查看更多>>摘要：This paper reports a systematic high-temperature creep behavior of dense U3Si2 pellets using a spark plasma sintering (SPS) apparatus at elevated temperatures and pressures under vacuum conditions. The stress exponent was subsequently derived to be 3.21 at 1173 K and 2.17 at 1223 K, respectively, indicating a grain boundary sliding creep mechanism. The creep activation energy was determined to be 203.6 & PLUSMN; 19.0 kJ/mol, which agrees well with the literature. Finite element modeling was performed using the creep parameters fitted from the strain-time plot. The results suggest an excellent match with the experimental data, confirming the validity of the experiments. Microstructure characterizations indicate that the main phase of the specimens after creep tests remains to be U3Si2, with a 4 mu m thick layer of nano sized particles induced from the diffusion between U3Si2 and alumina disc used to avoid electric current passing through the sample. The successful conduct of creep experiments demonstrates the great potential of SPS to perform high-temperature mechanical testing of nuclear fuels under vacuum conditions. The subsequent finite element modeling exhibits excellent capabilities for accurately predicting material performance in the creep tests and provides a practical tool in evaluating nuclear fuels' performance for a much-extended time scale.(C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Transmutation rhenium (Re) produced in tungsten (W) neutron irradiation not only segregates and pre-cipitates at grain boundaries (GBs) but also forms the sigma-phase (WRe) in the bulk. In this study, using a molecular dynamics (MD) method, we conducted collision cascade simulations in W and W-Re alloys with 5 or 10 at% Re atoms containing a GB/sigma-phase and systematically examined the effect of GB and the evolution of sigma-phase. We find the interstitials in W-Re alloy are preferentially absorbed by the GB region such that the number of vacancies in the bulk region is higher in W-Re alloys than in W; the defect distribution is sensitive to the distance of primary knock-on atoms from the GB plane. Furthermore, similar to the tendency in the GB region, interstitials are preferentially absorbed by the sigma-phase, and Re atoms tend to aggregate near the sigma-phase region. The absorption of sigma-phases and the GB region leads to a considerable defect aggregation, which provides suitable conditions for the regrowth of sigma-phase structure during long-term evolution. The results provide a reference for understanding the GB structure and precipitations in the displacement cascades of W and W-based alloy materials. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Understanding the microstructure-property correlation is critical for the performance evaluation of inservice materials and the development of advanced materials for nuclear reactor applications. Experimental studies are challenging for nuclear materials which are often hazardous. Recent developments in high-energy synchrotron X-ray (HEX) techniques offer the potential to address this challenge, by providing direct observations of internal responses to external stimuli in bulk-like materials, through in situ or 3D measurements. In this review, developments in HEX techniques are introduced and recent applications in nuclear materials are presented. The results offer unprecedented insights into materials performance and provide unique input to computational models.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The evaporation behavior of FLiNaK and FLiBe molten salts containing 5mol% ZrF4 was investigated by low pressure distillation method. It was found that compared with pure FLiNaK salt, the evaporation rates of LiF, NaF and KF decreased sharply in the ZrF4-FLiNaK salt; while in the case of ZrF4-FLiBe salt, the evaporation rate of LiF decreased to a certain degree, and that of BeF2 was almost the same as FLiBe salt without addition of ZrF4. XRD results showed that the fluorine were present as free anions in pure FLiNaK salt, while the formation of BeF4 2- existed in pure FLiBe salt. After the addition of ZrF4, the complexes of K3ZrF7 and Li2ZrF6 were observed in FLiNaK and FLiBe salts, respectively. The microstructure of salts showed the difference of coordinate numbers and activation energies of Zr-F by molecular dynamics (MD) simulation, which affected the evaporation behavior of the material. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Pure chromium is a promising candidate for coating of Zircalloy fuel rods in light water-cooled power reactors to avoid or delay hydrogen generation in accident scenarios. Void swelling of chromium is one possible contributor to coating-interface failure and needs to be studied. The effect of dpa rate on void swelling of Cr was studied using 5 MeV Fe ion irradiation to 15 peak dpa at peak dpa rates of 3.5 x 10(-5), 3.5 x 10(-4), and 3.5 x 10(-3) dpa/s, at six temperatures between 350 degrees C and 650 degrees C. The post-transient (steady-state) swelling rate of pure Cr is similar to 0.05%/dpa. Swelling in Cr also appeared to start at a much higher swelling rate at very low doses. The observed dependence of peak swelling temperature on dpa rate agrees well with earlier theoretical models and clearly demonstrated the well-known temperature shift phenomenon. After determination of the peak swelling temperatures under ion irradiation at three dpa rates we extrapolated downwards to dpa rates characteristic of both sodium-cooled fast reactors and light water-cooled reactors. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：This study aims to identify the creep behavior of Zircaloy-4 fuel claddings under simulated reactivity initiated accident (RIA) thermo-mechanical conditions. In a previous work ballooning creep tests performed in simulated RIA conditions were described. A challenge to overcome when analyzing these experiments is that ballooning tests imply structural effects during the deformation of the specimen that have to be taken into account to identify the creep behavior of the material. In this paper a FEMU (finite element model updating) based identification is proposed to identify the creep law of the cladding, weakly coupled to the phase transformation of the material at high temperatures. Since the loading conditions are solely known in the part of the optical field of the cameras used for stereocorrelation, only this region is modeled using a Love-Kirchhoff assumption to impose the boundary conditions through the sample thickness. A Norton creep law, whose parameters are expressed as a function of the beta phase fraction in the material, is identified and reproduces the first 10 s of the experiments with mean errors on the radial displacement rates of about 10%. Finally, an extension to higher time scale is proposed in Norton's law to model the non linearity in the material response by taking into account the grain growth contribution. (c) 2022 Published by Elsevier B.V.
Tuo, Jing-yiZhang, Rui-qianCai, Zhen-bingDu, Pei-nan...
15页
查看更多>>摘要：FeCrAl alloy has great application potential to replace traditional zirconium alloy as an accident-tolerant fuel (ATF) candidate material. In this study, Fe-13Cr-4Al-2Mo-0.65Nb-0.4Ta alloy was prepared into a thin-walled tube with a diameter of 9.5 mm and a wall thickness of 0.35 mm by cold rolling. The effects of different annealing temperatures on the microstructure morphology, texture growth direction, and me-chanical properties of FeCrAl alloy were studied., alloy underwent recovery and recrystallization with increasing annealing temperature, and the grain size increased. The theoretical calculation showed that the pinning action of Fe2Mo4C and Fe2Nb increased the dislocation density, and the interaction with the dislocation increased the room temperature strength. The addition of Ta led to the formation of more second-phase precipitates at the grain boundary, which hindered the growth and refined grains. The high-temperature stable second phase provided sufficient temperature strength for the alloy.(c) 2022 Elsevier B.V. All rights reserved.
Raiman, Stephen S.Kurley, J. MatthewSulejmanovic, DinoWilloughby, Adam...
10页
查看更多>>摘要：Type 316H stainless steel samples were exposed to flowing FLiNaK salt for 1000 h in a monometallic thermal convection loop (TCL) with a maximum temperature of 650 degrees C and a minimum of 540 degrees C. Samples in the hottest part of the TCL lost mass, with a maximum mass loss of 1.4 mg/cm(2), while samples in the coldest parts of the TCL gained mass, with a maximum mass gain of 1.0 mg/cm(2). Analysis of the samples that gained mass showed an Fe-rich layer on the sample surfaces, indicating that Fe, not Cr, was the primary deposition product in the TCL. Cr loss was apparent to a depth of ~5 mu m in the hot leg. Post-exposure analysis of the salt showed major increases in the Cr, Fe, and Mn contents. The TCL was modeled using the TRANSFORM code. Modeled values matched the experimental temperature measurements showing that TRANSFORM is capable of accurately simulating the TCL conditions. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Uranium in its metallic form is considered as a fuel for sodium fast reactors due to its higher thermal conductivity and high fissile material density relative to UO2 fuel. The metal is alloyed with zirconium to increase its stability at high temperatures and increase its solidus temperature. This work uses ab initio molecular dynamics to perform an evaluation of the mechanical and thermophysical properties of the gamma- (U,Zr) system at temperatures between 10 0 0 K and 1400 K. Among these properties are the equilibrium volume, bulk modulus, molar heat capacity, heat of formation, and the surface energy. The obtained re-sults are compared to experimental data and previous computational work available in the literature. This is the first study of gamma-(U,Zr) utilizing ab initio molecular dynamics, and reduces thermophysical property knowledge gaps that are currently present in the literature. Published by Elsevier B.V.
查看更多>>摘要：Radiation-induced hardening (RIH) is an important indicator for understanding the radiation-induced embrittlement and for new materials' selection for the core components in various nuclear energy systems. RIH has been studied mainly based on an assumption that the material has a homogeneous microstructure. However, in practical applications, the microstructure always exhibits an inhomogeneity such as strong texture in crystal orientation, lamellar grain boundary, consequently bringing anisotropy in RIH in these materials. In this review article, the recent anisotropic effects of RIH in nuclear structural materials are summarized, and the possible influencing factors are further discussed. Understanding such anisotropic effects of RIH is considered necessary not only for providing a precise evaluation of the in reactor degradation behaviors of current structural materials, but also for the development of new materials for future nuclear systems.(c) 2022 Elsevier B.V. All rights reserved.
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