Nuclear fuel mechanism and method for assembling same

Abstract

The invention discloses a nuclear fuel mechanism and an assembling method thereof, the nuclear fuel mechanism comprises a fuel rod lower end plug, a lower pipe seat assembly and an adjusting assembly, and the nuclear fuel mechanism can reduce flow-induced vibration of the fuel rod lower end plug in the horizontal direction. The connecting piece can be driven to move through the adjusting piece, so that the foreign matter preventing plate horizontally moves relative to the seat body, and at the moment, the central axis of the restraining through hole of the foreign matter preventing plate and the central axis of the restraining counter bore of the seat body are staggered, so that the limiting part of the fuel rod lower end plug is limited below the foreign matter preventing plate; the limiting part of the lower end plug of the fuel rod is limited between the foreign matter prevention plate and the seat body, so that the axial movement of the fuel rod is limited, and when the clamping force of the positioning grillwork is lost, the fuel rod is prevented from axially moving under the action of hydraulic lifting force or when the fuel assembly bears axial impact load; aggravation of fretting abrasion of the grillwork and the fuel rod is avoided, and failure of the fuel rod caused by the fact that the fuel rod falls and impacts the lower pipe base is avoided.

Description

Technical Field

[0001] The invention relates to the field of reactor nuclear fuel, and in particular to a nuclear fuel mechanism and an assembly method thereof. Background Art

[0002] A nuclear fuel assembly usually includes a number of fuel rods, a number of guide tubes and spacer grids, and an upper tube base assembly and a lower tube base assembly. In the fuel assembly, the fuel rod bundle is axially positioned between the upper tube base assembly and the lower tube base assembly by clamping the multi-layer spacer grids. The reactor coolant enters the fuel rod bundle inside the fuel assembly from the lower tube base assembly, flows out of the fuel assembly through the upper tube base assembly, and takes away the heat generated by the nuclear reaction of the fuel rod bundle.

[0003] In the existing fuel rod bundle constraint scheme, when the clamping force of the spacer grid is lost, the fuel rods may move axially under the action of hydraulic lifting force or when the fuel assembly is subjected to axial impact load, which aggravates the micro-motion wear between the fuel rods and the spacer grid. In addition, the fuel rods may fail when they fall and impact the lower tube socket after axial movement. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a nuclear fuel structure and an assembly method thereof.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a nuclear fuel mechanism, which includes a fuel rod lower end plug, a lower tube seat assembly and an adjustment assembly;

[0006] The fuel rod lower end plug comprises a positioning portion and a limiting portion fixedly connected to the positioning portion;

[0007] The lower tube seat assembly comprises a foreign body protection plate and a seat body, the foreign body protection plate is provided with a restraining through hole and a through hole, the restraining through hole is for the lower end plug of the fuel rod to pass through;

[0008] The upper surface of the seat body is provided with a restraining countersunk hole corresponding to the restraining through hole and an action groove corresponding to the through hole, and the restraining countersunk hole is used to accommodate the limiting part;

[0009] The side wall of the seat body is provided with a connecting hole connected with the action groove, the adjusting assembly comprises a connecting piece and an adjusting piece, the connecting piece is installed in the through hole and its end is located in the action groove, the adjusting piece is installed in the connecting hole and the connecting piece is in transmission connection with the adjusting piece;

[0010] The adjusting member can drive the connecting member to move, so that the foreign matter protection plate moves horizontally relative to the seat body, so that the limiting portion is limited below the foreign matter protection plate.

[0011] In some embodiments, the adjusting member is provided with a first threaded portion, and the end of the connecting member is provided with a second threaded portion matching the first threaded portion.

[0012] In some embodiments, a matching groove is also provided on the adjusting member.

[0013] In some embodiments, the nuclear fuel mechanism further comprises an anti-rotation component, the anti-rotation component is provided with a protrusion matching the matching groove, and a receiving groove is provided on a side of the anti-rotation component facing away from the protrusion.

[0014] In some embodiments, a side wall of the seat body is further provided with an installation groove for installing the anti-rotation component, and the installation groove is arranged corresponding to the connecting hole.

[0015] In some embodiments, the nuclear fuel mechanism further includes a fuel assembly guide tube, the anti-foreign matter plate is provided with a first assembly hole for the fuel assembly guide tube to pass through, and the base body is provided with a second assembly hole corresponding to the first assembly hole.

[0016] In some embodiments, the through hole is arranged perpendicular to the connecting hole.

[0017] In some embodiments, the connecting member is connected to the foreign object protection plate by welding.

[0018] In this embodiment, a method for assembling a nuclear fuel mechanism is also constructed, which is based on the nuclear fuel mechanism and includes the steps of:

[0019] S1. Install the adjusting member in the connecting hole of the seat body, install the connecting member in the through hole of the anti-foreign matter plate, and after the first threaded portion of the adjusting member and the second threaded portion of the connecting member are matched and connected in the action groove of the seat body, weld the connecting member to the anti-foreign matter plate;

[0020] S2. Use the adjusting member to adjust the position of the anti-foreign matter plate, and align the restraining through hole on the anti-foreign matter plate with the restraining countersunk hole on the seat body;

[0021] S3, passing the fuel rod lower end plug through the constraint through hole, and seating the limiting portion of the fuel rod lower end plug in the constraint counterbore;

[0022] S4. Rotate the adjusting member to make the foreign matter protection plate horizontally displace relative to the seat body, so that the limiting portion of the fuel rod lower end plug is restricted below the foreign matter protection plate.

[0023] In some embodiments, the steps include:

[0024] S5, installing the anti-rotation member into the installation groove, so that the protrusion of the anti-rotation member is matched and connected with the matching groove of the adjusting member;

[0025] S6. Use fasteners to fix the fuel assembly guide tube and the seat body.

[0026] The implementation of the present invention has the following beneficial effects: the fuel rod lower end plug can pass through the constraint through hole of the anti-foreign matter plate, and then the limiting part of the fuel rod lower end plug is located in the constraint counterbore of the seat body, and the radial wall of the constraint counterbore contacts the limiting part, thereby providing radial constraint for the fuel rod lower end plug, reducing the flow-induced vibration of the fuel rod lower end plug in the horizontal direction. The adjusting member can drive the connecting member to move, so that the anti-foreign matter plate moves horizontally relative to the seat body, at this time, the central axis of the constraint through hole of the anti-foreign matter plate is misaligned with the central axis of the constraint counterbore of the seat body, so that the limiting part of the fuel rod lower end plug is limited below the anti-foreign matter plate, and the limiting part of the fuel rod lower end plug is limited between the anti-foreign matter plate and the seat body, thereby limiting the axial movement of the fuel rod, and when the clamping force of the positioning grid is lost, it is ensured that the fuel rod will not move axially under the action of the hydraulic lifting force or when the fuel assembly is subjected to the axial impact load, thereby avoiding the aggravation of the grid and the fuel rod micro-motion abrasion and avoiding the fuel rod from falling and hitting the lower tube seat to cause the fuel rod failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work. In the drawings:

[0028] Figure 1 is a partial structural schematic diagram of a nuclear fuel mechanism in some embodiments of the present invention;

[0029] Figure 2 is a schematic diagram of the installation structure of the nuclear fuel mechanism in some embodiments of the present invention;

[0030] Figure 3 is a schematic structural diagram of a lower tube base assembly in some embodiments of the present invention;

[0031] Figure 4 is a schematic structural diagram of a seat body in some embodiments of the present invention;

[0032] Figure 5 yes Figure 4 An enlarged schematic diagram of point A;

[0033] Figure 6 is a schematic structural diagram of a foreign body protection plate in some embodiments of the present invention;

[0034] Figure 7 is a schematic diagram of the structure of the adjusting member in some embodiments of the present invention;

[0035] Figure 8 is a schematic diagram of the structure of the connecting member in some embodiments of the present invention;

[0036] Fig. 9 is a schematic structural diagram of an anti-rotation component in some embodiments of the present invention;

[0037] Fig.10 Schematic diagram of the structure of the lower end plug of the fuel rod in some embodiments of the present invention. DETAILED DESCRIPTION

[0038] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings, are constructed and operated in a specific direction, and are only for the convenience of describing the present technical solution, rather than indicating that the device or element referred to must have a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0039] It should also be noted that, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or there may be one or more intermediate elements. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", etc. can explicitly or implicitly include one or more of the features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0040] See also Figures 1 to 10 , is a nuclear fuel mechanism in some embodiments of the present invention, which includes a fuel rod lower end plug 1, a lower tube seat assembly 2 and an adjustment assembly 3. Fig.10As shown, the fuel rod lower end plug 1 includes a positioning portion 11 and a limiting portion 12 fixedly connected to the positioning portion 11, the positioning portion 11 is cylindrical, the limiting portion 12 is conical, and the size of the upper end surface of the limiting portion 12 is larger than the size of the positioning portion 11. In some embodiments, the positioning portion 11 is specifically formed integrally with the limiting portion 12, so that the stability between the positioning portion 11 and the limiting portion 12 can be increased.

[0041] like Figures 1 to 6 As shown, Figure 1 It is a partial structural diagram of a nuclear fuel mechanism. The lower tube seat assembly 2 includes an anti-foreign matter plate 21 and a seat body 22. The anti-foreign matter plate 21 is provided with a constraint through hole 211 and a through hole 212. The constraint through hole 211 is provided for the lower end plug 1 of the fuel rod to pass through. The upper surface of the seat body 22 is provided with a constraint counterbore 221 corresponding to the constraint through hole 211 and an action groove 222 corresponding to the through hole 212. The constraint counterbore 221 is used to accommodate the limit portion 12. The side wall of the seat body 22 is provided with a connecting hole 223 connected to the action groove 222. The adjustment assembly 3 includes a connecting member 31 and an adjusting member 32. The connecting member 31 is installed in the through hole 212 and its end is located in the action groove 222. The adjusting member 32 is installed in the connecting hole 223 and the connecting member 31 is connected to the adjusting member 32 in a transmission manner. Among them, the adjusting member 32 can drive the connecting member 31 to move, so that the anti-foreign matter plate 21 moves horizontally relative to the seat body 22, so that the limit portion 12 is limited below the anti-foreign matter plate 21. When the limiting portion 12 is located in the restraining counterbore 221 , the positioning portion 11 is located in the restraining through hole 211 .

[0042] The restraining countersunk hole 221 matches the shape of the limiting portion 12. In this embodiment, the positioning portion 11 is cylindrical, the limiting portion 12 is conical, and the restraining countersunk hole 221 is a conical hole that matches the shape of the limiting portion 12. In addition, the through hole 212 and the connecting hole 223 are vertically arranged, and the connecting member 31 is welded to the anti-foreign matter plate 21. The seat body 22 is also provided with a plurality of water flow holes 226.

[0043] It can be understood that the fuel rod lower end plug 1 can pass through the constraint through hole 211 of the anti-foreign matter plate 21, and then the limiting portion 12 of the fuel rod lower end plug 1 is seated in the constraint counterbore 221 of the seat body 22, and the radial wall surface of the constraint counterbore 221 contacts the limiting portion 12, thereby providing radial constraint for the fuel rod lower end plug 1 and reducing the flow-induced vibration of the fuel rod lower end plug 1 in the horizontal direction. The adjusting member 32 can drive the connecting member 31 to move, so that the anti-foreign matter plate 21 can move horizontally relative to the seat body 22. At this time, the central axis of the restraining through hole 211 of the anti-foreign matter plate 21 is misaligned with the central axis of the restraining counterbore 221 of the seat body 22, so that the limiting portion 12 of the lower end plug 1 of the fuel rod is restricted below the anti-foreign matter plate 21. By restricting the limiting portion 12 of the lower end plug 1 of the fuel rod between the anti-foreign matter plate 21 and the seat body 22, the axial movement of the fuel rod is restricted. When the clamping force of the positioning grid is lost, it is ensured that the fuel rod will not move axially under the action of the hydraulic lifting force or when the fuel assembly is subjected to an axial impact load, thereby avoiding the aggravation of the micro-motion abrasion of the grid and the fuel rod and avoiding the failure of the fuel rod caused by the fuel rod falling and hitting the lower tube seat.

[0044] The adjusting member 32 may be an adjusting bolt, and the connecting member 31 may be a pin. The adjusting member 32 drives the connecting member 31 to move, thereby adjusting the horizontal position of the anti-foreign object plate 21 on the seat body 22, so that the central axis of the restraining through hole 211 on the anti-foreign object plate 21 and the central axis of the restraining countersunk hole 221 on the seat body 22 can be misaligned or aligned.

[0045] like Figure 7 and Figure 8 As shown, the adjusting member 32 is provided with a first threaded portion 321, and the end of the connecting member 31 is provided with a second threaded portion 311 matching the first threaded portion 321, so that the adjusting member 32 and the connecting member 31 form a threaded connection, so that the adjusting member 32 can drive the connecting member 31 to move. The adjusting member 32 is also provided with a matching groove 322, which is specifically a straight groove, and an external tool can be inserted to realize the rotation of the adjusting member 32 in the seat body 22.

[0046] like Figure 1 , Figure 2 and Fig. 9 As shown, the nuclear fuel mechanism also includes an anti-rotation member 4, on which a protrusion 41 matching the matching groove 322 is provided, and a receiving groove 42 is provided on the side of the anti-rotation member 4 facing away from the protrusion 41. The protrusion 41 is specifically in the shape of a straight line, matching the shape of the matching groove 322, and the anti-rotation member 4 is used to prevent the adjustment member 32 from rotating and causing the anti-foreign matter plate 21 to shift in position. The receiving groove 42 is specifically a straight line groove, which can be used to insert an external tool to realize the assembly of the anti-rotation member 4. Figure 5As shown, the side wall of the seat body 22 is also provided with a mounting groove 224 for installing the anti-rotation component 4. The mounting groove 224 is arranged corresponding to the connecting hole 223. The size of the mounting groove 224 is larger than the size of the connecting hole 223. The mounting groove 224 is specifically an arc groove opened in the circumferential direction of the connecting hole 223. When the anti-rotation component 4 is matched with the adjusting component 32, the thin wall of the anti-rotation component 4 can be expanded into the mounting groove 224, and the anti-rotation component 4 is fixed in the mounting groove 224 to realize the anti-rotation function.

[0047] like Figure 1 , Figure 4 and Figure 6 As shown, the nuclear fuel mechanism further includes a fuel assembly guide tube 5, a first assembly hole 213 for the fuel assembly guide tube 5 to pass through is formed on the foreign matter prevention plate 21, and a second assembly hole 225 corresponding to the first assembly hole 213 is formed on the seat body 22. The first assembly hole 213 longitudinally penetrates the foreign matter prevention plate 21, and the second assembly hole 225 longitudinally penetrates the seat body 22, and the first assembly hole 213 and the second assembly hole 225 are used together for assembling the fuel assembly guide tube 5.

[0048] In this embodiment, a method for assembling a nuclear fuel mechanism is also constructed, which includes the steps of:

[0049] S1, install the adjusting member 32 in the connecting hole 223 of the seat body 22, install the connecting member 31 in the through hole 212 of the anti-foreign matter plate 21, and after the first threaded portion 321 of the adjusting member 32 is matched and connected with the second threaded portion 311 of the connecting member 31, weld the connecting member 31 to the anti-foreign matter plate 21;

[0050] S2, using the adjusting member 32 to adjust the position of the anti-foreign matter plate 21, and aligning the restraining through hole 211 on the anti-foreign matter plate 21 with the restraining counterbore 221 on the seat body 22;

[0051] S3, passing the fuel rod lower end plug 1 through the constraint through hole 211, and seating the limiting portion 12 of the fuel rod lower end plug 1 in the constraint counterbore 221;

[0052] S4. Rotate the adjusting member 32 to make the foreign matter protection plate 21 horizontally displace relative to the seat body 22 so that the limiting portion 12 of the fuel rod lower end plug 1 is restricted below the foreign matter protection plate 21 .

[0053] Specifically, in step S1, the anti-foreign matter plate 21 is placed above the seat 22 and the through hole 212 of the anti-foreign matter plate 21 and the connecting hole 223 of the seat 22 are located on the same side, the adjusting member 32 is installed in the connecting hole 223 and rotated to a proper position, and then the connecting member 31 is inserted into the action groove 222 through the through hole 212, and the first threaded portion 321 of the adjusting member 32 is matched and connected with the second threaded portion 311 of the connecting member 31, and then the upper part of the connecting member 31 is welded and fixed to the anti-foreign matter plate 21. The principles of steps S2 to S4 are discussed in detail above and will not be repeated here.

[0054] The assembly method of the nuclear fuel mechanism also includes the steps of:

[0055] S5, installing the anti-rotation member 4 into the installation groove 224, so that the protrusion 41 of the anti-rotation member 4 is matched and connected with the matching groove 322 of the adjustment member 32;

[0056] S6. Use fasteners 6 to fix the fuel assembly guide tube 5 and the seat body 22. The fasteners 6 may be bolts.

[0057] When the fuel rod is to be removed, the anti-rotation member 4 may be removed first, and then the position of the foreign matter prevention plate 21 may be adjusted by rotating the adjustment member 32 to achieve the removal operation.

[0058] In summary, the beneficial effects of the nuclear fuel structure and the assembly method thereof are as follows:

[0059] 1. Provide axial constraint for the fuel rod lower end plug 1, maintain the axial position of the fuel rod bundle in the fuel assembly, prevent the fuel rod from axially moving under the action of hydraulic lifting force when the clamping force of the spacer grid is lost or when the fuel assembly is subjected to axial impact load, avoid aggravating the micro-motion abrasion between the fuel rod and the spacer grid, and avoid the fuel rod from falling and impacting the lower tube seat after axial movement, causing the fuel rod to fail;

[0060] 2. The present invention does not introduce a new constraint structure outside the lower tube base component, has no effect on the coolant flow path of the fuel assembly, can maintain the pressure drop performance of the fuel assembly, and does not have the risk of damage to the fuel assembly caused by damage or loosening of the newly added constraint structure to form foreign matter under coolant flushing;

[0061] 3. Provide radial constraints for the fuel rod lower end plug 1 to reduce flow-induced vibration of the fuel rod lower end plug 1;

[0062] 4. The axial constraint provided by the present invention for the fuel rod is easy to adjust. Without disassembling the lower tube seat assembly 2, the axial constraint on the fuel rod can be adjusted by rotating the adjusting member 32, which facilitates the operation of pulling out and replacing rods inside and outside the stack.

[0063] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the scope covered by the claims of the present invention.

Claims

1. A nuclear fuel mechanism, characterized in that: It comprises a fuel rod lower end plug (1), a lower tube base assembly (2) and an adjustment assembly (3); The fuel rod lower end plug (1) comprises a positioning portion (11) and a limiting portion (12) fixedly connected to the positioning portion (11); The lower tube base assembly (2) comprises a foreign matter prevention plate (21) and a base body (22); the foreign matter prevention plate (21) is provided with a restraining through hole (211) and a through hole (212); the restraining through hole (211) is for the fuel rod lower end plug (1) to pass through; The upper surface of the seat body (22) is provided with a restraining counterbore (221) corresponding to the restraining through hole (211) and an action groove (222) corresponding to the through hole (212), wherein the restraining counterbore (221) is used to accommodate the limiting portion (12); The side wall of the seat body (22) is provided with a connecting hole (223) connected with the action groove (222); the adjusting assembly (3) comprises a connecting piece (31) and an adjusting piece (32); the connecting piece (31) is installed in the through hole (212) and its end is located in the action groove (222); the adjusting piece (32) is installed in the connecting hole (223) and the connecting piece (31) is transmission-connected with the adjusting piece (32); The adjusting member (32) can drive the connecting member (31) to move, so that the foreign matter protection plate (21) moves horizontally relative to the seat body (22), so that the limiting portion (12) is limited below the foreign matter protection plate (21).

2. The nuclear fuel mechanism according to claim 1, characterized in that: The adjusting member (32) is provided with a first threaded portion (321), and the end of the connecting member (31) is provided with a second threaded portion (311) matching the first threaded portion (321).

3. The nuclear fuel mechanism according to claim 1, characterized in that: The adjusting member (32) is also provided with a matching groove (322).

4. The nuclear fuel mechanism according to claim 3, characterized in that: The nuclear fuel mechanism also includes an anti-rotation component (4), the anti-rotation component (4) is provided with a protrusion (41) matching the matching groove (322), and the anti-rotation component (4) is provided with a receiving groove (42) on a side facing away from the protrusion (41).

5. The nuclear fuel mechanism according to claim 4, characterized in that: The side wall of the seat body (22) is also provided with an installation groove (224) for installing the anti-rotation component (4), and the installation groove (224) is arranged corresponding to the communication hole (223).

6. The nuclear fuel mechanism according to claim 1, characterized in that: The nuclear fuel mechanism also includes a fuel assembly guide tube (5), the foreign matter prevention plate (21) is provided with a first assembly hole (213) for the fuel assembly guide tube (5) to pass through, and the seat body (22) is provided with a second assembly hole (225) corresponding to the first assembly hole (213).

7. The nuclear fuel mechanism according to claim 1, characterized in that: The through hole (212) and the connecting hole (223) are arranged perpendicularly.

8. The nuclear fuel mechanism according to claim 1, characterized in that: The connecting piece (31) is connected to the foreign matter protection plate (21) by welding.

9. A method for assembling a nuclear fuel mechanism, based on the nuclear fuel mechanism according to any one of claims 1 to 8, characterized in that: Includes steps: S1, installing the adjusting member (32) in the connecting hole (223) of the seat body (22), installing the connecting member (31) in the through hole (212) of the anti-foreign matter plate (21), and after the first threaded portion (321) of the adjusting member (32) and the second threaded portion (311) of the connecting member (31) are matched and connected in the action groove (222) of the seat body (22), welding the connecting member (31) to the anti-foreign matter plate (21); S2, using the adjusting member (32) to adjust the position of the foreign matter protection plate (21), and aligning the restraining through hole (211) on the foreign matter protection plate (21) with the restraining counterbore (221) on the seat body (22); S3, passing the fuel rod lower end plug (1) through the restraining through hole (211), and seating the limiting portion (12) of the fuel rod lower end plug (1) in the restraining counterbore (221); S4. Rotate the adjusting member (32) to cause the foreign matter prevention plate (21) to be horizontally displaced relative to the seat body (22), so that the limiting portion (12) of the fuel rod lower end plug (1) is restricted below the foreign matter prevention plate (21).

10. The method for assembling a nuclear fuel mechanism according to claim 9, characterized in that: Also includes the steps: S5, installing the anti-rotation component (4) into the installation groove (224), so that the protruding portion (41) of the anti-rotation component (4) is matched and connected with the matching groove (322) of the adjusting component (32); S6. Using a fastener (6) to fix the fuel assembly guide tube (5) and the seat body (22) together.

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