Characterisation studies of Romanian bentonite as engineered barrier in radioactive waste repositories

The safety of radioactive waste disposal relies on multi-barrier containment of radionuclides by both engineered and natural systems. The bentonite as both buffer and backfill material has a key role for repository safety. This is because one of the favourable properties of bentonite is that the mineral montmorillonite swells when it is in contact with water. Since the space available is limited, this clay will perfectly fill the available voids. Because of Romania's complex geology, it is necessary to develop an efficient engineered barrier system (EBS). The disposal concept is to build an EBS that in a stable geological environment, provide sufficient margins in its long term performance for isolation of the waste, applicable to a range of potential geological conditions and their fixture evolution. In Romania the nuclear waste repository at Baita Bihor planned to use indigenous bentonite as backfill material; this clay, naturally occurring is found in deposits in our country. The aim of this paper is to try to describe romanian bentonite by determining its physical, chemical and mechanical characteristics. At the beginning we will present some characteristics of powder (uncompacted) bentonite like density, grain size and water content. Then the paper will contain the compaction characteristics (maximum dry density, optimum water content); for the beginning, the compaction tests were performed without mixing with other material. Also, another characteristics presented in this paper are liquid limit, plastic limit and plasticity index. Taking into account the importance of hydraulic properties, we performed the permeability test to determine the hydraulic conductivity of bentonite. (authors)