Patent Number: 047114363
Section: summary

CROSS-REFERENCE TO COPENDING APPLICATIONS Attention is drawn to the following copending, commonly assigned applications, all/each filed on even date and incorporated specifically by reference into the instant specification: (1) "FUEL GRID WITH SLEEVES WELDED IN NOTCHED GRID STRAPS", by R. Duncan, Ser. No. 414,232; now U.S. Pat. No. 4,521,374. (2) "PULSED LASER MACHINING APPARATUS", by R. A. Miller and G. D. Bucher, Ser. No. 414,264; now U.S. Pat. No. 4,560,856. (3) "APPARATUS AND METHOD FOR LASER MACHINING IN NON-REACTIVE ENVIRONMENT", by R. A. Miller and G. G. Lessman, Ser. No. 414,242; now U.S. Pat. No. 4,492,843. (4) "STRAP AND VANE POSITIONING FIXTURE FOR FUEL ROD GRID AND METHOD", by R. F. Antol, R. W. Kalkbrenner and R. M. Kobuck, Ser. No. 414,197; now U.S. Pat. No. 4,539,738. (5) "LASER MACHINING SYSTEM", by D. L. Wolfe, J. W. Clements and J. S. Kerrey, Ser. No. 414,241; now U.S. Pat. No. 4,541,055. (6) "MOVABLE MACHINING CHAMBER WITH ROTATABLE WORK PIECE FIXTURE", by R. F. Antol, R. Kalkbrenner and D. L. Wolfe, Ser. No. 414,263; now U.S. Pat. No. 4,501,949. (7) "WORKPIECE GRIPPING AND MANIPULATING APPARATUS FOR LASER WELDING SYSTEMS AND THE LIKE", by R. Kalkbrenner and R. Kobuck, Ser. No. 414,262; now U.S. Pat. No. 4,538,956. (8) "LASER LENS AND LIGHT ASSEMBLY", by R. Antol, R. Kalkbrenner and R. Kobuck, Ser. No. 414,205; now U.S. Pat. No. 4,518,843. (9) "WELDING PLATES FOR A FUEL ROD GRID", by R. M. Kobuck, R. Miller, R. W. Kalkbrenner, J. Kerrey and R. Duncan, Ser. No. 414,265; now U.S. Pat. No. 4,492,844. (10) "PLURAL COMPUTER CONTROL FOR SHARED LASER MACHINING", by J. W. Clements and W. D. Lanyi, Ser. No. 414,204; now U.S. Pat. No. 4,547,855. (11) "GRID AND SLEEVES WELDING FIXTURE AND METHOD", by J. S. Kerrey and R. Duncan, Ser. No. 414,203; now U.S. Pat. No. 4,522,330. (12) "CALIBRATION OF AUTOMATED LASER MACHINING APPARATUS" by J. W. Clements and J. R. Faulkner, Ser. No. 414,272; and now U.S. Pat. No. 4,545,018. (13) "RIGID SUPPORT FOR LASER MACHINING APPARATUS", by D. L. Wolfe, Ser. No, 414,191, now U.S. Pat. No. 4,493,967. BACKGROUND OF THE INVENTION Description of the Prior Art This invention, in its preferred form, relates to apparatus and a related method for assembling inner grid straps so as to form a grid of generally square configuration, and for providing outer grid straps on the grid formed from the inner grid straps. More particularly, the invention relates to (a) a grid assembly fixture for holding a first set of inner grid straps in parallel relationship, and for holding a second set of grid straps parallel to each other and perpendicular to the straps of the first set, and for holding outer grid straps, (b) to a retention strap for retaining the grid formed of the inner and outer grid straps in assembled relationship, and (c) to a method of assembling a grid from grid straps using the grid assembly fixture and retention strap. Nuclear fuel bundle assemblies include a matrix of nuclear fuel rods which are arrayed in rows and columns, and which are held in the desired configuration by a plurality of fuel rod grids. These grids are produced from "straps" which are linearly extending, generally rectangular elements, characterized by having slots extending from one edge approximately half way through the depth of the strap. The straps are assembled so that one strap is in mating relationship with the other strap. Thus, the slot of one strap engages the other strap at a portion thereof which is in alignment with the slot of that other strap, with the result that the grid is of the same depth as each of the straps which forms the grid. The resulting grid has a first set of straps which are substantially parallel to each other, and equally spaced, and a second set of straps which are parallel to each other and equally spaced, the straps of one set being perpendicular to the straps of the other set. All of the aforesaid straps are designated as "inner straps", and they are placed in mating relationship to form a square grid of square cells, in the above noted rows and columns. In addition, there are provided outer straps, which are placed on the four sides of the grid. The inner straps and outer straps were formerly assembled by first joining together two straps in mating relationship on a conventional table or plate. Typically, two additional straps were added, so that there resulted the four outer-most inner straps, which thereby formed a frame. The remaining inner straps were then placed in position, utilizing the frame provided by these first four placed straps. Then the outer straps where placed in position, and an encircling strap or holding strap was placed about the entire assembled grid. Further processing was then effected by placing brazing material at various locations on the grid, and the grid with the brazing material placed on it was then positioned in an oven, where brazing was effected. The above-described method and related apparatus resulted in a very time consuming operation. SUMMARY OF THE INVENTION It is therefore an object of this invention to provide equipment which will permit the rapid assembly of inner and outer grid straps into a grid. It is the most specific object of this invention to provide equipment, and attendant method, to permit assembly of inner and outer grid straps which will avoid excessive bending thereof. It is a still further object of the present invention to provide grid assembly equipment and method which will permit ready assembly of inner and outer grid straps without undue binding thereof, and which will provide for retention of the assembled grid for welding by a laser beam welding. It is yet another object of the present invention to provide a retention strap for an assembled fuel rod grid which will provide access for welding by a laser beam to all weld locations on the exterior of the grid. In accordance with these and other objects of the invention, there is disclosed a grid assembly fixture comprised of a generally flat plate of square plan form, having in a surface thereof a first set of equally spaced, parallel grooves and a second set of equally spaced, parallel grooves, the grooves of the two sets being perpendicular to each other. Preferably, the grid assembly fixture has a peripherally extending raised portion. In addition, bores are provided at the intersections of each two grooves, with smaller bores provided along one groove, adjacent an edge of the plate, so as to serve as locating holes. The plate is mounted on a support for rotation on both vertical and horizontal axes, and in an attendant method, there are positioned on the plate the straps of a first set, then the plate is rotated, and there are placed, in mating relationship with the straps of the first set, the straps of the second set. Thereafter, outer straps are provided, being supported on the plate, the outer straps having slots, and the inner straps having at their ends extending tabs, at least some of the tabs of the inner straps being caused to enter into the mating slots of the outer straps. The plate and grid are then tilted so that two of the outer straps face upwardly, and two bars of a retention strap, to be hereinbelow described, are placed on the two outer straps, and are held in position by clamps. The plate is then rotated, so that the other two outer straps face upwardly, and two additional bars of a retention strap are placed on these latter two outer straps, and are joined to the first two bars of the retention strap, thereby forming a complete retention strap encircling and engaging the outer straps forming the grid, after which the assembly of retention strap and grid may be removed from the the grid assembly plate. The retention strap is formed of four H-shaped bars having two end posts and a cross member between them. A first two and a second two of the bars are hingedly connected together by a hinge structure which causes the adjacent ends of the bars to be spaced from each other. There are thereby formed two pairs of hinged bars. Further, the bars are provided with releasable fastening elements, so that the two pairs of bars may be joined together to form a retention strap of four bars. The releasable fasteners are constructed so that the adjacent ends of two adjacent bars are in spaced relation. By this construction, a laser beam may pass in the space between adjacent ends of bars at all four corners of the grid, to permit corner welding of the grid, and in addition, the slot and tab welding may be effected since the cross member of the bars are located between upper and lower tab and slot connections of the inner and outer grid straps.