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  4. Microstructural explicit simulation of grain boundary diffusion in depleted UO₂
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Microstructural explicit simulation of grain boundary diffusion in depleted UO₂


Microstructural explicit simulation of grain boundary diffusion in depleted uranium oxide

Full metadata

Description

ABSTRACT The behavior of the fission products, as they are released from fission events during nuclear reaction, plays an important role in nuclear fuel performance. Fission product release can occur through grain boundary (GB) at low burnups; therefore, this study simulates the mass transport of fission gases in a 2-D GB network to look into the effects of GB characteristics on this phenomenon, with emphasis on conditions that can lead to percolation. A finite element model was created based on the microstructure of a depleted UO2 sample characterized by Electron Backscattering Diffraction (EBSD). The GBs were categorized into high (D2), low (D1) and bulk diffusivity (Dbulk) based on their misorientation angles and Coincident Site Lattice (CSL) types. The simulation was run using different diffusivity ratios (D2/Dbulk) ranging from 1 to 10^8. The model was set up in three ways: constant temperature case, temperature gradient effects and window methods that mimic the environments in a Light Water Reactor (LWR). In general, the formation of percolation paths was observed at a ratio higher than 10^4 in the measured GB network, which had a 68% fraction of high diffusivity GBs. The presence of temperature gradient created an uneven concentration distribution and decreased the overall mass flux. Finally, radial temperature and fission gas concentration profiles were obtained for a fuel pellet in operation using an approximate 1-D model. The 100 µm long microstructurally explicit model was used to simulate, to the scale of a real UO2 pellet, the mass transport at different radial positions, with boundary conditions obtained from the profiles. Stronger percolation effects were observed at the intermediate and periphery position of the pellet. The results also showed that highest mass flux happens at the edge of a pellet at steady state to accommodate for the sharp concentration drop.

Date Created
2011
Contributors
  • Lim, Harn Chyi (Author)
  • Peralta, Pedro (Thesis advisor)
  • Dey, Sandwip (Committee member)
  • Sieradzki, Karl (Committee member)
  • Arizona State University (Publisher)
Topical Subject
  • Materials Science
  • engineering
  • Nuclear engineering
  • Coincident Site Lattice
  • Diffusion
  • Grain Boundary
  • Percolation
  • Simulation
  • Uranium oxides
  • Kirkendall effect
  • Uranium oxides
  • Nuclear fission
Resource Type
Text
Genre
Masters Thesis
Academic theses
Extent
x, 82 p. : ill. (some col.)
Language
eng
Copyright Statement
In Copyright
Reuse Permissions
All Rights Reserved
Primary Member of
ASU Electronic Theses and Dissertations
Peer-reviewed
No
Open Access
No
Handle
https://hdl.handle.net/2286/R.I.14416
Embargo Release Date
Sun, 12/01/2013 - 17:05
Statement of Responsibility
by Harn Chyi Lim
Description Source
Retrieved on Oct. 26, 2012
Level of coding
full
Note
Partial requirement for: M.S., Arizona State University, 2011
Note type
thesis
Includes bibliographical references (p. 78-82)
Note type
bibliography
Field of study: Materials science and engineering
System Created
  • 2012-08-24 06:11:34
System Modified
  • 2021-08-30 01:49:31
  •     
  • 1 year 6 months ago
Additional Formats
  • OAI Dublin Core
  • MODS XML

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