Oxygen diffusion and hydrogen solubility in tetragonal zirconia
The effect of hydrogen on corrosion of the cladding of a partially uncovered core is an important issue in severe nuclear accident analysis. Besides the effect of the external influence of steam starvation, corrosion of Zircaloy may be reduced in H{sub 2}O/H{sub 2} mixtures because of a decrease in oxygen mobility in the oxide scale due to the presence of dissolved hydrogen. However, there is no information on how much hydrogen dissolves in zirconium oxide nor whether dissolved hydrogen affects oxygen diffusion in the oxide layer. Even in the absence of hydrogen, the oxygen self diffusion coefficient in tetragonal zirconia (ZrO{sub 2}) is not known. The gas-solid isotope exchange method with the continuously recording gravimetric technique was used for the measurement of the oxygen tracer diffusion coefficient. The isotope reaction is, ZrO{sup 16}{sub 2} + 2H{sub 2}O{sup 18} = ZrO{sup 18}{sub 2} + 2H{sub 2}O{sup 16}. Mixtures of H{sub 2}O/He and H{sub 2}O/H{sub 2} were used to elucidate the hydrogen effect. Both single-crystal and polycrystalline zirconia were used as samples. The oxygen diffusion in zirconia was found to be strongly dependent on the impurities (extrinsic diffusion). Based on the different impurity levels of the samples, the oxygen vacancy diffusivity was found to be: D{sub v} (cm{sup 2}/s) = (4.7 +/- 1.8) {times} 10{sup {minus}3}exp({minus}{sup (15.4{plus minus}1.2)kcal/mol}{sub RT}). Grain boundary diffusion is dominant in polycrystalline zirconia due to the movement of grains for stress relaxation during oxidation. The solubility of hydrogen in zirconia was measured by vacuum extraction of hydrogen from a sample infused with hydrogen. Mass spectrometric detection of the released hydrogen by the modulated beam method was used.
- Research Organization:
- California Univ., Berkeley, CA (USA)
- OSTI ID:
- 6011937
- Country of Publication:
- United States
- Language:
- English
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ACCIDENTS
BWR TYPE REACTORS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
CORROSION
CRYSTALS
DIFFUSION
DISSOLUTION
ELEMENTS
GRAVIMETRIC ANALYSIS
HYDROGEN
ISOTOPIC EXCHANGE
LOSS OF COOLANT
MASS SPECTROMETERS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MONOCRYSTALS
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PERMEABILITY
POLYCRYSTALS
PRESSURE DEPENDENCE
PWR TYPE REACTORS
QUANTITATIVE CHEMICAL ANALYSIS
REACTOR ACCIDENTS
REACTORS
SELF-DIFFUSION
SOLUBILITY
SORPTIVE PROPERTIES
SPECTROMETERS
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
USES
WATER COOLED REACTORS
WATER MODERATED REACTORS
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES