Calorimetric determination of energetics of solid solutions of UO2+x with CaO and Y2O3

Mazeina, Lena; Navrotsky, Alexandra; Greenblatt, Martha

doi:10.1016/j.jnucmat.2007.03.269

Cited by 13 publications

(13 citation statements)

References 27 publications

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“…While Mazeina et al [16] presented initial calorimetric data on Ca-and Y-doped uranium oxides, the energetics of the system have not been explored over the whole range and the oxygen content of the samples was not determined accurately. For instance, they reported one sample, Y 0.32 U 0.68 O 2.13 with a enthalpy of drop solution of -55.3 ± 1.2 kJ/mol, which is between the two Y 0.32 U 0.68 O 2-0.5x+y samples in this paper (see Table 3), -50.99 ± 1.35 kJ/mol and -57.84 ± 1.91 kJ/mol.…”

Section: Resultsmentioning

confidence: 99%

“…Despite these uncertainties, it appears that the enthalpy of oxidation of uranium in all these solid solutions is very similar to that of the oxidation of UO 2 to UO 3 . In a previous paper [16], Mazeina et. al.…”

Section: Enthalpies Of Formation ‫ܪ∆‬ ௫ and ‫ܪ∆‬ ௫ା௫௬mentioning

confidence: 94%

“…al. performed the first direct measurements by high temperature oxide melt solution calorimetry of the enthalpy of formation in the solid solutions of UO 2±x with CaO and YO 1.5 [16].…”

Section: Introductionmentioning

confidence: 99%

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Thermochemistry of rare earth doped uranium oxides LnxU1−xO2−0.5x+y (Ln = La, Y, Nd)

Zhang

Navrotsky

2015

Journal of Nuclear Materials

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Lanthanum, yttrium, and neodymium doped uranium dioxide samples in the fluorite structure have been synthesized, characterized in terms of metal ratio and oxygen content, and their enthalpies of formation measured by high temperature oxide melt solution calorimetry. For oxides doped with 10 to 50 mol % rare earth (Ln) cations, the formation enthalpies from constituent oxides (LnO 1.5 , UO 2 and UO 3 in a reaction not involving oxidation or reduction) become increasingly exothermic with increasing rare earth content, while showing no significant dependence on the varying uranium oxidation state. The oxidation enthalpy of Ln x U 1-x O 2-0.5x+y is similar to that of UO 2 to UO 3 for all three rare earth doped systems. Though this may suggest that the oxidized uranium in these systems is energetically similar to that in the hexavalent state, thermochemical data alone can not constrain whether the uranium is present as U 5+ , U 6+ , or a mixture of oxidation states. The formation enthalpies from elements calculated from the calorimetric data are generally consistent with those from free energy measurements.

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Section: Resultsmentioning

confidence: 99%

Section: Enthalpies Of Formation ‫ܪ∆‬ ௫ and ‫ܪ∆‬ ௫ା௫௬mentioning

confidence: 94%

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Thermochemistry of rare earth doped uranium oxides LnxU1−xO2−0.5x+y (Ln = La, Y, Nd)

Zhang

Navrotsky

2015

Journal of Nuclear Materials

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“…While the effect of rare earth substitution on oxygen chemical potentials, lattice constants and thermal conductivity in UO 2 has been well studied (e.g., [9,10] and references therein), and initial experimental and computational studies of formation energetics in urania-rare earth solid solutions have been recently reported [11,12], explicit investigations of defect-clustering behavior has been addressed in relatively few studies [12,13,14]. Computational modeling based on classical ionic pair potentials [14] and defect chemistry models [13] concludes that defect clustering is energetically favorable (as it must be in order for clustering to occur, because clustering decreases the entropy); however, a detailed study of systematic trends in energetics and clustering tendencies with varying concentrations and types of rare earth trivalent cations (M 3+ ) has not been reported to the best of our knowledge.…”

Section: Introductionmentioning

confidence: 99%

Energetics and defect clustering trends for trivalent rare earth cations substituted in UO2

Solomon

Navrotsky

Asta

2015

Journal of Nuclear Materials

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Trends in the energetics and defect clustering tendencies for UO 2 compounds substituted with trivalent rare earth cations (M 3+ ) are investigated computationally using methods based on density functional theory. Higher energetic stability of U 1−x M x O 2−0.5x solid solutions relative to constituent oxides and increased preference for higher oxygen coordination around the trivalent cation are found with increasing size of the M 3+ species. The implications of the computational results for the effect of trivalent fission products on oxygen ion mobility in spent fuel are discussed.

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“…However, the energetics and defect ordering tendencies of these systems remain far less studied compared to other fluorite-structured oxides [5][6][7][8][9][10][11][12]. Specifically, only one calorimetry study [22] and one ionic pair potential modeling investigation [23] have been reported to date. The aim of the current work is to provide further insight into the thermochemical behavior of UO 2 doped with trivalent cations through the application of density functional theory (DFT)-based calculations in which we explore stability and defect ordering/clustering trends with respect to relative cation sizes.…”

Section: Introductionmentioning

confidence: 99%

Computational study of the energetics and defect clustering tendencies for Y- and La-doped UO2

et al. 2014

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The energetics and defect ordering tendencies in solid solutions of fluorite-structured UO 2 with trivalent rare earth cations (M 3+ = Y, La) are investigated computationally using a combination of ionic pair potential and density functional theory based methods. Calculated enthalpies of formation with respect to constituent oxides show higher energetic stability for La solid solutions than for Y. Additionally, calculations performed for different atomic configurations show a preference for reduced (increased) oxygen vacancy coordination around La (Y) dopants. The current results are shown to be qualitatively consistent with related calculations and calorimetric measurements of heats of formation in other trivalent doped fluorite oxides, which show a tendency for increasing stability and increasing preference for higher oxygen coordination with increasing size of the trivalent impurity. The implications of these results are discussed in the context of the effect of trivalent impurities on oxygen ion mobilities in UO 2 , which are relevant to the understanding of experimental observations concerning the effect of trivalent fission products on the oxidative corrosion rates of spent nuclear fuel.

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Calorimetric determination of energetics of solid solutions of UO2+x with CaO and Y2O3

Cited by 13 publications

References 27 publications

Thermochemistry of rare earth doped uranium oxides LnxU1−xO2−0.5x+y (Ln = La, Y, Nd)

Thermochemistry of rare earth doped uranium oxides LnxU1−xO2−0.5x+y (Ln = La, Y, Nd)

Energetics and defect clustering trends for trivalent rare earth cations substituted in UO2

Computational study of the energetics and defect clustering tendencies for Y- and La-doped UO2

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