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study the possible anisotropy, two additional instrumented boreholes have been installed (Fig. 2,
left).
Figure 2 (left): The ATLAS heater (8 m long, up to 1800 W) and monitoring boreholes (temperature
and pore water pressures). The 3D model is also shown (right). The heating power applied during
the first campaign.
During the first heating campaign (from April 2007 to April 2008), three different heating power
levels (400 W, 900 W and 1400 W) were applied (Fig. 2, right). The campaign has provided valuable
data on the thermal characteristics of the host rock. After extending the set-up with an additional
inclined borehole, the second heating campaign will investigate these topics more in detail.
2.2 Demonstration at large scale - the PRACLAY Heater and Seal Test
Initially, PRACLAY was about simulating as closely as possible a disposal gallery at real scale in
HADES. The review of the engineered barrier system design led to a reorientation of the PRA-
CLAY programme to a generic experiment, so that the experimental results remain valid in case the
repository design would change. The original scope of the PRACLAY experiment – demonstration
of the reference design for vitrified HLW – was enlarged to characterisation, verification, confirmation
and demonstration of relevant elements of the disposal system and their behaviour by means
of a combination of small surface and large in-situ experiments. Additional opportunities for large
scale surface testing of specific designs have been offered by the ESDRED Integrated Project, with
e.g. the gallery backfilling test.
The Heater Test will start after completion of the Seal that will close off the backfilled (and later
saturated) part of the PRACLAY gallery. The test will mainly consist in heating the host formation
through heater elements installed in the test gallery. The heating conditions have been established
based on the predicted repository conditions through thermal modelling [1]. The intention is that
within the limited time span of 10 years of heating, the largest thermal disturbances that would occur
in the real case are simulated. The resulting heating procedure specifies a constant temperature
of 80°C at the gallery outside during these 10 years. This temperature will be obtained gradually to
avoid excessive stresses in the gallery lining. The heater test will further give insight in the thermal
effect on the man-made structures (in particular the thermal stress in the gallery lining), and the
THM coupling behaviour of Boom Clay. Instrumented boreholes, installed from the connecting gal-
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