Patent Number: 045253242
Section: summary

Irradiated nuclear reactor fuel elements are kept in a basin filled with water where the radioactivity of the fuel elements falls off or decays with time. After a predetermined period of storage during which the heat generated by the radioactive decay falls off exponentially, the fuel elements are packed in transport containers and are brought to an interim storage facility. At this location, the fuel elements are stored before they are subjected to reprocessing. DE-OS No. 29 29 467 discloses such an intermediate storage facility which is configured as a dry storage facility whereat the fuel elements are placed into gas-tight storage containers after being removed from the transport containers. They are then placed in several storage rooms of a longitudinally extending storage building wherein they are stacked horizontally. The storage containers are cooled by natural convection. The cooling air gradually warms and moves upwardly and transfers the heat to the ambient by means of a heat exchanger. In a proposed embodiment of a storage room wherein the containers are horizontally stacked, horizontally arranged stationary storage tubes are provided within the room. The storage containers are packed into the storage tubes whereupon the tube is closed at its loading opening by means of a suitable plug. In this proposed embodiment, an indirect cooling of the storage containers is achieved by the rising cooling air. SUMMARY OF THE INVENTION It is an object of the invention to provide a dry storage facility of the kind referred to above wherein an improved transfer of heat between the rising cooling air and the storage containers or the storage tubes containing the storage containers is achieved. It is still another object of the invention to provide an arrangement of the storage tubes in a storage module which permits a substantial amount of space to be saved within the dry storage facility without reducing its storage capacity. A dry storage facility stores radioactive materials such as irradiated nuclear reactor fuel elements that release heat produced by radioactive decay, the radioactive materials being held in gas-tight elongated storage containers. The dry storage facility of the invention includes an enclosure having a storage module disposed therein for accommodating the elongated storage containers, the latter being grouped into a plurality of sets of containers. According to a feature of the invention, the storage module includes means for holding the sets of containers in respective horizontal planes arranged one atop the other. The holding means includes ancillary holding means for holding each two mutually adjacent ones of the sets so as to cause the containers in one plane to be disposed in a direction transverse to the containers in the next adjacent plane. Convection cooling means is provided for cooling the storage containers. The enclosure of the dry storage facility can be, for example, an underground storage facility or a specially reinforced concrete building with very thick walls. This crosswise arrangement of the elongated storage containers causes a swirling of the rising cooling air which always flows into the intermediate spaces defined by the storage containers or storage tubes and which spaces are covered from above by the next layer of storage containers or storage tubes. The formation of an upward verically rising laminar flow is almost completely prevented so that the heat transferred to the available air is improved. In a further advantageous embodiment of the invention, the storage room or module includes a plurality of storage tubes for holding corresponding ones of the storage containers, the storage tubes being grouped into a plurality of sets of storage tubes. The sets are mounted in the storage module in respective horizontal planes one atop the other with the tubes of each set extending in a direction transverse to the tubes of the next adjacent set. The tubes of each set also extend longitudinally at an angle to the longitudinal direction of the transport passageway. This arrangement of the storage tubes permits a saving to be realized in the floor space of the storage facility. The width of the transport passageway between the storage modules on both sides of the storage facility and the width of the track of the crane-like transport vehicle can be configured so as to be narrower than heretofore because the loading of the storage modules is conducted at an angle with respect to both the transport passageway and the track of the bridge crane of the transport vehicle. The sets of storage tubes in the storage module are stacked as described above. According to another feature of the invention, every other one of the sets of storage tubes of a storage module is arranged therein so that the longitudinal axes of the tubes extend in a first direction; whereas, the tubes of the remaining sets of storage tubes of the module extend in a second direction transverse to the first direction. The tubes of every other one of the sets extending in the first direction are laterally displaced from the tubes of the next adjacent set of tubes extending in the first direction; and, the tubes of every other one of the sets extending in the second direction are laterally displaced from the tubes of the next adjacent set of tubes extending in the second direction. Because of this advantageous arrangement of the storage tubes and the storage containers placed therein, the rising cooling air is caused to continuously change its direction as it rises in the module through the stack of storage tubes and is thereby swirled. This swirling action increases the contact of the rising cooling air with the surfaces of the storage tubes thereby increasing the quantity of heat transferred to and conducted away by the cooling air. According to a further feature of the invention, each of the storage modules can be configured as a separate block-like unit having a square base and being bounded on its four sides by vertical walls with two diagonally opposite corners of the unit defining a vertical diagonal plane bisecting the unit into two triangular halves. The storage modules are arranged along the side of the transport passageway so as cause the diagonal plane to extend parallel to the longitudinal direction of the passageway. Because of this arrangement of the storage modules with respect to the transport passageway, two of the vertical walls face the passageway and the storage module can be loaded in crosswise fashion with elongated storage containers through both of the last-mentioned vertical walls. More specifically, the storage module can be loaded with respective sets of storage containers which lie crosswise to each other. In this way, a very effective use of space is made possible in the storage area of the enclosure wherein the storage modules are arranged. With the arrangement above, one of the triangular halves of each of the storage modules faces the passageway whereas the other one of the triangular halves of each of the storage modules faces away from the passageway. The transport facility in the enclosure includes a bridge crane and overhead guide means such as guide rails for guiding the bridge crane above and along the transport passageway. According to a further feature of the invention, the triangular half of each of the storage modules facing the passageway can be configured so as to permit the overhead guide means to be disposed thereover. Also, and according to another feature, the other triangular half of the storage module is adapted to accommodate an exhaust conduit thereabove for conducting away the cooling medium from the storage module. With the above arrangement of the storage modules, both the transport passageway and the area taken up by the passageway and the storage modules as a group can be dimensioned so as to be narrower. The transport vehicle travels above half of the storage modules along the transport passageway. Half of the surface region of each storage module facing the passageway can be used for loading operations. The space requirements for the loading operation of the storage modules is therefore held to a minimum. The other triangular half of each storage module serves as an exhaust conduit which can be connected to a main exhaust conduit.