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Chloride diffusion in pore water in Olkiluoto veined gneiss and pegmatitic granite from a structural perspective

Published online by Cambridge University Press:  20 February 2017

J. Sammaljärvi ,
J. Ikonen ,
M. Voutilainen ,
P. Kekäläinen ,
A. Lindberg ,
M. Siitari-Kauppi ,
P. Pitkänen  and
L. Koskinen
J. Sammaljärvi*
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, Finland
J. Ikonen
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, Finland
M. Voutilainen
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, Finland
P. Kekäläinen
Affiliation:
Department of Physics, University of Jyväskylä, Finland
A. Lindberg
Affiliation:
Geological Survey of Finland, Finland
M. Siitari-Kauppi
Affiliation:
Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, Finland
P. Pitkänen
Affiliation:
Posiva oy, Olkiluoto, 27160 Eurajoki, Finland
L. Koskinen
Affiliation:
Posiva oy, Olkiluoto, 27160 Eurajoki, Finland
*
*(Email: [email protected])
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Abstract

Spent nuclear fuel from Finnish power plants is planned to be deposited deep in the crystalline bedrock in Olkiluoto, Finland. The bedrock and more specifically the elemental composition of ground water, which is composed of the fracture water and the matrix pore water, needs to be well characterized to assess the risks inherent to the long term safety of the site. To this end, it is valuable to investigate elemental composition of the matrix pore water since it tends to conserve hydrogeological signals for longer time spans compared to open fracture waters.

In this study, the chloride concentration of matrix pore water in veined gneiss (VGN) and pegmatitic granite (PGR) samples were investigated. Chloride was out-diffused from the naturally saturated rock cores into deionized water. Chloride pore diffusion coefficients were derived by modelling the chloride breakthrough curves obtained from the out-diffusion experiments. Two component modelling gave best fit to the experimental results. There two diffusion coefficients were (9±2)×10-11 m2/s and (0.5±0.1)×10-11 m2/s for PGR and (2.5±0.5)×10-11 m2/s and (0.4±0.1)×10-11 m2/s for VGN. Porosity distribution and total porosities of the rock samples were studied with the C-14-PMMA autoradiography. Porosity for PGR was found to be 0.6 % with large mineral transecting fissures, and porosity for VGN was found to be 0.7 % with highly porous mineral clusters connected to each other via grain boundaries and intragranular pores. The findings here show that heterogeneity has to be taken into account in modelling to find better agreement with the experimental results. C-14-PMMA autoradiography results indicate dual-component behavior for diffusion in PGR and VGN which were used in the modelling.

Keywords

Diffusionadsorptionporosity
Type
Articles
Information
MRS Advances , Volume 1 , Issue 61: Scientific Basis for Nuclear Waste Management XXXIX , 2016 , pp. 4047 - 4052
Copyright
Copyright © Materials Research Society 2017 

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References

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