| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+MI-WeA |
| Session: | Actinide and Rare Earth Theory (2:20-3:40 pm)/Nuclear Power, Waste Remediation and Applications (4:20-6:20 pm) |
| Presenter: | Michele Conroy, Pacific Northwest National Laboratory |
| Authors: | E.C. Buck, Pacific Northwest National Laboratory M.A. Conroy, Pacific Northwest National Laboratory J.A. Soltis, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
In this presentation, the history of Pu contamination at the Hanford site will be reviewed, including the various disposal locations, the quantities of Pu and co-contaminants disposed, and recent research efforts designed to unravel the chemical form of Pu in the environmental samples. Microanalytical information will also be presented for the sediments at the Z-9 site. The information will include the chemical characterization of the sediments at two bore holes drilled at the Z-9 sites. Although the majority of the plutonium is present as oxide, using both electron microscopy (EM) and x-ray absorption spectroscopy evidence was found for the formation of nano-sized mixed Pu and iron phosphate hydroxides that are structurally related to rhabdophane-group minerals. The Pu-phosphate formation may depend on the local microenvironment in the sediments, availability of phosphate, and hence the distribution of these minerals may control long-term migration of Pu in the soil. The presentation will also focus the role of in-situ EM can play in understanding nanoparticle formation and its subsequent interaction with substrates.
Iron (II) minerals, when in isolation, will control the fate of Pu; however, in a sediment with clay, calcite, and other soil minerals present as we observed in the Z9 sediments, other phases and elements may have a significant impact on the Pu chemistry. Nevertheless, the complexity found in the natural environments may lead to the formation of phases that may not be predicted in laboratory set-ups. Understanding the chemistry of Pu in complex media requires tools that can probe micro-environments. We have been exploring the use of in-situ EM to investigate the precipitation of Pu. All designs of cells for in-situ electron microscopy incorporate a membrane that prevents evaporation of the liquid sample in the microscope vacuum. We will describe other observations of Pu behaviour, morphology, and compositional changes studied with these new EM methods.