Patent Number: 046845020
Section: summary

CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending applications dealing with related subject matter and assigned to the assignee of the present invention: 1. "Reconstitutable Nuclear Reactor Fuel Assembly With Unitary Removable Top Nozzle Subassembly" by John M. Shallenberger, assigned U.S. Ser. No. 673,681 and filed Nov. 20, 1984, a continuation-in-part of copending U.S. patent application Ser. No. 457,790 filed Jan. 13, 1983. 2. "Improved Removable Top Nozzle Subassembly For A Reconstitutable Nuclear Fuel Assembly" by John F. Wilson et al, assigned U.S. Ser. No. 701,049 and filed Feb. 12, 1985. 3. "Integral Reusable Locking Arrangement For A Removable Top Nozzle Subassembly Of A Reconstitutable Nuclear Fuel Assembly" by Robert K. Gjertsen et al, assigned U.S. Ser. No. 857,675 and filed Apr. 30, 1986. 4. "Hold-Down Device Of Fuel Assembly Top Nozzle Employing Leaf Springs" by Robert K. Gjertsen et al, assigned U.S. Ser. No. 729,607 and filed May 2, 1985. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to reconstitutable fuel assemblies for nuclear reactors and, more particularly, is concerned with a top nozzle incorporating an alignment sleeve capture arrangement which eliminates all loose components during top nozzle removal and replacement in carrying out reconstitution of the fuel assembly. 2. Description of the Prior Art Conventional designs of fuel assemblies include a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the control rod guide thimbles which extend above and below the opposite ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in openings provided in the top nozzle. Conventional fuel assemblies also have employed a fuel assembly hold-down device to prevent the force of the upward coolant flow from lifting a fuel assembly into damaging contact with the upper core support plate of the reactor, while allowing for changes in fuel assembly length due to core induced thermal expansion and the like. Such hold-down devices have included the use of coil springs surrounding the guide thimbles, such as seen in U.S. Pat. Nos. 3,770,583 and 3,814,667 to Klumb et al and 4,269,661 to Kmonk et al, and in the first three patent applications cross-referenced above. Also, as exemplified by the fourth patent application cross-referenced above, recently it has been proposed that leaf springs be used in place of the coil springs. Due to occasional failure of some fuel rods during normal reactor operation and in view of the high costs associated with replacing fuel assemblies containing failed fuel rods, the trend is currently toward making fuel assemblies reconstitutable in order to minimize operating and maintenance expenses. Conventional reconstitutable fuel assemblies incorporate design features arranged to permit the removal and replacement of individual failed fuel rods. Reconstitution has been made possible by providing a fuel assembly with a removable top nozzle. The top nozzle is mechanically fastened in some instances, such as illustrated in the above cross-referenced applications, by a threaded arrangement to the upper end of each control rod guide thimble, and the top nozzle can be removed remotely from an irradiated fuel assembly while it is still submerged in a neutron-absorbing liquid. Once removal and replacement of the failed fuel rods have been carried out on the irradiated fuel assembly submerged at a work station and after the top nozzle has been remounted on the guide thimbles of the fuel assembly, the reconstituted assembly can then be reinserted into the reactor core and used until the end of its usefuel life. While the proposed removable top nozzle designs of the above cross-referenced patent applications have proved to be highly satisfactory ways to facilitate reconstitution of fuel assemblies, the top nozzle arrangement of the fourth cross-referenced application does require handling of loose parts for disassembly and replacement of the top nozzle, namely, the enlarged nuts threaded on the upper end portions of the guide thimbles which upper end portions can take the form of alignment sleeves threaded on the guide thimbles. Consequently, a need exists for a different approach to top nozzle attachment, one with the objective of removing and reattaching the top nozzle without creating any loose parts and yet maintains all of the desirable features of both the leaf spring and coil spring hold-down device designs of the above cross-referenced patent applications. SUMMARY OF THE INVENTION The present invention provides an alignment sleeve capture arrangement for the removable top nozzle designed to satisfy the aforementioned needs. While not so limited, the present invention is particularly suitable for incorporation in a top nozzle design in which the upper hold-down plate and lower adapter plate have no slidable interconnection, such as in the fourth cross-referenced application. In the absence of such interconnection, the upper and lower plates come apart upon disconnection and removal of the top nozzle from the guide thimbles of the fuel assembly. And, when alignment sleeves are used to threadably attach the top nozzle to the guide thimbles, they become separable from both upper and lower plates upon detachment of the top nozzle. The present invention eliminates any loose parts during top nozzle removal and replacement by providing an arrangement which captures the alignment sleeves within the upper hold-down plate such that they are removed with the upper plate. Accordingly, the present invention is set forth in a reconstitutable fuel assembly having at least one control rod guide thimble and a top nozzle, with the guide thimble including an upper end portion and the top nozzle including an upper hold-down plate having at least one passageway, at least one tubular alignment sleeve slidably extending through the passageway and being attachable to and detachable from the guide thimble upper end portion and means supported on the guide thimble upper end portion which, in turn, yieldably mounts the upper hold-down plate for relative movement along the alignment sleeve. The present invention is an alignment sleeve capture arrangement comprising: (a) means defining an annular cavity through the upper hold-down plate and in communication with the passageway therein, the cavity surrounding an upper portion of the alignment sleeve which extends axially through the cavity and the passageway; (b) upper means on the upper hold-down plate surrounding the alignment sleeve upper portion and defining an upper limit of the cavity; (c) lower means on the upper hold-down plate surrounding the alignment sleeve upper portion, spaced below the upper limit defining means, and defining a lower limit of the cavity; and (d) enlarged means attached on the alignment sleeve upper portion and having an outside diameter greater than respective inside diameters of the upper and lower cavity limit defining means but less than the inside diameter of the cavity such that the enlarged means can slide within the cavity with the alignment sleeve between the upper and lower limits thereof as the upper hold-down plate moves along the alignment sleeve and will retain the alignment sleeve slidably attached to the hold-down plate when the sleeve is detached from the guide thimble upper end portion. More particularly, the upper cavity limit defining means is a shoulder defined in the upper hold-down plate which forms a transition between the larger inside diameter of the cavity and a smaller inside diameter of the passageway. Also, the lower cavity limit defining means is a retainer attached to the upper hold-down plate and surrounding the alignment sleeve upper portion, with the retainer having a neck portion with a central hole through which the alignment sleeve extends and defining the inside diameter of the limit defining means which is less than the outside diameter of the enlarged means. Additionally, the retainer has a hollow body portion with one end attached to the hold-down plate and an opposite end integrally connected with the neck portion. The retainer body portion defines a portion of the cavity. Still further, the enlarged means is a bearing ring encircling and attached to the alignment sleeve upper portion. The bearing ring has an internal groove into which a section of the alignment sleeve upper portion is bulge fitted for rigidly connecting the ring to the alignment sleeve. The upper portion of the alignment sleeve has a reduced diametric size compared to a lower portion of the alignment sleeve which defines a radially extending ledge at the transition between the alignment sleeve portions on which the bearing ring is seated. These and other advantages and attainments 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.