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Through diffusion study on Olkiluoto veined gneiss and pegmatitic granite from a structural perspective

Published online by Cambridge University Press:  20 February 2017

Mikko Voutilainen ,
Jussi Ikonen ,
Juuso Sammaljärvi ,
Jukka Kuva ,
Antero Lindberg ,
Marja Siitari-Kauppi  and
Lasse Koskinen
Mikko Voutilainen*
Affiliation:
University of Helsinki, Department of Chemistry, P.O. Box 55 00014 University of Helsinki, Finland
Jussi Ikonen
Affiliation:
University of Helsinki, Department of Chemistry, P.O. Box 55 00014 University of Helsinki, Finland
Juuso Sammaljärvi
Affiliation:
University of Helsinki, Department of Chemistry, P.O. Box 55 00014 University of Helsinki, Finland
Jukka Kuva
Affiliation:
University of Jyväskylä, Department of Physics, P.O. Box 35, 40014 University of Jyväskylä, Finland
Antero Lindberg
Affiliation:
Geological Survey of Finland, Betonimiehenkuja 4, 02151 Espoo, Finland
Marja Siitari-Kauppi
Affiliation:
University of Helsinki, Department of Chemistry, P.O. Box 55 00014 University of Helsinki, Finland
Lasse Koskinen
Affiliation:
Posiva Oy, Olkiluoto, 27160 Eurajoki, Finland
*
*(Email: ma.voutilainen@helsinki.fi)
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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 needs to be well characterized to assess the risks inherent to the long term safety of the site. In the bedrock the possibly released radionuclides are mainly transported by water conducting fractures and their transport is retarded by diffusion and sorption. In porous materials these properties are typically linked to microscopic pore structure (pore size distribution, tortuosity and constrictivity) and chemical nature of the minerals and groundwater.

In this work transport properties of veined gneiss (VGN) and pegmatitic granite (PGR) samples from Olkiluoto were studied using various through diffusion experiments and the C-14-PMMA autoradiography. Through diffusion experiments were performed on rock cores using HTO and 36Cl in water phase and He in gas phase as tracers. The effective diffusion coefficients (De) determined for the VGN were found to be dependent on the tracer molecule (De(HTO) < De(He) < De(Cl)) whereas for the PGR such a dependence was not found. The porosity distributions determined by the C-14-PMMA autoradiography revealed the difference in the pore structure between the samples. The porosity of VGN consists mostly of grain boundary pores and pores between biotite lamellae. Due to a high content of nanometer scale pores anion exclusion affected the results of 36Cl and Knudsen diffusion the ones of He for VGN. Furthermore, in the PGR micrometer scale intra- and intergranular fissures form a connected network for diffusive transport and thus all tracers diffuse at the same rate.

Keywords

diffusionadsorptionporosity
Type
Articles
Information
MRS Advances , Volume 1 , Issue 61: Scientific Basis for Nuclear Waste Management XXXIX , 2016 , pp. 4041 - 4046
Copyright
Copyright © Materials Research Society 2017 

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References

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