Patent Number: 050842307
Section: summary

CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending application dealing with related subject matter and assigned to the assignee of the present invention: "Improved Hand Held Tool For Removing And Replacing A Top Nozzle Locking Tube" by John. D. Wood et al, assigned U.S. Ser. No. 07/562,286 and filed Aug. 3, 1990. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with an improved hand held tool for removing and replacing a removable top nozzle of a reconstitutable fuel assembly. 2. Description of the Prior Art In most nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a plurality of fuel rods and control rod guide thimbles held in an organized array by grids spaced along the fuel assembly length and attached to the control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend slightly above and below the ends of the fuel rods. At the top of the fuel assembly, the guide thimbles are attached in passageways provided in the adapter plate of the top nozzle. The guide thimbles may each include an upper sleeve for attachment to the top nozzle. During operation of such fuel assembly in a nuclear reactor, a few of the fuel rods may occasionally develop cracks along their lengths, thus establishing the possibility that fission products having radioactive characteristics may seep or otherwise pass into the primary coolant of the reactor. Since the fuel rods are supported by the grids in a spaced array with the guide thimbles between the top and bottom nozzles of the fuel assembly, it is difficult to detect and remove the failed fuel rods. Until recently, to gain access to these rods it was necessary to remove the affected fuel assembly from the nuclear reactor core and then remove the bottom nozzle after overturning the assembly. This is time consuming and requires large equipment for overturning. In view of the high costs associated with replacing fuel assemblies, reconstitutable fuel assemblies were developed to minimize operating and maintenance expenses. The general approach to making a fuel assembly reconstitutable is to provide it with a removable top nozzle. One reconstitutable fuel assembly construction is illustrated and described in U.S. Pat. Nos. 4,631,168 to Shallenberger et al, which is assigned to the assignee of the present invention. It incorporates an attaching structure for removably mounting the top nozzle on the upper ends of the control rod guide thimbles. The attaching structure includes a plurality of outer sockets defined in the adapter plate of the top nozzle, a plurality of inner sockets each formed on the upper end of one of the guide thimbles, and a plurality of removable locking tubes inserted in the inner sockets to maintain them in locking engagement with the outer sockets. Each outer socket is in the form of a passageway through the adapter plate which has an annular groove. Each inner socket is in the form of a hollow upper end portion of the guide thimble having an annular bulge which seats in the annular groove when the guide thimble end portion is inserted in the adapter plate passageway. A plurality of elongated axial slots are provided in the guide thimble upper end portion to permit inward elastic collapse of the slotted portion so as to allow the larger bulge diameter to be inserted within and removed from the annular circumferential groove in the passageway of the adapter plate. In such manner, the inner socket of the guide thimble is inserted into and withdrawn from locking engagement with the outer socket. The locking tube is inserted from above the top nozzle into a locking position in the hollow upper end portion of the guide thimble forming the inner socket. When inserted in its locking position, the locking tube retains the bulge of the inner socket in its expanded locking engagement with the annular groove and prevents the inner socket from being moved to a compressed releasing position in which it could be withdrawn from the outer socket. In such manner, the locking tubes maintain the inner sockets in locking engagement with the outer sockets, and thereby the attachment of the top nozzle on the upper ends of the guide thimbles. Furthermore, to prevent inadvertent escape due to vibration forces and the like, heretofore the locking tubes have been secured in their locking positions. In the one construction of the locking tubes disclosed in above-cited patent, after insertion of the locking tubes into their locking positions within the inner sockets of the hollow upper end portions of the guide thimbles, a pair of bulges are formed in the upper portion of each locking tube. These bulges fit into the circumferential bulge in the upper end portion of the guide thimble and provide an interference fit therewith. In another construction of the locking tubes disclosed in U.S. Pat. No. 4,699,758 to Shallenberger et al, which is also assigned to the assignee of the present invention, several small dimples are preformed on the exterior surface of the upper end portion of the locking tube circumferentially spaced from one another and projecting from the locking tube exterior surface. The use of the preformed dimples eliminates the necessity to form bulges in the locking tube after insertion into the locking position. Also the preformed dimples allow the locking tube to be reused, whereas the bulged locking tubes were discarded after each use. The reconstitutable fuel assembly construction briefly described above has proven to be an improvement by which domestic and foreign utilities can minimize both operating and maintenance expenses. A fixture developed for removing and replacing the top nozzle of the reconstitutable fuel assembly is disclosed in U.S. Pat. No. 4,664,875 to Shallenberger et al, also assigned to the assignee of the present invention. One major problem with the top nozzle removal and replacement fixture of the cited patent is the considerable weight of the fixture which makes it mandatory to employ an overhead crane and blocking device in order to maneuver the fixture to align and insert the lower ends of the alignments rods of the fixture through the guide thimble holes in the top nozzle and into the guide thimbles. Consequently, a need still remains for an alternative design of a tool to use to effectively and efficiently carry out removal and replacement of the top nozzle. SUMMARY OF THE INVENTION The present invention provides an improved hand held tool designed to satisfy the aforementioned needs. The tool is simple, lightweight, easy to use, and effective. The tool is capable of being manually held and actuated by a user and of precise operation in removing and replacing the top nozzle from and back on the reconstitutable fuel assembly. The design of the hand held tool permits a construction that weighs approximately 45 pounds, as compared to the prior art fixture which weights approximately 200 pounds. The resulting light weight of the tool of the present invention makes it readily hand operable, permitting elimination of the necessity for overhead cranes and blocking devices required with the prior art fixture. Removal and reinstallation of top nozzles can be accomplished faster. Accordingly, the present invention sets forth an improved hand held tool for removing a top nozzle from guide thimbles of a fuel assembly. The tool comprises: (a) a handling assembly including an upper handle and an elongated handle pole having spaced upper and lower ends, the handle pole being attached at the upper end to the upper handle and extending downwardly therefrom; (b) a lower tool head including an anchor assembly and a lift assembly, the anchor assembly being the lower end of the handle pole, matable with the guide thimble and actuatable between disengaged and engaged conditions with the guide thimble; (c) means for coupling the anchor assembly to the lower end of the handle pole and for coupling the lift assembly to the lower end of the handle pole, the coupling means being operable for connecting the lift assembly and the handle pole in a first connected relation in which the lift assembly is rotatably movable, by rotation of the handle pole, between unlocked and locked positions relative to the top nozzle and unlatched and latched positions relative to the anchor assembly or in a second connected relation in which the lift assembly is axially movable, by rotation of the handle pole, along the handle pole relative to the anchor assembly to cause lifting and detaching of the top nozzle from the guide thimble once the lift assembly is disposed in the latched position relative to the anchor assembly and in the locked position relative to the top nozzle and the anchor assembly is disposed in the engaged position with the guide thimble; and (d) means connected to the anchor assembly for actuating the anchor assembly between the disengaged and engaged conditions with the guide thimble, the actuating means being mounted on the handle pole and extending from the upper handle to the lower tool head. More particularly, the anchor assembly includes an elongated probe member insertable into the guide thimble, the probe member having an expansion sleeve movable between expanded and contracted positions for engaging and disengaging the guide thimble. Also, the anchor assembly includes a fluid-driven actuator drivingly coupled to the probe member for actuating the expansion sleeve between the expanded and contracted positions. The actuating means includes a pressurized fluid supply mounted on the handle pole adjacent the handle of the handling assembly, and a pressurized fluid supply line extending from the supply to the probe member. Further, the lift assembly includes a spider yoke having an upper central portion and a plurality of legs projecting radially outwardly and then downwardly from the central portion and terminating in abutments that underlie a lip on the top nozzle when the lift assembly is rotated to the locked position with the top nozzle and clear the lip on the top nozzle when the lift assembly is rotated to the unlocked position therewith. The central portion of the lift assembly spider yoke includes a central hub defining an internally threaded hole, and a central sleeve extending upwardly from the central hub and slidably fitted to the lower end of the handle pole. The coupling means includes a screw shaft member mounted to the lower end of the handle pole and threaded into the threaded hole of the central hub of the lift assembly spider yoke, a pin attached to the lower end of the handle pole, means defined in the central sleeve of the lift assembly spider yoke for receiving the pin in a seated relationship, and means engaging the pin and the central sleeve for normally imposing a biasing force on the pin that moves the pin toward an unseated relationship with the central sleeve in which the lift assembly assumes the second connected relation with the handle pole such that rotation of the pole causes threading rotation of the screw shaft relative to the central hub and thereby axial movement of the lift assembly relative to the handle pole and anchor assembly. The pin is capable of being moved into the seated relationship with the central sleeve, by imposing a downward force on the handle pole sufficient to overcome the biasing force toward the lift assembly, in which the lift assembly assumes the first connected relation with the handle pole such that rotation of the pole causes rotation of the lift assembly relative to the anchor assembly between the locked and unlocked positions relative to the top nozzle. The coupling means also includes a universal joint coupling the anchor assembly to the lower end of the handle pole to permit unidirectional pivotal movement of the anchor assembly relative to the guide thimble for aligning the anchor assembly therewith and mating with the guide thimble. These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.