A Calculation Method for Nonlinear Dynamic Characteristics of Pressurized Water Reactor Fuel Assemblies

Abstract

The present invention provides a method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly, which belongs to the field of nuclear power technology, and includes: obtaining the boundary conditions of a grid when it is not slipping and when it is slipping; modeling to obtain the control equation of the grid; solving the control equation of the grid to obtain the bending moment of one end of the grid to the guide tube; constructing the dynamic equation of the guide tube; using the modal superposition method to obtain the first discrete linear equation group; calculating the quasi-static loading response of the pressurized water reactor fuel assembly; discretizing the dynamic equation of the pressurized water reactor fuel assembly to obtain the second discrete linear equation group; solving the second discrete linear equation group to obtain the dynamic response of the pressurized water reactor fuel assembly. The present invention solves the problem of high-precision nonlinear dynamic modeling of fuel assemblies.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power, and in particular relates to a method for calculating nonlinear dynamic characteristics of a pressurized water reactor fuel assembly. Background Art

[0002] As a new type of clean energy, nuclear energy has a very important and positive significance for human production and life in the context of huge energy demand. Fuel assemblies, as the most core components of nuclear reactors, play an important role in accommodating reactants. Their safety is an important prerequisite for ensuring the overall safety of the reactor. However, in normal operation or accident conditions, the wear and damage of fuel assemblies seriously affect the safe operation of nuclear reactors. In order to fully consider the characteristics of fuel assemblies in the design stage and improve the safety redundancy of fuel assemblies through the design of related structures, it is very necessary to study the structural dynamic characteristics of fuel assemblies.

[0003] Establishing an accurate dynamic model of fuel assemblies is very important in the field of fuel assembly safety design. An accurate dynamic model can be used to simulate the structural dynamic response of fuel assemblies under reactor operating conditions and accident conditions. On the one hand, it can verify the safety of fuel assemblies under different conditions, and on the other hand, it can be used to calculate the local wear problem of fuel assemblies, which is of great significance for optimizing structural characteristics and increasing service life. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly, which is used to simulate and predict the dynamic characteristics of the fuel assembly.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly, comprising the following steps:

[0006] S1. Analyze the motion characteristics of the PWR fuel assembly structure to obtain the boundary conditions of the grid when it is not sliding and when it is sliding;

[0007] S2, using the Euler-Bernoulli beam model to model and obtain the control equations of the grid;

[0008] S3, using the boundary conditions of the grid when not sliding and when sliding, solving the control equation of the grid to obtain the bending moment of one end of the grid on the guide tube;

[0009] S4. According to the bending moment of one end of the grid on the guide tube, the dynamic equation of the guide tube is constructed using the Euler-Bernoulli beam model;

[0010] S5. According to the dynamic equation of the guide tube, a first discrete linear equation group is obtained by using a mode superposition method;

[0011] S6. Calculating the quasi-static loading response of the pressurized water reactor fuel assembly according to the first discrete linear equation group;

[0012] S7, discretizing the kinetic equations of the pressurized water reactor fuel assembly to obtain a second discrete linear equation group;

[0013] S8. Solve the second discrete linear equation group to obtain the dynamic response of the pressurized water reactor fuel assembly, and complete the calculation of the nonlinear dynamic characteristics of the pressurized water reactor fuel assembly.

[0014] Furthermore, the boundary condition of the grid in step S1 when there is no slip is expressed as follows:

[0015]

[0016] The boundary condition when the grid is sliding is expressed as follows:

[0017]

[0018] w e =-k s F s

[0019]

[0020]

[0021]

[0022]

[0023] Among them, Δθ GT Indicates the increment of the rotation angle of one end of the grid, F smax represents the maximum static friction, w G represents the displacement perpendicular to the grid axis, x G represents the coordinate along the grid axis, l G Indicates the width of the grid, w s represents the sliding displacement of the grid along the axial direction of the fuel rod, w e represents the axial deformation of the fuel rod, w F represents the displacement perpendicular to the axial direction of the fuel rod, x F represents the coordinate along the axial direction of the fuel rod, a F represents the cross-sectional area of ​​the fuel rod, Δθ represents the relative rotation angle between the fuel rod and the grid, and θ GT represents the rotation angle of one end of the grid, w GT represents the lateral displacement of the guide tube, x GT represents the coordinate along the axial direction of the guide tube, aGT Indicates the length coefficient of the guide tube, l GT represents the length of the guide tube, θ G represents the rotation angle of the other end of the grid, θ F represents the rotation angle of the fuel rod, k s represents the inverse of the equivalent stiffness of the grid boundary, F s represents the friction force provided by the fuel rods to the grid, k F represents the equivalent axial stiffness of the fuel rod, k GT Indicates the equivalent axial stiffness of the guide tube, E F represents the elastic modulus of the fuel rod, A F represents the cross-sectional area of ​​the fuel rod, E GT represents the elastic modulus of the guide tube, A GT represents the cross-sectional area of ​​the guide tube, l F Indicates the length of the fuel rod, M G represents the bending moment provided by the fuel rod to the grid, I F represents the cross-sectional inertia moment of the fuel rod, k M Represents the relative rotational stiffness between the grid and the fuel rods.

[0024] Furthermore, the control equation of the grid is expressed as follows:

[0025]

[0026] Among them, E G represents the elastic modulus of the grid, I G represents the cross-sectional moment of inertia of the grid, w G represents the displacement perpendicular to the grid axis, x G represents the coordinate along the grid axis, M G represents the bending moment provided by the fuel rod to the grid, F s represents the friction force provided by the fuel rods to the grid, l G Indicates the length of the grid.

[0027] Furthermore, the expression of the bending moment of one end of the grid to the guide tube is as follows:

[0028]

[0029] Among them, M GT represents the relationship between the bending moment acting on the guide tube and the local rotation angle, θ GT represents the rotation angle of one end of the grid, Δθ GT represents the change in the boundary angle at one end of the grid, w s represents the sliding displacement of the grid along the axial direction of the fuel rod, M G represents the bending moment provided by the fuel rods to the grid, F srepresents the friction force provided by the fuel rods to the grid, l G Indicates the length of the grid.

[0030] Furthermore, the dynamic equation of the guide tube is expressed as follows:

[0031]

[0032] Among them, x GT represents the coordinate along the axial direction of the guide tube, E GT represents the elastic modulus of the guide tube, l GT Indicates the length of the guide tube, w GT represents the displacement perpendicular to the axial direction of the guide tube, m and m(x GT ) are distributed couples, which are the bending moments of the guide tube about x. GT The derivative of , p represents the distributed force.

[0033] Furthermore, the expression of the first discrete linear equation system is as follows:

[0034] Kq=F

[0035] Among them, K represents the discretized stiffness matrix, q represents the discrete variable, and F represents the discretized external force vector.

[0036] Furthermore, the kinetic equation of the pressurized water reactor fuel assembly is expressed as follows:

[0037]

[0038]

[0039]

[0040]

[0041] Where ρ represents density, x GT represents the coordinate along the axial direction of the guide tube, w GT represents the displacement perpendicular to the axial direction of the guide tube, t represents the time, and E GT represents the elastic modulus of the guide tube, I GT represents the section inertia moment of the guide tube, m(x GT ) represents the distributed force couple, which is the bending moment of the guide tube about x GT The derivative of , p represents the distributed force, ρ GT Indicates the density of the guide tube material, A GT Indicates the cross-sectional area of ​​the guide tube, m F represents the mass of the fuel rod, δ represents the Dirac function, α GT Indicates the length coefficient of the guide tube, lGT represents the length of the guide tube, F0 represents the external excitation, and ω represents the external excitation frequency.

[0042] Furthermore, the expression of the second discrete linear equation is as follows:

[0043]

[0044] Among them, M represents the discretized mass matrix, K represents the discretized stiffness matrix, q represents the discrete variable, represents the discretized external force vector, represents the second derivative with respect to time.

[0045] The beneficial effects of the present invention are as follows: the present invention obtains the boundary conditions of the grid when it is not slipping and when it is slipping, solves the control equation of the grid, obtains the bending moment of one end of the grid to the guide tube, and then obtains the quasi-static loading response of the pressurized water reactor fuel assembly by obtaining the first discrete linear equation group according to the bending moment, and obtains the dynamic response of the pressurized water reactor fuel assembly by solving the dynamic equation of the pressurized water reactor fuel assembly. The present invention can effectively simulate and predict the dynamic characteristics of the fuel assembly through the above design. The present invention can be used to predict the dynamic behavior of the fuel assembly under normal operating conditions and accident conditions of the reactor, and provide a basis and foundation for functional design and safety design. The present invention can also predict the local slippage of the fuel assembly during vibration, that is, it can predict the wear of the fuel assembly, and also provide a necessary theoretical basis for safety and life design. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the fuel assembly structure in this embodiment.

[0047] Figure 2 Schematic diagram of the relationship among the fuel rods, guide tubes and grid structure in this embodiment.

[0048] Figure 3 This is a simplified schematic diagram of the fuel assembly structure in this embodiment.

[0049] Figure 4 This is a simplified fuel assembly motion analysis diagram in this embodiment.

[0050] Figure 5 The present invention is a flow chart of the method.

[0051] Figure 6 Schematic diagram of the guide tube structure in this embodiment. DETAILED DESCRIPTION

[0052] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0053] Example

[0054] like Figure 5 As shown, the present invention provides a method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly, and the implementation method thereof is as follows:

[0055] S1. Analyze the motion characteristics of the PWR fuel assembly structure to obtain the boundary conditions of the grid when it is not sliding and when it is sliding;

[0056] S2, using the Euler-Bernoulli beam model to model and obtain the control equations of the grid;

[0057] S3, using the boundary conditions of the grid when not sliding and when sliding, solving the control equation of the grid to obtain the bending moment of one end of the grid on the guide tube;

[0058] S4. According to the bending moment of one end of the grid on the guide tube, the dynamic equation of the guide tube is constructed using the Euler-Bernoulli beam model;

[0059] S5. According to the dynamic equation of the guide tube, a first discrete linear equation group is obtained by using a mode superposition method;

[0060] S6. Calculating the quasi-static loading response of the pressurized water reactor fuel assembly according to the first discrete linear equation group;

[0061] S7, discretizing the kinetic equations of the pressurized water reactor fuel assembly to obtain a second discrete linear equation group;

[0062] S8. Solve the second discrete linear equation group to obtain the dynamic response of the pressurized water reactor fuel assembly, and complete the calculation of the nonlinear dynamic characteristics of the pressurized water reactor fuel assembly.

[0063] In this embodiment, the schematic diagram of the structure of the pressurized water reactor fuel assembly is as follows: Figure 1 As shown. It mainly consists of three parts, fuel rods (yellow tubes), guide tubes (blue tubes) and grids. The pressurized water reactor fuel assembly structure is installed between the upper tube seat and the lower tube seat. In order to obtain the dynamic model of the fuel assembly, the structural dimensions of the fuel assembly are first simplified to a structure that is easy to model, and this simplified structure can retain all the structural characteristics and contact characteristics of the fuel assembly. The structural relationship between the fuel rods, guide tubes and grids is shown in Figure 2As shown. The guide tube is welded to the grid, and the fuel rod is clamped on the grid by friction through springs and rigid convexities. While retaining this structural feature, the size of the fuel assembly can be reduced as much as possible to obtain a 1×2 fuel assembly. That is, only one fuel rod, one guide tube and two grids are retained in the structure. The structural schematic diagram is shown in Figure 3 Based on the simplified fuel assembly structure, the characteristics of the fuel assembly during deformation can be analyzed. The structural motion analysis diagram is shown in Figure 4 shown. Figure 4 The three sub-figures represent: the structural relationship without deformation, deformation without relative slip between the grid and the fuel rods, and deformation with relative axial slip between the grid and the fuel rods.

[0064] In this embodiment, by analyzing the motion characteristics of the structure, the boundary conditions of the lattice structure when it is not sliding and when it is sliding can be obtained:

[0065] When the right end of the grid does not slide:

[0066]

[0067] When the right end of the grid is sliding:

[0068]

[0069] Where Δθ=θ G -θ F .

[0070] Using material mechanics related calculations, we can get:

[0071] w e =-k s F s

[0072] in:

[0073]

[0074]

[0075]

[0076] The third boundary condition is processed to obtain:

[0077]

[0078] in:

[0079]

[0080] Among them, Δθ GT Indicates the increment of the rotation angle of one end of the grid, Fsmax represents the maximum static friction, w G represents the displacement perpendicular to the grid axis, x G represents the coordinate along the grid axis, l G Indicates the width of the grid, w s represents the sliding displacement of the grid along the axial direction of the fuel rod, w e represents the axial deformation of the fuel rod, w F represents the displacement perpendicular to the axial direction of the fuel rod, x F represents the coordinate along the axial direction of the fuel rod, a F represents the cross-sectional area of ​​the fuel rod, Δθ represents the relative rotation angle between the fuel rod and the grid, and θ GT represents the rotation angle of one end of the grid, w GT represents the lateral displacement of the guide tube, x GT represents the coordinate along the axial direction of the guide tube, a GT Indicates the length coefficient of the guide tube, l GT represents the length of the guide tube, θ G represents the rotation angle of the other end of the grid, θ F represents the rotation angle of the fuel rod, k s represents the inverse of the equivalent stiffness of the grid boundary, F s represents the friction force provided by the fuel rods to the grid, k F represents the equivalent axial stiffness of the fuel rod, k GT Indicates the equivalent axial stiffness of the guide tube, E F represents the elastic modulus of the fuel rod, A F represents the cross-sectional area of ​​the fuel rod, E GT represents the elastic modulus of the guide tube, A GT represents the cross-sectional area of ​​the guide tube, l F Indicates the length of the fuel rod, M G represents the bending moment provided by the fuel rod to the grid, I F represents the cross-sectional inertia moment of the fuel rod, k M Represents the relative rotational stiffness between the grid and the fuel rods.

[0081] In this embodiment, the Euler-Bernoulli beam model can be used to model the grid to obtain the control equation of the grid:

[0082]

[0083] Among them, E G represents the elastic modulus of the grid, I G represents the cross-sectional moment of inertia of the grid, w G represents the displacement perpendicular to the grid axis, x G represents the coordinate along the grid axis, M Grepresents the bending moment provided by the fuel rods to the grid, F s represents the friction force provided by the fuel rods to the grid, l G Indicates the length of the grid.

[0084] In this embodiment, the analytical solution of this equation can be obtained by using two different boundary conditions:

[0085] When the right end of the grid does not slide:

[0086]

[0087]

[0088] Among them, k s Represents the inverse of the equivalent stiffness at one end of the grid, M G represents the bending moment provided by the fuel rod to the grid, a F 、a M , b F and b M Both represent coefficients, θ GT Indicates the rotation angle of one end of the grid.

[0089]

[0090]

[0091]

[0092]

[0093] Among them, λ and β are coefficients, I G represents the cross-sectional moment of inertia of the grid, E G represents the elastic modulus of the grid, I G represents the cross-sectional moment of inertia of the grid, w s Represents the sliding displacement of the grid along the axial direction of the fuel rod.

[0094] When the right end of the grid is sliding:

[0095]

[0096]

[0097]

[0098] in:

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] Among them, F s represents the friction force provided by the fuel rod to the grid, Δθ GT Indicates the increment of the rotation angle of one end of the grid, F smax represents the maximum static friction, M GT It represents the relationship between the bending moment acting on the guide tube and the local rotation angle, E G represents the elastic modulus of the grid, I G represents the cross-sectional moment of inertia of the grid, k s represents the inverse of the equivalent stiffness of the grid boundary, F s represents the friction force provided by the fuel rod to the grid, γ represents the coefficient, and E F represents the elastic modulus of the fuel rod, I F represents the cross-sectional inertia moment of the fuel rod, E G represents the elastic modulus of the grid, I G represents the cross-sectional moment of inertia of the grid, θ GT represents the rotation angle of one end of the grid, Ψ represents a function expression, θ GT represents the rotation angle of one end of the grid, α F represents the cross-sectional area of ​​the fuel rod, k M Represents the relative rotational stiffness between the grid and the fuel rods.

[0105] Then the bending moment of the left end of the grid on the guide tube can be written as:

[0106]

[0107] Among them, M GT represents the relationship between the bending moment acting on the guide tube and the local rotation angle, θ GT represents the rotation angle of one end of the grid, Δθ GT represents the increment of the rotation angle of one end of the grid, w s represents the sliding displacement of the grid along the axial direction of the fuel rod, M G represents the bending moment provided by the fuel rods to the grid, F s represents the friction force provided by the fuel rods to the grid, l G Indicates the length of the grid.

[0108] In this embodiment, a simplified overall structural dynamics model of the fuel assembly is constructed, and the structural schematic diagram of the guide tube is as follows: Figure 5 shown.

[0109] In this embodiment, the dynamic equation of the guide tube can be established based on the Euler-Bernoulli beam principle:

[0110]

[0111] Among them, x GT represents the coordinate along the axial direction of the guide tube, E GT represents the elastic modulus of the guide tube, l GT Indicates the length of the guide tube, w GT represents the displacement perpendicular to the axial direction of the guide tube, m represents the distributed force couple, and p represents the distributed force.

[0112] Using the modal superposition method, assuming:

[0113]

[0114] Among them, w GT represents the displacement perpendicular to the axial direction of the guide tube, k represents the discrete order, N represents the maximum value of the discrete order, q j represents a discrete variable, Φ j' represents the j'th basis of the discrete basis, x GT Indicates the coordinate along the axial direction of the guide tube.

[0115] Substituting this into the equation, we get the discrete equation:

[0116]

[0117] Among them, l GT Indicates the length of the grid, E GT represents the elastic modulus of the guide tube, I GT represents the section inertia moment of the guide tube, i” represents the discrete order, N represents the maximum value of the discrete order, x GT represents the coordinate along the axial direction of the guide tube, m(x GT ) represents the distributed force couple, p(x GT ) represents the distributed force, Φ i' represents the i'th basis of the discrete basis. After calculation, we can get the first discrete linear equation system:

[0118] Kq=F

[0119] Among them, K represents the discretized stiffness matrix, q represents the discrete variable, and F represents the discretized external force vector.

[0120] in,

[0121]

[0122]

[0123] Among them, K ijrepresents the value of the ijth variable in the discretized stiffness matrix, ξ j represents the dimensionless frequency of the discrete basis, i and j both represent the index in the stiffness matrix, F i represents the value of the i-th variable of the discretized force, M GT It represents the relationship between the bending moment acting on the guide tube and the local rotation angle, Φ′ i represents the first-order derivative of the ith basis of the discrete basis with respect to the displacement, F e represents external excitation, Φ i' represents the i'th basis of a discrete basis.

[0124] The quasi-static loading response of the fuel assembly can be calculated using this discrete linear equation set. Furthermore, the dynamic equation of the fuel assembly can be obtained by adding the inertia term:

[0125]

[0126] in:

[0127]

[0128]

[0129]

[0130] Where ρ represents density, x GT represents the coordinate along the axial direction of the guide tube, w GT represents the displacement perpendicular to the axial direction of the guide tube, t represents the time, and E GT represents the elastic modulus of the guide tube, I GT represents the section inertia moment of the guide tube, m(x GT ) represents the distributed force couple, which is the bending moment of the guide tube about x GT The derivative of , p represents the distributed force, ρ GT Indicates the density of the guide tube material, A GT Indicates the cross-sectional area of ​​the guide tube, m F represents the mass of the fuel rod, δ represents the Dirac function, α GT Indicates the length coefficient of the guide tube, l GT represents the length of the guide tube, F0 represents the external excitation, and ω represents the external excitation frequency.

[0131] In this embodiment, the Galerkin method can also be used to discretize the equation to obtain a second discrete linear equation system:

[0132]

[0133] Among them, M represents the discretized mass matrix, K represents the discretized stiffness matrix, q represents the discrete variable, represents the discretized external force vector, represents the second derivative with respect to time.

[0134] in:

[0135] M ij =δ ij ρ GT A GT l GT +m F Φ j′ (α GT l GT )Φ i′ (α GT l GT )

[0136]

[0137] Among them, M ij represents the ijth component of the discretized mass matrix, δ ij represents the Kronecker function, ρ GT Indicates the density of the guide tube material, A GT represents the cross-sectional area of ​​the guide tube, l GT Indicates the length of the guide tube, m F represents the mass of the fuel rod, Φ j' represents the j'th basis of the discrete basis, α GT Indicates the guide tube length coefficient, Φ i' represents the i'th basis of the discrete basis, represents the i-th component of the discrete external force, Φ′ i' represents the derivative of the ith basis of the discrete basis with respect to displacement, F0 represents the external excitation amplitude, and ω represents the external excitation frequency. The dynamic response of the fuel assembly can be obtained by solving the problem.

[0138] The present invention completes the calculation of nonlinear dynamic characteristics by obtaining the quasi-static loading response and the dynamic response.

[0139] The present invention can be used to predict the dynamic behavior of fuel assemblies under normal operating conditions and accident conditions of the reactor, providing a basis and foundation for functional design and safety design. At the same time, the local slippage of the fuel assembly during vibration can also be predicted, that is, the wear of the fuel assembly can be predicted, which also provides the necessary theoretical basis for safety and life design.

Claims

1. A method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly, characterized in that: The following steps are involved: S1. Analyze the motion characteristics of the PWR fuel assembly structure to obtain the boundary conditions of the grid when it is not sliding and when it is sliding; S2, using the Euler-Bernoulli beam model to model and obtain the control equations of the grid; S3, using the boundary conditions of the grid when not sliding and when sliding, solving the control equation of the grid to obtain the bending moment of one end of the grid on the guide tube; S4. According to the bending moment of one end of the grid on the guide tube, the dynamic equation of the guide tube is constructed using the Euler-Bernoulli beam model; S5. According to the dynamic equation of the guide tube, a first discrete linear equation group is obtained by using a mode superposition method; S6. Calculating the quasi-static loading response of the pressurized water reactor fuel assembly according to the first discrete linear equation group; S7, discretizing the kinetic equations of the pressurized water reactor fuel assembly to obtain a second discrete linear equation group; S8, solving the second discrete linear equation group to obtain the dynamic response of the pressurized water reactor fuel assembly, and completing the calculation of the nonlinear dynamic characteristics of the pressurized water reactor fuel assembly; The expression of the boundary condition of the grid when there is no slip in step S1 is as follows: The boundary condition when the grid is sliding is expressed as follows: in, represents the increment of the rotation angle of one end of the grid boundary, represents the maximum static friction, represents the displacement perpendicular to the grid axis, represents the coordinate along the grid axis, Indicates the width of the grid, represents the sliding displacement of the grid along the axial direction of the fuel rod, represents the axial deformation of the fuel rod, represents the displacement perpendicular to the axial direction of the fuel rod, represents the coordinate along the axial direction of the fuel rod, represents the cross-sectional area of ​​the fuel rod, represents the relative rotation angle between the fuel rod and the grid, represents the rotation angle of one end of the grid, represents the lateral displacement of the guide tube, represents the coordinate along the axial direction of the guide tube, represents the length coefficient of the guide tube, Indicates the length of the guide tube, represents the rotation angle of the other end of the grid, represents the rotation angle of the fuel rod, represents the inverse of the equivalent stiffness of the lattice boundary, It means that the fuel rods provide friction to the grid. represents the equivalent axial stiffness of the fuel rod, represents the equivalent axial stiffness of the guide tube, represents the elastic modulus of the fuel rod, represents the cross-sectional area of ​​the fuel rod, represents the elastic modulus of the guide tube, represents the cross-sectional area of ​​the guide tube, represents the length of the fuel rod, represents the bending moment provided by the fuel rods to the grid, represents the cross-sectional moment of inertia of the fuel rod, Represents the relative rotational stiffness between the grid and the fuel rods.

2. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The governing equations of the grid are expressed as follows: in, represents the elastic modulus of the lattice, represents the section moment of inertia of the grid, represents the displacement perpendicular to the grid axis, represents the coordinate along the grid axis, represents the bending moment provided by the fuel rods to the grid, It means that the fuel rods provide friction to the grid. Indicates the length of the grid.

3. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The expression of the bending moment of one end of the grid to the guide tube is as follows: in, It represents the relationship between the bending moment acting on the guide tube and the local rotation angle, represents the rotation angle of one end of the grid, represents the change in the boundary angle at one end of the grid, represents the sliding displacement of the grid along the axial direction of the fuel rod, represents the bending moment provided by the fuel rods to the grid, It means that the fuel rods provide friction to the grid. Indicates the length of the grid.

4. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The expression of the dynamic equation of the guide tube is as follows: in, represents the coordinate along the axial direction of the guide tube, represents the elastic modulus of the guide tube, Indicates the length of the guide tube, represents the displacement perpendicular to the axial direction of the guide tube, and Both represent distributed couples, which are the bending moments of the guide tubes with respect to The derivative of Represents distributed force.

5. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The expression of the first discrete linear equation system is as follows: in, represents the discretized stiffness matrix, represents a discrete variable, Represents the discretized external force vector.

6. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The expression of the kinetic equation of the PWR fuel assembly is as follows: in, represents density, represents the coordinate along the axial direction of the guide tube, represents the displacement perpendicular to the axial direction of the guide tube, t Indicates the time, represents the elastic modulus of the guide tube, represents the section moment of inertia of the guide tube, represents a distributed force couple, which is the bending moment of the guide tube about The derivative of represents the distributed force, represents the density of the guide tube material, represents the cross-sectional area of ​​the guide tube, represents the mass of the fuel rod, represents the Dirac function, represents the length coefficient of the guide tube, Indicates the length of the guide tube, Represents external motivation, Represents the external excitation frequency.

7. The method for calculating the nonlinear dynamic characteristics of a pressurized water reactor fuel assembly according to claim 1, characterized in that: The expression of the second discretized linear equation is as follows:

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