SANS INVESTIGATION OF PORE STRUCTURE IN NATURAL AND ENGINEERED MATERIALS FOR NUCLEAR WASTE REPOSITORY SYSTEMS

The pore characteristics and fluid transport behavior from the nano- to micrometer scale of natural and engineered materials at field conditions provide fundamental insights into their performance efficiency in regulating radionuclide transport in nuclear waste repositories. Small-angle neutron scattering (SANS) is the canonical technique to be used when probing the pore structure of condensed matters in the 1 to 1000 nm range. In this study, we have characterized the pore features of representative natural and engineered materials for nuclear waste repository systems including clays, rock salt, and clay-cement using SANS, and their evolution over the relevant ranges of humidity, temperature, and pressure, composition, and length scale. Our results demonstrate that each material shows unique pore features. The effects that impact on pore features include sample form and sample environment including humidity, temperature, and pressure. Analysis of the SANS data indicates significant alteration of clays on water diffusion and absorption behavior. These results suggest that SANS is particularly suited for in-situ studies of pore-scale characteristics of low-permeability media and the factors that impact their pore features. As emergent property, nano- to micro-scale structural characterization is crucial in providing insights into pore-scale processes, which are pertinent to upscale continuum model development for field applications.