Patent Number: 053032730
Section: summary

BACKGROUND ART This application claims the priority of Japanese Patent Application No. 3-357763 filed Dec. 26, 1991, which is incorporated herein by reference. The present invention pertains to an apparatus for assembling a nuclear fuel assembly. FIG. 6 depicts a known nuclear fuel assembly which is mounted on a nuclear reactor such as a pressurized water reactor. The assembly, generally designated at 1, includes a pair of top and bottom nozzles 2 and 3 arranged in a facing relation to each other and in a vertically spaced relation to each other. A plurality of guide pipes 4 such as control-rod guide pipes or instrument pipes are disposed so as to extend between the top and bottom nozzles 2 and 3, and fixedly secured thereto. A plurality of grids 4 are secured to the intermediate portions of the guide pipes 5 so as to be vertically spaced from one another, and a plurality of fuel rods 6 are inserted through and supported by the grids 4 so as to extend parallel to the guide pipes 5. As shown in FIGS. 7 and 8, each grid 5 is formed as follows. A plurality of straps 11, each in the form of a thin strip sheet, are assembled perpendicularly to each other into a grid 5 to define a number of grid cells 13. Springs 15 and dimples 16 for supporting a respective fuel rod 6 are formed on the walls of each grid cell in opposed relation to each other. More specifically, as shown in FIG. 8, a single spring 15 is formed on one side of each wall of the grid cell 13, while a pair of dimples 16 are formed on the other side of the same wall defining adjacent grid cell so as to sandwich the aforesaid spring 15, and a spring 15 and a pair of dimples 16 are opposed to each other and protrude into the same grid cell 13. Each fuel rod 6, which is inserted into the grid cell 13, is supported by being urged to the dimples 16 by the spring 15 opposing thereto. Furthermore, rectangular cut-outs 14 or openings are formed at the intersections of the straps 11. Those wall portions which sandwich the spring 15 therebetween and are spaced apart from each other in the longitudinal direction of the strap serve as ribs 23 with which hook portions 22 of a key member 21 are held in engagement. A conventional method for inserting the fuel rods 6 in the grid 5 thus constructed will now be described. First, a deflecting jig 24 as shown in FIG. 9 is inserted through the grid cell 13. The deflecting jig 24 comprises a cylindrical jig body 25 divided at its forward portion into four pieces, and a tapered pin 26 inserted in the jig body 25 for sliding movement therealong. When the tapered pin 26 is withdrawn or retracted in its axial direction while holding the deflecting jig 24 in the grid cell 13, the jig body 25 is enlarged to deflect the springs 15 as shown in FIG. 10. Subsequently, an elongated key member 21 of a generally rectangular cross-section is inserted into the cut-outs 14 from the lateral side of the grid 12, to bring the hooks 22 of the key member 21 into engagement with the ribs 23 to keep the springs deflected. Then, the deflecting jig 24 is removed from the grid. Thereafter, the fuel rod 6 is inserted in the grid cell 13, and the key member 21 is removed from the grids to release constriction of the spring. Thus, the fuel rod 6 is secured by being resiliently urged by the springs 15 toward the dimple 16 opposing thereto. However, inasmuch as the aforesaid tasks of deflecting the springs 15 and inserting the key member 21 are carried out manually, they are labor-intensive and time-consuming, resulting in low operational efficiency. Furthermore, the task of deflecting the springs 15 using the aforesaid deflecting jig 24 must be carried out carefully so as not to cause any twisting or shifting to the springs 15, without exerting any force thereon in a direction other than the acting direction of the spring 15. Therefore, the deflecting task requires a high level of skill, so that it has been desired to improve this task and achieve standardization of the operating procedure. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide an apparatus for assembling a nuclear fuel assembly which solves the aforesaid problems and achieves substantial reduction in working time and cost. According to the present invention, there is provided an apparatus for assembling a nuclear fuel assembly which includes a grid for supporting a plurality of fuel rods, the grid having a plurality of straps intersecting each other to define a plurality of grid cells therein, and a plurality of pairs of dimples and springs provided on the straps for supporting the fuel rods, the dimple and the spring being disposed in facing relation to each other, on wall portions of the straps, which cooperate with each other to define the grid cells, the dimple and the spring projecting into the grid cell, the apparatus comprising: deflecting means disposed adjacent to the grid for deflecting the spring away from the dimple opposing thereto; the deflecting means including a tubular member defining a plurality of circumferentially divided sleeve pieces, a rod member releasably inserted in the tubular member for sliding movement therealong, and drive means drivingly connected to the rod member for moving the rod member in the tubular member in a longitudinal direction thereof to bring the rod member into urging engagement with the sleeve pieces of the tubular member, whereby the sleeve pieces are deflected to be urged against the spring to deflect the same. In the foregoing apparatus, when the drive means is actuated, the rod member which is inserted in advance in the tubular member is moved by the drive means in a longitudinal direction thereof, and the rod member is brought into urging engagement with the sleeve pieces of the tubular member, so that the sleeve pieces are deflected to be urged against the spring to deflect the same. Thus, the deflecting operation of the spring on the strap of the grid can be mechanically carried out very efficiently by operating the apparatus, thereby achieving substantial reduction in working time and cost.