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

Radial distribution function, guu(r), of a 5×5×5 MD UO2 supercell with 17 uranium IFPs.Obstruction and distortion type defects are indicated on the graph. Obstruction type defects have sharper boundaries (pre-peaks) than distortion type defects.
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pone.0134500.g003: Radial distribution function, guu(r), of a 5×5×5 MD UO2 supercell with 17 uranium IFPs.Obstruction and distortion type defects are indicated on the graph. Obstruction type defects have sharper boundaries (pre-peaks) than distortion type defects.

Mentions: In this method, the number of defects, , is calculated by averaging the defect numbers over the number of time steps, nt, using the following relationship,Mα¯=∑i=1nt∑j=1NαKijnαβnt(1)where Kij represents the number of β ions around the jthα ion during the ith time step within the range Δr = rmax-rmin and nαβ is the first coordination number of the perfect crystal nuu = 12, noo = 6, nuo = 8. The rmin and rmax values are determined from the first peak of the radial distribution function, gαβ(r), constrained such that and . As a representative example, guu(r), used to determine the maximum and minimum values of r, is given in Fig 3. Distortion and obstruction type defects (see Fig 2) can, respectively, be considered to be displaced ions in channels and ions that occupy the center positions of channels. An obstruction type ion has a constant number of ions surrounding it which possess a particular position but a distortion type ion is much more mobile which has an indefinite position. Fig 3 shows a distinct pre-peak, just before the principal peak, that reflects the distribution of obstruction type FPs.


Swelling Mechanisms of UO2 Lattices with Defect Ingrowths.

Günay SD - PLoS ONE (2015)

Radial distribution function, guu(r), of a 5×5×5 MD UO2 supercell with 17 uranium IFPs.Obstruction and distortion type defects are indicated on the graph. Obstruction type defects have sharper boundaries (pre-peaks) than distortion type defects.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0134500.g003: Radial distribution function, guu(r), of a 5×5×5 MD UO2 supercell with 17 uranium IFPs.Obstruction and distortion type defects are indicated on the graph. Obstruction type defects have sharper boundaries (pre-peaks) than distortion type defects.
Mentions: In this method, the number of defects, , is calculated by averaging the defect numbers over the number of time steps, nt, using the following relationship,Mα¯=∑i=1nt∑j=1NαKijnαβnt(1)where Kij represents the number of β ions around the jthα ion during the ith time step within the range Δr = rmax-rmin and nαβ is the first coordination number of the perfect crystal nuu = 12, noo = 6, nuo = 8. The rmin and rmax values are determined from the first peak of the radial distribution function, gαβ(r), constrained such that and . As a representative example, guu(r), used to determine the maximum and minimum values of r, is given in Fig 3. Distortion and obstruction type defects (see Fig 2) can, respectively, be considered to be displaced ions in channels and ions that occupy the center positions of channels. An obstruction type ion has a constant number of ions surrounding it which possess a particular position but a distortion type ion is much more mobile which has an indefinite position. Fig 3 shows a distinct pre-peak, just before the principal peak, that reflects the distribution of obstruction type FPs.

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