Taking samples from the reactor components in preparation for dismantling the TRIGA reactor at the Medical University of Hannover

After shutting down the facility at the end of 1996 the spent TRIGA fuel elements from the research reactor at the Medical University of Hanover (MHH) were returned to the United States in the summer of 1999 and thus disposed of for the MHH. Consequently one of the main prerequisites for dismantling the TRIGA reactor as planned has been fulfilled. In preparation for dismantling the facility a number of samples were taken from the various reactor components in 2000. The aim of the samples being taken was to establish the radiological condition of the facility in more detail, in particular the condition of the activated components in the reactor tank and the biological shield in the core area. Up to now the calculated estimates for these components had been based mainly on the details provided in the facility documentation when operation started at the beginning of the 1970s, showing that the evaluation of the activity and dose rates was too high. This was confirmed in 1998 in the course of measuring contamination and dose rates when samples were taken from some reactor components before the fuel elements were removed. For example, drill samples were taken from the bottom part of a graphite blind element and from the central radiation beam tube in the core area and then analyzed by the U.R.A. Laboratory of the University of Regensburg. As it is planned to dismantle the reactor facility completely by hand, it is necessary to have realistic radiological data in order to prepare for the dismantling procedure. Furthermore, both the release of radioactive materials into the environment and the costs for external disposal of the radioactive waste from the dismantling of the reactor are to be kept to a minimum. (orig.)