查看更多>>摘要：During the burnup of U-Zr based metal fuels, lanthanide fission products migrate to fuel periphery and deposit on cladding inner surface, resulting in fuel-cladding chemical interaction (FCCI). Of the lanthanide fission products contained in irradiated U-Zr based fuels, neodymium (Nd) has the highest concentration. In this study, we performed out-of-pile diffusion couple testing to investigate the chemical interactions between neodymium (Nd) and four types of stainless steels (SSs), aiming at elucidating the effects of composition and microstructure on the chemical interactions. The four types of steels are Fe-Cr based oxide dispersion-strengthened (ODS) steel (ODS-1), Fe-Cr-Ni based ODS steel (ODS-2), additively man-ufactured (AM) 316L SS (A316), and wrought 316L SS (W316). The results show that the interdiffusion between the major constituents in ODS-1 (Fe and Cr) and Nd is suppressed, while nickel was the most active element during diffusion between ODS-2/A316/W316 and Nd, leaving a relatively large depletion area in ODS-2/A316/W316. Compared to W316, the 20 0-nm pores in the A316 assisted the interdiffusion between the steel constituents and Nd, while the large grain size resulted in slower diffusivity. The kinet-ics of chemical interaction between Nd and SSs is strongly dependent on the microstructure, including pore structure and grain size. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The Norgett-Robinson-Torrens displacements per atom function is commonly used to estimate the amount of atomic displacement produced by incident energetic particles. At low incident energy, this function is defined as a step function presenting a single threshold displacement damage energy. But materials have different threshold as a function of the crystallographic orientation. Molecular dynamic simulations show that a continuously varying damage energy probability is best suited to represent the threshold damage region. This work proposes a method to introduce in the NRT damage function a con-tinuous damage energy distribution. The impact of a change on the damage function in the threshold region is evaluated on the incident electrons' Non Ionizing energy Loss.(c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Outcomes of an activity on development and verification of models for Fission Gas Release in Light Water Reactor fuels during Loss-of-Coolant Accidents are described. The GRSW-A model of the FALCON code is extended to simulate the processes of fuel fragmentation and concomitant transient Fission Gas Release. The FRELAX code is redesigned with a view to simulation of bulk flow and diffusion of the gases in the rod free volume. Finally, close coupling of the updated FALCON and FRELAX codes is set up, referred to as the F2F coupled code system, due to which the two codes are being exchanging data during their simultaneous analysis. Three Halden LOCA experiments, IFA-650.12/13/14, using fuel irradiated in the Swiss Leibstadt NPP to a high level of fuel burnup are analyzed with the F2F coupled code system. Overall, the results of calculation for the selected three tests of the IFA-650 series are in good agreement, or conservative in comparison to the data. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )
Eckelmeyer, Kenneth H. H.Ludtka, Gerard M. M.Mackiewicz-Ludtka, GailChapman, Lloyd R. R....
28页
查看更多>>摘要：The effect of Ti content on phase transformations, microstructures, and mechanical properties of U-Ti alloys are described for alloys containing 0.3 wt.% to 2.0 wt.%Ti. Rapid cooling is required to overcome diffusional decomposition of gamma-phase and facilitate diffusionless transformation to supersaturated variants of alpha-phase. Critical cooling rate increases with increasing Ti content, opposite to the trend observed in U-Mo and U-Nb alloys. This difference occurs because the martensite transformation temperatures in these relatively dilute U-Ti alloys are above the knee of the C-curve for diffusional decomposition, unlike those in the more concentrated U-Mo and U-Nb alloys. In these U-Ti alloys critical cooling rate depends on the amount of undercooling required to reach M-s, which increases with increasing Ti content, and the time for diffusional decomposition to occur just above M-s, which decreases with increasing Ti content. The net result is that higher cooling rates are required as Ti content increases. Full quenching results in diffusionless transformation of gamma-phase to supersaturated variants of alpha-phase. Very dilute alloys transform via gamma -> beta -> alpha(m) sequence of massive transformations. Martensitic gamma -> alpha'(a) transformation begins at similar to 0.4%Ti, and 100% alpha'(a) microstructures are obtained from similar to 0.65% to similar to 1.4% Ti. A transition to banded alpha'(b) martensite occurs at similar to 1.5%Ti. Evidence suggests that the alpha'(a) to alpha'(b) transition may occur when the cubic gamma-phase first transforms to tetragonal gamma degrees, which in turn transforms to orthorhombic alpha'(b) via the sequence gamma -> gamma degrees -> alpha'(b). Fully quenched alloys exhibit moderate strengths and ductilities, and their supersaturation with Ti makes them amenable to subsequent age hardening. Subcritical quenching typically results in two-phase microstructures with lower ductilities and near-zero Ti-supersaturation, eliminating the possibility of subsequent age hardening. (C) 2021 Published by Elsevier B.V.
Murty, T. N.Vidhan, R. V. S. KrishnaAvinash, G.Sunil, Saurav...
7页
查看更多>>摘要：The precipitation of hydrides normal to the transverse direction in Zr-2.5%Nb pressure tube alloy when cooled under stress above a threshold value, is known as stress reorientation of hydrides. The ex-situ threshold stress values reported in the literature were determined using pre-charged samples heated to a peak temperature to dissolve all the hydrides, cooled to reorientation temperature followed by cooling under stress from reorientation temperature. Leger and Donner performed in-situ reorientation experiments using samples having hydride deposited on its surface. In both cases, hydride reorientation occurred during cooling. In the present investigation, for the first time, experiments were done to study the reorientation phenomenon using in-situ gaseous charging of samples under stress at a constant temperature using a specially designed set up. It is expected that the threshold stress determined by in-situ method used in the present investigation will more closely resemble the formation of radial hydrides under reactor operating conditions. In this work, the threshold stress values for reorientation of hydrides in Zr-2.5%Nb pressure tube material were determined using both in-situ and ex-situ methods. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In a light water reactor, nuclear fuel element melting is critical. This paper will introduce the experimen-tal studies on the melting and relocation behaviors of the single fuel rod and 3 x 3 fuel bundle imitators based on aluminum and zinc as alternative materials. The eutectic reaction can occur between Al and Zn. Moreover, the lower melting points of Al and Zn allow us to observe the experimental phenomena directly. In this paper, three single-rod experiments and a rod bundle experiment are discussed in de-tail. The results of the experiments are analyzed at both macro and micro levels. In the experiments of slowly increasing temperature, the melting phenomena of fuel rod imitators mainly include rod defor-mation, eutectic reaction, melting, erosion, and molten materials relocation. Among them, the existence of a eutectic reaction between materials will make the materials melt under their melting point, which significantly influences the melting time and behavior of the rod. Through this study, the nuclear fuel rods melting and relocation behaviors under the influence of the eutectic reaction can be observed, and the experimental results can provide data support for the development of related models. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：& nbsp;In the spent fuel storage phase, nuclear fuel cladding is subjected to increased embrittlement owing to a large amount of hydride precipitation. This study compares the differences in the hydrogen-induced cladding embrittlement of cold work stress-relief annealed (CWSR or SRA) Zircaloy-4 and Zr-Nb alloy cladding with ring compression test at the temperature of the spent fuel pool, which is approximately 40 & nbsp;C. Experiments demonstrate that an abrupt ductile to brittle (DTB) transition occurs at the critical hydrogen content of 560 and 490 wppm for Zircaloy-4 and the tested Zr-Nb cladding tubes, respectively. Even beyond the critical hydrogen content, sufficiently high cladding ductility with the offset strain > 10% is maintained up to ~& nbsp;90 MWd/kgU for both cladding materials on the rod-average basis. Extensive EBSD analyses coupled to thermodynamic modeling demonstrate that this is primarily due to the slightly larger grain diameter of Zircaloy-4 tube, which reduces the number of available sites for inter-granular hy-dride precipitation. Reduced inter-granular hydride precipitation prevents the extent of hydride interlink, thereby improving the hydride embrittlement resistance. Nevertheless, the tested Zr-Nb alloy cladding presents an extened discharge burnup limit for abrupt DTB transition owing the reduced in-core cladding oxidation rate. The presented understanding of microstructural effect on hydride interlink and resulting embrittlement may provide a basis for understanding the general hydride embrittlement phenomena of Zircaloy cladding which include, but not limited to, wet storage, dry storage, and post-accident ductility of high burnup Zircaloy cladding. (C) 2021 The Authors. Published by Elsevier B.V.& nbsp;
查看更多>>摘要：Preferred defect cluster configurations and diffusion behavior are calculated with the recently published BMD19 interatomic potential for alpha-zirconium and compared with results calculated from the M07 po-tentials. Both potentials predict that small SIA clusters form configurations contained entirely within a single basal plane, while large SIA clusters form perfect dislocation loops on first-order prismatic planes with Burgers vector b(->)= 1/3 < 1120 >. The MO7 potentials predict stable void formation for vacancy clusters while the BMD19 potential accurately indicates a preference for planar configurations on either first-order or second-order prismatic planes. Small basal vacancy clusters are found to form faulted pyramidal structures and only transform to faulted c-loops at larger sizes. In evaluating the defect diffusivity, single vacancies and interstitials are both found to exhibit anisotropic diffusion within the basal-plane. Small SIA clusters are found to migrate exclusively in 2-D within a single basal plane with the BMD19 potential but migrate in 3-D with the M07 #3 potential. Small vacancy clusters are either unstable or immobile with the M07 #3 and #2 potentials, while these clusters exhibit appreciable mobility either along the c -axis or in a quasi-isotropic manner with the BMD19 potential. The apparent difference in the diffusional anisotropies of defect clusters, rather than point defects, could be a critical component for improving predictive capabilities for mesoscale modeling of microstructural evolution in alpha-zirconium.(c) 2021 Elsevier B.V. All rights reserved.
Watkins, Jennifer K.Wagner, Adrian R.Middlemas, Scott C.Marshall, M. Craig...
9页
查看更多>>摘要：Uranium dioxide has been the primary fuel type used in light water reactors for more than 40 years and proven to be reliable and robust. However, the Fukushima-Daiichi nuclear accident has motivated new work evaluating fuels with characteristics promoting accident tolerance, including enhanced thermal conductivity. Recently, additives have been investigated to increase thermal conductivity, but research has been largely focused on non-fissile additions. This study investigated the use of fissile additives to not only increase the thermal conductivity but also increase the uranium loading. Uranium diboride was chosen as the additive for this study due to its promising corrosion behavior as well as its significantly higher thermal conductivity at 573 K (25 Wm(-1)K(-1)) when compared to UO2 (7 Wm(-1)K(-1)). Uranium diboride powder was fabricated via the arc melting technique and a ball milling process prior to mixing with UO2 in a 90/10 wt% UO2/UB2 ratio. Green bodies were made using a uniaxial die and subjected to a traditional pressureless sintering technique at 2073 K in argon. Sintered samples were analyzed via laser flash analysis for thermal diffusivity and differential scanning calorimetry for specific heat capacity in order to calculate thermal conductivity. The samples displayed an increase of 36-55% in thermal conductivity between 323 and 1273 K when compared to the benchmark samples (pure UO2) as reported in open literature.(c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Focused ion-beam scanning electron microscopy (FIB-SEM) and three-dimensional (3D) microscopy were applied to characterize the subsurface morphological features of oxide scales formed on an-2.0 at.% Ga plutonium (Pu) metal alloy. Using the FIB-SEM technique, a number of morphological features formed in the interior of the oxide scale from Pu metal's environmental exposure were observed and identified. Auger electron spectroscopy (AES) was utilized to characterize the cross-sectional composition and chem-istry of the oxide scale. The oxide scale formed during inert storage and operational environments was found to be highly variable in thickness and morphology, presenting some regions with a thin ( < 400 nm), dense oxide layer and others with a thick ( > 2 mu m) scale with substantial lateral cracking. After sub-sequent exposure to dry air environment, the oxide scale became thicker (-4 mu m) and slightly more porous. The changes following aging in a moist air environment were observed to be more severe, with the formation of a highly porous internal structure containing significant lateral and transverse cracking. In comparison to the scale formed on an-3.5 at.% Ga-Pu metal alloy, the oxide morphology of the lower gallium alloy investigated here exhibited greater variation in thickness and a noteworthy dependence on the presence of water vapor, particularly in terms of the internal porosity formed during growth of the oxide. (c) 2021 Elsevier B.V. All rights reserved.
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