Patent Number: 044926685
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing and initially to FIGS. 1-3, there is illustrated a new and improved device or apparatus 20 and method for preventing the rotation of an elongated rod 22 about its longitudinal axis in a nuclear fuel assembly. The elongated rod 22 is disposed between spaced-apart plates of the nuclear fuel assembly, for example, an upper tie plate and a lower tie plate, and may be a spacer capture fuel rod, a spacer capture water moderator rod, a spacer capture rod other than a fuel rod or a water moderated rod, a fuel rod, a water moderator rod, or any other elongated rod in a nuclear fuel assembly. The rod 22 includes a thin wall cylindrical tube 24 that is normally terminated at its upper end by an upper end plug (not illustrated). The device 20 includes a lower end plug 26 that is welded to and terminates the lower end of the tube 24. The lower end plug 26 is of a two-piece construction consisting of a cylindrical body 28 that is welded to the lower end of the tube 24 and a stud portion or member 30 having a threaded lower end 32 for receipt of locking or retaining means, such as a locking or retaining nut or washer (not illustrated). The stud member 30 may be joined to the cylindrical body 28 by any convenient means, such as welding. The cylindrical body includes a pair of diametrically oppositely disposed, longitudinally extending, internal flat portions or flats 34 formed at the lowermost end of the cylindrical body 28. The outer surface of the flats 34 is tapered radially or chamfered to provide lead in surfaces 36 to facilitate the insertion of the rod 22 through the cells of the spacer grids during the assembly of the nuclear fuel assembly. In accordance with an important feature of the present invention, the flats 34 are configured to seat against and engage a pair of diametrically oppositely disposed, elongated external or out-of-cavity flat portions or flats 38 formed on the upper outer surface of a cylindrical boss or sleeve 40 of a lower tie plate of a nuclear fuel assembly positioned at the intersection of four, transversely disposed, elongated, web portions or members 42 of a lower tie plate of a nuclear fuel assembly. The circumferentially enclosed cylindrical boss or sleeve 40 also includes a circumferentially enclosed internal cavity 43 through which the lower portion of the stud member 30, including its threaded lower end 32, passes for subsequent retention therein by the receipt of suitable locking or retaining means. Thus, the rod 22 may be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 30 within the cavity 43 of the sleeve 40 such that the flats 34 seat against and engage the flats 38 disposed outside of the cavity 43 of the sleeve 40. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 32 of the stud portion 30 to retain the flats 34 seated against and in engagement with the flats 38, thereby to prevent the rotation of the rod 22 about its longitudinal axis. In accordance with an important feature of the present invention, an alternate embodiment of a device 20' (FIGS. 4-7) for preventing the rotation of an elongated rod 22 about its longitudinal axis includes a lower end plug 44 welded to the lower longitudinal end of the tube 24. Preferably, the lower end plug 44 is formed as a unitary member, although it could also be formed as a multiple-piece construction in the same manner as the lower end plug 26. The lower end plug 44 includes an upper cylindrical body portion 46 having four elongated grooves 48 formed therein that have longitudinal axes parallel to the longitudinal axes of the lower end plug 44 and of the rod 22. Preferably, the four grooves 48 are disposed 90.degree. apart about the periphery of the body portion 46 to form a spline. The lowermost portion of the portion 46 is tapered radially or chamfered to provide lead in surfaces 36 to facilitate the insertion of the rod 22 through the cells of the spacer grids during the assembly of the nuclear fuel assembly. The lower end plug 44 further includes a lower elongated stud portion 50 of a reduced diameter, as compared to the body portion 46, terminating in a threaded lower end 52. The grooves 48 are configured to receive and engage four, radially inwardly protruding, key members 54 disposed 90.degree. apart at the upper end of an anti-rotation sleeve 56. The inner bore 58 of the anti-rotation sleeve 56 is preferably configured to be slightly larger than the outer diameter of the cylindrical boss or sleeve 40 disposed at the intersection of the four, transversely disposed, elongated, web portions or members 42. A lower end 60 of the sleeve 56 includes four, longitudinally extending, elongated slots 62 disposed 90.degree. apart about the periphery of the sleeve 56 for the receipt of and the engagement by the web portions 42. Preferably, the sleeve 56 is secured to the lower tie plate of the fuel assembly by any convenient means, for example, by tack welding to the web portions 42. The rod 22 may thus be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 50 within the internal cavity 43 of the sleeve 40 such that the grooves 48 receive and engage the key members 54. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 52 of the stud portion 50 to retain the key members 54 within and in engagement with the grooves 48, thereby to prevent the rotation of the rod 22 about its longitudinal axis. In accordance with a further important feature of the present invention, a further alternative embodiment of a device 20" (FIGS. 8-10) for preventing the rotation of an elongated rod 22 about its longitudinal axis includes a lower end plug 64 welded to the lower longitudinal end of the tube 24 of the elongated rod 22. The lower end plug 64 is of a two piece construction including a main body portion 66 and a cylindrical locking sleeve 68. The main body portion 66 includes an upper section 70 with a radially outwardly extending annular shoulder portion 72, the upper surface of which is welded to the tube 24 and the lower surface of which is welded to the locking sleeve 68. The main body portion 66 further includes a lower elongated stud portion 74 terminating in a threaded lower end 76. The locking sleeve 68 has four elongated slots 78 formed therein that have longitudinal axes parallel to the longitudinal axes of the lower end plug 64 and of the rod 22. Preferably, the slots 78 are disposed 90.degree. apart about the periphery of the lower portion of the sleeve 68 and are configured in width, depth and spacing to receive and mate with the four, transversely disposed, elongated, web portions or members 42 of the lower tie plate of the nuclear fuel assembly. The slots 78 are formed by and between four downwardly extending projections or fingers 80 of the sleeve 68. The fingers 80 include lowermost end surfaces 82. The rod 22 may thus be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 74 within the inner bore 43 of the sleeve 40 such that the slots 78 receive and engage the web members 42 such that the fingers 80 are disposed between the web members 42. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 76 of the stud portion 74 to retain the web members 42 within and in engagement with the slots 78, thereby to prevent the rotation of the rod 22 about its longitudinal axis. Obviously, many modifications and variations of the present invention are possible in light of the above disclosure. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.