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Title: Energetics of metastudtite and implications for nuclear waste alteration

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 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 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.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [2]
  1. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab.; Univ. of California, Davis, CA (United States). Dept. of Chemistry
  2. Univ. of California, Davis, CA (United States). Peter A. Rock Thermochemistry Lab.
  3. Forschungszentrum Julich (Germany). Inst. for Energy and Climate Research (IEK-6), Nuclear Waste Management
Publication Date:
Grant/Contract Number:
SC0001089; DESC0001089
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 111; Journal Issue: 50; Related Information: MSA partners with University of Notre Dame (lead); University of California, Davis; Florida State University; George Washington University; University of Michigan; University of Minnesota; Oak Ridge National Laboratory; Oregon state University; Rensselaer Polytechnic Institute; Savannah River National Laboratory; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Energy Frontier Research Centers (EFRC); Materials Science of Actinides (MSA)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; nuclear (including radiation effects); materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly); nuclear fuel alteration; stability; enthalpy of formation; uranium; metastudtite
OSTI Identifier:
1235149
Alternate Identifier(s):
OSTI ID: 1210536