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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.


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Radial distribution functions.guu(r) and goo(r) of UO2 with 50 uranium IFPs in a 8×8×8 MD supercell.
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pone.0134500.g009: Radial distribution functions.guu(r) and goo(r) of UO2 with 50 uranium IFPs in a 8×8×8 MD supercell.

Mentions: The plot of the radial distribution function obtained from the MD simulation, uranium interstitial defects are located between 2.75 and 3.4 Å from their surrounding uranium ions (Fig 9). Sharp peaks indicate immobile ions. Oxygen interstitials can be found between 3.2 and 3.4 Å away from other oxygen ions and show no significant peaks. Very few of oxygen interstitial ions are immobile and they could be observed from the <110> direction and were found to retain their positions within channels and were, thus, called obstruction type oxygen defects. Peaks associated with these oxygen defects are not present in Fig 9. We can assert that the peaks associated with the obstruction type oxygen defects could have merged with those associated with the distortion type oxygen defects. Obstruction type oxygen defects occur less frequently than distortion type oxygen defects and can only be observed at uranium IFP concentrations of 40 and greater.


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Radial distribution functions.guu(r) and goo(r) of UO2 with 50 uranium IFPs in a 8×8×8 MD supercell.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0134500.g009: Radial distribution functions.guu(r) and goo(r) of UO2 with 50 uranium IFPs in a 8×8×8 MD supercell.
Mentions: The plot of the radial distribution function obtained from the MD simulation, uranium interstitial defects are located between 2.75 and 3.4 Å from their surrounding uranium ions (Fig 9). Sharp peaks indicate immobile ions. Oxygen interstitials can be found between 3.2 and 3.4 Å away from other oxygen ions and show no significant peaks. Very few of oxygen interstitial ions are immobile and they could be observed from the <110> direction and were found to retain their positions within channels and were, thus, called obstruction type oxygen defects. Peaks associated with these oxygen defects are not present in Fig 9. We can assert that the peaks associated with the obstruction type oxygen defects could have merged with those associated with the distortion type oxygen defects. Obstruction type oxygen defects occur less frequently than distortion type oxygen defects and can only be observed at uranium IFP concentrations of 40 and greater.

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