Characterization of Uranium Speciation in a Metallic Matrix
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Characterization of Uranium Speciation in a Metallic Matrix Gini Curran, Patrick G. Allen1, Daniel F. Caputo, Ken R. Czerwinski Nuclear Engineering Department, Massachusetts Institute of Technology, 24-210, 77 Massachusetts Ave. Cambridge, MA 02139 1 Seaborg Institute, Lawrence Livermore National Laboratory, 7000 East Ave., PO Box 808, L-231, Livermore, CA 94551 ABSTRACT Three metallic slag samples recovered from the site of their inadvertent creation several decades after the fact were sectioned and analyzed to determine uranium speciation to evaluate environmental behavior as well as assess proliferation resistance of the waste form. Uranium concentration in the highly inhomogeneous samples was up to 5% by weight as determined by gamma spectroscopy. Sample sections were milled in a hardened steel ball mill for x-ray absorption spectroscopy analysis (XAS). Powders were digested in a mixture of heated concentrated nitric acid and peroxide and analyzed for elemental content using ICP-AES and ICP-MS. Though elemental content of the samples varied widely, high concentrations of Al were consistently found. Other metals of significance were Ti, Fe, Ni, Cu, Zn, and Sn. High Pb concentrations were occasionally found. XAS analysis revealed the samples contained primarily uranyl and another phase identified as a uranium-aluminum melt. INTRODUCTION Three metallic slag samples recovered after an extended period of subsurface disposal were analyzed to determine uranium speciation and concentration variation. The results will be used to evaluate environmental behavior as well as assess proliferation resistance of the waste form. The three samples were created inadvertently when uranium-bearing containers were exposed to a fire. They consist of a mixture of various metals and local sedimentation exposed to high heat for a short duration of time. Evidence of residual firefighting chemicals as well as some vegetation was also present. Subsamples were extracted from the interior and exterior of the three pieces. The speciation of the uranium was determined using x-ray absorption spectroscopy (XAS). The samples were also analyzed for elemental content using ICP-AES and ICP-MS. EXPERIMENTAL DETAILS Upon receipt, the three slags were washed to remove loose particles as well as organic matter that had integrated into the surfaces of the pieces during their lengthy environmental exposure. After cleaning, samples were obtained for elemental and XAS analysis by physically removing sections from various areas of the slags. The resulting samples ranged from hard metallic pieces to soft chips loosened from the surface. The samples were massed, and then milled into a fine powder in a hardened steel ball mill chamber. Some of the samples could not successfully be ground using this method and were not included in this analysis. Uranium content of each sample was determined using
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a HPGe detector. Table I lists samples and uranium content. Uranium content varied widely with sampling location. Table I. Sample list. Sample sets 1
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