Patent Number: 049869604
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, it is seen in FIG. 2 that the invention is generally referred to by the numeral 10. As seen in FIG. 1 nuclear reactor vessel 12 is generally comprised of core support structure 14, fuel assemblies 16, shroud 18, inlet nozzle 20, and outlet nozzle 22. The flow of coolant through reactor vessel 12, as symbolized by the arrows, is down annulus 24 via inlet 20, up through and around fuel assemblies 16, and out to steam generators not shown through outlet 22. End fitting 10 is positioned between fuel assemblies 16 and upper grid plate 26. End fitting 10 is generally comprised of main body portion 28, lower plate 30, and spring means 32. Main body portion 28, as seen in side view in FIG. 2 and partial cutaway top view in FIG. 3, is substantially box shaped and has two open opposed sides. An outwardly extending shoulder 34 is provided adjacent the upper edge and substantially at the midpoint of each side of main body portion 28. Shoulders 34 contact upper grid plate 26 in the core of reactor vessel 12 to retain end fitting 10 in the installed position. Upward pressure is provided from fuel assemblies below end fitting 10 and are typically in contact with end fitting 10 by means of guide tubes not shown. Main body portion 28 is provided with slots 38 adjacent the upper portion of each corner for receiving one end of spring means 32. An aperture 39 or handling window is provided on at least one side of main body portion 28 for ease of handling end fitting 10 during initial assembly or reconstitution of fuel assemblies 16. A bore 40 is provided at each corner and along the longitudinal axis of main body portion 28 for slidable mounting relative to lower plate 30. Lower plate 30 is square or rectangular in shape and provided with a guide pin 42 at each corner. In the preferred embodiment, guide pins 42 are threadably engaged in a bore in lower plate 30 and then tack welded in place. A slot 44 is provided in lower plate 30 on each side and offset from the end for receiving one end of spring 32. Lower plate 30 is adapted for attachment to fuel assemblies 16 by guide tubes or other suitable means known in the industry. Bores 48 are provided in lower plate 30 for passage of guide tubes therethrough. Openings 50 are provided in lower plate 30 for flow of coolant therethrough. The pattern shown is for illustrative purposes only and may be adapted to suit the particular application. In the preferred embodiment, spring means 32 is in the shape of a sideways V or hairpin spring. Spring 32 has a first angled end designed to fit into slot 44 in lower plate 30. The second straight end is received in slot 38 in main body portion 28 and welded in place. The first end of spring 32 is offset from the end of lower plate 30. This causes end fitting 10 to have preloaded tension against guide tubes used in fuel assemblies 16 and it is less prone to vibration induced spring failure. In the assembled state, main body portion 28 is resiliently biased away from lower plate 30. In this manner, pressure against lower plate 30 from fuel assemblies 16 is accommodated by compression of spring 32 and movement of lower plate 30 toward main body portion 28. Main body portion 28 is prevented for sliding off guide pins 42 by the use of stop means 46 attached to the end of each guide pin 42 after main body portion 28 has been mounted thereon. It should be noted that any suitable means such as a stop washer or a nut engaged on the end of each guide pin 42 may be used. In operation, end fitting 10 is assembled by welding the second end of spring 32 in slot 38 of main body portion 28. The first end of spring 32 is inserted into slot 44 in lower plate 30 as main body portion 28 is slidably mounted on pins 42. Stop means 46 is then attached to the end of pins 42 to prevent main body portion 28 from sliding off pins 42. During initial assembly of a reactor fuel assembly or during retrofit operations while reconstituting a fuel assembly, lower plate 30 is then attached to the top of a fuel assembly 16 by any suitable means known in the industry. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.