Patent Number: 
Section: claims

1. A casing internal part suitable for the dry intermediate storage of at least one irradiated fuel element, characterized in that it has a tiered structure which comprises at least two superposed modules, each of said modules, made of a material that is a good conductor of heat, with compartment(s) for accommodating said fuel element(s) in the central part and with at least one hollowed-out peripheral heat sink, being arranged on a support plate that is perforated to allow said fuel element(s) through; the perforated support plates of said structure being positioned and assembled by means of a retaining system, with a clearance left between the top of the module of one tier and the perforated support plate of the tier immediately above. 2. The casing internal part as claimed in claim 1, characterized in that said at least one compartment and said at least one hollowed-out pheriphal heat sink of each module are based on extruded elements. 3. The casing internal part as claimed in claim 2, characterized in that each module of its tiered structure comprises at least one prefabricated compartment. 4. The casing internal part as claimed in claim 1, characterized in that said at least one hollowed-out peripheral heat sink is an extruded element with or without fin(s) and with radiating surface(s). 5. The casing internal part as claimed in claim 1, characterized in that each module of its tiered structure comprises 1, 3, 4, 7, 12 or 15 compartments. 6. The casing internal part as claimed in claim 1, characterized in that said modules are made of aluminum; and/or, advantageously and, said retaining system and said perforated support plates are made of a material with high mechanical strength and are advantageously made of stainless steel. 7. The casing internal part as claimed in claim 1, characterized in that said retaining system comprises through bolts for, on the one hand, positioning and assembling the support plates and, on the other hand, transferring load from said casing internal part to the casing in which it is intended to be housed. 8. The casing internal part as claimed in claim 7, characterized in that said through bolts position each module on its support plate. 9. The casing internal part as claimed in claim 1, characterized in that its tiered structure comprises 2, 3, 4, 5 or 6 superposed modules. 10. The casing internal part as claimed in claim 1, characterized in that said at least one compartment has a square, hexagonal or circular cross section. 11. A casing suited to the dry intermediate storage of at least one irradiated fuel element, characterized in that it contains a casing internal part as claimed in claim 1 and comprises a bottom capable of withstanding the mass of said casing internal part and that of said at least one fuel element that is going to rest against it. 12. The casing as claimed in claim 11, characterized in that said casing and its casing internal part, which advantageously adopt the shape of right cylinders, have cross sections of roughly the same dimension(s). 13. A method for the dry intermediate storage of at least one irradiated fuel element comprising:the stable conditioning of said at least one irradiated fuel element in a casing within which the heat released by said at least one element is dissipated with no adverse effect on the structure of said at least one element,the intermediate storage of said sealed casing in a vertical pit cooled by the circulation of air,characterized in that said casing is a casing as claimed in claim 1. 14. The method as claimed in claim 13, characterized in that said casing contains several fuel elements. 15. The method as claimed in claim 13, characterized in that said at least one irradiated fuel is an element the power of which is 5 kW or lower.