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

The thermal decomposition of studtite (UO2)O2(H2O)2ยท2H2O 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.
Authors:
 [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
Publication Date:
OSTI Identifier:
1304726
Report Number(s):
LA-UR--16-23089
Journal ID: ISSN 0022-3115
Grant/Contract Number:
AC52-06NA25396; SC0001089
Type:
Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 478; Journal Issue: C; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY UO2; Studtite; Calorimetry; Enthalpy of formation; Nuclear fuel alteration