Patent Number: 047085711
Section: summary

FIELD OF THE INVENTION My present invention relates to a method of and to an apparatus for the introduction of metallic wastes into a melting furnace, to a method of operating a furnace for the melting of radioactive metallic wastes received in a transport vessel, and to an apparatus for melting radioactive metallic wastes as may be contained in a transport vessel having a cover. BACKGROUND OF THE INVENTION It is known to store or package metallic wastes from radioactive installations such as nuclear power plants and other installations having nuclear reactors in metallic transport vessels with transport vessel covers, the radioactive waste being sealed in such vessels at least for transport purposes. It is also known to melt such radioactive wastes to reduce the overall volume and to form a solidified mass from the melt which can be cast as an ingot or like structure in a suitable receptacle for terminal storage. In this form, radioactive materials tend to leak or otherwise pass significantly more slowly from the solidified mass. In this connection reference may be had to German Patent Document - Open Application DE-OS No. 25 54 257 in which a transport vessel of this type for receiving radioactive wastes can be filled at a nuclear power plant and melted at a location distal to that plant. A melting furnace is described in German Patent Document -Open Application DE-OS No. 30 02 695 which is formed with a gate so that the transport vessel can be emptied into the gate and the radioactive waste then discharged into the furnace upon the opening of the slider of this gate. It has been found that this system has the disadvantage that radioactive particles and what may be referred to as vagabond radioactivity can be liberated during such furnace filling processes. As a consequence, the furnace and the filling equipment therefore can or must form a radioactive cell which is constantly at a high level of radioactivity so that it must be especially constructed to prevent the escape of vagabond radioactivity to the environment. This is, of course, expensive and such systems are difficult to operate without at least some leakage of radioactivity. OBJECTS OF THE INVENTION It is the principal object of the present invention to provide a method of introducing radioactive wastes into a melting furnace whereby these disadvantages are obviated. Another object of the invention is to provide an apparatus for carrying out the improved method. It is also an object of my invention to provide an improved method of operating a furnace for the melting of radioactive metallic wastes whereby the drawbacks of earlier systems are obviated and, in particular, wayward radioactivity no longer can develop even without the use of expensive equipment to prevent against it. Yet another object of the invention is to provide a method of and an apparatus for the melting of radioactive wastes which can be utilized without special precautions but with, of course, appropriate shielding, in any conventional foundry application without having to provide a special radioactive cell for the purpose. SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention in which a transport vessel for the metallic radioactive wastes and which preferably is metallic itself so that it can be melted along with the waste, is inserted from above in a furnace charging container which is upwardly open and has a mouth adapted to be closed by a laterally retractable container cover. The container is then inverted about a horizontal axis to form the gate which is placed upon the mouth of the melting oven upon a seating ring which can be provided with a gate slider of this mouth and adapted to close the mouth of the oven or furnace. Upon the rotation of the container through 180.degree. about a horizontal axis to invert it, the container cover can be laterally retracted and the gate slider of the mouth of the furnace likewise horizontally withdrawn to permit the transport container with the radioactive waste to pass directly into the furnace. The furnace is then placed in operation and the contents thereof can be inductively melted under vacuum. The transport vessel generally consists of a thin wall cast vessel which is readily smelted in the smelting furnace. When the transport vessel is introduced into charging container, therefore, depending upon the nature of the radioactive waste, there generally is no danger that vagabond radioactivity will be emitted if the transport vessel has had its cover previously removed. However, while in one embodiment of the invention the cover of the transport vessel is removed, in another embodiment of the invention, the transport vessel has its cover merely loosened before the cover of the container is closed. In the latter case, the cover falls with the transport vessel into the furnace and is melted with the waste and the transport vessel therein. It is also possible in accordance with another embodiment of the invention to leave the transport vessel cover sealingly attached to the transport vessel, i.e. to do away with the step of loosening the vessel cover, in which case the invention provides for the perforation of the bottom of the transport vessel once it has been sealed in the container and the container has been inverted. The piercing of the bottom of the transport vessel can be effected by a fluid operated perforation punch adapted to form at least one hole sufficient to permit venting of gases from the transport vessel during the melting step so that a detrimental explosion or bursting of this vessel does not occur. The vent hole thus provided allows depressurization of the interior of the transport vessel within the melting furnace itself and so that there will be no dispersal of radiation to the environment through the vent hole. The advantages of the invention should be immediately apparent in that vagabond radioactivity no longer can escape into the environment utilizing the method and apparatus of the invention. There is no need to provide special hot cells or special constructions for the apparatus other than the normal radioactive shielding which one provides around the melting furnace to prevent escape of radiation through the walls thereof. Utilizing conventional techniques, a siphon arrangement in the form of a U-shaped tube can be used to transfer the melt to a receptacle in the form of an ingot mold and which simply provides the form for the ingot to be cast or is adapted to continue to receive the ingot after it has solidified as a final container for the radioactive waste. The ingot receiving receptacle has one leg of the U-shaped tube extending into it and is sealed, suction being applied thereto to draw the melt upwardly through the other leg of the U-shaped tube, this latter leg being introduced into the melt. Advantageously in the apparatus aspects of the invention, a furnace charging carriage is provided which is formed with means laterally supporting the container to enable it to be swung through 180.degree. from an upright position in which the container receives the transport vessel with or without the cover in the manner described, and enables the container to be inverted about the horizontal axis into a position in which the mouth of the container is turned downwardly. A guide can be provided whereby the outriggers which pivotally support the container can move along the charging carriage from the position in which the container receives the transport vessel into a position in which the mouth of the container can rest upon the seating ring at the furnace mouth. Advantageously, the means for retracting the container cover and the means for retracting the slider gate at the mouth of the furnace are angularly offset through 90.degree., the cover and the slider moving at right angles to one another to open the passage from the container into the furnace. Advantageously, the container bottom opposite its mouth is formed with a perforating device for perforating the bottom of the transport vessel in the manner described.