Patent Number: 045270651
Section: summary

FIELD OF THE INVENTION The invention relates to cast steel or cast iron containers for the long-term storage of irradiated nuclear reactor fuel elements or other radioactive materials. The containers have an external corrosion-resistant protective layer, preferably of a material such as ceramic, graphite or enamel. BACKGROUND OF THE INVENTION Containers for the long-term storage of radioactive materials must be mechanically stable, corrosion-resistant and sealed. The vessel of the container is therefore made from a material selected from the group including cast steel or cast iron to ensure that the container has the required mechanical stability. The resistance of cast steel or cast iron to corrosion is unsatisfactory for the purposes of long-term storage. It has therefore already been proposed that a corrosion-resistant protective layer be applied to the exterior of the cast steel or cast iron vessel of the container. Ceramic, graphite or enamel are suitable for forming the protective layer because of their good resistance to corrosion. It is also possible to use metallic corrosion-resistant layers which are applied galvanically or by thermal spraying. The operation of coating the large surface area of the vessel of the container is a technically expensive one. Due to the different properties of the material of the protective layer and the metal base body of the vessel of the container, there are differences in expansion, which result in stresses between the two contiguous surfaces. There is thus the danger of stress cracks being formed and the protective layer becoming detached. SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the invention to provide a container of the kind described above which has a corrosion protective coating that is simpler to apply and that is less sensitive to differential expansion stresses of the two contiguous materials. A container of the invention for the long-term storage of radioactive materials such as irradiated nuclear fuel elements includes a vessel-shaped base body made of a material selected from the group including cast iron and cast steel. The base body has an outer surface and an opening through which the radioactive material to be stored therein is passed. According to a feature of the invention, rib means made of corrosion-resistant material is formed on the surface of the base body to partition the same into a plurality of surface segments. A protective corrosion-resistant layer covers each of the surface segments. A cover is adapted for sealing the opening of the vessel-shaped body. The rib means can be a plurality of ribs projecting upwardly from the surface of the base body; and the protective coating can be made of a material selected from the group including: ceramic, graphite and enamel. The ribs which project from the outside surface of the base body divide the outer surface of the base body of the container vessel into surface segments. Each surface segment is of a smaller area than the entire surface of the vessel and can therefore be more easily coated than the entire vessel. Differential expansion stresses between the corrosion protective layer and the base body can be absorbed by the ribs. The ribs also serve to enhance the adhesion strength of the corrosion protective layer because each surface segment of the corrosion protective layer is held fast between the ribs. In an advantageous embodiment of the invention, the ribs are metal ribs which are applied to the surface of the base body of the vessel by the process of surface-layer welding and are made of a cold-weldable corrosion-resistant material. This process is described, for example, in the text "Handbuch der Schweisstechnik" by J. Ruge, Volume I, Second Edition, page 170, published by Springer-Verlag (1980). It is noted that a cold-weldable material is a material which can be welded without the necessity of conducting a follow-up heat treatment operation. A cold-weldable corrosion-resistant material of this kind of which the ribs can be made is NiMo16Cr16Ti, which is known in Germany under the trade name "Hastelloy C-4." The surface segments which are thus formed between the ribs can now be coated with a corrosion-resistant material for example by enamelling or thermal spraying. If the metal ribs project beyond the surface of the corrosion-resistant protective layer, the latter is protected from mechanical loadings. It has been found particularly advantageous for the edges of the vessel to be provided with rib planting or cladding. The edges of a container are generally required to withstand a higher mechanical loading than the surfaces of the container. Applying corrosion-resistant protective layers at the edges of the container can lead to difficulty because it is possible that the protective layer can rupture and break away from the vessel body at these edges.