Patent Number: 045434883
Section: summary

The present invention relates to an exchangeable basket for a container for the transportation and/or storage of spent nuclear fuel elements. The basket serves as a storage support for the fuel elements disposed in the container and comprises compartments which are shaped to closely conform to the exterior dimensions of the fuel elements. An insertion or storage basket is normally required when spent nuclear fuel is transported or stored in a container in order to simultaneously provide for receiving spent nuclear fuel elements and maintaining them in a desired position in the container for during transportation and also during storage. The respective necessary fuel element positions are formed as compartments in the basket into which the fuel elements are inserted. Each compartment's cross-section is designed in shape and dimensions according to the type of fuel element to be inserted so that the fuel elements can be inserted and removed without difficulty by remote control apparatus. The insertion or storage basket must be sufficiently stable that it can withstand the mechanical and thermal loads experienced during transportation. Also, the containers must be so constructed that the fuel elements to be conveyed will not be damaged during transportation and subsequent handling. In the prior art, such baskets are normally constructed as pure steel supports or, as massive blocks of non-ferrous metal. The compartments of the blocks are produced mechanically and in some cases they are steel clad. Steel frameworks are suitable as storage baskets if there is located in the baskets a corresponding liquid which can carry off from the container walls the residual heat produced from the fuel elements. The steel framework can consist of boron steel wherein the boron serves as a neutron absorber. The massive, non-ferrous constructions having compartments are suitable as storage baskets since they make it possible to draw off the residual heat produced since such material is a good heat conductor and does not require an additional heat transfer medium. Preferably, they consist of aluminum, copper or an alloy thereof. These alloys likewise can include boron or cadmium to act as neutron absorbers. Also the following materials are usable: cast iron, brass, bronze, lead, magnesium, uranium, concrete, argillaceous earth, ceramic, wood, carbon, resin. However, in the previously known storage containers, there have been a number of disadvantages. While the steel frames are stable at the high temperatures involved, they exhibit poor heat conducting properties. On the other hand, the block-type frames, at high temperatures, have low tensile strength but still have good heat conducting properties. Also, the production of these types of baskets has been very expensive since the demands on the compartments are very high in terms of the tolerances, grade of materials used and the surface qualities demanded. It is an object of the present invention to provide a storage basket for containers for transporting and/or storing spent nuclear fuel elements which combine the tensile strength of the steel frames with the good heat conductivity of the block-type frames made of non-ferrous metals. As a result, an insertion basket can be formed which resists both the mechanical and thermal stresses encountered and which makes good use of the heat conductivity of the material to remove the residual heat. SUMMARY OF THE INVENTION According to the present invention, there is provided a storage basket wherein appropriately shaped steel tubes are embedded with connecting elements in a casting of a good heat conductor such as a non-ferrous metal or a non-ferrous alloy. The manufacture is carried out in such a manner that the stainless steel tubes having circular or angular cross-sections are connected by connecting elements in a framework and then the framework and tubes are surrounded by casting with a non-ferrous metal. Preferably aluminum, copper or their alloys is used. The steel and non-ferrous metals can, if it is necessary, be provided with neutron absorbers. The present invention has the advantage that the steel framework, can be supported at the inner wall of the container. This concept insures great mechanical strength at high temperature. The non-ferrous metal block, being a good heat conductor, solves the problem of dealing with the residual heat of the spent fuel elements. Also, in the manufacture, the heat treatment of the inner surfaces of the steel tubes, the centering and the exact alignment of the tubular compartments, all can be carried out before the casting is effected. This is of a special significance if the cross-sections of the compartments are not circular. By pouring in the cast material, any gap formation is avoided between the compartments and the block which would result in poor heat transfer. The heat transfer by radiation from the fuel elements to the lodgements of the basket is substantially better for steel inserts than for non-ferrous untreated materials such as aluminum.