Fuel assembly grid and nuclear fuel assembly
By replacing the lower guide vane with a lower guide rail structure in the fuel assembly grid, the problems of strip detachment and flow dead zone on the outer side of the grid were solved, which enhanced fluid exchange and reduced pressure drop, thereby reducing the risk of vibration failure of the fuel assembly and the difficulty of hoisting.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- CHINA NUCLEAR POWER DESIGN COMPANY
- Filing Date
- 2025-08-14
- Publication Date
- 2026-05-21
Smart Images
Figure CN2025114547_21052026_PF_FP_ABST
Abstract
Description
Fuel assembly racks and nuclear fuel assemblies Cross-reference to related applications
[0001] This application is based on and claims priority to Chinese Patent Application No. 202411609307.1, filed on November 12, 2024, the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application relates to the field of nuclear reactor technology, and more particularly to fuel assembly grids and nuclear fuel assemblies. Background Technology
[0003] A typical pressurized water reactor (PWR) core contains a large number of fuel assemblies. Aside from differences in fuel concentration, the parameters and structures of the various fuel assemblies within a PWR core are essentially the same. To select optimal burnup and flatten the radial neutron flux distribution throughout the core, a zoned concentration distribution is typically employed, where the fuel concentration in assemblies at the core periphery is higher than that in assemblies at the core center. After a given core cycle (e.g., one year), fuel assemblies in the higher-concentration core zones are swapped to lower-concentration zones, while new fuel assemblies are installed in the highest-concentration zone, and depleted or burned-out assemblies are removed from the lowest-concentration zone.
[0004] Aside from differences in fuel concentration, the fuel assemblies within the reactor core all share the same structure. Each fuel assembly essentially consists of a lower mounting base, an upper mounting base, an instrument tube, numerous control rod guide tubes, fuel rods, and a grid. For example, in a typical fuel assembly, the fuel rods can be arranged in a square grid, with 17 rod positions on each side. Each fuel assembly has a total of 289 rod positions: 264 for fuel rods, 24 for guide tubes, and one for an instrument tube.
[0005] The structural framework of the fuel assembly consists of its lower tube seat, upper tube seat, and guide / instrument tubes. The guide tubes extend longitudinally between the lower and upper tube seats, providing a rigid connection. Besides working together to form a rigid framework, each of these components has its own specific function. The lower tube seat guides the reactor coolant upwards into the fuel assembly, the guide tubes provide a channel for the control rods to insert into and pass through the fuel assembly, and the upper tube seat provides a platform for the star-shaped assembly supporting the control rods. The upper tube seat also has an opening through which coolant flows, while the lower and upper tube seats together prevent fuel from leaking upwards or downwards from the fuel assembly.
[0006] In the prior art described above, lattice frames are used to precisely maintain the distance between fuel rods in the reactor core, prevent fuel rod vibration, provide lateral support for the fuel rods, and, to some extent, utilize friction to prevent longitudinal movement of the fuel rods. A conventional design of the lattice frame includes numerous intersecting slats shaped like egg racks. This shape is designed to form numerous individual grids that house and support the fuel rods and control rod guide tubes. Each lattice frame's grids, positioned at a given location along the fuel rod axial direction, typically utilize elastic springs and relatively rigid protrusions (called positioning rigid protrusions) formed within the metal of the intersecting slats. The springs and positioning rigid protrusions of each lattice grid contact the corresponding fuel rod extending through the grid using friction. Furthermore, outer slats (outer strips) are attached together, surrounding the lattice slats from all sides, giving the lattice frame strength and rigidity.
[0007] The lattice structures used in the prior art (specifically, application numbers CN86101339 and CN86102042) have the following drawbacks:
[0008] 1) Grid guide vanes are prone to causing the outer strips of the grid to detach. According to experience, the detachment of the outer strips of the fuel grid has occurred in many pressurized water reactors at home and abroad because the grid contains guide vanes, which are hook-shaped. If the design is not reasonable, they can easily hook onto adjacent components, causing the outer strips of the grid to detach. Specifically, as shown in Figure 1, it is a schematic diagram of the structure in the prior art where the upper grid 1 and the lower grid 2 are placed without hooking. However, when using the existing grid structure, the lower guide vane of the upper grid 1 and the upper guide vane of the lower grid 2 are prone to hooking during the stacking of multiple grids, as shown in Figure 2, thus causing the outer strips of the grid to detach.
[0009] 2) The lower guide vane of the outer strip of the grid is located on the front side. When adjacent components are in close contact, a flow dead zone is generated, resulting in turbulence and a large pressure drop. Specifically, as shown in Figure 3, if we take the upper grid 1 in Figure 1 as an example, if a high-speed fluid of 4 m / s is introduced into the bottom of the grid 1, the lower guide vane of the upper grid 1 under the impact of the 4 m / s high-speed fluid can easily introduce a very large excitation to the grid / fuel assembly (as shown in the dashed circle area in Figure 3, the high-speed fluid will hit the guide vane to form a triangular area), thus introducing a negative effect of flow turbulence into the grid.
[0010] 3) The flow dead zone of the guide vane changes the vibration characteristics of the fuel assembly and can easily induce fuel rod flow-induced vibration failure. According to experience feedback, multiple units have experienced grid spring breakage and fuel rod failure. The turbulence of the guide vane at the bottom of the grid can easily cause secondary damage. The turbulence generated by the guide vane has a deteriorating effect on fuel rod vibration.
[0011] 4) The presence of the lower guide vane weakens the mixing effect of the upper guide vane; the presence of the lower guide vane reduces the flow velocity in the local area, and the fluid is bypassed to the nearby grid. The volumetric flow rate of the upper guide vane in the axial position will decrease significantly, thereby greatly weakening the mixing effect of the upper guide vane.
[0012] 5) Due to the presence of the lower guide vane, more clamping force is required. More clamping force can easily cause the fuel assembly to bend more deeply, thereby aggravating the difficulty of hoisting and local thermal and physical penalties. Application content
[0013] This application provides a fuel assembly grid and a nuclear fuel assembly, aiming to solve the problem that in the prior art, the fuel assembly grid has a hook-shaped lower guide vane, which not only easily hooks onto adjacent fuel assemblies, causing the outer strip of the grid to fall off, but also the lower guide vane is on the frontal surface and generates flow dead zones and turbulence after being in close contact with adjacent fuel.
[0014] In a first aspect, embodiments of this application provide a fuel assembly grid, applicable to end grids, intermediate grids, or churning grids, wherein the fuel assembly grid includes: a grid body, a lower guide rail structure, and an upper guide wing; the lower guide rail structure is located at the bottom end of the grid body, and the upper guide wing is located at the top end of the grid body; wherein the lower guide rail structure includes a plurality of parallel transverse strips and a plurality of parallel longitudinal strips, the plurality of transverse strips and the plurality of longitudinal strips dividing the bottom of the grid body into a plurality of grids; each of the plurality of transverse strips and each of the plurality of longitudinal strips is inclinedly provided with a guide rail at both ends; each guide wing of the upper guide wing is aligned with the corresponding transverse strip or longitudinal strip in the lower guide rail structure.
[0015] Secondly, this application also provides a fuel assembly grid for use in annular grids. The fuel assembly grid includes a grid body, a lower guide rail structure, and an upper guide wing. The lower guide rail structure is located at the bottom of the grid body, and the upper guide wing is located at the top of the grid body. The lower guide rail structure includes multiple parallel transverse strips and multiple parallel longitudinal strips, which divide the bottom of the grid body into multiple grids. Guide rails are inclinedly arranged at both ends of each of the multiple transverse strips and at both ends of each of the multiple longitudinal strips. Each guide wing in the upper guide wing is staggered from the corresponding transverse or longitudinal strip in the lower guide rail structure.
[0016] Thirdly, embodiments of this application also provide a nuclear fuel assembly, characterized in that it includes a fuel assembly grid as described in the first aspect above, or a fuel assembly grid as described in the second aspect above.
[0017] This application provides a fuel assembly grid and a nuclear fuel assembly. The fuel assembly grid includes a grid body, a lower guide rail structure, and an upper guide wing. The lower guide rail structure is located at the bottom of the grid body, and the upper guide wing is located at the top of the grid body. The lower guide rail structure includes multiple parallel transverse strips and multiple parallel longitudinal strips, which divide the bottom of the grid body into multiple grids. Guide rails are inclinedly arranged at both ends of each of the multiple transverse strips and at both ends of each of the multiple longitudinal strips. Each guide wing in the upper guide wing is aligned or staggered with the corresponding transverse or longitudinal strip in the lower guide rail structure. The nuclear fuel assembly includes the aforementioned fuel assembly grid. The aforementioned grid structure ensures that when it comes into contact with the grid below, its lower guide rail structure will not insert into the upper guide wing in the lower grid. This not only prevents the outer strip of the grid from detaching due to hooking onto adjacent fuel assemblies, but also reduces the pressure drop of the entire grid and enhances fluid exchange between the inside of the grid and its edges. At the same time, the grid has a low pressure drop and eliminates the need for a lower guide wing structure. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 is a schematic diagram of a structure in the prior art where multiple grids are placed without any hooking phenomenon;
[0020] Figure 2 is a schematic diagram of the structure in the prior art where hooking occurs when multiple grids are placed;
[0021] Figure 3 is a schematic diagram of the flow turbulence formed in the grid when a high-speed fluid passes through the bottom of the grid in the prior art;
[0022] Figure 4 is a schematic diagram of the structure of the fuel assembly grid provided in an embodiment of this application;
[0023] Figure 5 is a schematic diagram of the front view structure of the fuel assembly grid provided in an embodiment of this application;
[0024] Figure 6 is a side view of the lower guide rail structure of the fuel assembly grid provided in the embodiment of this application;
[0025] Figure 7 is a schematic diagram of the structure of a fuel assembly grid provided in an embodiment of this application when stacked with another fuel assembly grid;
[0026] Figure 8 is a schematic diagram of fluid flowing from the lower guide rail structure into the grid body in the fuel assembly grid provided in the embodiment of this application;
[0027] Figure 9 is a schematic diagram of the structure of a fuel assembly grid provided in another embodiment of this application. Detailed Implementation
[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0029] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.
[0030] It should also be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this application specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.
[0031] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.
[0032] Please refer to Figures 4 and 5 simultaneously. Figure 4 is a structural schematic diagram of the fuel assembly grid provided in this embodiment of the application; Figure 5 is a front view structural schematic diagram of the fuel assembly grid provided in this embodiment of the application. As shown in Figures 4 and 5, this embodiment of the application discloses a fuel assembly grid, which is applied to an end grid, an intermediate grid, or a mixing grid. The fuel assembly grid 100 includes: a grid body 110, a lower guide rail structure 130, and an upper guide wing 120. The lower guide rail structure 130 is located at the bottom end of the grid body 110, and the upper guide wing 120 is located at the top end of the grid body 110. The lower guide rail structure 130 includes a plurality of parallel transverse strips 131 and a plurality of parallel transverse strips 131. Multiple longitudinal strips 132 are arranged, and the multiple transverse strips 131 and the multiple longitudinal strips 132 divide the bottom of the grid body 110 into grids 111; guide rails are inclinedly arranged at both ends of each transverse strip 1311 and each longitudinal strip 1321; each guide wing in the upper guide wing 120 is aligned with the corresponding transverse strip 1311 or longitudinal strip 1321 in the lower guide rail structure 130.
[0033] In this embodiment, the outer wall of the grid portion in the grid body 110 is attached with an outer grid strip, and the grid portion (not shown in the figure) includes multiple grid body grids with square cross-sections. For example, the grid portion includes fewer / more grids such as 17*17, 16*16, 15*15, or 13*13, that is, the overall cross-section of the grid portion can also be regarded as square. In the grid portion, each grid body grid is set as a hollow structure and is used to exclusively accommodate fuel rods, control rod guide tubes, or instrument tubes. Moreover, the inner wall of the hollow structure of each grid body grid is provided with an elastic spring and a positioning rigid protrusion (neither the spring nor the positioning rigid protrusion is shown in the figure) to contact the corresponding fuel rod, control rod guide tube, or instrument tube extending through the grid using friction. When the fuel rods, control rod guide tubes, or instrument tubes are placed in the hollow structure of each grid body grid in the grid portion, they are arranged in a square lattice. Outer strips 112 are provided around the four outer walls of the grid portion in the grid body 110, so that the outer strips 112 surround the grid portion of the grid body 110 from all sides, thereby giving the fuel assembly grid 100 strength and rigidity.
[0034] Furthermore, unlike existing fuel assembly grids where a lower guide wing is provided at the bottom of the outer strip, this embodiment does not have a lower guide wing at the bottom of the outer strip. Instead, the lower guide rail structure 130 is directly located at the bottom end of the grid body 110, more specifically at the bottom end of the grid portion within the grid body 110 (i.e., the lower guide rail structure 130 and the grid portion within the grid body 110 are integrally formed). With this configuration, when two adjacent fuel assembly grids are stacked, the lower guide rail structure of the upper fuel assembly grid will not insert into the upper guide wing of the lower fuel assembly grid (in the prior art, the lower guide wing on the fuel assembly grid protrudes and easily hooks onto the outer strip of adjacent fuel assemblies), reducing the risk of the lower guide wing inserting into adjacent assemblies.
[0035] Taking a lattice section of the lattice body 110 comprising 17*17 grids as an example, the lower guide rail structure 130 includes 16 parallel and equally spaced horizontal strips and 16 parallel and equally spaced vertical strips. Through this arrangement, the bottom of the lattice body 110 is divided into 17*17 grids 111, and each of these 17*17 grids 111 corresponds one-to-one with a lattice body grid in the lattice section; that is, each grid 111 aligns with one lattice body grid. Furthermore, guide rails (which can be more figuratively considered as a ramp structure) are inclinedly arranged at both ends of the 16 horizontal strips (i.e., the 16 vertical strips).
[0036] When two adjacent fuel assembly grids are stacked, the guide rail in the lower guide rail structure of the upper fuel assembly grid 100 contacts the upper guide wing of the lower fuel assembly grid 101, as shown in Figure 7. Compared with the prior art shown in Figure 2, this effectively avoids the hooking phenomenon between the upper and lower fuel assembly grids. The guide rail in the lower guide rail structure of the upper fuel assembly grid and the upper guide wing of the lower fuel assembly grid 101 together constitute the guiding function for lifting and refueling in nuclear fuel assemblies, which not only enhances the mixing effect at the grid edge (as shown in Figure 8), but also enhances the fluid exchange between the inside of the grid and the grid edge. For example, when a fuel assembly grid is specifically applied to a nuclear fuel assembly, if a high-speed fluid of 4 m / s flows over the lower guide rail structure, compared to existing grids using lower guide vanes, the existing grids using lower guide vanes are more likely to introduce very large excitation to the grid / fuel assembly (i.e., the high-speed fluid will impact the triangular area formed by the guide vanes, causing very large excitation, as shown in the dashed circle area in Figure 3; the high-speed fluid will introduce a negative effect of flow turbulence into the grid), while the lower guide rail structure will not bring about the negative effect caused by excitation. In this embodiment, because the lower guide rail structure replaces the lower guide vanes, the pressure drop of the fuel assembly grid decreases (because the projection of the lower guide rail structure on the bottom surface of the grid body is smaller than the projection of the existing lower guide vanes on the bottom surface of the grid body), and the pressure drop is distributed to other components in the nuclear fuel assembly.
[0037] To apply the fuel assembly grid of this embodiment to end grids, intermediate grids, or churning grids, each guide wing in the upper guide wing 120 can be aligned with a corresponding transverse or longitudinal strip in the lower guide rail structure 130. For example, taking a grid body 110 with a square cross-section and its grid portion comprising 17*17 grid body grids as an example, if 16 longitudinal strips are arranged parallel and at equal intervals on one inner sidewall of the grid portion, then 16 guide wings are correspondingly arranged at equal intervals on the top of the grid body 110 (more specifically, the top of the outer grid strip 112), and each guide wing is aligned with a lower longitudinal strip. Similarly, if 16 transverse strips are arranged parallel and at equal intervals on one inner sidewall of the grid portion, then 16 guide wings are correspondingly arranged at equal intervals on the top of the grid body 110 (more specifically, the top of the outer grid strip), and each guide wing is aligned with a lower transverse strip.
[0038] In one embodiment, as shown in Figures 4-7, the guide rails inclined at both ends of each of the plurality of transverse strips 1311 are respectively denoted as the first guide rail 1311a and the second guide rail 1311b. If the included angle between the first guide rail 1311a and the bottom end face of the grid body 110 is denoted as the first included angle θ1, and the included angle between the second guide rail 1311b and the bottom end face of the grid body 110 is denoted as the second included angle θ2, the first included angle θ1 and the second included angle θ2 are equal.
[0039] In this embodiment, after symmetrically setting the two ends of each of the plurality of transverse strips 1311 with the same tilt angle, the fuel assembly grid of this application embodiment has a symmetrical structure. When the first guide rail 1311a or the second guide rail 1311b comes into contact with another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into the adjacent assembly, but also prevents the outer strip of the grid from falling off during operation.
[0040] In one embodiment, as shown in Figures 4-7, the guide rails inclined at both ends of each longitudinal strip 132 in the plurality of longitudinal strips are respectively denoted as the third guide rail 1321a and the fourth guide rail 1321b. If the included angle between the third guide rail 1321a and the bottom end face of the grid body 110 is denoted as the third included angle θ3, and the included angle between the fourth guide rail 1321b and the bottom end face of the grid body 110 is denoted as the fourth included angle θ4, the third included angle θ3 and the fourth included angle θ4 are equal.
[0041] In this embodiment, similar to the first guide rail 1311a and the second guide rail 1311b, which are symmetrically arranged at both ends of each of the plurality of transverse strips 1311 with the same tilt angle, the third guide rail 1321a and the fourth guide rail 1321b, which are symmetrically arranged at both ends of each of the plurality of longitudinal strips 1321 with the same tilt angle, are also provided. Similarly, when the third guide rail 1321a or the fourth guide rail 1321b contacts another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into adjacent components but also prevents the outer strips of the grid from detaching during operation.
[0042] In one embodiment, as shown in Figures 4-7, the angle between the guide rails inclined at both ends of each of the plurality of transverse strips and the bottom surface of the grid body, and the angle between the guide rails inclined at both ends of each of the plurality of longitudinal strips and the bottom surface of the grid body, are both in the range of 40°-80°.
[0043] In this embodiment, the first included angle θ1 to the fourth included angle θ4 are all set to have the same value, and the range of the first included angle θ1 to the fourth included angle θ4 is set to 40°-80° (that is, the first included angle θ1 is equal to the third included angle θ3, and the range of the first included angle θ1, the second included angle θ2, the third included angle θ3 and the fourth included angle θ4 is 40°-80°). This allows any guide rail in the current pressure drop anti-snagging fuel assembly grid (that is, any one of the first guide rail 1311a, the second guide rail 1311b, the third guide rail 1321a and the fourth guide rail 1321b) to be compatible with the upper guide wing of another fuel assembly grid located below, reducing the difficulty of stacking and installing adjacent pressure drop anti-snagging fuel assembly grids. Similarly, when any one of the first guide rail 1311a, the second guide rail 1311b, the third guide rail 1321a, and the fourth guide rail 1321b comes into contact with another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into the adjacent assembly, but also prevents the outer strip of the grid from falling off during operation.
[0044] In one embodiment, as shown in Figures 4-7, the longitudinal height of the first guide slide rail 1311a, the second guide slide rail 1311b, the third guide slide rail 1321a, and the fourth guide slide rail 1321b is less than or equal to 13mm.
[0045] In this embodiment, in order to reduce the degree of modification to the grid body 110, the first guide slide rail 1311a, the second guide slide rail 1311b, the third guide slide rail 1321a and the fourth guide slide rail 1321b can be set in the lower guide slide rail structure 130. A straight line perpendicular to the bottom end face of the grid body 110 is recorded as the longitudinal axis. Then, the projected length (i.e., longitudinal height) of the first guide slide rail 1311a, the second guide slide rail 1311b, the third guide slide rail 1321a and the fourth guide slide rail 1321b relative to the longitudinal axis is less than or equal to 13mm. If the upper and lower ends of the first guide rail 1311a, the second guide rail 1311b, the third guide rail 1321a, and the fourth guide rail 1321b are all projected onto the longitudinal axis, and the plane passing through the projection points of the top ends of each guide rail on the longitudinal axis and parallel to the bottom surface of the grid body 110 is denoted as the first plane, and the plane passing through the projection points of the bottom ends of each guide rail on the longitudinal axis and parallel to the bottom surface of the grid body 110 is denoted as the second plane, the distance between the first plane and the second plane does not exceed 13mm. This ensures that when the lower guide rail structure 130 is added to the grid body 110 and integrally formed with it, the degree of modification to the grid body 110 is minimal. Firstly, this arrangement ensures that each guide rail in the lower guide rail structure not only guarantees the installation guidance function but also reduces the pressure drop of the fluid passing through the bottom of the grid. Secondly, the above structure reduces the overall pressure drop of the fuel assembly grid, thereby reducing the overall nuclear fuel assembly clamping force and reducing assembly bending.
[0046] In one embodiment, as shown in Figures 4-7, the upper guide wing 120 is disposed at the top end of the outer strip 112 of the grid body; if the total number of multiple guide wings disposed at the top end of each outer strip 112 in the grid body 110 is recorded as the first guide wing number, and the total number of grids included in the grid body 110 along the transverse or longitudinal direction is recorded as the first grid number, then the difference between the first grid number and the first guide wing number is equal to the first preset number difference value.
[0047] In this embodiment, the upper guide wing 120 is specifically disposed at the top of the outer strip 112 of the grid body, such that each guide wing in the upper guide wing 120 is aligned with the corresponding transverse or longitudinal strip in the lower guide rail structure 130. Taking a square-section grid body 110 with a grid portion comprising 17*17 grids as an example, the grid portion includes 17 grids in the transverse or longitudinal direction, i.e., the first grid number is 17. Since the grid body 110 comprising 17*17 grids includes 16 guide plates in the transverse or longitudinal direction, when each guide wing in the upper guide wing 120 is aligned with the corresponding transverse or longitudinal strip in the lower guide rail structure 130, 16 guide wings are also required, i.e., the first guide wing number is 16. At this time, the difference between the number of the first grid and the number of the first guide vanes is equal to the first preset number difference (that is, the first preset number difference is set to 1). Through the above setting method, the fuel assembly grid of this application embodiment can be specifically applied to the end grid, the middle grid, or the turbulence grid.
[0048] In one embodiment, as shown in Figures 4-7, among the multiple guide wings provided on the top end of each outer strip 112 of the grid body 110, the projection of each guide wing on the top surface of the grid body 110 is located in the area formed by the top surfaces of two adjacent grids in the grid body 110.
[0049] In this embodiment, referring to the above example, when the bottom of the grid body 110 with a square cross-section is divided into 17*17 grids 111, taking the upper guide wing 120 on one outer strip 112 of the grid body 110 as an example, when each guide wing in the upper guide wing 120 is aligned with the corresponding transverse or longitudinal strip in the lower guide rail structure 130, 16 guide wings need to be set. Since the top surface of the grid body 110 has 4 sides, a total of 4 outer strips 112 need to be set, each outer strip 112 has 16 guide wings, and a total of 64 guide wings are set on the 4 outer strips 112.
[0050] Taking the 16 guide vanes provided on an outer strip 112 of a grid as an example, the shape of each of the 16 guide vanes and the included angle between each guide vane and the top surface of the grid body are exactly the same. If the cross-section of each guide vane is an isosceles triangle and the included angle between each guide vane and the top surface of the grid body 110 is less than 90 degrees, then the projection of each guide vane onto the top surface of the grid body 110 is an isosceles triangle, and the projection of each guide vane onto the top surface of the grid body 110 is located in the area formed by the top surfaces of two adjacent grids in the grid body 110. More specifically, when each guide wing is projected onto the area formed by the top surfaces of two adjacent grids in the lattice body 110, the altitude of the base of the isosceles triangle coincides with the boundary line of the two adjacent grids. Furthermore, the area on one side of the altitude of the base of the isosceles triangle is located in one of the two adjacent grids in the lattice body 110, and the area on the other side of the altitude of the base of the isosceles triangle is located in the other of the two adjacent grids in the lattice body 110. It is evident that this symmetrical upper guide wing structure allows each guide wing to be aligned with a longitudinal or transverse strip, creating a structure that facilitates fluid flow.
[0051] This application also provides a fuel assembly grid according to another embodiment. Please refer to Figure 9, which is a structural schematic diagram of a fuel assembly grid provided in another embodiment of this application. As shown in Figure 9, another embodiment of this application discloses a fuel assembly grid applied to an annular grid. The fuel assembly grid 200 includes: a grid body 210, a lower guide rail structure 230, and an upper guide wing 220. The lower guide rail structure 230 is located at the bottom end of the grid body 210, and the upper guide wing 220 is located at the top end of the grid body 210. The lower guide rail structure 230 includes a plurality of parallel transverse strips 231 and a plurality of parallel longitudinal strips. The strips 232, the plurality of transverse strips 231 and the plurality of longitudinal strips 232 divide the bottom of the grid body 210 into a plurality of grids 211; both ends of each transverse strip 2311 and both ends of each longitudinal strip 2321 are inclinedly provided with guide rails; each guide wing in the upper guide wing 220 is staggered from the corresponding transverse strip 2311 or longitudinal strip 2321 in the lower guide rail structure 230.
[0052] In this embodiment, the outer wall of the grid portion in the grid body 210 is attached with a grid outer strip, and the grid portion (not shown in the figure) includes multiple grid body grids with square cross-sections. For example, the grid portion includes fewer / more grids such as 17*17, 16*16, 15*15, or 13*13, that is, the overall cross-section of the grid portion can also be regarded as square. In the grid portion, each grid body grid is set as a hollow structure and is used to exclusively accommodate fuel rods, control rod guide tubes, or instrument tubes. Moreover, the inner wall of the hollow structure of each grid body grid is provided with an elastic spring and a positioning rigid protrusion (neither the spring nor the positioning rigid protrusion is shown in the figure) to contact the corresponding fuel rods, control rod guide tubes, or instrument tubes extending through the grid using friction. When the fuel rods, control rod guide tubes, or instrument tubes are placed in the hollow structure of each grid body grid in the grid portion, they are arranged in a square dot matrix. Outer strips 212 are provided around the four outer walls of the grid portion in the grid body 210, so that the outer strips 212 surround the grid portion of the grid body 210 from all sides, thereby giving the fuel assembly grid 200 strength and rigidity.
[0053] Furthermore, unlike existing fuel assembly grids where a lower guide wing is provided at the bottom of the outer strip, this embodiment does not have a lower guide wing at the bottom of the outer strip. Instead, the lower guide rail structure 230 is directly located at the bottom end of the grid body 210, more specifically at the bottom end of the grid portion within the grid body 210 (i.e., the lower guide rail structure 230 and the grid portion within the grid body 210 are integrally formed). With this configuration, when two adjacent fuel assembly grids are stacked, the lower guide rail structure of the upper fuel assembly grid will not insert into the upper guide wing of the lower fuel assembly grid (in the prior art, the lower guide wing on the fuel assembly grid protrudes and easily hooks onto the outer strip of adjacent fuel assemblies), reducing the risk of the lower guide wing inserting into adjacent assemblies.
[0054] Taking a lattice section of the lattice body 210 comprising 17*17 grids as an example, the lower guide rail structure 230 includes 16 parallel and equally spaced horizontal strips and 16 parallel and equally spaced vertical strips. Through this arrangement, the bottom of the lattice body 210 is divided into 17*17 grids 211, and each of these 17*17 grids 211 corresponds one-to-one with a lattice body grid in the grid section; that is, each grid 211 aligns with one lattice body grid. Furthermore, guide rails (which can be more figuratively considered as a ramp structure) are inclinedly arranged at both ends of the 16 horizontal strips (i.e., the 16 vertical strips).
[0055] When two adjacent fuel assembly grids are stacked, the guide rail in the lower guide rail structure of the upper fuel assembly grid contacts the upper guide wing of the lower fuel assembly grid. Compared with the prior art shown in Figure 2, this effectively avoids the hooking phenomenon between the upper and lower fuel assembly grids. The guide rail in the lower guide rail structure of the upper fuel assembly grid and the upper guide wing of the lower fuel assembly grid together constitute the guiding function for lifting and refueling in nuclear fuel assemblies. This not only enhances the mixing effect at the grid edge but also strengthens the fluid exchange between the grid interior and the grid edge. For example, when a fuel assembly grid is specifically applied to a nuclear fuel assembly, if a high-speed fluid of 4 m / s flows over the lower guide rail structure, compared to existing grids using lower guide vanes, the existing grids using lower guide vanes are more likely to introduce very large excitation to the grid / fuel assembly (i.e., the high-speed fluid will impact the triangular area formed by the guide vanes, causing very large excitation, as shown in the dashed circle area in Figure 3; the high-speed fluid will introduce a negative effect of flow turbulence into the grid), while the lower guide rail structure will not bring about the negative effect caused by excitation. In this embodiment, because the lower guide rail structure replaces the lower guide vanes, the pressure drop of the fuel assembly grid decreases (because the projection of the lower guide rail structure on the bottom surface of the grid body is smaller than the projection of the existing lower guide vanes on the bottom surface of the grid body), and the pressure drop is distributed to other components in the nuclear fuel assembly.
[0056] To apply the fuel assembly grid of this embodiment to an annular grid, each guide wing in the upper guide wing 220 can be staggered from the corresponding transverse or longitudinal strip in the lower guide rail structure 230. This is the main difference from the fuel assembly grid in the previous embodiment of this application. For example, taking a grid body 210 with a square cross-section and its grid portion including 17*17 grid body grids as an example, if 16 longitudinal strips are arranged parallel and at equal intervals on one inner sidewall of the grid portion, then 8 guide wings are arranged at equal intervals on the top of the grid body 210 (more specifically, the top of the outer strip 212 of the grid), and each guide wing is not aligned with a longitudinal strip below it. Of course, if 16 transverse strips are arranged parallel and at equal intervals on one inner sidewall of the grid portion, then 8 guide wings are arranged at equal intervals on the top of the grid body 210 (more specifically, the top of the outer strip of the grid), and each guide wing is not aligned with a transverse strip below it.
[0057] In one embodiment, as shown in FIG9, the guide rails inclined at both ends of each of the plurality of transverse strips 2311 are respectively referred to as the first guide rail 2311a and the second guide rail 2311b. If the included angle between the first guide rail 2311a and the bottom end face of the grid body 210 is referred to as the first included angle, and the included angle between the second guide rail 2311b and the bottom end face of the grid body 210 is referred to as the second included angle, the first included angle and the second included angle are equal.
[0058] In this embodiment, after symmetrically setting the two ends of each of the plurality of transverse strips 2311 with the same tilt angle, the fuel assembly grid of this application embodiment has a symmetrical structure. When the first guide rail 2311a or the second guide rail 2311b comes into contact with another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into the adjacent component, but also prevents the outer strip of the grid from falling off during operation.
[0059] In one embodiment, as shown in FIG9, the guide rails inclined at both ends of each longitudinal strip 232 in the plurality of longitudinal strips are respectively referred to as the third guide rail 2321a and the fourth guide rail 2321b. If the included angle between the third guide rail 2321a and the bottom end face of the grid body 210 is referred to as the third included angle, and the included angle between the fourth guide rail 2321b and the bottom end face of the grid body 210 is referred to as the fourth included angle, the third included angle and the fourth included angle are equal.
[0060] In this embodiment, similar to the first guide rail 2311a and the second guide rail 2311b, which are symmetrically arranged at both ends of each of the plurality of transverse strips 2311 with the same tilt angle, the third guide rail 2321a and the fourth guide rail 2321b, which are symmetrically arranged at both ends of each of the plurality of longitudinal strips 2321 with the same tilt angle, are also provided. Similarly, when the third guide rail 2321a or the fourth guide rail 2321b contacts another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into adjacent components but also prevents the outer strips of the grid from detaching during operation.
[0061] In one embodiment, the angle between the guide rails inclined at both ends of each of the plurality of transverse strips and the bottom surface of the grid body, and the angle between the guide rails inclined at both ends of each of the plurality of longitudinal strips and the bottom surface of the grid body, are both in the range of 40°-80°.
[0062] In this embodiment, the first to fourth included angles are all set to have the same value, and the range of the first to fourth included angles is set to 40°-80° (that is, the first included angle is equal to the third included angle, and the range of the first included angle, the second included angle, the third included angle and the fourth included angle is 40°-80°). This allows any guide rail in the current pressure drop anti-snagging fuel assembly grid (that is, any one of the first guide rail 2311a, the second guide rail 2311b, the third guide rail 2321a and the fourth guide rail 2321b) to be compatible with the upper guide wing of another fuel assembly grid located below, reducing the difficulty of stacking and installing adjacent pressure drop anti-snagging fuel assembly grids. Similarly, when any one of the first guide rails 2311a, the second guide rail 2311b, the third guide rail 2321a, and the fourth guide rail 2321b comes into contact with another fuel assembly grid located below, it will not insert into the upper guide wing of the other fuel assembly grid. This not only reduces the risk of the lower guide wing inserting into the adjacent assembly, but also prevents the outer strip of the grid from falling off during operation.
[0063] In one embodiment, as shown in FIG9, the longitudinal height of the first guide slide rail 2311a, the second guide slide rail 2311b, the third guide slide rail 2321a and the fourth guide slide rail 2321b is less than or equal to 13mm.
[0064] In this embodiment, in order to reduce the degree of modification to the grid body 210, the first guide slide rail 2311a, the second guide slide rail 2311b, the third guide slide rail 2321a and the fourth guide slide rail 2321b can be set in the lower guide slide rail structure 230. A straight line perpendicular to the bottom end face of the grid body 210 is recorded as the longitudinal axis. Then, the projected length (i.e., longitudinal height) of the first guide slide rail 2311a, the second guide slide rail 2311b, the third guide slide rail 2321a and the fourth guide slide rail 2321b relative to the longitudinal axis is less than or equal to 13mm. If the upper and lower ends of the first guide rail 2311a, the second guide rail 2311b, the third guide rail 2321a, and the fourth guide rail 2321b are all projected onto the longitudinal axis, and the plane passing through the projection points of the top ends of each guide rail on the longitudinal axis and parallel to the bottom surface of the grid body 210 is denoted as the first plane, and the plane passing through the projection points of the bottom ends of each guide rail on the longitudinal axis and parallel to the bottom surface of the grid body 210 is denoted as the second plane, the distance between the first plane and the second plane does not exceed 13mm. This ensures that when the lower guide rail structure 230 is added to the grid body 210 and integrally formed with it, the degree of modification to the grid body 210 is minimal. Firstly, this arrangement ensures that each guide rail in the lower guide rail structure not only guarantees the installation guidance function but also reduces the pressure drop of the fluid passing through the bottom of the grid. Secondly, the above structure reduces the overall pressure drop of the fuel assembly grid, thereby reducing the overall nuclear fuel assembly clamping force and reducing assembly bending.
[0065] In one embodiment, as shown in FIG9, the upper guide wing 220 is disposed at the top end of the outer strip 212 of the grid body; if the total number of multiple guide wings disposed at the top end of each outer strip 212 in the grid body 210 is recorded as the second guide wing number, and the total number of grids included in the grid body 210 along the transverse or longitudinal direction is recorded as the first grid number, then the difference between the first grid number and the second guide wing number is equal to the second preset number difference value.
[0066] In this embodiment, the upper guide wing 220 is specifically disposed at the top of the outer strip 212 of the grid body, such that each guide wing in the upper guide wing 220 is staggered from the corresponding transverse or longitudinal strip in the lower guide rail structure 230. Taking a square-section grid body 210 with a grid portion comprising 17*17 grids as an example, the grid portion includes 17 grids in the transverse or longitudinal direction, i.e., the first grid number is 17. Since the grid body 210 comprising 17*17 grids includes 16 guide plates in the transverse or longitudinal direction, when each guide wing in the upper guide wing 220 is staggered from the corresponding transverse or longitudinal strip in the lower guide rail structure 230, 8 guide wings can be provided, i.e., the second guide wing number is 8. At this point, the difference between the number of the first grid and the number of the second guide vanes is equal to the second preset number difference (i.e., the second preset number difference is set to 9). Through the above configuration, the fuel assembly grid of this embodiment can be specifically applied to annular grids.
[0067] In one embodiment, as shown in FIG9, among the multiple guide wings provided on the top end of each outer strip 212 of the grid body 210, the projection of each guide wing on the top surface of the grid body 210 is located in the area of the top surface of one of the grids of the grid body 210.
[0068] In this embodiment, referring to the above example, when the grid body 210 has a square cross-section and its bottom is divided into 17*17 grids 211, taking the upper guide wing 220 on one outer grid strip 212 of the grid body 210 as an example, when each guide wing in the upper guide wing 220 is offset from the corresponding transverse or longitudinal strip in the lower guide rail structure 230, 8 guide wings can be provided. Since the top surface of the grid body 210 has 4 sides, a total of 4 outer grid strips 212 need to be provided, and each outer grid strip 212 has 8 guide wings, for a total of 32 guide wings provided on the 4 outer grid strips 212.
[0069] Taking the eight guide vanes arranged on an outer strip 212 of a grid as an example, the shape of each of the eight guide vanes and the included angle between each guide vane and the top surface of the grid body are exactly the same. If the cross-section of each guide vane is an isosceles triangle and the included angle between each guide vane and the top surface of the grid body 210 is less than 90 degrees, then the projection of each guide vane onto the top surface of the grid body 210 is an isosceles triangle, and the projection of each guide vane onto the top surface of the grid body 210 is located in the area where the top surface of one of the grid cells of the grid body 210 is located. It can be seen that through this upper guide vane structure, a structure that facilitates the circular flow of fluid is formed.
[0070] This application also provides a nuclear fuel assembly, which includes any one of the two fuel assembly grids described above.
[0071] In the nuclear fuel assembly, the lower guide vanes used in the prior art are eliminated in the fuel assembly grid, which reduces the pressure drop of the grid and the pressure drop of the entire nuclear fuel assembly. This also reduces the hydraulic lifting force in the entire nuclear fuel assembly, thereby reducing the required clamping force of the nuclear fuel assembly and reducing the degree of bending of the nuclear fuel assembly.
[0072] Furthermore, in nuclear fuel assemblies employing fuel assembly grids, placing the fuel rods within the hollow structure of the grid during implementation can significantly mitigate flow-induced vibrations and prevent damage to the fuel rod cladding.
[0073] In summary, the embodiments of this application provide a fuel assembly grid and a nuclear fuel assembly. The fuel assembly grid includes a grid body, a lower guide rail structure, and an upper guide wing. The lower guide rail structure is located at the bottom of the grid body, and the upper guide wing is located at the top of the grid body. The lower guide rail structure includes multiple parallel transverse strips and multiple parallel longitudinal strips, which divide the bottom of the grid body into multiple grids. Guide rails are inclinedly arranged at both ends of each of the multiple transverse strips and at both ends of each of the multiple longitudinal strips. Each guide wing in the upper guide wing is aligned or staggered with the corresponding transverse or longitudinal strip in the lower guide rail structure. The nuclear fuel assembly includes the aforementioned fuel assembly grid. The aforementioned grid structure ensures that when it comes into contact with the grid below, its lower guide rail structure will not insert into the upper guide wing in the lower grid. This not only prevents the outer strip of the grid from detaching due to hooking onto adjacent fuel assemblies, but also reduces the pressure drop of the entire grid and enhances fluid exchange between the inside of the grid and its edges. At the same time, the grid has a low pressure drop and eliminates the need for a lower guide wing structure.
[0074] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A fuel assembly lattice for use in an end lattice, an intermediate lattice, or a stirred lattice, characterized by, The fuel assembly grid includes: a grid body, a lower guide rail structure, and an upper guide wing; the lower guide rail structure is located at the bottom end of the grid body, and the upper guide wing is located at the top end of the grid body; wherein, the lower guide rail structure includes multiple parallel transverse strips and multiple parallel longitudinal strips, the multiple transverse strips and the multiple longitudinal strips dividing the bottom of the grid body into multiple grids; each of the multiple transverse strips and each of the multiple longitudinal strips is inclinedly provided with a guide rail at both ends; each guide wing in the upper guide wing is aligned with the corresponding transverse or longitudinal strip in the lower guide rail structure.
2. The fuel assembly lattice of claim 1, wherein, The guide rails at both ends of each of the plurality of transverse strips are respectively referred to as the first guide rail and the second guide rail. If the included angle between the first guide rail and the bottom end face of the grid body is referred to as the first included angle, and the included angle between the second guide rail and the bottom end face of the grid body is referred to as the second included angle, the first included angle and the second included angle are equal.
3. The fuel assembly lattice of claim 2, wherein, The guide rails inclined at both ends of each of the plurality of longitudinal strips are respectively referred to as the third guide rail and the fourth guide rail. If the included angle between the third guide rail and the bottom end face of the grid body is referred to as the third included angle, and the included angle between the fourth guide rail and the bottom end face of the grid body is referred to as the fourth included angle, the third included angle and the fourth included angle are equal.
4. The fuel assembly lattice of claim 3, wherein, The angle between the inclined guide rails at both ends of each of the plurality of transverse strips and the bottom surface of the lattice body, and the angle between the inclined guide rails at both ends of each of the plurality of longitudinal strips and the bottom surface of the lattice body, are both in the range of 40°-80°.
5. The fuel assembly spacer grid of claim 3, wherein, The longitudinal height of the first guide rail, the second guide rail, the third guide rail, and the fourth guide rail is less than or equal to 13mm.
6. The fuel assembly lattice of any of claims 1-5, wherein, The upper guide wing is located at the top of the outer strip of the grid body; if the total number of guide wings set at the top of each outer strip of the grid body is recorded as the first guide wing number, and the total number of grids included in the grid body along the horizontal or vertical direction is recorded as the first grid number, then the difference between the first grid number and the first guide wing number is equal to the first preset number difference value.
7. The fuel assembly spacer grid of claim 6, characterized in that In the lattice body, among the multiple guide wings provided at the top of each outer strip of the lattice, the projection of each guide wing on the top surface of the lattice body is located in the area formed by the top surfaces of two adjacent grids in the lattice body.
8. A fuel assembly lattice for use in a toroidal lattice, characterized in that The fuel assembly grid includes: a grid body, a lower guide rail structure, and an upper guide wing; the lower guide rail structure is located at the bottom end of the grid body, and the upper guide wing is located at the top end of the grid body; wherein, the lower guide rail structure includes multiple parallel transverse strips and multiple parallel longitudinal strips, the multiple transverse strips and the multiple longitudinal strips dividing the bottom of the grid body into multiple grids; each of the multiple transverse strips and each of the multiple longitudinal strips is inclinedly provided with a guide rail at both ends; each guide wing in the upper guide wing is staggered from the corresponding transverse or longitudinal strip in the lower guide rail structure.
9. The fuel assembly spacer grid of claim 8, characterized in that, The guide rails at both ends of each of the plurality of transverse strips are respectively referred to as the first guide rail and the second guide rail. If the included angle between the first guide rail and the bottom end face of the grid body is referred to as the first included angle, and the included angle between the second guide rail and the bottom end face of the grid body is referred to as the second included angle, the first included angle and the second included angle are equal.
10. The fuel assembly spacer grid of claim 9, characterized in that, The guide rails inclined at both ends of each of the plurality of longitudinal strips are respectively referred to as the third guide rail and the fourth guide rail. If the included angle between the third guide rail and the bottom end face of the grid body is referred to as the third included angle, and the included angle between the fourth guide rail and the bottom end face of the grid body is referred to as the fourth included angle, the third included angle and the fourth included angle are equal.
11. The fuel assembly lattice of claim 10, wherein, The angle between the inclined guide rails at both ends of each of the plurality of transverse strips and the bottom surface of the lattice body, and the angle between the inclined guide rails at both ends of each of the plurality of longitudinal strips and the bottom surface of the lattice body, are both in the range of 40°-80°.
12. The fuel assembly spacer grid of claim 10, wherein, The longitudinal height of the first guide rail, the second guide rail, the third guide rail, and the fourth guide rail is less than or equal to 13mm.
13. The fuel assembly lattice of any of claims 8-12, wherein, The upper guide wing is located at the top of the outer strip of the grid body; if the total number of guide wings set at the top of each outer strip of the grid body is recorded as the second guide wing number, and the total number of grids included in the grid body along the horizontal or vertical direction is recorded as the first grid number, then the difference between the first grid number and the second guide wing number is equal to the second preset number difference value.
14. The fuel assembly lattice of claim 13, wherein, In the lattice body, among the multiple guide wings provided at the top of each outer strip of the lattice, the projection of each guide wing on the top surface of the lattice body is located in the area of the top surface of one of the grids of the lattice body.
15. A nuclear fuel assembly characterized by, It includes the fuel assembly grid as described in any one of claims 1-7, or the fuel assembly grid as described in any one of claims 8-14.