Nuclear fuel assembly with enhanced anti-seismic performance and control rod value

Abstract

The invention relates to a nuclear fuel assembly suitable for a small modular reactor (SMR). Comprising a supporting grid 110 with 17 * 17 grid units, a plurality of fuel rods 120 arranged in the grid units of the supporting grid 110, a guide pipe 130 arranged and fixed in the grid units of the supporting grid 110, an upper fixing device 140 and a lower fixing device 150, wherein the upper fixing device 140 and the lower fixing device 150 are fixed to the top and the bottom of the guide pipe 130 respectively. Wherein the guide pipes 130 are arranged relative to a central unit of the supporting grid 110 according to the following mode: eight guide pipes are arranged in the main axis directions Ixx and Iyy, four guide pipes are arranged in the diagonal direction Ixy, and sixteen guide pipes are arranged in the non-diagonal directions Ixxy and Ixyy.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2024 - 0000467, filed on January 2, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a nuclear fuel assembly applicable to a Small Modular Reactor (SMR). Background Art

[0004] The core of a typical light water reactor includes a number of nuclear fuel assemblies, each nuclear fuel assembly including a number of long fuel rods and a number of tubular guide tubes for guiding control rods when the control rods move. The guide tubes are fixed to the upper fixing device and the lower fixing device of the nuclear fuel assembly, forming the framework of the nuclear fuel assembly.

[0005] The control rods contain a material that can absorb neutrons generated during the fission process. Conventionally, materials with a high neutron capture cross - section such as boron carbide (B4C), hafnium (Hf), or silver indium cadmium (Ag - In - Cd) are used.

[0006] For nuclear fuel assemblies of typical light water reactors, including the domestic APR1400 type, the design of the nuclear fuel assemblies is the same regardless of whether they are in the control rod position or the non - control rod position within the core. Even at core positions without guide control rods, all nuclear fuel assemblies are configured with guide tubes, which are used to construct a single framework structure of the nuclear fuel assembly.

[0007] A typical nuclear fuel assembly consists of a 17×17 support grid (mesh), with a total of 289 grid cells, of which 264 grid cells are equipped with fuel rods, 24 grid cells are equipped with guide tubes, and one grid cell is located in the center of the support grid for placing an instrument tube (also known as a measurement tube).

[0008] Meanwhile, the research and development of Small Modular Reactors (SMRs) is also underway. Such reactors can significantly reduce the volume and output power of traditional reactors. In theory, SMRs have the advantage of being small in size, making output control and reactor cooling easier.

[0009] The above is only to help understand the background of the present disclosure and does not mean that the present disclosure belongs to the scope of related technologies known to those skilled in the art.

[0010] Prior Art Documents

[0011] (Patent Document 1) Korean Patent Gazette No. 10-1994-0003796 (Publication Date: May 3, 1994)

[0012] (Patent Document 2) Korean Patent Gazette No. 10-1992-0007739 (Publication Date: September 16, 1992) Summary of the Invention

[0013] Technical Problem to be Solved

[0014] The present invention aims to provide a nuclear fuel assembly suitable for a small modular reactor (SMR).

[0015] Solution

[0016] To achieve the above object, a nuclear fuel assembly according to the present invention is provided, which includes a support grid having a 17×17 lattice unit; a plurality of fuel rods, each fuel rod being arranged in a lattice unit of the support grid; guide tubes arranged and fixed in the lattice units of the support grid; an upper fixing device and a lower fixing device respectively fixed to the top end and the bottom end of the guide tubes, wherein eight guide tubes are arranged in the principal axis directions Ixx and Iyy, four guide tubes are arranged in the diagonal direction Ixy, and sixteen guide tubes are arranged in the non-diagonal directions Ixxy and Ixyy with respect to the central unit of the support grid.

[0017] Optionally, the guide tubes are arranged at coordinates (6,0), (3,0), (-3,0), (-6,0), (0,6), (0,3), (0, -3), and (0, -6) in the principal axis direction.

[0018] Optionally, the guide tubes are respectively arranged at coordinates (5,5), (-5,-5), (-5,5), and (5,-5) in the diagonal direction.

[0019] Optionally, the guide tubes are respectively arranged along the non-diagonal directions at coordinates (6,3), (4,2), (-4,-2), (-6,-3), (-6,3), (-4,2), (4,-2), (6,-3), (3,6), (2,4), (-2,-4), (-3,-6), (-3,6), (-2,4), (2,-4), and (3,-6).

[0020] Next, according to the support grid assembly of the present invention, it includes a support grid having 17×17 grid cells, and sleeves fixed within the grid cells of the support grid and assembled with the guide tubes, wherein the sleeves are arranged relative to the central cell of the support grid in the following manner: eight sleeves are arranged in the principal axis directions Ixx and Iyy, four sleeves are arranged in the diagonal direction Ixy, and sixteen sleeves are arranged in the non-diagonal directions Ixxy and Ixyy.

[0021] Optionally, the sleeves are respectively arranged at coordinates (6,0), (3,0), (-3,0), (-6,0), (0,6), (0,3), (0, -3), and (0, -6) along the principal axis directions.

[0022] Optionally, the sleeves are respectively arranged at coordinates (5,5), (-5, -5), (-5,5), and (5, -5) in the diagonal direction.

[0023] Optionally, the sleeves are respectively arranged at coordinates (6,3), (4,2), (-4, -2), (-6, -3), (-6,3), (-4,2), (4, -2), (6, -3), (3,6), (2,4), (-2, -4), (-3, -6), (-3,6), (-2,4), (2, -4), and (3, -6) along the non-diagonal directions.

[0024] Advantages of the Invention

[0025] A nuclear fuel assembly according to the present invention includes a support grid having 17×17 grid cells, a plurality of fuel rods disposed within the grid cells of the support grid, guide tubes disposed and fixed within the grid cells of the support grid, and upper and lower fixing devices respectively fixed to the top and bottom of the guide tubes. Among them, the guide tubes are arranged relative to the central cell of the support grid in the following manner: 8 guide tubes are arranged along the principal axis directions Ixx and Iyy, 4 guide tubes are arranged along the diagonal direction Ixy, and 16 guide tubes are arranged along the asymmetric directions Ixxy and Ixyy. Thus, a total of 28 guide tubes are provided. This improves the control rod worth and simultaneously enhances the seismic resistance performance.

[0026] 1) Improve the control rod worth of the boric acid-free core

[0027] Typical commercial pressurized light water reactors operate with control rods fully withdrawn most of the time, and the excess reactivity is controlled by water-soluble boric acid and burnable absorbers. On the other hand, the latest development of small modular reactors prioritizes a boric acid-free core, requiring control rods to be inserted from the start of the cycle. The excess reactivity that is controlled by water-soluble boric acid and burnable absorbers in traditional commercial reactors can be controlled solely by enriched gadolinium burnable absorbers in the SMR core, and the remaining excess reactivity (less than 1000 pcm) can be controlled to criticality (keff = 1.0) by inserting regulating control rods. Therefore, the present invention meets the subcriticality requirement by improving the worth of the control rods.

[0028] 2) Improve seismic performance

[0029] The present invention increases the number of guide tubes fixed to the upper and lower fixing devices, improves the bending stiffness of the nuclear fuel assembly skeleton, increases the natural frequency, thereby reducing the displacement of the nuclear fuel assembly at the same energy level, and at the same time reducing the generated load, thereby improving the seismic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and other objects, features, and other advantages of the present disclosure will be more clearly understood from the following detailed description in conjunction with the accompanying drawings:

[0031] Figure 1 is a front view of a nuclear fuel assembly according to an embodiment of the present invention.

[0032] Figure 2 is a plan view showing the arrangement pattern of fuel rods in a support grid according to an embodiment of the present invention.

[0033] Figure 3 is a plan view of a control rod assembly according to an embodiment of the present invention.

[0034] Figure 4 Shows the subcriticality evaluation result diagram based on 24 control rods under ARI and N-1 conditions, presenting the evaluation results of all control rod insertion conditions except for the control rod N-1 with the largest diameter.

[0035] Figure 5 Shows the subcriticality evaluation result diagram based on 28 control rods under ARI and N-1 conditions, presenting the evaluation results of all control rod insertion conditions except for the control rod N-1 with the largest diameter. DETAILED DESCRIPTION OF THE INVENTION

[0036] The specific structural or functional descriptions presented in the embodiments of the present invention are only used to illustrate the embodiments that conform to the concept of the present invention, and the embodiments that conform to the concept of the present invention can be implemented in various forms. In addition, they should not be construed as limitations on the embodiments described herein, but should be construed as including all modifications, equivalents, or alternatives within the concept and technical scope of the present invention.

[0037] Meanwhile, the terms used in this specification are only for describing specific embodiments and are not used to limit the content of the present disclosure. Unless otherwise clearly stated in the context, singular expressions include plural expressions. It should be understood that the terms "including" or "having" used in this specification are used to indicate the existence of an implemented feature, number, step, operation, element, component, or a combination thereof, but do not preclude the existence or addition of one or more other features, numbers, steps, operations, elements, components, or a combination thereof in advance.

[0038] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0039] Figure 1 is a front view of a nuclear fuel assembly according to an embodiment of the present invention, in which the fuel rods are omitted.

[0040] Referring to Figure 1 , the nuclear fuel assembly 100 in this embodiment includes a support grid 110, a guide tube 130 placed and fixed within the grid cells of the support grid 110, an upper fixing device 140 and a lower fixing device 150 respectively fixed to the top and bottom of the guide tube 130, and fuel rods supported on the support grid 110 and axially aligned with the guide tube 130.

[0041] The upper fixing device 140 can be equipped with a helical spring or a leaf spring to provide a pressing force to prevent axial movement of the nuclear fuel assembly, and the lower fixing device 150 can be equipped with nozzles through which coolant is introduced.

[0042] The support grid 110 includes a plurality of grid plates assembled in the horizontal and vertical directions to form grid cells, and one fuel rod or guide tube is placed in each square grid cell, separated by the grid plates.

[0043] The support grid 110 can be provided with grooves and grid springs in the grid cells for inserting fuel rods to elastically support the fuel rods. The support grid 110 can also fix the guide tube through a sleeve, and the sleeve is installed in the grooves and grid springs within each grid cell for inserting the guide tube 130. Figure 1In [description], the support grid 110 is assembled with the guide tube 130 through the sleeve 111. However, the support grid 110 and the guide tube 130 can also be directly fixed by welding. Such a support grid 110 is usually made by metal plate manufacturing and welding processes, but can also be made using a molten metal 3D printing device, and is not limited to any specific manufacturing method.

[0044] Optionally, the support grid 110 is composed of 17×17 grid cells. The guide tubes 130 are arranged at different positions between the grid cells of the support grid 110, with a total of 28. The specific implementation will be described in detail below.

[0045] Figure 2 is a plan view showing the arrangement pattern of fuel rods in a support grid assembly according to an embodiment of the present invention. For ease of understanding, the horizontal direction of the support grid 110 is represented by the x-axis, the vertical direction is represented by the y-axis, the position of a specific grid cell is represented by a two-axis coordinate system of (x,y), and the coordinates of the central cell are (0,0). In Figure 2 In [description], represents -1.

[0046] See Figure 2 , the support grid 110 is composed of 17×17 grid cells. Among them, an instrument tube (also called a measurement tube) is placed in the central cell (0,0), and a total of 28 guide tubes are arranged at specific positions. The fuel rods 120 are arranged in the remaining grid cells, but Figure 2 the fuel rods are omitted in [description].

[0047] In the description of the present invention, based on the central cell (0,0), the principal axis direction refers to the horizontal direction Ixx and the vertical direction Iyy of the support grid 110, the diagonal direction refers to the diagonal direction Ixy of 45° (or 135°), and the non-diagonal direction refers to the diagonal direction Ixxy or Ixyy other than 45° (or 135°). The principal axis direction, diagonal direction, and non-diagonal direction include positive and negative directions.

[0048] Optionally, with respect to the central cell (0,0) of the support grid 110, 8 guide tubes are provided in the principal axis directions Ixx and Iyy, 4 guide tubes are provided in the diagonal direction Ixy, and 16 guide tubes are provided in the non-diagonal directions Ixxy and Ixyy. Therefore, a total of 28 guide tubes are provided in the support grid 110. As described above, each guide tube position on the support grid can be directly fixed to the guide tube, or a sleeve can be provided to fix the guide tube through the sleeve.

[0049] Optionally, the non-diagonal directions Ixxy and Ixyy may be arranged at equal angles θ with respect to the diagonal direction Ixy, which may include a first non-diagonal direction Ixxy biased towards the x-axis and a second non-diagonal direction Ixyy biased towards the y-axis. In this embodiment, the angle θ between the first non-diagonal direction Ixxy and the second non-diagonal direction Ixyy and the diagonal direction Ixy may be 18°.

[0050] The guide tubes are preferably arranged at coordinates (6,0), (3,0), (-3,0), (-6,0) in the horizontal direction Ixx and at coordinates (0,6), (0,3), (0,-3), (0,-6) in the vertical direction Iyy.

[0051] The guide tubes are preferably arranged at coordinates (5,5), (-5,-5), (-5,5), (5,-5) in the diagonal direction Ixy.

[0052] The guide tubes may be arranged at coordinates (6,3), (4,2), (-4,-2), and (-6,-3) and (-6,3), (-4,2), (4,-2), and (6,-3) in the first non-diagonal direction Ixxy, and at coordinates (3,6), (2,4), (-2,-4), and (-3,-6), and (-3,6), (-2,4), (2,-4), and (3,-6) in the second non-diagonal direction Ixyy.

[0053] Figure 3 is a plan view of a control rod assembly fabricated according to an embodiment of the present invention.

[0054] As Figure 3 shown, a control rod assembly 200 according to an embodiment of the present invention includes a cylindrical spider body 210, a plurality of spider vanes 220 radially extending from the spider body 210, and spider fingers 230 provided on the spider vanes 220 for clamping guide tubes. Each spider finger 230 corresponds to one of the above 28 guide tubes and is assembled with the control rod assembly 200.

[0055] Therefore, the present invention can insert 28 control rods into unique positions of a support grid having a 17×17 lattice to improve the operation without boric acid and seismic performance.

[0056] Specifically, from the perspective of the design of the nuclear fuel assembly, it has been confirmed that in a nuclear fuel assembly with a support grid of 17×17 lattice, when 28 control rods are used, the control rod worth increases by 17%, the nuclear fuel load decreases by 1.5%, and the seismic performance is improved. In addition, compared with a nuclear fuel assembly using traditional 24 control rods, the reactivity is relatively higher and the core cycle length is also increased.

[0057] In addition, the subcriticality assessment results of 24 control rods indicate that under ARI conditions, the effective multiplication factor (keff) is evaluated to be 0.95 or less, and under N-1 conditions, the effective multiplication factor (keff) is evaluated to be 0.99 or less. Therefore, the subcritical condition is evaluated to be met, and the safety margin is small (see Figure 4 ). For conservatism, under N-1 conditions, the subcriticality assessment of 28 control rods shows that the effective multiplication factor (keff) is evaluated to be 0.98, with a safety margin (see Figure 5 ). Compared with 24 control rods, this provides additional safety for shutdown and four additional spaces for the Top-Mounted In-Core Instrumentation Nozzle (TM-ICI) or control rod assemblies mounted on top in the core.

[0058] Secondly, from the perspective of mechanical design, the 28 control rods are designed to increase the control rod length related to operation without boric acid, which has the effect of facilitating the insertion / extraction of TM-ICI and control rods. In traditional nuclear power plants, the reactivity of the core is controlled by diluting the toxic substance boron in the cooling water, but this causes adverse effects such as fouling deposition on the main devices in the core and nuclear fuel. The present invention requires controlling the reactivity of the core only with control rods to achieve operation without boric acid in small modular reactors. Therefore, compared with existing control rods, the present invention is more effective for operation without boric acid by increasing the control rod worth.

[0059] In addition, the present invention can also enhance the mechanical properties of the nuclear fuel assembly skeleton by increasing the number of conduits fixed on the upper fixing device and the lower fixing device.

[0060] The above disclosure is not limited to the above embodiments and drawings. For those skilled in the art of the present disclosure, various substitutions, modifications, and changes can obviously be made without departing from the technical spirit of the present disclosure.

[0061] Reference Numeral Explanation

[0062] 100: Nuclear fuel assembly 110: Support grid

[0063] 111: Sleeve 120: Fuel rod

[0064] 130: Guide tube 140: Upper fixing device

[0065] 150: Lower fixing device

Claims

1. A nuclear fuel assembly, characterized in that, Comprising: A support grid with 17×17 grid cells, multiple fuel rods placed in the grid cells of the support grid, guide tubes placed and fixed in the grid cells of the support grid, and upper and lower fixing devices respectively fixed to the top and bottom of the guide tubes; Among them, relative to the central cell of the support grid: eight guide tubes are arranged in the principal axis directions Ixx and Iyy, four guide tubes are arranged in the diagonal direction Ixy, and sixteen guide tubes are arranged in the non-diagonal directions Ixxy and Ixyy.

2. The nuclear fuel assembly according to claim 1, wherein, The guide tubes are respectively arranged at coordinates (6,0), (3,0), (-3,0), (-6,0), (0,6), (0,3), (0, -3), and (0, -6) in the principal axis direction, wherein, in the coordinate system (x,y), x is the horizontal grid cell position relative to the central cell (0,0), and y is the vertical grid cell position relative to the central cell (0,0).

3. The nuclear fuel assembly according to claim 1, characterized in that, The guide tubes are respectively arranged at coordinates (5,5), (-5,-5), (-5,5), and (5,-5) in the diagonal direction, wherein, in the coordinate system (x,y), x is the horizontal grid cell position relative to the central cell (0,0), and y is the vertical grid cell position relative to the central cell (0,0).

4. The nuclear fuel assembly according to claim 1, characterized in that, The guide tubes are respectively arranged at coordinates (6,3), (4,2), (-4,-2), (-6,-3), (-6,3), (-4,2), (4,-2), (6,-3), (3,6), (2,4), (-2,-4), (-3,-6), (-3,6), (-2,4), (2,-4), and (3,-6) in the non-diagonal direction, wherein, in the coordinate system (x,y), x is the horizontal grid cell position relative to the central cell (0,0), and y is the vertical grid cell position relative to the central cell (0,0).

5. A support grid component, characterized in that, Comprising: A support grid with 17×17 grid cells, and sleeves fixed in the grid cells of the support grid and assembled with the guide tubes, wherein, the sleeves are arranged relative to the central cell of the support grid in the following manner: eight sleeves are arranged in the principal axis directions Ixx and Iyy, four sleeves are arranged in the diagonal direction Ixy, and sixteen sleeves are arranged in the non-diagonal directions Ixxy and Ixyy.

6. The support grid component according to claim 5, characterized in that, The sleeves are respectively arranged at coordinates (6,0), (3,0), (-3,0), (-6,0), (0,6), (0,3), (0, -3), and (0, -6) along the principal axis direction, wherein, in the coordinate system (x,y), x is the horizontal grid cell position relative to the central cell (0,0), and y is the vertical grid cell position relative to the central cell (0,0).

7. The support grid component according to claim 5, wherein The sleeves are respectively arranged at coordinates (5,5), (-5,-5), (-5,5), and (5,-5) in the diagonal direction, Among them, in the coordinate system (x, y), x is the horizontal grid cell position relative to the central cell (0, 0), and y is the vertical grid cell position relative to the central cell (0, 0).

8. The support grid assembly according to claim 5, characterized in that, The sleeves are respectively arranged at the coordinates (6, 3), (4, 2), (-4, -2), (-6, -3), (-6, 3), (-4, 2), (4, -2), (6, -3), (3, 6), (2, 4), (-2, -4), (-3, -6), (-3, 6), (-2, 4), (2, -4), and (3, -6) along the non-diagonal direction. Among them, in the coordinate system (x, y), x is the horizontal grid cell position relative to the central cell (0, 0), and y is the vertical grid cell position relative to the central cell (0, 0).

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