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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

Lattice changes versus initial numbers of oxygen Frenkel pairs in MD supercells.The values given near the data points represent the numbers of obstruction type oxygen FPs in the MD supercell at the ends of simulations. The inset is taken from Ref. 17 and shows experimental data for lattice parameter changes that result from defect ingrowth as a function of increasing fission dose.
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pone.0134500.g004: Lattice changes versus initial numbers of oxygen Frenkel pairs in MD supercells.The values given near the data points represent the numbers of obstruction type oxygen FPs in the MD supercell at the ends of simulations. The inset is taken from Ref. 17 and shows experimental data for lattice parameter changes that result from defect ingrowth as a function of increasing fission dose.

Mentions: Fig 4 presents plots of the number of IFPs versus relative lattice expansion, obtained using Günay [1] and Yakub [5] potentials, and experimentally determined relative lattice expansion versus fission data from Matzke [17]. MD simulations of NPT ensembles were run using 10 different initially defected systems with numbers of oxygen IFPs varied from 0 to 40. Only some of the oxygen IFPs avoided recombination during the 10 ps equilibration step. Following equilibration, the numbers of FPs present, indicated by the numbers near the data points in Fig 4, remained constant. Three distinct stages have been experimentally observed to occur when fission dose is increased [17,18]: isolated FPs are produced at a constant rate (14<log(F)<16), then newly produced displaced atoms are trapped at existing defect sites, resulting in interstitial clusters (16<log(F)<17.5), and, finally, no more new interstitials are produced. This final stage is known as super saturation (17.5<log(F)<18.5).


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Lattice changes versus initial numbers of oxygen Frenkel pairs in MD supercells.The values given near the data points represent the numbers of obstruction type oxygen FPs in the MD supercell at the ends of simulations. The inset is taken from Ref. 17 and shows experimental data for lattice parameter changes that result from defect ingrowth as a function of increasing fission dose.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0134500.g004: Lattice changes versus initial numbers of oxygen Frenkel pairs in MD supercells.The values given near the data points represent the numbers of obstruction type oxygen FPs in the MD supercell at the ends of simulations. The inset is taken from Ref. 17 and shows experimental data for lattice parameter changes that result from defect ingrowth as a function of increasing fission dose.
Mentions: Fig 4 presents plots of the number of IFPs versus relative lattice expansion, obtained using Günay [1] and Yakub [5] potentials, and experimentally determined relative lattice expansion versus fission data from Matzke [17]. MD simulations of NPT ensembles were run using 10 different initially defected systems with numbers of oxygen IFPs varied from 0 to 40. Only some of the oxygen IFPs avoided recombination during the 10 ps equilibration step. Following equilibration, the numbers of FPs present, indicated by the numbers near the data points in Fig 4, remained constant. Three distinct stages have been experimentally observed to occur when fission dose is increased [17,18]: isolated FPs are produced at a constant rate (14<log(F)<16), then newly produced displaced atoms are trapped at existing defect sites, resulting in interstitial clusters (16<log(F)<17.5), and, finally, no more new interstitials are produced. This final stage is known as super saturation (17.5<log(F)<18.5).

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