Grain boundary diffusion of Ag through polycrystalline SiC in TRISO fuel particles

Deng, Jie; Ko, Hyun-Seok; Demkowicz, Paul A.; Morgan, Dane; Szlufarska, Izabela

doi:10.1016/j.jnucmat.2015.09.054

Cited by 16 publications

(7 citation statements)

References 32 publications

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“…It is important to note that the Ag diffusion through a pc-SiC may depend not only on the diffusivity in a given GB but also on the microstructure topology, particularly how the GB types are connected to form a network. In this work we focus on estimating D in HEGBs, a specific type of GB, and no model of mesoscale diffusion through a GB network is considered (please see Refs [29,30] for mesoscale transport models). However, since the HEGBs form a percolating network, if they are found to a fast diffusion path we expect these mesoscale effects on the overall measured diffusion coefficient and its activation energy to be relatively minor [29].…”

Section: Introductionmentioning

confidence: 99%

“…In this work we focus on estimating D in HEGBs, a specific type of GB, and no model of mesoscale diffusion through a GB network is considered (please see Refs [29,30] for mesoscale transport models). However, since the HEGBs form a percolating network, if they are found to a fast diffusion path we expect these mesoscale effects on the overall measured diffusion coefficient and its activation energy to be relatively minor [29]. Therefore, in this work we will make direct comparisons between our calculated D values for the HEGB and experimentally measured D values from pc-SiC samples.…”

Section: Introductionmentioning

confidence: 99%

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Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

Deng

Szlufarska

et al. 2016

Computational Materials Science

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The diffusion of silver (Ag) impurities in high energy grain boundaries (HEGBs) of cubic (3C) silicon carbide (SiC) is studied using an ab initio based kinetic Monte Carlo (kMC) model. This study assesses the hypothesis that the HEGB diffusion is responsible for Ag release in TristructuralIsotropic (TRISO) fuel particles, and provides a specific example to increase understanding of impurity diffusion in highly disordered grain boundaries. The HEGB environment was modeled by an amorphous SiC (a-SiC), which approximately represents the local environments of HEGBs. The structure and stability of Ag defects were calculated using ab initio methods based on Density Functional Theory (DFT). The defect energetics suggested that the fastest diffusion takes place via an interstitial mechanism in a-SiC and that is what is modeled. Interstitial sites were identified by a gridded search and transition states were computed using the climbing image nudged elastic band method. The formation energy of Ag interstitials (relative to bulk Ag) and the Kinetic Resolved Activation (EKRA) energies between them were well approximated with Gaussian distributions that were then sampled in the kMC. The diffusion of Ag was simulated with the effective medium model using kMC. Ag diffusion coefficients were estimated for the temperature range of 1200-1600°C. Ag in a HEGB is predicted to exhibit an Arrhenius type diffusion and with a diffusion prefactor and effective activation energy of (2.73 ± 1.09) × 10 −10 m 2 s −1 and 2.79 ± 0.18 eV, respectively. The comparison between HEGB results to other theoretical studies suggested not only that GB diffusion is predominant over bulk diffusion, but also that the HEGB is one of fastest grain boundary paths for Ag diffusion in SiC. The Ag diffusion coefficient in the HEGB shows a good agreement with ionimplantation measurements, but is 2-3 orders of magnitude lower than the reported diffusion coefficient values extracted from integral release measurements on in-and out-of-pile samples. The discrepancy between GB diffusion and integral release measurements suggests that other contributions are responsible for fast release of Ag in some experiments and we propose that these contributions may arise from radiation enhanced diffusion.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

Deng

Szlufarska

et al. 2016

Computational Materials Science

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“…6(c) indicates that the elastic precursor compresses the material from 3.21 g/cm 3 to 4.21 g/cm 3 . The transformation shock wave additionally densifies the material to 4.91 g/cm 3 , which amounts to a 24% volume reduction at the strong elastic compression and an additional 14% volume reduction at the structural transformation. The total volume reduction at the strong shock at 4.0 km/s generated by the solid-solid transformation therefore amounts to 35%.…”

Section: Resultsmentioning

confidence: 99%

“…SiC is a well-known high strength ceramic material with outstanding properties that have been used in a wide range of applications, in particular, those involving extreme conditions of pressure, temperature, and wear such as in nuclear reactor cladding, [1][2][3] abrasives, 4 and gas turbines. 5 Owing to the low density and high strength, SiC is also an ideal material for armor.…”

Section: Introductionmentioning

confidence: 99%

Shock-induced microstructural response of mono- and nanocrystalline SiC ceramics

Branı́cio

Zhang

Rino

et al. 2018

Journal of Applied Physics

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The dynamic behavior of mono-and nanocrystalline SiC ceramics under plane shock loading is revealed using molecular-dynamics simulations. The generation of shock-induced elastic compression, plastic deformation, and structural phase transformation is characterized at different crystallographic directions as well as on a 5-nm grain size nanostructure at 10 K and 300 K. Shock profiles are calculated in a wide range of particle velocities 0.1-6.0 km/s. The predicted Hugoniot agree well with experimental data. Results indicate the generation of elastic waves for particle velocities below 0.8-1.9 km/s, depending on the crystallographic direction. In the intermediate range of particle velocities between 2 and 5 km/s, the shock wave splits into an elastic precursor and a zinc blende-to-rock salt structural transformation wave, which is triggered by shock pressure over the $90 GPa threshold value. A plastic wave, with a strong deformation twinning component, is generated ahead of the transformation wave for shocks in the velocity range between 1.5 and 3 km/s. For particle velocities greater than 5-6 km/s, a single overdriven transformation wave is generated. Surprisingly, shocks on the nanocrystalline sample reveal the absence of wave splitting, and elastic, plastic, and transformation wave components are seamlessly connected as the shock strength is continuously increased. The calculated strengths 15.2, 31.4, and 30.9 GPa for h001i, h111i, and h110i directions and 12.3 GPa for the nanocrystalline sample at the Hugoniot elastic limit are in excellent agreement with experimental data.

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“…In order to understand the mechanism(s) of Ag release, extensive studies, including out-of-pile release measurements from irradiated TRISO fuel [3][4][5][6], surrogate Ag diffusion experiments [7][8][9][10][11], and computer simulations [12][13][14][15] have been performed. While diffusion coefficients measured in laboratory diffusion couple experiments are in a very good agreement with values predicted by computer simulations, these diffusion coefficients are orders of magnitude lower than those observed in actual fuel release experiments.…”

Section: Introductionmentioning

confidence: 99%

Effect of carbon ion irradiation on Ag diffusion in SiC

Leng

Gerczak

et al. 2016

Journal of Nuclear Materials

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Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C-SiC, as well as Ag and single crystalline 4H-SiC samples before and after irradiation with C 2+ ions. The diffusion couple samples were exposed to temperatures of 1500C, 1535C, and 1569C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). Diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.

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Grain boundary diffusion of Ag through polycrystalline SiC in TRISO fuel particles

Cited by 16 publications

References 32 publications

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

Shock-induced microstructural response of mono- and nanocrystalline SiC ceramics

Effect of carbon ion irradiation on Ag diffusion in SiC

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