查看更多>>摘要：The addition of alloying elements plays an essential role in the behaviors of helium (He) produced by transmutation in metal alloys. The effects of solutes (Ni, Cr, Ti, P, Si, and C) on the behavior of He and He-He pairs in face-centered cubic (fcc) iron were investigated via first-principles calculations based on density functional theory (DFT). For the interactions between solutes and He, we found that Ti, P, Si, and C were more potent in attracting He than Ni and Cr in fcc iron. We determined the most stable configuration for the He-He pair, which is the substitutional-tetrahedral He pair with a binding energy of 1.60 eV. In considering the effect of solutes on the stability of the He-He pair, we proposed a unique definition of binding energy. By applying this definition, we suggest that Ti and P can weaken He self trapping, Cr and C are beneficial for He self-trapping, and Ni is similar to the matrix Fe itself. For the diffusion of He, which is the necessary process of forming the He bubble, we determined that the most stable interstitial (int) He is in a tetrahedral (tetra) site and can migrate with the energy barrier of 0.16 eV in pure fcc iron. We also found that Ti and Si can increase the barrier to 0.18 and 0.20 eV; on the contrary, Cr and P decrease the barrier to 0.10 and 0.06 eV, respectively. Summarizing the calculations, we conclude that Ti decreases while Cr increases the diffusion and self-trapping of He in fcc iron.(c) 2022 Elsevier B.V. All rights reserved.
Bhattacharya, ArunodayaLevine, Samara M.Zinkle, Steven J.Chen, Wei-Ying...
12页
查看更多>>摘要：In-situ irradiations using 1 MeV Kr2+ ions in a transmission electron microscope were performed on extraction replica samples containing M23C6 carbides and MX carbonitrides from two ferritic-martensitic (FM) steels: (i) 9%Cr-1%W-TaV based Eurofer97 and (ii) 9%Cr-1%Mo-VNb (all in wt.%) based additively manufactured (AM) Grade91 steel. The irradiations were performed between 100 and 773 K up to a maximum dose of similar to 2.4 displacements per atom (dpa). The M23C6 carbides are highly susceptible to radiation induced amorphization (RIA), while the MX type nanoprecipitates are highly amorphization resistant across the entire irradiation temperature range. Between 100 and 423 K, RIA of M23C6 carbides occurs very rapidly with critical amorphization doses ranging between similar to 0.35 and 0.9 dpa, increasing to higher doses at 573 K. Complete amorphization of the M23C6 carbides up to doses of similar to 2.4 dpa is not possible at 773 K under the present irradiation conditions. The critical amorphization dose of M23C6 carbides increases nearly exponentially with irradiation temperature. The critical temperature for the crystalline-to-amorphous phase transformation (T-c -> a) of M23C6 carbides irradiated as replica samples, i.e. without the surrounding metal matrix, was estimated to be-812 K. Comparing the present results with neutron irradiation data on bulk samples reveals a decrease in the critical amorphization dose for M23C6 and an increase of T-c -> a, highlighting the effect of dose rate on the amorphization behavior that is qualitatively consistent with literature on other non-metals. Changes in the minor chemistry of M23C6, such as presence or absence of W, V, Nb, Mo, seems to have little effect on the amorphization behavior. In-situ irradiations on extraction replica samples provide a novel pathway to explore radiation tolerance of nanoprecipitates in nuclear structural materials (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The purpose of the present study is to clarify the phase stability of the corroded layer in reduced activa-tion ferritic/martensitic steels under irradiation. The oxide film of F82H steel was subjected to ion irra-diation using 2.8 MeV-Fe2+ at 573 K. For post-irradiation experiments, grazing incident X-ray diffraction (GIXRD) and Raman analysis were conducted to clarify the features of the oxide layer with the variation of the irradiation dose. The dominant phase of the oxide film was identified as FeCr2O4, which co-existed with up to-30% of the residual matrix phase. The fraction of the residual matrix decreased as the irradi-ation dose increased, the phase transformation from FeCr(2)O(4)to Fe3O4 was confirmed. The hypothesis for the phase transformation of FeCr(2)O(4)to to Fe3O4 under irradiation was proposed based on the experimental results. Specifically, the FeCr(2)O(4)to phase is unstable under irradiation, and tends to become stable after ab-sorbing Fe atoms from the residual matrix in the corrosion layer. As a result, the Fe concentration in the oxide layer increased under irradiation, the phase transformation of FeCr(2)O(4)to to Fe3O4 is presumed under irradiation. However, concerns about the mechanism of the instability of FeCr2O4 under irradiation, and better stability of Fe3O4 phase relative to FeCr2O4 phase have to be further considered to achieve a better understanding. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The management of neptunium, an artificial element produced in nuclear reactors that is unsuitable for recycled fuel, is crucial for the development of long-term toxicity reduction. In this study, we focused on the direct synthesis of (U , M)O-2 solid solution ( M = Th, Np) by extending our recent progress in hydrothermal synthesis with additives. The homogeneity of the (U , M)O-2 ( M = Th, Np) systems prepared by supercritical hydrothermal reactions was investigated through crystallographic analysis based on Vegard's law, and the 23Na nuclear magnetc resonance (NMR) measurement of (U, Np, Na)O-2 solid solutions. Our experimental and analytical results revealed that (i) an optimal additive is ammonium carbonate and starting uranium valence is IV in the case of (U, Th)(O)(2+x), and (ii) an optimal additive is ethanol and starting uranium valence is VI in the case of (U, Np)(O)(2+x), for producing the homogeneous solid solutions by hydrothermal synthesis. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：With high mechanical strength, good corrosion resistance and small thermal neutron absorption cross-section, zirconium based alloys are widely used as the nuclear structural materials. Stress concentra-tion usually appears in zirconium-based-alloy components during their reactor service phase or the stor-age stage of spent fuels, which could induce the delayed hydride cracking (DHC) behavior to seriously threaten the nuclear safety. In this study, an innovative multi-field coupling theoretical frame is devel -oped, with the effects of texture factor, with the irradiation hardening and embrittlement effects as well as the hydride orientation contributions involved in the cohesive model, with the hydrogen diffusion affected by the irradiation-induced variations of Nb concentration. The multi-field coupling simulation results indicate that (1) the predictions of the DHC velocities for different irradiation doses are in good agreement with the experimental data, and the subcritical cracking traits can be captured, which vali-dates the effectiveness of the newly developed models; (2) the irradiation-enhanced hydrogen diffusion coefficient plays a dominant role in the increase of DHC velocity with the radiation dose; (3) the irra-diation hardening leads to the increases of hydrostatic stress gradient and the concentration gradient of solid-soluted hydrogen atoms, which accelerates the diffusion flux of hydrogen atoms towards the crack tip region; (4) essentially, it is the irradiation hardening that shortens the required length of hydrided zone to initiate new fracture, and quicken the multi-coupling cracking process. This work lays a founda-tion for the further study of delayed hydride cracking behavior.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The solubility of fission products in molten salts is an important factor in predicting their rate of release, and their buildup can affect the salts' performance. In this work, a molecular dynamics study of dissolved Ar, Xe, Cs+ and I- in molten FLiNaK is undertaken. The work includes a method for the determination of the interatomic potential parameters based on DFT calculations and tuned such that experimentally determined densities are achieved. Simulations were used to estimate diffusion coefficients for each solute. Additionally, the effects of dissolved CsI on the thermophysical properties, such as heat capacity, viscosity and thermal conductivity of the salt, are also predicted. Alchemical free energy calculations are used to determine the solutes' solvation free energies, and trends due to changes in concentration and temperature are examined and compared favourably to experimental results found in the literature. Thus, it was found that molecular dynamics simulations can be used to predict the behaviour of solutes in molten salts, and the effects of their presence on the properties of the salt. Crown Copyright (c) 2022 Published by Elsevier B.V. All rights reserved.
Shen, JieMarrow, T. JamesScotson, DanielJin, Xiaochao...
9页
查看更多>>摘要：The fracture toughness of the fine-grained nuclear graphite SNG742 has been investigated by observation of stable crack propagation in double cleavage drilled compression specimens. The three-dimensional displacement fields were obtained by digital volume correlation (DVC) of in situ laboratory X-ray computed tomographs. The crack tip location and crack opening displacements were determined using an image edge detection algorithm based on the wavelet modulus maxima. The Young modulus was estimated by fitting a finite element model to DVC displacement field data measured before crack initiation. Using the 3D crack geometry and the surrounding full-field 3D displacement fields as boundary conditions, the elastic strain energy release rate J and the three-dimensional stress intensity factors K-I to K-III were then evaluated via the contour integral method. Constant mode I critical stress intensity factor was obtained along the curved crack fronts, with negligible shearing modes. This method allows evaluation of the fracture toughness without prior knowledge of elastic properties, and has potential applications to assess the effects of high temperature, oxidation and irradiation in small specimens of nuclear graphite. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The reprocessing of nuclear fuel generates gaseous radionuclides including various isotopes of xenon, krypton and iodine. Iodine, mainly present as long-lived I-129 (half-life, 1.57 x 10(7) years) and short-lived I-131 (half-life, 8.02 days) is a particular concern because of its high volatility and mobility in the environment. Deep geological disposal is therefore favored over release into the marine environment or the atmosphere. To this end, gaseous iodine must first be captured in solid sorbents and then immobilized in a stable waste form. While the literature on iodine sorbents (also called filters) and iodine immobilization materials is extensive, the conversion of the sorbents into stable waste forms has not received as much attention. The aim of this review is to examine the links between these two research fields: iodine trapping on solid sorbents and iodine conditioning matrices described in the literature. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Irradiation-induced hardening and changes to mechanical properties can often lead to material degradation and can limit the operation of reactor components. In addition, changes to mechanical properties can be a precursor to other material environmental degradation. Dislocation loops, stacking fault tetrahedra (SFT), and voids are major irradiation-induced lattice defects that occur in structural materials and are often observed post-irradiation. However, these defects are often considered only as obstacles to dislocation motion, with hardening assumed to be dependent on the habit plane and Burgers vector of the defect. The stability and nature of dislocation loops and SFTs with temperature are often overlooked, and this may play a crucial role in the mechanical properties of structural materials. We combine high-resolution transmission electron microscopy (HR-TEM) and atomistic simulations to determine the atomistic configurations and thermal stability of dislocation loops and SFTs. Dislocation dissociations are observed in both vacancy and interstitial-type perfect dislocation loops as well as in vacancy-type Frank loops, whereas interstitial-type Frank loops remain stable and are the least influenced by temperature. Triangle-shaped intrinsic stacking faults are formed at the edges of Frank vacancy loops, and a direct transformation from triangle-shaped Frank vacancy loops to SFTs is observed in atomistic simulations. SFTs are energetically more stable than Frank vacancy loops based on formation energy calculations in pure face-centered cubic Fe, which may explain why vacancy-type Frank loops are infrequently observed experimentally. The motivation for this study is to develop a framework for the stability and nature of irradiation defects as a function of temperature, which will be subsequently used for more complex (alloy) systems.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The present work explored the surface reactions in SiC suspensions subjected to high temperature and Co-60-gamma irradiation, respectively. We observed for the first time the pH-dependent SiC dissolution by water at 300 & nbsp;C and 10 MPa produces a substantial CH4, while the formation of another product H-2 is decreased by the reaction time. On the other hand, the continuous H-2 production from water radiolysis is greatly enhanced by the presence of an interface possibly due to the interfacial charge transfer processes. Both of the reactions are accelerated by the increased active surface contacts that are associated with the decreased SiC particles size from 250 nm to 50 nm and rising weight percentage from 3% up to 7%. The XPS, FTIR, SEM, and XRD data found little microstructure changes by gamma irradiation, but noticeable corrosive surface during hydrothermal reactions. The study pointed out that gas release is an important factor that should be considered when SiC is applied for LWR fuel assemble. (c) 2022 Elsevier B.V. All rights reserved.
NSTL
Elsevier