Molecular dynamics study on planar clustering of xenon in UO2

Geng, Hua-Yun; Chen, Y.; Kaneta, Yasunori; Kinoshita, Motoyasu

doi:10.1016/j.jallcom.2007.03.030

Cited by 57 publications

(40 citation statements)

References 47 publications

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“…Mao et al 12 considered the segregation of yttrium (Y) to symmetric Σ5 tilt GBs in cubic zirconia (ZrO 2 ) using density functional theory (DFT). Y 3+ segregation to Zr 4+ sites in the GB was predicted to be energetically favorable compared to the bulk, in agreement with the experimental results of Dickey et al 13 It is clear, therefore, that segregation of external species to GBs and dislocations may play an important role in influencing material properties. This is especially true for UO 2 where segregation may affect fission gas distribution throughout a nuclear fuel grain.…”

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Segregation of xenon to dislocations and grain boundaries in uranium dioxide

et al. 2011

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It is well known that Xe, being insoluble in UO 2 , segregates to dislocations and grain boundaries, where bubbles may form resulting in fuel swelling. Less well known is how sensitive this segregation is to the structure of the dislocation or grain boundary. In this work, we employ pair potential calculations to examine Xe segregation to dislocations (edge and screw) and several representative grain boundaries (Σ5 tilt, Σ5 twist and random). Our calculations predict that the segregation trend depends significantly on the type of dislocation or grain boundary. In particular, we find that Xe prefers to segregate strongly to the random boundary as compared to the other two boundaries and to the screw dislocation rather than the edge. Furthermore, we observe that neither the volumetric strain nor the electrostatic potential of a site can be used to predict its segregation characteristics. These differences in segregation characteristics are expected to have important consequences for the retention and release of Xe in nuclear fuels. Finally, our results offer general insights into how atomic structure of extended defects influence species segregation.I. INTRODUCTION Segregation can be understood as the interaction between an isolated zero dimensional defect (in this case, an impurity) and multidimensional defects such as dislocations (1D), grain boundaries (GB) and free surfaces (3D). 11 The driving force for this process is the energy difference (segregation energy) between the isolated impurity in the bulk and that associated with an extended structural defect. If the energy at the structural defect site is lower than in the bulk, the local impurity concentration is higher at the structural defect than in bulk and conversely, if the energy at the defect site is higher than in the bulk, the impurity will remain in the bulk. Segregation phenomena influence many material properties such as ion transport (which has a strong effect, for example on sintering rates), electrical and chemical reactivity and grain growth.2 At higher concentrations, segregating impurities are known to form glassy or ordered phases and can cause structural transformations of the GB. 2,3 In the case of UO 2 nuclear fuel, fission gases such as xenon (Xe) are insoluble in the fuel matrix. 45 Therefore, Xe tends to segregate to dislocations and GBs forming fission gas bubbles. Xe may diffuse along the short circuit paths provided by these two defects and be released into the plenum region between the fuel rod and the cladding. 5 If the gases are released from the fuel, they contribute to the gaseous atmosphere within the fuel pin and the fuel pin internal pressure correspondingly increases; this can contribute to failure of the fuel pin. If these gases are retained inside the fuel, they form bubbles, which lead to swelling of the fuel matrix. Swelling is detrimental to fuel performance as it contributes to fuel-cladding mechanical interaction (FCMI); the resulting stresses can shorten the lifetime of the pin. 7 Swelling and release are compleme...

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confidence: 87%

“…The Xe interaction with the uranium and oxygen atoms has been fit to DFT+U energies by Geng et al 13 using a Lennard-Jones potential for Xe-Xe and Xe-O and a Born-Mayer term for the Xe-U interaction. Geng et al used this potential to examine Xe (111) planar clustering in UO 2 .…”

Section: Methodsmentioning

confidence: 99%

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

et al. 2011

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“…Due to its high impact on nuclear fuel performance the properties of Xe in UO 2±x have been extensively studied using a variety of theoretical 2,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and experimental techniques [3][4][5][25][26][27][28][29][30][31] . Matzke et al [3][4][5] have published several reviews on this topic and concluded that Xe diffusion can be represented by an Arrhenius model, D = D 0 e −Ea/k b T , with activation energies (E a ) that depend on UO 2±x stoichiometry.…”

Section: Thermodynamicsmentioning

confidence: 99%

U and Xe transport in UO2±x: Density functional theory calculations

et al. 2011

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The detrimental effects of the fission gas Xe on the performance of oxide nuclear fuels are well known. However, less well known are the mechanisms that govern fission gas evolution. Here, in order to better understand bulk Xe behavior (diffusion mechanisms) in UO2±x we calculate the relevant activation energies using density functional theory (DFT) techniques. By analyzing a combination of Xe solution thermodynamics, migration barriers and the interaction of dissolved Xe atoms with U, we demonstrate that Xe diffusion predominantly occurs via a vacancy-mediated mechanism. Since Xe transport is closely related to diffusion of U vacancies, we have also studied the activation energy for this process. In order to best reproduce experimental data for the Xe and U activation energies, it is critical to consider the active charge-compensation mechanism for intrinsic defects in UO2±x. Due to the high thermodynamic cost of reducing U 4+ ions, any defect formation occurring at a fixed composition, i.e. no change in UO2±x stoichiometry, always avoids such reactions, which, for example, implies that the ground-state configuration of an O Frenkel pair in UO2 does not involve any explicit local reduction (oxidation) of U ions at the O vacancy (interstitial).

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“…Using pair potential model, we studied the planar clustering of Xe aggregating in UO 2 [12] (Fig. 3).…”

Section: Computational Studymentioning

confidence: 99%

Recovery and restructuring induced by fission energy ions in high burnup nuclear fuel

Kinoshita

Yasunaga

Sonoda

et al. 2009

Nuclear Instruments and Methods in Physics Research Section B:

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In light water commercial reactors, extensive change of grain structure was found at high burnup ceramic fuels. The mechanism is driven by bombardment of fission energy fragments and studies were conducted by combining accelerator based experiments and computer science. Specimen of CeO 2 was used as simulation material of fuel ceramics. With swift heavy ion (Xe) irradiation on CeO 2 , with 210 MeV, change of valence charge and lattice deviation of cations were observed by XPS and XRD. Combined irradiations of Xe implantation and swift heavy ion irradiation successfully produced sub-micrometer sized subgrains, similar as that observed in commercial fuels. Studying components of mechanism scenarios, with first principle calculations using the VASP code, we found stable hyperstoichiometric defect structures of UO 2+x . Molecular dynamics studies revealed stability of Xe planar defects and also found rapid transport mode of oxygen-vacancy clusters.

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Molecular dynamics study on planar clustering of xenon in UO2

Cited by 57 publications

References 47 publications

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

U and Xe transport in UO2±x: Density functional theory calculations

Recovery and restructuring induced by fission energy ions in high burnup nuclear fuel

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