In Belgium, the URL HADES was constructed in the Boom Clay formation at the Mol site to investigate the feasibility of geological disposal in a clay formation. Since 1995, the URL R&D programme has focused on large scale demonstration tests like the PRACLAY Heater and Seal tests.

The main objective of the Heater Test is to demonstrate that the thermal load generated by the heat-emitting waste will not jeopardise the safety functions of the host rock.

The primary objective of the Seal Test is to provide suitable hydraulic boundary conditions for the Heater Test. The Seal Test also provides an opportunity to investigate the in-situ behaviour of a bentonite-based EBS.

The PRACLAY gallery was constructed in 2007 and the hydraulic seal was installed in 2010. The bentonite is hydrated both naturally and artificially. The swelling, total pressure and pore pressure of the bentonite are continuously measured and analysed by numerical simulations to get a better understanding of this hydration processes.

The timing of switching on the heater depends on the progress of the bentonite hydration, as a sufficient seal swelling is needed to fulfill its role. A set of conditions to be met for the heater switch-on and its schedule will be given.

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