Patent Number: 039829944
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, two mutually perpendicular fuel element grid plates 10, 11 are interlocked at common corner 12 to form a portion of a cellular grid structure of a type that is described in more complete detail, for example, in F. S. Jabsen, U.S. Pat. No. 3,665,586, granted on May 30, 1972 for "Nuclear Fuel Rod Supporting Arrangements" and assigned to the same assignee as this invention. The plates 10, 11 are generally flat and formed from sheet metal, and the like. Bosses 13, 14 on the plates 10, 11, respectively, are formed in the plates, by stamping, for instance, and protrude from the surfaces of the plates toward the center of the cell that is formed, in part, by the two plates. Apertures 15, 16 are cut in the plates 10, 11 at intervals that are equal to the length of one side of a cell. Interlocking the plates 10, 11 at the common corner 12 cause the apertures at the corner 12 to form a slit 17. A gap 20 of predetermined depth, moreover, is provided in the slit 17 between the perpendicular plates 10, 11. In a similar manner, the apertures in each pair of mutually intersecting plates within the grid structure combine to form an aligned row of slits, each of these slits forming its own respective gap. None of these gaps, however, may be less than a minimum separation that is determined by the dimensions of bar 21, a portion of which is shown in FIG. 2. As shown in the drawing, an illustrative example of the bar 21 is formed of suitable metal in the shape of a long, slender shank 22 that has a generally rectangular cross section. In this respect, it should be noted, the thickness of the shank 22 in the dimensions that are perpendicular to the plane of the drawing are significantly smaller than the width of the gap 20 to enable the bar 21 to pass through an aligned row of slits and rotate through an angle of about 90.degree. hereinafter described in more complete detail. The bar 21 also is provided with an array of stubs 21A, 21B, 21C. These stubs all protrude from one side of the shank 22 in a direction that is transverse to the longitudinal axis of the bar 21. The individual extents of the protrusions 21A, 21B, 21C, when added to the thicknesses of the adjacent portions of the shank 22 are greater than the gap 20 (FIG. 1) that is formed by the slits at the common corner 12. As shown in FIG. 2, the stubs 21A, 21B, 21C each are spaced from the opposite surface of the next adjacent stub a distance that is essentially equal to the separation between corresponding points in adjoining grid cells. Further in accordance with principles of the invention a grid cell 23, as shown in FIG. 3, is formed by means of portions of four plates 24, 25, 26, 27. The plates 24, 26 and the plates 25, 27 are generally parallel. The plates 25, 27, however, are perpendicular to and intersect with the plates 24, 26. A fuel rod 30 is lodged within the cell 23. As mentioned above, the fuel rod 30 is a long, slender metal tube that encloses a stack of nuclear fuel pellets. As shown in FIG. 3, bosses 31, 32, 33, 34 protrude toward the center of the grid cell 23 and engage or clutch the outer surface of the fuel rod 30 in order to stabilize the rod. Bar 35 is lodged within the cell 23 in a manner in which the lengthwise dimension of the bar is generally parallel to the grid plate 26. In order to insert the bar 35 into the cell structure, stubs 36, 37 on the bar are oriented in a direction that is generally parallel to the longitudinal axis of the fuel rod 30. The bar 35 is passed into and through the cell 23 by means of a lengthwise movement in the direction of arrow 40. Because gaps 41, 42 in the plates 25, 27, respectively, are greater than the transverse width of the bar 35, the bar passes through the gap 41, into the cell 23 and out of the cell by way of the gap 42 with relative ease. In a similar manner, bar 43, with protruding stubs 44, 45 is passed through the cell 23 by way of gaps 46, 47 in the plates 24, 26, respectively. The bars 35, 43 shown in FIG. 4 have been rotated in the directions shown by arrows 50, 51 through an angle of about 90.degree. in order to bridge the stub 36 on the bar 35 and the stub 44 on the bar 43 across the gaps 41, 46, respectively. Because the combined transverse length of each of the stubs 36, 44 and adjacent portions of the individual bars 35, 43 is greater than the transverse widths of the associated gaps 41, 46, the transverse ends of the stubs 36, 44 engage adjoining portions of the grid plates 25, 24, respectively. Lengthwise application of force to the bars 35, 43 in the directions of the arrows 52, 53, respectively, that are shown in FIG. 5 presses the stubs 36, 44 against the plates 25, 24 and thus deflects these plates out of their usual orientation relative to the center of the cell 23 and the longitudinal axis of the fuel rod 30. This temporarily induced deflection establishes clearances 54, 55 between the bosses 31, 32, respectively, and adjacent portions of the surface of the fuel rod 30. The small clearances 54, 55, however, are of sufficient magnitude to enable the fuel rod 30 to be withdrawn from the cell 23 in a direction that is parallel to the longitudinal axis of the rod and generally perpendicular to the plane of the drawing. After the fuel rod 30 has been removed from the cell 23, the lengthwise forces applied to the bars 35, 43 indicated by the arrows 52, 53 are relaxed to enable the temporarily deflected grid plates 24, 25 to once more assume their usual orientation with respect to the center of the cell 23. Save for the presence of the fuel rod 30, this specific grid cell wall relationship is illustrated in FIG. 4 of the drawing. The bars 35, 43, moreover, are withdrawn from the grid structure through a simple manipulation. In this respect, the bars 35, 43 are rotated either in the direction of the arrows 50, 51 through further angles of about 90.degree., or through other angles of essentially 90.degree. in directions opposite to those shown by means of the arrows 50, 51. These rotations, in any event, align the stubs 36, 44 with the vertical axis of the cell 23 to restore the bars 35, 43 to the configuration that is illustrated in FIG. 3 (again, save for the presence of the fuel rod 30). Clearance now is provided between the transverse widths of the bars 35,43 and the respective widths of the gaps 41, 42 and 46, 47 that will enable the bars to be withdrawn from the grid structure through the associated gaps. The fuel rod 30 (FIG. 5) is lodged in the structure of the cell 23 through an essentially reverse process. For example, the bars 35, 43 are inserted into the hitherto empty cell 23 with the stubs 36, 37, 44, 45 in general parallel alignment with the central axis of the cell. The bars 35, 43 are turned essentially through angles of 90.degree. in order to permit the stubs 36, 44 to bridge the gaps 41, 46 and engage adjacent portions of the grid plates 25, 24. Lengthwise forces, relative to the longitudinal axes of the bars 35, 43, are applied in the direction of the arrows 52, 53 to press the stubs 36, 44 against the respective plates 25, 24 in order to deflect the plates and open the clearances 55, 54. On establishing the clearances 54, 55, the fuel rod 30 can be inserted into the cell 23 through a longitudinal movement without being subjected to gouging and scraping from the bosses 31, 32, 33, 34. Upon lodging the fuel rod 30 within the cell 23, the lengthwise forces that were applied to the bars 35, 43 in the directions of the arrows 52, 53 are relaxed. This relaxation in the lengthwise forces permits the bosses 31, 32 to restore to the undeflected condition and thus clutch the surface of the fuel rod 30. The bars 35, 43 are rotated through respective 90.degree. angles to orient the stubs 36, 37, 44, 45 in a direction that will enable the bars 35, 43 to be withdrawn from the grid structure through the gaps 41, 42, 46, 47.