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Investigation of mineralogy, porosity and pore structure of Olkiluoto bedrock

Published online by Cambridge University Press:  30 June 2014

Juuso Sammaljärvi ,
Antero Lindberg ,
Jussi Ikonen ,
Mikko Voutilainen ,
Marja Siitari-Kauppi  and
Lasse Koskinen
Juuso Sammaljärvi
Affiliation:
Laboratory of Radiochemistry, University of Helsinki, Finland.
Antero Lindberg
Affiliation:
Geological Survey of Finland, Finland
Jussi Ikonen
Affiliation:
Laboratory of Radiochemistry, University of Helsinki, Finland.
Mikko Voutilainen
Affiliation:
Laboratory of Radiochemistry, University of Helsinki, Finland.
Marja Siitari-Kauppi
Affiliation:
Laboratory of Radiochemistry, University of Helsinki, Finland.
Lasse Koskinen
Affiliation:
Posiva Oy, Finland
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Abstract

Spent nuclear fuel from TVO's (Teollisuuden Voima Oy) and Fortum's nuclear power plants will be deposited deep in the crystalline bedrock in Olkiluoto, Western Finland. The bedrock needs to be well characterized to assess the risks inherent to the waste disposal at the site. If radionuclides (RN) are transported, it happens via water conducting fractures. Retardation may occur either by diffusion into stagnant pore water or by immobilization on mineral surfaces of the rock matrix.

RN’s retardation from flowing water is linked to parameters defining porosity and microscopic rock pore structure, such as pore size distribution, connectivity, tortuosity and constrictivity, and by the mineralogy and chemical nature of the minerals and charge of the pore surfaces.

In this work, centimeter scale rock cores from Olkiluoto were investigated. The work is part of the in situ project REPRO (Experiments to investigate Rock Matrix Retention Properties) where the diffusion and sorption of RN are studied experimentally. Porosity and pore structures were characterized with the PMMA autoradiography method and polarized microscopy, which was used also to ascertain the mineralogy of the samples.

The results show that the rock from the REPRO site has low porosity with a mean value of 0.5% and a range of 0.1-1.5%. Rock heterogeneity explains the variation of porosity values. Correlation between the porosity and the mineralogy was found. Areas of high porosity correspond to areas of altered minerals, such as cordierite, biotite and plagioclase, which cover spatially between 10 and 20% of the rock volume

Keywords

porositygeologictransportation
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1665: Symposium NW – Scientific Basis for Nuclear Waste Management XXXVII , 2014 , pp. 31 - 37
Copyright
Copyright © Materials Research Society 2014 

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References

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