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Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Bottom Line: In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method.Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects.Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects.

View Article: PubMed Central - PubMed

Affiliation: Yıldız Technical University, Department of Physics, Faculty of Science, Esenler, Istanbul, Turkey.

ABSTRACT
The swelling that occurs in uranium dioxide as a result of radiation-induced defect ingrowth is not fully understood. Experimental and theoretical groups have attempted to explain this phenomenon with various complex theories. In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method. Based on their resemblance to experimental data, the simulation results presented here show that fission induces only oxygen Frenkel pairs while alpha particle irradiation results in both oxygen and uranium Frenkel pair defects. Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects. It is shown that obstruction type Frenkel pairs are responsible for both fission- and alpha-particle-induced lattice swelling. Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects. Additionally, at high concentrations, some of the obstruction type uranium Frenkel pairs formed diatomic and triatomic structures with oxygen ions in their octahedral cages, increasing the slope of the linear dependence.

No MeSH data available.


Related in: MedlinePlus

Equilibrium state from the <110> direction of a UO2 supercell with 17 uranium IFPs seen.Distortion and obstruction type uranium (gray) defects are indicated with arrows. Distortion type defects are ions that have been slightly displaced into channels. Obstruction type defects are ions that occupy central positions within channels; they occupy special positions, have a constant coordination number, and can be considered to be ions trapped in cages. There is a relationship between the ingrowth of obstruction type defects and radiation-induced lattice expansion.
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pone.0134500.g002: Equilibrium state from the <110> direction of a UO2 supercell with 17 uranium IFPs seen.Distortion and obstruction type uranium (gray) defects are indicated with arrows. Distortion type defects are ions that have been slightly displaced into channels. Obstruction type defects are ions that occupy central positions within channels; they occupy special positions, have a constant coordination number, and can be considered to be ions trapped in cages. There is a relationship between the ingrowth of obstruction type defects and radiation-induced lattice expansion.

Mentions: Here, we describe how the numbers of oxygen and uranium FPs in the prepared samples were calculated. Although it is possible to visually determine numbers of defects using the VMD program [27], as can be seen from Fig 2, we have developed a method for calculating average FP numbers. The results obtained from this method were consistent with visual observations.


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Equilibrium state from the <110> direction of a UO2 supercell with 17 uranium IFPs seen.Distortion and obstruction type uranium (gray) defects are indicated with arrows. Distortion type defects are ions that have been slightly displaced into channels. Obstruction type defects are ions that occupy central positions within channels; they occupy special positions, have a constant coordination number, and can be considered to be ions trapped in cages. There is a relationship between the ingrowth of obstruction type defects and radiation-induced lattice expansion.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526661&req=5

pone.0134500.g002: Equilibrium state from the <110> direction of a UO2 supercell with 17 uranium IFPs seen.Distortion and obstruction type uranium (gray) defects are indicated with arrows. Distortion type defects are ions that have been slightly displaced into channels. Obstruction type defects are ions that occupy central positions within channels; they occupy special positions, have a constant coordination number, and can be considered to be ions trapped in cages. There is a relationship between the ingrowth of obstruction type defects and radiation-induced lattice expansion.
Mentions: Here, we describe how the numbers of oxygen and uranium FPs in the prepared samples were calculated. Although it is possible to visually determine numbers of defects using the VMD program [27], as can be seen from Fig 2, we have developed a method for calculating average FP numbers. The results obtained from this method were consistent with visual observations.

Bottom Line: In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method.Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects.Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects.

View Article: PubMed Central - PubMed

Affiliation: Yıldız Technical University, Department of Physics, Faculty of Science, Esenler, Istanbul, Turkey.

ABSTRACT
The swelling that occurs in uranium dioxide as a result of radiation-induced defect ingrowth is not fully understood. Experimental and theoretical groups have attempted to explain this phenomenon with various complex theories. In this study, experimental lattice expansion and lattice super saturation were accurately reproduced using a molecular dynamics simulation method. Based on their resemblance to experimental data, the simulation results presented here show that fission induces only oxygen Frenkel pairs while alpha particle irradiation results in both oxygen and uranium Frenkel pair defects. Moreover, in this work, defects are divided into two sub-groups, obstruction type defects and distortion type defects. It is shown that obstruction type Frenkel pairs are responsible for both fission- and alpha-particle-induced lattice swelling. Relative lattice expansion was found to vary linearly with the number of obstruction type uranium Frenkel defects. Additionally, at high concentrations, some of the obstruction type uranium Frenkel pairs formed diatomic and triatomic structures with oxygen ions in their octahedral cages, increasing the slope of the linear dependence.

No MeSH data available.


Related in: MedlinePlus