Oxygen diffusion in hypostoichiometric uranium dioxide

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1981

OSTI ID:6267524

Kim, K C

The tracer oxygen diffusivity in UO/sub 2-x/ has been measured along the lower two phase boundary. The diffusion couple consisted of two matched hypostoichiometric UO/sub 2/ wafers, one enriched with /sup 18/O and the other normal. These two were pressed together with a bond of liquid U in between. After a diffusion anneal the /sup 18/O concentration profile was determined by ion microprobe mass analysis, from which diffusion coefficients were obtained. The results showed much higher diffusion coefficients than those of stoichiometric UO/sub 2/. This directly proved that the major defect species in UO/sub 2-x/ is the anion vacancy. Activation energy of anion vacancy migration was measured to be 11.7 +- 3.0 kcal/mole. A diffusion model established for UO/sub 2/ and UO/sub 2+-x/ showed that in stoichiometric UO/sub 2/ both interstitials and vacancies contribute significantly to oxygen diffusion and neither can be neglected; at 1400/sup 0/C their contributions are about equal. This model was extended to nearly stoichiometric UO/sub 2+-x/ to predict oxygen diffusion coefficients in these stoichiometry ranges. Also deduced from the model were the Frenkel defect energy and entropy of 85.6 +- 9.2 kcal/mole and 18.2 +- 7.3 eu, respectively. Using these values, the contribution of Frenkel disorder to the excess enthalpy of UO/sub 2/ was evaluated. Calculation showed that Frenkel disorder accounts for 87% of the excess enthalpy at 3000/sup 0/K. A simple two band model for electronic excitation, with a band gap of 2.0 eV and effective electron mass of 7.6 m/sub e/, accounted for the remainder of the excess enthalpy.

• Research Organization: California Univ., Berkeley (USA)
• OSTI ID: 6267524
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ACTINIDE COMPOUNDS
CHALCOGENIDES
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIFFUSION
ELEMENTS
EVEN-EVEN NUCLEI
FRENKEL DEFECTS
ION MOBILITY
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
MATHEMATICAL MODELS
MOBILITY
NONMETALS
NUCLEI
OXIDES
OXYGEN
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PARTICLE MOBILITY
PHYSICAL PROPERTIES
POINT DEFECTS
STABLE ISOTOPES
TRACER TECHNIQUES
URANIUM COMPOUNDS
URANIUM DIOXIDE
URANIUM OXIDES
VACANCIES