Chemical signatures correlated with uranium oxide processing are of interest to forensic science for inferring sample provenance. Identification of temporal changes in chemical structures of process uranium materials as a function of controlled temperatures and relative humidities may provide additional information regarding sample history. In this study, a high-purity α-U3O8 sample and three other uranium oxide samples synthesized from reaction routes used in nuclear conversion processes were stored under controlled conditions over 2-3.5 years, and powder X-ray diffraction analysis and X-ray absorption spectroscopy were employed to characterize chemical speciation. Signatures measured from the α-U3O8 sample indicated that the material oxidized and hydrated after storage under high humidity conditions over time. Impurities, such as uranyl fluoride or schoepites, were initially detectable in the other uranium oxide samples. After storage under controlled conditions, the analyses of the samples revealed oxidation over time, although the signature of the uranyl fluoride impurity diminished. The presence of schoepite phases in older uranium oxide material is likely indicative of storage under high humidity and should be taken into account for assessing sample history. The absence of a signature from a chemical impurity, such as uranyl fluoride hydrate, in an older material may not preclude its presence at the initial time of production. LA-UR-15-21495.

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Changes in the visual characteristics of uranium oxide surfaces and morphology following storage under different conditions of temperature and relative humidity may provide insight into the history of an unknown sample. Sub-samples of three a-U 3 O 8 materials-one that was phase-pure and two that were phase-impure-were stored under controlled conditions for two years. Scanning electron microscopy was used to image the oxides before and after storage, and a morphology lexicon was used to characterize the images. Temporal changes in morphology were observed in some sub-samples, and changes were greatest following exposure to high relative humidity.

Experimental measurements and theoretical evaluation of changes in chemical speciation of α-UO3 using XRD, EXAFS, TGA, and DFT calculations.

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A c c e p t e d M a n u s c r i p t 1 HIGHLIGHTS  UF 6 hydrolysis was carried out under reaction conditions that were water deficient for preparation of UO 2 F 2 products. SEM Images of products of UF 6 hydrolysis deposited onto carbon conducting tape and aluminum tape showed different morphologies.  Morphologies of material deposited on aluminum after hydrolysis of UF 6 and stored under high humidity conditions change after one week.  Chemical characterization by powder X-ray diffraction analysis and -Fourier Transform Infrared Spectroscopy revealed formation of UOF 4 , a likely reaction intermediate in UF 6 hydrolysis.ABSTRACT: Characterization of the chemical speciation and morphologies of products formed from hydrolysis of uranium hexafluoride (UF 6 ) is important for predicting dispersion and contamination of released material, or health consequences from inhalation of air-borne particles. We report products of hydrolysis of UF 6 in which the quantity of water was insufficient for complete formation of UO 2 F 2 . Material was deposited onto carbon tape and aluminum. Scanning Electron Microscopy was employed to characterize textures and particle sizes, and powder X-ray diffraction analysis and μ-Fourier Transform Infrared Absorption spectroscopy were used to characterize chemical speciation. These results revealed that the ratio of H 2 O to UF 6, depository substrate composition, and storage conditions must be considered when evaluating chemical speciation, morphologic textures and particles size of UF 6 hydrolysis products. LA-UR-15-23846.

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