Untersuchung zur Methodik von Sterilisationsverfahren sowie mikrobielle Ueberwachung von Sorptionsexperimenten. Sorptionsexperimente zur Beeinflussung der Radionuklidmigration durch mikrobielle Aktivitaeten am Beispiel des Technetiums und Selen Abschlussbericht

Abstract

The knowledge about the influence of microbial activities on the radionuclide migration is not very extended up to now. The sorption behaviour of the redox sensitive radionuclides "9"5"mTc and "7"5Se was investigated under consideration of microbial metabolism and the development of bacterial populations in loose sediments. Recirculation column experiments (aerobe) were carried out as well as batch experiments (aerobe and anaerobe). Sterile experiments were compared with non sterile experiments. The investigation of sterilising methods with low impact on the physico chemical properties of sediments proved gamma irradiation to be the best choice. The addition of nutrients in batch experiments showed an immobilisation of Tc and Se combined with a decreasing redox value (Eh). Non sterile recirculation experiments showed a reproducible fixation of Tc and Se without any observed decrease of the redox value. The immobilisation occurred without any measurable alteration of the marco environment. These results are not understandable taking thermodynamic data into consideration. There was no fixation of Tc and Se within 95 days in sterile column experiments. The addition of micro-organisms isolated from the non sterile columns led to a decreasing redox values. The addition of biocide (5000 ppm NaN_3) to the non sterile columns resulted in a remobilisation of Tc but not of Se. To a great extend the micro-orgnisms identified within the non sterile columns were allochthonous. The immobilisation of Tc by living cells is much bigger than by autoclaved (dead) cells. A microbial population in the cap rock aquifers is highly probables as well as in the disposal site (after the excavation and filling period). The assessment of the cap rock aquifer's retardation capacity for the radionuclide migration may be overestimated not knowing the impact of the autochthonous microflora on those radionuclides interacting with micro-orgnisms. (orig.)SIGLEAvailable from TIB Hannover: F94B783+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman