Patent Number: 052157067
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIGS. 1, 2 and 3, shown there is an ultrasonic testing device 10 for determining the functional operability of individual fuel rods 21 of a fuel rod assembly 20. The fuel rod assembly 20 is supported by an upper plate (not shown) which is attached to an overhead crane. The assembly 20 is arranged within an assembly positioning channel 25 which is a U-shaped construction having a retractable side plates 22 and a base plate 23. The assembly is preferably arranged as a rectangular grouping of fuel rods. As discussed previously, the rods 21 contain uranium dioxide and helium gas disposed within a metallic cladding (typically zirconium alloy or stainless steel). The ultrasonic testing for water entry within the rods is performed by juxtaposition of ultrasonic probes 14 to each individual fuel rod within the assembly in succession. The probes 14 test only one lower portion ("test spot") of each rod. It is not necessary to test the entire rod. The ultrasonic probes 14 (here 4 are shown operating together) are movable in a horizontal plane by X-Y table 12. The X-Y table 12 positions the ultrasonic probes 14 by virtue of drive motors 13. Thus, the probes may be inserted and retracted from the fuel rod assembly to enable testing of each fuel rod in the assembly. Control over movement of the probes 14 is effected from a control console (not shown) connected to the X-Y table via cable connection 24, by depressing appropriate control switches. The present invention utilizes a plurality of parallel guide bars 31 for insertion between individual fuel rods prior to the start of any ultrasonic testing of the fuel rods. The guide bars 31 are part of a guide assembly 30 which includes holding base 34, bars 31, channel element 32, flange 33, front guide 35, lifting bale 36, hydraulic cylinder 37 and pins 38. The guide bars 31 are preferably constructed of heat treated Inconel which is provided with a hard coat of titanium nitride to minimize surface abrasion. The guide bars 31 are held in relative position by two pins 38 through holding base 34. A front guide 35, which is fixed in position relative to the movable guide bars 31, serves to maintain the bars in relative position as they are caused to move in and out of the fuel assembly. The alignment guide 30 is supported by a channel element 32 which is affixed via flange 33 to frame 11 of the X-Y table. Twin rail linear bearings 39 (see FIG. 3) are affixed to the underside of the channel element 32 for supporting the guide bar holding base. Fixed front guide 35 is also attached to the underside of the channel element 32. Power for moving the guide bars in and out is provided by a hydraulic cylinder 37. The entire alignment guide 30 is removable from the frame 11 with the assistance of lifting bale 36. In operation, it has been found useful to provide a TV camera 15 forming part of TV monitoring system to assure proper alignment of guide rods 31 between the fuel assembly fuel rods. It should be noted that the guide rods 31 are preferably inserted into the fuel assembly immediately above the test spot where the ultrasonic probes enter the fuel assembly. This temporarily skews the fuel rod arrangement in the fuel assembly into alignment prior to insertion of the ultrasonic probes. The guide bars are preferably inserted completely through a fuel assembly prior to ultrasonically testing each individual row of fuel rods. In a preferred arrangement as shown in FIGS. 4 and 5, the guide bars 31 are in the form of elongated blades having a small width dimension "A", corresponding to inter-rod spacings and a substantial larger height dimension "B". In one embodiment, the height dimension was approximately 0.75 inches. The width dimension will vary from one fuel rod to another but will typically be in the range of 0.061 inches to 0.124 inches. A preferred form of the fixed front guide 35 is illustrated in FIG. 6 and 7. In one set of tests, six fuel assemblies were retested employing a guide assembly according to the invention, after each showed failure of one fuel rod by ultrasonic testing without the assembly. Following retest with the guide assembly, four fuel assemblies tested "good" (functionally operable) while only two were confirmed to have a failed fuel rod. While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention.