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). In order to demonstrate at large scale the suitability of the Boom Clay to undergo the thermal load induced by the HLW, a large scale in-situ heater test, called PRACLAY heater test will be conducted in the URL of Belgium. The Praclay gallery hosting the heater test leaves an opportunity to study the possibility to seal a disposal drift in Boom clay and to test the feasibility to cut-off hydraulically any preferential pathway to the main access gallery through the EDZ (Excavation Damage Zone) and the lining with a seal in a horizontal drift (horizontal seal). This paper provides detailed consideration on the Thermal-Hydro-Mechanical boundary conditions for the design of the Praclay heater and seal tests with the support of numerical scoping calculations. It is believed that these important items considered in the Praclay heater test design constitute also key issues for the repository design. The outcome of the Praclay heater test will be an important milestone for the Belgian repository design.