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In subsurface repositories, active bacterial populations may directly influence the fate and transport of radionuclides including in salt repository systems like the Waste Isolation Pilot Plant in Carlsbad, NM. This research quantified the potential for transport and interaction between Chromohalobacter sp. and Cs in a high ionic strength system (2.6 M NaCl) containing natural minerals. Mini-column experiments showed that Chromohalobacter moved nearly un-retarded under these conditions and that there was neither association of Cs with microbes nor dolomite despite changes in bacterial metabolic phases. Growth batch experiments that monitored the potential uptake of Cs into the microbes confirmed results in column experiments where intracellular uptake of Cs by Chromohalobacter was not observed. These results show that Cs may be highly mobile if released in high ionic strength systems and/or carbonate minerals with negligible inhibition by these microbes. • No Chromohalobacter interaction with cesium at high salt. • No adsorption and intracellular uptake of cesium with Chromohalobacter. • Interaction of cesium with dolomite at high ionic strength. [ABSTRACT FROM AUTHOR]

Highlights: [•] Investigated U and 90Sr release from Dounreay sediment into seawater. [•] Batch and column experiments used, together with sequential extractions. [•] 90Sr was exchangeable and mobilised rapidly under erosion and inundation scenarios. [•] U release was limited by the sediment’s influence on the porewater pH (5.0–6.9). [•] At pH>6.9, U elution profile revealed slow release from a range of binding sites. [Copyright &y& Elsevier]

During the last two decades, the Mont Terri rock laboratory has hosted an extensive experimental research campaign focusing on improving our understanding of radionuclide transport within Opalinus Clay. The latest diffusion experiment, the Diffusion and Retention experiment B (DR-B) has been designed based on an entirely different concept compared to all predecessor experiments. With its novel experimental methodology, which uses in-situ X-ray fluorescence (XRF) to monitor the progress of an iodide plume within the Opalinus Clay, this experiment enables large-scale and long-term data acquisition and provides an alternative method for the validation of previously acquired radionuclide transport parameters. After briefly presenting conventional experimental methodologies used for field diffusion experiments and highlighting their limitations, this paper will focus on the pioneer experimental methodology developed for the DR-B experiment and give a preview of the results it has delivered thus far. Image 1 • Novel experimental set-up for the study of iodide ion diffusion in compacted clay. • In-situ downhole quantification of trace metal amounts. • Visualization of the impact of small-scale heterogeneities on transport properties. • Long-term and large-scale iodide diffusion data acquisition. • Merging of mineralogical, chemical and structural elements for data interpretation. [ABSTRACT FROM AUTHOR]

There is concern that sea level rise associated with projected climate change will lead to the inundation, flooding and erosion of soils and sediments contaminated with radionuclides at coastal nuclear sites, such as Dounreay (UK), with seawater. Here batch and column experiments were designed to simulate these scenarios and sequential extractions were used to identify the key radionuclide solid phase associations. Strontium was exchangeable and was mobilised rapidly by ion exchange with seawater Mg(2+) in both batch and column experiments. In contrast, U was more strongly bound to the sediments and mobilisation was initially limited by the influence of the sediment on the pH of the water. Release was only observed when the pH increased above 6.9, suggesting that the formation of soluble U(VI)-carbonate species was important. Under dynamic flow conditions, long term release was significant (47%), but controlled by slow desorption kinetics from a range of binding sites., (Copyright © 2013 Elsevier Ltd. All rights reserved.)