Fluid-Structure Coupling Simulation Method and System for Nonlinear Reactor System under Loss of Coolant Accident

Abstract

The present invention discloses a fluid-solid coupling simulation method and system for a nonlinear reactor system under a loss of coolant accident, and relates to the field of reactor fluid-solid coupling mechanics. The key points of the technical solution are: establishing a finite element model of a solid region and a fluid region according to the structural parameters of the reactor; simulating the contact relationship of nonlinear contact positions in the finite element model; solving the pressure change of the pressure vessel rupture under the loss of coolant accident condition; performing secondary modeling on the fluid region and the solid region in the finite element model; initializing the fluid pressure constant processing on the nonlinear finite element model after the secondary modeling; performing fluid-solid coupling calculation on the nonlinear finite element model after the pressure initialization, and obtaining the dynamic response result of the pressure vessel of the reactor loss of coolant accident. The present invention can effectively simulate the LOCA condition of a pressure vessel system with an initial internal pressure, thereby meeting the requirements for numerical simulation of the dynamic response of the pressure vessel under extreme conditions, and is more suitable for actual engineering use.

Description

Technical Field

[0001] The present invention relates to the field of reactor fluid-solid coupling mechanics, and more specifically, to a fluid-solid coupling simulation method and system for a nonlinear reactor system under a loss of coolant accident. Background Art

[0002] The reactor is the core of the reactor system, and its performance plays a vital role in the safety of the reactor. Loss of Coolant Accident (LOCA) is a kind of pipeline rupture accident. After the loss of coolant accident, the coolant will spray outward or leak out, generating jet thrust and causing pressure changes in the pressure vessel. The pressure relief wave passes through the primary cooling system and propagates to the pressure vessel, causing the reactor coolant system to be subjected to a large external load, resulting in vibration of the internal structure such as the hanging basket, which may cause serious consequences such as pipe throwing and equipment damage. The purpose of LOCA dynamic response analysis is to obtain the hydraulic load of the internal structure during the propagation of the pressure relief wave by studying the possible damage to the reactor cooling system and internal components after the loss of coolant accident, and calculate the dynamic response and dynamic stress of the internal structure, so as to evaluate the structural integrity and safety reliability of the reactor. Engineering design requires a method for high-fidelity numerical simulation of the dynamic response of the reactor under this extreme condition.

[0003] Traditional methods are all based on the analysis of the bar-beam model, which is relatively simple, with the number of units and nodes within 200. In recent years, with the development of computer conditions, fewer literatures have carried out refined modeling. The prior art discloses a fluid-solid coupling simulation method for a pressure vessel containing initial pressure under a loss of coolant accident, which realizes a high-precision simulation of the fluid-solid coupling dynamic response of the reactor under extreme conditions. Its idea mainly includes three stages: first, the Star-CD CFD code and Abaqus / Standard FEM-code are used to model and calculate the HDR v32 test, and then the APROS system code is used to obtain the pressure boundary conditions of the rupture as a two-phase calculation, and finally the third-party MPCCI coupling software is used to process the coupling between the CFD and FEM codes to realize the fluid-solid coupling numerical simulation. In addition, a fluid-solid coupling simulation method for a linear pressure vessel containing initial pressure using ANSYS software is also disclosed, which realizes a high-precision simulation of the fluid-solid coupling dynamic response of the reactor under extreme conditions.

[0004] However, the methods disclosed in the above two documents, whether using MPCCI software or ANSYS software, can realize the fluid-solid dynamic response of the pressure vessel under the loss of coolant accident based on CFD-CSD coupling analysis, but the model considered is only a linear reactor system. Since there are often many nonlinear contact relationships in actual reactor systems and other fluid-solid coupling systems, these methods cannot simulate this situation truly and accurately. There are a large number of nonlinear gaps in the real reactor, which poses a huge challenge to the convergence problem of CFD-CSD fluid-solid coupling calculation. Therefore, how to study and design a fluid-solid coupling simulation method and system for nonlinear reactor systems under loss of coolant accidents that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the purpose of the present invention is to provide a fluid-solid coupling simulation method and system for a nonlinear reactor system under a loss of coolant accident, which establishes a more realistic model of the pressure vessel structure and the fluid region in the reactor, greatly increases the number of grids, and significantly improves the analysis accuracy of large-scale numerical simulation of pressure vessels in engineering practice. It can effectively simulate the LOCA condition of a pressure vessel system containing an initial internal pressure, thereby meeting the requirements for numerical simulation of the dynamic response of pressure vessels under extreme conditions, and is more suitable for actual engineering use.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident is provided, comprising the following steps:

[0008] Establishing geometric models of the solid region and the fluid region according to the structural parameters of the reactor, and meshing the geometric models to obtain finite element models of the solid region and the fluid region;

[0009] Simulate contact relations with at least two nonlinear contact locations in a finite element model;

[0010] Solve the pressure change of the pressure vessel rupture under the condition of loss of coolant accident, and obtain the corresponding hydraulic load information as the pressure boundary condition of fluid-solid coupling simulation;

[0011] Secondary modeling of the fluid boundary conditions and fluid-solid coupling interface in the fluid region and the solid boundary conditions and fluid-solid coupling interface in the solid region in the finite element model;

[0012] The nonlinear finite element model after secondary modeling is initialized with constant fluid pressure, the corresponding part of the solid is pre-deformed, and the result after the initial pressure is applied is saved as the initial condition of the next step of transient fluid-solid coupling;

[0013] Fluid-solid coupling calculation is performed on the nonlinear finite element model after pressure initialization to obtain the dynamic response results of the pressure vessel in the reactor loss of coolant accident.

[0014] Furthermore, the structural parameters include geometric dimensions, material properties, support forms of the pressure vessel, and vibration modes and frequencies of the internal components.

[0015] Furthermore, the coordinate positions of the structural grid corresponding to the solid region and the fluid grid corresponding to the fluid region in the finite element model match each other, and all of them are hexahedral units.

[0016] Furthermore, the geometric model is constructed using the commercial software CATIA, and the finite element model is modeled using the commercial software Hypermesh;

[0017] Among them, the finite element model of the solid area is generated as a .inp file, and the finite element model of the fluid area is generated as a .cas file.

[0018] Furthermore, the contact relationship of the nonlinear contact position is equivalently simulated using multiple COMBIN39 units in ANSYS software.

[0019] Furthermore, the fluid region in the finite element model uses the Fluent module in the ANSYS software as a fluid solver to model the fluid behavior.

[0020] Furthermore, the solid region in the finite element model uses the TransientStructural module in the ANSYS software as a structural solver to model the structural behavior.

[0021] Secondly, a fluid-solid coupling simulation system for nonlinear reactor systems under loss of coolant accidents is provided, including:

[0022] A model building module is used to establish geometric models of the solid region and the fluid region according to the structural parameters of the reactor, and to mesh the geometric models to obtain finite element models of the solid region and the fluid region;

[0023] A contact simulation module is used to simulate the contact relationship of at least two nonlinear contact positions in the finite element model;

[0024] Boundary analysis module, used to solve the pressure change of the pressure vessel rupture under the condition of loss of coolant accident, and obtain the corresponding hydraulic load information as the pressure boundary condition of fluid-solid coupling simulation;

[0025] A secondary modeling module, used for secondary modeling of the fluid boundary conditions and fluid-solid coupling interface of the fluid region and the solid boundary conditions and fluid-solid coupling interface of the solid region in the finite element model;

[0026] The pressure application module is used to initialize the fluid pressure constant processing of the nonlinear finite element model after secondary modeling, pre-deform the corresponding part of the solid, and save the result after the initial pressure application as the initial condition of the next step of transient fluid-solid coupling;

[0027] The coupling analysis module is used to perform fluid-solid coupling calculation on the nonlinear finite element model after pressure initialization to obtain the dynamic response results of the pressure vessel in the reactor loss of coolant accident.

[0028] In a third aspect, a computer terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, a fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident as described in any one of the first aspects is implemented.

[0029] In a fourth aspect, a computer-readable medium is provided, on which a computer program is stored, and the computer program is executed by a processor to implement the fluid-solid coupling simulation method of a nonlinear reactor system under a loss of coolant accident as described in any one of the first aspects.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The fluid-solid coupling simulation method of a nonlinear reactor system under a loss of coolant accident provided by the present invention establishes a more realistic model of the pressure vessel structure and the fluid region in the reactor, greatly increases the number of grids (more than 300,000), and significantly improves the analysis accuracy of large-scale numerical simulation of pressure vessels in actual engineering. It can effectively simulate the LOCA condition of a pressure vessel system with initial internal pressure, thereby meeting the requirements for numerical simulation of the dynamic response of pressure vessels under extreme conditions, and is more suitable for actual engineering use;

[0032] 2. In view of the large number of nonlinear gaps in the real reactor, the present invention adopts COMBIN39 unit to consider the contact relationship of the actual structure, which can better consider nonlinear factors such as geometric nonlinearity and contact, so that the method of the invention has a wider range of applications and better simulates the real situation of complex structural connections; in the case of high-fidelity model consideration, it can better consider nonlinear connection factors, thereby improving the accuracy of the present invention for LOCA simulation;

[0033] 3. The present invention adopts widely used commercial software such as CATIA, Hypermesh, ANSYS, etc., making the inventive method easier to be accepted and promoted by engineering units. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0035] Figure 1 is a flow chart of Embodiment 1 of the present invention;

[0036] Figure 2 is the CAD drawing of the German HDR reactor in Example 1 of the present invention;

[0037] Figure 3 1 is a nonlinear finite element model diagram of the HDR stack in Example 1 of the present invention, (a) is a structural finite element model, (b) is a fluid finite element model, (c) is a nonlinearity of the upper end of the hanging basket, and (d) is a nonlinearity of the lower end of the hanging basket;

[0038] Figure 4 1 is a nonlinear spring displacement-load relationship diagram in Example 1 of the present invention, (a) is the spring at the upper end of the hanging basket, and (b) is the spring at the lower end of the hanging basket;

[0039] Figure 5 is the breach pressure boundary condition caused by LOCA in Example 1 of the present invention;

[0040] Figure 6 This is the System Coupling process in Embodiment 1 of the present invention;

[0041] Figure 7 1 is a fluid pressure distribution cloud map and a structural stress cloud map at different times in Example 1 of the present invention, (a) is a fluid pressure distribution cloud map at different times, (b) is an HDR structural stress cloud map at different times;

[0042] Figure 8 is the relative radial displacement between the hanging basket and the pressure vessel at different positions in Example 1 of the present invention, (a) is Z=2.3m, (b) Z = 8.85m,

[0043] Fig. 9 It is a system block diagram in Example 2 of the present invention. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0045] Example 1: Fluid-Solid Coupling Simulation Method for Nonlinear Reactor System under Loss of Coolant Accident Figure 1 As shown, it is specifically implemented by the following steps.

[0046] Step 1: Establish geometric models of the solid region and the fluid region according to the structural parameters of the reactor, and mesh the geometric models to obtain finite element models of the solid region and the fluid region.

[0047] Specifically, the geometric model is constructed using the commercial software CATIA, and the finite element model is modeled using the commercial software Hypermesh; the finite element model of the solid area is generated as a .inp file, and the finite element model of the fluid area is generated as a .cas file.

[0048] In this embodiment, the structural parameters include but are not limited to the geometric dimensions, material properties, support forms of the pressure vessel, and vibration modes and frequencies of the internal components.

[0049] The coordinate positions of the structural grid corresponding to the solid area and the fluid grid corresponding to the fluid area in the finite element model match each other, and all of them are hexahedral units.

[0050] Step 2: Simulate the contact relationship of at least two nonlinear contact locations in the finite element model.

[0051] In the case of a large mesh size, such as more than 300,000 cells, the nonlinear contact relationship in the model is considered at the same time, and generally more than 2 locations are selected. For locations with nonlinear contact, the COMBIN39 unit in ANSYS software is used to simulate its contact relationship.

[0052] Step 3: Solve the pressure change of the pressure vessel rupture under the loss of coolant accident condition, and obtain the corresponding hydraulic load information as the pressure boundary condition of the fluid-solid coupling simulation.

[0053] Specifically, the commercial software Flowmaster is used to solve the pressure change of the pressure vessel rupture under extreme working conditions (loss of coolant accident), and the corresponding hydraulic load information is obtained as the boundary condition of the fluid-solid coupling simulation.

[0054] Step 4: Perform secondary modeling on the fluid boundary conditions and fluid-solid coupling interface in the fluid region and the solid boundary conditions and fluid-solid coupling interface in the solid region in the finite element model.

[0055] Specifically, the fluid region in the finite element model uses the Fluent module in the ANSYS software as a fluid solver to model the fluid behavior, and the solid region in the finite element model uses the TransientStructural module in the ANSYS software as a structural solver to model the structural behavior.

[0056] Step 5: Initialize the fluid pressure constant processing of the nonlinear finite element model after secondary modeling, pre-deform the corresponding part of the solid, and save the result after the initial pressure is applied as the initial condition of the next step of transient fluid-solid coupling.

[0057] Step 6: Perform fluid-solid coupling calculation on the nonlinear finite element model after pressure initialization to obtain the dynamic response results of the pressure vessel in the reactor loss of coolant accident. After the coupling calculation is completed, enter the fluid and solid solvers to view the results respectively, and post-process the dynamic response results of the pressure vessel to guide the corresponding engineering design.

[0058] It should be noted that when using FLUENT for flow basin calculations, the information transfer between the structure and the flow field requires the system coupling module to be implemented. Therefore, the structure and fluid grids can be drawn as hexahedral grids with no common nodes at the fluid-solid interface, and calculations can also be carried out.

[0059] In addition, since Fluent is used for numerical simulation of the flow field, the breach pressure load of the loss of coolant accident is applied in the form of UDF (user defined function) in the Fluent analysis module. Since the fluid is in the Fluent analysis module, a prestress analysis step is required to calculate the initial pressure state to a steady state. When Fluent is used for fluid area modeling, the fluid can be viscous, swirling, and compressible, and the accuracy of fluid simulation is higher.

[0060] Take the German HDR reactor V34 experiment as an example. The geometric model and size parameters of the HDR experimental reactor pressure vessel (RPV) and core barrel (CB) are as follows: Figure 2 As shown, the complete basket and its upper and lower support structures are replaced by a lower mass ring, which weighs about half of the weight of the entire basket. The blowdown pipe is located at the cylindrical coordinate z = 8850 mm, All the main inlet and outlet nozzles of the pressure vessel are closed except the blowdown nozzle. The annular gap between the basket and the pressure vessel is called the downcomer.

[0061] For the HDR V34 test, the nonlinear position is the contact between the basket flange and the pressure vessel support boss and the collision between the lower part of the basket and the pressure vessel wall. The dynamic response of the nonlinear reactor system model under LOCA load is studied. The specific steps are as follows S10-S70.

[0062] S10: Use commercial software CATIA to build the solid area and fluid area models of the HDR experimental reactor with reference to the CAD drawings of the HDR experiment. Use commercial software Hypermesh to build finite element models of the solid area and fluid area of ​​the HDR experimental reactor respectively. Figure 3 , the structural mesh consists of approximately 60,000 8-node hexahedral elements with a maximum mesh size of 160 mm. The fluid mesh consists of approximately 290,000 hexahedral elements with a maximum mesh size of 150 mm. The coordinate positions of the structural mesh and the fluid mesh match each other to ensure that no errors are introduced when transferring data between the two solvers for fluid-structure interaction simulations.

[0063] After step S10, the method of the embodiment of the present application enters step S20, that is, using ANSYS nonlinear spring unit to simulate the nonlinear position displacement load relationship, using multiple COMBIN39 units to equivalently simulate the nonlinear connection relationship at the upper flange and the lower contact positions of the hanging basket, and defining Figure 4 Displacement-load relationship shown.

[0064] After step S20, the method of the embodiment of the present application enters step S30, namely: using the commercial software Flowmaster to solve the pressure change of the pressure vessel rupture under extreme working conditions (loss of coolant accident), and obtain the corresponding hydraulic load information as the boundary condition of the fluid-solid coupling simulation. Figure 5 The pressure history of the rupture nozzle for up to 10ms is depicted. After 10 milliseconds, the pressure at the rupture position reaches a constant value. Using the simplified pressure condition (red solid line) as the condition of the rupture boundary, the pressure change at the rupture is expressed as:

[0065]

[0066] Among them, P linear is the breach pressure of linear fitting, and t is the LOCA duration.

[0067] After step S30, the method of the embodiment of the present application enters step S401, that is: use ANSYS Fluent (as a fluid solver) to model the fluid behavior, and define the fluid boundary conditions, fluid-solid coupling interface, etc. CFD simulation was performed in ANSYS Fluent, and a double-precision 3D parallel pressure-based solver was selected to perform the computational fluid dynamics part of the HDR reactor LOCA dynamic transient analysis. The turbulence model used is a standard k-ε model with standard wall functions and default model constants, which is suitable for most engineering problems under large Reynolds numbers. Compressible water is selected from the Fluent material database as the fluid medium for the entire calculation domain. Taking into account the deformation of the fluid-solid coupling interface and the internal fluid, the dynamic grid is activated in Fluent, and a dynamic grid area of ​​the "System Coupling" type is allocated to the fluid-solid coupling interface, and a dynamic grid area of ​​the "Deforming" type is allocated to the internal grid of the fluid.

[0068] After step S30, the method of the embodiment of the present application enters step S402, that is: use ANSYS Mechanical (as a structural solver) to model the structural behavior, including the definition of solid boundary conditions, fluid-solid coupling interfaces, etc. Since the load on the structure comes from the fluid force transmitted by CFD, the structural setting items include two parts: defining boundary conditions and analysis settings. All surfaces of the HDR reactor that are in contact with the fluid are defined as "Fluid-Solid Interface", the bottom of the pressure vessel is fixed, and the symmetric surface of the model is defined as a symmetric boundary condition.

[0069] After step S401 and step 402, the method of the embodiment of the present application enters step S50, that is, the application of pre-pressure, using the ANSYS System Coupling module, initializing the fluid pressure to be constant, and pre-deforming the corresponding part of the solid. And save the result as the initial condition of the next step of transient fluid-solid coupling. During the initialization process, the Fluent pressure P is initialized to be constant, and the first transient analysis is performed. Only the force data is transferred from the fluid to the solid, and the displacement data transferred from the solid to the fluid is suppressed. After reaching the equilibrium state, after a sufficient number of iterations, the first transient analysis is terminated. This unidirectional transient analysis can reach an equilibrium state without changing the fluid pressure but with a prestressed structure.

[0070] After step S50, the method of the embodiment of the present application enters step S60, namely: fluid-solid coupling calculation, using the ANSYS System Coupling module to couple the fluid and structure solvers, define the time step of data transmission and solution calculation, and perform coupling calculation. Figure 6, in order to achieve the coupled behavior, the two solvers are connected to each other (as a coupling algorithm) by using the ANSYS SystemCoupling component. The coupling process is divided into 4 parts: CFD solver Fluent (column A), FEA solver ANSYS Mechanical (column B), system coupling System Coupling (column C) and post-processing (column D). The blue line represents the data transfer between the programs.

[0071] After step S60, the method of the embodiment of the present application enters step S70, that is, after the coupling calculation is completed, the fluid and solid solvers are respectively entered to view the results, and the dynamic response results of the pressure vessel, the internal components of the reactor are post-processed for the corresponding engineering structure mechanics design and evaluation. This is achieved by using column D in step 6. Figure 7 The pressure distribution cloud diagrams in the CFD model at different times and the stress distribution cloud diagrams of the internal structure at each time point are obtained by using the method of the present invention. It can be seen that the pressure reduction wave starts from the ruptured nozzle and propagates along the ruptured nozzle and downcomer area, and finally spreads in the entire range of the coolant. Figure 8 The relative radial displacement between the hanging basket and the pressure vessel at different positions simulated by the method of the present invention is consistent with the German HDR experimental situation.

[0072] It can be seen from the numerical simulation results that the dynamic response numerical simulation of the nonlinear V34 experimental loss of coolant accident of the German HDR reactor was carried out by the method of the present invention, and the simulation results that are very close to the experimental data were obtained. Compared with the methods in the literature, the method used in the present invention does not require the use of relatively niche simulation software, reducing the cost of obtaining and mastering unpopular software. By comparing the results with the methods in the literature, it can be seen that the method of the present invention obtains the dynamic response results of the pressure vessel internally very accurately.

[0073] Embodiment 2: A fluid-solid coupling simulation system for a nonlinear reactor system under a loss of coolant accident, the system is used to implement the fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident described in Embodiment 1, such as Fig. 9 As shown, it includes a model building module, a contact simulation module, a boundary analysis module, a secondary modeling module, a pressure application module and a coupling analysis module.

[0074] Among them, the model construction module is used to establish the geometric model of the solid area and the fluid area according to the structural parameters of the reactor, and to mesh the geometric model to obtain the finite element model of the solid area and the fluid area; the contact simulation module is used to simulate the contact relationship of at least two nonlinear contact positions in the finite element model; the boundary analysis module is used to solve the pressure change of the pressure vessel rupture under the loss of coolant accident condition, and obtain the corresponding hydraulic load information as the pressure boundary condition of the fluid-solid coupling simulation; the secondary modeling module is used to perform secondary modeling on the fluid boundary conditions and fluid-solid coupling interface of the fluid area and the solid boundary conditions and fluid-solid coupling interface of the solid area in the finite element model; the pressure application module is used to initialize the fluid pressure constant processing of the nonlinear finite element model after secondary modeling, pre-deform the corresponding part of the solid, and save the result after the initial pressure application as the initial condition of the next step of transient fluid-solid coupling; the coupling analysis module is used to perform fluid-solid coupling calculation on the nonlinear finite element model after pressure initialization to obtain the dynamic response result of the pressure vessel of the reactor loss of coolant accident.

[0075] Working principle: The present invention uses Transient Structural to carry out structural dynamics simulation, Fluent to carry out fluid dynamics simulation, adopts COMBIN39 unit to simulate the contact and collision relationship of the actual structure, and uses SystemCoupling module to simulate the real-time data transmission of solid and fluid areas respectively, ensuring that the numerical simulation of the dynamic response of the pressure vessel in the extreme working conditions (loss of coolant accident) has high accuracy.

[0076] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident, characterized by: The following steps are involved: Establishing geometric models of the solid region and the fluid region according to the structural parameters of the reactor, and meshing the geometric models to obtain finite element models of the solid region and the fluid region; Simulate contact relations with at least two nonlinear contact locations in a finite element model; Solve the pressure change of the pressure vessel rupture under the condition of loss of coolant accident, and obtain the corresponding hydraulic load information as the pressure boundary condition of fluid-solid coupling simulation; Perform secondary modeling on the fluid boundary conditions and fluid-solid coupling interface in the fluid region and the solid boundary conditions and fluid-solid coupling interface in the solid region in the finite element model; The nonlinear finite element model after secondary modeling is initialized with constant fluid pressure, the corresponding part of the solid is pre-deformed, and the result after the initial pressure is applied is saved as the initial condition of the next step of transient fluid-solid coupling; The nonlinear finite element model after pressure initialization is subjected to fluid-solid coupling calculation to obtain the dynamic response results of the pressure vessel in the reactor loss of coolant accident. The coordinate positions of the structural grid corresponding to the solid area and the fluid grid corresponding to the fluid area in the finite element model match each other, and all of them are hexahedral units; The contact relationship of the nonlinear contact position is equivalently simulated using multiple COMBIN39 units in ANSYS software.

2. The fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident according to claim 1 is characterized in that: The structural parameters include geometric dimensions, material properties, support forms of the pressure vessel, and vibration modes and frequencies of the components within the reactor.

3. The fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident according to claim 1, characterized in that: The geometric model is constructed using the commercial software CATIA, and the finite element model is modeled using the commercial software Hypermesh; Among them, the finite element model of the solid area is generated as a .inp file, and the finite element model of the fluid area is generated as a .cas file.

4. The fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident according to claim 1, characterized in that: The fluid region in the finite element model uses the Fluent module in the ANSYS software as a fluid solver to model the fluid behavior.

5. The fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident according to claim 1, characterized in that: The solid region in the finite element model uses the Transient Structural module in the ANSYS software as a structural solver to model the structural behavior.

6. Fluid-solid coupling simulation system for nonlinear reactor system under loss of coolant accident, characterized by: include: A model building module is used to establish geometric models of the solid region and the fluid region according to the structural parameters of the reactor, and to mesh the geometric models to obtain finite element models of the solid region and the fluid region; A contact simulation module is used to simulate the contact relationship of at least two nonlinear contact positions in the finite element model; Boundary analysis module, used to solve the pressure change of the pressure vessel rupture under the condition of loss of coolant accident, and obtain the corresponding hydraulic load information as the pressure boundary condition of fluid-solid coupling simulation; A secondary modeling module, used for secondary modeling of the fluid boundary conditions and fluid-solid coupling interface of the fluid region and the solid boundary conditions and fluid-solid coupling interface of the solid region in the finite element model; The pressure application module is used to initialize the fluid pressure constant processing of the nonlinear finite element model after secondary modeling, pre-deform the corresponding part of the solid, and save the result after the initial pressure application as the initial condition of the next step of transient fluid-solid coupling; The coupling analysis module is used to perform fluid-solid coupling calculation on the nonlinear finite element model after pressure initialization to obtain the dynamic response results of the pressure vessel in the reactor loss of coolant accident; The coordinate positions of the structural grid corresponding to the solid area and the fluid grid corresponding to the fluid area in the finite element model match each other, and all of them are hexahedral units; The contact relationship of the nonlinear contact position is equivalently simulated using multiple COMBIN39 units in ANSYS software.

7. A computer terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident as described in any one of claims 1 to 5 is implemented.

8. A computer readable medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement the fluid-solid coupling simulation method for a nonlinear reactor system under a loss of coolant accident as described in any one of claims 1 to 5.

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