Cross-scale analysis method for long-period vibration abrasion of pressurized water reactor fuel rod

Abstract

The invention provides a cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod, and relates to the technical field of fuel rod vibration abrasion analys.The method comprises the steps that information of external excitation loads borne by a fuel rod bundle under different deformation conditions is obtained by calculating geometric deformation characteristics of the pressurized water reactor fuel rod in the overall life period; carrying out initialization operation on the vibration abrasion calculation of the pressurized water reactor fuel rod; carrying out vibration abrasion transient calculation on the pressurized water reactor fuel rod in the current discrete time period to obtain an abrasion rate; calculating to obtain a long-period abrasion cumulant; and when the abrasion calculation of all discrete time periods is completed, outputting a long-period abrasion accumulation amount, otherwise, carrying out data exchange on the transient vibration abrasion calculation and the long-period abrasion accumulation calculation of the fuel rod. According to the method, the nonlinear dynamic modeling problem of the fuel rod-grillwork system and the cross-scale problem of transient abrasion rate and long-period abrasion accumulation are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel rod vibration abrasion analysis, and particularly relates to a cross-scale analysis method for long-term vibration abrasion of pressurized water reactor fuel rods. Background Art

[0002] A pressurized water reactor fuel assembly consists of an assembly skeleton and fuel rods. The fuel rods are composed of fuel pellets, cladding, gas cavity springs, end plugs, etc., and are fixed by clamping with multiple positioning grids. During the operation of the reactor, the fuel assembly will be subjected to the high-speed scouring of the coolant for a long time, which will induce the flow-induced vibration of the fuel rods, and then cause the fretting abrasion behavior between the fuel rods and the grids. Therefore, accurately simulating the vibration abrasion behavior of fuel rods and effectively predicting the long-term abrasion accumulation of fuel rods are crucial for the independent design of nuclear fuel and the evaluation of service performance.

[0003] The traditional engineering analysis method for fuel rod vibration abrasion is a linear cumulative analysis method based on random vibration theory and classical sliding abrasion theory. The main problems existing in this analysis method are:

[0004] The model is too simplified and does not consider the nonlinear effects of the fuel rod-grid system: The premise of random vibration theory is the modal analysis of fuel rods, and modal analysis is carried out for linear systems. Therefore, the traditional analysis method cannot consider any nonlinear effects.

[0005] The accuracy is insufficient and cannot represent the real vibration behavior of fuel rods: The root mean square amplitude of the fuel rod established by random vibration theory represents an average vibration amount of the fuel rod in a completely ideal state, while the real fuel rod is in a highly random motion state.

[0006] The envelope is insufficient and the abrasion accumulation calculation process is overly simplified: The traditional analysis method is based on the average amplitude and estimates the total abrasion amount in the form of simple harmonic motion at the first natural frequency. In the real motion state of the fuel rod, both the vibration amplitude and frequency are changing. Therefore, the slip distance and abrasion amount estimated by the traditional analysis method are not conservative enough.

[0007] So far, no solution that can effectively predict the long-term vibration abrasion of fuel rods has been seen. Therefore, developing a cross-scale analysis method suitable for the long-term vibration abrasion of pressurized water reactor fuel rods is of great significance for engineering design and evaluation. Summary of the Invention

[0008] In view of the above deficiencies in the prior art, the present invention provides a cross-scale analysis method for long-term vibration abrasion of pressurized water reactor fuel rods to solve the problems of nonlinear dynamics modeling of the fuel rod-grid system and the cross-scale problems of transient abrasion rate and long-term abrasion accumulation, and finally realize the high-precision prediction and analysis of the vibration abrasion behavior of fuel rods throughout their service life.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows: A cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod, comprising the following steps:

[0010] S1. By calculating the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life, obtain the external excitation load information received by the fuel rod bundle under different deformation conditions;

[0011] S2. Based on the geometric deformation characteristics and the external excitation load information, perform an initialization operation on the vibration abrasion calculation of the pressurized water reactor fuel rod;

[0012] S3. Perform transient calculation of the vibration abrasion of the pressurized water reactor fuel rod for the current discrete time period to obtain the abrasion rate;

[0013] S4. Calculate the long-period abrasion accumulation amount according to the abrasion rate;

[0014] S5. Determine whether the abrasion calculation for all discrete time periods is completed. If so, output the long-period abrasion accumulation amount; otherwise, proceed to S6;

[0015] S6. Perform data exchange between the transient vibration abrasion calculation and the long-period abrasion accumulation calculation of the fuel rod, and return to S3.

[0016] The beneficial effects of the present invention are as follows: The present invention proposes a method that combines the theories of vibration mechanics, solid mechanics, and fluid mechanics, realizing the coupled calculation of fuel rod vibration abrasion analysis, fuel rod thermodynamics deformation analysis, and fuel rod bundle computational fluid dynamics analysis; and realizing the cross-time-scale coupled calculation of the transient vibration abrasion calculation and the long-period abrasion accumulation calculation of the fuel rod, which can be used for the service performance evaluation of the vibration abrasion of the pressurized water reactor fuel rod. Compared with traditional engineering analysis methods, the geometric information, material information, fuel rod-grid clamping state, and coolant load conditions considered by the present invention are more complete, with higher generality; a reasonable mathematical model is adopted in the transient vibration abrasion calculation to replace the traditional empirical model, with higher calculation accuracy and conservativeness.

[0017] Further, the specific content of S1 is as follows:

[0018] Use finite element analysis software to model the nuclear thermal-hydraulic coupling calculation of a single pressurized water reactor fuel rod, and obtain the geometric information of the radial deformation varying with time at different height positions of the fuel rod, so as to obtain the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life;

[0019] Use computational fluid dynamics software to model the hydrodynamic model of the fuel rod bundle;

[0020] Based on the hydrodynamic model, taking the geometric deformation characteristics as the geometric input conditions of the calculation working conditions, a plurality of signal detection points are equidistantly set along the length direction on the surface of the fuel rod, and the frequency-domain data of the pressure at each signal point under the action of the coolant flow velocity during normal operation is calculated and obtained;

[0021] Based on the frequency-domain data, the pressure data in the time domain is obtained through Fourier transform to acquire the external excitation load information received by the fuel rod bundle under different deformation conditions, wherein the external excitation load information is used as the input for the transient vibration abrasion calculation in S3.

[0022] The beneficial effects of the above further solution are as follows: The characteristics of the geometric deformation of the fuel rod throughout its service life are fully considered, making the geometric boundary of the hydrodynamic calculation model more accurate. At the same time, the calculated geometric deformation history will also be used as an important input for the subsequent vibration abrasion calculation, making the geometric boundaries of the fuel rod vibration calculation model and the abrasion calculation model more accurate.

[0023] Furthermore, the specific content of S2 is as follows:

[0024] Determine the geometric dimensions of the initial state of the fuel rod-grid system; determine the irradiation models of the cladding, fuel pellets, and grid materials; determine the clamping boundary conditions between the grid and the fuel rod, and the initial state is three-point elastic support plus rotational constraint;

[0025] With reference to the geometric deformation characteristics and the external excitation load information, implement a non-fixed-step time discretization strategy for the entire calculation period, wherein the basis for the time discretization strategy is the change in the outer diameter of the cladding and the change trend of the external excitation frequency-domain spectrum;

[0026] According to the discrete time periods, determine the radial geometric dimensions of the fuel rod within each time period based on the obtained geometric deformation characteristics;

[0027] According to the discrete time periods, determine the pressure time-domain signals at multiple signal points on the surface of the fuel rod within each time period based on the obtained external excitation load information, and complete the initialization operation for the vibration abrasion calculation of the pressurized water reactor fuel rod, wherein the pressure time-domain signals are the external excitation information in the time domain.

[0028] The beneficial effects of the above further solution are as follows: Obtain more detailed input conditions for the vibration abrasion calculation of the fuel rod; the non-fixed-step time discretization strategy can more effectively consider the process characteristics of the geometric deformation of the fuel rod with the increase of burnup.

[0029] Furthermore, the specific content of S3 is as follows:

[0030] Construct a three-dimensional non-linear dynamics model of the fuel rod;

[0031] Discretize the three-dimensional non-linear dynamics model of the fuel rod and solve the discretized three-dimensional non-linear dynamics model of the fuel rod to obtain the total slip amount of the fuel rod within the coolant action time T;

[0032] Based on the total slip, the abrasion rate of each fuel rod-grid contact position is calculated using the abrasion rate model.

[0033] Furthermore, the expression of the three-dimensional non-linear dynamics model of the fuel rod is as follows:

[0034]

[0035] where E(Bu) represents the equivalent Young's modulus of the fuel rod at different burnups, I(Bu) represents the equivalent cross-sectional moment of inertia of the fuel rod at different burnups, rA(Bu) represents the linear density of the fuel rod at different burnups, w represents the lateral amplitude in the z-x plane, v represents the lateral amplitude in the y-x plane, x represents the position along the length of the fuel rod, t represents a certain moment, N i represents the number of external excitations in the z-x plane, i represents the i-th external excitation in the z-x plane, N k represents the number of external excitations in the y-x plane, k represents the k-th external excitation in the y-x plane, and represent the coolant loads at the and positions in the z-x plane and the y-x plane respectively, and this coolant load is obtained from the calculation of the external excitation load information. δ(·) represents the Dirac function, N j represents the number of grids, j represents the j-th grid, represents the position of the j-th grid in the length direction of the fuel rod, represents the position of the k-th external excitation in the y-x plane, represents the position of the i-th external excitation in the z-x plane, represents the normal support force in the z-x plane at the j-th grid, represents the tangential frictional force generated in the y-x plane, represents the normal support force in the y-x plane at the j-th grid, represents the tangential frictional force generated in the z-x plane.

[0036] The beneficial effect of the above further solution is: obtaining the important input conditions in the abrasion calculation, the slip amount and the real-time change of the pressing force at the fuel rod-grid clamping position.

[0037] Furthermore, the expression of the abrasion rate is as follows:

[0038]

[0039] where, represents the abrasion rate, H represents the cladding hardness, T represents the entire calculation time, S represents the abrasion coefficient, l(t) represents the slip distance at time t, which is obtained from the transient vibration abrasion calculation of w(x,t) and v(x,t), and P(t) represents the spring normal load at time t, which is obtained from the tangential frictional force calculated by the transient vibration abrasion calculation and the normal support force represents the total slip amount.

[0040] The beneficial effect of the above further solution is: According to the three-dimensional fuel rod vibration calculation results, the abrasion rate at each contact position of each grid can be calculated.

[0041] Further, the specific content of S4 is:

[0042] According to the abrasion rate, calculate the abrasion volume within the current discrete time period, and according to the abrasion volume, calculate the abrasion depth at each boss / spring position respectively;

[0043] Starting from the first discrete time period to the current discrete time period, cumulative calculation is carried out, and the long-term abrasion cumulative amount is obtained by obtaining the abrasion depth at each contact position.

[0044] Further, the expression of the long-term abrasion cumulative amount is as follows:

[0045]

[0046] where h total represents the long-term abrasion cumulative amount, h n represents the abrasion depth at each boss / spring position, n represents the discrete time period, V wear represents the abrasion volume within the current discrete time period n, L contact represents the width of the contact surface between the boss / spring and the fuel rod, and D represents the diameter of the fuel rod.

[0047] The beneficial effect of the above further solution is: The total abrasion volume and abrasion depth within the current discrete time period can be obtained through the abrasion rate; the abrasion depth provides important input conditions for the subsequent iterative calculation.

[0048] Further, the specific content of S6 is:

[0049] Use the calculated long-term abrasion cumulative amount and the radial geometric dimensions of the fuel rod in the next discrete time period to update the clamping relationship at each contact position between the fuel rod and the grid;

[0050] Call the external excitation load in the next discrete time period as the input for the transient vibration abrasion calculation;

[0051] Generate the material properties to be used in the next discrete time period based on the irradiation models of the cladding, fuel pellets, and spacer materials, which are used as the input for the transient vibration wear calculation in the next discrete time period.

[0052] The beneficial effects of the above further solution are as follows: The wear amount is cumulatively increased in a progressive manner. Through the non-fixed-step time discretization strategy, the calculated result of wear accumulation is closer to the wear characteristics of each operation cycle in the actual reactor. At the same time, it provides important input for the geometric size update and clamping force in the next stage. Description of the Drawings

[0053] Figure 1 It is the flowchart of the method of the present invention.

[0054] Figure 2 It is the three-dimensional vibration schematic diagram of the fuel rod of the present invention. Detailed Embodiments

[0055] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0056] Embodiment

[0057] As Figure 1 shown, the present invention provides a cross-scale analysis method for long-term vibration wear of a pressurized water reactor fuel rod, and its implementation method is as follows:

[0058] S1. By calculating the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life, obtain the external excitation load information received by the fuel rod bundle under different deformation conditions, and its implementation method is as follows:

[0059] Use finite element analysis software to model the nuclear-thermal coupling calculation of a single pressurized water reactor fuel rod, and obtain the geometric information of the radial deformation of the fuel rod at different height positions over time, so as to obtain the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life;

[0060] Use computational fluid dynamics software to model the hydrodynamic model of the fuel rod bundle;

[0061] Based on the hydrodynamic model, use the geometric deformation characteristics as the geometric input conditions of the calculation working condition, set a plurality of signal detection points at equal intervals along the length direction on the surface of the fuel rod, and calculate the frequency-domain data of the pressure at each signal point under the action of the normal operating coolant flow rate;

[0062] Based on the frequency-domain data, the pressure data in the time domain is obtained through Fourier transform to acquire the external excitation load information received by the fuel rod bundle under different deformation conditions. Among them, the external excitation load information is used as the input for the transient vibration abrasion calculation in S3.

[0063] In this embodiment, based on a commercial analysis program, the geometric deformation history of the fuel rod throughout its life cycle and the external excitation of the coolant received by the fuel rod bundle under different deformation conditions are calculated as follows:

[0064] 1.1. Use the finite element analysis software ABAQUS to establish a nuclear thermal-hydraulic coupling calculation model for a single fuel rod, obtain the parameter information of the radial deformation varying with time at different heights of the fuel rod, store the geometric information of the fuel rod after radial deformation every 30 days, a total of 18 times, and use this geometric information as the input condition to carry out computational fluid dynamics (CFD) modeling;

[0065] 1.2. Use the computational fluid dynamics software ANSYS-FLUENT to establish a hydraulic model of a 5x5 fuel rod bundle (with spacer grids). Take the 18 geometric features obtained in 1.1 as the geometric input conditions for 18 calculation cases. Set 50 signal detection points equidistantly along the length direction on the surface of the fuel rod, calculate the frequency-domain data of the pressure at each signal point under the action of the coolant flow velocity during normal operation, and then obtain the pressure data in the time domain through Fourier transform as the input condition for subsequent transient calculations. Among them, the hydraulic model is a common existing model and will not be specifically described here.

[0066] S2. Based on the geometric deformation characteristics and the external excitation load information, perform an initialization operation on the vibration abrasion calculation of the pressurized water reactor fuel rod. The implementation method is as follows:

[0067] Determine the geometric dimensions of the initial state of the fuel rod - spacer grid system; determine the irradiation models of the cladding, pellet, and spacer grid materials; determine the clamping boundary conditions between the spacer grid and the fuel rod, and the initial state is three-point elastic support plus rotational constraint;

[0068] Refer to the geometric deformation characteristics and the external excitation load information, and implement a non-uniform time discretization strategy for the entire calculation period. Among them, the basis for the time discretization strategy is the change in the outer diameter of the cladding and the change trend of the external excitation frequency-domain spectrum;

[0069] According to the discrete time periods, determine the radial geometric dimensions of the fuel rod within each time period based on the obtained geometric deformation characteristics;

[0070] According to the discrete time periods, determine the pressure time-domain signals at multiple signal points on the surface of the fuel rod within each time period based on the obtained external excitation load information, and complete the initialization operation of the vibration abrasion calculation of the pressurized water reactor fuel rod. Among them, the pressure time-domain signal is the external excitation information in the time domain.

[0071] In this embodiment, a self-written program is used to initialize the calculation of fuel rod vibration abrasion, which is specifically as follows:

[0072] 2.1. Determine the geometric dimensions of the fuel rod-grid system in the initial state (unirradiated), including the fuel rod diameter, length, active section length, and grid clamping point coordinates; determine the irradiation models of the cladding, pellet, and grid materials (including models of changes in Young's modulus, Poisson's ratio, density, etc. with irradiation); determine the clamping boundary conditions between the grid and the fuel rod, and the initial state is three-point elastic support plus rotational constraint.

[0073] 2.2. Refer to the radial geometric information of the fuel rod obtained in 1.1 and the external excitation load information obtained in 1.2, and implement a non-fixed-step time discretization strategy for the entire calculation period. The discretization is based on the change in the outer diameter of the cladding and the change trend of the external excitation frequency domain spectrum. Increase the number of discrete points in the interval with rapid changes and decrease the number of discrete points in the interval with stable changes. Here, it is assumed that the discretization is into N time periods.

[0074] 2.3. According to the time periods discretized in 2.2, determine the radial geometric dimensions of the fuel rod within each time period based on the calculation results in 1.1.

[0075] 2.4. According to the time periods discretized in 2.2, determine the pressure time-domain signals of 50 signal points on the surface of the fuel rod within each time period based on the calculation results in 1.2.

[0076] S3. Perform transient calculations on the vibration abrasion of the PWR fuel rod for the current discrete time period to obtain the abrasion rate. The implementation method is as follows:

[0077] Construct a three-dimensional non-linear dynamics model of the fuel rod;

[0078] Discretize the three-dimensional non-linear dynamics model of the fuel rod and solve the discretized three-dimensional non-linear dynamics model of the fuel rod to obtain the total slip of the fuel rod within the coolant action time T.

[0079] Based on the total slip, use the abrasion rate model to calculate the abrasion rate at each fuel rod-grid contact position.

[0080] In this embodiment, a self-written program is used to perform transient calculations on the vibration abrasion of the fuel rod for the current discrete time period (n), which is specifically as follows:

[0081] 3.1. Establish a three-dimensional non-linear dynamics model of the fuel rod based on the Bernoulli-Euler beam model. The calculation model is as Figure 2 shown, and the control equation is as follows:

[0082]

[0083] Among them, E(Bu) represents the equivalent Young's modulus of the fuel rod at different burnups, I(Bu) represents the equivalent cross-sectional moment of inertia of the fuel rod at different burnups, rA(Bu) represents the linear density of the fuel rod at different burnups, w represents the transverse amplitude in the z-x plane, v represents the transverse amplitude in the y-x plane, x represents the position along the length of the fuel rod, t represents a certain moment, N i represents the number of external excitations in the z-x plane, i represents the i-th external excitation in the z-x plane, N k represents the number of external excitations in the y-x plane, k represents the k-th external excitation in the y-x plane, and respectively represent the coolant loads at the and positions in the z-x plane and the y-x plane. This coolant load is derived from the calculation of the external excitation load information. δ(·) represents the Dirac function, N j represents the number of grids, j represents the j-th grid, represents the position of the j-th grid in the length direction of the fuel rod, represents the position of the k-th external excitation in the y-x plane, represents the position of the i-th external excitation in the z-x plane, represents the normal support force in the z-x plane at the j-th grid, represents the tangential frictional force generated in the y-x plane, represents the normal support force in the y-x plane at the j-th grid, represents the tangential frictional force generated in the z-x plane.

[0084] The above formula is discretized by the second-order Galerkin method, and the control equation is solved by the fourth-order Runge-Kutta method to calculate the total slip of the fuel rod during the coolant action time T;

[0085] 3.2. Calculate the abrasion rate for each fuel rod-grid contact position based on the abrasion rate model in Archard's metal sliding theory, as shown in the following formula:

[0086]

[0087] Among them, represents the abrasion rate, H represents the cladding hardness, T represents the entire calculation time, S represents the abrasion coefficient, l(t) represents the slip distance at time t, and this slip distance is obtained from the w(x,t) and v(x,t) calculated by the transient vibration abrasion calculation. P(t) represents the spring normal load at time t, and this spring normal load is obtained from the tangential frictional force and the normal support force represents the total slip.

[0088] S4. Calculate the long - term abrasion cumulative amount based on the abrasion rate, and the implementation method is as follows:

[0089] Calculate the abrasion volume within the current discrete time period according to the abrasion rate, and calculate the abrasion depth at each boss / spring position based on the abrasion volume;

[0090] Perform cumulative calculation from the first discrete time period to the current discrete time period. By obtaining the abrasion depth at each contact position, the long - term abrasion cumulative amount is obtained.

[0091] In this embodiment, a self - written program is used to calculate the long - term abrasion cumulative amount, which is specifically as follows:

[0092] 4.1. Based on the abrasion rate obtained in 3.2 Calculate the abrasion volume V within the current discrete time period (n) wear , and calculate the abrasion depth at each boss / spring position according to the abrasion depth calculation model as shown in the following formula:

[0093]

[0094] 4.2. Cumulatively calculate the abrasion depth at each contact position from the 1st discrete time period to the current discrete time period (n), as shown in the following formula.

[0095]

[0096] Among them, h total represents the long - term abrasion cumulative amount, h n represents the abrasion depth at each boss / spring position, n represents the discrete time period, V wear represents the abrasion volume within the current discrete time period n, L contact represents the width of the contact surface between the boss / spring and the fuel rod, and D represents the diameter of the fuel rod.

[0097] S5. Determine whether the abrasion calculation for all discrete time periods is completed. If so, output the long - term abrasion cumulative amount; otherwise, go to S6;

[0098] S6. Perform data exchange between the transient vibration abrasion calculation of the fuel rod and the long - term abrasion cumulative calculation, and return to S3. The implementation method is as follows:

[0099] Use the calculated long - term abrasion cumulative amount and the radial geometric dimensions of the fuel rod in the next discrete time period to update the clamping relationship at each contact position between the fuel rod and the grid;

[0100] Call the external excitation load in the next discrete time period as the input for the transient vibration abrasion calculation;

[0101] Generate the material properties to be used in the next discrete time period based on the irradiation models of the cladding, pellets, and spacer grid materials, and use them as the input for the transient vibration wear calculation in the next discrete time period.

[0102] In this embodiment, a self-written program is used to exchange data between the transient vibration wear calculation and the long-term wear accumulation calculation of the fuel rod. The specific steps are as follows:

[0103] 6.1. Update the clamping relationship between the fuel rod and the spacer grid at each contact position, including the clamping force, the deformation of the spring / rigid projection, and the determination of the spacer grid - fuel rod gap, based on the wear depth at each contact position calculated in 4.2 and the radial geometric dimensions of the fuel rod in the next discrete time period (n + 1) calculated in 2.3.

[0104] 6.2. Call the external excitation load in the next discrete time period (n + 1) as the input for the transient vibration wear calculation according to the calculation results in 2.4.

[0105] 6.3. Generate the material properties to be used in the next discrete time period (n + 1) based on the irradiation models of the cladding, pellets, and spacer grid materials, and use them as the input for the subsequent transient vibration wear calculation.

[0106] In summary, through the above design, the present invention solves the problems of non-linear dynamics modeling of the fuel rod - spacer grid system and the cross-scale problems of transient wear rate and long-term wear accumulation, and finally realizes the high-precision prediction and analysis of the vibration wear behavior of the fuel rod throughout its service life.

Claims

1. A cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod, characterized in that It includes the following steps: S1. By calculating the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life, obtain the external excitation load information received by the fuel rod bundle under different deformation conditions; S2. Based on the geometric deformation characteristics and the external excitation load information, perform an initialization operation on the vibration abrasion calculation of the pressurized water reactor fuel rod; S3. Perform transient calculation of the vibration abrasion of the pressurized water reactor fuel rod for the current discrete time period to obtain the abrasion rate; S4. Calculate the long-term abrasion accumulation based on the abrasion rate; S5. Determine whether the abrasion calculation for all discrete time periods is completed. If so, output the long-term abrasion accumulation. Otherwise, go to S6; S6. Perform data exchange between the transient vibration abrasion calculation and the long-term abrasion accumulation calculation of the fuel rod, and return to S3.

2. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 1, wherein The specific content of S1 is as follows: Using finite element analysis software, model the nuclear thermal-hydraulic coupling calculation of a single pressurized water reactor fuel rod to obtain the geometric information of the radial deformation of the fuel rod at different height positions over time, so as to obtain the geometric deformation characteristics of the pressurized water reactor fuel rod during the overall service life; Using computational fluid dynamics software, model the hydraulic model of the fuel rod bundle; Based on the hydraulic model, taking the geometric deformation characteristics as the geometric input conditions of the calculation working condition, set multiple signal detection points at equal intervals along the length direction on the surface of the fuel rod, and calculate the frequency-domain data of the pressure at each signal point under the action of the normal operating coolant flow rate; Based on the frequency-domain data, obtain the pressure data in the time domain through Fourier transform to obtain the external excitation load information received by the fuel rod bundle under different deformation conditions, where the external excitation load information is used as the input for the transient vibration abrasion calculation in S3.

3. The cross-scale analysis method for long-term vibration abrasion of a pressurized water reactor fuel rod according to claim 1, characterized in that, The specific content of S2 is as follows: Determine the geometric dimensions of the initial state of the fuel rod-grid system; determine the irradiation models of the cladding, pellet, and grid materials; determine the clamping boundary conditions between the grid and the fuel rod, and the initial state is three-point elastic support plus rotational constraint; Referring to the geometric deformation characteristics and the external excitation load information, implement a non-uniform time discretization strategy for the entire calculation period, where the basis of the time discretization strategy is the change in the outer diameter of the cladding and the change trend of the external excitation frequency-domain spectrum; According to the discrete time periods, determine the radial geometric dimensions of the fuel rod within each time period based on the obtained geometric deformation characteristics; According to the discrete time periods, determine the time-domain signals of the pressure at multiple signal points on the surface of the fuel rod within each time period based on the obtained external excitation load information, and complete the initialization operation of the vibration abrasion calculation of the pressurized water reactor fuel rod, where the time-domain signal of the pressure is the external excitation information in the time domain.

4. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 1, wherein The specific content of S3 is as follows: Construct a three-dimensional non-linear dynamics model of the fuel rod; Discretize the three-dimensional non-linear dynamics model of the fuel rod, and solve the discretized three-dimensional non-linear dynamics model of the fuel rod to obtain the total slip of the fuel rod during the coolant action time T; Based on the total slip, use the abrasion rate model to calculate the abrasion rate at each fuel rod-grid contact position.

5. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 4, characterized in that The expression of the three-dimensional non-linear dynamics model of the fuel rod is as follows: Among them, E(Bu) represents the equivalent Young's modulus of the fuel rod at different burnups, I(Bu) represents the equivalent cross-sectional moment of inertia of the fuel rod at different burnups, rA(Bu) represents the linear density of the fuel rod at different burnups, w represents the transverse amplitude in the z-x plane, v represents the transverse amplitude in the y-x plane, x represents the position along the length of the fuel rod, t represents a certain moment, N i represents the number of external excitations outside the z-x plane, i represents the i-th external excitation in the z-x plane, N k represents the number of external excitations outside the y-x plane, k represents the k-th external excitation in the y-x plane, and respectively represent the coolant loads at the and positions in the z-x plane and the y-x plane. This coolant load is derived from the calculation of the external excitation load information. δ(·) represents the Dirac function, N j represents the number of spacer grids, j represents the j-th spacer grid, represents the position of the j-th spacer grid in the length direction of the fuel rod, represents the position of the k-th external excitation in the y-x plane, represents the position of the i-th external excitation in the z-x plane, represents the normal support force in the z-x plane at the j-th spacer grid, represents the tangential frictional force generated in the y-x plane, represents the normal support force in the y-x plane at the j-th spacer grid, represents the tangential frictional force generated in the z-x plane.

6. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 5, characterized in that The expression of the abrasion rate is as follows: Among them, represents the abrasion rate, H represents the cladding hardness, T represents the entire calculation time, S represents the abrasion coefficient, l(t) represents the slip distance at time t, and this slip distance is obtained from the w(x,t) and v(x,t) calculated by transient vibration abrasion calculation. P(t) represents the spring normal load at time t, and this spring normal load is obtained from the tangential frictional force calculated by transient vibration abrasion calculation and the normal support force represents the total slip amount.

7. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 1, characterized in that The specific content of S4 is as follows: Calculate the abrasion volume within the current discrete time period according to the abrasion rate, and calculate the abrasion depth at each position of the ribs / springs respectively based on the abrasion volume. Perform cumulative calculations from the first discrete time period to the current discrete time period. By obtaining the abrasion depths at each contact position, the long-term abrasion cumulative amount is obtained.

8. The cross-scale analysis method for long-period vibration abrasion of a pressurized water reactor fuel rod according to claim 7, characterized in that The expression of the long-term abrasion cumulative amount is as follows: Among them, h total represents the long-term abrasion cumulative amount, h n represents the abrasion depth at each rib / spring position, n represents the discrete time period, V wear represents the abrasion volume within the current discrete time period n, L contact represents the width of the contact surface between the rib / spring and the fuel rod, and D represents the fuel rod diameter.

9. The cross-scale analysis method for long-term vibration abrasion of a pressurized water reactor fuel rod according to claim 1, characterized in that The specific content of S6 is as follows: Use the calculated long-term abrasion cumulative amount and the radial geometric dimensions of the fuel rod in the next discrete time period to update the clamping relationship at each contact position between the fuel rod and the grid. Call the external excitation load in the next discrete time period as the input for transient vibration abrasion calculation. Generate the material properties to be used in the next discrete time period according to the irradiation models of the cladding, fuel pellet, and grid materials, and use them as the input for transient vibration abrasion calculation in the next discrete time period.

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