Patent Number: 055132308
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a fuel rod for a nuclear reactor, having a metal cladding tube being filled with nuclear fuel, a metal seal plug, locking plug or stopper being welded to one end of the tube and in particular being formed of the same metal, and an annular bead on the outer surface of the cladding tube at a transition point between the cladding tube and the seal plug. The invention also relates to a welding apparatus for producing the fuel rod. Such a fuel rod is already typical and its annular bead has a sharp annular gradient. In other words, the cross section of the annular bead forms an acute triangle with an acute angle located at the annular gradient. Such a fuel rod can be produced in a welding apparatus with an electrode in which there is a bore for receiving one end of a cladding tube. The bore is chamfered, forming a frustoconical void that tapers toward the inside, on an end of the bore that faces toward a counter electrode which is displaceable relative to the aforementioned electrode and is intended to hold the seal plug. The frustoconical void determines the shape of the annular bead that forms from solidified welding melt when the seal plug is permanently welded to the cladding tube. The welded connection between the cladding tube and the seal plug is considered perfect if the frustoconical void of the electrode for the cladding tube is filled to a predetermined extent during welding with material of the cladding tube and the seal plug, which is ascertainable by experimentation. After the welding, the quality of the weld can be determined by measuring the height of the gradient of the annular bead at the weld between the seal plug and the cladding tube of the fuel rod. In order to produce nuclear reactor fuel assemblies that can be inserted into a nuclear reactor, the fuel rods must be threaded into a mesh of spacers, which as a rule are lattice-like. The annular bead at the weld between the cladding tube and the seal plug of the individual fuel rods is a hindrance to the threading operation. Therefore, after the quality of the weld has been measured and ascertained, the annular beads are mechanically machined down, for instance by being milled off, until it can be assumed that they will no longer hinder the threading of the fuel rods into the spacers. In the mechanical machining down process, damage to the cladding tube can occur, causing a fuel rod to be rejected. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a fuel rod for a nuclear reactor and a welding apparatus for producing the fuel rod, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which eliminate the operation of mechanical machining down. With the foregoing and other objects in view there is provided, in accordance with the invention, a fuel rod for a nuclear reactor, comprising a metal cladding tube being filled with nuclear fuel and having ends, an outer surface, and a longitudinal axis; a metal seal plug being welded to one of the ends of the cladding tube at a transition point and in particular being formed of the same metal, defining an annular bead on the outer surface of the cladding tube at the transition point; the annular bead having a cylindrical outer jacket surface with jacket lines being substantially parallel to the longitudinal axis of the cladding tube; and the annular bead having material being formed of the metal of the cladding tube and the metal of the seal plug. The outside diameter of the cylindrical jacket surface of the annular bead can be selected from the outset in such a way that threading the applicable fuel rod into cells of spacers without mechanical post-machining of the annular bead is possible. On the other hand, a conclusion as to the quality of the welded connection between the cladding tube and the seal plug of the applicable fuel rod can be drawn from the relative forward feed between the electrode having the cladding tube and the counter electrode having the seal plug as these parts are welded together. In accordance with another feature of the invention, the annular bead has at least two humps on the cylindrical outer jacket surface, each extending along one of the jacket lines of the jacket surface. In accordance with a further feature of the invention, the annular bead is resolidified from a welding melt. In accordance with an added feature of the invention, the cylindrical outer jacket surface of the annular bead is mechanically unmachined or unworked. In accordance with an additional feature of the invention, the cylindrical outer jacket surface of the annular bead has an encompassing depression formed therein in the annular bead containing the material of the cladding tube having the same microscopic structure as in the cladding tube. With the objects of the invention in view, there is also provided a welding apparatus for producing a fuel rod, comprising an electrode having a through bore formed therein for receiving one end of a cladding tube; and a counter electrode being displaceable relative to the electrode for holding a seal plug to be welded the one end of the cladding tube; the electrode having a cylindrical step or shoulder formed therein at an end of the through bore facing toward the counter electrode, the cylindrical step having a diameter being greater than the diameter of the through bore. With such a welding apparatus, a fuel rod according to the invention can be manufactured simply and economically. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a fuel rod for a nuclear reactor and a welding apparatus for producing the fuel rod, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.