Patent Number: 056688431
Section: summary

CROSS-REFERENCE TO RELATED APPLICATION This application is a Continuation of International Application Ser. No. PCT/DE95/00066, filed Jan. 18, 1995. BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to a storage cage for the storage and transport of a plurality of fuel assemblies, in particular fuel assemblies which have been used in a nuclear reactor for the release of energy by nuclear fission in fissionable material that is contained in the fuel assemblies. Both the storage and the possibly necessary transport of fuel assemblies, in particular after the fuel assemblies have been used in a nuclear reactor, necessitate an abundance of measures arising from reasons of radiation protection, a need to dissipate heat originating from radioactive decays in the fuel assemblies and a requirement of preventing the formation of an accumulation of fissionable material in which an automatic chain reaction of nuclear fissions could occur. The first-mentioned reason necessitates a careful shielding of an irradiated fuel assembly, the second-mentioned reason demands special measures for heat dissipation and the third-mentioned reason necessitates that a multiplicity of fuel assemblies always be gathered together in a narrow space only with an appropriate quantity of neutron-absorbing material. German Patent DE 32 21 810 C2 discloses a device for the storage of irradiated fuel assemblies. The device is to be disposed in a nuclear power station in the vicinity of the nuclear reactor and inside a guard shield surrounding the nuclear reactor. The device includes a storage pond filled with light water and a rack which is disposed in the storage pond and in which the irradiated fuel assemblies can be stored. The rack has a baseplate, on which casings made of boron-containing steel are mounted in a configuration in the manner of a honeycomb. Each casing serves for receiving a fuel assembly. The shielding of the fuel assemblies is guaranteed, in particular, through the use of water. The water also serves, together with the material of the casings, for the absorption of neutrons, in order to reliably rule out the buildup of a chain reaction. A method and a storage device for the treatment of spent fuel assemblies from nuclear power stations are disclosed in German Published, Non-Prosecuted Patent Application DE 34 00 929 A1. According to that publication, fuel assemblies which are to be removed from a nuclear power station are sealingly enclosed in cans inside the guard shield of the nuclear reactor. Only sealingly closed and, where appropriate, externally decontaminated cans are brought out of the guard shield and stored in an external storage device which is equipped with air cooling for the dissipation of heat energy from the fuel assemblies. German Published, Non-Prosecuted Patent Application DE 28 40 594 A, like German Patent DE 32 21 810 C, relates to a storage rack for fuel assemblies to be placed in a water pond. The storage rack is composed of rack parts which are disposed next to one another and, where appropriate, also one above the other. A rack part has projections and recesses at the edge of its cross section, which can be fitted together with corresponding recesses or projections in adjacent rack parts and which, in particular, form supporting surfaces between the rack parts. The rack formed from the rack parts, which can be stacked, in particular, in the manner of beer crates, can absorb not only vertically acting, but also horizontally acting forces. Published European Patent Application 0 385 186 A1 describes a fuel assembly storage rack with an outer frame which has transport lugs at its upper end and which includes a horizontal support plate at its lower end. Vertical tubes having a baseplate are disposed in the outer frame and through the use of which they are fastened to the support plate. Vertical wall surfaces of the tubes run parallel to one another and to the outer frame. In order to ensure the passage of cooling water, the baseplates or the vertical wall surfaces have perforations which are matched with corresponding perforations in the outer frame. The transport lugs serve for lifting the storage rack through the use of a lifting appliance into a fuel assembly storage pond which is provided and for positioning it there. U.S. Pat. No. 4,960,560 specifies a fuel assembly storage rack with a baseplate and cells being fastened to the base-plate, being extended perpendicularly to the latter and being intended for receiving fuel assemblies. The baseplate contains an aperture for each cell, for the entry of cooling liquid. In order to lift the storage rack, after its assembly, into the intended location in a fuel assembly storage pond, some of the apertures are formed in such a way that an appliance for lifting the storage rack can engage into them. Through the use of the appliance, the storage rack and the fuel assemblies which are disposed therein solely vertically relative to the baseplate, can be lifted into different positions within the fuel assembly storage pond. The known possibilities for the storage and transport of fuel assemblies always involve the need, where appropriate, to reload fuel assemblies individually from a first storage device into a second storage device, for example from a rack into a transport container. In view of the special requirements to be placed on the handling of such fuel assemblies, that means that handling should always take place only in a specially shielded environment. That also results in a very high outlay which is extremely undesirable, not the least for reasons of radiation protection, since individual fuel assemblies have to be moved for each reloading operation. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a storage cage for storage and transport of fuel assemblies, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which provides a possibility of substantially reducing outlay during transfer of fuel assemblies in comparison with the heretofore-known devices. With the foregoing and other objects in view there is provided, in accordance with the invention, a storage cage for the storage and transport of a plurality of fuel assemblies, comprising a baseplate having apertures formed therein; a plurality of casings each having an interior and each standing on the baseplate for receiving and storing a fuel assembly; each of the casings being associated with at least one of the apertures leading into the interior of the casing for supplying and discharging cooling liquid; each of the casings having a plurality of slots formed therein for supplying and discharging cooling gas; and at least one supporting wall forming a load-bearing part with the baseplate, the casings being fastened to the at least one supporting wall. On one hand, the storage cage can be disposed with a plurality of identical storage cages provided with irradiated fuel assemblies, in a water-filled storage pond, in order to store fuel assemblies directly next to a nuclear reactor. In order to ensure that the storage cage can be taken out of the storage pond easily, the baseplate has apertures formed therein, through which a cooling medium, such as water, can flow off out of the casings. Furthermore, the apertures serve for generating a natural circulation of the water along the fuel assemblies for the cooling thereof. Moreover, the storage cage together with the fuel assemblies can be introduced into a transport container and be anchored therein, in order to thereby allow easy transport of the fuel assemblies as a whole. For this purpose in particular, the storage cage has the supporting wall which absorbs all of the loads to be expected, even in the event that the storage cage does not stand on the baseplate for transport, but lies with the baseplate oriented vertically. Each casing is provided with a plurality of slots to ensure that the gas cooling of the fuel assemblies which is conventionally carried out in a transport container becomes possible. This affords a possibility for the storage, transfer and transport of fuel assemblies which largely avoids the handling of individual fuel assemblies. After the fuel assemblies have been introduced into the storage cage, it is only ever necessary for the storage cage as a whole to be moved. In accordance with another feature of the invention, the storage cage is constructed, particularly by the provision of a suitable anchor device, in such a way that it can be connected to a plurality of identical storage cages, with all of the baseplates being oriented horizontally, to form a storage rack. An anchor device of this type can, for example, be noses which have bores formed therein and which can be screwed through the use of bolts or the like to adjacent storage cages having corresponding noses. Configurations of catches and hooks, through the use of which mutually adjacent storage cages can be hooked in one another, are also possible. In accordance with a further feature of the invention, the storage cage can be stacked with another identical storage cage, with the baseplates being oriented horizontally. In accordance with an added feature of the invention, the storage cage is constructed in such a way that it can be anchored in a sealingly closeable associated container, particularly for transport purposes. In accordance with an additional feature of the invention, the casings of the storage cage are formed of a neutron-absorbing material, preferably of a boron-containing material, in particular boron-containing steel. Since boron-containing steel is relatively brittle, it usually requires an additional supporting device in order to ensure a sufficient load-bearing capacity of the storage cage. The supporting wall serves this purpose. In accordance with yet another feature of the invention, the baseplate and the supporting wall are formed of a rust-resistant steel. In accordance with yet a further feature of the invention, each casing of the storage cage is shrouded by an associated supporting wall. Such a storage cage does not have any exposed surfaces being formed of brittle material, which is particularly advantageous with respect to the load-bearing capacity of the storage cage. In accordance with a concomitant feature of the invention, the casings of the storage cage form an approximately cylindrical configuration, so that conventionally constructed, that is to say essentially cylindrical containers, can be used for transporting the storage cage. It goes without saying that the storage cage is provided, according to the requirements of the particular individual instance, with fastening elements for securing suitable lifting appliances. The fastening elements are furthermore advantageously constructed in such a way that they serve as rests and fastening points for a further storage cage which is to be placed onto the first-mentioned storage cage. It is also advantageous if the fastening elements of this type are constructed in such a way that they can serve for fastening the cage in a corresponding transport container. For this purpose, the storage cage is preferably also provided with lateral supports, in order to support the storage cage with negligible play in a container for transport, and where appropriate a horizontal storage of the container and of the fuel assemblies is necessary during transport. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a storage cage for storage and transport of fuel assemblies, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.