Decommissioning of the compact sodium-cooled nuclear reactor facility (KNK)

The Compact Sodium-cooled Nuclear Reactor Facility (KNK) was an experimental nuclear power plant of 20 MW electric power erected on the premises of the Karlsruhe Research Center. The plant was initially run as KNK I with a thermal core between 1971 and 1974 and then, between 1977 and 1991, with a fast core as the KNK II fast breeder plant. Under the decommissioning concept, the plant is to be decommissioned completely to green field conditions in ten steps, i.e. under the corresponding ten decommissioning permits, till the end of 2005. The decommissioning and demolition activities covered by decommissioning permits 1 to 8 have been nearly completed. Under the 9th Decommissioning Permit, the reactor vessel, the primary shield, and the biological shield are to be dismantled. The planning and assembly work has been started, the demolition activity should be started in January 2003. The difficulty involved especially in dismantling KNK, on the one hand, is posed by the residual sodium in the plant, which determines the choice of neither wet nor thermical techniques to be used in disassembly. Another difficulty is caused by the depth of activation by fast neutrons, as a result of which not only the reactor vessel proper, but also the entire primary shield and large parts of the biological shield must be disassembled and disposed of under remote control. The presentation gives an overview of the former decommissioning steps and of the concept for dismantling of the reactor vessel and the biological shield under remote control. (orig.)