Patent Number: 052710530
Section: description

PREFERRED EMBODIMENT OF THE INVENTION The numeral 10 generally designates a nuclear fuel assembly upper end fitting or top nozzle assembly which includes a holddown leaf spring assembly mounted thereon according to the principals of the invention. The upper end fitting 10 includes a top nozzle body weldment 12 of typical prior art design with certain modifications, as explained below, to accommodate the novel holddown leaf spring assembly of the invention. The holddown leaf springs 20, 22, 24 and 26, each comprises a unitary elongated metal bar. The bars 20 and 22 are top bars in the embodiment shown and the bars 24 and 26 are lower bars. They make up two stacks of two unitary elongated metal bars 20, 24 and 22, 26, respectively, adapted to be mounted to the fuel assembly end fitting or top nozzle body weldment 12 to perform the spring function. Each unitary elongated metal bar, 20, 22, 24, 26, has two substantially tapered width leg portions 20a, 20b, 22a, 22b, 24a, 24b, 26a and 26b, respectively. The tapered width leg portions of each bar are joined by an arcuate transition portion 28 therebetween adjacent the reduced width end of each of said width leg portions 20a, 20b, 22a, 22b, 24a, 24b, 26a, and 26b. The wider opposite ends 20c, 20d, 22c, 22d, 24c, 24d, 26c, and 26d, respectively, of the unitary elongated metal bars 20, 22, 24 and 26 which make up the leaf springs of the assembly, are mounted to the fuel assembly top nozzle or end fitting 12 at angled slots 30 thereof. The slots 30 make the attachment of the leaf spring assembly to the end fitting 12 at only the corners adjacent the alignment pin openings 12a or 12b. The other opposite corners 12c and 12d of end fitting 12 below the transition areas 28 are spaced therefrom such that an improved flow path from the nozzle openings 32 and 34 upwardly is accomplished and no restricting lip, as was typically present in prior art designs, is required. The slots 30 are best illustrated in FIG. 3. It will be seen that they cooperate with the wide ends 20c and 22c to capture and retain the ends of leg portions 20a and 22a. To facilitate this spring retention, openings 32 are provided in the leg portions of the leaf springs. The openings 32 align with openings 34 in end fitting 12 and welded or staked pins (not shown) secured therein. Alternatively, spring retention means which are screws within openings 32 at the bar ends opposite the transition portion 28 may be used and capped as shown in U.S. Pat. Nos. 5,053,191 and 4,792,429, both of which are incorporated herein by reference, but this requires increased machining and a greater number of parts to accomplish the spring retention function. The advantage of slot 30 is that the leg portions 20a and 22a, for example, may be made straight without the necessity of a localized stress inducing bend as was required by the typical prior art structures. To further reduce the possibility of a localized stressing, a contour as dotted in at 30a in FIG. 3 may be provided to avoid a sharp fulcrum and to thereby distribute any localized stressing as the spring stack of bars 20 and 22 flex. Thus, it will be seen that a novel design of holddown leaf spring assembly is provided which: reduces the amount of machining required to produce the springs, eliminates the necessity of a spring cap, reduces machining of the top nozzle weldment, reduces the number of parts which make up the top nozzle assembly, increases the flow area of the top nozzle upper marginal region and requires only one bending operation per spring instead of two.