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Energetics of metastudtite and implications for nuclear waste alteration [electronic resource].

Published:
Washington, D.C. : United States. Dept. of Energy. Office of Basic Energy Sciences, 2014. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
Physical Description:
pages 17,737-17,742 : digital, PDF file
Additional Creators:
United States. Department of Energy. Office of Basic Energy. Energy Frontier Research Centers (EFRC), United States. Department of Energy. Office of Basic Energy Sciences, and United States. Department of Energy. Office of Scientific and Technical Information
Access Online:
www.osti.gov

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Summary:
Metastudtite, (UO<sub>2</sub>)O<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>, 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. We observed four decomposition steps 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<sub>3</sub> to crystallize orthorhombic α-UO<sub>2.9</sub>; and reduction to crystalline U<sub>3</sub>O<sub>8</sub>. 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.
Subject(s):
Note:
Published through SciTech Connect., 11/24/2014., Proceedings of the National Academy of Sciences of the United States of America 111 50 ISSN 0027-8424 AM, and Xiaofeng Guo; Sergey V. Ushakov; Sabrina Labs; Hildegard Curtius; Dirk Bosbach; Alexandra Navrotsky.
Funding Information:
SC0001089
View MARC record | catkey: 24051481