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Title: Thermodynamic studies of studtite thermal decomposition pathways via amorphous intermediates UO3, U2O7, and UO4

Journal Article · · Journal of Nuclear Materials
 [1];  [2];  [1];  [3];  [4]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Earth and Environmental Sciences Division
  2. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab. and NEAT ORU; Washington State Univ., Pullman, WA (United States). Gene and Lina Voiland School of Chemical Engineering and Bioengineering
  3. Univ. of Notre Dame, IN (United States). Dept. of Civil and Environmental Engineering and Earth Sciences; Univ. of Notre Dame, IN (United States). Dept. of Chemistry and Biochemistry
  4. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab. and NEAT ORU

The thermal decomposition of studtite (UO2)O2(H2O)2·2H2O results in a series of intermediate X-ray amorphous materials with general composition UO3+x (x = 0, 0.5, 1). As an extension of a structural study on U2O7, this work provides detailed calorimetric data on these amorphous oxygen-rich materials since their energetics and thermal stability are unknown. These were characterized in situ by thermogravimetry, and mass spectrometry. Ex situ X-ray diffraction and infrared spectroscopy characterized their chemical bonding and local structures. This detailed characterization formed the basis for obtaining formation enthalpies by high temperature oxide melt solution calorimetry. The thermodynamic data demonstrate the metastability of the amorphous UO3+x materials, and explain their irreversible and spontaneous reactions to generate oxygen and form metaschoepite. Thus, formation of studtite in the nuclear fuel cycle, followed by heat treatment, can produce metastable amorphous UO3+x materials that pose the risk of significant O2 gas. Quantitative knowledge of the energy landscape of amorphous UO3+x was provided for stability analysis and assessment of conditions for decomposition.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC52-06NA25396; SC0001089; DESC0001089
OSTI ID:
1304726
Alternate ID(s):
OSTI ID: 1325346
Report Number(s):
LA-UR-16-23089
Journal Information:
Journal of Nuclear Materials, Vol. 478, Issue C; ISSN 0022-3115
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 33 works
Citation information provided by
Web of Science

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Sample seal-and-drop device and methodology for high temperature oxide melt solution calorimetric measurements of PuO 2 journal April 2019
Energetics of hydration on uranium oxide and peroxide surfaces journal June 2019