Thermodynamics of fission products in UO<sub>2 ±<i>x</i></sub>

Nerikar, Pankaj; Liu, X.-Y.; Uberuaga, Blas P.; Stanek, C. R.; Phillpot, Simon R.; Sinnott, Susan B.

doi:10.1088/0953-8984/21/43/435602

Cited by 58 publications

(62 citation statements)

References 39 publications

(74 reference statements)

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“…This is also consistent with experimental observations and previous calculation results. 14 However, there are other aspects to note for Xe segregation to the twist GB. First, we predict that there are sites at the GB that are energetically unfavorable compared to the bulk.…”

Section: Segregation To Dislocationsmentioning

confidence: 99%

“…Geng et al used this potential to examine Xe (111) planar clustering in UO 2 . From previous work, 14 it is known that the equilibrium solution site for Xe in stoichiometric UO 2 is a bound Schottky defect (a neutral tri-vacancy consisting of a uranium vacancy and two nearest neighbor oxygen vacancies) in UO 2 , although in hyperstoichiometric UO 2+x the equilibrium solution site is the isolated uranium vacancy. 22 For our segregation calculations, the Xe energy is calculated by replacing each uranium atom one-by-one with a Xe atom (Xe U '''' in Kroger-Vink notation).…”

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confidence: 99%

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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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Section: Segregation To Dislocationsmentioning

confidence: 99%

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confidence: 99%

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

et al. 2011

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“…Additionally, understanding of fission products in general type oxide ceramics yields scientific knowledge on the mutual interactions of fission products and associated defects, which may help to design better ceramic fuel forms [1]. Our previous modeling studies on fission products in oxides include MgO, HfO 2 , CeO 2 , and UO 2 [2][3][4]. Here, we report on fission product behavior in various polymorphs of zirconia (ZrO 2 ).…”

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confidence: 94%

First-principles prediction of the thermodynamic stability of xenon in monoclinic, tetragonal, and yttrium-stabilized cubic ZrO2

2011

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“…Where possible, comparison has also been made to literature UO 2 DFT results [14,44,45,46]. Figure 4 shows similar trends for the trapping energies for Xe and Kr defects in CeO 2 , ThO 2 , UO 2 and PuO 2 between the empirical potential and the DFT methods used in this paper.…”

Section: Validation Of Empirical Parametersmentioning

confidence: 53%

“…DFT results (partially filled columns) are reported from the literature [14,44,45,46] and the present study (using Table 2) for comparison with the new empirical potential potential (solid columns).…”

Section: Gas--ion Separation (å)mentioning

confidence: 99%

Development of Xe and Kr empirical potentials for CeO₂, ThO₂, UO₂and PuO₂, combining DFT with high temperature MD

Cooper

Kuganathan

Burr

et al. 2016

J. Phys.: Condens. Matter

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Abstract. The development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2 , ThO 2 , UO 2 and PuO 2 . These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2 , ThO 2 , UO 2 and PuO 2 , providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.

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Thermodynamics of fission products in UO_{2 ±x}

Cited by 58 publications

References 39 publications

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

First-principles prediction of the thermodynamic stability of xenon in monoclinic, tetragonal, and yttrium-stabilized cubic ZrO2

Development of Xe and Kr empirical potentials for CeO₂, ThO₂, UO₂and PuO₂, combining DFT with high temperature MD

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Thermodynamics of fission products in UO2 ±x

Cited by 58 publications

References 39 publications

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

Segregation of xenon to dislocations and grain boundaries in uranium dioxide

First-principles prediction of the thermodynamic stability of xenon in monoclinic, tetragonal, and yttrium-stabilized cubic ZrO2

Development of Xe and Kr empirical potentials for CeO2, ThO2, UO2and PuO2, combining DFT with high temperature MD

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Thermodynamics of fission products in UO_{2 ±x}

Development of Xe and Kr empirical potentials for CeO₂, ThO₂, UO₂and PuO₂, combining DFT with high temperature MD