Energetics of metastudtite and implications for nuclear waste alteration

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

Research output: Contribution to journalArticlepeer-review

45 Scopus citations

Abstract

Metastudtite, (UO2)O2(H2O)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 syntheticmetastudtitewas 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 UO3 to crystallize orthorhombic α-UO2.9; and reduction to crystalline U3O8. 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.

Original languageEnglish (US)
Pages (from-to)17737-17742
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Issue number50
DOIs
StatePublished - Dec 16 2014
Externally publishedYes

Keywords

  • Enthalpy of formation
  • Metastudtite
  • Nuclear fuel alteration
  • Stability
  • Uranium

ASJC Scopus subject areas

  • General

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