Patent Number: 059784300
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings particularly to FIG. 1, there is illustrated a schematic representation of a nuclear fuel bundle generally designated 10 comprised of a lower tie plate 12, a pair of water rods 14 secured at their lower ends to the tie plate 12, spacers 16 secured to the water rods 14 at spaced positions therealong and fuel rods 18 received through openings in the spacers 16 and secured to the lower tie plate 12. The water rods 14 are each comprised of essentially two sections, a lower central tube 20 and a tie bar assembly 22. The central tube 20 and tie bar assembly 22 of each water rod are secured to one another in a length adjustable manner by a structure which does not form part of the present invention. Suffice it to say that the lengths of the water rods 14 are adjustable in the axial direction within a limited range. As indicated previously, it is important in the present invention to ensure that the lengths of the water rods 14 from the upper surface of the lower tie plate 12 to the underside of seats 24 at the upper ends of the tie rod assemblies 22 are within designed lengths. Referring to FIGS. 2-5, the length gauge of the present invention includes an indicator location block 26, a digital indicator gauge 28, a standards rod 34 and an indicator set block 37. The digital indicator gauge 28 has a digital readout 30 and a movable extension pin 32. Location block 26 includes a pair of generally semi-cylindrical openings or recesses 38 open to opposite sides of body 26. The upper end of body 26 has a boss 39 with a central aperture 40 for receiving a boss 42 on gauge 28. The gauge 28 and extension pin 32 may be suitably secured to the boss 39 at location 36. Block 26 has a first reference surface 43 for engaging in use the seat 24 (in FIG. 1) of a tie rod assembly. The tip of the movable extension pin 32 constitutes a second reference surface 44. The standards rod 34 comprises an elongated gauge lab length certified cylindrical rod. The certified length of rod 34 from the face of the lower tie plate 12 on FIG. 2 to the top, i.e., flat surface 45, of the standards rod is an accurate specified length which when combined with the length between the first and second reference surfaces 43 and 44, respectively, on the indicator location block and gauge, with the gauge zeroed out after calibration, is the same as the specified length of the water rod from the face of the lower tie plate 12 to the seat 24. The standards rod 34 has a reduced diameter portion 46 at its lower end for reception in an opening not shown in the upper surface of the lower tie plate 12, such that the shoulder 48 abuts the tie plate surface. The opposite end of the standards rod 34 includes a hardened bearing surface 45 for receiving the tip 44 of the movable extension pin 32 of the gauge. Referring to FIGS. 3 and 4, the indicator set block 37 comprises a flat plate 50 having a pair of cylindrical projections 52 substantially straddling a reduced length cylindrical projection 54. The upper surfaces of the projection 52 and 54 constitute first and second datum surfaces, 56 and 64 respectively, of known distance between such surfaces used to provide the gauge with a predetermined indication; for example, as a zero position. To calibrate the gauge, one of the projections 52 is disposed in a recess 38 of the indicator location block 26 with its datum surface 56 bearing against a third reference surface 58 formed by a shoulder in part defining the recess 38. With the first datum surface 56 on the indicator set block 37 engaged against the third reference surface 58 on the indicator location block 26, and the second reference surface comprising the tip 44 of movable extension pin 32 bearing against the second datum surface 64 on the indicator set block, the gauge 28 can be zeroed out, i.e., manually adjusted to provide a zero reading. Prior to assembling the fuel bundle, the water rods 14 in FIG. 1 are secured to the tie plate 12 in a known manner, the assembly being positioned in a horizontal orientation. The length gauge is then employed to measure the lengths of the water rods so that adjustments of the axial length of the water rods can be made to meet the design lengths. To accomplish this, the reduced end 46 of the standards rod 34 in FIG. 2 is inserted into an opening of the tie plate 12 until shoulder 48 abuts the top surface of the tie plate. The indicator location block 26 is applied below the seat 24, i.e., a datum surface of one of the water rods, such that the arcuate recess 38 receives the reduced diameter upper end of the tie bar assembly 22 as illustrated in FIGS. 1 and 2. In that configuration the second reference surface, i.e., the tip 44 of the movable extension pin 32, bears against the hardened upper surface 45 of the standards rod 34. With the first reference surface 43 bearing against the seat 24 and the second reference surface 44 of movable extension pin 32 bearing against the upper end 45 of the standards rod 34, the gauge 28 will indicate any deviation of the length of the water rod from a designed length corresponding to the length of the standards rod plus the predetermined distance between the second reference surface 44 and the seat 24. Should a deviation be indicated by the digital readout 30 outside of required tolerances, the water rods must be adjusted in axial length to more precisely conform to the design length. Once the water rods have been adjusted in length, the gauge assembly (26 and 28) and the standards rod 34 are removed from the partial assembly. Next, the bundle 10 is assembled starting with the installation of the spacers 16 to the water rods 14. It will be appreciated that the spacers 16 are secured to the water rods 14 at axially spaced locations along the length of the fuel bundle 10 with each spacer having openings as conventional for receiving the water rods and the fuel rods 18. After securement of the spacers to the water rods, the standards rod is installed in the fuel bundle. To accomplish this, and referring to FIG. 6, a shaped end, for example a bullet nose 64, is installed on the reduced diameter end 46 of the standards rod 34. The standards rod is then inserted from the top of the fuel bundle through openings in the spacers toward the lower tie plate 12. The shaped end 64 facilitates insertion of the standards rod through the openings of the spacers. When the end of the standards rod extends in the region between the lowermost spacer and the lower tie plate 12, the shaped end 64 is removed and the reduced end portion 46 is inserted into the opening of the tie plate similarly as before, as illustrated in FIG. 7. With the standards rod in place, the fuel rods 18 are then inserted through the openings in the spacers and secured to the lower tie plate 12. If desired, an additional verification of the lengths of the water rods can be made at this time, as described in the previous paragraph. Lastly, a suitable lifting tool, not shown, is installed on the bundle to move the bundle from the horizontal assembly position to a vertical inspection stand, not shown. With the fuel bundle in a vertical orientation, and with the lifting tool removed, the gauge and indicator location block are applied to each water rod and measurements are taken similarly as previously described. Thus, any deviation of the length of the water rod from its designed length will be indicated by the gauge 28. Once the measurements are made and the water rods are verified to lie within the designed length, the gauge is removed and the standards rod is withdrawn axially from the tie plate and spacers. It will be appreciated that the standards rod is inserted in one of the openings of each spacer which is otherwise occupied by a fuel rod. Once the standards rod has been removed, a full length or part length fuel rod is inserted in the position previously occupied by the standards rod. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.