Characterization of Portuguese geomaterials, the clay component of ranas, as potential liners for low and intermediate radioactive disposal sites

Safety assessment of low and intermediate level waste (LILW) repositories requires the understanding of radionuclides sorption-desorption mechanisms, mainly the degree of interaction between radionuclides and mineral surfaces. Among the different radionuclides that are part of the Portuguese radwastes' inventory 137Cs is one of the most important from the radiological point of view due to its high radiotoxicity. The clay component of natural geomaterials termed ranas, originated from an area located in the NE Mainland of Portugal, was studied for their potential as effective barriers. These geomaterials (grains-size fractions <63 μm, <36 μm) were characterized in terms of cationic exchange capacity (CEC), frayed edge sites (FES) and radiocaesium interception potential (RIP). Organic matter content and pH were also determined. The fractions were mineralogically analyzed by X-ray diffraction and by instrumental neutron activation analysis (INAA) for chemical elemental composition. Smectite (montmorillonite), illite, kaolinite were identified. The capacity of FES is related to the samples granulometry as opposed to what was observed for CEC and RIP. The behavior of ranas was not similar for all samples which may be related to differences in mineralogy. Future studies with regard to the behaviour of radiocaesium are expected to clarify the possible application of these geomaterials as liner/backfill/buffer for a LILW repository. (author)