Establishment of characterizing parameters of clay as a filling material and coverage for repository

The multiple barriers of a repository should be able to provide adequate containment of radionuclides during all the previewed time for the operation and institutional control. One of these barriers is the backfill layer, located between the waste packages and other barriers. Furthermore, after shutting the disposal units with concrete, various materials are used to compose the final coverage of the deposition area. The backfill and the cover layer can be composed of clay or clay mixed with cement, with soil or with rocks. The last layer is a vegetation cover. The selection of the best clay should take into consideration some physical-chemical and mechanical properties. Bentonite is a clay with high absorption capacity, and large volume change in moistening and drying processes, being also effective in the contaminant retention. Additionally, it presents unique properties, such as high swelling potential. Some bentonite characterization works have been developed in the Laboratory of Cementation at CDTN/CNEN (LABCIM/CDTN). The sequence of experiments was: granulometric analysis, moisture, compaction test, hydraulic conductivity and cation exchange capacity. Some initial characterization results are presented and discussed. The paper summarizes these previous studies in order to have the basis for creating a protocol for characterization of a bentonite as a reference material. (author)