Patent Number: 053435044
Section: description

DETAILED DESCRIPTION The spring constant gauge of the present invention, generally indicated at 10 in FIG. 1, is illustrated in position to measure the spring constant of a spring 12 assembled with a pair of ferrules 14 and 16 of a nuclear fuel bundle spacer, generally indicated at 18. For details of the spacer construction, reference may be had to the above-cited Matzner et al. patent, the disclosure of which is expressly incorporated herein by reference. As mentioned above in connection with this patent, spring 12 is a double-acting loop spring of generally elliptical shape having one resilient side 12a acting in ferrule 14 and a second resilient side 12b acting in ferrule 16. Thus, spring side 12a exerts a force on a fuel rod (not shown) inserted through ferrule 14 to bias it against inwardly formed stops 20, best seen in FIG. 2, thereby maintaining the fuel rod centered within the ferrule bore. Spring side 12b performs the same function with respect to a fuel rod inserted through ferrule 16. Gauge 10 is uniquely structured to accurately measure the spring constant of the individual spring sides 12a, 12b to determine if spring 12 meets quality assurance standards. Thus, as seen in FIGS. 1 and 2, gauge 10 includes a gauge body, generally indicated at 22, having a depending cylindrical probe 24 for insertion into a ferrule, ferrule 14 in the drawing. The upper end of the gauge body is joined with a handle 25 to accommodate manual or robotic manipulation of the gauge into spring constant gauging position. An integral flange 26, extending laterally from the gauge body, serves to mount a cylindrical alignment rod 28 via a shouldered bolt 30 extending through a clearance hole 32 in the flange and threaded into a counter-sunk and tapped axial bore 34 in the alignment rod. Thus, as probe 22 is inserted into ferrule 14, alignment rod 28 is inserted into ferrule 16. The diameters of the alignment rod and the probe are each equal to the nominal diameter of a fuel rod, and thus their insertions into the ferrule bores simulate the presence of fuel rods. The shoulder of bolt 30 bottoms out on the shoulder of bore 34 before the bolt head can clamp down on flange 26 to provide for limited floating motion of the alignment rod relative to the probe body. This feature accommodates acceptably minor nonparallelism between the axes of the alignment rod and the probe as spring 12 forces them against stops 20 and into centered portions in their respective ferrule bores. A plunger 36 is received in a bore 38 formed in the probe, which is oriented transversely to probe axis 39. The plunger is loosely captured in this bore by a roll pin 40 passing through a transversely elongated hole 42 in the plunger. Thus the plunger is free for limited reciprocation in its bore. The axial location of the plunger is such that its face 43, which is of a curvature corresponding to that of a fuel rod peripheral surface, confronts and is acted upon by side 12a of the spring, while spring side 12b is being loaded by the presence of the alignment rod in ferrule 16. The plunger is then subjected to the fuel rod-centering force exerted by spring side 12a in ferrule 14. The gauge body 22, including probe 24, is formed with an axially elongated slot 44 opening at its lower end into transverse bore 38 for accommodating an elongated arm 46 pivotally mounted to the gauge body at a mid-length point by a roll pin 48. The lower end of the arm extends into a slot 50 formed in the plunger to present a contact surface in engagement with the plunger at the bottom surface of the slot. The upper end of the arm is positioned to engage the tip 51 of a miniature load cell 52 slidingly received in a transverse bore 54 formed in the gauge body. The load cell may be of a conventional button strain gauge type, such as an Omega model LCK-25 available from Omega Engineering of Stamford, Conn. A micrometer, generally indicated at 56, is mounted to gauge body 22 by means of a bushing 58 having external threads engaging a tapped hole 60 in the gauge body and internal threads engaging a threaded collar 62 of the micrometer. The spindle 64 of the micrometer extends coaxially with bore 54 into abutting engagement with the back end of load cell 52. Rotation of the micrometer thimble 66 adjusts the extension of spindle 64 in convention fashion, which is seen to be effective in linearly varying the position of the load cell in bore 54. By virtue of the mechanical coupling provided by pivotal arm 46, variation of the linear position of the load cell in its bore 54 correspondingly varies the linear position of plunger 36 in its bore 38, resulting in deflection variation of side 12a of spring 12. The micrometer can be easily calibrated to a zero deflection reading by varying the extension position of spindle 64 until the output of load cell 52 is reduced to a zero spring force reading. Then thimble 66 is rotated to produce a measured deflection of side 12a of spring 12 and a spring force reading is taken from the load cell. Preferably spring force readings are taken at several spring deflection values and analyzed to determine an appropriate spring constant value i.e., the ratio of spring force or load to spring deflection, for each of the sides 12a, 12b of the springs. As seen in FIG. 1, spring deflection readings may be taken from a micrometer display 68. Preferably however, particularly in the case of spring constant gauging in a "hot cell", spring force measurements by the load cell and spring deflection measurements by the micrometer are read out over leads 70 and 72, respectively, to a remote spring constant indicating meter 74. Moving gauge 10 between gauging positions and rotation of the micrometer thimble are effected by manually controlled manipulators or automatically controlled "pick and place" robotic apparatus. A micrometer particularly suited for application in the present invention is a Series 350-712 digimatic micrometer head available from Mitutoyo of Paramus, N.J. It will be appreciated that, rather than a simple spring constant meter, the load cell and micrometer readouts may be fed to a data acquisition system where they are processed and recorded for subsequent printout of the spring constants of the individual springs identified by their locations in spacer 18. Completing the description of the gauge construction, an L-shaped spacer cover includes a vertical portion 76 affixed to gauge body 22 by screws 78 and a lateral portion 80 having holes 82 through which alignment rod 28 and probe 24 extend. The lateral portion serves a spacing function by engaging the upper edges of the ferrules to control the depth of alignment rod-probe insertion and thus ensure that the plunger face is properly aligned with the spring side whose spring constant is to be measured. The present invention thus provides a compact gauge which is conveniently inserted into the multiple ferrules of a nuclear fuel bundle spacer in succession to accurately measure the spring constants of the multiplicity of springs in the spacer. This quality assurance test can be performed expeditiously to qualify spacers for service in a reactor. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification be considered as exemplary only with the true scope and spirit of the invention being indicated by the following claims.