PILOT RESEARCH ON DIFFUSION PARAMETERS OF U235 FISSION PRODUCTS IN SLOVAK BENTONITES. 1 Renata Adamcova , 2 Michal Galambos , 3 Tatiana Durmekova , 4 Olga Rosskopfova , 5 Adrian Krajnak , 6 Patricia Ekkertova 1,2,3,4,5,6 Comenius University In Bratislava, Faculty Of Natural Sciences, Mlynska Dolina, 842 15 Bratislava, Slovakia; *[email protected] Keywords: bentonite, dry bulk density, diffusion test, apparent diffusion coefficient, U235 fission products Many scientific papers deal with sorption properties of bentonites, e. g. sorption of heavy metals in mineral linings of municipal landfills, or of radionuclides in technical bentonite barriers of the deep geological repository of radioactive waste (DGR RW) (Kugler et al., 2002; Missana et al., 2008; Galambos et al., 2011). Most work with radionuclides was done by batch tests that give only distribution coefficients Kd expressing the ratio of equilibrium between ions in the solution and ions sorbed on the solid phase, or in a best case, the maximum sorption capacity is the result (Galambos et al., 2012). Short duration is the advantage of batch tests, up to 24 hours, mostly less. Therefore, many authors use Kd also for the calculation of the retardation factor Rf from various equations. Retardation factors indicate, how many times is the migration velocity of the studied substance lower compared to the nonsorbed tracer, and together with the apparent diffusion coefficient Da, they cannot be avoided in the mathematical modeling of the pollution distribution in the geological environment. Da cannot be determined from batch tests and Rf calculated from Kd differs highly from diffusion tests data, it can be thousand times higher (Maes et al., 2008; Valderrama, 2010). Within data on sorption properties of Slovak bentonites, realistic diffusion parameters, i. e. from diffusion tests, are missing. Regarding plans for DGR RW, it is necessary to determine parameters of U235 fission products diffusion, while parameters of nonsorbed tracers are interesting also for municipal landfill sealing. Methodology development for the laboratory diffusion tests enabling prediction of these parameters from the bentonite dry bulk density is one of the partial goals of a new research project VEGA 1/0828/13 granted by the Ministry of Education, Science, Research and Sport of the Slovak Republic. Dry bulk density of the bentonite barrier in the RW repository will be extremely high and migration slow (Pacovsky et al., 2007; Garcia Gutierrez et al., 2011). Diffusion experiments under such conditions require years, with low success warranty. Therefore, diffusion tests will be carried out on samples of various consistency and lower dry bulk densities pressed from bentonite paste. The goal is to describe diffusion parameters of selected bentonites as functions of their dry bulk density. Using densitydependent trendlines, apparent diffusion coefficients Da and retardation factors Rf of selected radionuclides and tracers will be predicted for the highdensity bentonite. It is similar to trendlines already constructed by some authors for the swelling pressure as a function of the dry bulk density of the compacted/pressed bentonite (e. g. www.grimsel.com/febex). Research backgrounds, proposed methodology with exact time schedule, as well as expected particular scientific and practical contributions will be presented at the conference, in order to recognize possible weak points of the project in the discussion with the highly qualified international conference audience and to take corrective measures at the very first beginnings of the project if it appears necessary. References Galambos, M., Rosskopfova, O., Kufcakova, J. and Rajec, P. (2011) Utilization of Slovak bentonites in deposition of highlevel radioactive waste and spent nuclear fuel. Journal of Radioanalytical and Nuclear Chemistry, 288, 3, 765777. Galambos, M., Suchanek, P. and Rosskopfova, O. (2012) Sorption of anthropogenic radionuclides on natural and synthetic inorganic sorbents. Journal of Radioanalytical and Nuclear Chemistry, 293, 2, 613633. GarciaGutierrez, M., Cormenzana, J.L., Missana, T., Alonso, U. and Mingarro, M. (2011) Diffusion of strongly sorbing cations (60Co and 152Eu) in compacted FEBEX bentonite. Physics and Chemistry of the Earth, 36, 17081713. Kugler, H., Ottner, F., Froeschl, H., Adamcova, R. and Schwaighofer, B. (2002) Retention of inorganic pollutants in clayey base sealings of municipal landfills. Applied Clay Science, 21, 12, 4558. Maes, N., Salah, S., Jacques, D., Aertsens, M., Van Gompel, M., De Canniere, M. and Velitchkova, N. (2008) Retention of Cs in Boom Clay: Comparison of data from batch sorption tests and diffusion experiments on intact clay cores. Physics and Chemistry of the Earth, 33, 149155. Missana, T., GarciaGuttierez, M. and Alonso, U. (2008) Sorption of strontium onto illite/smectite mixed clays. Physics and Chemistry of the Earth, 33, 156162. Pacovsky, J., Svoboda, J. and Zapletal, L. (2007) Saturation development in the bentonite barrier of the MockUpCZ geotechnical experiment. Physics and Chemistry of the Earth, 32, 767779. Valderrama, C. (2010) Transport of strontium through a Cabentonite (Almeria, Spain) and comparison with MX80 bentonite: Experimental and modeling. Water Soil Pollution, 214, 1 4.
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