Patent Number: 048428086
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear fuel rods for use in nuclear reactors and, more particularly, is concerned with a system and method for collating nuclear fuel pellets so as to facilitate subsequent filling of fuel rods with pellets in multiple zones of different nuclear fuel enrichments. 2. Description of the Prior Art In a typical nuclear reactor, the reactor core includes a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include top and bottom nozzles with a plurality of elongated transversely spaced guide thimbles extending longitudinally between and connected at opposite ends to the nozzles and a plurality of transverse support grids axially spaced along the guide thimbles. Also, each fuel assembly is composed of a multiplicity of elongated fuel elements or rods transversely spaced apart from one another and from the guide thimbles and supported by the transverse grids between the top and bottom nozzles. The fuel rods each contain fissile material in the form of a plurality generally cylindrical nuclear fuel pellets maintained in a row or stack thereof in the rod. The fuel rods are grouped together in an array which is organized so as to provide a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. Up to the present time, generally a given fuel rod has been filled with nuclear fuel pellets of the same enrichment. In filling a typical fuel rod, pellets of the same enrichment are continually fed from supply trays into the fuel rod until the specified depth of fill has been achieved. The supply trays are used up completely. A partial tray left after completing a batch of twenty-five fuel rods is used to start the fill of the next batch. Various systems have been used in the past to fill the fuel rods with fuel pellets. Representative of the prior art are the systems disclosed in U.S. Pat. Nos. to Gerkey (4,158,601)--assigned to the assignee of the present invention--and Gheri (4,495,146), and Japanese Pat. No. 61-4999 to Mitsubishi. Recently, nuclear fuel rods with pellets in multiple zones of different enrichments have been introduced. These new zoned fuel rods contain short lengths of "blanket" pellets at each end. The fuel rods additionally have pellets grouped within from three to five zones of different enrichments between the end zones of blanket pellets. Pellets for filling these enrichment-zoned fuel rods will first need to be assembled into the desired sequences of enrichment zones before filling of the fuel rods can commence. One approach to assembling fuel pellets in the desired sequence of enrichment zones for filling a fuel rod is by manual effort. However, this approach envisions individual handling of each pellet which is highly labor-intensive and time-consuming and subject to human error. A much more desirable approach is to assemble the different zones of fuel pellet by use of a highly-mechanized and automated system which would be substantially free of human error. Consequently, a need exists for an automated system capable of assembling pellets of different enrichments into the desired sequence of enrichment zones of pellets so that specified sequences of pellets will be produced for subsequent loading into fuel rods. SUMMARY OF THE INVENTION The present invention provides a fuel pellet collating system and method designed to satisfy the aforementioned needs. The collating system and method of the present invention is adapted to handle and transfer trays of pellets of various enrichments, to measure, record, and sum the lengths of the various pellet zones, and to load these measured rows or stacks of zoned pellets into a collated storage and transport cabinet so that pellets in the specified sequence of enrichment zones will be subsequently loaded into the fuel rods. In the pellet collating system and method of the present invention, a multiplicity of rows of pellets, for instance twenty-five rows, are handled simultaneously. Accordingly, the present invention is directed to a system of collating nuclear fuel pellets which comprises: (a) means for positioning a plurality of pellet supply trays and a plurality of pellet storage trays, each supply tray being adapted to support in at least one row thereon a plurality of pellets of an enrichment different from the enrichments of pellets on at least some other of said supply trays, each storage tray being adapted to support in at least one row thereon a plurality of pellets of an enrichment different from the enrichments of pellets on at least some other of said storage trays; (b) a pellet collating line including a serially-arranged pellet input station, pellet measuring and collating work station and pellet output station; (c) means for transferring supply trays one at time between the tray positioning means and the input station and for transferring storage trays one at a time between the tray positioning means and the output station; and (d) pellet collating means disposed adjacent the pellet collating line and being operable for moving pellets in the at least one row thereof onto the work station from a given one supply tray on the input station, for measuring a desired length of pellets on the work station and separating the measured length of pellets from the remaining pellets, if there be any, for moving the measured length of pellets from the work station onto a given one storage tray on the output station, and for moving the remaining pellets, if there be any, from the work station back onto the one given supply tray on the input station. More particularly, the pellet collating means includes means in the form of an input sweep head disposed adjacent the input station and being operable for sweeping pellets in the at least one row thereof onto the work station from the one pellet supply tray on the input station, means in the form of a gripping and measuring head disposed adjacent the work station and being operable for measuring the desired length of pellets and separating the measured length of pellets from the remaining pellets, if there be any, and means in the form of an output sweep head disposed adjacent the output station and being operable for sweeping the measured length of pellets from the work station onto the one pellet storage tray on the output station. One of the input and output sweep heads and of the gripping and measuring head is also operable to sweep the remaining pellets, if there be any, from the work station back onto the one pellet supply tray on the input station. Also, the present invention is directed to a method of collating nuclear fuel pellets which comprises the steps of: (a) supporting a plurality of pellet supply trays and a plurality of pellet storage trays at a tray positioning station, each of the supply trays supporting in at least one row thereon a plurality of nuclear fuel pellets of an enrichment different from the enrichments of pellets on at least some other of the supply trays, each of the storage tray being adapted to receive in at least one row thereon a plurality of nuclear fuel pellets of an enrichment different from the enrichments of pellets on at least some other of the storage trays; (b) transferring one supply tray from the tray positioning station and disposing the same on an input station of a pellet collating line; (c) transferring one storage tray from the tray positioning station and disposing the same on an output station of the pellet collating line; (d) sweeping pellets in the at least one row thereof from the one supply tray on the input station onto a work station of the pellet collating line located between the input and output stations thereof; (e) measuring a desired length of pellets in the at least one row thereof on the work station and separating the measured length of pellets from the remaining pellets, if there be any, in the row thereof; (f) sweeping the remaining pellets, if there be any, in the row thereof from the work station back onto the one supply tray on the input station; (g) transferring the one supply tray and remaining pellets, if there be any, thereon from the input station back to the tray support station; (h) sweeping the measured length of pellets from the work station onto the one storage tray on the output station; and (i) transferring the one storage tray and measured length of pellets thereon from the output station back to the tray positioning station. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.