Workreport 2007-33



Mineralogical Characterization of Gouge Fillings in ONKALO Facility at Olkiluoto


Gehör, S.



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Posiva Oy submitted an application to the Finnish Government in May 1999 for the Decision in Principle to choose Olkiluoto in the municipality of Eurajoki as the site of the final disposal facility for spent nuclear fuel. A positive decision was made at the end of 2000 by the Government. The Finnish Parliament ratified the decision in May 2001. The decision makes it possible for Posiva to focus the confirming bedrock investigations at Olkiluoto, where in the next few years an underground rock characterisation facility, ONKALO, will be constructed. The construction of the ONKALO access tunnel started in September 2004.

The purpose of this work was to evaluate the chemical and mineralogical compositions of the gouge fillings from eleven samples selected from the tunnel passage lengths of 68 m, 70 m, 81 m, 87 m, 130 m, 295 m, 409 m, 522 m, 901m, 957 m and 960 m. Special interest was designed for characterizing the clay phases and for determination of their swelling potential.

The gouge fillings were dry and wet screened and their mineralogical properties were investigated by the methods of X-ray and thermogravimetry. The chemical composition of the less than 2 µm grain size was analysed by XRF.

The mineralogical study proved that half of analysed gouge fillings contain montmorillonite. The main mineral phases, identified include quartz, chlorite-group phases, illite, kaolinite, montmorillonite (smectite group), calcite, and feldspars. Bulk rock XRF analysis for the < 2 µm fractions show comparatively wide compositional range, specially in relation with SiO2, Al2O3 and K2O. The highest contents of the aforementioned oxides in among the samples studied are found from the montmorillonite-bearing clay fractions. The content of sulphur is typically less than 2 % in the clay fraction and 5.5 % S in maximum.


ONKALO, mineralogical characterization


Mineralogical Characterization of Gouge Fillings in ONKALO Facility at Olkiluoto (pdf) (2.5 MB)


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