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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

Initial view from the x direction of a MD supercell sample with 20 oxygen IFPs.Arrows indicate the displacements of atoms from their lattice sites to their interstitial positions. Each color represents a different layer along the x direction.
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pone.0134500.g001: Initial view from the x direction of a MD supercell sample with 20 oxygen IFPs.Arrows indicate the displacements of atoms from their lattice sites to their interstitial positions. Each color represents a different layer along the x direction.

Mentions: 5×5×5 supercells of irradiated samples with different defect concentrations were prepared by randomly moving ions from lattice sites to interstitial positions within the layers. A representative supercell with such defects is shown in Fig 1. Hereafter, these ions will be referred to as initial Frenkel pair (IFP) defects and those present after equilibration will be referred to as Frenkel pair (FP) defects. To minimize annihilation effects, IFP defects were not included in successive layers, so that vacancies and interstitials did not directly terminate one another. Each defect layer has approximately the same number of IFPs. The same simulation procedure was used for both defected and perfect supercell boxes. Uranium dioxide supercells with several different IFP concentrations, based on dose experiments [17], were prepared. In order to correlate the sublattice (oxygen or uranium sublattice) effects with irradiation type, supercells were constructed with either oxygen IFPs or uranium IFPs but not both. Numbers of semi-empirical potentials have been developed in order to model the interactions between the ions of UO2 [15]. Most of these potentials parameterized with respect to lattice constant, bulk modulus and/or elastic constants satisfactorily estimate the thermophysical properties of UO2 at low temperature but do not able to reproduce the lattice properties at high temperatures at solid phase as well as liquid phase.


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Initial view from the x direction of a MD supercell sample with 20 oxygen IFPs.Arrows indicate the displacements of atoms from their lattice sites to their interstitial positions. Each color represents a different layer along the x direction.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0134500.g001: Initial view from the x direction of a MD supercell sample with 20 oxygen IFPs.Arrows indicate the displacements of atoms from their lattice sites to their interstitial positions. Each color represents a different layer along the x direction.
Mentions: 5×5×5 supercells of irradiated samples with different defect concentrations were prepared by randomly moving ions from lattice sites to interstitial positions within the layers. A representative supercell with such defects is shown in Fig 1. Hereafter, these ions will be referred to as initial Frenkel pair (IFP) defects and those present after equilibration will be referred to as Frenkel pair (FP) defects. To minimize annihilation effects, IFP defects were not included in successive layers, so that vacancies and interstitials did not directly terminate one another. Each defect layer has approximately the same number of IFPs. The same simulation procedure was used for both defected and perfect supercell boxes. Uranium dioxide supercells with several different IFP concentrations, based on dose experiments [17], were prepared. In order to correlate the sublattice (oxygen or uranium sublattice) effects with irradiation type, supercells were constructed with either oxygen IFPs or uranium IFPs but not both. Numbers of semi-empirical potentials have been developed in order to model the interactions between the ions of UO2 [15]. Most of these potentials parameterized with respect to lattice constant, bulk modulus and/or elastic constants satisfactorily estimate the thermophysical properties of UO2 at low temperature but do not able to reproduce the lattice properties at high temperatures at solid phase as well as liquid phase.

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