查看更多>>摘要：The effect of proton irradiation fluence on microstructure evolution and lead-bismuth eutectic (LBE) corrosion behavior of 11Cr1Si ferritic/martensitic (F/M) steels was investigated. The results revealed that dislocations and black dots were the two main types of TEM-visible defects of all irradiated samples. Proton irradiation did not alter the duplex structure of the oxide layer but significantly increased the corrosion rate, and this was attributed to the irradiation-induced defects responsible for the irradiation-enhanced outward diffusion of Fe and inward diffusion of O atoms. (c) 2022 Elsevier B.V.
Ofori-Opoku, NanaPrudil, Andrew A.Welland, Michael J.
17页
查看更多>>摘要：The time-evolution of an intergranular bubble population is considered using the Included Phase Model (IPM). The model considers the generation and coupled transport of vacancies and gas atoms driven by interfacial energy, elasticity, and internal energy in a framework that admits complex interface morphology. The model predicts overpressure, bubble growth, coarsening, and coalescence leading to the formation of interconnected high-aspect-ratio bubbles on the grain face. The computational efficiency of this model is leveraged to simulate sets of 250 bubbles over time, which compare well with the CAGR-UOXSWELL SEM measurements and the established SIFGRS model. Analysis of the simulation results highlights the importance of the bubble density as an indicator of bubble structure formed by coalescence and suggests that the two-point autocorrelation function captures the formation of an interconnected network which could improve release thresholds. Crown Copyright (c) 2022 Published by Elsevier B.V. All rights reserved.
查看更多>>摘要：In fission based nuclear reactors the fuel is subject to an intense neutron environment that drives the fission chain reaction. Due to this process fission fragments are created with energies reaching 1 MeV/amu that lose energy primarily through inelastic interactions with the electronic structure producing electronic excitations. Subsequently, these excitations thermalize through electron-phonon interactions resulting in the formation of a high temperature thermal spike and associated pressure spike. This process promotes atomic mobility that is expected to evolve lattice defects, including the annealing of latent ion tracks. In this work, a multigroup model for electron energy transport is developed and applied to molecular dynamics simulations in the LAMMPS code to examine fission energy deposition and fission effects in nuclear fuel. This technique utilizes MCNP Monte Carlo electron transport calculations to determine the initial injection of fission energy. To provide a more predictive approach than semi-empirical two-temperature models, the electron-phonon interactions are defined to include multiphonon energy transfer as a function of atomic and electron temperature, and are evaluated from electronic structure calculations using the VASP density functional theory code and PHONON lattice dynamics code. Application of this model to fission energy deposition in uranium dioxide predicts ion track formation and fission enhanced atomic mobility behavior within reasonable agreement of experimental trends. Furthermore, simulations of fission fragment interactions with latent ion tracks demonstrate an annealing effect due to this enhanced mobility.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Uranium mononitride is a strong candidate for an advanced nuclear fuel. In this work we use density functional theory to model the diffusivity of matrix U atoms, as well as the noble gas (Ng) fission products Kr and Xe, at the atomic scale under three stoichiometric conditions (U-rich, stoichiometric, N-rich). U self-diffusion is found to be dependent on stoichiometry, being largest under N-rich conditions. The U formation entropy significantly affects the U self-diffusion coefficient, indicating that it is necessary to consider the vibrational properties of the system to accurately describe diffusion properties in UN. The calculated Kr and Xe diffusion coefficients from the U vacancy (V U )-assisted mechanism are much larger than by interstitial mechanisms under the three stoichiometric conditions studied. The two mechanisms show opposite stoichiometric dependence, with the former increasing from U-rich to N-rich conditions and the latter decreasing. Kr moves significantly more quickly than Xe via the interstitial mechanism due to the larger atomic radius of the latter, while the effect of atomic size on the V U -assisted mechanism is negligible, indicating similar diffusivity of Kr and Xe in UN. The good agreement with experiment of our calculated Xe monovacancy-assisted diffusion coefficient indicates that the monovacancy-assisted mechanism governs the Ng diffusion in UN, and supports the accuracy of our theoretical model. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：To investigate the thermal evolution of vacancy-type defects and the relationship between the evolution of vacancy-type defects and the formation of fuzz structure on the surface of W-Ni-Fe heavy alloys irradiated with He ions, isochronal annealing treatments at temperatures from 100 degrees C to 10 0 0 degrees C were conducted on the irradiated 97W-2Ni-Fe alloy. The evolution of microdefects was characterized by positron annihilation spectroscopy (PAS). Thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to supplement the positron annihilation method. A large number of vacancy-type defects were produced in the 97W-2Ni-Fe alloy after irradiation at room temperature and isochronal annealing, and the main defect types of positron capture changed at three stages: RT-60 0 degrees C, 600-800 degrees C, and 800-1000 degrees C. SEM found that a large number of nanoscale protrusions appeared on the surface of samples annealed at 800 degrees C, and these nanoscale protrusions were seeds of fuzz structures. The formation of fuzz structure is closely related to the movement of vacancy-type defects by PAS, TDS, SEM, and other characterization methods. In addition, we found that the high density Ni and Fe in the matrix phase of the 97W-2Ni-Fe alloy as He capture points would accelerate the nucleation and growth of He bubbles and promote the growth of the fuzz structure.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Irradiation response and deformation mechanisms of additively manufactured (AM) 316 L stainless steel were studied by atomic scale characterization and micro-pillar compression. The AM 316 L stainless steels were fabricated by direct energy deposition, a laser-based additive manufacturing process. Irradiation with 2 MeV protons at 360 degrees C was performed to create similar to 1.8 displacements-per-atom (dpa) damage in AM 316 L. Deformation behaviors of the as-manufactured, annealed, and proton-irradiated variants were studied, focusing on the effects of manufacturing-induced pores, residual stress, and irradiation-introduced defects (dislocation loops and voids). Micro-pillars were prepared from grains of pre-selected orientation, avoiding contributions of grain boundaries and allowing determination of resolved shear stress on {111} glide planes. Transmission electron microscopy was used to characterize the pre- and post-deformation microstructure. It was found that in the as-manufactured alloy variant, moving dislocations were the major deformation carrier, with noticeable blocking by fabrication-induced pores, In the annealed variant, hardness was reduced, and deformation was also accomplished by dislocation gliding. In the protonirradiated variant, significant twinning was observed. Comparing measured resolved shear stress and predicted critical stress for dislocation dissociation, we conclude that irradiation hardening became high enough to activate twinning. Therefore, the deformation mechanism changes from dislocation gliding to twinning. The study is important for both processing optimization and performance evaluation of AM alloys for reactor applications.
Jin, MiaomiaoDennett, Cody A.Hurley, David H.Khafizov, Marat...
9页
查看更多>>摘要：Radiation damage can significantly degrade the thermal conductivity of ThO 2 due to enhanced phonondefect scattering. To quantify the effect of radiation-induced defects on thermal transport, we employ non-equilibrium molecular dynamics simulations to estimate the thermal conductivity in the presence of various types of defects. For each defect species, the phonon-defect scattering cross-section is extracted based on analytical models. In addition, the impact from two types of experimentally-observed dislocation loops (perfect and faulted) on thermal transport is examined with respect to the loop size and orientation. Notably, simulation cell size effects are analytically and quantitatively addressed via a phononmean-free-path-resolved analysis. It can be concluded that, for a given total number of defect sites per unit volume, agglomerating defects into larger clusters improves thermal conductivity compared to isolated defects. Importantly, this work provides quantitative information towards the defect-specific thermal conductivity, and phonon-defect scattering cross-sections, which can serve as inputs to large-scale transport models to quantify the evolution of overall thermal conductivity of ThO 2 under irradiation. (c) 2022 Elsevier B.V. All rights reserved.
Chronis, Alexandros G.Sigalas, Michael M.Virot, FrancoisBarrachin, Marc...
6页
查看更多>>摘要：The dust concern in ITER fusion facility calls for improvement of the knowledge of their fundamental properties because important safety issues are associated with them; including radiological hazard, toxicity as well as chemical reactivity in terms of explosion risks. Additional risk related to the particle class of nanometric size has to be futhermore consider due to their impact on biological environment since their production in fusion facility has been put in evidence. Specifically, although no data has been acquired on beryllium nanoparticles (NPs) and their reactivity within tritium, the aim of this present paper is to establish a first comprehensive picture of beryllium - hydrogen based nanoparticles. The structural and electronic properties of Ben and BenHm NPs of "medium " sizes are investigated using Density Functional Theory calculations. Starting from bare NPs to find the relevant nanoparticle shape, the insertion sites of hydrogen are then identified and characterized. Finally, our study focusses on the highly hydrogenated particles which are studied and the relative stability trends are established. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Understanding the statistical properties of mechanical properties of non-irradiated and neutron-irradiated SiC/SiC composites is essential for component design. This study aims to evaluate the detailed damage accumulation behavior of composites focusing on two fracture parameters: proportional limit stress (PLS) and acoustic emission (AE) onset stress. The developmental underwater AE technique, which is benefit in non-contact in-situ failure monitoring method during mechanical testing and in handle of the irradiated material, was first applied to evaluate damage accumulation behavior. Two types of chemical vapor infiltration SiC/SiC composites were used: one reinforced with Hi-Nicalon Type-S SiC fiber and one reinforced with Tyranno-SA3 SiC fiber in the form of satin-woven 2D fabrics with pyrolytic carbon interface. Neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory reached a fluence of 30 dpa at a temperature of 620-670 C. Four-point flexural tests were conducted to evaluate post-irradiation strength. Weibull statistics did not suggest marked degradation of composite strength. Detailed failure behavior evaluated by AE demonstrated no irradiation-induced change of the AE onset stress (i.e., crack initiation equivalent stress). Failure probability analysis suggests that increasing the reliability of composites (i.e., the Weibull modulus rather than strength itself) is essential to expanding the design margin and benefiting from a probabilistic design approach. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Segregation of fission products and their effect on E3[110]/(111) UO2 grain boundary cohesive energy were analyzed via first principles calculations. The most stable segregation sites were investigated for zirconium, molybdenum, cesium, and xenon in UO2. Molybdenum, cesium, and xenon showed segregation tendencies on the E3[110]/(111) UO2 grain boundary but zirconium did not. The grain boundary cohesive energy was analyzed for the structure in which each segregation element was located at the most preferred segregation site. The results showed that zirconium and molybdenum strengthened the grain boundary cohesion, whereas cesium and xenon weakened it. This study shows which fission products cause the weakening of the irradiated UO2 grain boundary, which could help model irradiated fuel performance. (c) 2022 Elsevier B.V. All rights reserved.
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