The THM boundary conditions control in the design of the large scale in situ PRACLAY heater test

In Belgium, the Boom Clay was selected as a potential host formation for the disposal of the HLW nuclear wastes. In order to demonstrate at large scale the suitability of the Boom Clay as a host rock, in terms of performance of the disposal system, to undergo the thermal load induced by the HLW, a large scale in-situ heater test, called PRACLAYheater test is being designed and will be conducted in the Underground Laboratory HADES, excavated at 223 m depth in the Boom Clay near Mol city. Numerical THM (Thermal-Hydro-Mechanical) scoping calculations revealed that the THM boundary conditions imposed by the repository design influence highly the THM disturbances into the host rock. Consequently, it was decided to perform the PRACLAYin situ heater test under most penalizing THM conditions to build confidence on the performance of the Boom Clay as a host rock. Based on numerical calculations, this paper presents detailed considerations of the THM boundary conditions impact on the design of the PRACLAYheater test. It is believed that the outcome of the PRACLAYheater test will be an important milestone for the Belgian repository design.