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Journal of Nuclear Materials
North-Holland
Journal of Nuclear Materials

North-Holland

0022-3115

Journal of Nuclear Materials/Journal Journal of Nuclear MaterialsSCIISTPEIAHCI
正式出版
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    Hybrid functional/embedded cluster study of uranium and actinide (actinide = Np, Pu, Am or Cm) mixed dioxides bulk and {110} surfaces

    Chen J.-L.Kaltsoyannis N.
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.Understanding actinide (An) mixed oxides (MOX) is important for the development of minor An bearing U-Pu MOX nuclear fuel, and the long-term storage of spent nuclear fuel. In this work, we systematically simulate AnO2 (An = U, Np, Pu, Am, and Cm) and U-An MOX (An = Np, Pu, Am, and Cm) bulk and {110} surfaces using hybrid density functional theory within an embedded cluster model, focusing on the spin density of An and the density of states of AnO2 bulk and surface for the An series from U to Cm; spin density transfer is found between O and An and is discussed in detail. For U-An MOX bulk and surface, geometric structure, U and An spin densities and the densities of states are presented. Clear conclusions can be drawn regarding the oxidation state of An in the U-Np and U-Cm MOX systems, while U-Pu MOX and U-Am MOX are less clear but and sensitive to the simulation method, suggesting they are in a transition region between the U-Np and U-Cm systems.
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    Monitoring the gradual change in oxidation state during surface oxidation or reduction of uranium oxides by photoemission spectroscopy of the 5f states

    Jamal G.E.Jonsson M.Gouder T.Eloirdi R....
    5页
    查看更多>>摘要：© 2022Photoelectron spectroscopy study of the U5f emission gives valuable insight into the surface oxidation mechanism of uranium oxides. Its intensity is directly related to the electron count nf, which decreases with increasing oxidation number (U(IV): nf=2; U(V): nf=1; U(VI): nf=0). n5f can be quantified by analysing the U5f/U4f intensity ratio and using a standard of known composition. In addition, the 5f emission has a characteristic multiplet shape, directly related to n5f, which can be used to distinguish the 5f2 and 5f1 configuration of U(IV) and U(V), respectively. Three independent methods are used to determine the surface oxidation state: the U5f/U4f intensity ratio, the relative intensities of the U4f oxide shifted peaks, and the O1s/U4f intensity ratio. The first two reveal the concentration of the U in each oxide, the third indicates the total concentration of oxygen. These methods are applied to follow the surface modification of UO2 films when exposed to various oxidative conditions: molecular and atomic oxygen and water plasma at 400°C. In addition, the reduction of UO3 by atomic H is studied. Molecular oxygen oxidizes UO2 to UO2+x(x = 0.22), containing both U(IV) and U(V). Atomic oxygen also oxidizes U(IV) to U(V) at low dosages, but then continues oxidizing U(V) to U(VI) (UO3) at high dosages. Conversely, atomic hydrogen reduces UO3. In the early phase of reduction U(V) forms exclusively – no U(IV) is observed. Water plasma first transforms almost all UO2 (surface and subsurface) into U(V). With further plasma exposure the surface is oxidized to about 80% U(VI) and 20% U(V). Up to this point, a small fraction of U(IV) remains at the surface. Once it disappears, the surface oxidation stops and further water plasma exposure now leads to surface reduction into U(V) (the 5f1 peak increases again). Despite the reduction at high dosage, the O1s/U4f intensity ratio keeps increasing.
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    Compositionally graded specimen made by laser additive manufacturing as a high-throughput method to study radiation damages and irradiation-assisted stress corrosion cracking

    Hawkins L.He L.Bachhav M.Schwen D....
    5页
    查看更多>>摘要：© 2021This study demonstrates the feasibility of using compositionally gradient specimens, fabricated by laser additive manufacturing (AM) and post-AM thermo-mechanical treatment, to accelerate alloy synthesis, radiation experiment, and the assessment of irradiation properties in light water reactor environments. The effects of minor Hafnium (Hf) doping in austenitic 316L stainless steel (SS) was selected as the topic of interest. By comparing to the data in literature, we confirmed that the compositionally graded specimen produces the same trend of void swelling, dislocation loops, radiation-induced segregation (RIS), radiation hardening as the wrought specimen produced by cast/forging process. Hf suppressed most radiation damages through strong interaction with point defects. The work also demonstrates the use of compositionally gradient specimens to study the irradiation-assisted stress corrosion cracking (IASCC) susceptibility of Hf-modified SS. While the suppression of radiation hardening and RIS are consistent with the IASCC mitigation by Hf, we emphasize Hf can alter the intrinsic deformation behavior of 316L SS, which reduces grain-boundary strain localization. The advantages and challenges of using compositionally gradient design for high-throughput nuclear alloy development and qualification are also discussed.
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    Effect of He on the hardness and incipient plasticity of W films during nanoindentation

    Wang Z.Xia T.Shi Y.Jiang Z....
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.In future fusion reactors, the production and accumulation of helium (He) will lead to a dramatic mechanical failure for the material. Tungsten (W) is considered as one of the most promising plasma facing materials. In order to study the effect of He on mechanical properties of W, the novel He-charged W films with a homogeneous He dose profile were fabricated by the magnetron sputtering device. The prepared samples in this study can well avoid the problems like damage gradient effect, indentation size effect, and soft substrate effect during the nanoindentation test, which will appear in the samples obtained by conventional high energy He+ implantation. Nanoindentation results showed that the hardness of the films increased with the increasing He content, and the hardness-depth relationship is in good agreement with the Nix-Gao model. The pop-in events can be observed in the pure W film, which were absent in the He-charged films. Results of molecular dynamics (MD) simulations proved that, the He bubble not only promotes the nucleation and propagation of dislocations, but also hinders the dislocation movement, which leads to a smoother transition from elastic to plastic deformation in the indentation process.
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    Ionization-induced defect annealing by fission product ions in SiC and its implication for UO2-SiC composite fuels

    Guo D.Gong H.Li L.Wen J....
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.Based on molecular dynamics simulations on damage production and accumulation, and ionization-induced annealing of defects, a kinetic model on defect evolution has been developed for silicon carbide, and has been applied to investigate the effects of ionization-induced defect annealing by fission products on the evolution of radiation damage in the SiC of UO2-SiC composite fuels. The simulations indicate that fission product (FP) ions can induce defect recovery in pre-existing displacement cascades in SiC, the extent of which seems relevant to the spatial correlation of primary damage. The model predicts that the defect annealing by FP ions can suppress defect accumulation in the SiC of UO2-SiC composite fuels, which helps to improve the thermal conductivity of the composite fuels under irradiation, and the effect decreases with the distance from the UO2 matrix. The results indicate that defect annealing by FP ions plays an important role in the defect evolution in the SiC of UO2-SiC composites, and should be considered in evaluating the performance of UO2-SiC composite fuels under irradiation and in the design of composite fuels.
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    Crystal mechanics-based thermo-elastic constitutive modeling of orthorhombic uranium using generalized spherical harmonics and first-order bounding theories

    Marki R.E.Knezevic M.Brindley K.A.McCabe R.J....
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.In earlier works, a mathematical procedure for invertible microstructure-property linkages was developed using computationally efficient spectral methods for polycrystalline cubic and hexagonal metals. This paper formulates such invertible microstructure–property linkages for orthorhombic polycrystalline metals relying on the generalized spherical harmonics (GSH) spectral basis. The procedure is used to compute property closures of orthorhombic polycrystals. The closures represent the complete set of theoretically possible combinations of effective properties for a selected material. The procedure relies on the first-order bounding theories and considers orientation distribution functions (ODFs) as the main microstructural descriptor influencing homogenized properties. Numerous examples of these closures involving second-rank thermal expansion and fourth-rank elastic stiffness tensorial properties over a broad range of temperatures are presented for α-uranium (α-U). In doing so, certain key properties of these closures are exploited to facilitate their computation with drastically reduced computational effort. Along with the recently developed GSH-based interpolation procedure for ODFs from coarsely spaced experimental measurement grids to finely spaced finite element mesh resolution grids presented in Barrett et al., the developed computationally efficient ODF-effective property linkages are used to establish a crystal mechanics-based simulation framework coupled with the finite element method (FEM). The ODF dependent thermal expansion and elastic stiffness tensors are efficiently calculated at every integration point and used by the FEM to predict the overall distortion of a hemispherical part made of α-U during heating. It is shown that the developed framework can be used to simulate microstructurally heterogeneous components under thermo-mechanical loadings in a computationally efficient manner.
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    Challenges and opportunities to alloyed and composite fuel architectures to mitigate high uranium density fuel oxidation: Uranium diboride and uranium carbide

    Watkins J.K.Wagner A.R.Jaques B.J.Gonzales A....
    5页
    查看更多>>摘要：© 2021The challenges and opportunities to alloyed and composite fuel architectures designed and intended to mitigate oxidation of the fuel during a cladding breach of a water-cooled reactor are discussed in this manuscript focused on the oxidation performance of uranium diboride and uranium monocarbide. Several high uranium density fuels are under consideration for deployment as accident tolerant and/or advanced technology nuclear reactor fuels, including UN, U3Si2, UB2, and UC. Presented here is the literature for UB2 and UC degradation modes, thermodynamics, and oxidation performance of the pure compounds and reported alloyed and composite architectures. Furthermore, this review covers the materials and techniques for the incorporation of additives, dopants, or composite fuel architectures to improve the oxidation behavior for high uranium density fuels for use in LWRs.
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    The microstructure, mechanical-thermal properties and softening resistance of Y4Al2O9 dispersion-strengthened Cu alloy

    Zhou Y.Yi G.Zhang P.Yin S....
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.Oxide dispersion-strengthened copper (ODS-Cu) alloys with yttrium oxide nanoparticles are promising heat sink materials in fusion reactor due to their high strength, thermal conductivity and thermodynamic stability. The particle size and number density of oxide nanoparticles can be improved via addition of microalloying element. In this study, the atomized Cu-Y alloy, Al and Cu2O were used as the Y source, the microalloying element and the oxidant material, respectively, to fabricate ODS-Cu alloy by mechanical alloying method. After spark plasma sintering and annealing, a ODS-Cu alloy with a microstructure containing Y4Al2O9 nanoparticles homogeneously distributed in Cu(Al) solid solution matrix was successfully fabricated. It is found that a crystallographic orientation relationship of (31¯2)Y4Al2O9∥(11¯1)Cu(Al) was formed between Y4Al2O9 nanoparticles and Cu(Al) matrix and the lattice mismatch was 0.337%. The small lattice mismatch reduced the nucleation barrier for Y4Al2O9 nanoparticles so a mean particle size of 4.8 nm and a number density of 2.16×1024 m−3 were obtained in the alloy. Consequently, the microhardness was enhanced via Hall-Petch strengthening, dislocation strengthening and dispersion strengthening. The softening temperature of ODS-Cu alloy was improved to higher than 1000 °C due to the thermodynamic stability and the pinning effect of Y4Al2O9 nanoparticles. In addition, the thermal conductivity of Cu-1Y-9Al-0.3Cu2O alloy is close to other copper alloys as the volume fraction of Y4Al2O9 nanoparticles is limited. Cu-1Y-9Al-0.3Cu2O alloy provides a good overall performance, which may be used as heat sink materials under severe conditions.
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    A molecular dynamics study of a cascade induced irradiation creep mechanism in pure copper

    Khiara N.Onimus F.Dupuy L.Crocombette J.-P....
    5页
    查看更多>>摘要：© 2022Recently, in-situ TEM straining experiments on pure copper have unraveled a high stress irradiation creep mechanism. Irradiation induced unpinning of dislocations from defects has been observed and the mean pinning lifetime has been determined. In the present study, molecular dynamics simulations are performed on pure copper to investigate the impact of collision cascades on screw dislocations pinned on Frank loops under high-applied stresses at 300 K in order to further quantitatively elucidate this mechanism. The simulations indicate two possible dislocation unpinning mechanisms. Unpinning can occur through loop destruction when the cascade is generated on the pinning points of the dislocation (type 1 unpinning). Unpinning can also be triggered by the shear stresses building up around a cascade generated in front of the dislocation in the glide plane (type 2 unpinning). Type 2 unpinning generally leads to dislocation repinning on cascade residues, so that it should only marginally contribute to irradiation creep. The mean pinning lifetime due to type 1 unpinning in the conditions of the in-situ TEM experiments is derived from a simple model previously developed for zirconium, and is found in the same orders of magnitude as in the experiments.
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    Impact of impurities on the fabrication and performances of yttrium-doped thoria electrolyte ceramics

    Clavier N.Cherkaski Y.Dacheux N.Brissonneau L....
    5页
    查看更多>>摘要：© 2021 Elsevier B.V.The effect of several impuritites on the life-cycle of yttria-doped thoria electrolyte was evaluated in this study. All the oxides exhibited the single-phase fluorite-type structure expected for such materials, while the variation of the unit cell parameter attested for the incorporation of the impurities in the lattice. Doping with 0.2 – 1 wt.% of Al, Si or Zr only slightly affected the morphology of the powders, as well as the microstructure of the pellets obtained after sintering, even if a deleterious effect, leading to the fragilization of the samples, was observed for high silicon contents. The presence of silicon and zirconium in the ceramic further modified its electrical properties. The grain conductivity was always found to decrease. Impedance spectroscopy also revealed a strong modification of the signal assigned to grain boundaries, which evidenced that impurities partially migrated during the sintering step. Finally, corrosion tests undertaken in liquid sodium at 773 K showed that the pellets were fragilized by the presence of silicon or high zirconium contents, possibly through the formation of Na2MO3 ternary oxides at the grain boundaries. From a general point of view, silicon seems to be the most harmful impurity that should be especially checked during the fabrication processes.
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    • NSTL