RETURN OF THE FUEL FROM THE GERMAN COMPACT SODIUM-COOLED NUCLEAR REACTOR FACILITY KNK II WITH THE CASTOR® KNK

The Compact Sodium-Cooled Nuclear Reactor Facility KNK II, located at the German Research Centre Karlsruhe has been operated from 1977 to 1991 as a prototype facility for the Fast Breeder Reactor SNR 300. The fuel of the KNK II consisted of fuel assemblies (FA) with highly enriched Uranium-/Plutonium-MOX fuel. The FA were transported to C.E.A (France) in 1993 for reprocessing. However, due to the low solubility of the MOX fuel 2413 fuel rods from 27 FA could not be reprocessed. They were encapsulated and stored in a pool of the French research centre Cadarache. In a project organized by the Research Centre Karlsruhe, these fuel rods will be returned to Germany to be stored for a maximum of 40 years in the interim storage facility ZLN near Greifswald. For the return and the interim storage of the fuel, 4 transport and storage casks of the type CASTOR® KNK were designed by GNS Gesellschaft für Nuklear-Service mbH especially for this project. Regarding criticality safety, a significant challenge for the cask design was the fuel composition with an uranium enrichment of up to 93 % 235U and a plutonium content of up to 35 % of the total heavy metal mass. Due to these high fissile contents of the fuel, the cask baskets were equipped with additional absorber components (borated aluminium sheets with 20 w/o B4C) to limit the necessary cask number. The transport was investigated by Nuclear Cargo + Service GmbH. Since C.E.A. at Cadarache has no railway access, the 4 heavy CASTOR® KNK casks must be transported in one batch by road to a railway station near Cadarache and from there in one batch by rail to the interim storage facility ZLN. Rail transports with nuclear materials of this kind will be performed for the first time in Germany. The project started in September 2001 and the planned project deadline is at the end of 2008. The paper will give an overview of the actual status of the project, the design characteristics of the CASTOR® KNK and the transport logistics.