Oxidation behaviour of uranium and neptunium in stabilised zirconia

Journal Article · Tue Dec 15 04:00:00 EST 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.09.022· OSTI ID:21372426

Walter, Marcus ^[1]; Somers, Joseph ^[1]; Bouexiere, Daniel; Gaczynski, Piotr ^[1]; Brendebach, Boris ^[2]

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1. European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe (Germany)
2. Forschungszentrum Karlsruhe, Institut fuer Nukleare Entsorgung (INE), P.O. Box 3640, D-76021 Karlsruhe (Germany)

Yttria stabilised zirconia (YSZ) based (Zr,Y,U)O{sub 2-x} and (Zr,Y,Np)O{sub 2-x} solid solutions with 6 and 20 mol% actinide were prepared with Y/Zr ratios ranging from 0.2 to 2.0 to investigate uranium and neptunium oxidation behaviour depending on the oxygen vacancies in the defect fluorite lattice. Sintering at 1600 deg. C in Ar/H{sub 2} yields a cubic, fluorite-type structure with U(IV) and Np(IV). Annealing (Zr,Y,U)O{sub 2-x} with Y/Zr=0.2 at 800 deg. C in air results in a tetragonal phase, whereas (Zr,Y,U)O{sub 2-x} with higher Y/Zr ratios and (Zr,Y,Np)O{sub 2-x} retain the cubic structure. XANES and O/M measurements indicate mixed U(V)-U(VI) and Np(IV)-Np(V) oxidation states after oxidation. Based on X-ray diffraction, O/M and EXAFS measurements, different oxidation mechanisms are identified for U- and Np-doped stabilised zirconia. In contrast to U, excess oxygen vacancies are needed to oxidise Np in (Zr,Y,Np)O{sub 2-x} as the oxidation process competes with Zr for oxygen vacancies. As a consequence, U(VI) and Np(V) can only be obtained in stabilised zirconia with Y/Zr=1 but not in YSZ with Y/Zr=0.2. - Graphical abstract: The O/U ratio in oxidised (Zr,Y,U)O{sub 2-x} depends on the Y/U ratio, whereas O/Np in (Zr,Y,Np)O{sub 2-x} correlates with the Y/(Zr+Np) ratio. This indicates that both Zr and Np compete for oxygen vacancies, which hinders the Np oxidation at low Y/Zr ratios. Display Omitted

• OSTI ID: 21372426
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 12 Vol. 182; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
ACTINIDE COMPOUNDS
ANNEALING
ARGON
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIFFRACTION
DOPED MATERIALS
ELEMENTS
FABRICATION
FINE STRUCTURE
FLUIDS
GASES
HEAT TREATMENTS
HYDROGEN
MANAGEMENT
MATERIALS
MINERALS
NEPTUNIUM COMPOUNDS
NEPTUNIUM OXIDES
NONMETALS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
POINT DEFECTS
PYROCHLORE
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE MANAGEMENT
RARE GASES
SCATTERING
SINTERING
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
TRANSURANIUM COMPOUNDS
URANIUM COMPOUNDS
URANIUM OXIDES
VACANCIES
WASTE DISPOSAL
WASTE MANAGEMENT
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY
YTTRIUM COMPOUNDS
YTTRIUM OXIDES
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES