CFD analysis-based fuel assembly test piece design method and calculation device

Abstract

The invention discloses a CFD analysis-based fuel assembly test piece design method and a calculation device, and belongs to the field of nuclear power. The CFD analysis-based fuel assembly test piece design method comprises the following steps that a fuel assembly model with a fuel rod matrix and a fuel grid is provided, a test piece model comprising an electric heating rod matrix and a test piece grid is established, the electric heating rod matrix is smaller than the fuel rod matrix, and the test grid has variable geometric parameters; performing CFD analysis on the fuel assembly model and the test piece model, and respectively calculating test parameters; iterating the variable geometric parameters until the difference between the test parameters of the fuel assembly model and the test piece model is smaller than a given threshold value, and finally obtaining the fuel assembly test piece model. According to the method, the real fuel assembly model can be approximately equivalently replaced by the simplified test piece model, the CHF test cost is reduced, and the test efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and particularly relates to a design method and a calculation device for a fuel assembly test piece based on CFD analysis. Background Art

[0002] Critical heat flux (CHF) is an important limiting thermal-hydraulic parameter related to reactor safety, and is closely related to the safety and economy of the reactor. CHF is affected by the combined effects of hydrodynamic and thermodynamic phenomena, and the mechanism is complex. Currently, it is generally obtained through CHF tests. Conventional CHF tests need to be carried out using real fuel assemblies, which are costly and risky. Some technical solutions propose to replace real fuel rods with electric heating rods to simulate the heat generation of fuel assemblies in order to reduce costs and improve safety; however, on the one hand, fuel assemblies usually have a complex structure, including 17×17 fuel rods, which are difficult to simulate; on the other hand, the current required for electric heating rods to simulate the heat generation of fuel rods is very high, and existing power supplies cannot meet the power supply requirements. Therefore, providing a simplified fuel assembly test piece has positive significance for reducing the cost of CHF tests, improving efficiency and safety. Summary of the Invention

[0003] The purpose of the present invention is to provide a design method for a fuel assembly test piece based on CFD analysis to simplify the structure of the CHF test piece. The present invention also provides a calculation device.

[0004] According to an embodiment of one aspect of the present invention, a design method for a fuel assembly test piece based on CFD analysis is provided, and the method includes the following steps:

[0005] Step a): Provide a fuel assembly model including a fuel rod matrix and a fuel spacer grid, and the parameters of the fuel assembly model include the fuel rod cladding wall, the dimensions and quantities of the fuel spacer grid, and the position parameters and geometric parameters of the springs, ribs, mixing vanes, solder joints and grooves of the fuel spacer grid, as well as the heat generation power of the fuel rods;

[0006] Step b): Establish a test piece model including an electric heating rod matrix and a test piece grid, the electric heating rod matrix is smaller than the fuel rod matrix, the electric heating rods and the fuel rods have the same diameter and heat generation power, the test piece grid of the test piece model has the same thickness as the fuel spacer grid, and the test piece grid of the test piece model has variable geometric parameters, and the variable geometric parameters include the positions and geometric structures of the springs, ribs, mixing vanes, solder joints and grooves of the grid;

[0007] Step c): Perform CFD analysis in the flow field on the fuel assembly model and the test piece model respectively, and calculate and check parameters respectively, and the check parameters include the transverse flow field distribution, the temperature field distribution, the transverse flow intensity and the temperature distribution uniformity;

[0008] Step d): When the difference between any of the inspection parameters calculated based on the fuel assembly model and the test piece model exceeds a given threshold, one or more of the variable geometric parameters of the test piece model are changed, and step c) is repeated for iterative calculation until the differences of all the inspection parameters do not exceed the given threshold; the test piece model at this time is used as the fuel assembly test piece model.

[0009] Through this method, it is possible to effectively achieve the equivalent replacement of a full-size standard fuel assembly with a simplified test piece, reduce the test cost, and reduce the resource consumption of simulation tests. The fuel assembly test piece manufactured based on the fuel assembly test piece model obtained by this method can be used for CHF tests and obtain CHF test results with good consistency under real working conditions.

[0010] Further, in some embodiments, in step a), the fuel rod matrix is set as a 17×17 matrix; in step b), the electric heating rod matrix is set as a 5×5 matrix.

[0011] 17×17 is the fuel assembly specification commonly used in commercial reactors such as CAP1400; a 5×5 test piece can accurately characterize the fluid characteristics of a real fuel assembly on the basis of effectively simplifying the test piece structure.

[0012] Further, in some embodiments, in step c), the calculation region of the geometric model used in the CFD analysis is set as the stable region of the heating section of the fuel assembly model and the test piece model, and the stable region of the heating section is the region where the flow and heat transfer characteristics of the flow field are not affected by the inlet effect and the outlet backflow.

[0013] Further, in some embodiments, in step c), the physical model adopted in the CFD analysis includes a fluid region and two solid regions. The medium in the fluid region is the coolant, and the solid regions are the grid region and the rod region respectively. The grid region is set as the fuel grid or the test piece grid, and the rod region is set as the fuel rod or the electric heating rod.

[0014] Further, in some embodiments, in step c), the solid medium is set as zirconium alloy.

[0015] Further, in some embodiments, in step d), the calculation method of the transverse flow intensity SFI is:

[0016]

[0017] where u x is the fluid velocity in the x direction in the flow field, u zis the fluid velocity in the z - direction in the flow field, u y,bulk is the average axial fluid velocity in the flow field, A is the cross - sectional area of the calculation region, where the x and z directions are in the radial plane of the fuel assembly model or the test piece model, and y is the axis of the fuel assembly model or the test piece model.

[0018] Further, in some embodiments, in step d), the temperature distribution uniformity is characterized by the standard deviation of the temperature distribution T dev and its calculation method is:

[0019]

[0020] where T i is the fluid temperature at grid i in the fuel assembly model or the test piece model, T avg is the average fluid temperature of the process of the calculation cross - section, and A is the cross - sectional area of the calculation cross - section.

[0021] Further, in some embodiments, the given threshold does not exceed 30% of the corresponding test parameter of the fuel assembly model.

[0022] Further, in some embodiments, in step b), the test piece model further includes a support structure, the support structure is arranged between the test piece grids adjacent axially in the test piece model, and the support structure satisfies:

[0023] In step c), the influence of the support structure on the calculation result of the CFD analysis is less than a given limit value;

[0024] When the electric heating rod is in the energized state, the support structure provides radial support for the electric heating rod, so that the bending degree of the electric heating rod does not exceed a given bending limit value.

[0025] According to an embodiment of another aspect of the present invention, a computing device is provided, the computing device includes a memory and a processor, wherein, the memory stores a computing program, when the computing program is executed by the processor, it can implement the fuel assembly test piece design method based on CFD analysis provided in any of the foregoing embodiments. Brief Description of the Drawings

[0026] Figure 1 is a schematic diagram of the fuel grid structure in an embodiment;

[0027] Figure 2 is a schematic diagram of the cross - sectional structure of the fuel grid in an embodiment;

[0028] Figure 3 is a schematic diagram of the structure of the test piece grid in an embodiment;

[0029] Figure 4 Schematic diagram of the fuel assembly test piece structure in an embodiment;

[0030] Figure 5 Schematic diagram of the support structure in an embodiment;

[0031] Figure 6 Flowchart of the design method of the fuel assembly test piece based on CFD analysis in an embodiment.

[0032] Meanings of the reference numerals: 1 - metal strip; 2 - mixing wing; 3 - spring; 4 - rigid protrusion; 5 - fuel rod; 6 - solder joint; 7 - test piece grid; 8 - support grid; 9 - electric heating rod; 10 - support structure; 11 - step a); 12 - step b); 13 - step c); 14 - step d).

[0033] The purpose of the above-mentioned drawings is to make a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, rather than aiming to limit the present invention. For the sake of concise expression, the above-mentioned drawings only schematically show the structures related to the technical features of the present invention, and do not strictly draw the complete structure and all details according to the actual proportion. Detailed implementation manners

[0034] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0035] The mention of "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of this article. The phrase appearing at various positions in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments in this article can be combined with other embodiments without structural conflicts.

[0036] In the description of this article, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "coupling" should be understood in a broad sense. For example, it can be a movable connection, a fixed connection or integrated. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to specific situations.

[0037] In the description of this article, terms indicating orientation or positional relationships such as "upper", "lower", "left", "right", "lateral", "longitudinal", "height", "length", "width" are intended to accurately describe the embodiments and simplify the description, rather than limiting that the parts or structures involved must have a specific orientation, be installed or operated in a specific orientation, and cannot be understood as a limitation to the embodiments in this article.

[0038] In the description of this article, terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary-secondary relationship of the described technical features. In the description of this article, the meaning of "a plurality of" is at least two.

[0039] Critical Heat Flux (CHF) is an important limiting thermal-hydraulic parameter related to reactor safety, and its magnitude directly affects the safety and economy of the reactor. One of the thermal-hydraulic design criteria for pressurized water reactors is that departure from nuclear boiling (DNB) should not occur in the core under normal operation or medium-frequency accident conditions (i.e., Class I and Class II conditions). To quantitatively evaluate the margin of the reactor from the occurrence of departure from nuclear boiling, it is first necessary to determine the CHF value. CHF is determined by the combined effect of hydrodynamic and thermodynamic phenomena. Due to its complex mechanism, all current CHF correlations used for the licensing application of pressurized water reactor nuclear power plants are based on full-length fuel rod bundle CHF tests.

[0040] If real fuel assemblies are used to conduct rod bundle CHF tests, it involves the risk of radioactive material leakage, with high test costs, high risks, long cycles, and difficulties in collecting test data. At the same time, real fuel assemblies have a large number of fuel rods (usually 17×17), complex structures, large amounts of calculation and analysis work, and low efficiency. Further, if simulated electrically heated rods are used to replace real fuel rods, it is difficult for conventional power supplies to supply power to too many electrically heated rods simultaneously, resulting in difficulties in manufacturing simulated test pieces. Therefore, establishing a standardized and process-based pre-analysis method is of practical significance for reasonably and accurately predicting the influence of grid characteristics on coolant flow and heat transfer, and for exposing potential risks in the implementation process of CHF tests in advance.

[0041] As Figure 1 and Figure 2 shown, the fuel grid includes multiple metal strips 1, and these metal strips 1 are vertically crossed to form a grid-like structure, and the installation positions of fuel rods 5 are formed in the grids. The metal strips 1 are welded together through welding points 6. Protruding springs 3 are provided on the walls of the metal strips 1 facing the fuel rods 5, and the springs 3 press the fuel rods 5 through elastic deformation; rigid protrusions 4 are also provided on the metal strips 1, and the rigid protrusions 4 have strong structural rigidity and can form radial limits on the fuel rods 5. Multiple inclined mixing wings 2 are provided at the top of the fuel grid. The structure of the mixing wings 2 is generally triangular and is usually arranged at the diagonal positions of the squares formed by the intersection of the metal strips 1. Under normal conditions, the cooling water flows along the axial direction of the fuel rods 5, and under the guiding action of the mixing wings 2, the flow direction changes. Combining Figure 3 with Figure 3The transverse flows in different directions indicated by the red and blue arrows. Further, grooves (not shown) for guiding the flow are provided on the surface of the metal strip 1. Under actual working conditions, the positions, dimensions, and specific shape structures of the mixing wing 2, spring 3, rigid projection 4, solder joint 6, and grooves will have complex and significant effects on the fluid behavior of the cooling water. During the process of using a small-sized fuel assembly test piece to replace the full-sized fuel assembly, there are complex mutual influences between the position parameters and geometric parameters of the above structures, making it difficult to ensure the accuracy of the simulation of the fuel assembly test piece.

[0042] To solve the above problems, an embodiment of one aspect of the present invention provides a design method for a fuel assembly test piece based on CFD (Computational Fluid Dynamics) analysis. By means of CFD simulation analysis, a large-scale fuel assembly is simplified into an equivalent small-scale test piece, while retaining the thermodynamic and hydrodynamic characteristics of the fuel assembly during the simplification of the structure, making it possible to use a test piece with electric heating rods to replace the real fuel assembly to carry out accurate CHF evaluation.

[0043] This method is as Figure 6 shown and includes the following steps:

[0044] Step a) 11: Provide a real fuel assembly model to be simulated. The real fuel assembly includes a fuel rod matrix and a fuel grid. In a preferred embodiment, the fuel assembly of the CAP1400 type reactor uses a 17×17 fuel rod matrix, and both the fuel rod cladding and the fuel grid use zirconium alloy. The parameters of the fuel assembly model include the thickness dimensions, quantities of the fuel rod cladding wall and the metal strip 1 of the fuel grid, and the key geometric features on the fuel grid. These key geometric features include: the quantities, position parameters, dimensions, and geometric profiles (such as the shapes and curvatures of the protruding parts of the spring 3 and the rigid projection 4) of the spring 3, rigid projection 4, solder joint 6, and groove structure; and the quantities, position parameters, angles, and profile structures (including the areas, shapes, and curvatures of the mixing wing 2) of the mixing wing 2. Additionally, it also includes the heat generation power data of the fuel rod 5.

[0045] The fuel assembly model can be modeled according to engineering data or directly called from an existing database.

[0046] Step b) 12: Establish a test piece model. Combining Figure 4 , the test piece model includes electric heating rods 9 and a test piece grid 7. In a preferred embodiment, the fuel assembly model of the CAP1400 type reactor is equivalently replaced by a 5×5 test piece model, in which the electric heating rods 9 are arranged in a 5×5 matrix. According to the different structures of the simulated fuel assembly, all of the 5×5 matrix can be set as electric heating rods 9, or the electric heating rod 9 at the central position can be replaced by a control rod guide tube (if any) in the fuel assembly.

[0047] The electric heating rod 9 has the same diameter as the fuel rod 5, and its rated power is the same as that of the fuel rods in the fuel assembly; combined with Figure 1 , the test piece grid 7 has the same thickness as the metal strip 1 of the fuel grid. The test piece grid 7 is also provided with mixing wings, springs, rigid protrusions, solder joints and groove structures. The parameters of these structures are used as the variable geometric parameters of the test piece grid 7, specifically including the positions and dimensions, geometric profiles, etc. of the spring, rigid protrusion, solder joint and groove structures, as well as the position and geometric structure of the mixing wing 2.

[0048] The initial structure of the test piece grid 7 is designed based on the structure of the fuel grid, and is constructed by replacing and splicing the fuel grid strips according to the flow direction of the coolant in the fuel grid area under actual working conditions. Specifically, the fuel grid under actual working conditions is geometrically modeled, and parameters such as the lattice arrangement form of the fuel grid, the lattice arrangement form of the guide tube grid (if any), the mixing wing arrangement form, and the gap between the peripheral rods and the flow channel wall are retained, so that the coolant forms an equivalent flow characteristic in the test piece grid 7 as in the fuel grid. Specifically, as Figure 3 shown, the coolant can form a regular transverse flow under the influence of the test piece grid 7 (as shown by the arrows in Figure 3 ), and the flow direction of the transverse flow, the intersection and symmetry relationship between the transverse flows in different directions are all consistent with the flow characteristics of the coolant in the actual fuel grid, so that the coolant flows uniformly in the model area.

[0049] According to the research of the present invention, replacing the 17×17 specification fuel assembly with a larger-scale test piece model such as a 6×6 matrix will lead to overly complex calculations. The increase in the number of electric heating rods results in a significant increase in power, and there are also difficulties in power supply; while a smaller-scale test piece such as a 4×4 matrix cannot accurately reflect the thermodynamic and hydrodynamic characteristics of the fuel assembly, and there will be relatively significant deviations in the CHF test results.

[0050] When using the electric heating rod to simulate the heat generation of the fuel rod, the current intensity in the electric heating rod is relatively high, and there is a risk of bending the electric heating rod due to the mutual influence of the electromagnetic forces between adjacent electric heating rods. Therefore, in the preferred embodiment, as Figure 4 shown, in the test piece model, a support grid 8 as a support structure is provided between adjacent test piece grids 7 to provide radial limit support for the electric heating rod 9. In a further preferred embodiment, as Figure 5As shown in the figure, it includes a support grid frame 8 and a support structure 10 arranged on the grid wall formed by the support grid frame 8. The support structure 10 is set as a rigid protrusion, and the support structure 10 can provide radial limit support for the electric heating rod 9, and its structural strength meets the requirement that when the electric heating rod is energized, the support structure 10 can support the electric heating rod 9 so that the bending degree of the electric heating rod 9 under the energized state does not exceed the given bending limit value. The size of the support structure 10 should be controlled to prevent the support structure 10 from interfering with the coolant flow behavior in the test piece grid frame 7 area. In some other embodiments, the support structure 10 can also be obtained by removing the mixing wings of the test piece grid frame 7 and removing the structures that have a greater impact on the coolant flow behavior. In some embodiments, when the distance between the test piece grid frames 7 is small, the support structure may not be provided.

[0051] Step c)13: Perform CFD analysis in the flow field for the fuel assembly model and the test piece model respectively.

[0052] The CFD analysis uses a geometric model that simulates the geometric structure and dimensions and a physical model that simulates the physical properties and physical parameters.

[0053] Among them, the calculation area of the geometric model is the stable area of the heating section of the fuel assembly model and the test piece model. The stable area of the heating section is defined as the area where the flow and heat transfer characteristics of the flow field medium are not affected by the inlet effect and the outlet backflow. The modeling and mesh generation of the geometric model can be achieved through the built-in functions of general CFD simulation software or through specially written programs.

[0054] The physical model includes a fluid region and two solid regions. The medium in the fluid region is set as the coolant, and for the embodiments where the simulation object is a pressurized water reactor, the medium is set as water. The two solid regions are respectively set as the grid frame region and the rod body region. For the CFD analysis calculation process for the fuel assembly model, the grid frame region is the fuel grid frame, and the rod body region is the fuel rod; for the CFD analysis calculation process for the test piece model, the grid frame region is the test piece grid frame, and the rod body region is the electric heating rod. According to different structural designs, the solid regions are set as corresponding materials so that the physical performance parameters (including specific heat capacity, density, thermal conductivity, etc.) of the grid frame region and the rod body region are consistent with the object to be simulated; in the analysis of the CAP1400 type reactor, the solid regions are set as zirconium alloy, and in other embodiments, they can also be set as materials such as stainless steel or nickel-based alloy. Among them, the physical performance parameters used in the fluid region and the solid regions can be retrieved from a public database or set manually according to the actual test results.

[0055] Through CFD analysis, the inspection parameters of the fuel assembly model and the test piece model in the flow field are calculated respectively, and the accuracy of the simulation of the fuel assembly model by the test piece model is determined by the difference of the inspection parameters. The inspection parameters include the transverse flow field distribution, the temperature field distribution, the transverse flow field intensity, and the temperature distribution uniformity.

[0056] Specifically, the calculation method of the transverse flow field intensity is as follows:

[0057]

[0058] wherein, the x and z directions are in the radial plane of the fuel rod or the electrically heated rod, y is the axial direction, and u x is the fluid velocity in the x direction in the flow field simulated and calculated, and u z is the fluid velocity in the z direction in the flow field, and u y,bulk is the average axial fluid velocity in the flow field, A is the cross-sectional area of the calculation region, and here the fluid velocity is the flow velocity of the coolant.

[0059] The temperature field distribution uniformity is characterized by the standard deviation of the temperature distribution, and its calculation method is as follows:

[0060]

[0061] wherein, T i is the fluid temperature at grid i in the fuel assembly model or the test piece model, and T avg is the average temperature of the fluid (coolant) in the flow field on the cross-section of the calculation region.

[0062] Step d)14: Compare the inspection parameters calculated for the fuel assembly model with those calculated for the test piece model respectively. When the differences between all the inspection parameters do not exceed the given threshold, it is considered that the test piece model at this time can accurately simulate the thermodynamic characteristics and hydrodynamic characteristics of the fuel assembly model, and can be used as the final fuel assembly test piece model. Then, a CHF simulation test piece is manufactured based on the corresponding geometric parameters of the model, and a CHF test analysis is carried out.

[0063] When any one of the inspection parameters exceeds the given threshold, the variable geometric parameters of the test piece model need to be adjusted and iterative calculations are performed until the differences between all the inspection parameters do not exceed the given threshold, and then the iteration stops. In a preferred embodiment, the given threshold can be set to 30% of the corresponding inspection parameter calculated based on the fuel assembly model. For example, for the standard deviation of the temperature distribution, when the value calculated based on the test piece model is within the range of 70%-130% of the calculation result based on the fuel assembly model, it is considered not to exceed the threshold, and if it exceeds this range, the variable geometric parameters of the test piece model need to be adjusted and iterated.

[0064] Specifically, the adjustment of variable geometric parameters includes but is not limited to: adjusting the angle, area, and geometric profile of the mixing wing; adjusting the positions and dimensions of the springs, rigid protrusions, and grooves; and adjusting the size, position, quantity, and shape of the solder joints under the condition of not affecting the structural strength. During the adjustment process, according to the specific calculation results combined with engineering experience, one of the variable geometric parameters can be selected for adjustment, or multiple parameters can be selected for adjustment.

[0065] The fuel assembly test piece model determined by the method provided in the above embodiment can be used to manufacture the finished fuel assembly test piece based on the structure and dimensions of the fuel assembly test piece model. The resulting finished fuel assembly test piece can replace the real fuel assembly to carry out the CHF analysis test, accurately reflect the flow and heat transfer characteristics of the coolant in the fuel assembly under specific working conditions, improve the efficiency of reactor safety assessment, and reduce the CHF test cost.

[0066] The fuel assembly test piece design method based on CFD analysis provided in the above embodiment can be implemented by the computing device provided in another embodiment of the present invention. The computing device includes a memory and a processor. The fuel assembly test piece design program is stored in the memory. When the fuel assembly test piece design program is executed by the processor, it can implement the fuel assembly test design method based on CFD analysis provided in the foregoing embodiment. Among them, the fuel assembly test piece design program can be written based on a general computer language and can also be programmed and implemented in a general or special computing program; the computing device can use a general computer or a special computing device, virtual machine, or cloud computing device. Specifically, in some embodiments, the computing device receives the fuel assembly model input by the operator in step a), or directly retrieves the fuel assembly model from an existing database and imports it into the fuel assembly test piece design program; further, the computing device supports the operator to complete the test piece model modeling in step b) in the fuel assembly test piece design program; the fuel assembly test piece design program can perform CFD analysis on the fuel assembly model and the test piece model to complete the calculation of the inspection parameters in step c); the computing device program supports the operator to adjust the variable geometric parameters in the fuel assembly test piece design program according to the calculation results and complete the iterative calculation, and finally output the fuel assembly test piece model.

[0067] The purpose of the above embodiment is to further elaborate on the present invention in combination with the drawings so that those skilled in the art can understand the technical concept of the present invention. Based on the disclosed content of the present invention, optimizing or equivalently replacing the involved method steps, and combining the implementation manners in different embodiments without conflict in structure and principle all fall within the protection scope of the present invention.

Claims

1. A fuel assembly test piece design method based on CFD analysis, characterized in that: The following steps are involved: Step a): providing a fuel assembly model including a fuel rod matrix and a fuel grid, wherein the parameters of the fuel assembly model include the size and quantity of the fuel rod cladding wall and the fuel grid, and the position parameters and geometric parameters of the springs, rigid convexities, mixing wings, welding points and grooves of the fuel grid, and the heating power of the fuel rods; Step b): establishing a test piece model including an electric heating rod matrix and a test piece grid, wherein the electric heating rod matrix is ​​smaller than the fuel rod matrix, the electric heating rods and the fuel rods have the same diameter and heating power, the test piece grid and the fuel grid have the same thickness, and the test piece grid of the test piece model has variable geometric parameters, and the variable geometric parameters include the positions and geometric structures of springs, rigid convexities, mixing wings, weld points and grooves of the grid; Step c): performing CFD analysis in the flow field on the fuel assembly model and the test piece model respectively, and calculating inspection parameters respectively, wherein the inspection parameters include lateral flow field distribution, temperature field distribution, lateral flow intensity and temperature distribution uniformity; Step d): when the difference between any one of the verification parameters calculated based on the fuel assembly model and the test piece model exceeds a given threshold, one or more of the variable geometric parameters of the test piece model are changed, and step c) is repeated to perform iterative calculation until the differences of all the verification parameters do not exceed the given threshold; The test piece model at this time is used as the fuel assembly test piece model.

2. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1, characterized in that: In the step a), the fuel rod matrix is ​​set as a 17×17 matrix; in the step b), the electric heating rod matrix is ​​set as a 5×5 matrix.

3. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1 or 2, characterized in that: In the step c), the calculation area of ​​the geometric model used in the CFD analysis is set to the heating section stable area of ​​the fuel assembly model and the test piece model, and the heating section stable area is the area where the flow and heat transfer characteristics of the flow field are not affected by the inlet effect and the outlet reflux.

4. The method for designing a fuel assembly test piece based on CFD analysis according to claim 3, characterized in that: In the step c), the physical model used in the CFD analysis includes a fluid region and two solid regions, the medium of the fluid region is a coolant, and the solid regions are a grid region and a rod region, the grid region is set as the fuel grid or the test piece grid, and the rod region is set as the fuel rod or the electric heating rod.

5. The method for designing a fuel assembly test piece based on CFD analysis according to claim 4, characterized in that: In the step c), the solid medium is configured as a zirconium alloy.

6. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1 or 2, characterized in that: In the step d), the calculation method of the transverse flow field intensity SFI is: Among them, u x is the fluid velocity in the x direction in the flow field, u z is the fluid velocity in the z direction in the flow field, u y,bulk is the average axial fluid velocity in the flow field, A is the cross-sectional area of ​​the calculation region, wherein the x and z directions are in the radial plane of the fuel assembly model or the test piece model, and y is the axial direction of the fuel assembly model or the test piece model.

7. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1 or 2, characterized in that: In step d), the temperature distribution uniformity is measured by the temperature distribution standard deviation T dev Characterization, the calculation method is: Among them, T i is the fluid temperature of the flow field at the grid i in the fuel assembly model or the test piece model, T avg is the average temperature of the fluid in the flow field of the calculation cross section, and A is the calculation cross section area.

8. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1 or 2, characterized in that: The given threshold does not exceed 30% of the corresponding verification parameter of the fuel assembly model.

9. The method for designing a fuel assembly test piece based on CFD analysis according to claim 1 or 2, characterized in that: In the step b), the test piece model further comprises a support structure, which is arranged between the test piece grids adjacent to each other in the axial direction of the test piece model, and the support structure satisfies: In the step c), the influence of the support structure on the calculation result of the CFD analysis is less than a given limit value; When the electric heating rod is powered on, the support structure provides radial support to the electric heating rod so that the bending degree of the electric heating rod does not exceed a given bending limit.

10. A computing device, comprising a memory and a processor, characterized in that: The memory stores a calculation program, and when the calculation program is executed by the processor, the fuel assembly test piece design method based on CFD analysis according to any one of claims 1 to 9 can be implemented.

Images