Control rod guide thimble fixing device and fixing method

Abstract

To apply various cranes.SOLUTION: A control rod guide fixing device includes: a main body part 2 which is provided so as to be insertable into a control rod guide thimble 56 from an opening 54C of an upper nozzle 54 of a fuel assembly; an actuating part 3 which engages and attaches the main body part 2 to the inner surface of the control rod guide thimble 56; a position regulating mechanism (flange part 2B, moving part 3A, operating part 3C, each engaging part 2C, and pressing part 3B) which arranges the upper ends of the main body part 2 and the actuating part 3 inside a recess 54D so as to be located below the upper surface 54Aa of a substrate 54A of an upper nozzle 54 when the recess 54D which is formed around the opening 54C so as to be recessed downward from the upper surface 54Aa of the substrate 54A of the upper nozzle 54, and the main body 2 is attached to the control rod guide thimble 56.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a control rod guide thimble securing device, a securing method, and a top nozzle for a fuel assembly. [Background technology]

[0002] For example, Patent Document 1 discloses a repair sleeve for stress corrosion cracking of a sleeve connecting an upper nozzle and a control rod guide thimble of a fuel assembly. The repair sleeve includes a shaft formed to fit into the opening of the control rod guide thimble of the upper nozzle, and a tendon provided on the shaft and having a protrusion that is inserted into the recess where the sleeve and the control rod guide thimble fit together. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4662459 Summary of the Invention [Problem to be solved by the invention]

[0004] Fuel assemblies with repair sleeves attached can be safely lifted by a refueling machine at a nuclear power plant. However, fuel assemblies with repair sleeves protruding above the top surface of the base plate of the top nozzle may not be able to be lifted by other cranes because the repair sleeves interfere with the protruding portion and the top nozzle cannot be engaged.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a control rod guide thimble fixing device, fixing method, and upper nozzle that can be used with various cranes. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, a control rod guide thimble fixing device according to one aspect of the present disclosure comprises: a main body portion that is insertable into the interior of a control rod guide thimble from an opening of an upper nozzle of a fuel assembly; an actuating portion that engages and attaches the main body portion to the inner surface of the control rod guide thimble; and a positioning mechanism that forms a recess around the opening so as to be recessed downward from the upper surface of the base plate of the upper nozzle, and that positions the upper ends of the main body portion and the actuating portion inside the recess so that they are located below the upper surface when the main body portion is attached to the control rod guide thimble.

[0007] In order to achieve the above-mentioned object, a control rod guide thimble fixing method according to one aspect of the present disclosure includes the steps of: forming a recess around an opening connected to a control rod guide thimble so that the recess is recessed downward from the upper surface of a base plate of an upper nozzle of a fuel assembly; inserting a main body portion of a control rod guide thimble fixing device into the control rod guide thimble through the opening and accommodating the main body portion within the recess so that the upper end of the main body portion is positioned below the upper surface; and operating an actuating part of the control rod guide thimble fixing device to engage and attach the main body portion to the inner surface of the control rod guide thimble, and accommodating the main body portion within the recess so that the upper end of the actuating part is positioned below the upper surface.

[0008] In order to achieve the above-mentioned object, a control rod guide thimble fixing method according to one aspect of the present disclosure includes the steps of: replacing an existing top nozzle provided in a fuel assembly with a new top nozzle having a recess formed around an opening connected to the control rod guide thimble so as to be recessed downward from the upper surface of a substrate; inserting a main body portion of a control rod guide thimble fixing device into the control rod guide thimble from the opening and accommodating the main body portion within the recess so that the upper end of the main body portion is positioned below the upper surface; and operating an actuating part of the control rod guide thimble fixing device to engage and attach the main body portion to the inner surface of the control rod guide thimble, and accommodating the main body portion within the recess so that the upper end of the actuating part is positioned below the upper surface.

[0009] In order to achieve the above-mentioned object, an upper nozzle for a fuel assembly according to one embodiment of the present disclosure has a recess formed around an opening connected to a control rod guide thimble so as to be recessed downward from the upper surface of the substrate. [Effects of the Invention]

[0010] The present disclosure is applicable to a variety of cranes. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic side view showing the configuration of a fuel assembly. [Figure 2] FIG. 2 is a schematic enlarged cross-sectional view showing the upper part of the fuel assembly. [Figure 3] FIG. 3 is a cross-sectional view showing an example of the configuration of a control rod guide thimble fixing device. [Figure 4] FIG. 4 is a flowchart showing a method for fixing a control rod guide thimble. [Figure 5] FIG. 5 is a flowchart showing a method for fixing a control rod guide thimble. [Figure 6] FIG. 6 is a process diagram showing a method for fixing a control rod guide thimble. [Figure 7] FIG. 7 is a process diagram showing a method for fixing a control rod guide thimble. [Figure 8] FIG. 8 is a process diagram showing a method for fixing a control rod guide thimble. [Figure 9] FIG. 9 is a process diagram showing a method for fixing a control rod guide thimble. [Figure 10] FIG. 10 is a process diagram showing a method for fixing a control rod guide thimble. [Figure 11] FIG. 11 is a cross-sectional view showing another example of the configuration of the control rod guide thimble fixing device. [Figure 12] FIG. 12 is a cross-sectional view showing another example of the configuration of the control rod guide thimble fixing device. [Figure 13] FIG. 13 is a schematic diagram showing the effect of the control rod guide thimble fixing device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the present disclosure is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially identical.

[0013] Fig. 1 is a schematic side view showing the configuration of a fuel assembly, and Fig. 2 is a schematic enlarged cross-sectional view showing the upper part of the fuel assembly.

[0014] The fuel assembly 51 shown in FIGS. 1 and 2 is a fuel assembly for a pressurized water reactor (PWR). The fuel assembly 51 is formed long in the vertical direction. The fuel assembly 51 includes fuel rods 52, a support grid 53 that bundles the fuel rods 52, an upper nozzle 54 provided at the upper end of the fuel rods 52 in the longitudinal direction, a lower nozzle 55 provided at the lower end of the fuel rods 52 in the longitudinal direction, and a control rod guide thimble 56 that connects the upper nozzle 54 and the lower nozzle 55. Although not shown in the figures, the fuel rods 52 are arranged inside a cylindrical fuel cladding tube that is long in the vertical direction, and multiple nuclear fuel pellets are arranged in the longitudinal direction of the fuel cladding tube. The support grid 53 constitutes multiple grids through which the multiple fuel rods 52 are inserted, and the multiple fuel rods 52 are installed at multiple locations (10 locations in FIG. 1) in the longitudinal direction at predetermined intervals. The top nozzle 54 is rectangular in plan view, with upper protrusions 54B protruding upward from the four corners of a rectangular base plate 54A. As shown in FIG. 2, the upper protrusions 54B have inward-facing locking portions 54Ba formed at their upper ends. The bottom nozzle 55 is rectangular in plan view, with lower protrusions 55B protruding downward from the four corners of a rectangular base plate 55A. The control rod guide thimble 56, into which a control rod is inserted from above, is formed as a vertically elongated cylindrical shape. The control rod guide thimble 56 has a cylindrical central axis CL extending vertically. The lower end of the control rod guide thimble 56 is joined to the base plate 55A of the bottom nozzle 55. As shown in FIG. 2, the upper end of the control rod guide thimble 56 is connected to the base plate 54A of the top nozzle 54 via a cylindrical sleeve 57. A through-hole 54Ab is formed in the base plate 54A of the top nozzle 54, penetrating in the vertical direction. A sleeve 57 is inserted into the through-hole 54Ab so as not to protrude upward from the upper surface 54Aa of the base plate 54A, and its upper end is joined to the base plate 54A by welding. The upper end of the control rod guide thimble 56 is inserted into the lower end of the sleeve 57, and the sleeve is joined by tube expansion. As a result, an opening 54C is formed in the upper surface 54Aa of the base plate 54A in the top nozzle 54, which is connected to the control rod guide thimble 56 via the sleeve 57.

[0015] The fuel assembly 51 configured in this manner has the upper nozzle 54 at the top end attached to a crane, and the upper nozzle 54 and the lower nozzle 55 are connected by control rod guide thimbles 56, so that the entire assembly can be lifted and moved or installed.

[0016] FIG. 3 is a cross-sectional view showing an example of the configuration of a control rod guide thimble fixing device.

[0017] The control rod guide thimble fixing device (hereinafter referred to as the fixing device) 1 of the embodiment is used to repair and fix a control rod guide thimble 56 and a sleeve 57 in a spent fuel assembly 51 in a nuclear reactor when the soundness of the joint between the control rod guide thimble 56 and the sleeve 57 is reduced due to stress corrosion cracking. In the embodiment, a recess 54D is formed around an opening 54C so as to recess downward from an upper surface 54Aa in a base plate 54A of an upper nozzle 54 on which the fixing device 1 is provided. The recess 54D does not penetrate the base plate 54A vertically, but is formed downward from the upper surface 54Aa to a depth W so as to open only to the upper surface 54Aa, and its bottom surface 54Da is formed flat along (preferably parallel to) the upper surface 54Aa. When the recess 54D is provided, the opening 54C of the base plate 54A is formed at the bottom surface 54Da of the recess 54D.

[0018] The fixing device 1 of the embodiment includes a main body portion 2 and an actuation portion 3.

[0019] The main body 2 is provided so as to be insertable into the control rod guide thimble 56 from an opening 54C of the upper nozzle 54 of the fuel assembly 51. The main body 2 includes a support portion 2A, a flange portion 2B, an engagement portion 2C, and a movable portion 2D.

[0020] The support portion 2A is formed with an outer diameter that allows it to be inserted into the sleeve 57 or the control rod guide thimble 56 from the opening 54C. The support portion 2A is configured to allow the operating portion 3 to move in the vertical direction and to support it at the moved position. In the embodiment, the support portion 2A has a through hole 2Aa formed therein, through which the operating portion 3 can pass in the vertical direction along the central axis CL when inserted from the opening 54C, and a female screw is formed in this through hole 2Aa.

[0021] The flange portion 2B is provided at the upper end of the support portion 2A, and when the support portion 2A is inserted through the opening 54C, the flange portion 2B expands outward away from the central axis CL and has a diameter larger than that of the opening 54C. The flange portion 2B is preferably formed in an annular (ring-like) shape around the central axis CL, but may be formed in a non-circular annular shape or may be formed by cutting out a portion of the annular (ring-like) shape. The flange portion 2B has an outer diameter D2 that is smaller than the inner diameter D1 of the recess 54D and a thickness T that is smaller than the depth W of the recess 54D. Therefore, when the support portion 2A is inserted through the opening 54C, the flange portion 2B abuts against the bottom surface 54Da of the recess 54D and is accommodated inside the recess 54D.

[0022] The engaging portion 2C is formed with an outer diameter that allows it to be inserted into the control rod guide thimble 56 from the opening 54C via the sleeve 57. The engaging portion 2C is formed by dividing a ring shape into multiple pieces in the circumferential direction based on the central axis CL. Each engaging portion 2C has an outer surface 2Ca that can come into contact with the inner surface of the control rod guide thimble 56. Each engaging portion 2C also has an inner surface 2Cb that is inclined downward so as to move away from the central axis CL.

[0023] The movable portion 2D connects each of the engaging portions 2C to the support portion 2A, and is formed to be deformable or displaceable so that each of the engaging portions 2C can approach or move away from each other with respect to the central axis CL.

[0024] The actuating unit 3 is attached by engaging the engaging portion 2C of the main body 2 with the inner surface of the control rod guide thimble 56. The actuating unit 3 includes a moving portion 3A, a pressing portion 3B, and an operating portion 3C.

[0025] The moving part 3A is formed in a rod shape extending in the vertical direction along the central axis CL so as to be inserted into the through hole 2Aa of the support part 2A of the main body part 2. The moving part 3A is provided so as to be movable in the vertical direction while inserted into the through hole 2Aa. In the embodiment, the moving part 3A has a male thread formed on the circumferential surface 3Aa that is screwed into the female thread formed in the through hole 2Aa. Therefore, the moving part 3A moves in the vertical direction relative to the support part 2A of the main body part 2 by being rotated about the central axis CL.

[0026] The pressing portion 3B is disposed at the lower end of the moving portion 3A and has an outer diameter large enough to be inserted into the control rod guide thimble 56 through the opening 54C via the sleeve 57. The pressing portion 3B moves vertically together with the moving portion 3A. The pressing portion 3B has an outer surface 3Ba that slopes downward and away from the central axis CL. This outer surface 3Ba faces the inner surfaces 2Cb of the engagement portions 2C of the main body 2. When the outer surface 3Ba moves upward in conjunction with the movement of the moving portion 3A, it abuts against the inner surfaces 2Cb of the engagement portions 2C. When the outer surface 3Ba moves further upward in conjunction with further movement of the moving portion 3A, the mutual slope between the outer surface 3Ba and the inner surfaces 2Cb of the engagement portions 2C presses the engagement portions 2C outward, away from the central axis CL. When the engagement portions 2C are pressed outward, the outer surfaces 2Ca of the engagement portions 2C come into contact with the inner surfaces of the control rod guide thimbles 56 and are pressed into engagement. This causes the main body 2 to be attached to the control rod guide thimble 56 .

[0027] The operating unit 3C is disposed at the upper end of the moving unit 3A, protrudes upward from the through-hole 2Aa of the support unit 2A in the main body 2, and is accessible from above the substrate 54A of the upper nozzle 54. Therefore, the operating unit 3C of the actuation unit 3 is rotated about the central axis CL from above the substrate 54A. The operating unit 3C is also configured to be unscrewed and detached from the moving unit 3A when the tightening torque applied to the moving unit 3A exceeds a predetermined value.

[0028] In the fixing device 1 configured in this manner, the operating section 3 and the main body section 2 are integrally provided with the moving section 3A inserted into the support section 2A of the main body section 2.

[0029] When the operating part 3C is rotated, the moving part 3A of the fixing device 1 moves up and down, and when the moving part 3A moves upward (see FIG. 9), the pressing part 3B causes each of the engaging parts 2C of the main body 2 to engage with the control rod guide thimble 56, and the main body 2 is attached to the control rod guide thimble 56. When each of the engaging parts 2C engages with the control rod guide thimble 56, the pressing part 3B engages with each of the engaging parts 2C, and a tightening torque is generated in the moving part 3A actuation part 3 via the operating part 3C. When the tightening torque applied to the moving part 3A exceeds a predetermined value, the operating part 3C is twisted off from the moving part 3A (see FIG. 10).

[0030] When the main body 2 of the fixing device 1 is attached to the control rod guide thimble 56, the flange portion 2B of the main body 2 abuts against the bottom surface 54Da of the recess 54D formed in the base plate 54A of the upper nozzle 54, so that the control rod guide thimble 56 is fixed to the upper nozzle 54 via the main body 2.

[0031] Fig. 4 is a flowchart showing a control rod guide thimble fixing method. Fig. 5 is a flowchart showing a control rod guide thimble fixing method. Fig. 6 is a process chart showing a control rod guide thimble fixing method. Fig. 7 is a process chart showing a control rod guide thimble fixing method. Fig. 8 is a process chart showing a control rod guide thimble fixing method. Fig. 9 is a process chart showing a control rod guide thimble fixing method. Fig. 10 is a process chart showing a control rod guide thimble fixing method.

[0032] 4, in the control rod guide thimble fixing method using the fixing device 1 described above, if the inspection of the spent fuel assembly 51 reveals that the soundness of the joint between the control rod guide thimble 56 and the sleeve 57 has deteriorated, it is determined in step S1 that reinforcement is necessary (step S1: Yes). If it is determined that reinforcement is necessary, it is necessary to fix the control rod guide thimble 56 using the fixing device 1.

[0033] Here, in step S2, if any of the many fuel rods 52 is found to be leaking (step S2: Yes), the fuel rod 52 is removed. Therefore, in order to remove the leaking fuel rod 52, in step S3, the top nozzle 54 is removed, and the leaking fuel rod 52 is then replaced with a new top nozzle 54. Note that if there is no leaking fuel rod 52 (step S2: No), the top nozzle 54 is not replaced.

[0034] In step S4, the fixing device 1 is used to reinforce the fixing of the control rod guide thimble 56.

[0035] As shown in FIG. 5, reinforcement using the fixing device 1 involves forming the recess 54D described above in the base plate 54A of the top nozzle 54 in step S41. That is, the state shown in FIG. 6 is changed to the state shown in FIG. 7. As shown in FIG. 6, the sleeve 57 is inserted into the through-hole 54Ab in the base plate 54A, and its upper end is welded to the base plate 54A. The sleeve 57 has its upper end expanded and fitted into a groove 54Aba, which is formed with a larger diameter on the inner wall of the through-hole 54Ab in the base plate 54A. The recess 54D is formed by cutting the welded portion at the upper end of the sleeve 57 and a portion of the expanded portion at the upper end together with a portion of the base plate 54A, as shown in FIG. 7. After cutting, the upper end of the sleeve 57 does not protrude above the bottom surface 54Da of the recess 54D. This occurs when there is no leaking fuel rod 52 and the top nozzle 54 is not replaced, or when there is a leaking fuel rod 52 and the recess 54D is not formed in the replaced top nozzle 54. In addition, when there is a leaking fuel rod 52 and the upper nozzle 54 is to be replaced, an upper nozzle 54 is prepared in advance with a recess 54D formed in it, with the through hole 54Ab as a part of it, and the upper end of the sleeve 57 is cut to match this recess 54D and the through hole 54Ab.

[0036] Next, in step S42, the fixing device 1 is inserted into the control rod guide thimble 56. That is, as shown in FIG. 8 , the main body 2 of the fixing device 1 is inserted into the control rod guide thimble 56 through the opening 54C of the upper nozzle 54, and the flange 2B at the upper end of the main body 2 is accommodated in the recess 54D so as to be positioned below the upper surface 54Aa of the base plate 54A. This insertion of the fixing device 1 can be performed using a tool 4. The tool 4 includes a tool main body 4A suspended from above, a first gripping part 4B capable of gripping the flange 2B of the fixing device 1, and a second gripping part 4C capable of gripping the operating part 3C and rotating the operating part 3C about the central axis CL. When inserting the fixing device 1 into the control rod guide thimble 56, the flange 2B is gripped with the first gripping part 4B of the tool 4, and the fixing device 1 is inserted into the control rod guide thimble 56.

[0037] Next, in step S43, the locking device 1 is attached to the control rod guide thimble 56. That is, as shown in FIG. 9, the tool 4 grasps the operating part 3C with the second gripping part 4C and rotates it around the central axis CL so that the actuating part 3 moves upward, while also lifting the tool 4 itself. As the actuating part 3 moves upward, the outer surfaces 2Ca of the engaging parts 2C engage with the inner surfaces of the control rod guide thimble 56, and the locking device 1 is attached to the control rod guide thimble 56. Then, as the actuating part 3 further rotates and moves upward, the tightening torque on the moving part 3A exceeds a predetermined value, and the operating part 3C is unscrewed and detached from the moving part 3A, as shown in FIG. 10. That is, the detachment of the operating part 3C from the moving part 3A confirms that the locking device 1 has been attached to the control rod guide thimble 56.

[0038] 10, when the locking device 1 is attached to the control rod guide thimble 56 and the operating part 3C is released, the size and shape of each of the engaging parts 2C and the pressing part 3B are set as a regulating means relative to the inner diameter of the control rod guide thimble 56 so that the upper end of the moving part 3A is positioned within the depth W of the recess 54D. That is, when the locking device 1 is attached to the control rod guide thimble 56, the flange part 2B at the uppermost end of the main body part 2 and the moving part 3A at the uppermost end of the operating part 3 are housed inside the recess 54D.

[0039] 11 and 12 are cross-sectional views showing other configuration examples of the control rod guide thimble fixing device.

[0040] As shown in FIG. 11 , a fixing device 11 as another configuration example has an operating portion 31C different from that of the fixing device 1 described above. The operating portion 31C is formed as a polygonal hole. Although not shown in the figure, a polygonal rod member is inserted into the hole of the operating portion 31C as a second gripping portion and fitted therein. Therefore, the fixing device 11 is attached to the control rod guide thimble 56 by fitting the second gripping portion into the operating portion 31C with a tool, rotating the fixing device 11 around the central axis CL so that the actuating portion 3 moves upward, and then lifting the tool itself. The outer surfaces 2Ca of the engaging portions 2C engage with the inner surfaces of the control rod guide thimble 56, thereby attaching the fixing device 11 to the control rod guide thimble 56. Furthermore, the size and shape of the engaging portions 2C and the pressing portion 3B are set as a regulating means relative to the inner diameter of the control rod guide thimble 56 so that the upper end of the moving portion 3A is positioned within the depth W of the recess 54D when the fixing device 11 is attached to the control rod guide thimble 56. That is, the fixing device 11 attached to the control rod guide thimble 56 has the flange portion 2B at the uppermost end of the main body portion 2 and the moving portion 3A at the uppermost end of the operating portion 3 housed inside the recess 54D.

[0041] As shown in FIG. 12 , another example of the fixing device 21 has a support portion 21A and a moving portion 31A that are different from those of the fixing device 1 described above. The inner surface of the through-hole 21Aa in the support portion 21A and the outer surface 31Aa of the moving portion 31A are engaged with each other so that they can move relative to each other in the vertical direction. Therefore, the fixing device 21 is attached to the control rod guide thimble 56 by engaging the second gripping portion 4C with the operating portion 3C using the tool 4 and then lifting the tool itself so that the actuating portion 3 moves upward. The outer surfaces 2Ca of the engaging portions 2C engage with the inner surfaces of the control rod guide thimble 56, and the fixing device 21 is attached to the control rod guide thimble 56. When torque is applied to the fixing device 21 to move it upward, the operating portion 3C is disengaged from the moving portion 3A. That is, the disengagement of the operating portion 3C from the moving portion 3A confirms that the fixing device 21 is attached to the control rod guide thimble 56. Furthermore, the sizes and shapes of the engaging portions 2C and pressing portions 3B are set as regulating means relative to the inner diameter of the control rod guide thimble 56 so that, when the fixing device 21 is attached to the control rod guide thimble 56, the upper end of the moving portion 3A is positioned within the depth W of the recess 54D. That is, when the fixing device 21 is attached to the control rod guide thimble 56, the flange portion 2B at the uppermost end of the main body portion 2 and the moving portion 3A at the uppermost end of the operating portion 3 are housed inside the recess 54D.

[0042] As such, the fixing devices 1, 11, 21 of the embodiments comprise a main body portion 2 that is insertable into the control rod guide thimble 56 from the opening 54C of the upper nozzle 54 of the fuel assembly 51, an actuating portion 3 that engages and attaches the main body portion 2 to the inner surface of the control rod guide thimble 56, and a position control mechanism (flange portion 2B, moving portion 3A, 31A, operating portion 3C, 31C, each engaging portion 2C and pressing portion 3B) that forms a recess 54D around the opening 54C so as to be recessed downward from the upper surface 54Aa of the base plate 54A of the upper nozzle 54, and that positions the upper ends of the main body portion 2 and the actuating portion 3 inside the recess 54D so that they are positioned lower than the upper surface 54Aa of the base plate 54A of the upper nozzle 54 when the main body portion 2 is attached to the control rod guide thimble 56.

[0043] According to the fixing devices 1, 11, and 21 of this embodiment, when the main body 2 is attached to the control rod guide thimble 56, the positioning mechanism positions the upper ends of the main body 2 and the actuator 3 inside the recess 54D and below the upper surface 54Aa of the base plate 54A of the top nozzle 54. Therefore, when fixing the control rod guide thimble 56, no part protrudes from the upper surface 54Aa of the base plate 54A of the top nozzle 54. As shown in FIG. 13 , some crane 101 has a configuration in which its bottom surface 101a abuts against the upper surface 54Aa of the base plate 54A, while its claws 101b engage with the locking portions 54Ba of the upper protrusions 54B of the top nozzle 54. By applying this fixing device 1, 11, and 21, even such a crane 101 can lift a fuel assembly 51. Therefore, the fixing devices 1, 11, and 21 of the embodiment allow various cranes to be used.

[0044] In addition, in the fixing device 1, 21 of the embodiment, the position control mechanism comprises: a flange portion 2B that forms the upper end of the main body portion 2, is housed in the recess 54D and abuts against the bottom surface 54Da of the recess 54D, and is positioned below the upper surface 54Aa; a moving portion 3A, 31A that forms the upper end of the operating portion 3, is arranged to be movable in the vertical direction when the main body portion 2 is attached to the control rod guide thimble 56, and is positioned below the upper surface 54Aa when the main body portion 2 is attached to the control rod guide thimble 56; and an operating portion 3C that is arranged at the upper end of the moving portion 3A, is engaged with a tool 4 that operates the moving portion 3A, and is configured to be detachable from the moving portion 3A.

[0045] According to the fixing devices 1, 21 of this embodiment, the device components can be arranged inside the recess 54D so as not to protrude above the upper surface 54Aa. Moreover, when the operating unit 3C is detached from the moving unit 3A, it can be confirmed that the main body 2 is attached to the control rod guide thimble 56. Furthermore, since the operating unit 3C is detached from the moving unit 3A, it is possible to prevent the operating unit 3C from protruding above the upper surface 54Aa even if the moving stroke of the moving unit 3A is set long, so that the depth W of the recess 54D can be reduced and the strength of the substrate 54A can be ensured.

[0046] In addition, in the fixing devices 1, 11, 21 of the embodiments, the position control mechanism comprises a flange portion 2B that forms the upper end of the main body portion 2, is accommodated in the recess 54D and abuts against the bottom surface 54Da of the recess 54D, and is positioned below the upper surface 54Aa, a moving portion 3A, 31A that forms the upper end of the operating portion 3, is movable in the vertical direction when the main body portion 2 is attached to the control rod guide thimble 56, and is positioned below the upper surface 54Aa when the main body portion 2 is attached to the control rod guide thimble 56, and a determining means (each engaging portion 2C and pressing portion 3B) that determines the operating range of the moving portion 3A, 31A so that the upper end of the moving portion 3A, 31A is positioned below the upper surface 54Aa when the main body portion 2 is attached to the control rod guide thimble 56.

[0047] According to the fixing devices 1, 11, and 21 of this embodiment, the device components can be disposed inside the recess 54D so as not to protrude above the upper surface 54Aa.

[0048] In addition, in the fixing devices 1, 11 of the embodiments, the operating part 3 is provided so as to be movable up and down by rotation, and the main body part 2 is fitted to and engaged with the inner surface of the control rod guide thimble 56 as the operating part 3 moves.

[0049] According to the fixing device 1, 11 of this embodiment, the main body 2 is engaged with and attached to the control rod guide thimble 56 by rotating the actuating part 3, and it is possible to confirm that the main body 2 has been attached to the control rod guide thimble 56 by the torque fluctuations and rotation speed of the rotation.

[0050] The fixing method of the embodiment includes the steps of: forming a recess 54D around an opening 54C connected to the control rod guide thimble 56 so as to be recessed downward from the upper surface 54Aa of the base plate 54A of the upper nozzle 54 of the fuel assembly 51; inserting the main body 2 of the fixing device 1, 11, 21 from the opening 54C into the control rod guide thimble 56 and accommodating it inside the recess 54D so that the upper end of the main body 2 is positioned below the upper surface 54Aa; and operating the operating part 3 of the fixing device 1, 11, 21 to engage and attach the main body 2 to the inner surface of the control rod guide thimble 56, and accommodating it inside the recess 54D so that the upper end of the operating part 3 is positioned below the upper surface 54Aa.

[0051] According to the fixing method of this embodiment, when the main body 2 is attached to the control rod guide thimble 56, the upper ends of the main body 2 and the actuator 3 are positioned inside the recess 54D so as to be lower than the upper surface 54Aa of the base plate 54A of the top nozzle 54. Therefore, when fixing the control rod guide thimble 56, no part protrudes from the upper surface 54Aa of the base plate 54A of the top nozzle 54. As shown in FIG. 13 , there is a crane 101 configured such that its bottom surface 101a abuts against the upper surface 54Aa of the base plate 54A, and its claws 101b engage with the locking portions 54Ba of the upper protrusions 54B of the top nozzle 54. According to this fixing method, even such a crane 101 can lift the fuel assembly 51. Therefore, the fixing method of this embodiment can be used with various cranes.

[0052] The fixing method of the embodiment includes the steps of: replacing the existing top nozzle 54 provided in the fuel assembly 51 with a new top nozzle 54 having a recess 54D formed around an opening 54C connected to the control rod guide thimble 56 so as to be recessed downward from the upper surface 54Aa of the substrate 54A; inserting the main body 2 of the fixing device 1, 11, 21 into the control rod guide thimble 56 from the opening 54C and accommodating it inside the recess 54D so that the upper end of the main body 2 is positioned below the upper surface 54Aa; and operating the operating part 3 of the fixing device 1, 11, 21 to engage and attach the main body 2 to the inner surface of the control rod guide thimble 56, and accommodating it inside the recess 54D so that the upper end of the operating part 3 is positioned below the upper surface 54Aa.

[0053] According to the fixing method of this embodiment, when the main body 2 is attached to the control rod guide thimble 56, the upper ends of the main body 2 and the actuator 3 are positioned inside the recess 54D so as to be lower than the upper surface 54Aa of the base plate 54A of the top nozzle 54. Therefore, when fixing the control rod guide thimble 56, no part protrudes from the upper surface 54Aa of the base plate 54A of the top nozzle 54. As shown in FIG. 13 , there is a crane 101 configured such that its bottom surface 101a abuts against the upper surface 54Aa of the base plate 54A, and its claws 101b engage with the locking portions 54Ba of the upper protrusions 54B of the top nozzle 54. According to this fixing method, even such a crane 101 can lift the fuel assembly 51. Therefore, the fixing method of this embodiment can be used with various cranes.

[0054] In the fuel assembly upper nozzle 54 of the embodiment, a recess 54D is formed around an opening 54C connected to the control rod guide thimble 56 so as to be recessed downward from an upper surface 54Aa of a base plate 54A.

[0055] According to the top nozzle 54 of this embodiment, the upper ends of the fixing devices 1, 11, and 21 that fix the control rod guide thimbles 56 can be disposed inside the recess 54D so as to be located below the upper surface 54Aa of the base plate 54A of the top nozzle 54. Therefore, when fixing the control rod guide thimbles 56, no part protrudes from the upper surface 54Aa of the base plate 54A of the top nozzle 54. As shown in FIG. 13 , a crane 101 has a configuration in which its bottom surface 101a abuts against the upper surface 54Aa of the base plate 54A, and its claws 101b engage with the locking portions 54Ba of the upper protrusions 54B of the top nozzle 54. According to this top nozzle 54, even such a crane 101 can lift the fuel assembly 51. Therefore, the top nozzle 54 of this embodiment can be used with various cranes. [Explanation of symbols]

[0056] 1,11,21 Fixing device 2 Main body 2B flange 3. Operating unit 3A,31A Moving part 3C,31C Operation section 4 Tools 51 Fuel assembly 54 Upper nozzle 54A board 54Aa top surface 54C opening 54D Recess 54Da bottom 56 Control rod guide thimble

Claims

1. a main body portion that can be inserted into the control rod guide thimble from an opening of the upper nozzle of the fuel assembly; an actuation portion that engages and mounts the main body portion on the inner surface of the control rod guide thimble; a position restriction mechanism that forms a recess around the opening so as to be recessed downward from an upper surface of the base plate of the upper nozzle, and that positions upper ends of the main body and the operating unit inside the recess so as to be located below the upper surface when the main body is attached to the control rod guide thimble; A control rod guide thimble fixing device comprising:

2. The position restriction mechanism includes: a flange portion that forms an upper end portion of the main body portion, is accommodated in the recess, abuts against a bottom surface of the recess, and is positioned below the upper surface; a moving part that constitutes an upper end of the actuation part, that is provided so as to be movable in the vertical direction when the main body part is attached to the control rod guide thimble, and that is disposed below the upper surface when the main body part is attached to the control rod guide thimble; an operating unit provided at an upper end of the moving unit, the operating unit being configured to be engaged with a tool for operating the moving unit and to be detachable from the moving unit; 2. The control rod guide thimble locking device of claim 1, comprising:

3. The position restriction mechanism includes: a flange portion that forms an upper end portion of the main body portion, is accommodated in the recess, abuts against a bottom surface of the recess, and is positioned below the upper surface; a moving part that constitutes an upper end of the actuation part, that is provided so as to be movable in the vertical direction when the main body part is attached to the control rod guide thimble, and that is disposed below the upper surface when the main body part is attached to the control rod guide thimble; a defining means for defining an operation range of the movable portion so that an upper end of the movable portion is positioned below the upper surface when the main body portion is attached to the control rod guide thimble; 2. The control rod guide thimble locking device of claim 1, comprising:

4. The operating unit is provided so as to be movable in the up and down direction by rotation, The main body portion is engaged with and attached to the inner surface of the control rod guide thimble as the actuating portion moves. A control rod guide thimble fixing device according to any one of claims 1 to 3.

5. forming a recess around an opening connected to a control rod guide thimble so as to be recessed downward from an upper surface of a base plate of the upper nozzle of the fuel assembly; a step of inserting a main body of the control rod guide thimble fixing device into the control rod guide thimble through the opening and accommodating the main body within the recess so that an upper end of the main body is positioned below the upper surface; a step of engaging and attaching the main body to the inner surface of the control rod guide thimble by operating an actuating part of the control rod guide thimble fixing device, and accommodating the main body within the recess so that the upper end of the actuating part is positioned below the upper surface; A control rod guide thimble fixing method, comprising:

6. replacing an existing top nozzle provided in a fuel assembly with a new top nozzle having a recess formed around an opening connected to a control rod guide thimble so as to be recessed downward from an upper surface of a substrate; a step of inserting a main body of the control rod guide thimble fixing device into the control rod guide thimble through the opening and accommodating the main body within the recess so that an upper end of the main body is positioned below the upper surface; a step of engaging and attaching the main body to the inner surface of the control rod guide thimble by operating an actuating part of the control rod guide thimble fixing device, and accommodating the main body within the recess so that the upper end of the actuating part is positioned below the upper surface; A control rod guide thimble fixing method, comprising:

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