Patent Number: 043307116
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more specifically to the drawings the combination container consists of a removable inner container 1 having a cover 3, which optionally consist of several component parts and an outer container 2 having a cover 4. The bottom 10 and the jacket 11 of the outer container are so dimensioned in their thicknesses that they either completely or at least preponderantly shield off the gamma and neutron radiation of the container contents from the outside. The inner container 1, moreover, is fixed axially in the outer container 2 in such a manner that the inner container cover 3 and the outer container 4 do not contact. The radial position of the inner container 1 in the outer container 2 is fixed by a narrowed cross section 12 of the inner space of the outer container 2 proceeding downwardly to the bottom 10 wherein this narrowing preferably is produced by a correspondingly wedge shaped constructed profile 13 to the outer wall 14 of the inner container 1 and the inner wall 15 of the outer container 2. The outer wall 14 of the inner container 1 is tightly sealed against the inner wall 15 of the outer container 2 by means of sealing element 5. By dimensioning of the outer container 2 to the shielding wall thickness this container has a very high mechanical strength and so is substantially protected against damage in the case of accidents during transportation. Besides because of the omission of a heat transferring gas or liquid between inner container 1 and outer container 2 it is without pressure in normal operation so that no sealing problems occur. The heat transfer takes place over the small gap between the two containers, preferably, however, via the contacting profile 13 to the outer wall 14 of the inner container 1 and the inner wall 15 of the outer container 2. The gap between outer container 2 and the inner container 1 is so sealed through the sealing element 5 that in loading the container there cannot take place contamination of the outside of the inner container. The inner container is fixed axially in the jacket 11 of the outer container, preferably via holding down device 6, which is received in corresponding recesses 16 of the outer container jacket 11 in such manner that the cover 4 and therewith the seal 17 of the outer container 2 is not loaded. The combination container of the invention has a relatively thin-walled inner container which is produced simply and cheaply and on a large scale, for example it is made of commercial tubular material. There are placed high requirements on a stored container in regard to the sealability. However, as is known it is difficult to carry out the customary examination such as X-ray and supersonic testing in thick walled container. With relatively thin walled containers according to the invention this test procedure causes no problem. The outer container 2 in combination with the transportation cover 4 fulfills all of the requirements for a Type B container in regard to handling mechanical integrity, heat transfer, tightness and shielding in normal transportation and in the case of accident. This outer container 2 can be made of all work materials and combination of work materials known in the practice and literature, such as wrought iron, cast iron, lead, depleted uranium, copper or synthetic resin. Since the outer container 2 is only employed for transportation and can be utilized for a great number of inner containers 1 there is required in regard to the storage only a very limited number of the outer containers 2. Therefore there can be placed especially high requirements on the selection of material, construction, manufacture and testing without mentionably increasing the total cost of the storage. These safety reserves in the transportation are very valuable to this most risky part in the entire storage strategy. Especial requirements are placed on the sealing in a storage container. This seal should have constant good sealing properties during the entire storage time since during the collecting of many storage containers even leak rates which are admissible for individual transportation containers would lead to the release of noteworthy activity. Prerequisite for applying such a seal is good accessibility of the seal. The present container combination permits this accessibility in an outstanding manner through the fact that the cover 3 of the inner container 1 acts as a shielding cover. Therefore so long as the inner container 1 is still located in the outer container 2 the place of sealing is freely accessible and the permanent seal required for the storage can be installed without requiring for this purpose remote control devices and a hot cell or a water tank for radiological protection. The inner container 1 and the shielding cover 3 additionally are made tight with a seal 8. This seal 8 above all is effective through the weight of the stationary container itself and prevents a contamination of the space between the outer container cover 4 and the inner container cover 3. Therefore it is possible to insert the permanent seal required for storage first at the place of storage. This has the advantage that this important operation for the security of the storage always can be undertaken at a stationary device by the same crew, not every nuclear power plant must be equipped with devices and the routine loading in the nuclear power plant is not hindered. This sealing of the gap between the inner container 1 and the outer container 2 through the seal 5 has the advantage that the inner container 1 need not be decontaminated before its insertion in the storage shield. Therefore there is not accumulated any secondary waste in the provided operation which would require additional apparatus to attend to and therewith high operating costs. For the permanent sealing for the storage the inner container 1 and shielding cover 3 can each be provided with a welded end 9 on which they can be welded or soldered for gas tight storage. The gap between inner container 1 and cover 3, however, can also be so formed that it can be filled with a low melting metal. The emptying and washing of the inner container is carried out in known manner. During the transportation the inner container 1 must be so fixed in the outer container 2 that even under conditions of an accident the transportation cover 4 and its sealing system 17 is not burdened by the inner container 1 and its content. This is solved according to the invention with a holding down device 6 at whose periphery distributed brackets fit in corresponding recesses 16 of the jacket 11 of the outer container 2 and through twisting according to the bayonnet principle is secured on the container. The security against twisting is reached through screwable tension elements 7 which simultaneously shuts the shielding cover. The tension element 7 can contain a pack of springs to compensate for the longitudinal tension of the box. The outer container 2 advantageously can have cooling couplings 18 which can be joined with spirally arranged cooling channels 19 on the inner surface of the outer container 2. Thus it is possible to cool the container contents before emptying in a reprocessing plant without needing to open the inner container 1. The cooling connection 18 can also be connected to a cooling circuit during the transportation so that the fuel element temperature is lowered in the transportation. As shown in FIGS. 2-5 it is particularly advantageous to form the profile 13 hollowly on the inner wall 15 of the outer container 2 and to integrate it in the cooling circuit via the cooling channel 19. The cover 3 of the inner container 1 can be erected of several parts and for example can consist of a thin walled true cover portion and a thick walled shielding portion. Through this the shielding portion can also be used repeatedly since it is not needed in the storage in corresponding warehousing. The heat is transferred from the inner container 1 of the outer container 2 by free convection and radiation. There is not needed an additional heat transfer medium which might fail in the case of an accident. After the loading of the inner container 1 the inner container heats up first more quickly than the outer container 2 so that the gap between inner and outer container which is conditional by the manufacture is smaller and therewith the heat transfer is better. Still better heat transfer is produced if the inner container 1 has wedge shaped profiles 13 (see FIGS. 2, 3) over the entire length which fit into corresponding wedge shaped profiles 13' in the outer container 2 so that there is always metallic contact between inner and outer container and therewith metallic heat conductance occurs. The tolerance between inner and outer container is then obtained through different positions of inner and outer container and must be compensated for via seal 5. The entire disclosure of German priority application Ser. No. P2915376.2 is hereby incorporated by reference.