The UK Committee on Radioactive Waste Management (CoRWM) recommended, in
2006, that geological disposal coupled with safe and secure interim storage should
have been the way forward for the long-term management of the UK’s higher activity
wastes. The design of the underground repository contemplates the presence of
bentonite plugs to seal access galleries and deposition boreholes and hence the
interaction between the clay-based backfill material and the underground water.
Remote monitoring of the fluid saturation of the barrier, the waste canisters and of the
surrounding subsurface Geological Disposal Facility environment assumes a relevant
importance to guarantee the safety of the repository and to increase the confidence and
the reliance of the communities living in areas potentially affected by the repository
over time.
This remote monitoring of the Engineered Barrier System represents a technical
challenge due to the unsuitability of some of the traditional geotechnical techniques or
to the intrinsic unreliability of many geophysical prospecting techniques in providing
information about the evolution of the Thermo-Hydro-Mechanical-Chemical coupling
of the system over long timescales up to and including post-closure evolution.
In this project, I offer an initial approach to an innovative way of using mineral
magnetism, and, in particular, I analyse the possible exploitation of corrosion-induced
variations of the magnetic properties of several magnetic materials to monitor water
saturation in the Engineered Barrier System and its evolution through time.
Initially the reactivity of several natural and synthetic materials is tested under
different “extreme” conditions to analyse the feasibility of the research concept and
identify the materials more adapt to carry out the job. The effects that the corrosion of
the magnetic materials has on the clay matrix is also analysed in detail throughout all
the thesis work.
The initial tests lead to the identification of specific transitions in the hysteretic
behaviour of three of the initial candidates (Nd-Fe-B, AlNiCo and SmCo alloys).
These three materials are subsequently tested under conditions closer to a real
“evolved” Barrier System, where the groundwater interacts, with cementiferous grout
producing hyperalkaline leachates.
The final tests consider the temporal evolution (after 4, 8 and 12 months) of the
magnetic properties of these materials in a dysoxic environment under imposed fluid-flow.
The results show a clear change in the hysteretic properties of the three materials
analysed and the feasibility of the monitoring of the Barrier fluid saturation in the
short-term. Furthermore, the corrosion of the magnets, under the conditions applied,
did not cause formation of non-swelling clays