Patent Number: 051241161
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 1-3 that the invention is generally indicated by the numeral 10. Grid key 10 is formed in the shape of a rectangular bar to provide a main body portion 12 having first and second ends 14, 16. Main body portion 12 is bent near first end 14 to form a 45 degree angle in main body portion 12. In the preferred embodiment the bend in main body portion 12 is approximately 0.19 inch from first end 14 and has a bend radius of approximately 0.09 inch. First end 14 is provided with two rectangular extensions or tabs 18 that extend outwardly in opposite directions from first end 14 at a right angle to main body portion 12 to define a T-shape at first end 14. In the preferred embodiment tabs 18 are integral with main body portion 12 for ease of fabrication and strength. The following terms will be used for the sake of clarity in referring to the various dimensions of tabs 18 and main body portion 12. The dimension of tabs 18 from first end 14 back toward the bend in main body portion 12 shall be indicated as the length of tabs 18. The dimension across both tabs 18 shall be indicated as the width across tabs 18 with the corresponding dimension across main body portion 12 being indicated as the width of main body portion 12. The thickness of tabs 18 and main body portion 12 is that dimension perpendicular to the width. During loading of fuel rods into the exterior grid cells of a fuel assembly grid key 10 is used in the following manner. As seen in FIG. 4, first end 14 is inserted into window 20 of exterior grid strip 22. In this first position tabs 18 are parallel to the longitudinal axis of grid assembly 24, exterior grid strip 22, and interior grid strip 26. Each grid assembly 24 used in a nuclear fuel assembly to position fuel rods radially relative to each other is formed from a plurality of grid strips interleaved together to form cells between the strips that receive the fuel rods. Main body portion 12 is positioned such that the outside radius of the bend in main body portion 12, designated by the numeral 28, faces away from exterior grid strip 22 and the inside radius of the bend, designated by the numeral 30, faces exterior grid strip 24. Main body portion 12 is then rotated 90 degrees to a position where main body portion 12 is parallel with the longitudinal axis of grid assembly 24, tabs 18 are perpendicular to the longitudinal axis of grid assembly 24, and first end 14 is resting on the edge of interior grid strip 26. In this position tabs 18 extend beyond the edge of window 20. Main body portion 12 is then pulled away from exterior grid strip 22 and moved approximately 90 degrees in a vertical rotating motion. As seen in FIG. 5 and 6, this causes outside radius 28 to bear against interior grid strip 26 and tabs 18 to pull exterior grid strip 22 outward as main body portion 12 is moved. As main body portion 12 is moved, this causes rotation of tabs 18 from their first position where their length is between exterior grid strip 22 and interior grid strip 26 to a second position where the thickness of tabs 18 is between exterior grid strip 22 and interior grid strip 26. It is the thickness of tabs 18, which is greater than their length, that provides the camming effect in the keying or lifting of exterior grid strip 22. Dimple 32 on the interior side of exterior grid strip 22 is thus moved away the cell and a fuel rod may then be inserted into the cell without dimple 32 scratching the fuel rod. After a fuel rod is inserted grid key 10 is removed by reversing the steps used to allow insertion of the fuel rod. For ease of illustration only a portion of a grid assembly is shown. Grid key 10 may be formed from any suitable material such as 17-4 ph stainless steel or nylon or other plastics that are strong enough for such use and are easily produced by a molding process. The length and thickness of tabs 18 are adjusted according to the type of grid assembly and the space between interior grid strip 26 and exterior grid strip 22. As an example, in a zircalloy grid tested the dimension of tabs 18 from first end 14 back toward the bend (the length of tabs 18) is preferably 0.035 inch whereas in an inconel grid the preferred dimension is 0.068 inch. The width of main body portion 12 for such grids is 0.100 inch and 0.180 inch respectively while the thickness of main body portion 12 and tabs 18 is 0.059 and 0.078 inch respectively. The width across both tabs 18 for either type of grid is preferably 0.265 inch. The preferred length of main body portion 12 from the bend to second end 16 is 0.75 inch. 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.