The crystal structure of γ-UO3

Engmann, Rolf; Wolff, Philippe

doi:10.1107/s0365110x63002656

Cited by 47 publications

(15 citation statements)

References 1 publication

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“…Uranium enriched from either ore concentrates or recycled spent nuclear fuel undergoes a refinement process that produces the intermediate species UO 3 from the denitration of uranyl nitrate hexahydrate (UNH) after purification (typically) by solvent extraction. The trioxide uranium species is then reduced to UO 2 and subsequently converted to UF 4 , and ultimately UF 6 , by fluorination prior to enrichment. The UO 3 species is also an intermediate product of uranium mining from carbonate rich gangue.…”

Section: Importance Of Uo 3 Within the Nuclear Fuel Cyclementioning

confidence: 99%

Investigation of Uranium Polymorphs

Sweet¹,

Henager²,

Hu³

et al. 2011

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Executive SummaryThe UO 3 -water system is complex and has not been fully characterized, even though these species are common throughout the nuclear fuel cycle. As an example, most production processes for UO 3 result in a mixture of up to six or more different polymorphic phases, and small differences in these conditions will affect phase genesis that ultimately result in measureable changes to the end product. As a result, this polymorphic feature of the UO 3 -water system may be useful as a means for determining process history. This research effort attempts to better characterize the UO 3 -water system with a variety of optical techniques for the purpose of developing some predictive capability for estimating process history in polymorphic phases of unknown origin. Three commercially relevant production methods for the production of UO 3 were explored. Previously unreported low temperature routes to β-and γ-UO 3 were discovered. Raman and fluorescence spectroscopic libraries were established for pure and mixed polymorphic forms of UO 3 in addition to the common hydrolysis products of UO 3 . An advantage of the sensitivity of optical fluorescence microscopy over x-ray diffraction has been demonstrated. Preliminary aging studies of the α and γ forms of UO 3 have been conducted. In addition, development of a 3-D phase field model used to predict phase genesis of the system was initiated. Thermodynamic and structural constants that will feed the model have been gathered from the literature for most of the UO 3 polymorphic phases.v

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Section: Importance Of Uo 3 Within the Nuclear Fuel Cyclementioning

confidence: 99%

Investigation of Uranium Polymorphs

Sweet¹,

Henager²,

Hu³

et al. 2011

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“…Numerous structural determinations have been made on uranium(VI) oxides [5][6][7][8][9][10], hydroxides [11,12] and alkali metal uranates [10, 13 -15]. In contrast, the structure of the hydrated oxide, U0 2 (0H) 2 · H 2 0, has been studied by X-ray diffraction (XRD), but atomic coordinates have yet to be determined [16][17][18][19][20][21], The difficulty in obtaining a detailed structure by XRD for natural as well as synthetic schoepite polymorphs most likely arises from the tendency towards amorphous structures in these materials, owing to the variability in the degree of hydration.…”

Section: Introductionmentioning

confidence: 99%

Determinations of Uranium Structures by EXAFS: Schoepite and Other U(VI) Oxide Precipitates

et al. 1996

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We have investigated the structures of U(VI) oxides precipitated from room temperature aqueous solutions at low ionic strength as a function of pH. Using the uranium Lm-edge extended Xray absorption fine structure (EXAFS) and infrared (IR) spectroscopies as probes of the local structure around the uranium, a trend is observed whereby the axial oxygen bond lengths from the uranyl groups increase from 1.80 A at pH = 7 to 1.86 A at pH = 11. Shifts in the IR spectral frequencies support this assignment. A concomitant decrease in the equatorial oxygen and nearest-neighbor uranium bond lengths also occurs with increasing pH. Expansion of the linear 0=U=0 group is seen directly at the L m absorption edge where multiple scattering resonances systematically shift in energy. EXAFS curve-fitting analysis on these precipitates and a sample of synthetic schoepite indicate that the structure of the species formed at pH = 7 is similar to the structure of schoepite. At pH = 11, the precipitate structure is similar to that of a uranate.

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“…The complexity of the cu-UO, structure has also been shown by Siegel and Hoekstra [6], who used both spectroscopic and X-ray methods. The structure of p-UO, has been examined by Debets [7] and that of y-UO, by Engmann and de Wolff [8], by Siegel and Hoekstra [9], and by Loopstra et al [lo]. In both structures, uranium atoms having six-and sevenfold coordination with oxygen atoms occur; however, the atomic arrangement in y-UO, is markedly different from that in /?-UO,.…”

Section: Introductionmentioning

confidence: 99%