Limits...
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

Relative lattice expansion versus number of uranium IFPs, calculated using the Yakub and Günay potentials.The inset was taken from Ref. 21 and shows experimental lattice expansion as a function of cumulative dose.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4526661&req=5

pone.0134500.g012: Relative lattice expansion versus number of uranium IFPs, calculated using the Yakub and Günay potentials.The inset was taken from Ref. 21 and shows experimental lattice expansion as a function of cumulative dose.

Mentions: In Fig 12, obstruction type oxygen defects appear when ~35 to 80 uranium IFPs are present and lattice swelling decays exponentially, approaching a maximum, to saturation value. As the graph reaches a point of saturation value, data show a high variability. Here, octahedral cages of uranium or oxygen-uranium ions collapse at some point due to the enlargement of the lattice, which results in a decrease in lattice expansion. Moreover, reforming of these cages results in an increase in the lattice expansion, which turns out to be high-scattered data towards the saturation value in Fig 12. When obstruction type uranium ions are included in the supercell and obstruction type oxygen ions agglomerate around obstruction type uranium ions, lattice swelling reaches a saturation point and no space remains for obstruction defects. These saturation points were found to occur at 0.3–0.4% for the Günay potential and 1–1.1% for the Yakub potential. When the supercell size was increased from 5×5×5 to 8×8×8, the saturation value obtained from the Yakub potential agreed better with the experimental value, 0.84%.


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Relative lattice expansion versus number of uranium IFPs, calculated using the Yakub and Günay potentials.The inset was taken from Ref. 21 and shows experimental lattice expansion as a function of cumulative dose.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0134500.g012: Relative lattice expansion versus number of uranium IFPs, calculated using the Yakub and Günay potentials.The inset was taken from Ref. 21 and shows experimental lattice expansion as a function of cumulative dose.
Mentions: In Fig 12, obstruction type oxygen defects appear when ~35 to 80 uranium IFPs are present and lattice swelling decays exponentially, approaching a maximum, to saturation value. As the graph reaches a point of saturation value, data show a high variability. Here, octahedral cages of uranium or oxygen-uranium ions collapse at some point due to the enlargement of the lattice, which results in a decrease in lattice expansion. Moreover, reforming of these cages results in an increase in the lattice expansion, which turns out to be high-scattered data towards the saturation value in Fig 12. When obstruction type uranium ions are included in the supercell and obstruction type oxygen ions agglomerate around obstruction type uranium ions, lattice swelling reaches a saturation point and no space remains for obstruction defects. These saturation points were found to occur at 0.3–0.4% for the Günay potential and 1–1.1% for the Yakub potential. When the supercell size was increased from 5×5×5 to 8×8×8, the saturation value obtained from the Yakub potential agreed better with the experimental value, 0.84%.

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