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Radionuclide Retardation in Granitic Rocks by Matrix Diffusion and Sorption

Published online by Cambridge University Press:  01 February 2011

P. Hölttä ,
M. Siitari-Kauppi ,
M. Kelokaski  and
V. Tukiainen
P. Hölttä
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 University of Helsinki, Finland
M. Siitari-Kauppi
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 University of Helsinki, Finland
M. Kelokaski
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 University of Helsinki, Finland
V. Tukiainen
Affiliation:
VTT Processes, Nuclear Energy, P.O.Box 1608, FIN-02044 VTT, Finland
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Abstract

Radionuclide retardation in mica gneiss, unaltered, moderately and strongly altered tonalite was studied by a thin section, batch, in-diffusion and column methods. Objectives were to examine retention processes in different scales and understand the influence of the rock matrix heterogeneity. Attempts were made for a more detailed interpretation of experiments using migration models used in performance assessments adapted for interpreting the laboratory scale experiments. Batch experiments were explained adequately using matrix diffusion-sorption model, instantaneous kinetic sorption model or model in which both mechanisms were taken into account. A numerical code FTRANS was able to interpret in-diffusion of calcium into the saturated porous matrix. Elution curves of calcium for the moderately and strongly altered tonalite fracture columns were explained adequately using FTRANS code and parameters obtained from in-diffusion calculations. Kd-values for intact rock obtained from fracture column experiments were lower than Kd-values for crushed rock indicating that batch experiments overestimate the retardation of radionuclides. Higher sorption and fair dependence on fraction size was obtained for altered tonalites due to the composition of alteration minerals and large specific surface areas.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1107: Scientific Basis for Nuclear Waste Management XXXI , 2008 , 621
Copyright
Copyright © Materials Research Society 2008

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