Design and development of large-scale in-situ PRACLAY heater test and horizontal high-level radioactive waste disposal gallery seal test in Belgian HADES

In Belgium, the Boom clay was selected as a potential host formation for the disposal of high-level radioactive waste (HLW). To demonstrate the suitability of Boom clay for bearing thermal load induced by the HLW, a large-scale in-situ heater test, called PRACLAY heater test, will be conducted in the underground research laboratory (URL) in Mol. Owing to the limitations of the test (a short period of time compared with that considered in a real repository, different boundary conditions, etc.), the test is designed to simulate, in a conservative way, the most critical state and phenomena that could occur in the host rock. The PRACLAY gallery was excavated at the end of 2007; the heating phase will begin in 2010 and will last for at least 10 years. The PRACLAY gallery itself leaves an opportunity to study the possibilities of sealing a disposal drift in Boom clay and testing the feasibility of hydraulic cut-off of any preferential pathway to the main access gallery through the excavation damage zone (EDZ) and the lining with a seal in a horizontal drift (horizontal seal). Indeed, this is a generic problem for all deep geological disposal facilities for HLW. An annular seal made of compacted swelling bentonite will be installed in the front of the heated part of the PRACLAY gallery for these purposes. This paper provides detailed considerations on the thermo-hydro-mechanical (THM) boundary conditions for the design of the PRACLAY heater test and the seal test with the support of numerical calculations. It is believed that these important items considered in the PRACLAY heater test design also constitute key issues for the repository design. The outcome of the PRACLAY heater test will be an important milestone for the Belgian repository design.