Patent Number: 047131993
Section: summary

The invention concerns a depository, particularly a dry depository, for radioactive waste and spent fuel cells comprising a concrete storage block having cooling channels for circulation of air to remove residual heat from the stored waste. In the storing of such materials, particularly temporary storage of spontaneously-heating radioactive materials, care must be taken to prevent the release of radioactive substances due to overheating. Depositories for the dry storage of spontaneously-heating radioactive materials have been disclosed in which the storage material is packed in containers and the containers are inserted into vertical tubular shafts, whose floor consists of the grid of a storage rack. The storage rack is made of steel and is located in a shielded storage cell. The depository has several storage cells. The cooling of the containers heated by residual heat is provided by natural convection. For this purpose, an annular gap is left between container and storage shaft. Atmospheric air as cooling air enters through an air supply opening under the storage rack, picks up heat while passing through the annular gap and flows through an exhaust opening to the environment. The space underneath the storage rack serves as an air supply chamber for the stabilizing and uniform distribution of the cooling air in the storage shafts. The space above the storage rack serves as a used air chamber. The cooling air is fed from the outside via air supply openings in the air supply shafts. The air supply openings are above ground and lead at an angle upward into the air supply shafts. The air supply openings and also the exhaust openings are so made and equipped that rain, dust, etc., are prevented from entering. In these known depositories the disadvantages are the relatively big constructional expense and the associated high costs. It is also a known practice to use monolithic concrete blocks with cast vertical channels instead of the storage rack and shafts of steel, for accommodating the radioactive materials. Because of the temperature differences and variations that occur, there is the danger of damage to the concrete block, since there is no compensation for thermal tensions. The construction of the known depository is relatively expensive. Dismantling is possible only with great expense. The object of the present invention is to provide an improved and safer concrete depository having a storage block composed of concrete blocks with vertical channels therethrough, the blocks being piled up in adjacent rows with the channels aligned. The present fuel cells are disposed within the channels with an annular space surrounding them for cooling air. The embodiment of the invention actually provides for a structure on the modular construction principle. The individual small concrete block units are easily and cheaply produced. They are easily installable for the building of the storage blocks and correspondingly easily removable. The storage block can be built up by sections. The embodiment of the invention leads to an improved and more efficient natural cooling of the material stored in the channels. The cooling air flows upward in the channels of the concrete block as in a chimney. A blower is not necessary. The natural draft is sufficient and provides an inherently safe cooling system. The construction with individually-combined concrete blocks avoids harmful thermal tensions in the storage block as a whole. The depository of the invention is thus inherently safe in this respect, also. In one form of the invention the blocks rest on ribs projecting above the concrete floor or base, and the spaces between the ribs provide conduits which communicate with the vertical channels in the blocks for air circulation. In another form of the invention, the metal storage containers for the radioactive waste and spent fuel cells have radial ribs along their length to conduct heat to the cooling air passing through the vertical channels. An increase in seismic security is achieved by bracing the stacked individual concrete blocks against the base plate and bracing the containers against blocks. The metal storage containers may be suspended within the channels of the concrete blocks with the use of supports resting on the top of the stack. This has the advantage that the longer part of the storage container beneath the support can expand freely and unhindered downwardly without any harmful forces being exerted on any structural part. By providing air filters in the air inlet openings, dust, micro-organisms, etc., are prevented from getting into the depository. In a preferred form of the invention the individual blocks have on their tops and bottoms mating centering elements to facilitate the stacking and arrangement of the concrete blocks. A sealing sleeve is provided for sealing off from the environment the upper part of the storage and cooling channels or the opening in the concrete ceiling. The sleeve can accommodate itself to thermal movements of the portion of the storage container extending into the opening in the concrete ceiling. Preferably the upper end of the storage container is enlarged and has an annular shoulder which rests on a cooperating ledge in the opening through the ceiling. A shielding plug fits in the enlargement. In order to secure the optimum protection against the penetration of water, especially ground water, into the depository, a water sensing means is provided to monitor the presence of water and actuate a pump. Water is thereby prevented from getting into the space underneath the storage blocks and into the storage and cooling channels and interfering with or interrupting the natural draft cooling. The invention will now be explained in more detail with reference to the attached drawings.