Reactor core three-dimensional thermal hydraulic analysis method and system

Abstract

The invention provides a three-dimensional thermal hydraulic analysis method and system for a reactor core. The method comprises the following steps: analyzing the type of the reactor core, dividing an outer-layer grid and a computational grid, and establishing a conservation mapping relation and a transfer equation set; the friction effect caused by the viscosity of the coolant is decomposed, and a source term is used to characterize the exchange of physical quantities caused by turbulence mixing; establishing a three-dimensional control equation set formed by mass, momentum and energy conservation equations for flow and heat transfer phenomena in the coolant channel, and forming a complete matrix equation set in combination with the transfer equation set; setting physical field boundary conditions and initial conditions of the reactor core, and setting an initial field; and carrying out iterative solution on the complete matrix equation set to obtain the thermal hydraulic parameters. According to the method, cross flow distribution and finer speed distribution in a coolant channel can be solved through thermal-hydraulic analysis, the prediction capacity of local thermal-hydraulic parameters is remarkably improved, and the method can be used for more accurate thermal-hydraulic analysis.

Description

Technical Field

[0001] The invention relates to the technical field of reactor thermal hydraulic design, and in particular to a three-dimensional thermal hydraulic analysis method and system for a reactor core. Background Art

[0002] The purpose of reactor thermal hydraulic design is to clarify the core's heat transfer capacity and coolant flow characteristics, and to ensure that the heat generated by the reactor core can be safely and reliably removed through the coolant. In order to ensure the safety and economy of the reactor, it is necessary to understand the changes in its thermal hydraulic parameters and ensure that the thermal parameters do not exceed the design limits of the thermal design criteria. At present, the core thermal hydraulic calculation and analysis methods mainly include single-channel analysis method, sub-channel analysis method and computational fluid dynamics (CFD) analysis method. In the single-channel analysis method, all coolant channels that need to be calculated are regarded as isolated and closed, and do not exchange mass, momentum and energy with other coolant channels. This analysis method is not suitable for open coolant channels of pressurized water reactors. In order to better simulate the mixing effect between coolant channels, a sub-channel analysis method has been developed and corresponding programs have been compiled, such as COBRA-TF and MATRA programs. However, the subchannel analysis method believes that the axial velocity is much greater than the lateral velocity, and the lateral momentum equation cannot be strictly solved. The actual three-dimensional flow of the core can only be simplified to a two-dimensional flow for solution. Therefore, the three-dimensional flow field of the actual flow cannot be analyzed, and the parameters such as the coolant flow rate and temperature obtained are all average values ​​in the channel, ignoring the fine distribution of the physical field in the coolant channel. With the rapid development of computer computing resources, the CFD method can be used to perform three-dimensional fine modeling of the core to solve three-dimensional flow field, temperature field and other information, but due to the existing computing resources, it is still impractical to perform CFD calculation and analysis on the core in engineering.

[0003] In summary, the single-channel analysis method and the sub-channel analysis method have low fidelity, but low requirements for computing resources, fast calculation speed, simple modeling, etc. The CFD method has the characteristics of high requirements for computing resources, slow calculation speed, complex modeling but high fidelity, etc. In view of the characteristics of the above-mentioned thermal-hydraulic analysis methods of different scales, the present invention takes the advantages of both and improves their shortcomings, so as to use an intermediate-fidelity thermal-hydraulic calculation method to quickly calculate the core and realize medium-fidelity, full-core steady-state and transient analysis. Summary of the invention

[0004] The purpose of the present invention is to provide a three-dimensional thermal-hydraulic analysis method and system for a reactor core, which supports thermal-hydraulic calculation and analysis of a reactor type containing an open fuel assembly; supports the calculation and solution of three-dimensional flow fields of fine grid element sub-channels, which can solve the defects of low solution resolution of sub-channel analysis methods, inability to solve cross-flow distribution, and inability to solve three-dimensional flow fields; supports the decomposition of friction effects caused by coolant viscosity, and explicitly and separately calculates the mixing of physical quantities caused by turbulent mixing, so as to reduce the computational complexity and uncertainty caused by simulating complex turbulent motion.

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

[0006] A three-dimensional thermal hydraulic analysis method for a reactor core comprises the following steps:

[0007] S1, analyze the reactor core type, determine the type of rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship;

[0008] S2, decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing;

[0009] S3, based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing, a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations is established for the flow and heat transfer phenomena in the coolant channel. Combined with the transfer equation group, the three-dimensional control equation group is discretized to form a complete matrix equation group for solving the coolant flow and heat transfer problems;

[0010] S4, setting the physical field boundary conditions and initial conditions of the reactor core, and setting the initial field, wherein the initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system;

[0011] S5, iteratively solve the complete matrix equations to obtain thermal-hydraulic parameters.

[0012] Furthermore, the method also includes: S6, iteratively updating the thermal-hydraulic parameters obtained by the solution and judging whether the iteration has converged, wherein judging whether the iteration has converged specifically refers to: during the iteration process, judging whether the equation residual of the complete matrix equation group meets the convergence requirements, if so, exiting the iteration, obtaining the converged solution at this moment, and updating the time step; if not, continuing the iterative solution.

[0013] Furthermore, the method further includes S7, determining whether the solution process is completed:

[0014] It is determined whether the solution time exceeds the set numerical calculation time. If not, steps S3-S5 are repeated to cycle to the next time step; otherwise, the solution process is terminated and the thermal-hydraulic parameters obtained by the solution are output.

[0015] Furthermore, in S1, the fine gate element sub-channel control volume is divided to form an outer grid, and the molecular channel control volume is divided to form a calculation grid, which specifically includes:

[0016] S1.1, the outer grid is the natural geometric division of the coolant flow channel between the core rod bundles. The computational grid is divided according to the computational efficiency, spatial resolution requirements and cross-flow flow characteristics. The outer grid is further refined to obtain the computational grid, so that the formed computational grid is finer than the outer grid but coarser than the CFD grid.

[0017] Furthermore, in S1, a conservation mapping relationship between the physical parameters of the outer grid and the computational grid is established, and based on the conservation mapping relationship, a transfer equation group is established, including:

[0018] S1.2, use the volume weighting method to establish the conservation mapping relationship between the outer grid and the computational grid, as shown in the following formula:

[0019]

[0020] The symbol φ represents the physical quantity parameter transferred between the two layers of grids, and the symbol V represents the volume of the control body, unit: m 3 , when the calculation object is two-dimensional, it degenerates into area, unit: m 2 ; The subscript symbol o represents the outer grid, the subscript symbol c represents the calculation grid, the subscript symbol j represents the number of the outer grid, and the subscript symbol i represents the number of the inner grid;

[0021] S1.3, based on the conservation mapping relationship between the two layers of grids, the existing core coolant flow and heat transfer model is used to calculate the corresponding constitutive equations on the outer grid to obtain the corresponding physical parameters. The corresponding physical parameters calculated are then mapped to the computational grid and written in matrix form to generate a group of transfer equations, as shown in the following formula:

[0022]

[0023] The symbol F represents the existing core coolant flow and heat transfer model, and the symbol Ψ represents the physical parameters ultimately sought by the above model.

[0024] Furthermore, in S2, the friction effect caused by the viscosity of the coolant is decomposed into the friction between the coolant and the wall and the friction between the coolants, and the corresponding friction pressure drop relationship is obtained. The source term is used to characterize the exchange of physical quantities caused by turbulent mixing, specifically including:

[0025] S2.1, decompose the friction effect caused by the viscosity of the coolant by region and flow direction, the region includes the grid region and the light rod region, the flow direction includes the lateral flow and the axial flow, and determine the friction pressure drop to be calculated for the axial light rod region, the axial grid region, the lateral light rod region, and the lateral grid region;

[0026] S2.2, the friction pressure drop to be calculated is decomposed into the friction between coolants and the friction between coolants and the wall, and implicit and explicit calculations are performed respectively to finally obtain the corresponding friction pressure drop relationship;

[0027] S2.3, using experimental correlations or numerical solutions using validated computational fluid dynamics software to calculate the exchange of physical quantities caused by turbulent mixing, and obtaining the final turbulent mixing source term relationship.

[0028] Furthermore, in S3, the three-dimensional control equations are discretized in combination with the transfer equations to form a complete matrix equations for solving the coolant flow and heat transfer problems, specifically including:

[0029] The mass conservation equation, momentum conservation equation and energy conservation equation are triple-integrated in the fine grid element sub-channel control volume and the midpoint rule is applied to obtain the semi-discrete equations.

[0030] According to the requirements of computational efficiency and computational accuracy, appropriate discrete formats are selected for the transient terms, convection terms, diffusion terms and source terms in the semi-discrete equations to be discretized, and finally a complete matrix equation group with the following form is formed:

[0031]

[0032] Among them, the symbol a 11 ,a 12 ,…a NN are the components of the discrete equation coefficient matrix; symbols φ1, φ2, …φ N are the thermal-hydraulic parameters to be solved; symbols b1, b2, …b N is the source term of the discretized equation.

[0033] Furthermore, in said S4, the physical field boundary conditions include flow boundary conditions and thermal boundary conditions.

[0034] Given the wall boundary, inlet and outlet flow rates, inlet velocity, and outlet pressure, the flow boundary conditions are obtained;

[0035] The thermal boundary conditions are obtained by giving a heat flux density or solving the fuel rod heat transfer model.

[0036] Furthermore, in S5, the complete matrix equations are iteratively solved to obtain thermal hydraulic parameters, which specifically include:

[0037] S5.1, using the time marching method to solve the transient physical field of the outer layer, updating the solution at each time layer and judging whether the set time has ended;

[0038] S5.2, use the time marching method to solve the transient physical field of the outer layer, set the time step, if it is the first iteration, use the initial field as the initial guess value to start the iteration, if it is not the first iteration, assign the converged solution of the previous moment to the physical field of this moment as the initial guess value, the physical field includes the velocity field, pressure field, temperature field and the mass flow rate of the control body interface;

[0039] S5.3, solving the energy conservation equation to obtain the temperature of the coolant, and then obtaining the physical property parameters including the fuel rod surface temperature, coolant temperature, and coolant density;

[0040] S5.4, within each time layer, assemble and solve the linearized momentum equation according to S3 and S4, assemble and solve the pressure correction equation using Rhie-Chow interpolation, and iteratively update the solution process parameters, wherein the iterative update includes updating the solutions obtained by the momentum equation and the pressure correction equation.

[0041] The present invention also provides a reactor core three-dimensional thermal hydraulic analysis system, which is used to execute the above reactor core three-dimensional thermal hydraulic analysis method, comprising:

[0042] The grid division module is used to analyze the reactor core type, determine the type of the rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship;

[0043] Friction pressure drop and turbulent mixing analysis module, which is used to decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing;

[0044] The complete matrix equation building module is used to establish a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations for the flow and heat transfer phenomena in the coolant channel based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing. The three-dimensional control equation group is discretized in combination with the transfer equation group to form a complete matrix equation group for solving coolant flow and heat transfer problems;

[0045] An initial parameter setting module is used to set the physical field boundary conditions and initial conditions of the reactor core and set the initial field. The initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system.

[0046] The thermal hydraulic solution module is used to iteratively solve the complete matrix equations to obtain the thermal hydraulic parameters.

[0047] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0048] 1) Abandoning the axial flow occupancy assumption of the traditional sub-channel analysis method, the three-dimensional fluid flow and heat transfer control equations are used to describe the flow and heat transfer process of the coolant, and the transverse momentum equation is strictly processed. Compared with the traditional sub-channel method, there is no need to simplify the three-dimensional problem in two dimensions, and complex three-dimensional flow fields can be solved.

[0049] 2) The friction effect caused by the viscosity of the coolant is decomposed to reduce the difficulty of numerical simulation of complex turbulent motion. Compared with the Reynolds average (RANS), large eddy simulation (LES) and direct numerical simulation (DNS) methods used in traditional CFD methods, this method has faster convergence speed and higher stability;

[0050] 3) Numerical solution is performed on the fine grid element control volume (computational grid). Compared with the traditional sub-channel analysis method, it can simulate more precise flow fields, temperature fields and cross-flow distributions in the coolant channels, and is more in line with the actual thermal-hydraulic processes in the core coolant channels.

[0051] The three-dimensional thermal-hydraulic analysis method of the reactor core provided by the present invention can solve the cross-flow distribution and the more detailed velocity distribution inside the coolant channel for thermal-hydraulic analysis, significantly improves the prediction ability of local thermal-hydraulic parameters, and can be used for more accurate thermal-hydraulic analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0053] Figure 1 It is a schematic diagram of the process of the three-dimensional thermal hydraulic analysis method of the reactor core according to an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of a grid system consisting of an outer grid and a computational grid for a single coolant channel of the present invention;

[0055] Figure 3 Schematic diagram of four ways of dividing the computing grid according to an embodiment of the present invention;

[0056] Figure 4 A double-layer grid system for a rod bundle calculation example of the present invention is presented, and a calculation example of a specific pressurized water reactor rod bundle fine grid element sub-channel is presented; Figure 4 The setting of the inlet and outlet outer boundaries and the cross-flow distribution inside the coolant channel and adjacent coolant channels are shown;

[0057] Figure 5 for Figure 4 The comparison chart of the calculation results of the transverse flow velocity of the fine grid element sub-channel of the PWR rod bundle shown, wherein the orange curve represents the result calculated by the calibrated computational fluid dynamics software as the benchmark value for comparative analysis, and the blue curve represents the result calculated by the method of the present invention;

[0058] Figure 6 for Figure 4 The cross-flow velocity distribution contour diagram of the PWR rod bundle fine grid element sub-channel example is shown. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] As stated in the background technology, the single-channel analysis method and the sub-channel analysis method have low fidelity, but have low requirements for computing resources, fast calculation speed, simple modeling, etc. The CFD method has the characteristics of high requirements for computing resources, slow calculation speed, complex modeling but high fidelity, etc. In view of the characteristics of the above-mentioned different thermal-hydraulic analysis methods, the present invention takes the advantages of both and improves their shortcomings, so as to use an intermediate-fidelity thermal-hydraulic calculation method to quickly calculate the core, and realize medium-fidelity, three-dimensional full-core steady-state and transient analysis. The three-dimensional thermal-hydraulic analysis method of the reactor core provided by the present invention is a three-dimensional fine gate element sub-channel thermal-hydraulic analysis method, which is used to solve the technical problems in the prior art.

[0061] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] like Figure 1 As shown, the three-dimensional thermal hydraulic analysis method of the reactor core provided by the present invention comprises the following steps:

[0063] S1, analyze the reactor core type, determine the type of rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship;

[0064] Specifically, the S1 determines the core type and solution scale. Based on the type of rod bundle channel to be solved and the solution domain, in order to solve the detailed flow field and temperature field distribution in the coolant channel, it is necessary to divide the fine grid element sub-channel control body. In order to use the existing flow and heat transfer model in the fine grid element sub-channel control body, it is necessary to additionally divide the sub-channel control body to form an outer grid and a computational grid. Since the two layers of grids are different in grid type, size, and number, it is necessary to establish a conservation mapping relationship between the physical parameters of the outer grid and the computational grid to ensure the conservation of data exchange between mass, momentum, and energy between the two layers of grids. The two-layer mapping relationship between the two layers of grids is written in matrix form to obtain a set of transfer equations that can ensure the conservation of physical parameter transfer between the two layers of grids;

[0065] S2, decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing;

[0066] S2 can reduce the computational complexity and uncertainty caused by simulating complex turbulent motion;

[0067] The step S2 specifically includes: when decomposing the friction effect caused by the viscosity of the coolant, it is necessary to decompose it by region and flow direction. In terms of partition, the friction effect caused by the viscosity of the coolant in the grid area needs to consider the additional friction pressure drop caused by the intermixing mechanical components more than the friction effect caused by the light rod area. In the flow direction, the friction pressure drop of the lateral flow and the axial friction pressure drop should also be calculated separately using different friction pressure drop models. Therefore, it is necessary to calculate the friction pressure drop in the axial light rod area, the friction pressure drop in the axial grid area, the friction pressure drop in the lateral light rod area, and the friction pressure drop in the lateral grid area separately;

[0068] S3, based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing, a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations is established for the flow and heat transfer phenomena in the coolant channel. Combined with the transfer equation group, the three-dimensional control equation group is discretized to form a complete matrix equation group for solving the coolant flow and heat transfer problems;

[0069] The three-dimensional control equations are used to describe the flow and heat transfer process of the coolant in the channel and between adjacent coolant channels, including boundary conditions, turbulent mixing, and friction pressure drop, so that the equations are closed and easy to solve; the transfer equations and the control equations are combined to obtain a matrix equation group, which is a complete matrix equation group that can ultimately solve the coolant flow and heat transfer problem;

[0070] S4, setting the physical field boundary conditions and initial conditions of the reactor core, and setting the initial field, wherein the initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system;

[0071] Among them, in order to be able to iteratively solve, the initial field needs to be set;

[0072] S5, iteratively solving the complete matrix equations to obtain thermal hydraulic parameters;

[0073] S6, iteratively update the thermal-hydraulic parameters obtained by the solution and determine whether the iteration has converged, wherein determining whether the iteration has converged specifically refers to: during the iteration process, determining whether the equation residual of the complete matrix equation group meets the convergence requirements. If so, exit the iteration, obtain the converged solution at this moment, and update the time step; if not, continue the iterative solution.

[0074] S7, determine whether the solution process is finished: determine whether the solution time exceeds the set numerical calculation time. If not, repeat steps S3-S5 to cycle for the next time step; otherwise, end the solution process and output the thermal-hydraulic parameters obtained by the solution.

[0075] For example, for S1, if the core type is a pressurized water reactor, the subchannel control volume and the fine gate element subchannel control volume are divided according to the solution scale to form an outer grid and a computational grid, and a conservation mapping relationship between the grid numbers and physical parameters of the outer grid and the computational grid is established, specifically including:

[0076] In order to use the existing flow and heat transfer models, a double-layer grid is used for numerical calculations. The flow and heat transfer models are applied on the outer grid and the computational grid, respectively, and the flow field and temperature field of the coolant are calculated.

[0077] The outer grid is the natural geometric division of the coolant flow channel between the core rod bundles. The computational grid needs to be divided according to the computational efficiency, spatial resolution requirements and cross-flow flow characteristics. The computational grid is further refined on the basis of the outer grid to obtain the computational grid, so that the formed computational grid is finer than the outer grid, but coarser than the CFD grid.

[0078] Preferably, the S1 is implemented by analyzing the core type and solution scale, dividing the grid, determining the mapping relationship, and establishing the transfer equation group, which may specifically include:

[0079] Step S1.1: Analyze the core type and solution scale, and divide the grid.

[0080] The core types that can be numerically simulated by this method can be pressurized water reactors, sodium-cooled fast reactors, lead-bismuth fast reactors, and other reactor types whose coolant channels are open channels without box wall components. Taking the core of a pressurized water reactor as an example, in order to be able to use the existing flow and heat transfer models, a double-layer grid is used for numerical calculations, and the flow and heat transfer models are applied on the outer grid and the computational grid, and the flow field and temperature field of the coolant are calculated.

[0081] The outer grid is the natural geometric division of the coolant flow channel between the core rod bundles. The computational grid needs to be divided according to the computational efficiency, spatial resolution requirements and the flow characteristics of the cross flow, and further refined division is performed on the basis of the outer grid to obtain the computational grid, so that the formed computational grid is finer than the outer grid, but coarser than the CFD grid. The present invention can be applied to any type of grid that meets the above characteristics;

[0082] Taking a single coolant channel surrounded by four fuel rods as an example, the outer grid is the natural geometric division of the coolant channel between the rods, such as Figure 2 As shown, this is the grid system surrounded by orange lines. Figure 2 The grid surrounded by white lines is the computational grid. There is only one way to divide the outer grid, but there are many ways to divide the computational grid. Figure 3 Four computational grid partitioning styles are shown;

[0083] Step S1.2: Establish a mapping relationship between two layers of grids.

[0084] The obtained parameters such as velocity and temperature are solved on the computational grid. However, since the outer grid and the computational grid are different in terms of the number of grids, grid type, and grid size, one outer grid corresponds to several computational grids. In order to ensure the conservation of physical quantities such as mass and momentum during data transfer between the two grids, the mapping relationship between the two grids needs to be established using volume weighting, as shown in the following formula:

[0085]

[0086] The symbol φ represents the physical quantity parameter transferred between the two layers of grids, and the symbol V represents the volume of the control body, unit: m 3 , when the calculation object is two-dimensional, it degenerates into area, unit: m 2 ; The subscript symbol o represents the outer grid, the subscript symbol c represents the calculation grid, the subscript symbol j represents the number of the outer grid, and the subscript symbol i represents the number of the inner grid.

[0087] by Figure 2 The above process is explained by taking the temperature parameter transfer between the computational grid and the outer grid as an example.

[0088] One outer grid corresponds to 16 calculation grids. The weighted average of the temperature volume (area) on each calculation grid is calculated, and then the 16 weighted averages of the temperature volume (area) are summed to obtain the temperature calculation value on the outer grid.

[0089] Step S1.3: Establish the transfer equations.

[0090] Based on the mapping relationship between the two layers of grids, the existing core coolant flow and heat transfer model is used to calculate the corresponding constitutive equations on the outer grid to obtain the corresponding physical parameters. The above physical parameters are then mapped to the computational grid and written in matrix form to generate a group of transfer equations, as shown in the following formula:

[0091]

[0092] The symbol F represents the core coolant flow and heat transfer model to be used, and the symbol Ψ represents the physical parameters ultimately required by the above model. The transfer equations have no restrictions on the form and number of flow and heat transfer models.

[0093] Taking the friction pressure drop model of the transverse optical rod area in the core of a pressurized water reactor as an example, the transfer equations of the above model are as follows:

[0094]

[0095] in,

[0096] (φ 1,c ,φ 2,c ,φ 3,c )=(f l ,f t ,Re)

[0097] That is, the laminar friction coefficient f required by the above pressure drop model is l , turbulent friction coefficient f tThe laminar friction coefficient, turbulent friction coefficient and Reynolds number Re on the outer grid are obtained through mapping from the computational grid and written into a matrix form for direct solution, and finally the friction resistance coefficient Ψ of the lateral light rod zone is obtained.

[0098] Preferably, S2 implements decomposing the friction effect caused by the viscosity of the coolant and using a momentum source to characterize turbulent mixing, which may specifically include:

[0099] Step S2.1: Analyze the viscous friction effect and decompose it.

[0100] The viscous friction effect is decomposed into the friction between coolants and the friction between coolants and the wall. The diffusion term reflecting the friction effect is triple-integrated on the computational grid and calculated using the Gaussian formula, as shown in the following formula:

[0101]

[0102] Among them, the symbol is the viscous stress tensor; symbol n is the surface unit normal vector; symbol Ω is the volume of the control volume; symbol S is the surface area of ​​the control volume; subscript f represents the fluid; subscript w represents the wall.

[0103] The friction between the coolant and the wall is calculated using the following formula:

[0104]

[0105] Where, symbol f is the friction coefficient, symbol ρ is the density of the coolant, unit: kg / m 3 ; The symbol v is the velocity vector of the coolant, and its component units are m / s; the subscript o represents the outer grid.

[0106] The coolant-to-coolant friction is calculated using the following formula:

[0107]

[0108] Wherein, symbol μ is the viscosity coefficient of coolant, unit: kg / (m·s).

[0109] The above contents are explained by taking the transverse light rod area of ​​the PWR core as an example. The diffusion term equation is triple-integrated on the computational grid, the friction effect is decomposed and calculated, and the corresponding semi-discrete equation is as follows:

[0110]

[0111] Step S2.2: Calculate source terms to characterize the turbulent mixing between coolant channels.

[0112] Mixing mechanical components such as mixing wings will cause strong turbulent mixing. In order to calculate the influence of turbulent mixing on the mixing of physical quantities, the present invention uses appropriate experimental correlations to explicitly calculate turbulent mixing and add it to the source term, as shown in the following formula:

[0113]

[0114] Taking the core of a pressurized water reactor as an example, the mixing of physical quantities caused by turbulent mixing is as follows:

[0115]

[0116] Among them, the symbol M M It is the momentum exchanged due to turbulent mixing, and its unit is kg / (m·s); symbol W f is the cross-flow velocity between adjacent control bodies, unit: m / s; is the physical quantity caused by turbulent mixing; S f is the area of ​​the interface between adjacent control bodies, unit: m 2 ; The subscript P represents the current control body; the subscript N represents the adjacent control body of the current control body.

[0117] Preferably, the step S3 implements: establishing and discretizing a control equation group to form a complete matrix equation group, which may specifically include:

[0118] Step S31: Establishing a control equation group: Based on the decomposition of the friction effect of viscosity and the calculation of turbulent mixing, a three-dimensional control equation group is established for the flow and heat transfer phenomena in the coolant channel. The equation group is as follows:

[0119] The mass conservation equation:

[0120]

[0121] Momentum conservation equation:

[0122]

[0123] Energy conservation equation:

[0124]

[0125] Where, symbol ρ is the density of the coolant, unit: kg / m 3 ; Symbols u, v, w are the speed of the coolant in the x, y, z directions respectively, unit: m / s; symbol p is the pressure, unit: Pa; symbol g x , g y , g z They are the gravitational acceleration in the x, y, and z directions, in m / s 2; Symbol T is the temperature of the coolant, unit: K; Symbol k represents the thermal conductivity, unit: W / (m·K); Symbol M Mx 、M My 、M Mz are the turbulent mixing quantities of momentum in the x, y, and z directions, respectively, in kg / (m·s); symbol M E is the energy of turbulent mixing, unit: J / (m 2 ·s); symbol S Mx , S My , S Mz The momentum sources in the x, y, and z directions are formed by friction and form resistance pressure drop introduced by the fuel bundle, assembly box wall, and spacer grid, respectively. Unit: kg / (m 2 ·s 2 ); symbol S E is the energy source term, unit: J / (m 3 ·s).

[0126] Step S32: Discretize the control equations to form a complete matrix equation group: In the period from t to t+Δt, perform triple integration on the mass conservation equation, momentum conservation equation, and energy conservation equation in the fine grid element control volume and apply the midpoint rule to obtain the following semi-discrete equations:

[0127] Semi-discrete equation for conservation of mass:

[0128]

[0129] Semi-discrete equation for conservation of momentum:

[0130]

[0131] Energy conservation semi-discrete equation:

[0132]

[0133] Among them, V C Represents the volume of the control volume, unit: m 3 ; The subscript f represents the calculated value at the interface of the control volume; the superscript v represents the three directions of the momentum equation, which are x, y, and z directions; the following table f:nb(C) represents the surface surrounding the current control volume C;

[0134] According to the requirements of computational efficiency and accuracy, appropriate discrete formats are selected for the transient terms, convection terms, diffusion terms and source terms in the above semi-discrete equations to discretize them, and finally a complete matrix equation group with the following form is formed:

[0135]

[0136] Among them, the symbol a11 ,a 12 ,…a NN are the components of the discrete equation coefficient matrix; symbols φ1, φ2, …φ N is the physical quantity to be determined, such as velocity, pressure, temperature; symbols b1, b2, ... b N is the source term of the discretized equation.

[0137] Preferably, S4 implements: setting physical field boundary conditions, initial conditions and initial fields.

[0138] The present invention needs to set boundary conditions and initial conditions according to the research object and the coolant flow and heat transfer problem being studied. The types of flow boundary conditions are generally wall boundary conditions, given mass flow outlet boundaries, given velocity inlet boundaries, etc. The thermal boundary conditions are obtained by giving a heat flux density or solving the fuel rod heat transfer model. If the transient physical field is solved, the initial conditions must also be set. In order to be able to iteratively solve the complete matrix equation group, the initial field needs to be given. The setting of the initial field does not affect the final solution, so the temperature field, pressure field and velocity field can be set to zero field.

[0139] Preferably, step S5: solving the matrix equations, specifically comprises:

[0140] S5.1. Use the time marching method to solve the transient physical field of the outer layer, update the solution at each time layer and determine whether the set time has ended.

[0141] S5.2. Use the time marching method to solve the transient physical field of the outer layer. Set the time step. If it is the first iteration, use the initial field as the initial guess value to start the iteration. If it is not the first iteration, assign the converged solution of the previous moment to the physical field of this moment as the initial guess value. The physical field includes the velocity field, pressure field, temperature field and the mass flow of the control body interface.

[0142] S5.3. Solve the energy conservation equation to obtain the coolant temperature, and then obtain the physical parameters such as fuel rod surface temperature, coolant temperature, coolant density, etc.

[0143] S5.4. In each time layer, assemble the momentum equation in discrete form according to step S3 and step S4, and solve it to obtain the velocity field v * , use Rhie-Chow interpolation to calculate the mass flow rate on the interface, as shown below:

[0144]

[0145] m f =Aρv f ·S f

[0146]

[0147] Wherein, symbol v is the velocity of the coolant, unit: m / s; symbol p is the pressure of the coolant, unit: Pa; symbol ρ is the density of the coolant, unit: kg / m 3 ; Symbol m is mass flow, unit: kg / s; symbol S f is the unit normal vector of the surface; symbol A is the area of ​​the surface, unit: m 2 ; Symbol a is the principal element of the discrete momentum coefficient; V represents the volume of the control body, unit: m 3 ; The subscript f represents the interface between adjacent control bodies; the superscripts u, v, w represent the x, y, z directions.

[0148] The pressure correction equation is assembled using the mass flow rate and solved to obtain the pressure correction value p'. The pressure correction value is used to correct the pressure and velocity, and the interface mass flow is recalculated using Rhie-Chow interpolation again.

[0149] Preferably, step S6 implements: judging the convergence and updating the relevant physical property parameters, including:

[0150] The solution and process parameters are iteratively updated and it is judged whether the iteration converges. The physical property parameters are updated according to the solved temperature field. The iterative convergence judgment refers to judging whether the equation residual meets the convergence requirements in the loop. If the convergence requirements are met, the loop is exited to obtain the converged solution at this moment. The time step t=t+Δt is updated. If the convergence requirements are not met, the loop is continued.

[0151] Step S7: Determine whether the numerical solution process is completed.

[0152] Determine whether the time exceeds the set end time. If it does not exceed the set end time, the next time step cycle will be performed. Otherwise, the numerical solution process ends and the solved physical fields such as velocity field, pressure field, temperature field, etc. are output.

[0153] Depend on Figure 4 , Figure 5 , Figure 6 It can be seen that the thermal-hydraulic analysis using the method of the present invention can solve the cross-flow distribution and the more detailed velocity distribution inside the coolant channel, significantly improve the prediction ability of local thermal-hydraulic parameters, and can be used for more accurate thermal-hydraulic analysis.

[0154] The present invention also provides a reactor core three-dimensional thermal hydraulic analysis system, which is used to execute the above reactor core three-dimensional thermal hydraulic analysis method, comprising:

[0155] The grid division module is used to analyze the reactor core type, determine the type of the rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship;

[0156] Friction pressure drop and turbulent mixing analysis module, which is used to decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing;

[0157] The complete matrix equation building module is used to establish a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations for the flow and heat transfer phenomena in the coolant channel based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing. The three-dimensional control equation group is discretized in combination with the transfer equation group to form a complete matrix equation group for solving coolant flow and heat transfer problems;

[0158] An initial parameter setting module is used to set the physical field boundary conditions and initial conditions of the reactor core and set the initial field. The initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system.

[0159] The thermal hydraulic solution module is used to iteratively solve the complete matrix equations to obtain the thermal hydraulic parameters.

[0160] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0161] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A three-dimensional thermal hydraulic analysis method for a reactor core, characterized in that: The following steps are involved: S1, analyze the reactor core type, determine the type of rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship; S2, decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing; S3, based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing, a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations is established for the flow and heat transfer phenomena in the coolant channel. Combined with the transfer equation group, the three-dimensional control equation group is discretized to form a complete matrix equation group for solving the coolant flow and heat transfer problems; S4, setting the physical field boundary conditions and initial conditions of the reactor core, and setting the initial field, wherein the initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system; S5, iteratively solve the complete matrix equations to obtain thermal-hydraulic parameters.

2. The three-dimensional thermal-hydraulic analysis method of a reactor core according to claim 1, characterized in that: The method also includes: S6, iteratively updating the thermal-hydraulic parameters obtained by the solution and judging whether the iteration has converged, wherein judging whether the iteration has converged specifically refers to: judging whether the equation residual of the complete matrix equation group meets the convergence requirements during the iteration process, if so, exiting the iteration, obtaining the converged solution at this moment, and updating the time step; if not, continuing the iterative solution.

3. The three-dimensional thermal-hydraulic analysis method of a reactor core according to claim 1, characterized in that: The method further comprises S7, determining whether the solution process is finished: It is determined whether the solution time exceeds the set numerical calculation time. If not, steps S3-S5 are repeated to cycle to the next time step; otherwise, the solution process is terminated and the thermal-hydraulic parameters obtained by the solution are output.

4. The three-dimensional thermal-hydraulic analysis method for a reactor core according to claim 1, characterized in that: In S1, the fine gate element sub-channel control volume is divided to form an outer grid, and the molecular channel control volume is divided to form a calculation grid, which specifically includes: S1.1, the outer grid is the natural geometric division of the coolant flow channel between the core rod bundles. The computational grid is divided according to the computational efficiency, spatial resolution requirements and cross-flow flow characteristics. The outer grid is further refined to obtain the computational grid, so that the formed computational grid is finer than the outer grid but coarser than the CFD grid.

5. The three-dimensional thermal-hydraulic analysis method of a reactor core according to claim 1, characterized in that: In S1, a conservation mapping relationship between the physical parameters of the outer grid and the computational grid is established, and based on the conservation mapping relationship, a transfer equation group is established, including: S1.2, use the volume weighting method to establish the conservation mapping relationship between the outer grid and the computational grid, as shown in the following formula: The symbol φ represents the physical quantity parameter transferred between the two layers of grids, and the symbol V represents the volume of the control body, unit: m 3 , when the calculation object is two-dimensional, it degenerates into area, unit: m 2 ; The subscript symbol o represents the outer grid, the subscript symbol c represents the calculation grid, the subscript symbol j represents the number of the outer grid, and the subscript symbol i represents the number of the inner grid; S1.3, based on the conservation mapping relationship between the two layers of grids, the existing core coolant flow and heat transfer model is used to calculate the corresponding constitutive equations on the outer grid to obtain the corresponding physical parameters. The corresponding physical parameters calculated are then mapped to the computational grid and written in matrix form to generate a group of transfer equations, as shown in the following formula: The symbol F represents the existing core coolant flow and heat transfer model, and the symbol Ψ represents the physical parameters ultimately sought by the above model.

6. The three-dimensional thermal-hydraulic analysis method for a reactor core according to claim 1, characterized in that: In S2, the friction effect caused by the viscosity of the coolant is decomposed into the friction between the coolant and the wall and the friction between the coolants, and the corresponding friction pressure drop relationship is obtained. The source term is used to characterize the exchange of physical quantities caused by turbulent mixing, specifically including: S2.1, decompose the friction effect caused by the viscosity of the coolant by region and flow direction, the region includes the grid region and the light rod region, the flow direction includes the lateral flow and the axial flow, and determine the friction pressure drop to be calculated for the axial light rod region, the axial grid region, the lateral light rod region, and the lateral grid region; S2.2, the friction pressure drop to be calculated is decomposed into the friction between coolants and the friction between coolants and the wall, and implicit and explicit calculations are performed respectively to finally obtain the corresponding friction pressure drop relationship; S2.3, using experimental correlations or numerical solutions using validated computational fluid dynamics software to calculate the exchange of physical quantities caused by turbulent mixing, and obtaining the final turbulent mixing source term relationship.

7. The three-dimensional thermal-hydraulic analysis method of a reactor core according to claim 1, characterized in that: In S3, the three-dimensional control equations are discretized in combination with the transfer equations to form a complete matrix equations for solving the coolant flow and heat transfer problems, specifically including: The mass conservation equation, momentum conservation equation and energy conservation equation are triple-integrated in the fine grid element sub-channel control volume and the midpoint rule is applied to obtain the semi-discrete equations. According to the requirements of computational efficiency and computational accuracy, appropriate discrete formats are selected for the transient terms, convection terms, diffusion terms and source terms in the semi-discrete equations to be discretized, and finally a complete matrix equation group with the following form is formed: Among them, the symbol a 11 ,a 12 ,…a NN are the components of the discrete equation coefficient matrix; symbols φ1, φ2, …φ N are the thermal-hydraulic parameters to be solved; symbols b1, b2, …b N is the source term of the discretized equation.

8. The three-dimensional thermal-hydraulic analysis method for a reactor core according to claim 1, characterized in that: In S4, the physical field boundary conditions include flow boundary conditions and thermal boundary conditions. Given the wall boundary, inlet and outlet flow rates, inlet velocity, and outlet pressure, the flow boundary conditions are obtained; The thermal boundary conditions are obtained by giving a heat flux density or solving the fuel rod heat transfer model.

9. The three-dimensional thermal-hydraulic analysis method for a reactor core according to claim 1, characterized in that: In S5, the complete matrix equations are iteratively solved to obtain thermal hydraulic parameters, which specifically include: S5.1, using the time marching method to solve the transient physical field of the outer layer, updating the solution at each time layer and judging whether the set time has ended; S5.2, use the time marching method to solve the transient physical field of the outer layer, set the time step, if it is the first iteration, use the initial field as the initial guess value to start the iteration, if it is not the first iteration, assign the converged solution of the previous moment to the physical field of this moment as the initial guess value, the physical field includes the velocity field, pressure field, temperature field and the mass flow rate of the control body interface; S5.3, solving the energy conservation equation to obtain the temperature of the coolant, and then obtaining the physical property parameters including the fuel rod surface temperature, coolant temperature, and coolant density; S5.4, within each time layer, assemble and solve the linearized momentum equation according to S3 and S4, assemble and solve the pressure correction equation using Rhie-Chow interpolation, and iteratively update the solution process parameters, wherein the iterative update includes updating the solutions obtained by the momentum equation and the pressure correction equation.

10. A three-dimensional thermal-hydraulic analysis system for a reactor core, used to execute the three-dimensional thermal-hydraulic analysis method for a reactor core according to any one of claims 1 to 9, characterized in that: include: The grid division module is used to analyze the reactor core type, determine the type of the rod bundle channel to be solved and the solution domain, divide the fine grid element sub-channel control volume to form an outer grid, divide the molecular channel control volume to form a computational grid, establish the conservation mapping relationship between the physical parameters of the outer grid and the computational grid, and establish the transfer equation group based on the conservation mapping relationship; Friction pressure drop and turbulent mixing analysis module, which is used to decompose the friction effect caused by the viscosity of the coolant into the friction between the coolant and the wall and the friction between the coolants, obtain the corresponding friction pressure drop relationship, and use the source term to characterize the exchange of physical quantities caused by turbulent mixing; The complete matrix equation building module is used to establish a three-dimensional control equation group consisting of mass, momentum, and energy conservation equations for the flow and heat transfer phenomena in the coolant channel based on the decomposition of the friction effect caused by viscosity and the exchange of physical quantities caused by turbulent mixing. The three-dimensional control equation group is discretized in combination with the transfer equation group to form a complete matrix equation group for solving coolant flow and heat transfer problems; An initial parameter setting module is used to set the physical field boundary conditions and initial conditions of the reactor core and set the initial field. The initial conditions include the initial values ​​of various physical parameters in the physical field to be solved under steady-state conditions or transient conditions of the reactor system. The thermal hydraulic solution module is used to iteratively solve the complete matrix equations to obtain the thermal hydraulic parameters.

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