Patent Number: 042788927
Section: summary

FIELD OF THE INVENTION The present invention relates to a shielding transport or storage receptacle for radioactive wastes and, more particularly, to a receptacle of the type used to store radioactive substances such as irradiated nuclear reactor fuel elements with a minimum of release of radiation into the environment. BACKGROUND OF THE INVENTION In the above-identified copending application and elsewhere, a transport and storage vessel for radioactive wastes, especially for irradiated nuclear reactor fuel elements, has been made known which comprises a chamber defined by upright walls, i.e. a receptacle shell, a receptacle bottom and a shielding cover of the plug type which fits within the mouth of the receptacle. The shell of the vessel and the bottom are formed unitarily of cast iron, especially spherolitic cast iron, or cast steel, and the shell or walls are provided with a shoulder or flange configuration which can engage an outwardly extending flange on the plug-type shielding cover. The cast alloy or body can be provided with cells in which radiation-absorbing materials can be received, these cells being, for example, so orientated and constructed that they block straight-line paths from the interior of the receptacle outwardly. The radiation-shielding effect, however, is primarily a result of the thickness of the vessel shell and bottom and the thickness or height of the cover which not only must take up the static stresses of transport and storage, but must be sufficient to effect the predominant shielding or adsorption of the radiation from the radioactive wastes whether this radiation is gamma radiation or neutrons. In the earlier transport or storage vessels for the aforedescribed purpose, the shielding cover is held in place by threaded bolts. This enables, prior to the insertion of the cover, the introduction of the radioactive wastes into the interior of the vessel. The sealing between the shielding cover and the vessel walls is effective for long periods, but only as long as any sealing agent remains effective or the sealing structure formed by the flange arrangement remains effective. While such systems have proved to be effective, they nevertheless do not provide a closure which is not dependent upon the sealing means between the shielding cover and the receptacle nor do they permit control of the sealing, i.e. ascertainment of a failure of the shielding-cover seal. OBJECT OF THE INVENTION It is an object of the present invention to provide, in a shielding and transport vessel of the type described in the aforementioned copending application, which is hereby included in its entirety by reference, a hermetic closure of the vessel which is independent of the seal between the shielding cover and the vessel walls and which, in addition, affords sealing control or monitoring as may be required. SUMMARY OF THE INVENTION This object is achieved, in accordance with the present invention, in a receptacle or vessel for the shielding transport or shielding storage of radioactive wastes, especially irradiated fuel elements, which apart from the improvement described below can be of the type fully described in the above-identified application. According to the invention, the receptacle shell is formed along its upper face with an upstanding continuous annular welding lip which defines an annular opening into which an additional or safety cover can be fitted. The safety cover can, in accordance with this invention, be formed with an annular counterlip which lies adjacent the first-mentioned lip and defines an annular welding crevice or junction in which a deposit weld is formed along the upper face of the container. The bead of weldment between these lips can be formed readily by any cast iron or cast steel deposit welding technique because the lips themselves are separated from the mass of the container shell and the mass of the safety cover, respectively, by annular upwardly open grooves. Heat conduction away from the welding site is thus minimized. The safety cover thus overlies the shielding cover and is hermetically sealed to the container wall by the weld seam. In a construction in which the container is provided with a conduit opening from the upper end face into the upper part of the interior of the vessel to allow a fluid to be introduced into the vessel as described in the aforementioned application, the conduit being cast in place or being formed by a space in the cast material, the invention provides that the mouth of this conduit also be closed by the safety cover, i.e. that the safety cover extend over this mouth and that the bead of weldment be deposited outwardly thereof. The system of the present invention has been found to be highly effective in that it affords a seal for the vessel which is not dependent upon the seal between the shielded cover and the body of the vessel. The resulting shielding transport and/or shielding storage receptacle for radioactive waste thus fulfills all of the requirements for such a container and fulfilled by conventional containers with the additional advantage that a greater degree of safety is afforded. While the safety cover is welded onto the vessel wall to provide the hermetic seal, the contents of the vessel remain accessible since the bead of weldment can simply be burned away and the safety cover removed, thereby affording access to the shielding cover. It has been found to be advantageous to provide the safety cover with a bore to which a suction duct can be connected to ascertain whether the seal between the vessel and the shielding cover remains effective. In the event of a failure of the latter seal, the high pressure gas usually provided within the vessel, e.g. helium, can penetrate into the space beneath the safety cover and can be drawn by the suction duct from this space.