Disassembly of steel elements of the Stade nuclear power station. Disposal of control rod guide thimbles from KKI 1

In the course of decommissioning and dismantling PWR plants of older lines, activated steel elements arise, in addition to the usual core components, which had been installed in fuel element positions of the core edge region to protect the reactor pressure vessel from neutron-induced embrittlement. Twelve steel elements had to be conditioned for waste management within the decommissioning and disassembly phase of the Stade nuclear power station (KKS). The steel rods were dismantled from the skeletons under water, cut up, and loaded into MOSAIK registered inserts provided for this purpose. The packaging concept also included provisions for later loading of the skeleton parts into the MOSAIK registered inserts. In a second phase, the steel element skeletons were disassembled with underwater shears and added to the partly filled MOSAIK registered inserts. The full MOSAIK registered II-15 U EI casks were emplaced in the present MOSAIK registered cask store. They are to be transported to the KKS interim store. Removal to an external interim store or a future repository is planned for a later date. BWR plants give rise to control rod guide thimbles for disposal chiefly in the course of decommissioning. The small number of these parts arising during plant operation often create problems in fuel element storage pools because of their large volumes. Two control rod guide thimbles had to be disposed of in the Isar 1 nuclear power station. An underwater saw was developed for this purpose which was used to disassemble two control rod guide thimbles in KKI 1 in 2005. The thimbles were cut up, packed in drums, and these drums were emplaced in high-density concrete casks of the KONRAD-I type. The activated top sections were packed in a MOSAIK registered II-15 U EI cask under water and, after drainage and drying of the cask, shipped to the Karlsruhe Research Center, disassembled again, packaged, and compacted under high pressure. (orig.)