Plutonium Speciation, Solubilization,And Migration in soils

The DOE is currently conducting cleanup activities at its nuclear weapons development sites, many of which have accumulated plutonium (Pu) in soils for 50 years. To properly control Pu migration within Federal areas and onto public lands, to better evaluate the public risk, and to design effective remediation strategies, a fundamental understanding of Pu speciation and environmental transport is needed. Our goal is to use characterization, mobility, thermodynamic, and mineral-interaction data to develop better models of radionuclide transport and risk assessment which will enable the development of science-based decontamination strategies. In addition, if direct characterization of Pu in samples from a contaminated site reveal that the Pu is predominantly in an exceedingly low soluble, low mobility form, then acceptable, reasonable limits for site remediation and closure can be set in a directly defensible manner. Our overarching research approach has the following three interrelated facets: characterization of Pu in samples from a contaminated site; fundamental study of environmentally-relevant Pu species; and thermodynamic geochemical modeling of PU speciation and mobility. This approach differs from those of most other projects funded at a similar level because of its very broad scope and the range of specific methods and techniques used in the research. While one can argue that our approach is overly ambitious, it is absolutely mandated by the state of actinide environmental science. Unlike most other contaminant metals, the knowledge on Pu within each of these subfields is woefully inadequate to support site remediation and stewardship. There are also clear transition paths for each type of information, i.e. site characterization results can be used by owners and stake holders to better understand their contamination problems and remediation issues; fundamental data on Pu species can fill important gaps in existing geochemical databases; thermodynamic modeling using improved data and better defined site conditions can be used to predict long-term contaminant behavior and can suggest particular Pu species for further study. Within this context, the specific tasks described in our original proposal are the following: l Site Characterization. The total plutonium content in soils surrounding the Rocky Flats Environmental Technology Site (RFETS) had been thoroughly characterized previously; however, less work has been done to separate plutonium in these soils into its sources (site activities at Rocky Flats or global fallout) and no work has successfully determined the speciation of the plutonium. Personnel at the site supported this effort by providing information, samples, and mechanisms to disseminate our results. Task 1--Characterize the plutonium in soils and groundwaters from the RFETS site, determining both the speciation, including concentration, isotopic ratio (239/240), oxidation state and specific chemical form, and the distribution, from a microscopic level (particle size, association with other elements) to a macroscopic level (depth in soil, location). To our knowledge, characterization with this level of detail has never been done for an environmental plutonium sample. Task 2--Communicate these results to the site to assist in site management, remediation, and stewardship