Patent Number: 047479965
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings, FIG. 1 illustrates the lower portion of a conventional nuclear fuel assembly 10 of the type commonly used in commercial nuclear power reactors. The assembly 10 comprises a plurality of fuel rods 12, each of which encloses a stack of fuel elements inside a tube, with the tube being sealed at each end by end plugs. The fuel rods 12 are assembled in a square array when viewed in cross section, which typically measures about twenty one centimeters along each side, and the rods are held in a laterally spaced apart arrangement by a "skeleton" which includes a number of grids 14 which are spaced at lengthwise intervals. The individual fuel rods are mounted to the grids by means of spring mountings (not shown), which permit limited axial movement of each rod. Control rod guide thimbles 16 extend parallel to the rods 12 for interconnection of the grids 14, and the guide thimbles 16 extend beyond the ends of the rods and secure top and bottom nozzles, with only the bottom nozzle 17 being shown in FIG. 1. As is well understood by those skilled in the art, a predetermined gap distance D is necessary between each end of each fuel rod and the surface of the adjacent nozzle to assure proper functioning of the fuel rod. The tool of the present invention is indicated generally at 18 in the drawings, and comprises an expander 20 composed of two elongate generally parallel and laterally spaced apart arms 21, 22, which extend in a longitudinal direction. The arms are each composed of a relatively thin, flat metallic strip having a substantially smooth and flat outer surface, and the two arms include first laterally aligned ends 23, 24 and opposite laterally aligned free ends 25, 26. The expander 20 also includes a yoke 28 composed of a block of metallic material which is fixedly interconnected between the first ends 23, 24 of the two arms. The opposite free ends 25, 26 of the arms are thus readily flexible and movable toward and away from each other in the lateral direction. The tool 18 further includes an actuator 30 positioned between and parallel to the two arms of the expander, and the actuator 30 includes a first end portion which extends freely through a longitudinal opening 32 in the yoke 28 so as to be axially movable with respect thereto, and the opening 32 has a square cross section. The first end portion is composed of a segment 33 of square cross section which is closely received in the opening 32, and which has a conforming square cross section. Also, the first end portion includes an outer threaded rod segment 34, which threadedly mounts a nut 35 which is positioned on the side of the yoke 28 opposite the free ends 25, 26 of the arms. The actuator 30 also includes an enlarged opposite end portion 36 which is positioned between the free ends of the arms. In addition, the tool 18 includes cooperating wedge surface means mounted to the arms and the actuator, for laterally separating the free ends of the arms upon longitudinal movement of the actuator in a predetermined direction with respect to the arms. This wedge surface means includes a plate 38 mounted on the inside of each of the arms, with the plates 38 defining an opposing pair of inclined surfaces 40, 41 positioned on respective ones of the free ends of the arms. Also, an oppositely facing pair of diverging surfaces 43, 44 are positioned on the opposite end portion 36 of the actuator. The diverging surfaces 43, 44 are adapted to be positioned between the opposing pair of inclined surfaces 40, 41, and such that axial movement of the actuator toward the right as seen in FIGS. 2-4 causes the divering surfaces to be drawn between the inclined surfaces so as to spread apart the free ends of the arms. Axial movement toward the left acts to remove the diverging surfaces from between the inclined surfaces to release the free ends of the two arms. The cooperating wedge surface means of the tool further includes an opposing pair of generally parallel second surfaces 46, 47 positioned on the plates 38 and so as to be positioned on respective ones of the free ends of the arms adjacent the laterally closest ends of the pair of inclined surfaces 40, 41, i.e. on the right side of the inclined surfaces as seen in FIGS. 2-4. These second surfaces 46, 47 are essentially parallel to each other when the arms are laterally spaced apart the predetermined distance D as shown in FIG. 3. The wedge surface means further includes a pair of oppositely facing outer surfaces 49, 50 mounted to the actuator and which are parallel to each other and positioned immediately adjacent the laterally most separated ends of the diverging surfaces 43, 44, i.e. at the left end of the diverging surfaces as seen in FIGS. 2-4. The distance between the parallel oppositely facing outer surfaces 49, 50 is designed so as to cause the arms to be laterally separated by the predetermined distance D when the actuator is axially moved so that the parallel outer surfaces are positioned directly between the opposing second surfaces of the arms as shown in FIG. 3, and the predetermined distance D is the maximum distance that the arms may be separated by the actuator. Viewing FIG. 2, it will be noted that the fuel rod 12' is illustrated to be at a level below the level of the remaining rods 12, and thus this fuel rod 12' needs to be adjusted upwardly. To effect this adjustment, the tool 18 is initially configured as shown in FIG. 2, and so that the free ends 25, 26 assume an initial closely spaced apart relationship. The forward or free end of the tool 18 is then inserted into the assembly between the nozzle 17 and the level of the lower ends of the fuel rods 12, and so that the free ends 25, 26 of the arms are disposed directly between the surface of the nozzle 17 and the end of the fuel rod 12'. Also, the two arms are manually pressed toward each other so that one or both of the arms flex inwardly and the free ends assume a relatively closely spaced apart and parallel relationship as seen in dashed lines in FIG. 2. The nut 35 is then manually rotated, so as to longitudinally move the actuator to the right as seen in FIGS. 2-4, and the conforming square profiles of the segment 33 of the actuator and the opening 32 through the yoke 28 serve to preclude relative rotation therebetween. Thus the actuator is moved longitudinally, and the wedging action between the inclined surfaces 40, 41 and the outer diverging surfaces 43, 44 acts to laterally separate the arms to the desired predetermined distance D, and shown in FIG. 3. Any further advance of the actuator to the right from the position shown in FIG. 3 will not change the separation of the arms, since the contacting surfaces are then parallel to each other. Thus further movement will not separate the arms beyond the desired predetermined maximum separation, which by design conforms to the desired separation distance D between the surface of the nozzle and the ends of the rods. In addition, the manual flexing of the arms is preferably maintained during the movement from the closely spaced apart initial position as seen in FIG. 2 to the expanded position as seen in FIG. 3, so as to maintain a parallel relationship of the free ends 25, 26 during such movement and thereby avoid lateral forces being imparted to the misaligned fuel rod 12'. Once the rod 12' has been adjusted upwardly to its proper position, the nut 35 is threaded in the reverse direction and the actuator is then moved to the left as seen in FIGS. 2-4. The two arms are then manually pressed toward each other so as to return to the initial closely spaced position, and the tool may then be removed from the assembly. In the event fuel rods are at an elevation above the proper level with respect to the bottom nozzle 17, the tool of the present invention is moved to the top of the assembly and placed between the top nozzle (not shown) and the top end of the fuel rods. The misaligned fuel rod is then moved downwardly by a corresponding procedure. The expander 20 of the tool 18 of the present invention typically measures about seventeen centimeters in longitudinal length, and so that the free ends of the arms may be inserted into the space between the ends of the rods and the surface of the nozzle and reach a position below any one of the fuel rods 12. Also, the tool is preferably constructed entirely of stainless steel or similar non-corrosive metallic material, so as to avoid any possible contamination of the fuel assembly. As noted above, the two arms 21, 22 of the expander are preferably manually deflected to assume a substantially parallel relationship as they are laterally moved apart by the longitudinal movement of the actuator, and thus a misaligned fuel rod may be moved upwardly without being subjected to any substantial lateral bending forces. Further, since the fuel rod is in contact with the generally flat and smooth exterior surface of the upper arm, the likelihood of a lateral force being applied to the rod is even further reduced. From the above description, it will be apparent that the tool 18 of the present invention permits the gap between the fuel rods 12 and nozzle 17 to be corrected by moving any misaligned fuel rod without requiring the nozzle to be removed from the fuel assembly. Also, the tool provides for such correction of the gap separation without risking undue lateral forces being applied to the end of the rod. In the drawings and specification there has been set forth a preferred embodiment of the invention and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.