Characterization of the Penetration Mechanisms of Water into Polycrystalline UO2

2010 ◽  
Vol 1265 ◽  
Author(s):  
Ilaria Marchetti ◽  
Fabio Belloni ◽  
Jerome Himbert ◽  
Paul Carbol ◽  
Thomas Fanghänel
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Spent Nuclear Fuel ◽  
Secondary Ion Mass Spectrometry ◽  
Depth Profiling ◽  
Water Diffusion ◽  
Lattice Diffusion ◽  
Boundary Diffusion Coefficient ◽  
Key Issues ◽  
Boundary Width

AbstractFollowing containment failure in the scenario of geological disposal of spent nuclear fuel, the penetration rate of groundwater into the UO2 matrix could cause a rapid increase of the fraction of inventory becoming available for prompt dissolution. In this respect, oxygen and water diffusion mechanisms are key issues to investigate. In this work, secondary-ion-mass-spectrometry (SIMS) depth profiling has been applied to characterize a polycrystalline UO2 pellet exposed to 18O-labelled water at room temperature. 18O depth profiling up to 25 μm beneath the pellet surface clearly indicates a combination of oxygen diffusion into the UO2 lattice and water diffusion along grain boundaries, behaving as high diffusivity paths. The lattice diffusion coefficient of oxygen, DL, and the quantity δDB – product of the grain boundary width, δ, and the grain boundary diffusion coefficient of water, DB – have been measured, resulting in DL = (2.5 ± 0.1) × 10-24 m2 s-1 and δDB = (7.5 ± 0.3) × 10-24 m3 s-1.

Interface Reaction and Atomic Transport During COSi2 Film Formation

1992 ◽  
Vol 260 ◽  
Author(s):  
Z. G. Xiao ◽  
J. W. Honeycutt ◽  
G. A. Rozgonyi
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Film Formation ◽  
Microstructural Analysis ◽  
Interface Reaction ◽  
Lattice Diffusion ◽  
Atomic Transport ◽  
Transmission Electron ◽  
Boundary Diffusion Coefficient ◽  
Short Annealing

ABSTRACTThe formation process of COSi2 films grown from Co deposited on a Si single crystal was investigated as a function of very short annealing times by transmission electron microscopy and x-ray diffraction. Information on the interfacial reactions and atomic transport phenomena was obtained from a microstructural analysis of the CoxSiy layers formed. It was demonstrated that Co is the dominant diffusion species during COSi2 formation. Co atoms are generated at the COSi2/COSi2 interface via the reaction 2CoSi=CoSi2+Co and diffuse to the COSi2/Si interface, where they react with Si by Co+2Si=CoSi2. Direct microscopic evidence indicates that diffusivity of Co atoms along a COSi2 grain boundary greatly exceeds that through the COSi2 lattice. The grain boundary diffusion coefficient is estimated to be up to 100 times larger than the lattice diffusion coefficient. On this basis the influence of grain size on COSi2 film formation is discussed.

The Influence of Grain Boundary Migration on the Diffusion Behaviour of Thin Films

1980 ◽  
Vol 35 (6) ◽  
pp. 613-618
Author(s):  
E. Ehrmann-Falkenau ◽  
A. Wagendristel
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Boundary Surface ◽  
Depth Profiling ◽  
Lattice Diffusion ◽  
Grain Boundary Migration ◽  
Order Of Magnitude ◽  
Diffusion Behaviour

Simultaneous grain boundary-, surface- and lattice diffusion in hypothetical thin film couples of miscible components was computer simulated. On this basis the diffusion into fixed and moving grain boundaries is discussed with respect to the determination of diffusivities by depth profiling methods. The data evaluated from the synthesised depth profiles according to Whipple-Le Claire as well as to Gilmer and Farrell were compared with the diffusivities used for the computation. Agreement was found for systems with a fixed grain boundary network. Moving grain boundaries, however, may cause errors of an order of magnitude towards lower grain boundary diffusivities

Pressure, temperature, water content, and oxygen fugacity dependence of the Mg grain-boundary diffusion coefficient in forsterite

2018 ◽  
Vol 103 (9) ◽  
pp. 1354-1361 ◽  
Author(s):  
Hongzhan Fei ◽  
Sanae Koizumi ◽  
Naoya Sakamoto ◽  
Minako Hashiguchi ◽  
Hisayoshi Yurimoto ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Water Content ◽  
Oxygen Fugacity ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Boundary Diffusion Coefficient ◽  
Temperature Water

Ti and Ni Grain Boundary Diffusion in B2 NiTi Compound

2015 ◽  
Vol 363 ◽  
pp. 137-141 ◽  
Author(s):  
Dan Dan Liu ◽  
Jochen Fiebig ◽  
Martin Peterlechner ◽  
Simon Trubel ◽  
Matthias Wegner ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Boundary Structure ◽  
Segregation Coefficient ◽  
Radiotracer Technique ◽  
Grain Boundary Structure ◽  
Boundary Diffusion Coefficient ◽  
Boundary Triple ◽  
Boundary Width

The radiotracer technique was used to measure the grain boundary diffusion of44Ti and63Ni in slightly Ni-rich polycrystalline NiTi compound in the temperature range of 673 - 923 K. The temperature dependence of the grain boundary triple productP(P=sδDgb,sis the segregation coefficient,δis the grain boundary width, andDgbis the grain boundary diffusion coefficient) for Ti and Ni was determined. The triple products of both Ti and Ni grain boundary diffusion in NiTi reveal a unique behavior with significant deviations from an Arrhenius-type dependence. Probable evolution of the grain boundary structure with temperature was used to interpret this phenomenon.

Diffusion of Arsenic in Single Crystalline CoSi2

1995 ◽  
Vol 402 ◽  
Author(s):  
A. Pisch ◽  
J. Cardenas ◽  
B. G. Svensson ◽  
C. S. Petersson
Keyword(s):  
Diffusion Coefficient ◽  
Secondary Ion Mass Spectrometry ◽  
Lattice Diffusion ◽  
High Dose ◽  
Exponential Factor ◽  
Self Diffusion ◽  
Different Temperatures ◽  
Secondary Ion ◽  
Self Diffusion Coefficient ◽  
Different Doses

AbstractThe lattice diffusion of arsenic in CoSi2 has been studied in the temperature range from 750°C to 950°C. Two types of bulk samples were used: single crystals prepared by a modified Czochralski pulling technique from a radio frequency levitated melt and polycrystals synthesised by quenching from the melt. The latter samples were subsequently annealed in vacuum at 900°C and displayed grain sizes in the millimetre range. Starting from an ion implanted arsenic profile with two different doses (5·1014 and 5·1015 cm−2) the concentration versus depth profiles after annealing at different temperatures and different times were measured using secondary ion mass spectrometry (SIMS). Contrary to previous studies by other authors substantial diffusion has been observed with an activation energy of 3.3 eV and a pre-exponential factor of 7.37 cm2/s for the diffusion coefficient. These values are very close to the self diffusion coefficient of Si in CoSi2 suggesting that the As atoms migrate via thermal vacancies on nearest neighbour lattice sites by a similar type of mechanism as the Si (and Co) atoms. In the high dose implanted polycrystalline samples arsenic precipitation occurred which gives an estimate for the solid solubility in the 1019 atoms/cm3 range at 800 °C.

Diffusion of Hydrogen in 6H Silicon Carbide

1996 ◽  
Vol 423 ◽  
Author(s):  
M. K. Linnarsson ◽  
J. P. Doyle ◽  
B. G. Svensson
Keyword(s):  
Mass Spectrometry ◽  
Activation Energy ◽  
Silicon Carbide ◽  
Diffusion Coefficient ◽  
Secondary Ion Mass Spectrometry ◽  
Depth Profiling ◽  
Defect Complexes ◽  
Induced Defects ◽  
Secondary Ion ◽  
Diffusion Of Hydrogen

Abstract6H polytype silicon carbide (SiC) samples of n-type have been implanted with 50 keV H+ ions and subsequently annealed at temperatures between 200 °C and 1150 °C. Using depth profiling by secondary ion mass spectrometry motion of hydrogen is observed in the implanted region for temperatures above 700 °C. A diffusion coefficient of ∼10−14 cm2/s is extracted at 800°C with an approximate activation energy of ∼3.5 eV. Hydrogen displays strong interaction with the implantation-induced defects and stable hydrogen-defect complexes are formed. These complexes anneal out at temperatures in excess of 900°C and are tentatively identified as Carbon-Hydrogen centers at a Si vacancy.

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