Stoffliche Charakterisierung radioaktiver Abfallprodukte durch ein Multi-Element-Analyseverfahren basierend auf der instrumentellen Neutronen-Aktivierungs-Analyse – MEDINA –

摘要

Radioactive waste has to meet the specifications and acceptance criteria defined by national regulatoryand management authorities for its intermediate and final storage. In Germany the Federal Office forRadiation Protection (Bundesamt für Strahlenschutz - BfS) has established waste acceptancerequirements for the Konrad repository. Konrad is the disposal for radioactive waste with negligible heatgeneration and is located near the city of Salzgitter and is currently under construction. It will startoperation not before the year 2021. The waste-acceptance-requirements are derived from a site-specificsafety assessment. They include specific requirements on waste forms, packaging as well as limitations toactivities of individual radionuclides and limitations to masses of non-radioactive harmful substances. Theamount of chemically toxic elements in the waste is limited in order to avoid pollution of undergroundwater reserves. To comply with these requirements every waste package has to be characterised in itsradiological and chemical composition. This characterisation can be performed on the basis of existingdocumentation or, if the documentation is insufficient, on further analytical analysis. Segmented orintegral gamma-scanning as well as active or passive neutron counting are used worldwide as the standardmeasurement methods for the radiological characterisation and quality checking of radioactive waste.These techniques determine the isotope specific activity of waste packages, but they do not allow thedetection of non-radioactive hazardous substances inside the waste packages.Against this background the Institute of Nuclear Engineering and Technology Transfer (NET) at RWTHAachen University and the Institute of Safety Research and Reactor Technology at ForschungszentrumJülich jointly develop an innovative non-destructive analytical technique called MEDINA - “Multi-Element Detection based on Instrumental Neutron Activation” for the identification and quantification oftoxic elements in radioactive waste forms. The physical basis of MEDINA is the Prompt- and Delayed-Gamma-Neutron-Activation-Analysis (P&DGNAA). The neutron activation analysis of material samplesin the gram range is state-of-the-art of science and technology under use of thermal or cold neutrons atresearch reactors. The thereof retrieved nuclear data and the results of the feasibility study for thecharacterization of large-volume samples up to a volume of 50 l /1-5/ are the scientific basis of thepresent dissertation. With a newly developed test facility and an innovative algorithms for a rotationallydependent analysis the element quantification of larger inhomogeneous samples can be performed bytaking into account the gamma and neutron self-shielding for the first time....