Patent Number: 047023910
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a containmant with a long-time corrosion resistant protective cover for tightly sealed containers with highly radioactive content such as steel containers enclosing radioactive waste molten into glass or burnt-out fuel elements of nuclear reactors. The invention also is concerned with the manufacture of a mechanically, chemically and thermally stable packaging including a safe barrier for the isolation of environmentally dangerous materials in geologic formations. It is concerned in this connection with the final storage of highly radioactive waste encased in molten glass in deep bore holes of salt formations. Highly radioactive glass-encased waste has not yet been placed into final storage. The packaging used so far for highly radioactive waste materials does not fulfill the barrier requirements for long-time isolation in final storage locations. The barrier systems presently employed, which include outer corrosion protection, have the following disadvantages: The corrosion protective enclosure is not in full contact with the steel container which forms the structure resistant to mechanical damage. The enclosure is therefore subject to damage as a result of thermal expansion or by exposure to outer forces as they may be caused by collapse of the storage bore. The enclosure is especially sensitive in areas where it is not in contact with the container, as adjacent the lid and cylinder section of the container and adjacent the bottom and cylinder section of the container. With this kind of corrosion protection, which is applied in the form of a protective layer, welding of narrow-groove joints must be performed under cover gas in order to provide for weld seam quality with regard to corrosion resistance which is comparable with non-welded corrosion protective structures. However, sufficient cover gas protection cannot be guaranteed under the given conditions. The requirements for a corrosion protection structure which is tightly joined to the inner steel container and which permits good cover gas flushing of the weld joint are actually opposing one another. Stacking of such containmants in a drill hole causes crevice corrosion problems since the corrosion protective structure of one container comes in direct contact with the corrosion protective structure of the container stacked on top. If a grapping structure is arranged above the containers they cannot accept the load upon stacking. Also the provision of a grapping structure represents a weak point for the containment as far as corrosion protection is concerned. Fixing of such a containment in a transport container in which the lid and the bottom of the containment are at the same time top and bottom of a radiation shielding structure is not possible without adversely affecting the corrosion protection means. It is the object of the present invention to provide a long-time corrosion protection enclosure for containments with highly radioactive content which does not have the disadvantages referred to above and which insures safe enclosure of the highly radioactive materials over a long period of time. SUMMARY OF THE INVENTION Such safe enclosure is insured by a containment with a long-time corrosion resistant protective cover for a container which retains the highly radioactive content. The containment consists of a thick-walled metallic containment cylinder having a bottom and lid mounted at its opposite lower and upper ends for closing the containment cylinder. The containment cylinder and the bottom and lid are fully surrounded and sealed-in by corrosion protective linings and layers which are preferably explosion welded onto the cylinder and the bottom and lid surfaces. Additionally there are provided cover and bottom plates which are joined to the lid and bottom, respectively, and have diameters larger than the containment cylinder and the lid and bottom so that they project radially to thereby prevent mechanical damage to the corrosion protective layers and liners especially when the containment is lowered into a deep hole drilled into the ground for the reception of the containment for long-term storage of the radioactive materials therein. Packaging of radioactive material in accordance with the present invention fulfills optimally all the requirements for corrosion protection and also for mechanical, thermal and chemical stability postulated for final storage in deep bore holes of salt formations. The disadvantages of prior art arrangements are avoided, especially by the following features: A lining of corrosion resistant material such as a titanium-palladium alloy is tightly applied by outside explosion plating. This avoids the requirement for flushing with protection gases at the weld seams and certainly provides for a tight fit of the corrosion protective linings. Maximum surface quality of the closure seams is obtained by electron beam welding in a vacuum and subsequent application of an outer smooth weld bead. The omission of the use of undesirable gases as well as the high surface quality of the weld seam substantially increase corrosion resistance. The bottom and the cover lid of the containment are essentially identical and therefore may be welded with identical welding parameters. The bottom closure seam which, after welding, is still accessible may therefore be utilized as a measure for the quality control of the cover lid welding seam which is applied remotely under hot cell operating conditions. The top and bottom steel plates which are welded onto the container have a diameter which is somewhat larger than the bottom and top ends of the container and are provided with corrosion protection such as a layer of a titanium-palladium alloy which is applied by explosion plating. The arrangement permits stacking of the containers in an end storage bore without fission corrosion problems and without the occurrence of tension concentration points at the corrosion protection structure. The bottom and top steel plates with the corrosion protective layers explosion welded to one side thereof which are welded to the container also permit fixation of the whole enclosure in a transport container without adverse effects for the corrosion protection. The arrangement is the same at the top and bottom of the transport container. A gripping structure formed by a recess in the top plug structure permits stacking of the containments in final storage bores.