Patent Number: 050376039
Section: description

DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown an elevational view of a prior art reconstitutable nuclear reactor fuel assembly, represented in vertically foreshortened form and being generally designated by the numeral 10. Basically, the fuel assembly 10 includes a lower end structure or bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 14 which project upwardly from the bottom nozzle 12. The assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated fuel rods 18 transversely spaced and supported by the grids 16. Also, the assembly 10 has an instrumentation tube 20 located in the center thereof and an upper end structure or top nozzle 22 removably attached to the upper ends of the guide thimbles 14, in a manner fully described below, to form an integral assembly capable of being handled without damaging the assembly parts. As mentioned above, the fuel rods 18 in the array thereof in the assembly 10 are held in spaced relationship with one another by the grids 16 spaced along the fuel assembly length. Each fuel rod 18 includes nuclear fuel pellets 24 and the opposite ends of the rod are closed by upper and lower end plugs 26,28 to hermetically seal the rod. Commonly, a plenum spring 30 is disposed between the upper end plug 26 and the pellets 24 to maintain the pellets in a tight, stacked relationship within the rod 18. The fuel pellets 24 composed of fissile material are responsible for creating the reactive power of the nuclear reactor. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the fuel assemblies of the core in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods 32 are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. Specifically, the top nozzle 22 includes a rod cluster control mechanism 34 having an internally threaded cylinder member 36 with a plurality of radially extending flukes or arms 38. Each arm 38 is interconnected to a control rod 32 such that the control mechanism 34 is operable to move the control rods 32 vertically in the guide thimbles 14 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. Prior Art Top Nozzle Attaching Structure As illustrated in FIGS. 1, 2 and 7, the top nozzle 22 has a lower adapter plate 40 with a plurality of control rod passageways 42 (only one being shown) formed through the adapter plate. The control rod guide thimbles 14 have their uppermost end portions 44 coaxially positioned within the passageways 42 in the adapter plate 40. For gaining access to the fuel rods 18, the adapter plate 40 of the top nozzle 22 is removably connected to the upper end portions 44 of the guide thimbles 14 by a prior art attaching structure, generally designated 46. The prior art attaching structure 46 is generally the same as described in above-cited U.S. Pat. No. 4,631,168, the disclosure of which is hereby incorporated by reference thereto. Thus, the attaching structure 46 will be described herein only to the extent necessary to facilitate a complete understanding of the improved tool 48 of the present invention, to be described later on in reference to FIGS. 8-18, which is employed in removing and replacing the top nozzle 22 of the fuel assembly 10. Referring to FIGS. 2-7, the top nozzle attaching structure 46 of the reconstitutable fuel assembly 10 includes a plurality of outer sockets 50 (only one being shown) defined in the top nozzle adapter plate 40 by the plurality of passageways 42 (also only one being shown) which each contains an annular circumferential groove 52 (only one being shown), a plurality of inner sockets 54 (only one being shown) defined on the upper end portions 44 of the guide thimbles 14, and a plurality of locking tubes 56 (only one being shown) inserted in the inner sockets 54 to maintain them in locking engagement with the outer sockets 50. Each inner socket 54 of the attaching structure 46 is defined by an annular circumferential bulge 58 on the hollow upper end portion 44 of one guide thimble 14 only a short distance below its upper edge. A plurality of elongated axial slots 60 are formed in the upper end portion 44 of each guide thimble 14 to permit inward elastic collapse of the slotted end portion to a compressed position so as to allow the circumferential bulge 58 thereon to be inserted within and removed from the annular groove 52 via the adapter plate passageway 42. The annular bulge 58 seats in the annular groove 52 when the guide thimble end portion 44 is inserted in the adapter plate passageway 42 and has assumed an expanded position. In such manner, the inner socket 54 of each guide thimble 14 is inserted into and withdrawn from locking engagement with one of the outer sockets 50 of the adapter plate 40. More particularly, the axially extending passageway 42 in the adapter plate 40 which defines the outer socket 50 is composed of an upper bore 62 and a lower bore 64. The lower bore 64 is of considerably greater axial length than the upper bore 62 and contains the annular groove 52 which is spaced a short distance below a ledge 66 formed at the intersection of the upper and lower bores 62,64. The lower bore 64 has a diameter which is greater than that of the upper bore 62, therefore, the ledge 66 faces in a downward direction. The primary purpose of the ledge 66 is to serve as a stop or an alignment guide for proper axial positioning of the upper end portion 44 in the passageway 42 when the inner socket 54 is inserted into the outer socket 50. As seen in FIG. 7, the upper edge of the guide thimble upper end portion 44 abuts the ledge 66. The locking tube 56 is inserted from above the top nozzle 22 into its respective locking position in the hollow upper end portion 44 of one guide thimble 14 forming one inner socket 54. When the locking tube 56 is inserted in its locking position, as seen in FIG. 7, it retains the bulge 58 of the inner socket 54 in the latter's expanded locking engagement with the annular groove 52 and prevents the inner socket 54 from being moved to its compressed releasing position in which it could be withdrawn from the outer socket 50. In such manner, each locking tube 56 maintains its respective one inner socket 54 in locking engagement with the outer socket 50 and thereby the attachment of the top nozzle 22 on the upper end portion 44 of each guide thimble 14. Additionally, securing means in the form of a slightly outwardly flared (for instance 1-2 degrees) upper peripheral marginal edge portion 68 and a plurality of small dimples 70 located along the exterior of the locking tube 56 are provided to secure the locking tube 56 at the locking position. Thus, when the locking tube 56 is inserted into the inner socket 54, a tight frictional fit is formed with the inner socket. Although the flared upper marginal edge portion 68 does not provide a positive securement, the dimples 70 do. The dimples 70 are preformed by any suitable method, such as by die forming or being coined, and so configured to have a generally pyramidal shape such that the metal forming the dimples substantially resists yielding and dimensional change regardless of the number of insertions and withdrawals of the locking tube 56 into and from the locking position. Also, when the locking tube 56 is inserted into the upper end portion 44 of the guide thimble 14, the dimples 70 are located at the elevation of the circumferential bulge 58 and are spaced in alignment circumferentially about the exterior of the locking tube so as to extend into the bulge 58. In such manner, the dimples 70 provide a positive interference fit with the guide thimble upper end portion 44 at the bulge 58 thereof which prevents inadvertent withdrawal of the locking tube 56 from the locking position. Improved Hand Held Tool of the Present Invention Referring to FIGS. 8-17, there is illustrated the improved tool 48 of the present invention for removing and replacing the locking tube 56 from a locking position in the upper end portion 44 of the guide thimble 14. In its basic components, the tool 48 includes an elongated hollow tubular assembly 72, an actuator assembly 74, a bail assembly 76, a force-imparting member 78, and a hand-operated actuating mechanism 80. The tubular assembly 72 of the tool 48 has upper and lower opposite end portions 72A, 72B. The bail assembly 76 of the tool 48 is fixedly attached to the upper end portion 72A of the tubular assembly 72, whereas the lower end portion 72B of the tubular assembly 72 is insertable in the locking tube 56. The bail assembly 76 includes a generally flat plate 82 fixed to the upper end portion 72A of the tubular assembly 72 and a U-shaped handle 84 connected to and extending upwardly from the plate 82 for a user to use in gripping the tool 48. The plate 82 serves as a member for receiving a force impacted thereon by the force-imparting member 78. The force-imparting member 78 is disposed about the upper end portion 72A of the tubular assembly 72 and is slidably movable therealong in a reciprocating manner for delivering any number of desired forceful impacts against the force-receiving plate 82 of the bail assembly 76. The force-imparting member 78 is a cylindrical body having an exterior knurled surface 78A for gripping by a user. More particularly, the tubular assembly 72 is composed of an upper elongated hollow tube 86, a lower guide member 88 and a plurality of lifting members 90. The lower guide member 88 and lifting members 90 are connected to and extend axially from a common tubular base portion 92. The tubular base portion 92 has a male end fitting 92A which is threadably connected to a female end fitting 86A in a lower end of the upper tube 86 of the tubular assembly 72. The lower guide member 88 is composed of a elongated hollow tubular element 94 having an open lower end 94A and a guide element 96 interfitting the open end 94A of the tubular element 94. The guide element 96 has a body portion projecting from the tubular element 94 which defines an upper cylindrical segment 96A and a lower conical nose 96B. The upper cylindrical segment 96A has a section 96C of reduced diameter which is inserted into and attached to the end 94A of the tubular element 94. Further, the end 94A of the tubular element 94 and the cylindrical segment 96A of the guide element body portion 96 have substantially the same outside diameter so as to provide a continuous smooth transition 98 from the tubular element end 94A to the guide element body portion 96. The conical nose 96B and the smooth transition 98 on the guide member 88 facilitates ease of alignment and insertion of the guide member 88 into the hollow locking tube 56 without catching on the upper edge 56A of the locking tube 56 at the transition 98 of the guide member 88. Also, the tubular element 94 at a region thereof spaced above its lower end 94A has a plurality of apertures 100 (best seen in FIGS. 16 and 18) defined at circumferentially spaced locations about the tubular element. The locking tube lifting members 90 extend within and in concentric relation with the hollow tubular element 94 of the guide member 88. Each lifting member 90 is composed of an elongated finger element 90A rigidly attached at its upper end to the tubular base portion 92 and having a tapered tip 90B at its lower end and a barb-shaped catch element 90C projecting radially outwardly from a central axis A (FIG. 8) of the tubular assembly 72 and tubular element 94 and aligned with the apertures 100 (FIGS. 16 and 18) in the tubular element 94. The finger elements 90A are normally disposed in a contracted condition, as seen in FIGS. 8-10 and 19, and are resiliently yieldable to deflect radially outwardly to an expanded condition, as seen in FIGS. 20 and 21 upon application of radially outwardly directed forces thereon. Upon removal of such forces, the finger elements 70A will return to the contracted condition. In the expanded condition of the finger elements 90A, the catch elements 90C defined on the respective finger elements 90A project from the tubular element 94 through the apertures 100 so as to underlie and engage a lower edge 56B of the locking tube 56, as seen in FIGS. 20, 21 and 23. On the other hand, in the contracted condition of the finger elements 90A, the catch elements 90C are retracted from the apertures 100 and disposed inside of the tubular element 94 so as to be disengaged from the lower edge 56B of locking tube 56, as seen in FIG. 19. The actuator assembly 74 of the tool 48 is mounted through the tubular assembly 72 for axial movement therealong and has upper and lower end portions 74A, 74B. The actuating mechanism 80 has a pivotal lever 102 pivotally mounted by a bracket 103 attached to the plate 82 of the bail assembly 76. The lever 102 is coupled to the upper end portion 74A of the actuator assembly 74. Pivoting of the lever 102 between its solid and dashed line positions, as seen in FIG. 8, causes axial movement of the actuator assembly through a stroke of a precise length downwardly and upwardly relative to the stationarily-held tubular assembly 72. More particularly, the actuator assembly 74 includes elongated upper and lower shaft members 104, 106 threadably connected together in a tandem arrangement. The upper shaft member 104 at the upper end portion 74A of the actuator assembly 74 is connected to the lever 102, whereas the lower shaft member 106 at the lower end portion 74B of the actuator assembly 74 extends between the lifting members 90 of the tubular assembly 72. The upper shaft member 104 is movably mounted within the upper hollow tube 86 of the tubular assembly 72 by annular bushings 105 attached in and spaced axial along the tube 86. The lower shaft member 106 has upper and lower tandemly-arranged shaft segments 106A, 106B. The upper shaft segment 106A is larger in outside diameter than the lower shaft segment 106B. Pivotal movement of the lever 102 from the solid to dashed line position of FIG. 8 pushes the actuator assembly 74 downwardly along the central axis A, inserting the upper shaft segment 106A between and removing the lower shaft segment 106B from between the lifting members 90. The larger diameter upper shaft segment 106A forces the lifting members 90 to deflect radially outward from the contracted condition of FIG. 19 to the expanded condition of FIG. 20 which extends the catch elements 90C through the apertures 100 into underlying relation and engagement with the lower edge 56B of the locking tube 56. On the other hand, pivotal movement of the lever 102 from the dashed to solid line position of FIG. 8 pulls the actuator assembly 74 upwardly along the central axis A, removing the upper shaft segment 106A from between and inserting the lower shaft segment 106B between the lifting members 90. The smaller diameter lower shaft segment 106B permits the lifting members 90 to deflect radially inward back to their contracted condition of FIG. 19, which retracts the catch elements 90C from the apertures 100 and out of engagement with the lower edge 56B of the locking tube 56. The actuator assembly 74 also includes a retractor member 108 attached to a lower end 106C of the lower shaft member 106. The retractor member 108 is a cylindrical body having a tapered recessed portion 108A for engaging the tapered tips 90B of the lifting members 90 when the actuator assembly 74 is moved in the upward direction. The inwardly and downwardly inclined configuration of the tapered recessed portion 108A of the retractor member 108 ensures that the lifting members 90 are forced to deflect from the expanded to contracted condition and their catch elements 90C are disengaged from the lower edge 56B of the locking tube 56. As seen in FIG. 21, with the lifting members 90 in their expanded condition, the removed locking tube 56 is captured on the outer tubular element 94 between the lifting member catch elements 90C and a downwardly-facing ledge 110 defined on the outer tubular element 94 by an enlarged tubular head 112 formed on the upper end of the tubular element. When the lifting members 90 are deflected back to their contracted condition, the locking tube 56 is released and can drop off the lower end portion 72B of the tubular assembly past the guide member 88. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.