A HETEROGENEOUS BENTONITE BARRIER AFTER 18 YEARS OPERATION: FINAL PHYSICAL STATE OF THE BENTONITE BARRIER OF THE FEBEX IN SITU TEST

Abstract

The FEBEX in situ experiment was a full-scale test reproducing the near-field of a nuclear waste repository. It was performed in a gallery excavated in granite, with a heater whose surface temperature was set to100°C simulating the waste canister and a bentonite barrier composed of highly-compacted blocks. The test was completely dismantled after eighteen years of operation. Numerous samples of bentonite were taken for the on-site determination of dry density and water content.

The on-site measurements showed that the physical state of the barrier was very much affected by the processes to which it had been subjected, namely hydration with the granite groundwater and/or thermal gradient. Although the degree of saturation of the bentonite was overall quite high, there were important water content and dry density gradients everywhere in the barrier, but steeper around the heater. These gradients did not impair the performance of the barrier, but imply that the barrier can be irreversibly inhomogeneous.