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esults obtained so far. Most of the bibliographic references included refer to studies carried out
during the project.
2. Transport in crystalline rocks: PA relevant processes
Groundwater chemistry
RNs mainly migrate dissolved in the groundwater: the chemistry of the water (salinity, pH, Eh,
complexing agents) is one of the main parameters controlling the aqueous speciation of RNs, their
solubility and their retention in the medium. Chemistry influences several other processes, colloid
formation and stability amongst others. When studying a crystalline medium, first key points are to
understand what chemical reactions and sorption processes occur in the host rock (also in the presence
of the engineered barrier) and what their effects on radionuclide mobility are (WP 4.1). Geochemical
characterization includes the identification of water types and presence of elements affecting
the water chemistry and its evolution (water/rock interactions, water paths, residence times,
flow/mixing region, redox condition, effects of micro-organisms or colloids). Furthermore, to know
if present geochemical models are able to account for these processes and if they are adequately
calibrated in front of real systems is necessary.
Site specific studies, as those carried out in the Swedish sites Forsmark and Simpevarp (WP4.5),
represent a direct support for PA [6]. The evaluation of field geochemical data (Eh, pH, TOC, colloids
presence, Mg-Ca, etc…) is needed to verify if they met safety criteria for site selection. On the
other hand, these studies are fundamental to understand phenomena that cannot be obtained from
laboratory studies. The understanding of the hydro-geochemical conditions of the past and present
is the basis to predict future evolutions. Therefore, the complete characterization of a site allows
gaining capability and confidence for the extrapolation of data when the information is scarce or not
available. In certain environments as the Fennoscandian shield, the climate may have also very important
effects. For this reason, different methodologies were implemented to understand the effects
of glacial melt water intrusion [7].
In-situ studies carried out at the FEBEX site serve to quantify mass transfer processes from the bentonite
to granite, to perform in-depth analysis of the effects of the bentonite on the water chemistry
and to analyse the presence and stability of bentonite colloids in realistic conditions. Attention is
focused on hydro-geological structure (fractures, fault regions, lamprophyre...) previously identified
[8]. Within FUNMIG, at the end of 2005, two investigation boreholes FU05.001 and FU05.002
were drilled quasi parallel to the FEBEX gallery, and relatively near to the bentonite surface (30
and 60 cm respectively) [9]. To characterize the crystalline rock, three short boreholes were additionally
drilled for the geophysical experiments (FU05.003, -4 and -5) [8]. Several other boreholes
around the gallery already existed (19 radial boreholes, FBX, Bous, etc.) that represent additional
source of information both for hydro-geochemistry and hydrogeology. A schematic of FEBEX tunnel
with the location of the new boreholes and main hydro-geological structures is presented in Figure
1.
Several water sampling campaigns were carried out for both water chemistry and colloid analyses.
The waters from the new boreholes are slightly alkaline and with low electrical conductivity being
very favourable conditions for bentonite colloid stability [4], so that this place is very adequate to
study colloid generation and mobility processes. On the other hand, the migration through granite of
conservative ions like I - and ReO4 - (installed in 1996 with the FEBEX experiment, Figure 1) and
other “natural” tracers from the bentonite (Cl - , Na + ..) is being studied. I - was observed both in
FU05.001 (interval 4, 0.46 ppm) and in FU05.002 (interval 3, 0.85 ppm) in correspondence to the
initial location of the I - impregnated filter papers (Figure 1). The fact that only iodine and not rhenium
was detected must be related to the reducing conditions present in Grimsel waters. The mobility
of Re would be greatly affected if reduction to the oxidation state (IV) occurred.
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