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  • Author or Editor: P. Bertsch x
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The legacy of nuclear weapons production has resulted in vast tracks of land contaminated with fission products, mainly 137Cs, and at the U.S. Department of Energy's Savannah River Site (SRS) alone there is over 120 km2 of land contaminated with low-levels of 137Cs. Soils on the SRS are highly weathered and dominated by sand-sized quartz grains with the clay fraction consisting primarily of kaolinite and crystalline and poorly crystalline iron oxides (<5&). Our results showed that the majority of 137Cs in the Lower Three Runs Creek floodplain were retained in the sand-sized fraction (>52 mm) of the soil. Frayed edge site measurements were performed in order to probe the interaction between 137Cs and the sand fraction, with the results indicating that the vast majority of the 137Cs was strongly retained and existed in the residual fraction. These results prompted examination into the mineralogy of the soils in a hope to elucidate the mechanisms of 137Cs retention by the sand fraction. The results from this study provide new evidence for selective retention of 137Cs in larger-grained particles than previously demonstrated.

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Two complimentary spectroscopic techniques, X-ray absorption and fluorescence spectroscopy have been conducted at spatial scales of 1 to 25 μm on uranium contaminated soil sediments collected from two former nuclear materials processing facilities of the DOE: Fernald, OH and Savannah River Site, SC. A method of imbedding particles in a non-reactive Si polymer was developed such that individual particles could be examined before and after extraction with a wide range of chemicals typically used in sequential extraction techniques and others proposed forex situ chemical intervention technologies. Using both the micro-X-ray fluorescence (XRF) and micro-X-ray Absorption Near Edge Structure (XANES) techniques, both elemental and oxidation state distribution maps were generated on individual particles before and following chemical extraction. XANES can determine the relative proportion of U(VI) and U(IV) in phases comprising individual particles before and after extraction and showed that greater than 85% of the uranium existed as hexavalent U(VI). Fluorescence spectra of contaminated particles containing mainly U(VI) revealed populations of uranyl hydroxide phases and demonstrated the relative efficacy and specificity of each extraction method. Correlation of XAS and fluorescence data at micron scales provides information of U oxidation state as well as chemical form in heterogeneous samples.

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