Fuel assembly of boiling-water reactor, and reactor core

Abstract

To provide a fuel assembly for boiling-water reactors capable of constraining a spacer to a specified height, and a reactor core.SOLUTION: A fuel assembly for boiling-water reactors is a fuel assembly for boiling-water reactors that includes multiple fuel rods, a spacer, and a channel box. The fuel assembly has: at least one recess on the inner wall of one side of the channel box for each constraint height of the spacer; a convex part at a position facing the recess when the spacer is set at a predetermined heigh on the outer surface of the spacer band facing the channel box; and an elastic material that is placed on the spacer band, facing the outer peripheral surface of the spacer band having the convex portion.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a fuel assembly and core for a boiling water nuclear reactor. [Background technology]

[0002] This paper relates to a fuel assembly for a boiling water reactor, which is composed of fuel rods, spacers, a channel box, etc., and to the core technology of a boiling water reactor loaded with one or more such fuel assemblies.

[0003] Background art in this technical field includes, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-275376) and Patent Document 2 (Japanese Patent Laid-Open No. 2022-65354).

[0004] Patent document 1 describes a structural diagram of a spacer restraint mechanism consisting of protrusions and leaf springs provided on the surface of a cross-shaped partition member that divides the inside of a channel box of a fuel assembly of a large boiling water reactor in the cross-sectional direction.

[0005] Patent document 2 describes a structural diagram of a spacer restraint mechanism that is composed of components that operate using the fluid force of a mixture of steam and water that rises within the fuel assembly during reactor operation, and a processed channel box. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-275376 [Patent Document 2] Japanese Patent Publication No. 2022-65354 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 describes a structural diagram of a spacer restraint mechanism consisting of protrusions and leaf springs provided on the surface of a cross-shaped partition member that divides the inside of a channel box of a large boiling water reactor fuel assembly in the cross-sectional direction. A separate fuel rod bundle is installed in each of the partitioned spaces within the channel box. However, forming protrusions on the surface of the partition plate, which has a plate-like structure similar to that of the channel box of a conventional fuel assembly, and installing leaf springs requires welding of separate parts, which may result in loose parts due to damage to the welds caused by the load caused by repeated installation and removal of the fuel rod bundles or channel box.

[0008] Patent Document 2 shows a structural diagram of a spacer restraint mechanism that is made up of components that operate by the fluid force of a mixture of steam and water that rises inside the fuel assembly when the reactor is operating, and a processed channel box, etc. This technology is designed to prevent the spacer position from moving upward when the reactor is operating with the fuel assembly loaded in the core, so it cannot prevent the spacer position from moving downward, and in principle, the spacer position restraint function cannot be expected in a state where no fluid force exists, such as when the spent fuel is stored in a pool.

[0009] An object of the present invention is to provide a fuel assembly and a core for a boiling water reactor in which spacers can be restrained at a predetermined height. [Means for solving the problem]

[0010] The fuel assembly for a boiling water reactor of the present invention is a fuel assembly for a boiling water reactor comprising fuel rods, a spacer, and a channel box, characterized in that the inner wall surface of one side of the channel box has at least one recess for each restraint height of the spacer, the spacer band outer surface facing the channel box has a convex portion at a position facing the concave portion when the spacer is installed at a predetermined height, and an elastic body is provided on the spacer band that faces the outer peripheral surface of the spacer band having the convex portion.

[0011] Alternatively, the fuel assembly for a boiling water reactor of the present invention is a fuel assembly for a boiling water reactor comprising fuel rods, a spacer, and a channel box, characterized in that the inner wall surface of the corner portion of the channel box has at least one recess for each restraining height of the spacer, the outer surface of the spacer band facing the corner portion of the channel box of the spacer has a convex portion at a position facing the concave portion when the spacer is installed at a predetermined height, and an elastic body is provided on the spacer band at a diagonal position on the outer peripheral surface of the spacer band having the convex portion.

[0012] Alternatively, the core of the present invention is characterized in that it is a core loaded with fuel assemblies of the above boiling water reactor. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a fuel assembly and a core for a boiling water reactor in which spacers can be restrained at a predetermined height. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a longitudinal sectional view showing the configuration of a fuel assembly of a current boiling water reactor. [Figure 2] 1 is a side view of a water rod of a fuel assembly of a current boiling water reactor. [Figure 3] 1A and 1B are top and side views showing the main structure of a spacer in a fuel assembly of a current boiling water reactor. [Figure 4] 1A and 1B are schematic top views showing a spacer and a channel box in Example 1, and bird's-eye views (views taken from arrows A and B) showing the structure of a protrusion and a spring on the spacer together with a part of a spacer band. [Figure 5] 1 is a bird's-eye view showing the structure of recesses in Example 1, and a bird's-eye view showing the relationship between the arrangement of recesses provided on the inner wall surface of a channel box and the height at which the spacers are restrained, together with a part of the channel box. [Figure 6]5 is a longitudinal cross-sectional view (view taken along the CC' arrows in FIG. 4) that schematically shows a method for installing a spring on a spacer band in the first embodiment. [Figure 7] 10 is a bird's-eye view schematically showing a method of installing springs on spacer bands in a modified example of the first embodiment. FIG. [Figure 8] 10A and 10B are schematic top views showing a spacer and a channel box in Example 2, and bird's-eye views (views seen from arrows D and E) showing the structure of the convex portion and spring on the spacer together with a part of the spacer band. [Figure 9] 10A and 10B are a bird's-eye view showing the structure of a recess in Example 3, and a bird's-eye view and a side view showing the structure of a protrusion provided on a spacer band together with a part of the spacer band. [Figure 10] 10A and 10B are a bird's-eye view and a longitudinal sectional view showing the structure of a recess in Example 4. FIG. [Figure 11] 13 is a bird's-eye view showing the structure of a recess in Example 6, and a bird's-eye view showing the arrangement of recesses provided on the inner wall surface of a channel box together with a part of the channel box. [Figure 12] 13 is a bird's-eye view showing the state in which four types of loop springs are installed on a spacer band in Example 7. FIG. [Figure 13] FIG. 13 is a bird's-eye view showing the structure of four types of springs integrally formed on a spacer band in Example 7. [Figure 14] 13 is a bird's-eye view showing two types of spring structures integrally formed on corner portions of a spacer band in Example 7. FIG. [Figure 15] 13A and 13B are a bird's-eye view and a longitudinal cross-sectional view (view taken along the arrows F-F') showing the state in which convex members are installed on spacer bands in Example 8, and a bird's-eye view showing the state in which convex members are installed on corner portions of spacer bands. [Figure 16] 13 is a bird's-eye view showing the structure of a recess in Example 9 together with a part of a channel box, and a bird's-eye view showing a protrusion provided on a spacer band together with a part of a spacer or alone. [Figure 17]FIG. 22 is a bird's-eye view schematically showing the arrangement of recesses provided on the inner wall surface of the channel box in Example 10, together with a part of the channel box. [Figure 18] FIG. 16 is a top view schematically showing the relative positions of the convex portions provided on the spacer bands for each stage of the spacer and the concave portions provided on the inner wall surface of the channel box in Example 11. [Figure 19] FIG. 22 is a vertical cross-sectional view schematically showing a state in which a spacer is constrained and a state in which a channel box is being mounted in Example 12. DETAILED DESCRIPTION OF THE INVENTION

[0015] In a boiling water reactor (BWR) in which multiple fuel assemblies are loaded into the core and cross-sectional control rods are inserted between the fuel assemblies, there is a need for a BWR in which multiple fuel rods are densely packed in the channel box of the fuel assembly and voids are generated in the channel box during operation to harden the neutron spectrum and improve the fission plutonium conversion ratio. There is also a need for a backfit fuel assembly that can be loaded into the core of an existing BWR and can also be used to form a mixed core with conventional fuel assemblies.

[0016] In this backfitted fuel assembly, the fuel rod diameter and other features are the same as those of current fuel assemblies, but the water rods commonly used in current conventional fuel assemblies are not used, and fuel rods are placed in the areas that would be occupied by water rods. This is because the function of water rods is to soften the neutron spectrum, which hinders the improvement of the fission plutonium conversion ratio. Meanwhile, to maintain a constant spacing between the fuel rods arranged in a lattice pattern (e.g., a 10x10 square lattice pattern) within the fuel assembly and to reduce vibration and bending of the fuel rods during transport, the fuel rods are mechanically bundled at multiple points (e.g., eight points) along their length with components called spacers to maintain a predetermined spacing between them, forming a so-called fuel rod bundle.

[0017] In the fuel rod bundles of current conventional fuel assemblies, water rods are used to restrain the longitudinal position of the spacers. However, as mentioned above, water rods are not used in backfit fuel assemblies with improved fission plutonium conversion ratios. Therefore, a spacer restraint mechanism that does not rely on water rods is required.

[0018] Several spacer restraint mechanisms were devised and used in the period from the boiling water reactor test reactor to the introduction of water rods. However, special fuel rods specifically designed for spacer restraint were used in fuel assemblies immediately prior to the introduction of water rods. These special fuel rods are called segmented rods. These rods are constructed to a standard length by connecting short fuel rods longitudinally via components with spacer restraint structures. These fuel rods have many issues, including higher manufacturing costs than standard fuel rods, the presence of non-heat-generating spacer restraint structures that result in longitudinal regions that cannot be used as fuel rods, and the presence of multiple longitudinal welded connections that result in inferior mechanical strength compared to standard fuel rods.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Example]

[0020] First, the components of a current fuel assembly 200 of a boiling water reactor and conventional means for restricting the height of the spacer 4 will be described with reference to FIGS. 1 to 3, and specific examples will be described with reference to FIGS.

[0021] 1 is a vertical cross-sectional view showing the configuration of a current fuel assembly 200. Fuel rods 21 and water rods 22 are mechanically bound together by spacers 4 to form a fuel rod bundle. The fuel rods 21 have upper end plugs 21a and lower end plugs 22b that fit into through-holes in an upper tie plate 23 and a lower tie plate 24. A channel box 20 is installed outside the fuel rod bundle, whose upper and lower ends are supported by the upper tie plate 23 and the lower tie plate 24.

[0022] The channel box 20 can be removed from the fuel assembly by pulling it out and pushing it in from above in Fig. 1. Although not shown in Fig. 1, when the channel box 20 is installed, it is fixed to the upper tie plate 23 using a special member. The lower tie plate 24 has a debris filter 25.

[0023] 2 is a side view of the water rod 22 of the fuel assembly 200 shown in FIG. 1. The water rod 22 is a hollow circular tube through which water passes upward. It has a water inlet hole 22c and a water outlet hole 22d near the upper and lower ends of the hollow portion, and an upper end plug 22a and a lower end plug 22b that fit into through holes in the upper tie plate 23 and the lower tie plate 24, respectively. A pair of spacer tabs 22e is provided on the outer wall surface of the water rod for each spacer position, sandwiching the spacer positions indicated by dashed lines above and below. All of the spacer tabs 22e are located at the same circumferential position on the water rod 22. Furthermore, the joint between the lower tie plate 24 and the lower end plug 22b of the water rod 22 has a mechanism that restrains the circumferential rotation angle of the water rod 22 in a specific circumferential direction after the lower end plug 22b is inserted into the lower tie plate 24.

[0024] 3 is a top view and a side view showing the main structure of a spacer 4 in a fuel assembly 200 of a current boiling water reactor. The spacer 4 shown in the figure is a type known as a lattice or grid type, and is composed of dividers 6, which are plate-like structures that form a lattice structure that restrains the positions of fuel rods 21 and water rods 22 within the cross section of the fuel assembly 200, and spacer bands 5 that form the outer periphery surrounding the dividers 6. The dividers 6 have stops 7 that restrain the positions of the fuel rods 21, and spacer springs, which are elastic bodies that press the fuel rods 21 against the stops 7, about two per fuel rod 21.

[0025] The stop 7 and the spacer band 5 have spacer tabs, which are convex portions for providing a gap between the outer surfaces of the stop 7 and the channel box 20. The spacer 4 also has flow tabs 10 for preventing mechanical interference with the lower end of the channel box 20 when the channel box 20 is attached to the fuel rod bundle.

[0026] Here, we will briefly explain how the water rods 22 are used to restrain the vertical position of the spacers 4. As described above, the outer surfaces of the water rods 22 have spacer tabs 22e that restrain the vertical position of the spacers 4 in the longitudinal direction of the fuel rods 21. These spacer tabs 22e are arranged at the same circumferential position on the water rods 22. The spacer tabs 22e in Figure 3 show the orientation of the spacer tabs 22e in a state where the position of the spacers 4 is not restrained, or when the spacers 4 are being arranged during the assembly of the fuel rod bundle. When the water rods 22 are oriented in this circumferential direction, there is no mechanical interference between the dividers 6 and the spacer tabs 22e.

[0027] 3, when the water rods 22 are rotated 45 degrees in the circumferential direction, the spacer tabs 22f come into mechanical interference with the dividers 6, and the position of each spacer 4 is constrained within a predetermined range in the longitudinal direction of the fuel rod. This embodiment provides a method for constraining the spacers 4 in the longitudinal direction of the fuel rods in a fuel assembly under conditions where the water rods 22 and spacer tabs 22e described above cannot be used.

[0028] FIG. 4 is a top schematic diagram showing the spacer 4 and channel box 20 in Example 1, and bird's-eye views (views viewed from arrows A and B) showing the structure of the protrusion 1 and the spring 3, which is an elastic body, on the spacer 4 together with a part of the spacer band 5. The fuel rod bundle literally consists of only the fuel rods 21 and the spacer 4, the spacer 4 has two protrusions and two springs 3, and the channel box 20 has two recesses 2, with the tip portion of the protrusion 1 fitting into the recess 2. FIGS. 4(a) and 4(b) show the vicinity of the protrusion 1 (viewed from arrow A in FIG. 4(a)) and the vicinity of the spring 3 (viewed from arrow B in FIG. 4(a)). The protrusion 1 is a bent plate structure formed by pressing on the spacer band 5, and its vertical height from the outer surface of the spacer band 5 is greater than the height of the spacer tab in the same direction. The spring 3 is a loop-shaped spring made by pressing a thin plate and is a separate part from the spacer 4, and the circumferential movement of the spacer band 5 and the occurrence of tilting when subjected to a compressive load are suppressed by the flow tab 10 and the notches 5b provided at the bottom end of the spacer band. When no load is applied, the vertical height of the spring 3 from the outer surface of the spacer band 5 is greater than the vertical height of the spacer tab 9. Due to the dimensional relationship between the spacer tab 9, the protrusion 1, and the spring 3, as shown in Figure 4(a), the tip of the protrusion 1 fits into the recess 2 due to the pressing force of the spring 3, and movement of the spacer 4 in the longitudinal direction of the fuel rod can be suppressed.

[0029] 5 is a bird's-eye view showing the structure of the recess 2 in Example 1 and a bird's-eye view showing the relationship between the arrangement of the recess 2 provided on the inner wall surface of the channel box 20 and the height at which the spacer 4 is confined, along with a part of the channel box 20. The recess 2 in Example 1 is substantially cone-shaped, and can be formed easily and with high precision by a machine tool such as a drill.

[0030] In addition, in Example 1, the recesses 2 are formed on only one surface of the inner wall surface of the channel box 20, and the positions and number of the recesses 2 formed in the plane perpendicular to the longitudinal direction of the fuel rods are the same for all spacer heights. By arranging the recesses 2 in this way, the shape and dimensions of the spacers 4 equipped with the protrusions 1 and the springs 3 can also be made the same.

[0031] Next, a method for installing the springs 3 in Example 1 will be described with reference to Figures 6 and 7. Figure 6 is a vertical cross-sectional view (view taken along arrows CC' in Figure 4) that schematically shows a method for installing the springs 3 on the spacer bands 5 in Example 1, and Figure 7 is a bird's-eye view that schematically shows a method for installing the springs on the spacer bands 5 in a modified example of Example 1.

[0032] The two types of springs shown in this diagram are both welded at welding point 101 to form a closed loop structure, preventing loose parts. Furthermore, these springs 3 are positioned so that they pass through stops 7 formed on the spacer band 5, which minimizes circumferential movement of the springs 3 around the spacer band 5 and tilting when subjected to a compressive load.

[0033] In the spring 3 shown in FIG. 6( a ), the pressing point 100 when compressed is limited to the spacer band 5 , but in the spring 3 shown in FIG. 6( b ), the pressing point 100 is the fuel rod 21 .

[0034] The installation method of the spring 3 shown in FIG. 7 reduces the risk of loose parts without requiring additional processing such as welding to form a loop. As shown in FIG. 7, the divider 6 and spacer band 5 are connected by fitting a plate-shaped protrusion 6a on the side end surface of the divider 6 into a slit-shaped opening 5c ​​in the spacer band 5 and then securing the spring 3 by welding or other methods. The spring 3 shown in this figure is not loop-shaped, and has an opening 3a larger than the slit-shaped opening 5c ​​on the inside of the spacer band 5 when the spacer band 5 is attached, facing the slit-shaped opening 5c. The protrusion height of the plate-shaped protrusion 6a of the divider 6 in this embodiment is greater than that of a typical plate-shaped protrusion 6a by at least the thickness of the spring 3, thereby enabling both the connection and fixation of the divider 6 to the spacer band 5 and the installation of the spring 3 on the spacer band 5. As long as the risk of the spring 3 falling off or becoming a loose part is within an acceptable range, either the upper or lower opening 3a may be used to install the spring 3.

[0035] Furthermore, for example, the spring 3 shown in a bird's-eye view in Figure 4(c) can also be installed on the spacer band 5 without welding by using the divider 6 shown in Figure 7(b), if it has an integral member with an opening 3a inside the spacer band 5 and the positional relationship between the opening 3a and the slit-shaped opening 5c ​​on the spacer band 5 is the same as that of the spring 3 shown in Figure 7(b).

[0036] According to this embodiment, in a fuel assembly for a boiling water reactor that does not have a non-heat-generating structure such as a water rod that penetrates the spacer and can be used to restrain the spacer in the longitudinal direction of the fuel rod, it is possible to provide a fuel assembly for a boiling water reactor that can restrain the spacer at a predetermined height when a channel box is attached, such as during core loading, and a core loaded with such a fuel assembly, without processing the fuel cladding tube of the fuel rod or using special fuel rods whose effective length range is divided in the vertical direction. [Example]

[0037] Example 2 will be described with reference to Fig. 8. Fig. 8 is a schematic top view showing the spacer 4 and the channel box 20 in Example 2, and bird's-eye views (views viewed from arrows D and E) showing the structures of the protrusions 1 and springs 3 on the spacer 4 together with a part of the spacer band 5.

[0038] In this embodiment, the protrusion 1 and spring 3 are installed at a corner portion 5a of the spacer band 5. Because the inner wall surface of the channel box 20 that comes into contact with the spring 3 is curved, a small protrusion 3b is provided on the spring 3 by press working or the like to ensure point contact. The recess 2 of the spring 3 is provided at one location on the inner wall surface of the corner of the channel box 20 (the lower left corner in Figure 8(a)), and the protrusion 1 fits into the recess 2 at this position, restricting the position of the spacer 4 relative to the channel box 20.

[0039] However, in terms of the thermal characteristics of the fuel assembly, it is not desirable for the spacers 4 to be twisted relative to the channel box 20 in a cross section perpendicular to the longitudinal direction of the fuel rods. Such a state is resolved by simultaneously bringing all of the spacer tabs 9 arranged on the outer surface of the spacer band 5 into contact with the inner wall surface of the channel box 20 that they face.

[0040] In the first embodiment, two springs 3 are installed on the same straight flat portion of the spacer band 5, and the pressing force of these springs 3 causes two spacer tabs 9 provided on opposing straight flat portions of the spacer band 5 to simultaneously contact the inner wall surface of the channel box 20. In the second embodiment, the pressing force of the springs 3 is in the diagonal direction of the channel box 20 and spacer band 5, which have a substantially square cross section, so that the spacer tabs 9 provided on two straight planes of the spacer band 5 sandwiching the corner portion 5a having the protrusion 1 contact the inner wall surface of the channel box. By increasing the number of straight flat portions of the spacer band 5 having spacer tabs 9 contacting the inner wall surface of the channel box 20, it is possible to suppress the vibration of the fuel rod bundle, which is made up of the fuel rods 21 and the spacers 4, inside the channel box 20. [Example]

[0041] Example 3 will be described with reference to Fig. 9. Fig. 9 is a bird's-eye view showing the structure of recessed portion 2 in Example 3, and a bird's-eye view and a side view showing the structure of protruding portion 1 provided on spacer band 5 together with a part of spacer band 5. This example relates to recessed portion 2 and protruding portion 1, and can also be applied to recessed portion 2 and protruding portion 1 in Examples 1 and 2 described above.

[0042] This embodiment restrains the relative position of the spacer 4 with respect to the channel box 20 in the longitudinal direction of the fuel rod. Further desirable characteristics are that the restraint of the spacer 4 can be released when a load of a certain level or more is applied that moves the channel box 20 up and down, and that the magnitude of the load required for release is relatively small when the spacer 4 moves downward with respect to the channel box 20. This is a requirement for achieving a good balance between the ease of removing the channel box 20 (the spacer 4 reduces the load required for moving downward from the restrained position) and the difficulty of moving the spacer 4 upward due to fluid force when loading the fuel assembly into the core (increases the load required for moving the spacer 4 upward from the restrained position). This embodiment meets this requirement.

[0043] In the recess 2 in Example 3, the upper end surface 2a and the lower end surface 2b of the recess are perpendicular to the inner wall surface of the channel box 20. Therefore, when the fitting portion of the protrusion 1 has vertically symmetrical dimensions and shapes, the load required to release the constraint of the spacer 4 due to the fitting of the protrusion 1 into the recess 2 is the same in both the vertical movement directions of the spacer 4.

[0044] Therefore, in this embodiment, as shown in Figures 9(a) and (b), the shape of the convex portion 1 is a generally trapezoid that is asymmetrical in the vertical plane perpendicular to the outer surface of the spacer band 5. As shown in Figure 9(b), the two legs of the generally trapezoid, with a lower base length of H1, form the upper end surface 1a of the convex portion and the lower end surface 1b of the convex portion. In this embodiment, the angle between the lower base and the leg corresponding to the upper end surface 2a of the recess is θ1a, and the angle between the lower base and the leg corresponding to the lower end surface θ2b is θ1b, where θ1a > θ1b. The absolute values ​​of the angles θ1a and θ1b and the desired unique relationship between them can be determined based on the pressing pressure of the spring 3, the set value of the vertical load required to release the spacer 4 from its constraint, the static friction force of sliding, and other factors. By making θ1a > θ1b, it becomes easier to release the constraint downward than upward.

[0045] θ1a is the smaller of the angles formed by the upper end face of a convex portion on the outer wall surface of the spacer band, or a portion that can be essentially regarded as the upper end face, and the outer wall surface of the spacer band in a cross section perpendicular to the spacer band surface and parallel to the vertical direction, and is inclined at an angle greater than 0° and less than 90°. This makes it easier to release the constraint on the spacer 4.

[0046] θ1b is the smaller of the angles formed between the lower end surface of a convex portion on the outer wall surface of the spacer band, or a portion that can be essentially regarded as the lower end surface, and the outer wall surface of the spacer band in a cross section perpendicular to the spacer band surface and parallel to the vertical direction, and is inclined at an angle greater than 0° and less than 90°. This makes it easier to release the constraint on the spacer 4. [Example]

[0047] Example 4 will be described with reference to Fig. 10. Fig. 10 is a bird's-eye view and a vertical cross-sectional view showing the structure of the recess 2 in Example 4.

[0048] In this embodiment, the shape of the recess 2 is a generally trapezoid that is asymmetrical in the vertical plane perpendicular to the outer surface of the spacer band 5, providing the same characteristics as those achieved in the third embodiment. As shown in Figures 10(a) and 10(c), the cross section of the recess 2 at the point where it is most recessed in this embodiment has a generally trapezoidal shape with a lower base length of H2, with the two legs of the trapezoid forming the upper end surface 2a and the lower end surface 2b of the recess. In this embodiment, θ2a is the angle formed by the leg corresponding to the lower base and the upper end surface 2a of the recess, and θ1b is the angle formed by the leg corresponding to the lower base and the lower end surface θ2b, where θ2a > θ2b. The absolute values ​​of the angles θ2a and θ2b and the desired unique relationship between them can be determined from the pressing pressure of the spring 3, the vertical load setting required to release the constraint of the spacer 4, the static friction force of sliding, and other factors.

[0049] The three-dimensional shape of the recess may be formed by a curved surface as shown in Fig. 10(b). In this case, the slopes of the upper end surface 2a and the lower end surface 2b of the recess are given by the dashed lines 2a' and 2b' in the figure, which correspond to the average gradients of the curves.

[0050] The angle θ2a is the smaller one of the angles formed in a cross-section perpendicular to the surface of the spacer band and parallel to the vertical direction between the upper end surface of the recess provided on the inner wall surface of the channel box or a portion substantially regarded as the upper end surface and the outer wall surface of the spacer band, and is inclined such that it is greater than 0° and less than 90°. This facilitates the release of the restraint of the spacer 4.

[0051] The angle θ2b is the smaller one of the angles formed in a cross-section perpendicular to the surface of the spacer band and parallel to the vertical direction between the lower end surface of the recess provided on the inner wall surface of the channel box or a portion corresponding to the lower end surface and the outer wall surface of the spacer band, and is inclined such that it is greater than 0° and less than 90°. This facilitates the release of the restraint of the spacer 4.

Example

[0052] Example 5 will be described with reference to FIGS. 9(c) and 10(c). This example is one of the optimal examples when Examples 3 and 4 are combined and implemented.

[0053] When Examples 3 and 4 are combined and implemented, it is necessary that H1 < H2, θ1a ≤ θ2a, and θ1b ≤ θ2b from the condition that the convex portion 1 can be fitted into the recess 2. If these conditions are satisfied, the object of the present invention can be achieved. Further, to suppress the upward movement of the spacer 4, the static friction force and the dynamic friction force between the upper end surface 2a of the recess and the upper end surface 1a of the convex portion can be utilized.

[0054] Specifically, θ1a = θ2a is set so that the upper end surface 2a of the recess and the upper end surface 1a of the protrusion come into close contact just before the upward constraint of the spacer 4 is released. Furthermore, for example, if the static friction force and kinetic friction force are greater than desired values, the absolute value of the entire upward constraint force of the spacer 4, including the constraint force due to the pressing pressure of the spring 3, can be easily adjusted to the desired value by reducing the absolute values ​​of θ1a and θ2a while maintaining the relationship θ1a = θ2a. Similarly, with regard to the upward constraint force of the spacer 4, if the inclination angles of the lower end surface 2b of the recess and the lower end surface 1b of the protrusion are made to match (θ1b = θ2b), the static and kinetic friction forces between the two surfaces can be maximized. [Example]

[0055] Example 6 will be described with reference to Fig. 11. Fig. 11 is a bird's-eye view showing the structure of the recessed portion 2 in Example 6 and a bird's-eye view showing the arrangement of the recessed portions 2 provided on the inner wall surface of the channel box 20 together with a part of the channel box 20.

[0056] In Examples 1 to 5, the inclination of the upper end surface 2a of the recess 2 in the depth direction is used to adjust the restraining force against the upward movement of the protrusion 1. With this method, it may be necessary to make the recess 2 deeper to obtain the necessary restraining force.

[0057] In this embodiment, the recess 2 is composed of a vertically oriented linear groove and a linear groove connected to its upper end, which is inclined in a plane parallel to the inner wall surface of the channel box 20. The lower end surface 2b of the recess, which has the inclined vertical linear groove, increases in width downward to smoothly guide the protrusion 1 on the spacer into the linear groove when the channel box 20 is installed. When the protrusion 1 fitted into the recess 2 reaches the inclined linear groove, the protrusion 1 is subjected to a diagonally downward force from the side wall of the groove, which is perpendicular to the inclination of the linear groove in a plane parallel to the inner wall surface of the channel box. The downward component of this diagonally downward force in the longitudinal direction of the fuel rod inhibits the upward movement of the protrusion 1, acting as a restraining force against the upward movement of the spacer 4 in the longitudinal direction of the fuel rod. Because the recess 2 is inclined on the inner wall surface of the channel box 20, the depth of the recess 2 required to obtain the same restraining force can be made smaller than in Examples 3 to 5. As a result, the risk of deformation or strength reduction of the channel box 20 due to the processing of the recess 2 can be reduced. [Example]

[0058] Seventh embodiment will be described with reference to Figures 12 to 14. The description of this embodiment relates to a spring 3 having unique features in terms of the installation method and shape implemented in combination with the first to sixth embodiments.

[0059] FIG. 12 is a bird's-eye view showing the state in which four types of loop-shaped springs 3 are installed on the spacer band 5 in Example 7, and each spring 3 has its own advantages.

[0060] The spring 3 shown in Figure 14(a) is a lantern type with open top and bottom ends. The lantern type allows the projected area in the direction of coolant flow when the core is loaded into the fuel assembly to be smaller than that of a typical loop type, and it is possible to suppress the increase in pressure loss caused by the installation of the spring 3. The lantern type spring shape shown in the figure is also applied to fuel rod springs 8, and has a wealth of experience in use, manufacturing, and material quality control.

[0061] The spring 3 shown in Figure 12(b) is composed of a short, vertically oriented plate spring with small protrusions 3b on two horizontally oriented loop springs. The advantage of spring 3 is that the vertical length can be reduced without reducing the displacement range due to the same pressing pressure or compression. The spring 3 with small protrusions 3b shown in Figure 12(c) has the shape of a typical loop spring, but only uses the opening surface associated with the formation of stop 7 on spacer band 5. The advantage of this installation method is that no processing or design changes to spacer 4 are required to install spring 3 on spacer band 5.

[0062] The spring 3 shown in Figure 12(d) is installed so as to cover the spacer tab 9, whose position has been changed to the position of the spring 3. As described in the explanation of Example 1, the height of the spring 3 from the outer surface of the spacer band 5 must be greater than the height of the spacer tab 9. If this installation method of the spring 3 is used, the above condition regarding the height of the spring 3 is always met.

[0063] 13 is a bird's-eye view showing the structure of four types of springs 3 formed integrally with the spacer band 5 in Example 7. All of these springs 3 have the common advantages of being relatively easy to form on the spacer band 5 by press working alone and having an extremely low risk of loose parts, but each also has its own unique advantages.

[0064] The shape and forming method of the spring 3 with the small protrusion 3b shown in Figure 13(a) are the same as those of the fuel rod spring 8 formed integrally on the divider 6, and have a long track record in terms of use, manufacturing, and material quality control.

[0065] 13(b) is formed by forming a small protrusion 3b on a spacer tab 9 and then forming horizontal slit-like openings above and below the small protrusion 3b to form a portion of the spacer tab 9 including the small protrusion 3b into a plate-shaped spring 3. In this embodiment, the spacer tab 9 for forming the spring is additionally provided on the spacer band 5, but a similar spring mechanism may also be formed on an existing spacer tab 9. Also, in this embodiment, parallel linear openings are used to form a portion of the spacer tab 9 into a spring, but the longitudinal direction of this pair of openings may be vertical, and the distance between the two openings in the longitudinal and perpendicular directions, which defines the width of the spring 3, may vary in the longitudinal direction to provide the spring 3 with appropriate pressing characteristics.

[0066] The shape and manufacturing method of the spring 3 shown in Figures 13(c) and (d) are similar to those of the fuel rod spring 8 used in fuel assembly spacers for pressurized water reactors, and have a long history of use, manufacturing, and material quality control. In Figure 13(c), the spring 3 is installed independently of the spacer tab 9. However, as is clear from Example 1 and other examples, the spacer tab 9 installed on the outer surface of the straight plate portion of the spacer band 5 on which the spring 3 is arranged is no longer required to perform its original function of maintaining a gap between the outer surface of the straight plate portion of the spacer band 5 and the inner wall surface of the channel box 20 it faces at a certain value or more. For this reason, as shown in Figure 13(d), the spring 3 may be formed integrally on the spacer band 5 instead of the spacer tab.

[0067] The springs 3 formed integrally with the spacer band 5 at the corner portions 5a of the spacer band shown in Figures 14(a) and (b) are a substitute for the loop springs, which are separate members from the spacers 4 installed at the corner portions 5a of the spacer band in Example 2. The corner portions 5a of the spacer band have strict width restrictions in processing the spring 3 structure, but the shapes and manufacturing methods of Figures 14(a) and (b) are similar to those of Figures 13(a) and (d), respectively, and have a proven track record in use with fuel rod springs 8, which also have strict width restrictions in processing, as well as in manufacturing and material quality control. [Example]

[0068] Example 8 will be described with reference to Fig. 15. Fig. 15 shows a bird's-eye view and a longitudinal cross-sectional view (view taken along arrows F-F') illustrating the state in which the convex portion 1 member is installed on the spacer band 5 in this example, and also shows the bird's-eye view illustrating the state in which the convex portion 1 member is installed on the corner portion 5a of the spacer band 5.

[0069] In the explanations of Examples 1 to 6, the convex portions 1 are formed integrally on the spacer bands 5 or the corner portions 5a of the spacer bands 5. This is to provide strength to the convex portions 1 and minimize the risk of partial breakage of the convex portions 1 or loose parts due to the load on the convex portions 1 generated when the channel box is detached. However, when multiple types of spacers 4 with different positions of the convex portions 1 are used in a single fuel assembly 200, it is naturally necessary to manufacture multiple types of spacers 4.

[0070] In this embodiment, the protrusion 1 is a separate part that can be attached to the spacer 4 later. By attaching the separate protrusion 1 to a spacer 4 that does not have a protrusion 1 formed thereon, it is possible to easily manufacture spacers 4 with different placement of the protrusion 1.

[0071] Figures 15(a) and (c) show the installation of the protrusions 1 in this embodiment on the straight flat plate portion and corner portion 5a of the spacer band 5, respectively. The member having the protrusions 1 in this embodiment is made by pressing a plate material that is thicker and more rigid than the spring 3, and is installed on the spacer band 5 or the like using the elasticity of the member itself, as shown in the longitudinal cross section in Figure 15(b). Although not shown, the risk of loose parts can be reduced by further welding to the spacer band 5. [Example]

[0072] Example 9 will be described with reference to Fig. 16. Fig. 16 is a bird's-eye view showing the structure of the recess in Example 9 together with a part of the channel box, and a bird's-eye view showing the protrusions provided on the spacer band together with a part of the spacer or alone.

[0073] 16(a), the recess 2 in this embodiment has a convex hole 1c therein, and the shape of the convex portion 2c inside the recess 2 is a substantially conical shape with a tip surface, the diameter of which tapers toward the tip surface. Note that this tip surface is the inner wall surface of the channel box 20 before the recess 2 is formed.

[0074] 16(a) to 16(e) show the shape of the convex portion 1 that mechanically interferes with the convex portion 2c inside the recess 2 when the spacer 4 is restrained on the inner wall surface of the channel box 20 at the height of the spacer 4 in this embodiment. In embodiments 3 to 5, the slopes of the upper and lower end surfaces of the convex portion 1 and the recess 2 were used to adjust the balance between the ease of removing the channel box 20 and the difficulty of moving the spacer 4 upward due to fluid force when loading the fuel assemblies into the core, but in this embodiment, the gradient of the change in diameter of the convex portion 2c inside the recess 2 in the direction perpendicular to the inner wall surface of the channel box 20, and the shape and dimensions of the hole or notch provided on the convex portion 1 are used.

[0075] The convex portion 1 shown in Figure 16(a) has a circular hole 1c into which the convex portion 2c inside the recessed portion 2 can fit. The side wall of the hole 1c is tapered so that the diameter increases on the side facing the channel box, making it easier for the contact with the convex portion 2c inside the recessed portion 2 to be line contact. This reduces the risk of damage to the convex portion 2c or the circular hole 1c due to the load concentrating on one point when there is mechanical interference between the convex portion 2c inside the recessed portion 2 and the circular hole 1c. However, with this structure, it is essentially impossible to adjust the balance between the ease of removing the channel box 20 and the difficulty of moving the spacer 4 upward due to fluid force when loading the fuel assemblies into the core.

[0076] 16(c) is provided with a circular hole 1c, the flat surface on the convex portion 1 is inclined in the longitudinal direction of the fuel rod, and the inclination is such that the lower side is closer to the inner wall surface of the channel box 20. By providing such an inclination to the flat surface on the convex portion 1, the constraint by the convex portion 2c inside the recessed portion 2 fitted into the circular hole 1c is less likely to be released when the spacer 4 receives an upward force, and upward movement of the spacer 4 can be made more difficult than downward movement.

[0077] In the partially circular cutout structure 1d provided on the convex portion 1 shown in Figure 16(d), the straight portion below the circular portion is horizontal, but the straight portion above it is inclined at θ1x relative to the horizontal. Even with this structure, the constraint by the convex portion 2c inside the recess 2 fitted into the partially circular cutout structure 1d is less likely to be released when the spacer 4 is subjected to an upward force, making it more difficult to move the spacer 4 upward than downward. A similar effect can be achieved by making the partially circular cutout structure 1d horizontally U-shaped and making the straight portion above the circular portion shorter than the straight portion below it. [Example]

[0078] Example 10 will be described with reference to Fig. 17. Fig. 17 is a bird's-eye view that schematically shows the arrangement of recesses provided on the inner wall surface of the channel box in Example 10, together with a part of the channel box.

[0079] In this embodiment, the spacer 4 is constrained on the inner wall surface of the channel box 20 by utilizing a simple mechanical interference state in which the convex portion 1 on the spacer 4 is fitted into the concave portion 2 on the inner wall surface of the channel box 20. This method can constrain the spacer 4 at a predetermined height by simply performing the work of attaching the channel box 20 to the fuel assembly 200, which is also performed for the current fuel assembly 200. On the other hand, if the positions of the combinations of the convex portion 1 and the concave portion 2 of multiple spacers 4 of different heights are the same in a plane perpendicular to the longitudinal direction of the fuel rod, the convex portion 1 and the concave portion 2 will be fitted into and released from the concave portion 2 multiple times during the process of attaching the channel box 20.

[0080] The engagement and release of the protrusions 1 into the recesses 2, which is unnecessary for achieving the object of this embodiment, is undesirable from the viewpoint of reducing the risk of damage or breakage of the recesses 2 of the protrusions 1. For example, in Example 1, in which the arrangement of the recesses 2 on the inner wall surface of the channel box is schematically shown in Figure 5(b), the positions of the combinations of the protrusions 1 and the recesses 2 in a plane perpendicular to the longitudinal direction of the fuel rods are the same for all spacers 4. Therefore, the engagement and release of the protrusions 1 into the recesses 2, which is unnecessary for the final restraint of the spacers 4, occurs multiple times, except for the spacer 4 at the bottom. When the number of spacer 4 stages is eight, the engagement and release of the protrusions 1 into the recesses 2 occurs seven times at the position of the combination of the protrusions 1 and the recesses 2 for the spacer 4 at the top. This embodiment can significantly reduce or eliminate the occurrence of the engagement and release of the protrusions 1 into the recesses 2 during the process of attaching or detaching the channel box 20.

[0081] The recesses 2 on the inner wall surface of the channel box 20, a portion of which is shown in Figure 17, are all installed on one of the four flat surfaces of the channel box 20, but their positions in the plane perpendicular to the longitudinal direction of the fuel rods are all different for each spacer height. The position of the protrusions 1 on the spacer 4 must also be changed for each spacer height in accordance with the arrangement of the recesses 2 on the inner wall surface of the channel box 20. By using the method of installing the protrusions 1 on the spacer 4 described in Example 8, in which the protrusions 1 are separate members from the spacer band 5, all spacers 4 can be made identical except for the mounting position of the member having the protrusions 1. By changing the combination positions of the protrusions 1 and recesses 2 at all spacer heights, unnecessary engagement of the protrusions 1 into the recesses 2 and their release during the process of attaching and detaching the channel box 20 can be completely eliminated. [Example]

[0082] Example 11 will be described with reference to Fig. 18. Fig. 18 is a top view schematically showing the relative positions of the convex portions provided on the spacer bands for each stage of the spacer and the concave portions provided on the inner wall surface of the channel box in Example 11.

[0083] In Example 10, the position of the combination of the convex portion 1 and the concave portion 2 over the entire spacer height is limited to one of the four flat surfaces of the inner wall surface of the channel box 20, but even if the flat surfaces or corner portions of the other three surfaces of the channel box 20 are also used, it is possible to completely eliminate the unnecessary insertion and release of the convex portion 1 into the concave portion 2 during the process of attaching and detaching the channel box 20.

[0084] As described above, this embodiment is an example of a case where the positions of the combinations of the convex portions 1 and the concave portions 2 are allocated not only on the flat portions of the four faces of the channel box 20 but also on the corner portions, and the drawings show the positions of the convex portions 1 and the springs 3 in the plane perpendicular to the longitudinal direction of the fuel rods of each spacer 4. The approximate squares in the drawings represent the spacer bands 5, and the white triangles and black squares represent the convex portions 1 and the springs 3, respectively.

[0085] In this embodiment, for example, the spacers 4 of embodiment 2 are used in the first to fourth stages, and the spacers of embodiment 1 are used in the fifth to eighth stages. This embodiment can also be combined with the method of arranging a plurality of positions for combining the convex portion 1 and the concave portion 2 in one flat surface of the channel box 20, as described in embodiment 10. For example, if two positions for combining the convex portion 1 and the concave portion 2 are arranged in one flat surface of the channel box 20, then with the flat surfaces of the four sides of the channel box 20 and two types of spacers 4 (four each), it is possible to completely eliminate the unnecessary fitting of the convex portion 1 into the concave portion 2 and the release of the convex portion 1 from the concave portion 2 during the process of attaching and detaching the channel box 20. [Example]

[0086] Example 12 will be described with reference to Fig. 19. Fig. 19 is a vertical cross-sectional view schematically showing a state when a spacer is restrained and during installation of a channel box in Example 12. In this example, even if the positions of the combinations of the convex portions 1 and concave portions 2 of the heights of a plurality of spacers 4 are the same in a plane perpendicular to the longitudinal direction of the fuel rod, it is possible to completely eliminate the occurrence of unnecessary fitting of the convex portions 1 into the concave portions 2 and their release during the installation and removal process of the channel box 20.

[0087] In this embodiment, first, as shown in Fig. 19(a), for the spacer 4 with a lower spacer height to be constrained, the height widths H1a, H1b, and H1c in the longitudinal direction of the fuel rod of the convex portions 1 (1Ha, 1Hb, 1Hc) it has are made smaller, and the height widths H2a, H2b, and H2c in the longitudinal direction of the fuel rod of the concave portions 2 (2Ha, 2Hb, 2Hc) on the inner wall of the channel box 20 are also made smaller in the longitudinal direction of the fuel rod as the height is lower. Further, the height width of the concave portion 2 at the stage of interest is made smaller than the height width in the longitudinal direction of the fuel rod of the convex portion 1 on the spacer 4 that is constrained one step above when the spacer 4 is constrained. These relationships are given by, for example, H1a < H2a < H1b < H2b < H1c < H2c in Fig. 19(a). Under this relationship, as shown in Fig. 19(b), during the process of attaching the channel box, the relationship that the height width of the convex portion 1 > the height width of the concave portion 2 always holds, and the occurrence of unnecessary fitting of the convex portion 1 into the concave portion 2 and its release during the process of attaching and detaching the channel box 20 can be avoided.

[0088] The application range of this embodiment is limited to one or more ranges in the longitudinal direction of the fuel rod. There are many configurations that, even when combined with Embodiment 10 or Embodiment 11, can completely eliminate the occurrence of unnecessary fitting of the convex portion 1 into the concave portion 2 and its release during the process of attaching and detaching the channel box 20. Also, the avoidance of the occurrence of unnecessary fitting of the convex portion 1 into the concave portion 2 and its release is also possible by applying the above-described relationship of the height width in the longitudinal direction of the fuel rod to the magnitude relationship of the lateral widths of the convex portion 1 and the concave portion 2 in a cross-section perpendicular to the longitudinal direction of the fuel rod.

[0089] By loading the fuel assembly of this embodiment as described above into the reactor core, the aforementioned effects can be obtained.

Explanation of Reference Numerals

[0090] 1...convex portion, 1a...upper end surface of convex portion, 1b...lower end surface of convex portion, 1c...hole, 1d...notch structure, 2...recess, 2a...upper end surface of recess, 2b...lower end surface of recess, 2c...convex portion, 3...spring, 3a...opening, 3b...small convex portion, 4...spacer, 5...spacer band, 5a...corner portion, 5b...notch, 6...divider, 6a...plate-shaped protrusion portion, 7...stop, 8...fuel rod spring, 9...spacer tab, 10... Flow tab, 20...channel box, 21...fuel rod, 21a...upper end plug, 21b...lower end plug of fuel rod, 22...water rod, 22a...upper end plug, 22b...lower end plug, 22c...inlet hole, 22d...outlet hole, 22e...spacer tab, 22f...spacer tab, 23...upper tie plate, 24...lower tie plate, 25...debris filter, 100...pressing point, 101...welding point, 200...fuel assembly

Claims

1. In a fuel assembly of a boiling water reactor including a fuel rod, a spacer, and a channel box, the channel box has at least one recess on an inner wall surface of one side thereof for each restraint height of the spacer; a spacer band of the spacer having a protrusion on an outer surface thereof facing the channel box, the protrusion being located at a position facing the recess when the spacer is installed at a predetermined height; 10. A fuel assembly for a boiling water reactor, comprising: an elastic body on the spacer band facing the outer peripheral surface of the spacer band having the convex portion.

2. In a fuel assembly of a boiling water reactor including a fuel rod, a spacer, and a channel box, At least one recess is provided on an inner wall surface of a corner portion of the channel box for each restraint height of the spacer, a spacer band of the spacer having a protrusion on an outer surface thereof facing a corner of the channel box, the protrusion being located at a position facing the recess when the spacer is installed at a predetermined height; 10. A fuel assembly for a boiling water reactor, comprising: elastic bodies on the outer peripheral surface of each of said spacer bands at diagonal positions on said outer peripheral surface of said spacer bands having said convex portions.

3. 3. The fuel assembly for a boiling water reactor according to claim 1, A fuel assembly for a boiling water reactor, characterized in that the smaller of the angles θ1a formed between the upper end surface of the convex portion on the outer wall surface of the spacer band or a portion that can be substantially regarded as the upper end surface and the outer wall surface of the spacer band in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction is greater than 0° and less than 90°.

4. 3. The fuel assembly for a boiling water reactor according to claim 1, A fuel assembly for a boiling water reactor, characterized in that the smaller of the angles θ1b formed between the lower end surface of the convex portion on the outer wall surface of the spacer band or a portion that can be substantially regarded as the lower end surface and the outer wall surface of the spacer band in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction is greater than 0° and less than 90°.

5. 5. The fuel assembly for a boiling water reactor according to claim 4, 1. A fuel assembly for a boiling water reactor, characterized in that the smaller of the angles θ1a formed between the upper end surface of the convex portion on the outer wall surface of the spacer band or a portion that can be substantially regarded as the upper end surface and the outer wall surface of the spacer band in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction is greater than the angle θ1b.

6. 3. The fuel assembly for a boiling water reactor according to claim 1, A fuel assembly for a boiling water reactor, characterized in that the smaller of the angles θ2a formed between the upper end surface of the recess on the inner wall surface of the channel box or a portion that can be substantially regarded as the upper end surface and the outer wall surface of the spacer band in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction is greater than 0° and less than 90°.

7. 3. The fuel assembly for a boiling water reactor according to claim 1, a lower end surface of the recess on the inner wall surface of the channel box or a portion corresponding to the lower end surface and an outer wall surface of the spacer band, the smaller of the angles θ2b being greater than 0° and less than 90° in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction.

8. 8. The fuel assembly for a boiling water reactor according to claim 7, a fuel assembly for a boiling water reactor, characterized in that the angle θ2b is smaller than the smaller angle θ2a between the upper end surface of the recess or a portion that can be substantially regarded as the upper end surface and the outer wall surface of the spacer band in a cross section perpendicular to the surface of the spacer band and parallel to the vertical direction.

9. 3. The fuel assembly for a boiling water reactor according to claim 1, 1. A fuel assembly for a boiling water reactor, wherein the recess formed on the inner wall surface of the channel box is composed of a vertical groove of a finite length and a groove of a finite length that is continuous with the vertical groove and is inclined with respect to the vertical direction.

10. 3. The fuel assembly for a boiling water reactor according to claim 1, a recess formed on the inner wall surface of the channel box having a rotor structure therein whose central axis is perpendicular to the inner wall surface of the channel box and whose tip height is located between the inner wall surface of the channel box and a bottom surface of the recess or a planar structure that can be substantially regarded as the bottom surface, and a circular hole or a notch is provided on a protrusion formed on the outer wall surface of the spacer band.

11. 11. The fuel assembly for a boiling water reactor according to claim 10, 10. A fuel assembly for a boiling water reactor, comprising: a convex rotor structure provided inside the recess on the inner wall surface of the channel box, the radius of which increases toward the bottom surface of the recess.

12. 3. The fuel assembly for a boiling water reactor according to claim 1, 10. A fuel assembly for a boiling water reactor, wherein the recesses provided on the inner wall surface of the channel box are located at a plurality of different positions for each restraint height of the spacer in a cross section perpendicular to the vertical direction.

13. 13. The fuel assembly for a boiling water reactor according to claim 12, 10. A fuel assembly for a boiling water reactor, wherein the recesses provided on the inner wall surface of the channel box are all located at different positions in a cross section perpendicular to the vertical direction for each restraint height of the spacer.

14. 3. The fuel assembly for a boiling water reactor according to claim 1, A fuel assembly for a boiling water reactor, characterized in that the effective width of the recessed portion formed on the inner wall surface of the channel box in the longitudinal direction of the fuel rod or the effective width in the direction perpendicular to the longitudinal direction of the fuel rod varies depending on the restraining height of the spacer or the position in a cross section perpendicular to the longitudinal direction of the fuel rod.

15. 3. The fuel assembly for a boiling water reactor according to claim 1, A fuel assembly for a boiling water reactor, characterized in that the recesses on the inner wall surface of the channel box have a range in one or more locations in the longitudinal direction of the fuel rods where the effective width in the longitudinal direction of the fuel rods at each restraining height of the spacers is larger toward the upper side in the longitudinal direction of the fuel rods.

16. A reactor core loaded with the fuel assemblies of a boiling water reactor according to claim 1 or 2.

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