Patent Number: 051851245
Section: description

Corresponding reference numerals refer to like parts throughout the several views of the drawings. DETAILED DESCRIPTION The gauging apparatus of the present invention is applied in its embodiment to check the critical dimensional characteristics of cells 10 utilized in a nuclear fuel bundle spacer, generally indicated at 12 in FIG. 1, to establish the spacings between fuel rods 14 making up the bundle. Each cell may be of the type disclosed in commonly assigned, copending application entitled "Composite Spacer With Inconel grid and Zircaloy Band", U.S. Pat. No. 5,089,221, issued Feb. 18, 1991. As such, each cell is constructed having octagonally shaped end bands 15 interconnected by a pair of resilient legs which serve as springs 18. Two flat panels of each of the end bands are formed ends with inwardly projecting stops 16 in diametrically opposed relation to springs 18. When a fuel rod 14 is inserted through the cell, the springs act to bias the fuel rod against stops 16 to center it in the cell. When the cells are conjoined in matrix or egg crate array to create spacer 12, the stops of the multiplicity of cells also establish the spacings between fuel rods 14. Since rod to rod spacing Y in a fuel bundle is a critical dimension, the dimensional characteristics of the individual cells that contribute to the establishment of this spacing must be held to strict tolerances. The gauging apparatus of the present invention provides a convenient quality assurance check of these critical cell dimensional characteristics. Turning to FIG. 2, the gauging apparatus of the invention includes a fixture, generally indicated 20, having a planar base 22 and a pair of upstanding, parallel sidewalls 24 and 26 in perpendicular relation to the base. As seen in FIGS. 3 and 5, the separation W between the sidewalls is equal to the nominal cell width measured between diametrically opposed flat panels of the cell end bands 15, and the sidewall height is also equal to dimension W. To gauge the dimensional characteristics of a cell, it is placed in fixture 20. The corrected gauging position of the cell in the fixture is with the flat panels of the cell end bands between the two stop- containing panels resting squarely on fixture base 22. If it fits between sidewalls 24 and 26 with minimal play, its width dimension W in the horizontal direction is accepted. To check cell width W in the vertical direction, a plate 36 is placed across the tops of the fixture sidewalls 24, 26. If the cell fits between this plate and fixture base 22 with minimal play, this width dimension is accepted. As best seen in FIGURE 4, a pair of steps 28, upstanding from the fixture base, are separated by a distance L that is slightly greater than the nominal length of a cell. If a cell can assume a gauging position between steps 28 with minimal gaps between the cell ends and these steps, its length is considered acceptable. Referring to FIGS. 3 and 4, a pin 30 is then inserted though the cell bore defined by end bands 15. This pin is semicylinderical, such that its cylindrical surface portion 30a rests on stops 16 with its flat surface portion 30b well clear of springs 18 which are seen to be in their relaxed states. Thus, the springs do not press pin 30 against the stops, which would tend to distort the essentially free standing cell. The diameter of the cylindrical portion of pin 30 is equal to the nominal diameter of a fuel rod. It will be appreciated that such distortion can not occur when the cells are conjoined in spacer array. As seen in FIG. 1, the orientations of the cells in the spacer are such that only the flat band panels of adjacent cells are joined in abutting relation. Thus, it is the gap X between a fuel rod 14 and the exterior flat panel surface that establishes critical fuel rod spacing Y and in fact equals Y/2. Therefore, gap X established by stops 16 is a critical cell dimensional characteristic. To check this critical dimension, a pair of "go, no go" feeler gauges 32 and 34, seen in FIG. 4, are utilized. Feeler gauge 32 has a thickness equal to the minimum allowable gap X dimension, while feeler gauge 34 has a thickness slightly larger than the maximum allowable gap X dimension. Thus, if feeler gauge 32 can not be inserted through the gaps X between pin 30 and the fixture base and sidewalls, the minimum allowable gap dimensional requirement is not met, and the cell is disqualified. On the other hand, if feeler gauge 34 can be inserted through any one of the gaps, the cell fails the maximum allowable gap dimension requirement and is rejected. These gap dimensions are checked by the feeler gauges just beyond both ends of the cell, and fixture sidewall 26 is relieved, as indicated at 26a in FIG. 4, to facilitate introduction of the gauges. In practice, it is only necessary to gauge the gaps between the pin and the fixture base and between the pin and one fixture sidewall. If these gaps are in-tolerance, then the gaps between a fuel rod and the exterior surfaces of respectively diametrically opposed flat panels of the end bands 15 will also be in-tolerance. A fuel rod will thus be essentially centered in the cell, as is required to achieve requisite rod spacing throughout the spacer. Referring to FIG. 5, if the quality assurance checks of the flat panel gaps X indicate their dimensions to be in-tolerance, it remains to check the relaxed positions of the springs 18 as a gauge of whether they will exert adequate spring force to bias a fuel rod into a centered position in the cell against stops 16. To this end, plate 36 is placed across the top of fixture 20 to fully confine and thus maintain the shape of the cell, and a cylindrical pin 38 is then inserted through the cell to rest on stops 16. The diameter of this pin is selected to be sufficiently less than the fuel rod nominal diameter, such that springs 18 should lightly contact pin 38. If they do, it is determined that the springs, as formed, are in requisite relaxed positions to exert adequate centering forces on a fuel rod when inserted through the cell. However, if the springs do not contact pin 38, the cell is rejected for defective springs. FIG. 6 illustrates a gauging fixture 44 dimensioned such that separation W between its sidewalls 46 is equal to the nominal width, i.e., diameter, of a tubular spacer cell 48, such as disclosed in commonly assigned Matzner et al. U.S. Pat. No. 4,508,679. The height W of the sidewalls, measured from base 50, is also equal to the nominal cell diameter. Thus, when a cell 48 is placed in fixture 44, the sidewalls serve as a gauge of the cell diameter, as does a plate 50 resting on the top edges of the sidewalls. A pin 52 of a diameter equal to the nominal diameter of a fuel rod is inserted through the cell bore to rest on stops 54. "GO, no go" feeler gauges are then utilized to check the gaps between pin 52 and the base and between the pin and at least one sidewall of the fixture. Steps 28 on fixture base 50 gauge the cell length. The present invention thus provides gauging apparatus for facilitating the quality assurance inspection of individual spacer cells to determine that their dimensional characteristics are such that requisite fuel rod spacing will be achieved when the cells are assembled in a spacer array. With frequent utilization of the gauging apparatus, excursions in the cell manufacturing process trending toward out-of-tolerance fuel rod spacings can be detected early and corrected. The gauging apparatus can also play a role in refining the tooling to emphasize accuracy in imparting those dimensional characteristics to the cell that are critical to achieving acceptable fuel rod spacing. It is seen from the foregoing that the objectives set forth, including those made apparent from the preceding Detailed Description, are efficiently attained, and, since certain changes may be made in the construction set forth without departing from the scope of the invention, it is intended that all matters of detail be taken as illustrative and not in a limiting sense.