Euradwaste '08 - EU Bookshop - Europa

Pressure [bar, abs.]
3,4
2,9
2,4
1,9
1,4
0,9
sensor 1
sensor 2
03.04.05
12.10.05
22.04.06
31.10.06
11.05.07
19.11.07
29.05.08
Figure 3.4.3: Evolution of total pressure at
top of the mock-up seal
Pressure [bar]
253
2,1
1,9
1,7
1,5
1,3
1,1
0,9
0,7
27.10.05
26.02.06
28.06.06
28.10.06
27.02.07
30.06.07
30.10.07
Sensor 1
Sensor 2
29.02.08
30.06.08
Figure 3.4.2: Evolution of total pressure at top
of the in-situ seal
Figure 3.4.2 shows the evolution of the total pressure in one of the respective in-situ experiment
with the same material mixture for comparison. After about 24 moths of testing, the total pressure
stabilizes at values similar to those determined on the laboratory test samples (compare the value of
0.2 – 0.4 MPa Table 3.4-1) and that observed in the mock-up. Thus, similar sealing properties as
observed in these preceding investigations can be expected in the in-situ experiments. Although the
pressure seems to have reached its final value in this in-situ experiment the respective water breakthrough
did not take place during the hitherto testing period. Testing will thus be continued in the
forthcoming months including the determination of the gas entry/break-through pressure of the
saturated seal and the remaining gas permeability after gas break-through.
3.5 Non-intrusive monitoring development and testing (NDA)
Context
Under ESDRED Module 1, a programme was implemented to non-intrusively monitor an existing
Nagra experimental demonstration, the HG-A experiment, at Mont Terri. Following consideration
of repository concepts, monitoring objectives and potential non-intrusive techniques, ESDRED
Module 1 partners concluded that cross-hole seismic tomography was the most promising technique
to investigate changes in the backfill and saturation conditions of a micro-tunnel.
The HG-A experiment is one of a number that have been undertaken in the Opalinus Clay rocks of
the Mont Terri underground rock laboratory (URL) in Switzerland. The HG-A experiment was designed
to mimic the evolution of a sealed disposal tunnel, replicating the phases of buffer saturation
and gas generation (following corrosion processes of the disposal canister). The aims of the HG-A
experiment are to identify gas migration and to measure gas migration through the host rock (the
Opalinus Clay geology) and along the engineered seals of a filled tunnel.
Investigations in the HG-A experiment focus on a 1m diameter micro-tunnel, which was back-filled
with a coarse grained sand mixture ( 2 - 6 mm grain size) and closed with a hydraulic megapacker.
There was nothing in the tunnel to represent the wasteform or a metallic waste package. The
study covered several phases, representing backfill emplacement, saturation of the micro-tunnel and
gas generation. For the non-intrusive studies, the degree of saturation, gas storage and pressure
build-up, and its effects on the geophysical data were monitored over the various phases of the HG-