The PRACLAY Experiment at URL HADES, Mol, Belgium

In Belgium, Boom Clay is considered as one of the potential host formations for the disposal of the High Level radioactive Waste (HLW). The URL HADES at 223 m depth at Mol site was constructed in order to study the feasibility of HLW disposal in Boom Clay. Since 1995, the URL R&D program has focused on large scale demonstration tests like the PRACLAY experiment. The PRACLAY in-situ experiments include a set of three tests: The gallery and crossing test, PRACLAY Heater test and PRACLAY seal test. The main aim of the Heater test is to study at a large scale the thermal impact of a HLW repository on the host rock. The test is housed in the PRACLAY gallery. A hydraulic seal, made of compacted swelling and low permeable bentonite annular ring was installed at the intersection between the heated and the non-heated part of the gallery. The primary objective of the seal is to provide undrained hydraulic boundary conditions for the Heater Test. The PRACLAY gallery was constructed in 2007 and the hydraulic seal was installed in 2010. The bentonite is hydrated by natural and artificial process. The swelling, total pressure and pore pressure of the bentonite are continuously measured and analyzed by numerical simulations to get a better understanding of this hydration processes. The performance of the seal is tested systematically by means of gas injection breakthrough tests and permeability tests at interface bentonite / Boom Clay and in the Boom Clay around the seal. The PRACLAY Heater will be turned on at the end of Oct. 2014, since a sufficient seal swelling has been attained to fulfill its role for the PRACLAY Heater test. This paper will focus on the PRACLAY Seal test: How we understand the process behind the hydration of the bentonite and how we test the performance of the bentonite seal.