Decommissioning and dismantling of nuclear installations after their service life are connected with the necessity of the disassembling, handling and disposing of a large amount of radioactive equipment and structures. In particular, the concrete used as a biological reactor shield and graphite as a moderator-reflector represent the majority of waste requiring geological disposal. To reduce this undesirable volume to the minimum and to successfully plan the dismantling and disposal of radioactive materials to storage facilities, the activation of the structures should be accurately evaluated.
In the framework of the decommissioning and the dismantling of the experimental reactor of the University of Strasbourg, detailed activation estimates have been conducted to characterise the graphite and the structural materials present in the reactor environment. For this purpose, the chemical composition of fresh graphite samples and different types of concrete has been determined by activation analysis in the research reactors OSIRIS and ORPHEE of CEA Saclay (France). Then, the activation of graphite, concrete and other materials has been calculated in the whole reactor as a function of the three main nuclear data libraries, i.e. ENDF, JEF and JENDL. In parallel, the activation of representative graphite and concrete samples has been measured experimentally.
The comparison of theoretical predictions with experimental values validates the approach and the methodology used in the present study and tests the consistency and the reliability of the nuclear data used for activation analysis. We believe that a similar approach could also be used for the decommissioning of industrial nuclear reactors.
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