Multi-scale coupling analysis method for interaction system of high-temperature liquid metal and jet water

Abstract

A multi-scale coupling analysis method for a high-temperature liquid metal and jet water interaction system mainly comprises the following steps as shown in an attached drawing: 1, carrying out geometric modeling and grid division on a liquid metal pool type space, jet water and other pipeline systems, and setting a valve action sequence; 2, setting a coupling boundary, and establishing an IPC communication pipeline; 3, performing steady-state calculation, and mutually providing initial boundaries for overall initialization; 4, a system program is imported into the boundary of the two-dimensional fluid domain, the fluid state in the pipeline under the decompression heating condition is calculated, and boundary information in a result is written into the IPC pipeline; 5, the two-dimensional fluid program reads source items from the system program, thermodynamic parameter distribution of the molten pool is calculated, and boundary information is provided; and 6, judging the action condition of the component at the current moment and repeating the step 4 and the step 5 until the calculation time reaches the end moment. The method provided by the invention can simulate the whole interaction process of liquid metal and jet water and embody the influence of flash evaporation in a critical flow jet boundary and an injection pipeline on jet.

Description

Technical Field

[0001] The present invention relates to the technical field of safety analysis of liquid metal fast reactors, and particularly to a multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water. Background Art

[0002] In some designs of fourth-generation reactors, liquid metal is used as the primary coolant, and water is used as the working medium in the secondary circuit. The two working media exchange heat through the tube wall of the steam generator. Since the tube wall is thin and the pressure difference on both sides is huge, it bears a certain amount of thermal stress and large mechanical loads. Therefore, the heat transfer tube wall is a relatively weak part of the reactor core, and the probability of a rupture accident should be considered. During the process of a heat transfer tube rupture accident, due to the pressure difference, the water on the secondary side will enter the molten metal pool in the form of a jet, generating intense thermodynamic reactions, including pressure wave transmission, bubble migration and entrainment, steam explosion and other phenomena, which may threaten the integrity of the heat transfer tube and in-core equipment. Therefore, the research on this problem is of great value.

[0003] At present, domestic and foreign researchers have conducted extensive research on the coolant-coolant interaction (CCI) phenomenon in this accident, and carried out experiments on high-pressure water jets into the molten metal pool to explore its overall effect. However, the theories proposed are often focused on the phenomena in the liquid metal pool, and there is a lack of measurement results and quantitative analysis on the relevant properties of the injection pipeline. Some numerical simulations ignore the modeling of the injection pipeline and greatly simplify the inlet boundary, unable to accurately reflect the influence of the rapid pressure relief of the injection pipeline and the high-temperature area at the outlet on the jet boundary state, thus reducing the reliability of comparison and verification with the overall experimental results. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the object of the present invention is to propose a multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water. This method analyzes the molten metal pool, injection pipeline and pressure relief pipeline through the bidirectional coupling of a special program and a system program. This method can simulate the fluid state of the pressure relief pipeline, continuously provide relatively accurate inlet boundary conditions for the special program, broaden the simulation range of the experiment, and improve the credibility of the verification of the mechanism model of the special program.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] Step 1: Geometric modeling and mesh generation are performed on the liquid metal pool - type space and the jet water pipeline system. The dedicated program calculation domain where the liquid metal pool is located is a two - dimensional space, and the system program calculation domain where the jet water pipeline is located is a one - dimensional space. For the liquid metal pool area, a geometric model that precisely matches the target problem is established according to the constitutive model, and appropriate two - dimensional meshes are generated. For the jet water pipeline system, in addition to geometric conditions, factors such as gravity pressure drop, flow pressure drop, form resistance pressure drop, and the influence of valves in the system on flow need to be considered. The one - dimensional control volume nodes of the system are divided, and then the time series of valve triggering during transient calculations are set according to the triggering conditions of components in actual experiments or designs. In addition, in some experiments of the interaction between liquid metal and jet water, in addition to the water injection system and the liquid metal pool, there may also be a pressure - relief pipeline located at the top of the liquid metal pool, and the pressure - relief pipeline can be established in the same system program model as the jet water pipeline.

[0007] Step 2: Set the coupling boundaries according to the calculation problem and establish an inter - process communication (IPC) pipeline. In this calculation problem, the liquid metal pool has a two - way coupling relationship with the water injection pipeline and the pressure - relief pipeline respectively. That is, the liquid metal pool calculation program provides the boundary for the system program, and at the same time, the calculation results of the system program also provide the source terms for the liquid metal pool calculation program. In this calculation problem, the pressure of the liquid metal pool is lower than that of the water injection pipeline and higher than that of the pressure - relief pipeline. The steam - water mixture is injected into the liquid metal pool unidirectionally. Due to gravity, the inlet of the pressure - relief pipeline is gas, so the liquid metal phase only exists in the two - dimensional calculation domain of its dedicated program, and the system program only calculates the vapor - liquid two - phase flow mainly composed of water - working medium. According to this characteristic, two - way coupling boundaries can be set for the liquid metal pool, the water injection pipeline, and the pressure - relief pipeline respectively. The specific methods are as follows:

[0008] 1) For the water injection pipeline on the system program side, take the bottom pressure of the dedicated program liquid metal pool as its outlet boundary pressure P P,B , set the boundary control volume composition as single - component saturated steam, and take the liquid metal temperature T P,B at the bottom of the pool as the right - hand boundary temperature of the heat component of the water injection pipeline outlet wall.

[0009] 2) For the pressure - relief pipeline, take the top pressure of the liquid metal pool as its inlet boundary pressure P P,T , take the temperature of the gas space at the top of the pool as its inlet boundary temperature T P,T , and take the non - condensable gas fraction at the top of the pool as the non - condensable gas mass fraction x P,nc,T of its inlet boundary, and set the boundary control volume composition as a two - component gas boundary for calculating the transport of non - condensable gas in it.

[0010] 3) For the liquid metal pool, the bottom jet inlet boundary is a flow boundary, including the pressure P in from the part of the water injection pipeline on the system program side close to the outlet, the void fraction αin , mass flow rate of liquid water w f,in , the mass flow rate of steam flowing into g,in , liquid water specific enthalpy H f,in , steam specific enthalpy H g,in The boundary of the pressure relief pipeline outlet is also the flow boundary. The boundary parameters include the pressure P at the entrance of the system program pressure relief pipeline. out , vacuolar fraction α out , mass flow rate of liquid water outflow w f,out , the mass flow rate of outflowing steam w g,out , liquid water specific enthalpy H f,out , steam specific enthalpy H g,out and the mass fraction of non-condensable gas x nc,out and other parameters;

[0011] After determining the boundary variables, two IPC communication channels are established, specifying the read and write order of each data, and used to send boundary information to another program. This method ensures the complete transmission of the array while having a faster speed, reducing the time taken for data transmission and increasing the frequency of interaction.

[0012] Step 3: The dedicated program and the system program calculation domain perform steady-state calculations separately, and use the calculation result values of the adjacent boundary positions to provide each other with the initial coupling boundary to complete the overall initialization. The initialization of the coupling calculation requires high coordination of the coupling boundary parameters. If the boundary is initially set to an unreasonable value, it is easy to cause abnormal output results in the adjacent boundary area, which in turn causes abnormal boundary values transmitted to the other program, causing the calculation to diverge and unable to obtain the steady-state conditions that meet the calculation premise. Therefore, it is necessary to first perform steady-state calculations of each program without coupling, and record the coupling boundary parameter values provided by each program to the other as the initial boundary value of the coupling calculation. This step can build a stable initial state for the coupling calculation, based on which the subsequent transient analysis can be started;

[0013] Step 4: Import the boundary information from the two-dimensional fluid domain, perform system program calculations, and write the boundary information in the results into the IPC communication pipeline. This step is mainly used to calculate the two-phase critical flow jet after the downstream valve of the high-pressure water injection system is opened, the flash effect caused by rapid pressure relief in the high-pressure water tank and pipeline, and provide more accurate boundary conditions for the jet. In this problem, different critical flow models are used according to the actual phase fraction. For the supercooled fluid, according to the Bernoulli equation, the critical flow velocity is

[0014]

[0015] Where:

[0016] V c—— Critical velocity m·s -1 ;

[0017] V up —— Upstream velocity m·s -1 ;

[0018] P up —— Upstream pressure Pa;

[0019] P t —— Pressure at the injection port Pa;

[0020] ρ f —— Density of water kg·m -3 ;

[0021] For two-phase critical flow, the improved Trapp-Ransom model is adopted,

[0022]

[0023] In the formula:

[0024] a HE —— Homogeneous equilibrium sonic velocity m·s -1 ;

[0025] P s —— Saturation pressure Pa;

[0026] T —— Temperature K;

[0027] v —— Specific volume kg·m -3 ;

[0028] X —— Gas holdup;

[0029] C pg —— Specific heat capacity at constant pressure of gas phase J·kg -1 ·K -1 ; T g —— Temperature of gas phase K;

[0030] v g —— Specific volume of gas phase kg·m -3 ;

[0031] κ g —— Isothermal compressibility of gas phase Pa -1 ;

[0032] β g —— Coefficient of thermal expansion of gas phase K -1 ; C pf —— Specific heat capacity at constant pressure of liquid phase J·kg -1 ·K -1 ; T f —— Temperature of liquid phase K;

[0033] v f —— liquid specific volume kg·m -3 ;

[0034] κ f —— isothermal liquid compressibility Pa -1 ;

[0035] β f —— liquid expansion coefficient K -1 ;

[0036] h g —— gas specific enthalpy J·kg -1 ;

[0037] h f —— liquid specific enthalpy J·kg -1 ;

[0038] T s —— saturation temperature K;

[0039] Combining the two-phase momentum equation, the gas and liquid velocities under critical flow conditions can be obtained. Since a part of the injection pipe wall contacts the liquid metal region, during the jet flow process, in addition to the change in void fraction caused by pressure reduction, wall heat transfer is also an important part. In the high-temperature axial flow region, the critical enthalpy for generating mainstream bubbles is

[0040]

[0041] In the formula:

[0042] h cr —— critical enthalpy J·kg -1 ;

[0043] —— liquid saturation enthalpy J·kg -1 ;

[0044] Nu—— Nusselt number;

[0045] Pe—— Peclet number;

[0046] The wall steam generation rate is

[0047]

[0048] In the formula:

[0049] Γ w —— wall steam generation rate kg·m -2 ·s -1 ;

[0050] q f —— heat flux transferred from the wall to the liquid J·m -2 ·s -1;

[0051] A w —— Heating area m 2 ;

[0052] —— Gas-phase saturation enthalpy J·kg -1 ;

[0053] ρ g —— Gas-phase density kg·m -3 ;

[0054] h fg —— Saturation enthalpy difference between gas phase and liquid phase J·kg -1 ;

[0055] ε—— Vaporization potential coefficient;

[0056] After solving in a time step, the calculated parameter values of [P in , α in , w f,in , w g,in , H f,in , H g,in , P out , α out , w f,out , w g,out , H f,out , H g,out , w nc,out are written into the pipeline and sent to the dedicated program;

[0057] Step 5: Read the boundary conditions from the system program as source terms, perform two-dimensional fluid domain calculations, and provide boundary information. In this step, the dedicated program reads the data parameters in the pipeline and assigns them to the subroutine variables used to calculate the source terms. The source terms include two types, one is the inflow source term and the other is the outflow source term, corresponding to the injection pipeline and the pressure relief pipeline in the system program model respectively. With the boundaries provided by the system program, the dedicated program can obtain a more accurate simulation of the injection and pressure relief states, update the source terms in the mass, momentum, and energy conservation equations, construct the solution matrix, and then solve to calculate a more accurate physical field in the molten pool. After the calculation of the current time step is completed, according to the boundary information provided by the dedicated program in Step 2, the relevant parameters [P P,B , T P,B , P P,T , T P,T , x P,nc,T are written into the pipeline and sent to the system program as the boundary conditions for the next time step of the system program;

[0058] Step 6: Determine the component action conditions according to the current time and repeat Steps 4 and 5 until the calculation time reaches the end time. After the system program and the special program both complete the calculation of one time step, it is necessary to determine whether the current time step has reached the preset end time. If the end time is reached, stop the calculation of the entire problem. If the end time is not reached, advance one time step and execute the judgment of all trigger conditions within the new time step to obtain the action conditions of all valves in the coupled system at the new moment, and return to Step 3 for a new round of coupled calculation; through the above steps, the flow state in the jet pipeline can be simulated and calculated in the problem of the interaction between liquid metal and jet water, thereby improving the calculation accuracy of the overall problem, facilitating the subsequent verification of the relevant models in the two-dimensional calculation domain, and playing a role in the safety analysis of the reactor.

[0059] Preferably, the special program uses the SEINA program, which has a constitutive model for heat and mass transfer of molten metal, liquid water, steam and non-condensable gas under different flow patterns and can be used for the calculation of two-dimensional multiphase flow severe thermohydraulic phenomena.

[0060] Preferably, the system program uses any one of the RELAP5, CATHARE and RETRAN programs. The above system programs have the ability to simulate the heat transfer and heat exchange of steam-water two-phase flow, can well reflect the two-phase flow phenomenon in the pipeline, have a flexible modeling method and high solution efficiency, and can provide a relatively accurate two-phase flow boundary for SEINA.

[0061] The method of the present invention is a multi-scale coupling analysis method for the interaction system of high-temperature liquid metal and jet water, which plays an optimizing role in the overall calculation and verification of the heat transfer tube rupture accident of the liquid metal fast reactor and is of great significance for the safety analysis of the fast reactor.

[0062] Compared with the prior art, the multi-scale coupling analysis method for the interaction system of high-temperature liquid metal and jet water of the present invention has the following advantages:

[0063] 1. Consider the flashing phenomenon caused by pressure relief in the injection pipeline and wall heating, and can provide more refined inlet jet two-phase boundary conditions for the special program;

[0064] 2. Considering the characteristics of coupling boundaries at different positions, an asymmetric coupling parameter combination is adopted to expand the simulation range;

[0065] 3. The coupling boundary data is sent unidirectionally through a two-column communication IPC pipeline, which improves the efficiency of external coupling;

[0066] In summary, this method can analyze the overall phenomenon of the interaction between liquid metal and jet water more comprehensively, effectively and efficiently. Description of the Drawings [[ID=H27]]

[0067] Figure 1 It is a flowchart of a multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water in the present invention.

[0068] Figure 2 It is a schematic diagram of the overall model of a multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water in the present invention.

[0069] Figure 3 Some simulation results of the pool water injection experimental system are shown. Specific embodiments

[0070] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0071] A numerical analysis method for the accident of the rupture of the casing of a core neutron detector in the present invention has a process as Figure 1 shown and the steps are as follows:

[0072] Step 1: Conduct geometric modeling and mesh generation for the liquid metal pool space and the jet water pipeline system. The calculation domain of the special program where the liquid metal pool is located is a two-dimensional space, and the calculation domain of the system program where the jet water pipeline is located is a one-dimensional space. For the liquid metal pool area, accurately establish a geometric model matching its target problem according to the constitutive model and generate appropriate two-dimensional meshes. Generally, the constitutive model of the special program is applicable to the mesoscopic to macroscopic scales, so the mesh size should not be too small, otherwise the calculation accuracy will be reduced. For the jet water pipeline system, in addition to geometric conditions, gravity pressure drop, flow pressure drop, form resistance pressure drop, and the influence of valves in the system on the flow also need to be considered, and the one-dimensional control volume nodes of the system are divided. Then, according to the triggering situation of components in actual experiments or designs, set the time series of valve triggering during transient calculations. In addition, in some experiments of the interaction between liquid metal and jet water, in addition to the water injection system and the liquid metal pool, there may also be a pressure relief pipeline located at the top of the liquid metal pool. The pressure relief pipeline can be established in the same system program model as the jet water pipeline, as Figure 2A typical experimental simulation model is shown, which includes a molten metal pool, a water injection pipeline, and a pressure relief pipeline. The parts with numbers are the system program models, and the two-dimensional grid in the figure is the dedicated program model. The system program models are composed of one-dimensional control volumes connected together. For the water injection pipeline, its pressure water tank is represented by a pipeline component containing 5 axial control volumes. The top of the water tank uses a time-dependent control volume to simulate the pressure maintaining mechanism. The lower part of the water tank is connected to the pipeline, and two valves are arranged on the pipeline. The pipeline above valve 130 is connected to the molten pool area. To simulate the influence of pipe wall heating, a heat component numbered 138 is set to synchronize the wall temperature of the pipeline part in the molten pool. Before the valve is opened, the pipeline part is full of steam. The inlet of the pressure relief pipeline model of the system program is control volume 131, and a trigger valve numbered 136 is arranged in the pipeline to control the opening and closing of the pressure relief pipeline. After the valve is opened, the front and rear areas are connected, and the end is a pressure relief tank, which is simulated by a pipeline component containing 5 axial control volumes. The dedicated program uses a two-dimensional RZ coordinate system grid to simulate the calculation domain of the liquid metal pool.

[0073] Step 2: Set the coupling boundary according to the calculation problem and establish an IPC communication pipeline. In this problem, the liquid metal pool has a two-way coupling relationship with the water injection pipeline and the pressure relief pipeline respectively, that is, the liquid metal pool calculation program provides the boundary for the system program, and at the same time, the calculation results of the system program also provide the source term for the liquid metal pool calculation program. In this problem, the pressure of the liquid metal pool is lower than that of the water injection pipeline and higher than that of the pressure relief pipeline. The steam-water mixture shoots into the liquid metal pool unidirectionally. Also due to the gravity factor, the inlet of the pressure relief pipeline is gas. Therefore, the liquid metal phase only exists in the two-dimensional calculation domain of its dedicated program, and the system program only calculates the vapor-liquid two-phase flow mainly composed of water working medium. According to this characteristic, two-way coupling boundaries can be set for the liquid metal pool, the water injection pipeline, and the pressure relief pipeline respectively. The specific methods are as follows:

[0074] 1) For the water injection pipeline on the system program side, take the bottom pressure of the liquid metal pool in the dedicated program as its outlet boundary pressure P P,B , and set the boundary control volume composition to single-component saturated steam. Take the liquid metal temperature T P,B at the bottom of the pool as the right boundary temperature of the heat component on the outlet wall of the water injection pipeline;

[0075] 2) For the pressure relief pipeline, take the top pressure of the liquid metal pool as its inlet boundary pressure P P,T , the temperature of the gas space at the top of the pool as its inlet boundary temperature T P,T , and the non-condensable gas fraction at the top of the pool as the non-condensable gas mass fraction x P,nc,T of its inlet boundary. Set the boundary control volume composition to a two-component gas boundary for calculating the transport of non-condensable gas in it;

[0076] 3) For the liquid metal pool, the bottom jet inlet boundary is a flow boundary, including the pressure P from the part near the outlet of the system program water injection pipeline in , void fraction α in , mass flow rate w of the inflowing liquid water f,in , mass flow rate w of the inflowing steam g,in , specific enthalpy H of the liquid water f,in , specific enthalpy H of the vapor g,in and other parameters. The outlet boundary of its pressure relief pipeline is also a flow boundary, and the boundary parameters include the pressure P near the inlet of the system program pressure relief pipeline out , void fraction α out , mass flow rate w of the outflowing liquid water f,out , mass flow rate w of the outflowing steam g,out , specific enthalpy H of the liquid water f,out , specific enthalpy H of the vapor g,out and non-condensable gas mass fraction x nc,out and other parameters;

[0077] The corresponding situation of the coupling boundary is as Figure 2 shown. For the dedicated program, set the first grid in the lower left corner of the figure as the inflow boundary calculation area, and set the first grid in the upper left corner as the pressure relief boundary calculation area. The boundary calculation area will receive boundary data from other programs in subsequent steps. For the system program, the time-related control volumes 129, 131 and the thermal component 138 are the coupling boundary regions. After determining the boundary variables, establish two IPC communication pipelines, specify the read and write order of their respective data, and use them to send boundary information to another program. This method has a fast speed while ensuring the complete transfer of the array, reduces the time occupied by data transfer, and improves the interaction frequency;

[0078] Step 3: The dedicated program and the system program calculation domains perform steady-state calculations respectively, and use the calculation result values at the adjacent positions of the boundary to provide the initial coupling boundary for each other to complete the overall initialization. The initialization of the coupling calculation has high requirements for the coordination of the coupling boundary parameters. If unreasonable values are set for the boundary initially, it is easy to cause abnormal output results in the adjacent areas of the boundary, and then cause abnormal boundary values passed to another program, resulting in calculation divergence and inability to obtain the steady-state conditions that meet the calculation prerequisites. Therefore, it is necessary to first perform the steady-state calculations of the two programs separately without coupling, and record the coupling boundary parameter values provided by each program to the other as the initial boundary values for the coupling calculation. This step can build a stable initial state for the coupling calculation, and based on this initial state, subsequent transient analysis can be started;

[0079] Step 4: Import the boundary information from the two-dimensional fluid domain, perform system program calculations, and write the boundary information in the results to the IPC communication pipeline. This step is mainly used to calculate the two-phase critical flow jet after the downstream valve of the high-pressure water injection system is opened, and the flashing effect caused by rapid pressure relief in the high-pressure water tank and pipeline, and to provide relatively accurate boundary conditions for the jet. In this problem, different critical flow models are adopted according to the actual phase fraction. For subcooled fluids, according to Bernoulli's equation, the critical flow velocity is

[0080]

[0081] In the formula:

[0082] V c —— Critical velocity m·s -1 ;

[0083] V up —— Upstream velocity m·s -1 ;

[0084] P up —— Upstream pressure Pa;

[0085] P t —— Pressure at the injection port Pa;

[0086] ρ f —— Density of water kg·m -3 ;

[0087] For two-phase critical flow, the improved Trapp-Ransom model is adopted,

[0088]

[0089]

[0090] In the formula:

[0091] a HE —— Homogeneous equilibrium sound velocity m·s -1 ;

[0092] P s —— Saturation pressure Pa;

[0093] T—— Temperature K;

[0094] v—— Specific volume kg·m -3 ;

[0095] X—— Gas content rate;

[0096] C pg —— Specific heat capacity at constant pressure of gas phase J·kg -1 ·K -1 ;

[0097] T g —— Gas phase temperature K;

[0098] v g —— Gas phase specific volume kg·m -3 ;

[0099] κ g —— Isothermal gas phase compressibility Pa -1 ;

[0100] β g —— Gas phase expansion coefficient K -1 ;

[0101] C pf —— Liquid phase specific heat capacity at constant pressure J·kg -1 ·K -1 ;

[0102] T f —— Liquid phase temperature K;

[0103] v f —— Liquid phase specific volume kg·m -3 ;

[0104] κ f —— Isothermal liquid phase compressibility Pa -1 ;

[0105] β f —— Liquid phase expansion coefficient K -1 ;

[0106] h g —— Gas phase specific enthalpy J·kg -1 ;

[0107] h f —— Liquid phase specific enthalpy J·kg -1 ;

[0108] T s —— Saturation temperature K;

[0109] Combining the two-phase momentum equation, the gas phase and liquid phase velocities in the critical flow state can be obtained. Since a part of the injection pipe wall contacts the liquid metal region, during the jet flow process, in addition to the change in void fraction caused by pressure reduction, wall heat transfer is also an important part. In the high-temperature axial flow region, the critical enthalpy for generating the main stream bubbles is

[0110]

[0111] In the formula:

[0112] h cr —— Critical enthalpy J·kg -1 ;

[0113] —— Liquid-phase saturated enthalpy J·kg -1 ;

[0114] Nu—— Nusselt number;

[0115] Pe—— Peclet number;

[0116] The wall steam generation rate is

[0117]

[0118] In the formula:

[0119] Γ w —— Wall steam generation rate kg·m -2 ·s -1 ;

[0120] q f —— Heat flux transferred from the wall to the liquid phase J·m -2 ·s -1 ;

[0121] A w —— Heating area m 2 ;

[0122] —— Gas-phase saturated enthalpy J·kg -1 ;

[0123] ρ g —— Gas-phase density kg·m -3 ;

[0124] h fg —— Saturation enthalpy difference between the gas phase and the liquid phase J·kg -1 ;

[0125] ε—— Vaporization potential coefficient;

[0126] The calculated parameter values of [P in , α in , w f,in , w g,in , H f,in , H g,in , P out , α out , w f,out , w g,out , H f,out , H g,out , w nc,out will be written into the pipeline and sent to a dedicated program;

[0127] Step 5: Read in the boundary conditions from the system program as source terms, perform two-dimensional fluid domain calculations, and provide boundary information. In this step, the dedicated program reads the data parameters in the pipeline and assigns them to the subroutine variables for calculating the source terms. The source terms include two types, one is the inflow source term and the other is the outflow source term, which correspond to the water injection pipeline and the pressure relief pipeline in the system program model respectively. With the boundaries provided by the system program, the dedicated program can obtain a more accurate simulation of the water injection and pressure relief states, update the source terms in the mass, momentum, and energy conservation equations, construct the solution matrix, and then solve to calculate a more accurate physical field in the molten pool. After the calculation of the current time step is completed, according to the boundary information provided by the dedicated program in Step 2, the relevant parameters P,B , T P,B , P P,T , T P,T , x P,nc,T are written into the pipeline and sent to the system program as the boundary conditions for the system program in the next time step. Since there is no non-condensable gas on the inlet side, this boundary is not completely balanced. This setting method is more flexible, and different combinations of boundary parameters can be set according to different situations;

[0128] Step 6: Judge the component action conditions according to the current moment and repeat Steps 4 and 5 until the calculation time reaches the end moment. After the system program and the dedicated program have both completed the calculation of a time step, it is necessary to judge whether the current time step has reached the preset end time. If the end time is reached, the calculation of the entire problem is stopped. If the end time is not reached, advance one time step and execute the judgment of all trigger conditions within the new time step to obtain the action conditions of all valves in the coupled system at the new moment, and then return to Step 3 for a new round of coupled calculations; Through the above steps, the flow state in the jet pipeline can be simulated and calculated in the problem of the interaction between liquid metal and jet water. Figure 3 Some results of the simulation of the molten pool water injection experimental system are shown. At the initial moment of the experiment, the pressure in the pressure water tank is 4 MPa, the pressure in the molten pool is 0.2 MPa, the water temperature is 240 °C, and the initial temperature of the molten pool is 400 °C. The water injection valve opens at 1 s, and the outlet parameters of the water injection pipeline will change dynamically with the change of the molten pool pressure. The results of the 139th pipe are taken to draw a curve graph. It can be seen that within 5 s, the two-phase velocity at the jet boundary shows a trend of increasing first and then decreasing. After the valve opens, the liquid phase fraction jumps to 0.4 instantaneously, and then gradually decreases and finally stabilizes. This method can provide real-time state parameters of the boundary according to the dynamic changes of the temperature and pressure in the molten pool, thereby improving the calculation accuracy of the overall problem and facilitating the subsequent verification of the relevant models in the two-dimensional calculation domain, and playing a role in the safety analysis of the reactor.

[0129] In summary, through Step 1, the discrete computational domain of the overall simulation system is initially established; through Step 2, the interactive channels for the coupling boundary parameters of the model are set; through Step 3, the overall initialization of the coupling system is carried out to ensure that the coupling calculation can continue; next, by repeating Steps 4, 5, and 6, continuously performing system program solutions, dedicated program solutions, and updating their boundaries and component triggering conditions, the flow field state in the system can be simulated, giving full play to the respective roles of the system program and the dedicated program, enabling the corresponding phenomena to be reflected in the simulation. This method can expand the scope of experimental simulation, which is beneficial to verifying relevant mechanism models and providing references for reactor safety research.

Claims

1. A multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water, characterized in that: The steps are as follows: Step 1: Geometric modeling and mesh generation are performed on the liquid metal pool-type space and the jet water pipeline system. The dedicated program calculation domain where the liquid metal pool is located is a two-dimensional space, and the system program calculation domain where the jet water pipeline is located is a one-dimensional space. For the liquid metal pool area, a geometric model matching its target problem is accurately established according to the constitutive model and an adapted two-dimensional mesh is generated. For the jet water pipeline system, in addition to geometric conditions, the influence of gravity pressure drop, flow pressure drop, form resistance pressure drop, and valves in the system on the flow needs to be considered, and one-dimensional control volume nodes of the system are divided. Thereafter, the time series of valve triggering during transient calculations is set according to the triggering conditions of components in actual experiments or designs. In addition, in some experiments on the interaction between liquid metal and jet water, in addition to the water injection system and the liquid metal pool, there may also be a pressure relief pipeline located at the top of the liquid metal pool, and the pressure relief pipeline and the jet water pipeline are established in the same system program model; Step 2: Coupling boundaries are set according to the calculation problem, and an inter-process communication IPC pipeline is established. In this calculation problem, the liquid metal pool has a two-way coupling relationship with the water injection pipeline and the pressure relief pipeline respectively, that is, the liquid metal pool calculation program provides the boundary for the system program, and at the same time, the calculation results of the system program also provide source terms for the liquid metal pool calculation program. In this calculation problem, the pressure of the liquid metal pool is lower than that of the water injection pipeline and higher than that of the pressure relief pipeline. The steam-water mixture is injected into the liquid metal pool unidirectionally. Also due to gravity, the inlet of the pressure relief pipeline is gas, so the liquid metal phase only exists in the two-dimensional calculation domain of its dedicated program, and the system program only calculates the vapor-liquid two-phase flow mainly composed of water working medium. According to this characteristic, two-way coupling boundaries are set for the liquid metal pool, the water injection pipeline, and the pressure relief pipeline respectively. The specific method is as follows: 1) For the water injection pipeline on the system program side, take the bottom pressure of the dedicated program liquid metal pool as its outlet boundary pressure P P,B , set the boundary control volume composition to single-component saturated steam, and take the liquid metal temperature T at the bottom of the pool P,B as the right boundary temperature of the heat component on the outlet wall of the water injection pipeline; 2) For the pressure relief pipeline, take the pressure at the top of the liquid metal pool as its inlet boundary pressure P P,T , the temperature of the gas space at the top of the pool as its inlet boundary temperature T P,T , and the non-condensable gas fraction at the top of the pool as the non-condensable gas mass fraction x at its inlet boundary P,nc,T , and set the boundary control volume composition as a two-component gas boundary for calculating the transport of non-condensable gas therein; 3) For the liquid metal pool, the bottom jet inlet boundary is a flow boundary, including the pressure P from the pressure of the system program water injection pipeline near the outlet part in , void fraction α in , mass flow rate w of the inflowing liquid water f,in , mass flow rate w of the inflowing steam g,in , specific enthalpy H of the liquid water f,in , specific enthalpy H of the vapor g,in parameter. Its relief pipeline outlet boundary is also a flow boundary, and the boundary parameters include the pressure P near the inlet of the system program relief pipeline out , void fraction α out , mass flow rate w of the outflowing liquid water f,out , mass flow rate w of the outflowing steam g,out , specific enthalpy H of the liquid water f,out , specific enthalpy H of the vapor g,out and non-condensable gas mass fraction x nc,out parameter; After determining the boundary variables, two IPC communication pipelines are established, and the read-write order of their respective data is specified to send boundary information to another program. This method ensures the complete transfer of the array while being fast, reduces the time occupied by data transfer, and improves the interaction frequency; Step 3: Steady-state calculations are performed on the dedicated program and the system program calculation domains respectively, and the calculation result values at the adjacent positions of the boundaries are used to provide the initial coupling boundary for each other to complete the overall initialization. The initialization of the coupled calculation has high requirements for the coordination of the coupling boundary parameters. If unreasonable values are set for the boundaries initially, it is easy to cause abnormal output results in the adjacent areas of the boundaries, and then lead to abnormal boundary values passed to another program, resulting in calculation divergence and unable to obtain the steady-state conditions that meet the calculation prerequisites. Therefore, it is necessary to first perform the steady-state calculations of the two programs separately without coupling, and record the coupling boundary parameter values provided by each program to the other as the initial boundary values for the coupled calculation. This step constructs a stable initial state for the coupled calculation, and subsequent transient analysis is started based on this initial state; Step 4: Import the boundary information from the two-dimensional fluid domain, perform system program calculations, and write the boundary information in the results into the IPC communication pipeline. This step is mainly used to calculate the two-phase critical flow jet after the downstream valve of the high-pressure water injection system is opened and the flashing effect caused by rapid pressure relief in the high-pressure water tank and pipeline, and provide accurate boundary conditions for the jet. Different critical flow models are adopted according to the actual phase fraction. For subcooled fluids, according to Bernoulli's equation, the critical flow velocity is where: V c —— Critical speed m·s -1 ; V up —— upstream velocity m·s -1 ; P up —— upstream pressure Pa; P t —— Pressure Pa at the injection port; ρ f —— Density of water, kg·m -3 ; For two-phase critical flow, the improved Trapp-Ransom model is adopted. where: a HE —— Homogeneous equilibrium sound velocity, m·s -1 ; P s —— Saturated pressure, Pa; T——temperature in K; v——specific volume kg·m -3 ; X——gas content rate; C pg —— Specific heat capacity at constant pressure in the gas phase, J·kg -1 ·K -1 ; T g —— Gas phase temperature K; v g —— Specific volume of gas, kg·m -3 ; κ g —— Isothermal gas compressibility, Pa -1 ; β g —— Gas expansion coefficient K -1 ; C pf —— Liquid-phase specific heat capacity at constant pressure, J·kg -1 ·K -1 ; T f —— Liquid phase temperature K; v f —— liquid specific volume kg·m -3 ; κ f —— Isothermal liquid compressibility, Pa -1 ; β f —— Coefficient of liquid-phase expansion K -1 ; h g —— Specific enthalpy of gas phase, J·kg -1 ; h f —— Specific enthalpy of liquid phase J·kg -1 ; T s —— saturation temperature K; Combined with the two-phase momentum equation, the gas-phase and liquid-phase velocities in the critical flow state can be obtained. Since a part of the injection pipe wall contacts the liquid metal area, during the jet process, in addition to the change in void fraction caused by pressure reduction, wall heat transfer is also an important part. In the high-temperature axial flow region, the critical enthalpy for generating mainstream bubbles is where: h cr —— Critical enthalpy J·kg -1 ; —— Liquid-phase saturation enthalpy J·kg -1 ; Nu——Nusselt number; Pe——Peclet number; The wall steam generation rate is where: Γ w —— Wall steam generation rate kg·m -2 ·s -1 ; q f —— Heat flux transferred from the wall to the liquid phase, J·m -2 ·s -1 ; A w —— Heating area m 2 ; —— Gas-phase saturation enthalpy J·kg -1 ; ρ g —— Gas phase density kg·m -3 ; h fg —— Saturated enthalpy difference between gas phase and liquid phase, J·kg -1 ; ε——vaporization potential coefficient; After the solution of one time step, the calculated values of [P in , α in , w f,in , w g,in , H f,in , H g,in , P out , α out , w f,out , w g,out , H f,out , H g,out , w nc,out parameter values are written into the pipeline and sent to a dedicated program; Step 5: Read in the boundary conditions from the system program as source terms, perform two-dimensional fluid domain calculations, and provide boundary information. In this step, the dedicated program reads the data parameters in the pipeline and assigns them to the subroutine variables used to calculate the source terms. The source terms include two types, one is the inflow source term and the other is the outflow source term, corresponding to the injection pipeline and the pressure relief pipeline in the system program model respectively. With the boundaries provided by the system program, the dedicated program can obtain a more accurate simulation of the injection and pressure relief states, update the source terms in the mass, momentum, and energy conservation equations, construct the solution matrix, and then solve to calculate a more accurate physical field in the molten pool. After the calculation of the current time step is completed, according to the boundary information provided by the dedicated program in Step 2, the relevant parameters P,B , T P,B , P P,T , T P,T , x P,nc,T are written into the pipeline and sent to the system program as the boundary conditions for the next time step of the system program; Step 6: Judge the component action situation according to the current moment and repeat Steps 4 and 5 until the calculation time reaches the end moment. After both the system program and the special program complete the calculation of a time step, it is necessary to judge whether the current time step has reached the preset end time. If the end time is reached, stop the entire calculation. If the end time is not reached, advance one time step and execute the judgment of all trigger conditions within the new time step to obtain the action situation of all valves in the coupled system at the new moment, and return to Step 3 for a new round of coupled calculations.

2. The multi-scale coupling analysis method of a high-temperature liquid metal and jet water interaction system according to claim 1, characterized in that: The special program adopts the SEINA program.

3. A multi-scale coupling analysis method for a system of the interaction between high-temperature liquid metal and jet water according to claim 1, characterized in that: The system program adopts any one of the RELAP5, CATHARE, and RETRAN programs.

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