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Energetics of metastudtite and implications for nuclear waste alteration

Guo, Xiaofeng ; Ushakov, Sergey V. ; Labs, Sabrina ; Curtius, Hildegard ; Bosbach, Dirk ; Navrotsky, Alexandra

Proceedings of the National Academy of Sciences - PNAS, 2014-12, Vol.111 (50), p.17737-17742 [Periódico revisado por pares]

United States: National Academy of Sciences

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  • Título:
    Energetics of metastudtite and implications for nuclear waste alteration
  • Autor: Guo, Xiaofeng ; Ushakov, Sergey V. ; Labs, Sabrina ; Curtius, Hildegard ; Bosbach, Dirk ; Navrotsky, Alexandra
  • Assuntos: Decomposition ; Differential scanning calorimetry ; Enthalpy ; enthalpy of formation ; Heat measurement ; High temperature ; MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES ; materials and chemistry by design ; metastudtite ; Minerals ; nuclear (including radiation effects) ; nuclear fuel alteration ; Oxygen ; Peroxides ; Physical Sciences ; Radioactive wastes ; Spent fuels ; stability ; synthesis (novel materials) ; synthesis (self-assembly) ; Thermal decomposition ; Thermodynamics ; Uranium
  • É parte de: Proceedings of the National Academy of Sciences - PNAS, 2014-12, Vol.111 (50), p.17737-17742
  • Notas: http://dx.doi.org/10.1073/pnas.1421144111
    ObjectType-Article-1
    SourceType-Scholarly Journals-1
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    USDOE Office of Science (SC), Basic Energy Sciences (BES)
    DESC0001089; SC0001089
    Contributed by Alexandra Navrotsky, November 5, 2014 (sent for review August 28, 2014)
    Author contributions: X.G., S.V.U., S.L., H.C., D.B., and A.N. designed research; X.G. and S.L. performed research; X.G., S.V.U., S.L., H.C., D.B., and A.N. analyzed data; and X.G., S.V.U., S.L., and A.N. wrote the paper.
  • Descrição: Significance Uranium peroxides, metastudtite and studtite, can be formed on exposure of UO ₂ based nuclear fuels to water during geological disposal or as a result of reactor accidents. We report detailed structural and thermochemical analysis of the metastudtite decomposition process. The thermodynamic data confirm the irreversible transformation from studtite to metastudtite and show that metastudtite can be a major oxidized corrosion product at the surface of UO ₂ and contribute a significant pathway to dissolution. The prevalence of metastudtite may require additional tailoring of waste forms to minimize this dissolution pathway for uranium. Metastudtite, (UO ₂)O ₂(H ₂O) ₂, is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, −1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220 °C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400 °C to 530 °C; oxygen loss from amorphous UO ₃ to crystallize orthorhombic α-UO ₂.₉; and reduction to crystalline U ₃O ₈. This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water.
  • Editor: United States: National Academy of Sciences
  • Idioma: Inglês
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