Focused ion beam–scanning electron microscope examination of high burn-up UO2 in the center of a pellet

Noirot, J.; Zacharie-Aubrun, I.; Blay, Thierry

doi:10.1016/j.net.2017.12.002

Cited by 34 publications

(24 citation statements)

References 11 publications

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“…As a consequence, we observed the disappearance of such grain boundaries for temperatures higher than 1000 K. This is an interesting result when considering that those low misorientation grain boundaries are separating subdomains in highly irradiated areas in spent fuel. 22 Further studies might show that those domains could be annealed at high temperature, due to the low stability of low angle STGBs.…”

Section: Discussionmentioning

confidence: 99%

“…This is of particular interest, since it was shown as early as 1950 by Read et al that grain boundaries have different characteristics depending on whether their angle of misorientation is greater or lower than 15° 21 . On the one hand, to study STGBs with an angle greater than 15° is crucial because these have lower CSL indices and are therefore likely to be observed more often in polycrystals 19,22,23 . On the other hand, recent experimental observations seem to indicate that low misorientation boundaries (or grain sub‐boundaries) appear under irradiation 22 and mechanical stress 23 of the UO 2 polycrystals.…”

Section: Introductionmentioning

confidence: 99%

“…21 On the one hand, to study STGBs with an angle greater than 15° is crucial because these have lower CSL indices and are therefore likely to be observed more often in polycrystals. 19,22,23 On the other hand, recent experimental observations seem to indicate that low misorientation boundaries (or grain sub-boundaries) appear under irradiation 22 and mechanical stress 23 of the UO 2 polycrystals. It is therefore also important to study their characteristics.…”

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

2021

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Molecular dynamics and CRG empirical potential are used in this work to study the symmetrical tilt grain boundaries around the [001] axis in UO2. The analysis of atomic structures obtained by simulation shows excellent agreement with the Read and Schokley model (Read WT, Shockley W. Dislocation Models of Crystal Grain Boundaries. Physical Review. 1950;78:275) predicting the existence of regular dislocations in these grain boundaries. We calculated their energy of formation and cleavage as well as the energy of formation of Schottky defects and incorporation of xenon and krypton atoms in their proximity. This allowed us to determine how these properties evolve for this series of grain boundaries presenting similar geometric characteristics, as a function of the misorientation angle. In addition, the boundary between small and large misorientation grain boundaries has been determined around 20°, close to the value of 15° reported in literature.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

2021

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“…The selected bubble volume evaluations (step f) were done by the use of the FIB-SEM. In fact, in case of complex shapes [7] , SEM image of the polished surface is unable to provide a good estimation of the size and volume of the object. With FIB-SEM, a 3D tomography by FIB serial cuts was realized in the SEM for the selected bubble.…”

Section: Fuel After Power Ramp -Sample Amentioning

confidence: 99%

Determination of the pressure in micrometric bubbles in irradiated nuclear fuels

Dowek

Cagna

Noirot

et al. 2021

Journal of Nuclear Materials

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In oxide nuclear fuels, at high burn-up or during high temperature periods such as ramp tests, out-ofpile heating tests, or any irradiations at high linear heat rates, fission gases can form micrometric or quasi-micrometric bubbles. During nominal operations, these bubbles participate to the pellet swelling, to the decrease of the fuel thermal conductivity and are involved in the mechanisms leading to fission gas release. During events involving a temperature increase, the resulting increase in the internal pressure of the bubbles might play a role in fuel fragmentation and in the opening of grain boundaries. The gas densities inside these bubbles are therefore one of the useful experimental information for the understanding of the fuel behaviour, and for the fuel behaviour code progress and validation. Two methods were developed to evaluate the gas density in the quasi-micrometric bubbles, using electron probe micro analyser, secondary ion mass spectrometry and focused ion beam scanning electron microscope together. The first method provides a mean gas density for all quasi-micrometric bubbles in a given area. The second method provides a gas density in a single selected bubble. In addition to the gas density, the 3D size and shape of the selected bubble is measured and can be related to the gas density result. In this work, these methods were applied to the bubbles formed in the centre of a PWR Cr doped UO 2 at 38.8 GWd/t U after a ramp test in the Osiris reactor, with a 12 h plateau at 470 W/cm, and to the bubbles formed in a PWR Cr doped UO 2 at 62.8 GWd/t U in the centre of the pellet and on the bubbles of the high burn-up structure on the rim. Both show the high pressures reached in these bubbles.

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“…The mechanism of fission gas release out of the fuel can be understood as a two step process: the transfer of gas atoms from the grain to the grain boundaries, and then the coalescence and interlinkage of grain-boundary bubbles to give pathways to outside the fuel. While the latter is clearly observed at high temperatures (T ≥ 1400 0 C), it has recently been questioned for base irradiation [2]. The former step of gas atoms transfer within the grain has been a topic of debate for the past few decades [3,4].…”

Section: Introductionmentioning

confidence: 99%

A new spatially resolved model for defects and fission gas bubbles interaction at the mesoscale

Verma

Noirot

Maugis

2019

Nuclear Instruments and Methods in Physics Research Section B:

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Fission gases, especially Xenon, produced during irradiation in a nuclear fuel, have very low solubility in the U O 2 fuel matrix and precipitate into bubbles. These gas bubbles interact with point defects of the fuel (vacancies, selfinterstitials, etc.) causing significant microstructural evolution which may eventually affect the overall performance of the fuel. Spatially resolved models are developed to predict and model the microstructural change at the mesoscale. We present a new model, which focuses on modeling the interaction between point defects and xenon gas bubbles. This new model overcomes the limitation of the existing cluster dynamics models as it can account for spatialization as well as the limitation of the spatially resolved phase-field models as it can also account for very small defect clusters, even below the individual grid spacing. The modeling of the phenomena of coalescence of two bubbles in a vacancy supersaturation and the vanishing of a small bubble in the presence of a larger bubble (Ostwald ripening) prove the credibility of the new model. 2-D analysis of a case depicting the movement and growth of bubbles in a vacancy concentration gradient is presented and is in good agreement with the associated physics.

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Focused ion beam–scanning electron microscope examination of high burn-up UO2 in the center of a pellet

Cited by 34 publications

References 11 publications

Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

Determination of the pressure in micrometric bubbles in irradiated nuclear fuels

A new spatially resolved model for defects and fission gas bubbles interaction at the mesoscale

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Focused ion beam–scanning electron microscope examination of high burn-up UO2 in the center of a pellet

Cited by 34 publications

References 11 publications

Molecular dynamics study of UO2 symmetric tilt grain boundaries around [001] axis

Molecular dynamics study of UO2 symmetric tilt grain boundaries around [001] axis

Determination of the pressure in micrometric bubbles in irradiated nuclear fuels

A new spatially resolved model for defects and fission gas bubbles interaction at the mesoscale

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Product

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Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis