Patent Number: 046801596
Section: summary

FIELD OF THE INVENTION The invention relates to a storage container for receiving fuel rods of irradiated nuclear reactor fuel elements. The storage container includes a storage chamber having a circular cross-section for accommodating an insert cage for holding cans filled with fuel rods. BACKGROUND OF THE INVENTION For the transportation and storage of irradiated nuclear reactor fuel elements, it is customary to utilize shielded transport and storage containers made of spheroidal cast iron or steel. The inner chamber of the containers can have a round or square cross-section. Containers with a circular inner chamber have the advantage of being easier to manufacture and of optimally utilizing the storage space. The irradiated fuel elements are received in these storage containers in special insert cages. In addition to the accommodation of complete fuel elements, it has already been proposed to disassemble the fuel elements and to load the individual fuel rods of these fuel elements closely packed into a storage container. Considerable space savings can be achieved thereby. European Pat. No. 0005623 discloses that the storage container is thus capable of holding a larger amount of fuel elements. According to a state-of-the-art disclosure made in German published patent application No. DE-OS 3,222,822, the fuel rods removed from the fuel elements are closely packed into cans the geometry of which corresponds approximately to one fuel element. The filled cans are then placed into the receiving shaft-like compartments of the insert cage, these compartments being actually configured to hold the fuel elements. An important technical problem of the storage of individual fuel rods packed as closely as possible in a storage container is the temperaure control of this storage unit. As a result of the decay heat of the radioactive fuel, the temperature within the storage unit may increase inadmissibly. Dissipating the heat from the interior of the fuel rod package involves problems. Consequently, this heat dissipation problem may be the reason for limited packing densities or extended previous decay times of the fuel elements until they can be loaded into the storage container. SUMMARY OF THE INVENTION It is therefore an object of the invention to configure a container of the type initially described such that a good heat dissipation from the storage unit is accomplished and that the fuel rods are not impermissibly impaired by heat. This object is achieved by the storage container of the invention in that: the individual cans are arranged in circular form in the insert cage; the cross-section of the cans is a circular segment; hold-down springs bear on the upper end surfaces of the cans; and, the radial extension of the can segments towards the center is limited so that an empty square shaft is formed in the middle of the insert cage. Providing the individual fuel-rod cans with a circular-segmental cross-section adapts them well to the round cross-section of the storage space. The curved rear surfaces of the fuel-rod cans rest snugly against the circular inner wall of the container, thereby providing for a good heat transfer between the cans and the storage container. The hold-down springs urge respective ones of the fuel-rod cans in an axially parallel direction against the bottom of the storage container so that the good heat transfer is ensured there also. The empty square shaft formed in the middle of the storage space may be used to accommodate the scrap, that is, spacers and the like which result from separating out individual fuel rods. This structural material of the disassembled fuel elements has a substantially lower heat output than the fuel rods. In addition, it is not affected by heat and is capable of tolerating heat increases unprotected. By contrast, the irradiated fuel rods are not permitted to exceed the temperature limits prescribed by the authorizing governmental agencies because of the risk of leakage. Fissile gases or other radioactive material would then escape. According to another feature of the invention, double-walled partition units define a hollow space between two adjacent fuel-rod cans. Sectioning the circular storage space in this manner permits fuel-rod cans of identical configuration to be used. Advantageously, one fuel-rod can will accommodate the fuel rods of one fuel element. In addition, the hollow spaces in the partition segments afford the possibility of loading neutron-absorbing or heat-conductive materials. A feature of this embodiment of the invention is that the fuel-rod cans can be made to all have the same configuration. In another advantageous embodiment of the invention, inclined guides coact with inclined engagement surfaces in the insert cage, and lower guide surfaces eliminate a clearance which may be present between the curved rear surfaces of the fuel-rod cans and the circular inner wall of the storage container. The invention provides a storage container for accommodating individual fuel rods, which permits the storage of fuel rods having a higher after-heat output. Therefore, after removal of the fuel elements from the spent fuel storage pool and their disassembly into individual fuel rods, the fuel rods may be directly loaded into the container provided for terminal storage. Further interim storage for heat dissipation is not necessary.