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Title: Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation

Authors:
ORCiD logo; ; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1396790
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Volume: 479; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 15:28:08; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Country of Publication:
Netherlands
Language:
English

Citation Formats

Hu, Shenyang, Burkes, Douglas E., Lavender, Curt A., Senor, David J., Setyawan, Wahyu, and Xu, Zhijie. Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation. Netherlands: N. p., 2016. Web. doi:10.1016/j.jnucmat.2016.07.012.
Hu, Shenyang, Burkes, Douglas E., Lavender, Curt A., Senor, David J., Setyawan, Wahyu, & Xu, Zhijie. Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation. Netherlands. doi:10.1016/j.jnucmat.2016.07.012.
Hu, Shenyang, Burkes, Douglas E., Lavender, Curt A., Senor, David J., Setyawan, Wahyu, and Xu, Zhijie. 2016. "Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation". Netherlands. doi:10.1016/j.jnucmat.2016.07.012.
@article{osti_1396790,
title = {Formation mechanism of gas bubble superlattice in UMo metal fuels: Phase-field modeling investigation},
author = {Hu, Shenyang and Burkes, Douglas E. and Lavender, Curt A. and Senor, David J. and Setyawan, Wahyu and Xu, Zhijie},
abstractNote = {},
doi = {10.1016/j.jnucmat.2016.07.012},
journal = {Journal of Nuclear Materials},
number = C,
volume = 479,
place = {Netherlands},
year = 2016,
month =
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.jnucmat.2016.07.012

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  • Nano-gas bubble superlattices are often observed in irradiated UMo nuclear fuels. However, the for- mation mechanism of gas bubble superlattices is not well understood. A number of physical processes may affect the gas bubble nucleation and growth; hence, the morphology of gas bubble microstructures including size and spatial distributions. In this work, a phase-field model integrating a first-passage Monte Carlo method to investigate the formation mechanism of gas bubble superlattices was devel- oped. Six physical processes are taken into account in the model: 1) heterogeneous generation of gas atoms, vacancies, and interstitials informed from atomistic simulations; 2) one-dimensional (1-D) migration of interstitials; 3) irradiation-induced dissolution of gas atoms; 4) recombination between vacancies and interstitials; 5) elastic interaction; and 6) heterogeneous nucleation of gas bubbles. We found that the elastic interaction doesn’t cause the gas bubble alignment, and fast 1-D migration of interstitials alongmore » $$\langle$$110$$\rangle$$ directions in the body-centered cubic U matrix causes the gas bubble alignment along $$\langle$$110$$\rangle$$ directions. It implies that 1-D interstitial migration along [110] direction should be the primary mechanism of a fcc gas bubble superlattice which is observed in bcc UMo alloys. Simulations also show that fission rates, saturated gas concentration, and elastic interaction all affect the morphology of gas bubble microstructures.« less
  • Flexoelectricity refers to electric polarization generated by heterogeneous mechanical strains, namely strain gradients, in materials of arbitrary crystal symmetries. Despite more than 50 years of work on this effect, an accurate identification of its coupling strength remains an experimental challenge for most materials, which impedes its wide recognition. Here, we show the presence of flexoelectricity in the recently discovered polar vortices in PbTiO 3 /SrTiO 3 superlattices based on a combination of machine-learning analysis of the atomic-scale electron microscopy imaging data and phenomenological phase-field modeling. By scrutinizing the influence of flexocoupling on the global vortex structure, we match theory andmore » experiment using computer vision methodologies to determine the flexoelectric coefficients for PbTiO 3 and SrTiO 3. Here, our findings highlight the inherent, nontrivial role of flexoelectricity in the generation of emergent complex polarization morphologies and demonstrate a viable approach to delineating this effect, conducive to the deeper exploration of both topics.« less
  • We reveal the microscopic vacancy trapping mechanism for H bubble formation in W based on first-principles calculations of the energetics of H-vacancy interaction and the kinetics of H segregation. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of H{sub 2} molecule and nucleation of H bubble inside the vacancy. The critical H density on the vacancy surface before the H{sub 2} formation is found to be 10{sup 19}-10{sup 20} H atoms per m{sup 2}. We believe that such mechanism is generally applicable for H bubble formationmore » in metals and metal alloys.« less
  • Transmission electron microscopy characterization of irradiated U-7wt% Mo dispersion fuel was performed on various samples to understand the effect of irradiation parameters (fission density, fission rate, and temperature) on the self-organized fission-gas-bubble superlattice that forms in the irradiated U-Mo fuel. The bubble superlattice was seen to form a face-centered cubic structure coherent with the host U-7wt% Mo body centered cubic structure. At a fission density between 3.0 and 4.5 x 10 21 fiss/cm 3, the superlattice bubbles appear to have reached a saturation size with additional fission gas associated with increasing burnup predominately accumulating along grain boundaries. At a fissionmore » density of ~4.5x10 21 fiss/cm 3, the U-7wt% Mo microstructure undergoes grain subdivision and can no longer support the ordered bubble superlattice. The fuel grains are primarily less than 500 nm in diameter with micron-size fission-gas bubbles present on the grain boundaries. Solid fission products decorate the inside surface of the micron-sized fission-gas bubbles. Residual superlattice bubbles are seen in areas where fuel grains remain micron sized. Potential mechanisms of the formation and collapse of the bubble superlattice are discussed.« less
  • Fission product accumulation and gas bubble microstructure evolution in nuclear fuels strongly affect thermo-mechanical properties such as thermal conductivity, gas release, volumetric swelling and cracking, and hence the fuel performance. In this paper, a general phase-field model is developed to predict gas bubble formation and evolution. Important materials processes and thermodynamic properties including the generation of gas atoms and vacancies, sinks for vacancies and gas atoms, the elastic interaction among defects, gas re-solution, and inhomogeneity of elasticity and diffusivity are accounted for in the model. The simulations demonstrate the potential application of the phase-field method in investigating 1) heterogeneous nucleationmore » of gas bubbles at defects; 2) effect of elastic interaction, inhomogeneity of material properties, and gas re-solution on gas bubble microstructures; and 3) effective properties from the output of phase-field simulations such as distribution of defects, gas bubbles, and stress fields.« less