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ehaviour expected based on measurements on rock samples, data modelling also shows that for
strongly sorbing tracers, complexities in mass transfer (borehole mixing, diffusion in filters, etc.)
strongly influence experimental data, making clear-cut estimations of values for diffusion-retention
parameters in the undisturbed clayrock difficult. Some of these ambiguities will certainly be removed,
at least for the more mobile tracers, when information on tracer distribution in the surrounding
rock becomes available (post-FUNMIG) for providing further constraints on model interpretations.
Finally, Pu(V) diffusion into Opalinus clayrock samples kept under in-situ confining pressures was
measured by FZK-INE, with results from both batch and in-diffusion experiments showing that Pu
is reduced to the Pu(IV), probably by Fe(II) contained in rock minerals (probably chlorite), and is
retained (sorption or other process?) on preferential sites.
Callovo-Oxfordian
The Callovo-Oxfordian research program is, by design, quite similar to that described for the
Opalinus clayrock since one of the objectives of RTDC3 was to generate comparable data sets for
different clayrocks in order to identify common characteristics and eventual significant differences
in RN migration properties. The principal difference between the two is in the working hypothesis,
and consequent experimental approach, taken by a consortium of French partners (CEA, ERM,
Hydr’asa, Andra) for quantifying and modelling migration of highly-sorbing RN in clayrock. The
guiding assumption here was that, given the very small spatial scales covered by RN migration during
the time frames of in-diffusion experiments owing to the preponderant effect of sorption, it
would be important to be able to quantify how tracer mass present in the diffusion profile was distributed
relative to rock mineral constituents and associated porosity. The approach taken involved
carrying out, on a single, oriented cm-scale volume of clayrock:
Characterization of the mineral-pore space organization and construction of the corresponding
2-3D numerical models, including analysis of grain organization (cf. §2.2), followed by TDD
modelling of diffusion of non sorbing tracers (cf. §3.2);
In-diffusing a highly-sorbing tracer (Eu, Cu) into the rock (gradient perpendicular to sedimentation
plane) for a given period, then sectioning the rock perpendicular to bedding;
Simultaneous mapping of tracer mass and mineral grain 2D spatial distributions, relative to the
in-diffusion surface, using LIBS and Electron Probe Micro Analyser (calculation of the average
diffusion profile), followed by construction of numerical models of the in-diffusion zone;
Inverse modelling of tracer diffusion (source term, spatial distribution) to determine Da values
for the porous mineral zones (clay matrix + disseminated pyrite), followed by comparison with
batch Kd.
The results for Cu(II) (the most complete dataset available) are rich in information concerning both
tracer migration phenomena and potential experimental artefacts which can make measurements on
such small rock volumes difficult to interpret. Regarding the former, it was found (i) that Cu does
not penetrate into, nor sorb significantly onto, the carbonate and quartz grains and associates preferentially
with the pyrite minerals dispersed in the clay matrix, (ii) Cu diffusion profiles (clay and
pyrite) developed over a distance of roughly 2 mm into the rock and (iii) that evaluation of the entire
dataset (reservoir + profile) yields values for De (2.5 * 10 -10 m 2 .s -1 ) and Rd (3500 mg/L) which
are consistent both with results showing that De for cations in the COx are generally significantly
higher than the value for HTO (~ 2.5*10 -11 m 2 s -1 ) and measurements of Kd(Cu) which give values
in the 3000 to 9000 range (note that Rd could be controlled by the redox reactivity of this tracer).
On the other hand, detailed analysis also shows that the roughly 50 m layer of rock in contact
with the source solution is significantly perturbed, both in terms of its mineral-porosity composi-
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