查看更多>>摘要：The irradiation swelling of U-10Mo fuels is one of the critical factors to affect the in-pile structural in-tegrity and dimensional stability of fuel plates. In this study, a mechanistic model of fission gas swelling for U-10Mo fuels is newly developed with a new evolution model of bubble density, considering the fis-sion gas diffusion behavior and the grain recrystallization. The developed theoretical frame is validated by comparing the predictions in this study with diverse experimental data quantitatively and qualitatively, including the fission gas swelling, total irradiation swelling, the evolution rules of the bubble density and the bubble size, together with the thickness increments of fuel foil in a monolithic U-10Mo/Al fuel plates. The correlation of the irradiation creep with the fission-gas-swelling induced porosity for U-10Mo fuels is firstly considered in the simulation of irradiation-induced thermal-mechanical behaviors in Al-cladded monolithic fuel plates, and a new creep coefficient of dense U-10Mo fuels is identified as 180 x 10(-22) mm(3)/MPa. The research results indicate that the developed fission gas swelling model has a satisfac-tory prediction ability, especially for higher burnup cases, and can describe the dominant dependences of external pressure and temperature found in the related experiments. In addition, parametric studies have been carried out to investigate the influences of temperature, external pressure and grain-boundary diffusion enhancement factor on the related fission gas behaviors. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Kizane, GuntaLeys, Julia M.Knitter, ReginaAntuzevics, Andris...
11页
查看更多>>摘要：Lithium orthosilicate (Li4SiO4) containing ceramics are currently being developed as potential solid-state candidate materials for tritium breeding in future thermonuclear fusion reactors. Under the expected operational conditions, the tritium breeding material will be exposed to the simultaneous influence of several strong energetic factors, for example, radiation, temperature, magnetic field, etc. In the present work, thermal properties of the formed and accumulated paramagnetic radiation-induced defects (containing unpaired electrons) in the Li4SiO4 pebbles with a 2.5 wt.% surplus of silicon dioxide (SiO2) were investigated after irradiation with photons of different types and energies: X-rays with an energy up to 45 keV, gamma rays with an average energy of 1.25 MeV, and bremsstrahlung with an energy up to 6 MeV. The photon-irradiated pebbles were analysed using two complementary spectroscopic methods: electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL). Individual signals contributing to the acquired EPR spectra, TSL glow curves and spectra were distinguished, deconvoluted and simulated in order to obtain a more detailed understanding about the local structure, electron configuration, and thermal stability of the accumulated radiation-induced defects. The simulation and deconvolution data were also compared with the results, which have been acquired for the long-term neutron-irradiated pebbles from the HICU experiment (High neutron fluence Irradiation of pebble staCks for fUsion). (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：A stacking fault tetrahedron (SFT) is a very common kind of defects in face-centered cubic metals under irradiation environment. The grain boundary (GB) migration can effectively heal the SFT through the GBSFT interaction to improve the irradiation resistance of materials. In this study, the GB-SFT interactions in pure Ni and NiFe bicrystals subjected to shear loading were investigated by the molecular dynamics simulations. After the GB-SFT interaction, the GB in pure Ni is pinned, and a void appears as it migrates further, but the GB in NiFe solid solution alloys still remains flat. The migrating GB in the alloys has a higher efficiency to heal the SFT than that in pure Ni. The GB roughening caused by the alloying element brings more transitional structural units into the GB to accommodate more vacancies. As a result, similar to elevated temperature, increasing Fe atom concentration could improve the capacity of GB to heal the SFT.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：This work presents the electrochemical behavior of U3O8 and the formation of Al-U intermetallics in LiCl-KCl-AlCl3 melts at 813 K by various electrochemical test methods. The signals of three intermetallics attributed to Al2U, Al3U and Al4U were detected in the electrochemical curves. The standard Gibbs free energy of formation of Al-U intermetallics, the partial molar Gibbs free energies and activity of U in two phase coexisting states were calculated based on the open circuit chronopotentiometry at 813 and 843 K. U was extracted from U3O8 by forming Al-U intermetallics on Al sheet via potentiostatic electrolysis at -2.0 V in LiCl-KCl-AlCl3-U3O8 molten salt. The X-ray diffraction (XRD) indicated that Al4U, Al3U and Al2U phases were formed. The densely arranged flower-shaped Al-U intermetallics were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). In addition, the extraction efficiency of U(IV) was 92.3% after potentiostatic electrolysis at -2.0 V for 10 h. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：P92 alloy, a candidate structural material for supercritical water reactors, was irradiated with 1 MeV Fe ions at 1, 3, and 7 dpa at room temperature, 300, 450, and 550 degrees C. Slow positron beam Doppler broadening spectroscopy was used to characterize the evolution of the open-volume defects. Irradiation of the Fe9Cr alloy at 300 degrees C induced an unexcepted phenomenon in which the S parameter decreased with an increasing irradiation dose; the phenomenon was ascribed to the pinning effect of Cr on dislocation loops, which promoted the recovery of vacancies. Whereas the reduction in the S parameter was generally inhibited in the P92 alloy. These distinctions are related to the evolution of vacancies. We show that the migration of vacancies hindered by C atoms is mainly related to carbon-vacancy complexes in the P92 alloy at approximately 300 degrees C. As the irradiation temperature increased, the complexes gradually dissociated, and the vacancies were captured and annihilated with interstitial atoms. A better understanding of the evolution of vacancies is helpful for investigating irradiation swelling.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：In nuclear reactors, the helium (He) production and retention from intensity particle irradiation can degrade the physical and mechanical properties of Ni-based alloys. Understanding the fundamental behaviors of He in metals is a critical issue in the development of nuclear materials. In this research, the influence of Cr/Mo/W additions on the stability, migration, and clustering of He in face-centered cubic (fcc) nickel were systematically studied by using density functional theory (DFT). The formation and binding energies show that Cr and Mo/W atoms affect the occupying priority of tetrahedral interstitial He in Ni lattice. The interstitial He prefers to occupy the first nearest neighbor octahedral site with the presence of Cr, while it would locate far away from Mo/W addition. For He migration around alloying elements, the barrier of interstitial He in NiCr is slightly higher than that of pure Ni, while NiMo and NiW systems have a relatively lower barrier. The effective diffusivity of interstitial He atom in Ni-based alloys significantly decreases with the increase of the temperature and Cr/Mo/W concentration. Moreover, when He aggregates at vacancy, the Cr/Mo/W can weaken the formation energy of He clusters and hamper their growth to larger sizes. All these results provide microscopic insights into Cr/Mo/W alloying effect on helium behaviors in Ni-based materials. (c) 2022 Elsevier B.V. All rights reserved.
Evans, Jordan A.Lebensohn, Ricardo A.Harter, Jackson R.Weaver, Kevan D....
19页
查看更多>>摘要：Tristructural isotropic (TRISO) particles show great promise as a candidate fuel for use in several next generation high-temperature nuclear reactor designs due to their structural integrity and fuel performance at high temperatures and burnups. Computational codes exist that can simulate TRISO fuel performance characteristics and failure probabilities under extreme conditions which require knowledge of the TRISO coatings' thermophysical properties. The thermophysical descriptions of the TRISO particle's layers (i.e., buffer, pyrolytic carbon, and silicon carbide) currently used in fuel performance codes, however, assume that many of these properties are constant with respect to temperature or texture. In this paper, we obtain the full elastic stiffness tensors of the carbon and silicon carbide layers, which have transversely isotropic symmetry. The calculated elastic properties of each of the coating layers are in remarkable agreement with the current models at room temperature and correct orientations. Additionally, the textured 3C-SiC layer was found to exhibit novel auxetic behavior above 1500 degrees C. The anisotropic temperature-dependent thermal conductivities of the carbon layers were calculated using acoustical Gruneisen-Debye theory which are in excellent agreement with current models at room temperature and correct orientations. These texture-and temperature-dependent relationships can be incorporated into the thermophysical description of TRISO particles in order to more accurately model fuel performance and failure probabilities under extreme conditions in forthcoming high-fidelity computational simulations.
Garner, F. A.Velikodnyi, A. N.Voyevodin, V. N.Kalchenko, A. S....
9页
查看更多>>摘要：The radiation performance of 18Cr10NiTi-ODS steel with the addition of Y2O3-ZrO2 nano-oxides was compared with that of non-ODS 18Cr10NiTi austenitic steel in terms of radiation-induced hardening and cavity swelling. TEM observations were performed to evaluate the effect of grain refinement and nano-sized oxide precipitates on microstructural changes and radiation tolerance in specimens exposed to 1.8 MeV Cr3+ or 1.4 MeV Ar+ irradiations over a wide range of temperatures. Formation of homogenously distributed voids was observed in both alloys upon Cr3+ irradiation but the ODS steel exhibited a considerably broader temperature range of void formation and lower overall swelling. Cavity formation in steels irradiated with Ar+ showed a strong dependence on Ar/dpa ratio. Argon addition was found to enhance the nucleation of cavities, which act as point defects sinks that reduce void swelling. The largest swelling resistance was observed in the ODS steel due to the combined effect of mechanical alloying and Ar gas co-injection. The hardening behavior was investigated in both non-irradiated and Ar+ irradiated samples at room temperature and elevated temperatures by means of nano-indentation. Along with the strengthening effect of radiation-induced dislocations, gas-filled nano-cavities strongly contribute to the hardening of irradiated alloys with a tendency to increase the barrier strength of nano-cavities with decreasing cavity size. The ODS variant was found to be somewhat less susceptible to radiation hardening compared to non-ODS 18Cr10NiTi steel. (C) 2022 Published by Elsevier B.V.
Kane, Joshua J.Marshall, Douglas W.Cordes, Nikolaus L.Chuirazzi, William C....
23页
查看更多>>摘要：Low-enriched uranium oxycarbide (LEUCO) and surrogate tristructural isotropic (TRISO)-coated-particle compacts with particle volumetric packing fractions of 25%, 40%, and 48% were imaged utilizing X-ray-computed tomography. Subsequent 3D image analysis identified and further quantified kernel size, sphericity, and observed porosity. In addition, the spatial distribution, coordination number, and kernel -nearest neighbors were analyzed and compared for the different packing fractions. Metrics such as ob-served porosity and sphericity enabled quantification and screening for abnormal kernels within TRISO compacts. Assessment of TRISO particle location confirmed and further quantified a non-uniform distri-bution of TRISO particles with the spatial distribution in the radial direction being roughly described as a dampened sinusoidal function. The amplitude and frequency of this non-uniform distribution increased with increasing packing fraction. Measured kernel-nearest neighbor distances indicated two regions along the radial surfaces of compacts where TRISO particles are more likely to be in intimate contact with one another. These regions were found: (1) at upper and lower faces of compacts (i.e., corners); (2) offset similar to 10% of a compact's length from the axial center near the exterior surface. Within these regions, small quantities of defective TRISO surrogate particles (48% packing fraction) and defective LEUCO TRISO par-ticles (40% packing fraction) were found. No defective particles were found within 25% packing fraction LEUCO TRISO compacts.
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