Characterization of Swelling Clays as Buffer/ Backfill Material for Geological Repositories of Immobilized Radioactive Liquid Waste

After gaining considerable expertise in establishing and exercising waste management strategy by immobilization of high-level radioactive liquid waste (HLW) in borosilicate glass matrix followed by its interim storage, it is envisaged to focus on geologic disposal of radioactive waste packages. The multi barrier disposal system is considered one of the options for isolation of radioactive waste from human environment for an extended period of time. The engineered barrier comprises of waste form, canisters, over packs, buffer and backfill material whereas host rock serves as the natural barrier. The buffer and backfill materials play an important role because it can retard the migration of radionuclides by delaying the contact with ground water and associated sorption. Characterization and demonstration of efficacy of swelling clays in repository condition forms an integral part of studies ensuring the safe disposal of high level radioactive waste. Natural clays may be used solely or as a phase in a buffer/backfilling mixture because of its low hydraulic conductivity, high specific surface area and in some cases swelling ability. Long term performance of these materials has to be assessed with respect to their suitability as candidate backfill material. Twenty six nos. of swelling clay samples were collected from the natural deposits of different locations from western zone of the country. Samples collected have been taken up for detailed characterization of clay with respect to mineralogical, physico chemical, chemical, microscopic and geotechnical properties. From the X-ray diffraction patterns presented and the d-values associated with the patterns, montmorrilonite and quartz have been identified as major phases present in all the samples of swelling clay. Energy Dispersive X-Ray (EDX) analysis of the swelling clay samples mainly indicated presence of Si, Al, Na, K, Mg supporting thereby the X-Ray diffraction data. SEM micrographs of two typical clay samples at different magnifications indicate flake like surface morphology. The clay samples were found to be having swelling ability indicating smectite rich composition and optimum CEC. While chemical analysis indicates the presence of SiO2, Al2O3, Fe2O3, MgO, Na2O, CaO as major elements, higher amount of chlorides is INTERNATIONAL JOURNAL OF ENVIRONMENTAL ENGINEERING SCIENCE [IJEES] 226 attributed to the marine origin of the clay. Present paper given an account the experimental studies carried out to evaluate the potentiality of using swelling clays as buffer/backfill material for geological repositories of immobilized highlevel radioactive liquid waste.