Aiming to implement the Brazilian repository for disposal of low and intermediate level of radioactive wastes, the “Project RBMN” is being coordinated by CNEN. The repository is made of multiple barriers in order to prevent or retain the migration of radionuclides throughout these paths to the environment. Clays are used as backfill and coverage layers, which are the repository natural barriers. Recently, in Nuclear Technology Development Center (CDTN) a protocol for clay characterization was elaborated, and it was used the Brazilian bentonite as a reference. In this protocol are established some physical and chemical tests and their reference values that are essential for the characterization of materials to be used as backfill and coverage layers in the surface repository. This research intended to evaluate the applicability of this protocol to characterize soil without and with bentonite. The bentonite content added to the soil was 30%. The results were compared with the reference values of the protocol and literature for materials with similar mineralogical features. The results showed an increase of the specific surface and of the cation exchange capacity, as the result of the bentonite addition. The hydraulic conductivity is significant decreased by the addition of bentonite.

The use of nuclear technology is growing in Brazil, where it is possible to carry out the entire nuclear fuel cycle. This technology generates radioactive waste that must be treated before being released into the environment or stored in suitable facilities. Then, the first national repository - CENTENA - will be implemented, where all low and intermediate level radioactive waste generated in Brazilian territory will be safely stored. One of the barriers that will compose the repository will be composed of natural materials such as soils and clays, the latter for having a high adsorption and cation exchange capacities and swelling potential. The purpose of the article is to show the research carried out in Centro de Desenvolvimento da Tecnologia Nuclear (CDTN) with natural materials aiming their use in natural barriers. Four materials were characterized: CDTN soil, this soil with bentonite, expanded vermiculite and bentonite, using the clay characterization protocol. Primary mineralogical, physical and chemical analyzes were performed, such as X-ray diffraction, scanning electron microscopy, particle size distribution, specific surface area and cation exchange capacity. The results showed that these clays are potentially candidates for composing CENTENA's natural barriers.