation state (meaning that the liquid and steam are in dynamic equilibrium), and control the water level in the pressure vessel simulation body to be lower than the centerline height of the heat pipe section to ensure that the steam can enter the heat pipe section and flow to the steam generator as soon as possible.

[0092] Simulated accident process: Activate the rupture simulation component to simulate a coolant loss accident, causing the main coolant simulation loop to enter the natural circulation and water seal formation stage; as the coolant is lost, the pressure in the main loop drops, the fluid begins to boil and generates a large amount of steam. During this process, condensate or carried water will accumulate in the U-shaped transition section, gradually forming a "water seal" that blocks the steam flow.

[0093] Multidimensional data acquisition: Real-time images of the gas-liquid two-phase fluid flow pattern within the U-shaped transition section are acquired using a visual measurement and acquisition system, and real-time water level data of each key section in the main coolant simulation loop are simultaneously acquired using a liquid level measuring device; real-time gas-liquid two-phase fluid flow pattern within the U-shaped transition section is acquired using a visual measurement and acquisition system (such as a high-speed camera and ERT); real-time water level data of each key section in the loop (pressure vessel, evaporator, U-tube, etc.) is simultaneously recorded using a liquid level measuring device.

[0094] Construct an evolution model: Based on the real-time water level data, establish the dynamic equilibrium relationship of the main coolant simulation loop, and calculate the total driving force and total resistance of the water seal fluid flow; the total driving force is the force that pushes the fluid to overcome the water seal (usually originating from the liquid level difference and density difference between the core side and the evaporator side); the total resistance is the force that hinders the fluid flow (mainly originating from the gravity of the liquid column accumulated in the U-shaped tube section and frictional resistance).

[0095] Determine the transition boundary: By comparing the magnitude of the total driving force and the total flow resistance, the water seal state is determined, and the transition boundary conditions for water seal removal are determined based on the determination result.

[0096] When the total resistance is greater than the total driving force, the water seal is determined to be maintained (system blockage). When the total driving force is greater than the total resistance, the water seal is determined to be cleared (circulation recovery). The moment when the total driving force exceeds the total resistance (critical point) is captured, and the thermal parameters of the system at this time (such as pressure, flow rate, etc.) are recorded, which constitute the transition boundary conditions for water seal clearing.

[0097] The specific implementation details and algorithm logic are as follows:

[0098] The dynamic equilibrium relationship of the main coolant simulation loop is as follows: ,in: This refers to the water level in the lower section of the pressure vessel. This refers to the water level in the rising section of the pressure vessel. The water level in the descending section of the evaporator simulator; This refers to the water level in the lowering section of the water seal. The water level in the rising section of the evaporator simulator; This refers to the water level in the rising section of the water seal.

[0099] The total driving force for fluid flow in the U-shaped transition section is denoted as ; the resultant force represents the force that overcomes the loop resistance and attempts to clear the water seal.

[0100] represents the total resistance to fluid flow in the U-shaped transition section. represents the force resisting the water seal and hindering the natural circulation from returning to normal.

[0101] By using the collected real-time water level data, the values ​​of the total driving force and total resistance are continuously calculated to obtain the rules for determining the water seal status:

[0102] Real-time monitoring of the numerical changes in the total driving force and the total resistance;

[0103] When the total resistance is greater than the total driving force, it is determined that the main coolant simulation circuit is in a state of natural circulation interruption, and the water seal is maintained; the static pressure generated by the liquid column accumulated in the rising section of the U-shaped tube is too large, and the driving pressure difference in the circuit is insufficient to push it open, the water seal structure exists stably, and the steam cannot be effectively discharged.

[0104] When the total driving force exceeds the total resistance, the water seal is determined to be cleared, and the main coolant simulation loop resumes natural circulation; the accumulated driving pressure difference in the loop has exceeded the static pressure limit of the liquid column. At this point, the water seal is determined to be cleared, and the accumulated fluid is flushed out of the U-shaped pipe section.

[0105] The critical moment when the total driving force changes from less than to greater than the total resistance is determined as the moment when the water seal is cleared.

[0106] In addition, the determined water seal clearance transition boundary conditions include at least the following parameters: U-shaped transition section inlet steam flow rate and main coolant simulation loop system pressure.

[0107] Example 4

[0108] This embodiment is an extension of Embodiment 3.

[0109] To investigate the impact of different boundary conditions on water seal behavior, the method further includes a multi-condition flow pattern identification step:

[0110] By adjusting the rupture size adjustment component, changing the heating power of the electric heating component, and adjusting the installation height of the U-shaped transition section, multiple sets of water seal visualization tests were conducted under different rupture sizes, different steam flow rates, and different U-shaped pipe section heights.

[0111] Under the above-mentioned multiple working conditions, based on the images acquired by the visualization measurement and acquisition system, the water seal flow patterns during the entire test cycle are identified, and the water seal flow patterns are classified and organized to determine the flow pattern conversion conditions between different flow patterns.

[0112] This step also introduces digital methods, and the method further includes numerical simulation extension steps:

[0113] A CFD model (a virtual model that is geometrically consistent with the physical system) is constructed, and the effectiveness of the CFD model is verified using the real-time water level data and the transformation boundary conditions. If the simulation results match the experimental results, the CFD model is proven to be effective.

[0114] We used the validated CFD model to conduct water seal removal simulations with a wide parameter range to obtain microscopic parameters of the water seal removal process that cannot be directly measured under experimental conditions.

[0115] Furthermore, the method also includes model correction and prediction steps:

[0116] Based on experimental and simulation data, a dimensionless flow ratio-visualized flow pattern map was established.

[0117] By using graphs to correct the dynamic equilibrium relationship, a predictive model for quantitatively predicting the water seal transition boundary is constructed.

[0118] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0119] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0120] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above invention, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A research system for the evolution of water seals in an advanced pressurized water reactor U-shaped tube section, characterized in that, include: The main coolant simulation circuit includes a pressure vessel simulation body (1), an evaporator simulation body (6), and a main pump simulation body (4) connected in sequence; wherein the pressure vessel simulation body (1) and the evaporator simulation body (6) are connected by a heat pipe section (7), the evaporator simulation body (6) and the main pump simulation body (4) are connected by a U-shaped transition section (5), and the main pump simulation body (4) and the pressure vessel simulation body (1) are connected by a cold pipe section (3); A break simulation component is installed on the main coolant simulation circuit to simulate a water loss accident. A visual measurement and acquisition system is set in the U-shaped transition section (5) to acquire the fluid flow pattern and thermal-hydraulic parameters during the water seal evolution process.

2. The research system for the evolution of water seals in the U-shaped tube section of an advanced pressurized water reactor according to claim 1, characterized in that, The breach simulation component includes: The rupture simulation pipeline (2) has one end connected to the cold pipe section (3) of the main coolant simulation circuit, and the other end connected to the discharge space; A rupture opening device is installed on the rupture simulation pipeline (2) and is used to control the opening of the rupture water loss accident simulation. A rupture size adjustment component is provided on the rupture simulation pipeline (2) to adjust the flow area of ​​the rupture simulation pipeline (2) to simulate ruptures of different sizes.

3. The research system for the evolution of water seals in the U-shaped tube section of an advanced pressurized water reactor according to claim 1, characterized in that, The visualization measurement and acquisition system includes: A resistive tomography sensor (10) is arranged on the pipeline of the U-shaped transition section (5) to acquire gas-liquid two-phase distribution data in the cross-section of the pipeline; A high-speed camera (9) is arranged outside the U-shaped transition section (5) to capture dynamic images of fluid flow; The data acquisition and processing unit (11) is connected to the resistivity tomography sensor (10) and the high-speed camera (9) respectively, and is used to synchronously acquire and process the distributed data and dynamic images.

4. The research system for the evolution of water seals in advanced pressurized water reactor U-sections according to claim 1, characterized in that, It also includes multiple sets of liquid level measuring devices (8), which are respectively set in: The descending and ascending sections of the pressure vessel simulator (1) are used to measure the water level in the descending section and the water level in the ascending section of the pressure vessel. The rising section and the falling section of the evaporator simulator (6) are used to measure the water level of the rising section and the water level of the falling section of the evaporator simulator (6); The descending and ascending sides of the U-shaped transition section (5) are used to measure the water level of the descending section and the water level of the ascending section of the water seal.

5. The research system for the evolution of water seals in the U-shaped tube section of an advanced pressurized water reactor according to claim 1, characterized in that, The pressure vessel simulator (1) contains a core simulator, which includes an electric heating component for heating the fluid in the main coolant simulation loop to generate steam that drives natural circulation.

6. A research method for the evolution of water seals in U-shaped sections of advanced pressurized water reactors, characterized in that, Based on the research system as described in any one of claims 1 to 5, the research method includes the following steps: Establish initial operating conditions: Heat and pressurize the fluid in the main coolant simulation loop to reach the preset saturation state, and control the water level in the pressure vessel simulation body to be lower than the centerline height of the heat pipe section; Simulated accident process: Activate the breach simulation component to simulate a coolant loss accident, causing the main coolant simulation circuit to enter the natural circulation and water seal formation stage; Multidimensional data acquisition: Real-time images of the gas-liquid two-phase fluid flow pattern in the U-shaped transition section are obtained using a visualization measurement and acquisition system, and real-time water level data of each key section in the main coolant simulation loop are collected simultaneously using a liquid level measurement device. Construct an evolution model: Based on the real-time water level data, establish the dynamic equilibrium relationship of the main coolant simulation loop, and calculate the total driving force and total resistance of the water seal fluid flow; Determine the transition boundary: By comparing the magnitude of the total driving force and the total flow resistance, the water seal state is determined, and the transition boundary conditions for water seal removal are determined based on the determination result.

7. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 6, characterized in that, The dynamic equilibrium relationship of the main coolant simulation loop is as follows: ,in: This refers to the water level in the lower section of the pressure vessel. This refers to the water level in the rising section of the pressure vessel. The water level in the descending section of the evaporator simulator; This refers to the water level in the lowering section of the water seal. The water level in the rising section of the evaporator simulator; This refers to the water level in the rising section of the water seal. The total driving force for fluid flow in the U-shaped transition section; This represents the total resistance to fluid flow in the U-shaped transition section.

8. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 6, characterized in that, The rules for determining the water seal status are as follows: Real-time monitoring of the numerical changes in the total driving force and the total resistance; When the total resistance is greater than the total driving force, it is determined that the main coolant simulation circuit is in a state of natural circulation interruption, and the water seal is maintained; When the total driving force is greater than the total resistance, it is determined that the water seal is cleared and the main coolant simulation circuit resumes natural circulation. The critical moment when the total driving force changes from less than to greater than the total resistance is determined as the moment when the water seal is cleared.

9. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 6, characterized in that, The determined water seal clearance transition boundary conditions include at least the following parameters: U-shaped transition section inlet steam flow rate and main coolant simulation loop system pressure.

10. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 6, characterized in that, The method also includes a multi-condition flow pattern identification step: By adjusting the rupture size adjustment component, changing the heating power of the electric heating component, and adjusting the installation height of the U-shaped transition section, multiple sets of water seal visualization tests were conducted under different rupture sizes, different steam flow rates, and different U-shaped pipe section heights. Based on the images acquired by the visualization measurement and acquisition system, the water seal flow patterns during the entire experimental cycle are identified, and the water seal flow patterns are classified and organized to determine the flow pattern conversion conditions between different flow patterns.

11. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 10, characterized in that, The method also includes a numerical simulation extension step: A CFD model is constructed, and the effectiveness of the CFD model is verified using the real-time water level data and the transformation boundary conditions. We used the validated CFD model to conduct water seal removal simulations with a wide parameter range to obtain microscopic parameters of the water seal removal process that cannot be directly measured under experimental conditions.

12. The research method for the evolution of water seal in the U-shaped tube section of an advanced pressurized water reactor according to claim 11, characterized in that, The method also includes model correction and prediction steps: Based on experimental and simulation data, a dimensionless flow ratio-visualized flow pattern map was established. By using graphs to correct the dynamic equilibrium relationship, a predictive model for quantitatively predicting the water seal transition boundary is constructed.

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