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access shafts, providing higher permeability for water and gases. The EDZ could act as a preferential
pathway for radionuclide transport and may play an important role in the overall performance of
a repository, particularly in scenarios with early canister and seal failure. The extent and the characteristics
of the affected zone may vary significantly.
Prior to NF-PRO, a large number of studies were published regarding EDZ in terms of phenomenology
in different host rocks. Nevertheless, a need was identified for a deeper knowledge of EDZrelated
phenomena in order to establish a better basis for abstracting a PA model of transport in the
EDZ from a detailed scientific description of the processes.
Characterisation of the EDZ
As part of NF-PRO, conventional methods and techniques were applied to study the initiation of the
EDZ and to measure key characteristics and associated parameter values of the EDZ. In addition to
in situ measurements, laboratory tests on rock samples were performed. Experimental data were
compared with results from numerical modelling studies. New techniques for in situ EDZ characterisation
were developed and improved: these include seismic-acoustic monitoring, ultra-sonic logging,
seismic and geoelectric tomography and very high resolution ultrasonic logging.
Short-term evolution of the EDZ
Important progress has been made by NF-PRO with respect to investigations of the phase of repository
operation (short-term evolution of the EDZ). During this phase, ventilation of drifts may cause
desaturation and induce thermo-hydro-mechanical effects and/or chemical perturbations in the host
rock. In general, results from experimental work by NF-PRO on indurated and soft clay rocks indicate
that the extent of the affected zone in the host is very limited. The size of the altered host rock
in the experimental gallery at -445m in the Callovo-Oxfordian formation (Meuse/Haute-Marne
URL, Bure, France) and in the ventilation II experiment in the Opalinus Clay (Mont Terri URF)
typically is in the range of 20 to 60 centimetres. In situ experiments to study the zone affected by
oxidation around the Test Draft in the HADES URF (Mol, Belgium) evidence that the oxidised
zone extents less than one metre in the Boom Clay. The affected zone is associated with open fractures
that form during excavation. Diffusion of oxygen in the Boom Clay is a very slow process,
which is negligible relative to instantaneous oxidation along fractures.
Long-term evolution of the EDZ
Investigations under NF-PRO on the long-term evolution of the EDZ focussed on self-sealing and
gas transport processes in clays and salt host rock.
Laboratory and in situ experiments performed under NF-PRO on plastic and indurated clays have
provided new quantitative data on self-sealing of the EDZ (i.e. the decrease of permeability with
time) and have expanded knowledge on different factors (thermal, mechanical, chemical…) involved.
Short-term microscale processes contributing to self-sealing include swelling of smectite
minerals, mechanical closing due to the plasticity of clay minerals and creep. In the long term, precipitation
of minerals such as carbonates plays a role in self-sealing processes. Other factors such as
resaturation and thermal impact will lead to a quasi-complete self sealing of the EDZ. Observations
made on plastic clays (e.g. Boom Clay) indicate that self-sealing may result in a progressive restoring
of permeability to values comparable to those of undisturbed rock, although residual microscale
evidence of features initially formed in the EDZ network may remain. In indurated clays like the
Callovo-Oxfordian clay, open fractures of the EDZ progressively close and very low permeability
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