Porewater in Compacted Water-Saturated MX-80 Bentonite

Abstract

ABSTRACTBentonite is planned to be used in many countries as a buffer material in repositories for spent nuclear fuel. The proper understanding and modelling of the functioning of the water-saturated bentonite requires knowledge about the bentonite microstructure and also the way water is distributed between different phases. This paper presents experimental results from our studies of water in compacted, water-saturated MX-80 bentonite at dry densities in the range 0.7-1.6 g/cm3. Three techniques, Cl-porosity, SAXS and proton NMR measurements, were applied to samples kept at room temperature, while TEM imaging was applied to high pressure frozen samples. The combined results of these techniques strongly indicate that the two major water phases in the compacted MX-80 bentonite samples are ‘interlayer’ and ‘non-interlayer’ water. The results of the relative amounts of different water types by SAXS and NMR are very similar. The results by Cl-porosity measurement indicate that only part of the non-interlayer water is available for anions. Those observations are discussed in comparison to TEM micrographs. Our study provides solid experimental evidence for the presence of two major water phases in water-saturated bentonite and estimates their relative proportions and pore sizes.