Oxidation and anion lattice defect signatures of hypostoichiometric lanthanide-doped UO2

Olds, Travis A.; Karcher, Samuel E.; Kriegsman, Kyle W.; Guo, Xiaofeng; McCloy, John S.

doi:10.1016/j.jnucmat.2019.151959

Cited by 25 publications

(19 citation statements)

References 47 publications

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“…While it has been shown that a zircon doped with 10 wt% 239 Pu would become fully amorphous after only 1,400 years, 37 preliminary calculation have shown that very little Pu would be ultimately released over a 500,000 year time span due to the relatively short half-life of 239 Pu as well as the retained low solubility of amorphous zircon. 25,27 Thus, as uranium is the main component of spent nuclear fuel 25,27,[38][39][40] and cerium constitutes a useful surrogate for plutonium, [41][42][43][44] these minerals are also representative of how long-lived actinides will behave when incorporated into the zircon structure. These actinide-loaded crystalline waste forms would then be permanently disposed of in either a mined geologic repository or deep borehole.…”

Section: Introductionmentioning

confidence: 99%

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

et al. 2021

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Orthosilicates adopt the zircon structure-types (I41/amd), consisting of isolated SiO4 tetrahedra joined by A-site metal cations, such as Ce and U. They are of significant interest in the fields of geochemistry, mineralogy, nuclear waste form development and material science. Stetindite (CeSiO4) and coffinite (USiO4) can be formed under hydrothermal conditions despite both being thermodynamically metastable. Water has been hypothesized to play a significant role in stabilizing and forming these orthosilicate phases, though little experimental evidence exists. To understand the effects of hydration or hydroxylation on these orthosilicates, in situ high temperature synchrotron and laboratory-based X-ray diffraction was conducted from 25 °C to ~850 °C. Stetindite maintains its I41/amd symmetry with increasing temperature but exhibits a discontinuous expansion along the a-axis during heating, presumably due to the removal of water confined in the [001] channels, which shrink against thermal expansion along the a-axis. Additional in situ high temperature Raman and FTIR spectroscopy also confirmed the presence of the confined water. Coffinite was also found to expand nonlinearly up to 600 °C, and then thermally decompose into a mixture of UO2 and SiO2. A combination of dehydration and dehydroxylation is proposed for explaining the thermal behavior of coffinite synthesized hydrothermally. Additionally, we investigated high temperature structures of two coffinite-thorite solid solutions, uranothorite (UxTh1-xSiO4), which displayed complex variations in composition during heating that was attributed to the negative enthalpy of mixing. Lastly, for the first time, the coefficients of thermal expansion of CeSiO4, USiO4, U0.46Th0.54SiO4, and U0.9Th0.1SiO4 were determined to be αV = 4.21 × 10 -6

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Section: Introductionmentioning

confidence: 99%

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

et al. 2021

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“…Recent computational studies on lanthanide-doped UO 2 [22] have shown that trivalent cation size influences oxidation, in that the strain associated with small cations results in stabilization from further contraction upon oxidation; this result is supported by our previous investigations where Yb:UO 2 showed delayed oxidation compared with Nd:UO 2 . [1] In the case here, there may be a different effect, because Zr is considerably smaller than Th and results in worse oxidation, but the charge compensation mechanism is not present, so the effects of oxygen vacancies and interstitials will be different for the tetravalent dopants. The structural mechanisms of the differences in oxidation behavior of these doped materials thus need further exploration, such as with in situ Raman studies as shown here.…”

Section: In Situ Heat Stage Ramanmentioning

confidence: 85%

“…UO 2 was prepared using the nitrate precipitation method, as described previously. [1] For doped samples, the respective nitrate salt was added to the uranyl nitrate solution. Ammonium peroxide was then added to the aqueous nitrate solution until a pH of 9 was reached.…”

Section: Sample Synthesismentioning

confidence: 99%

“…Samples of previously described [1] lanthanide-doped UO 2 were irradiated at the Dalton Cumbrian Facility, United Kingdom. Eight millimeter diameter pellets, $2 mm thick, of undoped and (Ce, Nd, or Yb)-doped UO 2 were mounted such that one side of each pellet was exposed.…”

Section: Sample Synthesismentioning

confidence: 99%

“…Raman spectroscopy has been used extensively to study the structure of uranium oxides and defects caused by rare-earth doping, oxidation, irradiation, isotope enrichment, and the formation of surface alteration secondary phases. [1][2][3][4][5][6] UO 2 is particularly well-suited for study with Raman spectroscopy, because the perfect fluorite lattice has only a few Raman active modes, but anion-related defects in UO 2 generate many more. Pure UO 2 has a sharp T 2g Raman mode at 445 cm À1 and the first-order longitudinal optical (1LO) mode at 575 cm À1 .…”

Section: Introductionmentioning

confidence: 99%

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Benefits of using multiple Raman laser wavelengths for characterizing defects in a UO₂ matrix

Karcher

Mohun

Olds

et al. 2022

J Raman Spectroscopy

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Raman spectroscopy is one of the most useful techniques for studying the structure of UO 2 and changes due to specific defects caused by doping, changes in stoichiometry, irradiation, or heating under oxidizing conditions. In this paper, we illustrate several aspects of the application of Raman techniques to the study of UO 2 , including the use of wavelength-dependent excitation (455, 532, and 785 nm) to assess the effects of doping (Nd, Th, and Zr), ion irradiation, and in situ heating and oxidation (UO 2 to U 3 O 8 ). Additionally, we show examples of how correlative microscopy is possible using electron backscatter diffraction combined with Raman maps of specific vibration bands or of laser-induced luminescence generated by rare-earth dopants in the matrix.For each of these applications, we suggest optimal excitation wavelengths that vary depending on the desired data. Blue (455 nm) excitation tends to promote oxidation even at low powers, but because Raman spectra change little with doping, irradiation-induced changes are easier to observe. Green (532 nm) excitation is optimal for observing electron-phonon resonance effects in UO 2 and offers a good compromise for high-temperature oxidation experiments, delivering high-quality spectra for both UO 2 and U 3 O 8 . Infrared (785 nm) excitation is best for observing "defect" bands associated with doping in UO 2 , as changes with irradiation are small. Raman spectroscopy is particularly suited for studying the stability of UO 2 towards oxidation in the presence of dopants simulating fission products, where electron-phonon resonant effects, dopant ion luminescence, and mapping can be used together to investigate structural rearrangement as a function of temperature. These techniques can offer insight into microstructural changes in UO 2 fuels at higher burnups envisioned in future reactors.

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Isotopic effect of oxygen on the Raman mapping of a polycrystalline uranium dioxide UO₂

Gaillard,

Sarrasin,

Panetier

et al. 2024

J Raman Spectroscopy

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Uranium dioxide (UO2) is a widely studied material due to its use as fuel in pressurised water reactors (PWR), and Raman spectroscopy is a technique of choice to characterise the evolution of its microstructure. UO2 crystallises in a fluorite CaF2 (space group Fm‐3m) structure that gives rise to a unique Raman signature, the T2g band. However, several other bands are often detected whose attribution remains unclear. The present study gives new insights on the Raman spectrum of UO2 thanks to the combination of isotopic labelling with 18O and Raman imaging. In addition to the expected T2g, U2 (LO), 2LO and U3 bands, we have detected a doublet at 885 and 925 cm−1, a U* band at 555 cm−1 in some specific areas and two bands located at 367 and 1196 cm−1. All Raman bands shift under the effect of the replacement of 16O by 18O, excepting for the U* band that could not be detected anymore. The isotopic shift ratio could be determined for 20% and 30% 18O labelling. No discrepancy in band position is observed between grains and grain boundaries, except for the U2(LO) band. We also evidence a difference between the U defect bands and the 885 and 925 cm−1 doublet bands evolution under labelling, although the latter also seems to be connected to the presence of defects in the material.

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Oxidation and anion lattice defect signatures of hypostoichiometric lanthanide-doped UO2

Cited by 25 publications

References 47 publications

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

Benefits of using multiple Raman laser wavelengths for characterizing defects in a UO₂ matrix

Isotopic effect of oxygen on the Raman mapping of a polycrystalline uranium dioxide UO₂

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Oxidation and anion lattice defect signatures of hypostoichiometric lanthanide-doped UO2

Cited by 25 publications

References 47 publications

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO4 (M = Ce, U)

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO4 (M = Ce, U)

Benefits of using multiple Raman laser wavelengths for characterizing defects in a UO2 matrix

Isotopic effect of oxygen on the Raman mapping of a polycrystalline uranium dioxide UO2

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Product

Resources

About

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

The Role of Water and Hydroxyl Groups in the Structures of Stetindite and Coffinite, MSiO₄ (M = Ce, U)

Benefits of using multiple Raman laser wavelengths for characterizing defects in a UO₂ matrix

Isotopic effect of oxygen on the Raman mapping of a polycrystalline uranium dioxide UO₂