Patent Number: 048572608
Section: summary

The present invention relates to automated apparatus for expediting handling, processing, and quality inspection procedures involved in the manufacture of nuclear fuel rods. BACKGROUND OF THE INVENTION A nuclear fuel rod is comprised of a column of fuel pellets sealed in an elongated cladding tube typically formed of a zirconium alloy. In the process of manufacturing nuclear fuel rods, the first major operation prior to loading the tubes with fuel pellets is to seal off one of their open ends by welding an end plug thereto in a first weld operation. In accordance with established practice, tubes are brought to a welding table where an operator utilizes equipment to mate an end plug with an open end of each of a succession of tubes. The mated items are then welded together using an inert gas-arc welder and, after the weld has cooled sufficiently, a quality assurance technician inspects the weld to determine if it meets predetermined quality control standards, including, inter alia, weld integrity and weld bead diameter. Following inspection, the welded tube is placed in the appropriate accept or reject trays, and the welding operation begins anew on the next tube. After a pre-established number of acceptable tubes have accumulated, all or a selected number thereof may be subjected to additional quality assurance tests and then transported to a fuel loading operation. It is thus seen that this welding operation is a time consuming, labor intensive process. Human participation in the welding and quality assurance operations with respect to each first end plug weld imposes a serious bottleneck on nuclear fuel rod production. This problem is exacerbated because each end plug weld must cool in the inert gas environment of the welder to avoid undesirable oxidation of the weld. Thus, otherwise productive time is spent waiting for a weld to cool rather than welding another end plug to another tube. Furthermore, because some quality assurance inspections are made on individual tubes while at the weld table, additional delays enter the process, further reducing productivity. Moreover, if the first end plug weld is created as a flush weld, rather than a bead weld, visual inspection is an inadequate test of weld integrity. Human participation in the welding and inspection operations also can have a detrimental effect on the fuel rod quality. As the amount of handling increases, so does the possibility of scratching the tube surfaces. Exterior surface scratches negatively impact fuel rod integrity and lifetime due to an increased likelihood of corrosion thereat; furthermore, they lack cosmetic appeal, which is important to some customers. OBJECTS OF THE INVENTION It is an object of the present invention to provide new and improved apparatus for welding an end plug to an open end of a nuclear fuel cladding tube. Another object of the present invention is to provide automated apparatus for welding a separate end plug to a plurality of tubes in rapid succession. Yet another object of the present invention is to provide automated apparatus of the above-character, wherein the end plug welds and the tubes are inspected for quality assurance. A further object of the present invention is to provide automated apparatus of the above-character, wherein quality assurance inspection is performed on each and every end plug weld without human intervention. A still further object of the present invention is to provide automated apparatus of the above-character, wherein productivity is dramatically increased, while labor content is minimized. It is yet a further object of the present invention to provide automated apparatus of the above-character, wherein the operations of end plug welding and the various quality assurance inspections are performed in tandem with respect to a plurality of tubes at an expeditious rate. Still another object of the present invention is to provide automated apparatus of the above-character, wherein quality assurance inspection data are collected and collated with respect to each end plug-welded tube. Yet another object of the present invention is to provide automated apparatus of the above-character, wherein the individual tubes are transported successively through the various operating stations of the apparatus in a reliable and safe manner. Other objects of the invention will in part be obvious and in part appear hereinafter. SUMMARY OF THE INVENTION The foregoing objects of the present invention are achieved by providing automated first weld apparatus for welding end plugs to nuclear fuel cladding tubes and thereafter conducting a series of inspections of each end plug weld to determine whether it meets established quality assurance standards, all in rapid succession. The apparatus includes an input queue for accumulating a plurality of tubes; a welding station where an end plug is welded to an open end of each tube; a cooldown station for rapidly cooling the end plug weld; a reader station for reading the serial number imprinted on each end plug; an inspection station where each end plug weld is ultrasonically inspected for integrity; and a tube transporter for conveying each tube to each of these stations in succession. The apparatus preferably also includes a second weld inspection station where weld diameter and end plug-tube concentricity are guaged for acceptability, and a barrier inspection station where the presence and thickness of any zirconium interior tube liner are determined. The data obtained from these various inspection stations are gathered by data acquisition means, collated on the basis of end plug serial numbers, and compared against predetermined quality control standards to determine whether the end plug welds are acceptable or rejectable. As a result of this determination, the tubes are automatically sorted into accepted and rejected lots. The automated first weld apparatus of the present invention preferably further includes a rod accumulator to which accepted tubes are conveyed for visual inspection by a quality assurance technician. These and other objects of the present invention, along with features and advantages thereof, will become apparent from the following detailed specification when read in conjunction with the accompanying drawings.