Patent Number: 053612833
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is generally related to nuclear fuel assemblies and more particularly to a reusable locking arrangement for guide tubes and upper end fittings. 2. General Background In a nuclear reactor core, each fuel assembly is fitted with a number of guide tubes that are used to receive control rods. In the nuclear industry, the tubes that are used to receive control rods are referred to as guide tubes or thimble tubes and the upper internal structure that these tubes are attached to are referred to as an upper end fitting or a top nozzle, depending on the manufacturer. Therefore, it should be understood that references herein to a guide tube and upper end fitting should be considered as also referring to a thimble tube and top nozzle. The guide tubes have a relative thin wall thickness and thus require a sleeve at the upper end to provide the necessary support for attachment points and shoulder stops. During assembly, the guide tubes are inserted into the spacer grids. The upper end fitting is then aligned with, received on, and attached to the upper end sleeves of the guide tubes. Typically, upper end fittings and sleeves are attached to one another by the use of threaded joints and locking cups. When it becomes necessary to remove an irradiated fuel assembly upper end fitting or nozzle at the reactor site, the work must be done with remotely controlled tooling under water. This results in the handling of a number of parts and provides the potential for cross threading the fasteners during installation. The remote handling of a number of parts under water increases the potential for loose parts in the system that can damage the reactor and increases working time. Patents directed to nuclear fuel assembly end fitting retainers that applicant is aware of include the following. U.S. Pat. No. 3,769,158 discloses the use of an end fitting over fuel rods where a reduced neck extending through the opening in the end fitting has resilient split rings in grooves and engage the end fitting. U.S. Pat. No. 3,828,868 discloses guide tubes that are threadably attached to the end fitting. U.S. Pat. No. 4,699,761 discloses the use of a threaded sleeve on the upper end of the guide tube. SUMMARY OF THE INVENTION The invention addresses the above need. What is provided is an integral, reusable inexpensive locking arrangement between the guide tube assembly and upper end fitting that eliminates all loose fastener components at the reactor site. A retainer sleeve is fabricated to cooperate with the upper end sleeve of the guide tube assembly. Slots adjacent to the upper end of the sleeve receive rigid tabs on the upper end sleeve to hold the retainer sleeve and upper end sleeve together. The retainer sleeve is formed from a cylindrical tube that has a plurality of flexible tabs spaced around the circumference of the tube substantially at the mid section of the tube. Optional lower tabs serve to center the guide tube assembly in the upper end fitting and provide a more rigid connection. The mid section tabs are received against the shoulders of slots provided along the walls of the hole in the upper end fitting and serve to retain the guide tube assembly and upper end fitting in the installed position. The retainer sleeve is rotated to force the tabs inward to allow for removal of the upper end fitting from the guide tube assembly.