Bulg. J. Phys. vol.34 no.s1 (2007), pp. 085-086



Analytics for Decommissioning Nuclear Facilities Based on Works at the Rossendorf Research Site

R. Knappik, M. Köhler, E. Franke
Nuclear Engineering and Analytics Rossendorf Inc. Verein für Kernverfahrenstechnik und Analytik Rossendorf e.V. (VKTA), Dresden, Germany
Abstract. A series of nuclear-technical facilities, radiochemical and radiopharmaceutical laboratories was in operation in the Central Institute of Nuclear Research Rossendorf, founded in 1956, until the beginning of the nineties of the past century. Their decommissioning and the disposal of the radioactive waste and of the weakly decontaminated residual materials is the responsibility of VTKA and started in 1992. The decommissioning includes among others an area with facilities for waste and sewage treatment and for waste storage, the research reactors and the former isotope production buildings with hot cells for handling highly enriched uranium/fission product solutions. First of all a large number of radionuclides (α-, β- and γ-emitters) were generated in a research reactor of Soviet construction and processed at the Rossendorf Research Center. All that caused contaminated components of facilities, building structures, soils etc. as well as activated materials. The radionuclides are measured and determined at the diversion of analytics of the VKTA, which also works as a service provider for other clients Europe-wide (nuclear power stations, firms of consulting engineers, authorities or the like). With the help of examples from many years of experience it is demonstrated which measuring-technological and laboratory analytical results are necessary in radiological investigation, control of decontamination operations, preliminary release measurements, release measurements as well as declaration of radioactive waste and residual materials in order to achieve an "Green Meadow" at the end. The applied measuring methods
− Direct alpha and gamma spectrometry,
In-situ gamma spectrometry,
− Sampling with nuclide specific radionuclide analytics,
− Measurements by using pipe and borehole detectors,
− Integrated gamma measurements using the equipment for release measurement at the VTKA
are mentioned. Mainly the results of laboratory analytics are presented. They were gained in the laboratory for Environmental and Radionuclide Analytics certified according to DIN EN ISO/IEC 17025. Initially the basic conditions are explained, particularly for release and release data of the German Radiation Protection Ordinance to fix a bench mark for exactness and detection limits of the required measuring methods. The necessary determination of the respective nuclides in the very different materials (e.g. concrete, steel, cast-iron, Al, graphite, soil) can only partly be predicted, when contaminated or activated. Therefore results from preliminary inspections must be considered and/or finally the correctness of the measuring data must be checked by comparing the results of the contamination measurement with that of the nuclide analysis, particularly when alpha or beta emitters are present (e.g. Pu isotopes, H-3, C-14, Sr-90). So the content of trace elements (e.g. U) in special materials of reactor components determines up to which extent transuranium elements (Np to Cm) arise. Test results of special materials, first of all of graphite, are presented. They could be checked by activation calculations, too. Therefore samples were taken from different positions of the thermal reactor column to determine the change of the nuclide vector and, with regard to disposal, to distinguish between waste and graphite for release. Generally the problem of alpha emitters is described (partly of beta emitters, too), because they play a special role in decommissioning and release for reasons of radiation protection. Additionally it is pointed out, how contamination focuses arisen by accumulation of radioactivity in containers, pipelines and on laboratory surfaces were characterized. Relating to the release measurement we deal with measurements of the building structures and the use of devices for release measurements or for in-situ gamma spectrometry in connection with the single nuclide determination.

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