A fuel assembly grid equivalent collision test method and test device

Abstract

The present invention provides a fuel assembly grid equivalent collision test method and test device, which relates to the technical field of fuel assembly testing equipment and solves the technical problem that the fuel assembly grid equivalent collision test method does not test the collision characteristics of actual working conditions. The fuel assembly grid equivalent collision test device includes a simulated core panel inner frame, an outer water tank assembly, a loading device and a test element. The fuel assembly is placed in the simulated core panel inner frame; the simulated core panel inner frame is placed in the outer water tank assembly; the space between the outer water tank assembly and the simulated core panel inner frame and the inside of the simulated core panel inner frame are filled with fluid medium; the loading device passes through the outer water tank assembly and the simulated core panel inner frame and is connected to the fuel assembly grid by transmission; the test element is installed on the simulated core panel inner frame to measure the physical quantity of the fuel assembly grid collision. The present invention is used for testing the collision characteristics of the fuel assembly grid under actual working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel assembly testing equipment, and in particular to a fuel assembly grid equivalent collision test method and test device. Background Art

[0002] like Figure 1 As shown, a PWR bundle fuel assembly consists of an upper tube socket 15, multiple layers of grids (the grid dimensions, number of grids, and height vary for different fuel assemblies; each fuel assembly generally includes two types of grids: grid A 16 and grid B 17, each with distinct functions, dimensions, and mechanical properties), a lower tube socket 13, fuel rods 14, guide tubes, and instrumentation tubes 28. In actual use, the guide tubes and instrumentation tubes 28 are fixedly connected to each layer of the fuel assembly grids and the upper and lower tube sockets. The grids restrict the movement of the fuel rods using specially designed springs and rigid cams. The upper tube socket 15 is restrained by the reactor core's upper plate via leaf springs 18, while the lower tube socket 13 is restrained by the reactor core's lower plate.

[0003] According to the U.S. Nuclear Regulatory Commission's NUREG-0800 Standard Review Outline for Nuclear Power Plant Safety Analysis Reports, the seismic resistance of fuel assemblies under earthquake-induced LOCA conditions must be assessed to ensure their structural integrity and maintain the core's coolable geometry. According to China's GB / T 17569-2013, fuel assemblies are classified as safety-class Category I seismic items and should be seismically designed and qualified using earthquake motions equivalent to a safe shutdown earthquake. Numerical analysis is a primary approach to seismic design and qualification of fuel assemblies. During an earthquake, impacts occur between adjacent fuel assemblies within the reactor and between fuel assemblies and the core enclosure. A key task in numerical analysis is to assess the seismic impact forces acting on the fuel assembly grids at each layer. Therefore, it is necessary to rationally determine the grid's equivalent impact parameters (such as equivalent impact stiffness and equivalent impact damping). These equivalent impact stiffness and equivalent impact damping are key mechanical parameters of the fuel assembly.

[0004] Currently, the equivalent collision parameters of fuel assembly grids are determined based on the results of slingshot tests conducted in air. These tests, conducted in air, simulate the constraints imposed on the fuel assembly by the reactor core's upper and lower plates. A middle grid layer with greater rigidity is selected. To facilitate assembly stretching, a layer of annular steel hoops is placed around the grid's periphery. The hoops stretch the grid layer to a specified displacement, and then release the tensile load. The equivalent collision stiffness and equivalent collision damping of the fuel assembly grid are derived based on the recorded collision forces and displacements between the grid and the simulated core enclosure. In reality, the equivalent collision parameters obtained using this test method and apparatus reflect the collision characteristics between the grid's outer steel hoops and the simulated core enclosure. Since the tests are conducted in air, the test method does not reflect actual operating conditions, and therefore does not capture the actual collision characteristics between the grid and the enclosure. Summary of the Invention

[0005] The object of the present invention is to provide a fuel assembly grid equivalent collision test method and test device to solve the technical problem that the fuel assembly grid equivalent collision test method in the prior art does not test the collision characteristics of actual working conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a fuel assembly grid equivalent collision test device, comprising a simulated core enclosure inner frame, an outer water tank assembly, a loading device, and a test element, wherein:

[0008] The fuel assembly is placed in the inner frame of the simulated core shroud;

[0009] The simulated core shroud inner frame is placed in the outer water tank assembly;

[0010] The space between the outer water tank assembly and the simulated core shroud inner frame and the interior of the simulated core shroud inner frame are filled with fluid medium;

[0011] The loading device passes through the outer water tank assembly and the inner frame of the simulated core shroud and is then transmission-connected to the grid of the fuel assembly;

[0012] The test element is mounted on the inner frame of the simulated core shroud to measure physical quantities of fuel assembly grid collision.

[0013] As a further improvement of the present invention, the loading device includes a bracket, a fixed pulley A, a fixed pulley B, a magnetic tension release device, a steel wire rope and a grid steel hoop, wherein:

[0014] The bracket is fixed beside the outer water tank assembly, and the height of the bracket is adjustable;

[0015] The fixed pulley A is mounted on the top of the bracket;

[0016] The fixed pulley B is mounted on the side of the bracket away from the outer water tank assembly;

[0017] The grid steel hoop is U-shaped and is clamped on the outside of the grid of the fuel assembly;

[0018] One end of the steel wire rope is connected to the grid steel hoop, and the other end passes through the fixed pulley A and the fixed pulley B in sequence and is connected to the magnetic attraction stretching and releasing device.

[0019] As a further improvement of the present invention, the test element includes a displacement sensor and a collision force sensor installed on the inner frame of the simulated core shroud, and a force collision plate pressed against the surface of the collision force sensor.

[0020] As a further improvement of the present invention, there are two displacement sensors, which are arranged on the opposite side baffles of the inner frame of the simulated core panel; there are two collision force sensors, which are symmetrically arranged at both ends of the panel on one side of the inner frame of the simulated core panel.

[0021] As a further improvement of the present invention, the frame steel hoop includes a U-shaped steel hoop and a reinforcement plate fixed on the U-shaped steel hoop crossbeam, the U-shaped steel hoop and the reinforcement plate are both made of steel plates, and the thickness of the reinforcement plate is greater than the steel plate thickness of the U-shaped steel hoop; the reinforcement plate is also provided with a pull ring for the steel wire rope to pass through.

[0022] As a further improvement of the present invention, the bracket includes four columns, an angle steel beam connected between two adjacent columns, and a bracket base plate installed at the bottom of the four columns; each column is composed of four channel steels with different waist heights stacked together, and each channel steel is provided with multiple positioning holes, and the height adjustment of the column is achieved by passing bolts through different positioning holes of two adjacent channel steels.

[0023] As a further improvement of the present invention, the simulated core panel inner frame includes panels located on the left and right sides, baffles located on the front and rear sides, a simulated core upper plate and a simulated core lower plate located at the top and bottom; the simulated core upper plate and the simulated core lower plate are both provided with positioning pin mounting holes for positioning the fuel assemblies, and the inner cavity specifications of the simulated core panel inner frame are adapted to the fuel assembly specifications, so that after the fuel assembly is installed in the simulated core panel inner frame, the gap between the fuel assembly and the panel and the baffle is within the set gap range; a plurality of measuring holes are provided on the baffle near the panel position along the height direction; tie rod holes are respectively provided at corresponding positions of the simulated core panel inner frame and the outer water tank assembly, and the tie rod passes through the tie rod hole to realize the connection between the simulated core panel inner frame and the outer water tank assembly.

[0024] As a further improvement of the present invention, the outer water tank assembly includes an outer water tank and a steel support. The outer water tank is a rectangular box structure with a bottom plate. The outer side walls of the outer water tank are provided with criss-cross reinforcement ribs. The steel support is arranged around the outer water tank. The bottom of the outer water tank is pushed to the bottom of the inner frame of the simulated core panel by bolts on all four sides.

[0025] The present invention provides a fuel assembly grid equivalent collision test method, based on the fuel assembly grid equivalent collision test device, comprising the following steps:

[0026] Step S1, installation of the fuel assembly grid equivalent collision test apparatus: including installation of the outer water tank, installation of the test element, installation of the fuel assembly to be tested, installation of the steel support, installation and height adjustment of the loading device, and also including measurement of the initial gap value c;

[0027] Step S2, measuring the equivalent collision physical quantities of the fuel assembly grid: There is almost no collision between the upper and lower end grids of the fuel assembly and the coaming, so this is not considered in the calculation and analysis. Then, tests and measurements are conducted on all types of grids in the fuel assembly, and data on the horizontal displacement time history and the collision force time history of the coaming are collected;

[0028] Step S3, calculation and analysis of equivalent collision parameters of the fuel assembly grid: a finite element calculation model for analyzing a single fuel assembly is established, and finite element calculation is performed on the fuel assembly to obtain equivalent collision parameters of each layer of the grid.

[0029] As a further improvement of the present invention, in step S2, the grid types in the fuel assembly include grid A and grid B, wherein:

[0030] When testing grid A, the horizontal displacement time history and the impact force time history of each layer of grid A are collected sequentially. When measuring a certain layer of grid A, the fuel assembly is stretched until the grid A reaches the specified initial displacement. After the fuel assembly stabilizes for a set time, the power to the magnetic tension release device is disconnected. The fuel assembly rebounds and the grid A in that layer impacts the coaming. The test element then collects data. Three tests are conducted for each layer of grid A at the specified initial displacement, and the test results are averaged. The same method is used to obtain test data for the same layer of grid A at other specified initial displacements.

[0031] When testing grid B, the horizontal displacement time history of each layer of grid B and its adjacent layer of grid A and the collision force time history of the impact on the coaming are collected in sequence; when measuring a certain layer of grid B, the grid A adjacent to the grid B to be tested is stretched so that the grid A reaches the specified initial displacement. After the fuel assembly stabilizes for a set time, the power supply of the magnetic attraction stretching and releasing device is cut off. The fuel assembly rebounds and the adjacent layer of grid A and the grid B of the layer collide with the coaming. The test element collects data. Three tests are carried out for the specified initial displacement of the adjacent layer of grid A, and the test results are averaged. The same method is used to obtain test data for the adjacent layer of grid A at other specified initial displacements.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The fuel assembly grid equivalent collision test device provided by the present invention is a test device for the equivalent collision parameters of the actual grid of a rod-type fuel assembly in an aqueous environment. The test device is used to realize the collision of a single-layer grid (grid A) or a double-layer grid (grid B and the adjacent layer grid A) with a coaming under different initial tensile displacement conditions for grids of different types and heights. The relative displacement and collision force data of the grids are collected, and an iterative calculation is performed using a nonlinear finite element model of the fuel assembly to obtain a converged solution of the equivalent collision stiffness and equivalent collision damping of each layer of the fuel assembly. Based on this, the equivalent collision parameters of the actual grid material under aqueous environment conditions can be obtained.

[0034] The fuel assembly grid equivalent collision test device provided by the present invention has sufficient horizontal rigidity and provides a water environment under the condition of small gaps between the fuel assembly and the coaming plate and the baffle.

[0035] The fuel assembly grid equivalent collision test device provided by the present invention has equivalent collision parameters of the fuel assembly grid that are related to factors such as the material of the collision surface and the collision environment. This technology can obtain equivalent collision parameters of the actual grid material under water environment conditions.

[0036] The fuel assembly grid equivalent collision test device provided by the present invention can test and calculate the equivalent collision parameters of grids A and B of different types and heights respectively, which can improve the test accuracy and help protect the grid B with lower strength.

[0037] The fuel assembly grid equivalent collision test device provided by the present invention has two collision force sensors and two displacement sensors arranged on each grid to be tested, thereby reducing the impact of non-centering collisions.

[0038] The fuel assembly grid equivalent collision test device provided by the present invention is a technology for testing the equivalent collision parameters of the grid of a pressurized water reactor rod bundle fuel assembly in a water environment. It can be used as a reference for testing the collision parameters of fuel assemblies of other types of reactors, and of the grids of each layer of fuel assemblies and simulated core panels under anhydrous conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 Schematic diagram of the structure of the fuel assembly to be tested according to the present invention;

[0041] Figure 2 2. It is a schematic diagram of the three-dimensional structure of the fuel assembly grid equivalent collision test device of the present invention;

[0042] Figure 3 This is a front view of the inner frame of the simulated core panel in the fuel assembly grid equivalent collision test device of the present invention;

[0043] Figure 4 This is a structural diagram of a simulated core lower plate in a fuel assembly grid equivalent collision test device of the present invention;

[0044] Figure 5 This is a structural diagram of a simulated core upper plate in a fuel assembly grid equivalent collision test device of the present invention;

[0045] Figure 6 This is a front view of the outer water tank in the fuel assembly grid equivalent collision test device of the present invention;

[0046] Figure 7 is a top cross-sectional view of a fuel assembly grid equivalent collision test apparatus according to the present invention;

[0047] Figure 8 It is a structural schematic diagram of the grid steel hoop in the fuel assembly grid equivalent collision test device of the present invention.

[0048] In the figure, 1. Simulated core enclosure inner frame; 2. Simulated core lower plate; 3. Simulated core upper plate; 4. Fuel assembly; 5. Collision force sensor; 6. Steel support; 7. External water tank; 8. Cross-shaped reinforcement rib; 9. Support plate; 10. Lower pin mounting hole; 11. Upper pin mounting hole; 12. Leaf spring compression groove; 13. Lower tube seat; 14. Fuel rod; 15. Upper tube seat; 16. Grid A; 17. Grid B; 18. Leaf spring; 19. Grid Frame steel hoop; 20. Steel wire rope; 21. Fixed pulley A; 22. Fixed pulley B; 23. Magnetic tension release device; 24. Observation window; 25. Enclosure; 26. Baffle; 27. Bracket; 28. Guide tube and instrument tube; 29. ​​Pull rod hole; 30. Measuring hole; 31. Tightening bolt hole; 32. External water tank bottom plate; 33. Steel support bottom plate; 34. Bracket bottom plate; 35. LVDT displacement sensor; 36. Pull ring; 37. Force collision plate. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0050] like Figure 2 As shown, the present invention provides a fuel assembly grid equivalent collision test device, including a simulated core shroud inner frame 1, an outer water tank assembly, a loading device and a test element, wherein:

[0051] The fuel assembly (fuel pellets are replaced with simulated pellets of the same linear density) 4 is placed in the simulated core shroud inner frame 1;

[0052] The simulated core panel inner frame 1 is placed in the outer water tank assembly;

[0053] The space between the outer water tank assembly and the simulated core enclosure inner frame 1 and the interior of the simulated core enclosure inner frame 1 is filled with a fluid medium. It should be noted that the fluid medium referred to here is cold deionized water. This simulates a collision test of the fuel assembly grid in a water environment.

[0054] The loading device passes through the outer water tank assembly and the simulated core panel inner frame 1 and is connected to the grid of the fuel assembly 4 by transmission;

[0055] The test element is installed on the simulated core shroud inner frame 1 to measure the physical quantities of the fuel assembly 4 grid collision.

[0056] As an optional embodiment of the present invention, the loading device includes a bracket 27, a fixed pulley A21, a fixed pulley B22, a magnetic tension release device 23, a steel wire rope 20 and a grid steel hoop 19, wherein:

[0057] The bracket 27 is fixed to the side of the outer water tank assembly, and the height of the bracket 27 is adjustable; it should be noted that the bracket 27 is a steel bracket;

[0058] Fixed pulley A21 is mounted on top of bracket 27;

[0059] Fixed pulley B22 is mounted on the side of bracket 27 away from the outer water tank 7 assembly;

[0060] like Figure 7 and Figure 8 As shown, the grid steel hoop 19 is U-shaped and is clamped on the outside of the grid of the fuel assembly 4. Since the grid steel hoop 19 is U-shaped with one side open, there is no steel hoop blocking the fuel assembly 4 on the open side and the inner frame 1 of the simulated core enclosure. When the fuel assembly 4 is pulled and released, the fuel assembly 4 can directly hit the enclosure 25. Moreover, since the outer water tank assembly and the inner frame 1 of the simulated core enclosure are filled with water, a collision test under actual working conditions in a water environment is formed.

[0061] One end of the steel wire rope 20 is connected to the grid steel hoop 19 , and the other end passes through the fixed pulley A 21 and the fixed pulley B 22 in sequence and is connected to the magnetic attraction stretching and releasing device 23 .

[0062] Further, such as Figure 7 As shown, the test element includes a displacement sensor 35 and a collision force sensor 5 installed on the inner frame 1 of the simulated core shroud, and a force collision plate 37 pressed on the surface of the collision force sensor 5.

[0063] It should be noted that, in the present invention, the displacement sensor is an LVDT displacement sensor 35 .

[0064] There are two LVDT displacement sensors 35, which are set on the opposite side baffles of the inner frame 1 of the simulated core enclosure, specifically, on the two free arm sides of the grid steel hoop 19; there are two collision force sensors 5, which are symmetrically set at both ends of the enclosure on one side of the inner frame 1 of the simulated core enclosure, specifically, the collision force sensor 5 is installed on the open side of the grid steel hoop 19.

[0065] like Figure 8 As shown, the grid steel hoop 19 includes a U-shaped steel hoop and a reinforcement plate fixed on the U-shaped steel hoop crossbeam. The U-shaped steel hoop and the reinforcement plate are both made of steel plates, and the thickness of the reinforcement plate is greater than the steel plate thickness of the U-shaped steel hoop; a pull ring 36 for the steel wire rope 20 to pass through is also provided on the reinforcement plate.

[0066] like Figure 2As shown, the bracket 27 includes four columns, an angle steel beam connected between two adjacent columns, and a bracket base plate 34 installed at the bottom of the four columns; each column is composed of four channel steels of different waist heights, and each channel steel is provided with a plurality of positioning holes, and the height adjustment and fixed connection of the column are achieved by passing bolts through different positioning holes of two adjacent channel steels.

[0067] Furthermore, in the present invention, Figure 2 、 Figure 3 and Figure 7 As shown, the simulated core panel inner frame 1 includes panels 25 located on the left and right sides, baffles 26 located on the front and rear sides, a simulated core upper plate 3 and a simulated core lower plate 2 located on the top and bottom; both the simulated core upper plate 3 and the simulated core lower plate 2 are provided with positioning pin mounting holes for positioning the fuel assembly 4, specifically, upper pin mounting holes 11 are provided on the simulated core upper plate 3, and lower pin mounting holes 10 are provided on the simulated core lower plate 2. The inner cavity specifications of the simulated core panel inner frame 1 are adapted to the specifications of the fuel assembly 4, so that after the fuel assembly 4 is installed in the simulated core panel inner frame 1, the gap between the fuel assembly 4 and the panels 25 and the baffles 26 is within the set gap range. For example, the set gap can be 3 mm, and of course it can also be other Gap size; a plurality of measuring holes 30 are provided on the baffle 26 near the shroud 25 along the height direction. It should be noted that the measuring holes 30 here are provided near the shroud 25 on the open side of the grid steel hoop 19. During measurement, the measuring holes 30 on the front and rear baffles 26 of the simulated core shroud inner frame 1 are used to measure the initial gap value c between the tested grid of the fuel assembly 4 and the force collision plate 37 anchored on the shroud 25 using a feeler gauge; tie rod holes 29 are provided at corresponding positions of the simulated core shroud inner frame 1 and the outer water tank assembly, and the tie rods pass through the tie rod holes 29 to realize the connection between the simulated core shroud inner frame 1 and the outer water tank assembly. Specifically, the tie rod holes 29 are provided at 1 / 4, 1 / 2, and 3 / 4 height positions of the simulated core shroud inner frame 1 and the outer water tank 7.

[0068] like Figure 2 As shown, the outer water tank assembly includes an outer water tank 7 and steel supports 6. The outer water tank 7 is a rectangular box structure with a bottom plate. Cross-shaped reinforcement ribs 8 are arranged on the outer sidewalls of the outer water tank 7. The steel supports 6 are located around the outer water tank 7. The bottom of the outer water tank 7 is bolted to the bottom of the simulated core coaming inner frame 1. Multiple observation windows 24 are provided along the sidewalls of the outer water tank 7.

[0069] The present invention provides a fuel assembly four-grid equivalent collision test device. The equivalent collision parameters of the fuel assembly four-grid are related to factors such as the material of the collision surface and the collision environment. This technology can obtain the equivalent collision parameters of the actual grid material under water environment conditions.

[0070] The fuel assembly four-grid equivalent collision test device provided by the present invention can test and calculate the equivalent collision parameters of grids A and B of different types and heights respectively, which can improve the test accuracy and help protect the grid B with lower strength.

[0071] The fuel assembly 4-grid equivalent collision test device provided by the present invention has two collision force sensors 5 and two displacement sensors 35 arranged on each grid to be tested, thereby reducing the impact of non-centering collisions.

[0072] The fuel assembly 4-grid equivalent collision test device provided by the present invention is a technology for testing the equivalent collision parameters of 4-grid fuel assemblies of a pressurized water reactor rod bundle type in a water environment. It can be used as a reference for testing the collision parameters of fuel assemblies 4 of other types of reactors, and the collision parameters of each layer of grids of fuel assemblies 4 and simulated core panels under water-free conditions.

[0073] Example 1:

[0074] In this embodiment, a device for testing equivalent collision parameters between actual grids and simulated core panels of rod-type fuel assemblies in a water environment is provided to meet the needs of grid collision force response analysis of fuel assembly 4 under earthquake action and seismic safety assessment of fuel assembly 4. In this embodiment, the fuel pellets in fuel assembly 4 are replaced with simulated pellets with the same linear density. This embodiment specifically includes a test device with sufficient rigidity that can simulate the water environment conditions of a pressurized water reactor to test the equivalent collision parameters between different types of actual grids of fuel assembly 4 and simulated core panels. The test device can also be used for equivalent collision parameter testing of grids and simulated core panels of fuel assemblies under other environmental conditions (such as in air) and different types (including different assembly heights, different grid numbers) of fuel assemblies.

[0075] Specifically, the test device for equivalent collision parameter test of fuel assembly grid in water environment mainly consists of four parts: the inner frame 1 of the simulated core panel, the outer water tank assembly (6, 7), the loading device (19-23, 27) and the test element (5, 35, 37), such as Figure 2 、 Figure 7 shown.

[0076] like Figure 3-Figure 5As shown, the simulated core shroud inner frame 1 is welded to two simulated core shrouds 25 and front and rear baffles 26, with upper and lower flanges bolted to the simulated core lower plate 2 and simulated core upper plate 3. It is used to mount the fuel assembly 4 and limit the distance (e.g., 3 mm) between the simulated core shroud 25 and front and rear baffles 26 to simulate the actual small clearance conditions around the fuel assembly in a reactor. The simulated core lower plate 2 and simulated core upper plate 3 are each designed with two locating pin mounting holes: a lower pin mounting hole 10 and an upper pin mounting hole 11. The locating pins installed in these holes respectively enter the pin holes of the lower tube seat 13 and upper tube seat 15 of the fuel assembly 4. The front and rear baffles 26 are designed with a row of measuring holes 30 along the height direction for measuring the initial clearance c between the fuel assembly 4 grid and the shroud 25. The fuel assembly 4 grid equivalent collision test device provided by the present invention has sufficient horizontal rigidity and provides a water environment under small clearance conditions between the fuel assembly 4 and the shroud and baffles.

[0077] The outer water tank 7 is a rectangular box with an outer water tank bottom plate 32, which is used to fill water to meet the actual working environment of the fuel assembly 4. The outer water tank bottom plate 32 is fixed to the rigid ground by bolts. The outer sides of the outer water tank 7 are arranged with cross-shaped reinforcement ribs 8. Bolts are passed through the tightening bolt holes 31 around the bottom of the outer water tank 7 to apply a tightening force to the bottom of the simulated core enclosure inner frame 1. Pull rod holes 29 are arranged at 1 / 4 height, middle and 3 / 4 height along the four sides of the outer water tank 7 and the simulated core enclosure inner frame 1. The outer water tank 7 and the simulated core enclosure inner frame 1 are tightened and anchored by connecting the pull rods to improve the overall rigidity of the test device. Schematic diagram of the outer water tank 7 Figure 6 .

[0078] The steel support 6 is made of wide flange I-beam and channel steel welded together and arranged along one side of the short side and both sides of the long side of the outer water tank 7. Its steel support bottom plate 33 is fixed to the rigid ground by bolts, and the top is anchored to the outer water tank 7 by a support plate 9 and several bolts to improve the overall rigidity of the test device. Figure 2 .

[0079] The loading device consists of a grid steel hoop 19, a steel wire rope 20, a bracket 27, a fixed pulley A21 and a fixed pulley B22 fixed on the bracket 27, and a magnetic tension release device 23. Figure 2 、 Figure 7. The bracket 27 has four columns, and angle steel beams are welded between the four columns. Each column is made up of four channel steels with different waist heights. A number of positioning holes are opened on the channel steel. The height of the column is adjusted according to the position of the four grids of the stretched fuel assembly, and the two adjacent channel steels are fastened with bolts through the positioning holes. The fixed pulley A21 and the fixed pulley B22 are fixed to the top and side of the bracket 27 by bolts, and the bracket bottom plate 34 is fixed to the rigid ground by bolts. The grid steel hoop 19 is made of a U-shaped steel hoop bent from a thin steel plate and a thicker reinforcing steel plate (to increase rigidity and reduce deformation) anchored by bolts, see Figure 8 . The inner sides of the two free arms of the grid hoop 19 are bonded to the front and rear sides of the grid to be tested of the fuel assembly 4 by special glue. A pull ring 36 is installed on the screw hole in the middle of the grid hoop 19. One side of the steel wire rope 20 is connected to the pull ring 36, and the other side is led out to the outside of the outer water tank 7, and connected to the magnetic tension release device 23 through the fixed pulley A21 and the fixed pulley B22. Two LVDT displacement sensors 35 are installed on the front and rear baffles 26 of the inner frame 1 of the simulated core enclosure to measure the relative displacement between the assembly grid and the enclosure. Two collision force sensors 5 are installed on the simulated core enclosure 25 on the side adjacent to the fuel assembly 4, and a pre-tightening load is applied through the force collision plate 37 to measure the collision force between the assembly grid and the enclosure.

[0080] The present invention provides a fuel assembly 4-grid equivalent collision test device, which is a test device for the equivalent collision parameters of the actual grid of the rod bundle fuel assembly 4 in an aqueous environment. The test device is used to realize the collision of a single-layer grid (grid A) or a double-layer grid (grid B and the adjacent layer grid A) with the enclosure under different initial tensile displacement conditions for grids of different types and heights. The relative displacement and collision force data of the grids are collected, and an iterative calculation is performed using a nonlinear finite element model of the fuel assembly 4 to obtain a converged solution of the equivalent collision stiffness and equivalent collision damping of the fuel assembly 4 grid. Based on this, the equivalent collision parameters of the actual grid material under aqueous environment conditions can be obtained.

[0081] The present invention also provides a fuel assembly grid equivalent collision test method, which is based on the above-mentioned fuel assembly grid equivalent collision test device and includes the following steps:

[0082] Step S1, installation of the fuel assembly 4 grid equivalent collision test apparatus: including installation of the outer water tank 7, installation of the test element, installation of the fuel assembly 4 to be tested, installation of the steel support 6, and installation and height adjustment of the loading device, and also includes measurement of the initial gap value c;

[0083] Specifically, in step S1, the installation of the external water tank 7 involves installing a set of lower pins into the lower pin mounting holes 10 of the simulated core lower plate 2 of the simulated core shroud inner frame 1, and then anchoring the simulated core shroud inner frame 1 to the simulated core lower plate 2 via flanges. The installation of the test element involves installing a force collision plate 37 on a side panel 25 of the simulated core shroud inner frame 1, based on the height of the fuel assembly 4 grid to be tested. Two collision force sensors 5 are positioned within the force collision plate 37 and preloaded. Waterproof LVDT displacement sensors 35 are installed on the front and rear baffles 26. The data cables of the collision force sensors 5 and LVDT displacement sensors 35 must be waterproofed and routed from the top of the simulated core shroud inner frame 1. The inner sides of the two free arms of the grid steel hoop 19 are bonded to the front and rear sides of the fuel assembly 4 grid to be tested using a special adhesive. A steel wire rope 20 is connected via a pull ring 36, and sufficient length must be reserved for the steel wire rope 20.

[0084] In step S1, the installation of the test fuel assembly includes vertically hoisting the test fuel assembly 4 into the simulated core shroud inner frame 1. The simulated core lower plate 2 and simulated core upper plate 3 are then used to position the test fuel assembly 4. The lower pin on the simulated core lower plate 2 is inserted into the pin hole of the lower tube seat 13 of the fuel assembly 4. The steel wire rope 20 connecting the test grid is led out through the reserved hole on the side of the simulated core shroud 25 to the outside of the simulated core shroud inner frame 1. Then, the upper pin is installed in the upper pin installation hole 11 of the simulated core upper plate 3. The simulated core upper plate 3 is mounted to the upper flange of the simulated core shroud inner frame 1. The upper pin is inserted into the pin hole of the upper tube seat 15 of the fuel assembly 4. The upper flange of the simulated core shroud inner frame 1 is anchored to the simulated core upper plate 3 with bolts. The leaf spring 18 of the fuel assembly 4 is compressed to the designed displacement value through the leaf spring 18 compression groove 12. At this point, the installation of the test fuel assembly 4 is completed. The testing apparatus is machined with precision to ensure that the vertical axis of the fuel assembly 4 is perpendicular to the top surface of the simulated core lower plate 2 and the bottom surface of the simulated core upper plate 3. A feeler gauge is used to measure the initial clearance c between the test grid of the fuel assembly 4 and the force impact plate 37 anchored to the shroud, through the measurement holes 30 in the front and rear baffles 26 of the simulated core shroud inner frame 1. The clearances between the fuel assembly 4 and the front and rear baffles 26 and the simulated core shroud 25 are designed based on the clearance values ​​for components within the reactor. The grid directly impacts the force impact plate 37 in a water environment, obtaining realistic collision parameters between the grid and the shroud under actual grid material and environmental conditions.

[0085] Installation of the steel support 6 involves bolting the steel support 6 to the outer water tank 7 via the support plate 9. The outer water tank bottom plate 32 and the steel support bottom plate 33 are bolted to a rigid, horizontal surface. Next, the assembled simulated core shroud inner frame 1, simulated core lower plate 2, simulated core upper plate 3, and fuel assembly 4 are hoisted into the outer water tank 7. The steel wire rope 20 is guided through the pre-reserved holes on the side of the outer water tank 7. Screws are used to tighten the simulated core shroud inner frame 1 through the tightening bolt holes 31 at the bottom of the outer water tank 7. Tie rods are used to connect and anchor the outer water tank 7 and the simulated core shroud inner frame 1 through the tie rod holes 29. The upper flange of the outer water tank 7 is bolted to the simulated core upper plate 3. After installation, the height of the loading device bracket 27 is adjusted so that the steel wire rope extending from the outer water tank 7 is horizontal. The wire rope is then routed around fixed pulleys A21 and B22 and connected to the magnetic tension release device 23. This completes the installation of the test device. The test device has a large horizontal rigidity along the collision direction of the fuel assembly 4, which can ensure the effectiveness of the equivalent collision parameter testing technology of the fuel assembly 4 frame in a water environment.

[0086] Compared with the grid A, the equivalent collision stiffness and strength of the grid B are both very small. The present invention can obtain equivalent collision parameters of two different types of grids while ensuring the test accuracy.

[0087] Two collision force sensors 5 are arranged in the force collision plate 37 of the test grid, and an LVDT displacement sensor is arranged on each of the two surfaces of the test grid parallel to the loading direction. The average value of the two collision forces and the average value of the two horizontal displacements are used for calculation during analysis to reduce the impact of non-centering collisions of the fuel assembly 4.

[0088] Step S2: Measuring the equivalent collision physical quantities of the fuel assembly 4 grid: There is almost no collision between the upper and lower end grids of the fuel assembly 4 and the coaming, so this is not considered in the calculation and analysis. Then, tests and measurements are conducted on all grid types in the fuel assembly 4, and the horizontal displacement time history and the collision force time history data of the coaming are collected;

[0089] Specifically, the measurement of equivalent collision physical quantities of Grid A and Grid B includes:

[0090] A1. First, all grids of fuel assembly type A were tested separately. Figure 1For example, there are 8 layers of grids of type A. During the test, the acquisition equipment is turned on to start collecting the horizontal displacement time history of the grid A layer and the collision force time history of the collision with the simulated core shroud. The fuel assembly 4 is stretched so that the grid A reaches the specified initial displacement, such as u1 = 6mm. After the fuel assembly 4 stabilizes for the set time, the power supply of the magnetic stretching release device 23 is cut off, the fuel assembly rebounds and the grid A layer hits the simulated core shroud 25, and the data collection ends at this point. Three tests are carried out on the initial tensile displacement u1 of the grid A layer, and the test results are averaged. The coefficient of variation of the maximum collision force is required to be less than 0.05. The same method is used to obtain the initial displacement u1 of the grid A layer at other specified initial displacements u i Considering the maximum possible displacement of the actual fuel assembly 4 in the pressurized water reactor, the initial displacements can be 10 mm, 15 mm, and 20 mm, respectively, and n = 4.

[0091] A2. Since the equivalent collision stiffness of the fuel assembly 4 grid B17 is small and its strength is much lower than that of grid A, when determining the equivalent collision parameters of grid B, the grid B to be tested and its adjacent grid A are subjected to collision force and grid displacement tests at the same time. During the test, the acquisition equipment is turned on to start collecting the horizontal displacement time history of the grid B to be tested and its adjacent grid A and the collision force time history of their impact on the simulated core shroud. Stretch the grid A adjacent to the grid B to be tested so that the grid A reaches the specified initial displacement, such as u1 = 6mm. After the fuel assembly 4 stabilizes for the set time, cut off the power supply of the magnetic stretching release device 23, the fuel assembly rebounds, and the grid A and the grid B to be tested collide with the simulated core shroud 25. At this point, the data collection ends. Three tests are carried out on the initial tensile displacement u1 of the grid A of this layer, and the test results are averaged. The coefficient of variation of the maximum collision force is required to be less than 0.05. Using the same method, obtain the initial tensile displacement u1 of the grid A adjacent to the grid B to be tested at other specified initial tensile displacements u1. i Considering the maximum possible displacement of the actual fuel assembly 4 in the pressurized water reactor, the initial displacements can be 10 mm, 15 mm, and 20 mm, respectively, and n = 4.

[0092] Step S3, calculation and analysis of equivalent collision parameters of the fuel assembly grid: a finite element calculation model for analyzing a single fuel assembly 4 is established, and finite element calculation is performed on the fuel assembly 4 to obtain equivalent collision parameters of each layer of the grid.

[0093] After completing the data collection of A1, the data analysis and calculation process is performed, specifically:

[0094] B1. Establishing a finite element calculation model for the analysis of a single fuel assembly 4

[0095] [M]{A(t)}+[C]{V(t)}+[K]{D(t)}=-{Fnl (t)}

[0096] Where [M], [C], and [K] are the mass matrix, damping matrix, and stiffness matrix of a single fuel assembly 4, respectively. [M] includes the effect of the added mass of dynamic water in the water environment, and [C] generally adopts the Rayleigh damping matrix. {A(t)}, {V(t)}, and {D(t)} are the acceleration, velocity, and displacement vectors of the assembly at time t, respectively. {F nl (t)} is the nonlinear collision force vector of the core shroud 25 on the fuel assembly 4 grid at time t, including the impact of collision stiffness and collision damping. For this layer of grid A, the nonlinear collision force f at time t is nl (t) is

[0097] f nl (t) = k A ·d A (t)+c A ·v A (t)

[0098] Among them, k A 、c A are the equivalent collision stiffness and equivalent collision damping coefficient of the grid A hitting the simulated core panel 25; d A (t) is the gap between the grid A and the impact plate 37 on the simulated core shroud 25 at time t, which is calculated from the displacement D of the grid A at time t. A (t), initial gap value c between the grid A and the force collision plate 37 A OK, when

[0099] d A (t) = D A (t)+c A When ≥0, f nl (t) = 0;

[0100] when

[0101] d A (t) = D A (t)+c A <0, f nl (t) = k A ·d A (t)+c A ·v A (t), where v A (t) The velocity V of the frame A at time t A (t) OK.

[0102] The equivalent collision stiffness k of the grid A hitting the simulated core panel A and the equivalent collision damping coefficient c AThe initial equivalent collision stiffness of the grid A can be determined by an iterative method.

[0103] k A =P 2 A,max,i / (M A,span ·V 2 A,max,i )

[0104] Among them, P A,max,i Refers to stretching the grid A to a specified initial displacement u i The maximum collision force between the grid A and the simulated core panel obtained by the test when (i=1,2,3,……,n) is M A,span Refers to half of the total mass of the fuel assembly 4 within the upper and lower spans of the grid A at this layer, V A,max,i Refers to the maximum velocity of the grid A before it collides with the simulated core panel, which is determined by the first-order derivative of the measured grid displacement time history. A Generally, the damping ratio is 5%. A calculate.

[0105] Perform finite element calculation on fuel assembly 4, iterate and adjust the equivalent collision stiffness k between the grid A and the simulated core panel. A and the equivalent collision damping coefficient c A , and according to the convergence index R Q 、R T 、R U Determine k A 、c A The convergence value of

[0106]

[0107]

[0108]

[0109] Among them, Q max,m,i 、T m,i 、U max,m,i Refers to stretching the grid A to a specified initial displacement u i (i=1,2,3,……,n) The maximum collision force, collision duration and maximum displacement of the grid A rebound obtained after the mth iteration calculation, R Q 、R T 、R U Is a positive value. When Max(R Q 、R T 、R U )<0.02, the results converge.

[0110] According to A1 and B1 above, the equivalent collision parameters of all layers of grids of all types A can be determined. Generally speaking, the equivalent collision parameters of grids A of different heights are not much different.

[0111] B2. Same as B1, establish the finite element calculation model for the analysis of fuel assembly 4. Since the equivalent collision stiffness k of the grid A and the simulated core panel collision is A and the equivalent collision damping coefficient c A The nonlinear collision force f of the grid A at time t has been obtained. nl,A (t) can be determined. For the grid B, the nonlinear collision force f at time t is nl,B (t) is

[0112] f nl，B (t) = k B ·d B (t)+c B ·v B (t)

[0113] Among them, k B 、c B are the equivalent collision stiffness and equivalent collision damping coefficient of the grid B hitting the simulated core panel 25; d B (t) is the gap between the grid B at this layer and the impact plate 37 on the simulated core panel 25 at time t, which is calculated from the displacement D of the grid B at time t. B (t), initial gap value c between the grid B and the force collision plate 37 B OK, when

[0114] d B (t) = D B (t)+c B ≥0

[0115] When f nl,B (t) = 0; when

[0116] d B (t) = D B (t)+c B <0

[0117] When f nl,B (t) = k B ·d B (t)+c B ·v B (t), where v B (t) The velocity V of the frame B at time t B (t) OK.

[0118] The equivalent collision stiffness k of the impact of the grid B on the simulated core panel 25 is B and the equivalent collision damping coefficient c BThe initial equivalent collision stiffness of the grid B can be determined by an iterative method:

[0119] k B =P 2 B,max,i / (M B,span ·V 2 B,max,i )

[0120] Among them, P B,max,i Refers to stretching the adjacent layer grid A to the specified initial displacement u i The maximum collision force between the grid B and the simulated core panel obtained by the test when (i=1,2,3,……,n) is M B,span Refers to half of the total mass of the fuel assembly 4 within the upper and lower spans of the grid B at this layer, V B,max,i Refers to the maximum velocity of the grid B before it collides with the simulated core panel, which is determined by the first-order derivative of the measured grid displacement time history. B Generally, the damping ratio is 5%. B calculate.

[0121] Perform finite element calculation on fuel assembly 4, iterate and adjust the equivalent collision stiffness k of the grid B and the simulated core panel collision B and the equivalent collision damping coefficient c B , and according to the convergence index R Q '、R T '、R U 'Determine k B 、c B The convergence value of

[0122]

[0123]

[0124]

[0125] Among them, Q max,m,i '、T m,i '、U max,m,i ' refers to stretching the adjacent layer grid A to the specified initial displacement u i (i=1,2,3,……,n) The maximum collision force of the grid B, the collision duration and the maximum displacement of the grid B rebound obtained after the mth iteration calculation, R Q '、R T '、R U ' is a positive value. When Max(R Q '、R T '、R U ')<0.02, the results converge.

[0126] According to A2 and B2 above, the equivalent collision parameters of all layers of grids of all types B can be determined. Generally speaking, the equivalent collision parameters of grids B of different heights are not much different.

[0127] In step S2, the grid types in the fuel assembly 4 include grid A and grid B, wherein:

[0128] When testing the grid A, the horizontal displacement time history and the impact force time history of each layer of grid A are sequentially collected. When measuring a certain layer of grid A, the fuel assembly 4 is stretched until the grid A reaches the specified initial displacement. After the fuel assembly 4 stabilizes for a set time, the power supply of the magnetic attraction stretching release device 23 is cut off. The fuel assembly 4 rebounds and the grid A of that layer impacts the coaming. The test element collects data. Three tests are conducted for each layer of grid A at the specified initial displacement, and the test results are averaged. The same method is used to obtain test data for the grid A of that layer at other specified initial displacements.

[0129] When testing grid B, the horizontal displacement time history and the impact force time history of each layer of grid B and its adjacent layer of grid A are collected in sequence. When measuring a certain layer of grid B, the grid A adjacent to the grid B to be tested is stretched so that grid A reaches the specified initial displacement. After the fuel assembly 4 stabilizes for a set time, the power supply of the magnetic attraction stretching and releasing device 23 is cut off. The fuel assembly 4 rebounds and the adjacent layer of grid A and the grid B in this layer collide with the coaming. The test element collects data. Three tests are carried out for the specified initial displacement of the adjacent layer of grid A, and the test results are averaged. The same method is used to obtain test data for the adjacent layer of grid A at other specified initial displacements.

[0130] The present invention provides a technology for testing equivalent collision parameters of the actual grid of a fuel assembly 4 in an aqueous environment. Under conditions simulating the actual installation state of a rod-type fuel assembly 4 in a pressurized water reactor and a water environment, the collision force between the actual collision surfaces of different types of grids of the fuel assembly 4 and the simulated core enclosure, as well as the displacement of the grid of the fuel assembly 4, are tested to obtain the equivalent collision stiffness and equivalent collision damping between the grid and the enclosure in the aqueous environment. The designed test device sequentially tests grids of different types and heights. The displacement of the fuel assembly grid and the collision force between the grid and the simulated core panel are tested using two symmetrically arranged sets of sensors (displacement sensor and collision force sensor) to eliminate the influence of non-centering collision between the fuel assembly grid and the simulated core panel. The test device has sufficient rigidity along the collision direction (fundamental frequency greater than 50 Hz), and the rigidity of the simulated core panel collision surface is more than 10 times that of the fuel assembly grid, so as to accurately simulate the equivalent collision between the fuel assembly grid and the core panel in the actual core. The test device and test method can also be applied to the testing of equivalent collision parameters of the fuel assembly grid in air.

[0131] The design principle of the fuel assembly grid equivalent collision test method of the present invention is:

[0132] The test apparatus was used to simulate the collision of single-layer grids (grid A) or double-layer grids (grid B and adjacent grid A) with simulated core coamings under different initial tensile displacement conditions. The relative displacement and collision force data of the grids were collected. The nonlinear finite element model of fuel assembly 4 was used for iterative calculations to obtain converged solutions for the equivalent collision stiffness and equivalent collision damping of the grids of fuel assembly 4. The obtained data reflect the collision characteristics of the actual grid surface of fuel assembly 4 and the simulated core coaming in a water environment.

[0133] First of all, it should be noted that “inward” refers to the direction toward the center of the accommodating space, and “outward” refers to the direction away from the center of the accommodating space.

[0134] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "circumferential" and the like indicate positions or location relationships based on the attached drawings. Figure 1 The orientation or positional relationship shown is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0135] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0136] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0137] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0138] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0139] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A fuel assembly grid equivalent collision test device, characterized in that: It includes the simulated core panel inner frame, outer water tank assembly, loading device and test elements, including: The fuel assembly is placed in the inner frame of the simulated core shroud; The simulated core shroud inner frame is placed in the outer water tank assembly; The space between the outer water tank assembly and the simulated core shroud inner frame and the interior of the simulated core shroud inner frame are filled with fluid medium; The loading device passes through the outer water tank assembly and the inner frame of the simulated core shroud and is then transmission-connected to the grid of the fuel assembly; The test element is mounted on the inner frame of the simulated core shroud to measure physical quantities of fuel assembly grid collision; The loading device includes a bracket, a fixed pulley A, a fixed pulley B, a magnetic tension release device, a steel wire rope and a grid steel hoop, wherein: The bracket is fixed beside the outer water tank assembly, and the height of the bracket is adjustable; The fixed pulley A is installed on the top of the bracket; The fixed pulley B is mounted on the side of the bracket away from the outer water tank assembly; The grid steel hoop is U-shaped and is clamped on the outside of the grid of the fuel assembly; One end of the steel wire rope is connected to the grid steel hoop, and the other end passes through the fixed pulley A and the fixed pulley B in sequence and is connected to the magnetic attraction stretching and releasing device.

2. The fuel assembly grid equivalent collision test device according to claim 1, characterized in that: The test element includes a displacement sensor and a collision force sensor installed on the inner frame of the simulated core shroud, and a force collision plate pressed on the surface of the collision force sensor.

3. The fuel assembly grid equivalent collision test device according to claim 2, characterized in that: There are two displacement sensors, which are arranged on the opposite side baffles of the inner frame of the simulated core panel; there are two collision force sensors, which are symmetrically arranged at both ends of the panel on one side of the inner frame of the simulated core panel.

4. The fuel assembly grid equivalent collision test device according to claim 1, characterized in that: The grid steel hoop includes a U-shaped steel hoop and a reinforcement plate fixed on the U-shaped steel hoop crossbeam. The U-shaped steel hoop and the reinforcement plate are both made of steel plates, and the thickness of the reinforcement plate is greater than the steel plate thickness of the U-shaped steel hoop; the reinforcement plate is also provided with a pull ring for the steel wire rope to pass through.

5. The fuel assembly grid equivalent collision test device according to claim 1, characterized in that: The bracket includes four columns, an angle steel beam connected between two adjacent columns, and a bracket base plate installed at the bottom of the four columns; each column is composed of four channel steels with different waist heights stacked together, and each channel steel is provided with multiple positioning holes, and the height adjustment of the column is achieved by passing bolts through different positioning holes of two adjacent channel steels.

6. The fuel assembly grid equivalent collision test device according to claim 1, characterized in that: The simulated core panel inner frame includes panels located on the left and right sides, baffles located on the front and back sides, a simulated core upper plate and a simulated core lower plate located at the top and bottom; the simulated core upper plate and the simulated core lower plate are both provided with positioning pin mounting holes for positioning the fuel assemblies, and the inner cavity specifications of the simulated core panel inner frame are adapted to the fuel assembly specifications, so that after the fuel assembly is installed in the simulated core panel inner frame, the gap between the fuel assembly and the panel and the baffle is within the set gap range; a plurality of measuring holes are provided on the baffle near the panel position along the height direction; tie rod holes are respectively provided at corresponding positions of the simulated core panel inner frame and the outer water tank assembly, and the tie rod passes through the tie rod hole to realize the connection between the simulated core panel inner frame and the outer water tank assembly.

7. The fuel assembly grid equivalent collision test device according to claim 1, characterized in that: The outer water tank assembly includes an outer water tank and a steel support. The outer water tank is a rectangular box structure with a bottom plate. The outer side walls of the outer water tank are arranged with crisscross reinforcement ribs. The steel support is arranged around the outer water tank. The bottom of the outer water tank is pushed to the bottom of the inner frame of the simulated core panel by bolts on all four sides.

8. A fuel assembly grid equivalent collision test method, characterized in that: The fuel assembly grid equivalent collision test device according to any one of claims 1 to 7 comprises the following steps: Step S1, installation of the fuel assembly grid equivalent collision test apparatus: including installation of the outer water tank, installation of the test element, installation of the fuel assembly to be tested, installation of the steel support, installation and height adjustment of the loading device, and also including measurement of the initial gap value c; Step S2, measuring the equivalent collision physical quantities of the fuel assembly grid: There is almost no collision between the upper and lower end grids of the fuel assembly and the coaming, so this is not considered in the calculation and analysis. Then, tests and measurements are conducted on all types of grids in the fuel assembly, and data on the horizontal displacement time history and the collision force time history of the coaming are collected; Step S3, calculation and analysis of equivalent collision parameters of the fuel assembly grid: a finite element calculation model for analyzing a single fuel assembly is established, and finite element calculation is performed on the fuel assembly to obtain equivalent collision parameters of each layer of the grid.

9. The fuel assembly grid equivalent collision test method according to claim 8, characterized in that: In step S2, the grid types in the fuel assembly include grid A and grid B, wherein: When testing grid A, the horizontal displacement time history and the impact force time history of each layer of grid A are collected sequentially. When measuring a certain layer of grid A, the fuel assembly is stretched until the grid A reaches the specified initial displacement. After the fuel assembly stabilizes for a set time, the power to the magnetic tension release device is disconnected. The fuel assembly rebounds and the grid A in that layer impacts the coaming. The test element then collects data. Three tests are conducted for each layer of grid A at the specified initial displacement, and the test results are averaged. The same method is used to obtain test data for the same layer of grid A at other specified initial displacements. When testing grid B, the horizontal displacement time history of each layer of grid B and its adjacent layer of grid A and the collision force time history of the impact on the coaming are collected in sequence; when measuring a certain layer of grid B, the grid A adjacent to the grid B to be tested is stretched so that the grid A reaches the specified initial displacement. After the fuel assembly stabilizes for a set time, the power supply of the magnetic attraction stretching and releasing device is cut off. The fuel assembly rebounds and the adjacent layer of grid A and the grid B of the layer collide with the coaming. The test element collects data. Three tests are carried out for the specified initial displacement of the adjacent layer of grid A, and the test results are averaged. The same method is used to obtain test data for the adjacent layer of grid A at other specified initial displacements.

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