Fluid-structure interaction calculation method based on RELAP and ABAQUS

Abstract

The invention discloses a fluid-solid coupling calculation method based on RELAP and ABAQUS, and the method comprises the steps: carrying out the calculation of a reactor core fluid domain and the total power of a reactor core through RELAP, and obtaining the temperature, heat exchange coefficient and pressure distribution of a flow channel, and the total power of the reactor core; establishing a three-dimensional geometric model of a single fuel element in the ABAQUS, dividing grids and adding a sex model; a fluid-structure interaction interface is completed for ABAQUS secondary development; an FILM secondary development subprogram reads temperature and heat exchange coefficient distribution information in a time and space interpolation mode, and the function of convective heat exchange between a fluid domain and a solid domain is achieved; the DLOAD secondary development subprogram reads pressure distribution information in a time and space interpolation mode, and the function of transmitting pressure to the external boundary of the solid domain is achieved; the DFLUX secondary development subprogram reads reactor core power information through time interpolation according to element power distribution, so that the function of core heat release in a solid domain is realized; and calling a secondary development subprogram in the ABAQUS, and carrying out correlation calculation of a solid domain in a three-dimensional space to realize cross-dimension coupling.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluid-solid coupling problems, and specifically relates to a method for further solving the fluid-solid coupling problem and extending one-dimensional parameters to three-dimensional space by coupling two software numerical simulations, RELAP and ABAQUS. Background Art

[0002] RELAP is a program for optimal estimation of transient behavior of accident conditions of light water reactor cooling systems. Its application covers steady-state and transient analysis of the entire reactor system. It can calculate the thermal-hydraulic parameters of various accident conditions such as loss of coolant and loss of flow accidents in simulated reactor cooling systems. RELAP is a system analysis program that integrates two-fluid, six-equation hydraulics, one-dimensional heat conduction, and point reactor neutron dynamics. After steady-state or transient calculations, RELAP outputs the thermal-hydraulic parameters of the hydraulic channel along the axial direction to generate one-dimensional fluid domain calculation results. Through one-dimensional heat conduction calculations, the temperature parameters of the solid domain including the cladding and core are output radially to generate 1.5-dimensional solid domain calculation results.

[0003] ABAQUS is one of the most advanced large-scale general nonlinear finite element software in the world, capable of performing three-dimensional fluid-solid coupling calculation and analysis. In fluid-solid coupling calculations, by defining the convection heat transfer boundary conditions, pressure boundary conditions, and solid domain heat release boundary conditions between the solid domain and the fluid domain, the temperature, stress strain, and displacement parameters of the three-dimensional solid domain can be calculated through solution.

[0004] The mechanical analysis software ABAQUS is unable to model and calculate the entire reactor system, and therefore lacks transient fluid domain convective heat transfer boundary conditions, pressure boundary conditions, and solid domain heat release conditions under steady-state and transient conditions; and the system program RELAP can only calculate the thermal-hydraulic parameters of the one-dimensional fluid domain and the temperature distribution of the 1.5-dimensional solid domain; and for the more refined solid domain of a single fuel element in three-dimensional space, the system program RELAP cannot calculate the three-dimensional temperature, stress-strain, and displacement distribution parameters of a single fuel element. Summary of the invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a fluid-solid coupling calculation method based on RELAP and ABAQUS. The present invention uses RELAP and ABAQUS software for cross-dimensional coupling, which is conducive to expanding the one-dimensional calculation parameters of the fuel element to three dimensions, and obtaining refined three-dimensional solid domain thermodynamic parameters.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A fluid-solid coupling calculation method based on RELAP-ABAQUS uses the system program RELAP to perform calculations in the fluid domain, uses ABAQUS secondary development to create a fluid-solid coupling data interface, calls the secondary development subroutine in the three-dimensional solid domain calculation software ABAQUS, and performs relevant calculations in the solid domain, thereby obtaining the calculation results of the fluid-solid coupling problem, including the following steps:

[0008] Step 1: Establish a node diagram based on the actual reactor system, and model the actual reactor system based on the node diagram in the one-dimensional system analysis program RELAP; at the core of the reactor system, model different flow channels, and model the thermal components at the core according to the geometric form of the core fuel elements; in addition, it is necessary to compile point reactor dynamics information cards based on the reactor dynamics information; for accident conditions, by setting the restart card, the calculation process of solving the accident conditions using RELAP is realized;

[0009] Step 2: Use RELAP to calculate the reactor system modeled in step 1. Calculate the fluid domain at the core of the reactor system to obtain the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution of different flow channels in the core. For the calculation of point reactor dynamics, divide the calculated total reactor power by the total number of reactor elements to obtain the heat release power parameter of a single fuel element.

[0010] Step 3: Establish a three-dimensional geometric model of the solid domain of a single fuel element at the core of the reactor system and divide the grid. Use ABAQUS to establish a three-dimensional geometric model of the solid domain for a single fuel element. After dividing the grid, set the material properties, add the solid domain thermal conductivity model, specific heat capacity model, thermal expansion model, creep model, and elastoplastic model; for the convective heat transfer boundary conditions, in ABAQUS, select the convective heat transfer boundary of the solid domain, add the user-defined convective heat transfer boundary conditions, complete the call of the FILM subroutine in ABAQUS, and realize the convective heat transfer between the fluid domain and the solid domain; select the pressure boundary of the solid domain, add the user-defined pressure boundary conditions, complete the call of the DLOAD subroutine in ABAQUS, and realize the pressure boundary definition of the solid domain; select the volume heat release boundary of the solid domain, add the user-defined body heat flux load conditions, complete the call of the DFLUX subroutine in ABAQUS, and realize the volume heat release of the solid domain;

[0011] Step 4: Use FORTRAN language to complete the fluid-solid coupling interface of ABAQUS secondary development, and develop the FILM secondary development subroutine, DLOAD secondary development subroutine and DFLUX secondary development subroutine. The implementation method is as follows: in the FILM subroutine, define the fluid domain temperature H(1) and the boundary convection heat transfer coefficient SINK; in the DLOAD subroutine, define the boundary pressure F; in the DFLUX subroutine, define the core volume heat release power FLUX(1); in the process of defining the above variables, since the incremental step time of RELAP is different from that of ABAQUS, and RELAP is only one-dimensional The ABAQUS solid domain unit is in three-dimensional coordinates. Therefore, the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution obtained in step 2 are interpolated in time and space. The heat release power of a single fuel element obtained in step 2 is interpolated in time and the volume heat release rate of each part of the element is calculated according to the spatial power distribution. Then, it is defined in the FILM subroutine, DLOAD subroutine, and DFLUX subroutine. In the FILM subroutine, first, for the interpolation calculation of time, the temperature and heat transfer coefficient of any control body in the core flow channel under two adjacent time steps output by RELAP calculation are expressed as: tempf(t n )、tempf(t n+1 )、hthtc(t n )、hthtc(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the interpolation of the temperature and heat transfer coefficient at the control volume position at the ABAQUS time t is tempf(t n )+(tempf(t n+1 )-tempf(t n ))(tt n ) / (t n+1 -t n )、hthtc(t n )+(hthtc(t n+1 )-hthtc(t n ))(tt n ) / (t n+1 -t n ), the above operation is performed on each control body of the RELAP core flow channel to obtain the temperature and heat transfer coefficient of any control body at time t; then the spatial position is interpolated, and the time is interpolated. The temperature and heat transfer coefficient of any two adjacent control bodies at time t are expressed as tempf(z n )、tempf(z n+1 )、hthtc(z n)、hthtc(z n+1 ), where z n 、z n+1 are the axial coordinates of the two adjacent control body nodes. For the space between the two control body nodes at position z, the boundary conditions of the fluid temperature and heat transfer coefficient obtained by interpolation calculation are tempf(z n )+(tempf(z n+1 )-tempf(z n ))(zz n ) / (z n+1 -z n )、hthtc(z n )+(hthtc(z n+1 )-hthtc(z n ))(zz n ) / (z n+1 -z n ), and finally define the boundary conditions of temperature and heat transfer coefficient after interpolation of time and space in the FILM subroutine; in the DLOAD subroutine, firstly, for the interpolation calculation of time, the pressure of any control body of the core flow channel under two adjacent time steps output by RELAP calculation is expressed as: p(t n ), p(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the interpolation of the pressure at the position of the control body at the ABAQUS time t is p(t n )+(p(t n+1 )-p(t n ))(tt n ) / (t n+1 -t n ), perform the above operation on each control body of the RELAP core flow channel to obtain the pressure of any control body at time t; then interpolate the spatial position, and interpolate the time, and the pressure of any two adjacent control bodies at time t is expressed as p(z n )、p(z n+1 ), where z n 、z n+1 are the axial coordinates of the two adjacent control body nodes. For the space between the two control body nodes at position z, the pressure boundary condition obtained by interpolation calculation is p(z n )+(p(z n+1 )-p(z n ))(zz n ) / (z n+1 -z n), and finally define the pressure boundary conditions after time and space interpolation in the DLOAD subroutine; in the DFULX subroutine, firstly, for the time interpolation calculation, the total reactor power in two adjacent time steps output by RELAP calculation is expressed as: RKTPOW(t n )、RKTPOW(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the total power of the reactor at the ABAQUS time t is RKTPOW(t n )+(RKTPOW(t n+1 )-RKTPOW(t n ))(tt n ) / (t n+1 -t n ), the number of reactor fuel elements is N, and the power of a single element is (RKTPOW(t n )+(RKTPOW(t n+1 )-RKTPOW(t n ))(tt n ) / (t n+1 -t n )) / N; Then, for the calculation of space, the power allocated to each unit body is calculated according to the power of a single element and the power distribution of the element, and the volume heat release rate can be obtained by dividing the unit body power by the unit body volume. Finally, the volume heat release rate of each unit body obtained by interpolating the time and space is defined in the DFLUX subroutine; In the secondary development FILM subroutine, the secondary development DLOAD subroutine, and the secondary development DFLUX subroutine, unique unit numbers are assigned to different units to solve the conflict problem between multi-threaded calculation and external file reading;

[0012] Step 5: In ABAQUS, call the FILM secondary development subroutine, DLOAD secondary development subroutine, and DFLUX secondary development subroutine of ABAQUS in step 4 to complete the calculation of the solid domain and obtain the calculation results; complete the cross-dimensional coupling of the one-dimensional system analysis program RELAP and the three-dimensional solid domain calculation software ABAQUS.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention uses RELAP and ABAQUS software for cross-dimensional coupling, which is conducive to expanding the one-dimensional calculation parameters of the fuel element to three dimensions, and obtaining the refined three-dimensional solid domain thermodynamic parameters;

[0015] 2. The present invention conducts secondary development of the fluid-solid coupling interface in ABAQUS, and realizes the fluid-solid coupling calculation process under transient conditions by interpolating thermal hydraulic parameters in time and space. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a specific coupling process of the coupling calculation method of the present invention.

[0017] Figure 2 This is a schematic diagram of the interpolation of time and space performed by the secondary development FILM subroutine and the secondary development DLOAD subroutine.

[0018] Figure 3 Schematic diagram of the secondary development of the DFLUX subroutine to interpolate time and calculate the volume heat release rate based on the spatial power distribution.

[0019] Figure 4 This is a comparison chart of the outer surface temperature of the bottom cladding of the element calculated by RELAP and the average outer surface temperature at the corresponding position obtained by coupling RELAP and ABQAQUS. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with examples and drawings:

[0021] The following example uses the one-dimensional system analysis program RELAP to perform three-dimensional solid domain calculation software ABAQUS solid domain calculation to achieve coupling analysis through secondary development of the coupling interface. Figure 1 The coupling process diagram is further described as follows:

[0022] The present invention provides a fluid-solid coupling calculation method based on RELAP and ABAQUS. Figure 1 A schematic diagram of the coupling process is given. The dashed box in the figure is the coupling data interface. The specific coupling method is as follows:

[0023] Step 1: Establish a node diagram based on the actual reactor system, and model the actual reactor system based on the node diagram in the one-dimensional system analysis program RELAP; at the core of the reactor system, model different flow channels, and model the thermal components at the core according to the geometric form of the core fuel elements; in addition, it is necessary to compile point reactor dynamics information cards based on the reactor dynamics information; for accident conditions, by setting the restart card, the calculation process of solving the accident conditions using RELAP is realized;

[0024] Step 2: Use RELAP to calculate the reactor system modeled in step 1. Calculate the fluid domain at the core of the reactor system to obtain the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution of different flow channels in the core. For the calculation of point reactor dynamics, divide the calculated total reactor power by the total number of reactor elements to obtain the heat release power parameter of a single fuel element.

[0025] Step 3: Establish a three-dimensional geometric model of the solid domain of a single fuel element at the core of the reactor system and divide the grid. Use ABAQUS to establish a three-dimensional geometric model of the solid domain for a single fuel element. After dividing the grid, set the material properties, add the solid domain thermal conductivity model, specific heat capacity model, thermal expansion model, creep model, and elastoplastic model; for the convective heat transfer boundary conditions, in ABAQUS, select the convective heat transfer boundary of the solid domain, add the user-defined convective heat transfer boundary conditions, complete the call of the FILM subroutine in ABAQUS, and realize the convective heat transfer between the fluid domain and the solid domain; select the pressure boundary of the solid domain, add the user-defined pressure boundary conditions, complete the call of the DLOAD subroutine in ABAQUS, and realize the pressure boundary definition of the solid domain; select the volume heat release boundary of the solid domain, add the user-defined body heat flux load conditions, complete the call of the DFLUX subroutine in ABAQUS, and realize the volume heat release of the solid domain;

[0026] Step 4: Use FORTRAN language to secondary develop ABAQUS to complete the fluid-solid coupling interface, and develop the FILM secondary development subroutine, DLOAD secondary development subroutine and DFLUX secondary development subroutine. The implementation method is as follows: in the FILM subroutine, define the fluid domain temperature H(1) and the boundary convection heat transfer coefficient SINK; in the DLOAD subroutine, define the boundary pressure F; in the DFLUX subroutine, define the core volume heat release power FLUX(1); in the process of defining the above variables, since the incremental step time of RELAP and ABAQUS is different, and RELAP is only a one-dimensional program, while the ABAQUS solid domain unit is in three-dimensional coordinates, the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution obtained in step 2 are interpolated in time and space, and the heat release power of a single fuel element obtained in step 2 is interpolated in time and the volume heat release rate of each part of the element is calculated according to the spatial power distribution, and then defined in the FILM subroutine, DLOAD subroutine and DFLUX subroutine; the interpolation process of the FILM subroutine and the DLOAD subroutine is as follows Figure 2As shown in the figure, the core flow channel in RELAP is divided into ten control bodies along the vertical direction. The control body numbers are 1, 2...10, and the control body coordinates are z1, z2...z10. The parameter x can be expressed as the value of temperature, heat transfer coefficient and pressure output by RELAP at different times and different control body numbers. First, the time is interpolated. The two adjacent moments of RELAP output are represented as t1 and t2. When the total time t of the analysis step in ABAQUS is between the RELAP output time t1 and t2, the time is interpolated to obtain the output parameters x(t,1), x(t ,2)...x(t,10); When the position z of the subroutine call in ABAQUS is between the vertical coordinates z1 and z2 of the two control bodies, the axial position is interpolated to obtain the interpolation calculation parameter x(t,z) at time t and position z, where the parameter x(t,z) is the average value along the circumferential direction. In the secondary development subroutine, the interpolation calculated parameter x(t,z) is defined in the temperature H(1) in the FILM subroutine, the boundary convection heat transfer coefficient SINK and the pressure F in the DLOAD subroutine to realize the secondary development of the FILM subroutine and the DLOAD subroutine; In the FILM subroutine, firstly for The interpolation calculation of time, the temperature and heat transfer coefficient of any control body in the core flow channel under two adjacent time steps calculated and output by RELAP are expressed as: tempf(t1), tempf(t2), hthtc(t1), hthtc(t2), where t1 and t2 are the two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between t1 and t2, the interpolation of the temperature and heat transfer coefficient at the control body position at ABAQUS time t is tempf(t1)+(tempf(t2)-tempf(t1))(t-t1) / (t2-t 1) hthtc(t1)+(hthtc(t2)-hthtc(t1))(t-t1) / (t2-t1), perform the above operation on all control bodies of the RELAP core flow channel to obtain the temperature and heat transfer coefficient of all control bodies at time t; then interpolate the spatial position and interpolate the time, and the temperature and heat transfer coefficient of any two adjacent control bodies at time t are expressed as tempf(t,n), tempf(t,n+1), hthtc(t,n), hthtc(t,n+1), where n and n+1 are the numbers of the two adjacent control bodies, n=1, 2...9, z n 、z n+1 are the coordinates of the two adjacent control body nodes. For the position z between the two control body nodes, the boundary conditions of the fluid temperature and heat transfer coefficient obtained by interpolation calculation are tempf(t,n)+(tempf(t,n+1)-tempf(t,n))(zzn ) / (z n+1 -z n ),hthtc(t,n)+(hthtc(t,n+1)-hthtc(t,n))(zz n ) / (z n+1 -z n ), and finally define the boundary conditions of temperature and heat transfer coefficient after interpolation of time and space in the FILM subroutine; in the DLOAD subroutine, firstly, for the interpolation calculation of time, the pressure of any control body in the core flow channel under two adjacent time steps calculated and output by RELAP is expressed as: p(t1), p(t2), where t1 and t2 are the two adjacent time steps output by RELAP, respectively. When the total time t of the analysis step in ABAQUS is between these adjacent moments, for the ABAQUS moment t The interpolation of the pressure at the control body position over time is p(t1)+(p(t2)-p(t1))(t-t1) / (t2-t1). The above operation is performed for each control body in the RELAP core flow channel to obtain the pressure of any control body at time t. Then the spatial position is interpolated. After the interpolation calculation of time, the pressures of any two adjacent control bodies at time t are expressed as p(t,n) and p(t,n+1), respectively, where n and n+1 are the numbers of the two adjacent control bodies, n=1, 2...9, z n 、z n+1 are the coordinates of the two adjacent control body nodes. For the position z between the two control body nodes, the pressure boundary condition obtained by interpolation calculation is p(t,n)+(p(t,n+1)-p(t,n))(zz n ) / (z n+1 -z n ), and finally define the pressure boundary conditions after time and space interpolation in the DLOAD subroutine; the DFULX subroutine interpolates time and calculates the unit volume heat release rate according to the spatial power distribution of the element. Figure 3As shown, first, for the interpolation calculation of time, the total power of the reactor in two adjacent time steps calculated and output by RELAP is expressed as: RKTPOW(t1), RKTPOW(t2), where t1 and t2 are the two adjacent time steps output by RELAP, respectively. When the total time t of the analysis step in ABAQUS is between these adjacent moments, the total power of the reactor at ABAQUS moment t is RKTPOW(t1)+(RKTPOW(t2)-RKTPOW(t1))(t-t1) / (t2-t1). The number of reactor fuel elements is N, and the power of a single element is (RKTPOW(t1)+(RKTPOW(t2)-RKTPOW(t1))(t-t1) / (t 2-t1)) / N; then, for the calculation of space, according to the power of a single element and the power distribution of a single element in three-dimensional space, the power P(t) allocated to each unit body is calculated, and the power of each unit body is divided by the volume V of each unit body to obtain the volume heat release rate P(t) / V of the unit body. Finally, the volume heat release rate FLUX(1) of each unit body calculated by interpolating the time and calculating according to the power distribution in three-dimensional space is defined in the DFLUX subroutine to complete the secondary development of the DFLUX subroutine; in the secondary development FILM subroutine, the secondary development DLOAD subroutine, and the secondary development DFLUX subroutine, different units are assigned unique unit numbers to solve the conflict between multi-threaded calculation and external file reading:

[0027] Step 5: In ABAQUS, call the secondary development FILM subroutine, secondary development DLOAD subroutine and secondary development DFLUX subroutine in step 4 to complete the calculation of the solid domain and obtain the calculation results; complete the cross-dimensional coupling of the one-dimensional system analysis program RELAP and the three-dimensional solid domain calculation software ABAQUS; RELAP can calculate and output the solid domain temperature parameters including the cladding and core along the radial direction to generate 1.5-dimensional solid domain calculation results. Therefore, the correctness of the coupling calculation method is verified as follows: first, the transient loss of coolant accident conditions are calculated by RELAP to obtain the change of the outer surface temperature of the cladding at the bottom control body position of the core average channel with time; the three-dimensional calculation results of the plate-shaped fuel elements are calculated by the fluid-solid coupling calculation method of RELAP and ABAQUS, and the average temperature of all nodes on the outer surface of the cladding at the bottom control body position in the solid domain is extracted in ABAQUS. Figure 4 The comparison results of the outer surface temperature of the cladding at the bottom control body position of the core channel calculated by RELAP and the average temperature of the outer surface nodes of the cladding at the corresponding bottom control body position after coupling RELAP and ABAQUS are shown, verifying the correctness of the coupling method of the two software.

Claims

1. A fluid-solid coupling calculation method based on RELAP and ABAQUS, characterized by: The one-dimensional system analysis program RELAP is used to calculate the core fluid domain and the total core power, and the temperature, heat transfer coefficient, pressure distribution and total core power information of the flow field channel are obtained; In the three-dimensional solid domain calculation software ABAQUS, a three-dimensional geometric model of the solid domain of a single fuel element at the core of the reactor system is established, the grid is divided, and the physical property model is added; the fluid-solid coupling interface is completed by secondary development of ABAQUS using the FORTRAN language: the FILM secondary development subroutine reads the temperature and heat transfer coefficient distribution information by interpolating time and space, and realizes the function of convective heat transfer between the fluid domain and the solid domain; the DLOAD secondary development subroutine reads the pressure distribution information by interpolating time and space, and realizes the function of transferring the fluid domain pressure to the external boundary of the solid domain; the DFLUX secondary development subroutine reads the core power information by interpolating time and according to the element power distribution, and realizes the function of core heat release in the solid domain; the FILM secondary development subroutine, the DLOAD secondary development subroutine, and the DFLUX secondary development subroutine are called in ABAQUS to perform relevant calculations in the solid domain in three-dimensional space to realize cross-dimensional coupling; The method comprises the following steps: Step 1: Establish a node diagram based on the actual reactor system, and model the actual reactor system based on the node diagram in the one-dimensional system analysis program RELAP; at the core of the reactor system, model different flow channels, and model the thermal components at the core according to the geometric form of the core fuel elements; in addition, it is necessary to compile point reactor dynamics information cards based on the reactor dynamics information; for accident conditions, by setting the restart card, the calculation process of solving the accident conditions using RELAP is realized; Step 2: Use RELAP to calculate the reactor system modeled in step 1. Calculate the fluid domain at the core of the reactor system to obtain the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution of different flow channels in the core. For the calculation of point reactor dynamics, divide the calculated total reactor power by the total number of reactor elements to obtain the heat release power parameter of a single fuel element. Step 3: Establish a three-dimensional geometric model of the solid domain of a single fuel element at the core of the reactor system and divide the grid. Use ABAQUS to establish a three-dimensional geometric model of the solid domain for a single fuel element. After dividing the grid, set the material properties, add the solid domain thermal conductivity model, specific heat capacity model, thermal expansion model, creep model, and elastoplastic model; for the convective heat transfer boundary conditions, in ABAQUS, select the convective heat transfer boundary of the solid domain, add the user-defined convective heat transfer boundary conditions, complete the call of the FILM subroutine in ABAQUS, and realize the convective heat transfer between the fluid domain and the solid domain; select the pressure boundary of the solid domain, add the user-defined pressure boundary conditions, complete the call of the DLOAD subroutine in ABAQUS, and realize the pressure boundary definition of the solid domain; select the volume heat release boundary of the solid domain, add the user-defined body heat flux load conditions, complete the call of the DFLUX subroutine in ABAQUS, and realize the volume heat release of the solid domain; Step 4: Use FORTRAN language to complete the fluid-solid coupling interface of ABAQUS secondary development, and develop the FILM secondary development subroutine, DLOAD secondary development subroutine and DFLUX secondary development subroutine. The implementation method is as follows: in the FILM subroutine, define the fluid domain temperature H(1) and the boundary convection heat transfer coefficient SINK; in the DLOAD subroutine, define the boundary pressure F; in the DFLUX subroutine, define the core volume heat release power FLUX(1); in the process of defining the above variables, since the incremental step time of RELAP is different from that of ABAQUS, and RELAP is only one-dimensional The ABAQUS solid domain unit is in three-dimensional coordinates. Therefore, the fluid temperature distribution, heat transfer coefficient distribution, and pressure distribution obtained in step 2 are interpolated in time and space. The heat release power of a single fuel element obtained in step 2 is interpolated in time and the volume heat release rate of each part of the element is calculated according to the spatial power distribution. Then, it is defined in the FILM subroutine, DLOAD subroutine, and DFLUX subroutine. In the FILM subroutine, first, for the interpolation calculation of time, the temperature and heat transfer coefficient of any control body in the core flow channel under two adjacent time steps output by RELAP calculation are expressed as: tempf(t n )、tempf(t n+1 )、hthtc(t n )、hthtc(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the interpolation of the temperature and heat transfer coefficient at the control volume position at the ABAQUS time t is tempf(t n )+(tempf(t n+1 )-tempf(t n ))(tt n ) / (t n+1 -t n )、hthtc(t n )+(hthtc(t n+1 )-hthtc(t n ))(tt n ) / (t n+1 -t n ), the above operation is performed on each control body of the RELAP core flow channel to obtain the temperature and heat transfer coefficient of any control body at time t; then the spatial position is interpolated, and after the time is interpolated, the temperature and heat transfer coefficient of any two adjacent control bodies at time t are expressed as tempf(z n )、tempf(z n+1 )、hthtc(z n )、hthtc(z n+1 ), where z n 、z n+1 are the axial coordinates of the two adjacent control body nodes. For the space between the two control body nodes at position z, the boundary conditions of the fluid temperature and heat transfer coefficient obtained by interpolation calculation are tempf(z n )+(tempf(z n+1 )-tempf(z n ))(zz n ) / (z n+1 -z n )、hthtc(z n )+(hthtc(z n+1 )-hthtc(z n ))(zz n ) / (z n+1 -z n ), and finally define the boundary conditions of temperature and heat transfer coefficient after interpolation of time and space in the FILM subroutine; in the DLOAD subroutine, firstly, for the interpolation calculation of time, the pressure of any control body of the core flow channel under two adjacent time steps output by RELAP calculation is expressed as: p(t n )、p(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the interpolation of the pressure at the position of the control body at the ABAQUS time t is p(t n )+(p(t n+1 )-p(t n ))(tt n ) / (t n+1 -t n ), perform the above operation on each control body of the RELAP core flow channel to obtain the pressure of any control body at time t; then interpolate the spatial position, and interpolate the time, and the pressure of any two adjacent control bodies at time t is expressed as p(z n )、p(z n+1 ), where z n 、z n+1 are the axial coordinates of the two adjacent control body nodes. For the space between the two control body nodes at position z, the pressure boundary condition obtained by interpolation calculation is p(z n )+(p(z n+1 )-p(z n ))(zz n ) / (z n+1 -z n ), and finally define the pressure boundary conditions after time and space interpolation in the DLOAD subroutine; in the DFULX subroutine, firstly, for the time interpolation calculation, the total reactor power in two adjacent time steps output by RELAP calculation is expressed as: RKTPOW(t n )、RKTPOW(t n+1 ), where t n ,t n+1 are two adjacent time steps output by RELAP. When the total time t of the analysis step in ABAQUS is between these adjacent time steps, the total power of the reactor at the ABAQUS time t is RKTPOW(t n )+(RKTPOW(t n+1 )-RKTPOW(t n ))(tt n ) / (t n+1 -t n ), the number of reactor fuel elements is N, and the power of a single element is (RKTPOW(t n )+(RKTPOW(t n+1 )-RKTPOW(t n ))(tt n ) / (t n+1 -t n )) / N; Then, for the calculation of space, according to the power of a single element and the power distribution of the element, the power allocated to each unit body is calculated, and the volume heat release rate can be obtained by dividing the unit body power by the unit body volume. Finally, the volume heat release rate of each unit body obtained by interpolating time and space is defined in the DFLUX subroutine; in the secondary development FILM subroutine, the secondary development DLOAD subroutine, and the secondary development DFLUX subroutine, unique unit numbers are assigned to different units to solve the conflict between multi-threaded calculation and external file reading: Step 5: In ABAQUS, call the FILM secondary development subroutine, DLOAD secondary development subroutine, and DFLUX secondary development subroutine of ABAQUS in step 4 to complete the calculation of the solid domain and obtain the calculation results; complete the cross-dimensional coupling of the one-dimensional system analysis program RELAP and the three-dimensional solid domain calculation software ABAQUS.

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