查看更多>>摘要：We investigated thermal transport in swift heavy ion (SHI) irradiated insulating single crystalline oxide materials: yttrium aluminum garnet- Y3Al5O12 (YAG), sapphire (Al2O3), zinc oxide (ZnO) and magnesium oxide (MgO) irradiated by 167 MeV Xe ions at 10(12) - 10(14) ions/cm(2) fluences. Depth profiling of the thermal transport on nano-and micro-meter scales was assessed by time-domain thermoreflectance (TDTR) and modulated thermoreflectance (MTR) methods, respectively. This combination allowed us to isolate the conductivities of different sub-surface damage-regions characterized by their distinct microstructure evolution regimes. Thermal conductivity degradation in SHI irradiated YAG and Al2O3 is attributed to formation of ion tracks and subsequent amorphization, while in ZnO and MgO it is mostly due to point defects. Additionally, notably lower conductivity when probed by very low penetrating thermal waves is consistent with surface hillock formation. An analytical model based on Klemens-Callaway method for thermal conductivity coupled with a simplified microstructure evolution capturing saturation in defect concentration was used to obtain depth dependent damage across the ion impacted region. The studies showed that YAG has the highest damage profile resulting in the less dependence of thermal conductivity with the depth, while MgO on the contrary has the strongest dependence. The presented work sheds new light on how SHI induced defects affect thermal transport degradation and recovery of oxide ceramics as promising candidates for next generation nuclear reactor applications. (C)& nbsp;2022 The Authors. Published by Elsevier B.V.
查看更多>>摘要：The goal of this study was to evaluate a potential method to convert rare-earth (RE) fluorides to oxides through thermal conversion in air. The RE elements, which are common neutron poisons, could potentially be removed from fluoride-based molten salt reactors via precipitation through fluoride-tooxyfluoride or fluoride-to-oxide conversion mechanisms. In this study, the phase transformations of seven different REF3 com pounds (RE = La, Ce, Pr, Nd, Tm, Yb, and Lu) at temperatures ranging from 400 to 1400 & nbsp;C in air were investigated with X-ray diffraction. The LaF3, PrF3, NdF3, TmF3, YbF3, and LuF3 compounds transformed to oxyfluorides first and then to oxides, whereas CeF(3 & nbsp;)transformed directly to an oxide. A waste form option for the resulting REOx products is a lanthanide aluminoborosilicate (LABS) glass, which was demonstrated in this paper by converting NdF3 to Nd2O3 and immobilizing the Nd2O3 at 60 mass% in a LABS glass.& nbsp;(C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：This study reports on the distribution of helium (He) cavities in a hot-rolled W-Ni-Fe ductile-phase toughened tungsten (DPT W) composite irradiated to a dose and a helium concentration that are comparable to those in the material after 5-year irradiation in a conceptual fusion power plant. The DPT W sample consists of W particles embedded in a ductile-phase NiFeW matrix with a nominal composition of 90W7Ni-3Fe by weight. It was hot-rolled to a thickness reduction by 87% (87R DPT W). Sequential and individual irradiations of the material with 1.2 MeV Ni + ions to a fluence of 2.15 x 10 16 Ni + /cm 2 and 90 keV He + ions to 6.5 x 10 15 He + /cm 2 was performed at 973 K. Larger He cavities with a lower number density are observed in NiFeW than W. Helium cavities are aggregated preferentially along the NiFeW/W interphase boundary. This behavior is not observed along the W/W grain boundary under the same irradiation conditions. The average corrected cavity diameter or volume appears to be smaller in the sequentially irradiated sample than He + ion irradiated sample. There is no evidence for formation of visible voids or Ni precipitates in W phase irradiated with Ni + ions only. Diffusion, clustering and trapping of vacancies and He atoms during He + ion irradiation at 973 K may be responsible for the formation of the He cavities. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：CALPHAD models to compute the density and viscosity of four keystone systems related to Molten Salt Reactor (MSR) technology have been optimized: NaCl-UCl3, LiF-ThF4, LiF-UF4, and LiF-ThF4-UF4. Revised thermodynamic assessments of all four systems, using the modified quasichemical formalism in the quadruplet approximation for the description of the liquid solutions, are reported. In the case of NaCl-UCl3, phase diagram and mixing enthalpy data available in the literature are taken into account. For the fluoride systems, recently published data on some solid phases are taken into account, while retaining the most recently published descriptions of the liquid solutions. The densities of the liquid solutions are modelled using pressure-dependent terms of the excess Gibbs energy, while the viscosities are then modelled using an Eyring equation. Both state functions are related to the thermodynamic assessments through the quadruplet distributions. (C)& nbsp;2022 The Author(s). Published by Elsevier B.V.
Weilert, T. M.Walton, K. L.Loyalka, S. K.Brockman, J. D....
10页
查看更多>>摘要：Europium diffusion in graphite has been recognized to be of interest in high-temperature gas reactor safety analysis, particularly as an indicator of strontium diffusion. However, no measurements of europium diffusion coefficients have been reported in the literature. In this work, the effective diffusion coefficient of europium was measured using a time-release method. Natural europium was loaded into pre milled unirradiated IG-110 graphite spheres using a pressurized acid digestion vessel. The time-release experiments were performed in the temperature range 1823 K - 1973 K using a SiC diffusion cell connected to an inductively-coupled plasma mass spectrometer (ICP-MS) via a He gas line. The results of this work are:& nbsp;D-Eu, IG-110 = (1 . 5 x 10(-3)m(2)/(s))exp(-2 . 87 x10(5) J/mol /RT ) This effective diffusion coefficient can be used to aid in predictive modelling of europium transport in HTGRs. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Eriksson, J.Sundell, G.Andren, H. -O.Thuvander, M....
12页
查看更多>>摘要：Atom probe tomography was used in this work to study the metal close to the metal/oxide interface in the zirconium alloy Zircaloy-2 exposed to three and nine annual cycles of operation in a commercial boiling water reactor. The two exposure times correspond to before and after the onset of acceleration in corrosion, hydrogen pickup, and growth.& nbsp;The alloying elements Sn, Fe, Cr, and Ni were observed to be redistributed after exposure. After both three and nine cycles, clusters containing Fe and Cr and typically of a spheroidal shape with an approximate diameter of 5 nm were observed to be located in layers presumed to be layers of < a >-loops. On average, the cluster number density was slightly higher after nine cycles, with larger and more Cr-rich clusters. However, there were large grain-to-grain variations, which were larger than the differences between the two exposure times. Ni was only occasionally observed in the clusters. Sn was observed to be slightly enriched in the Fe-Cr clusters, but the Sn concentration was higher between than inside the layers of clusters. After nine cycles, clusters of Sn were detected in regions that were depleted of Fe and Cr. Enrichment of Sn, Fe, and Ni at features that appeared to be < c >-component loops was observed after nine cycles, whereas no such features were observed after three cycles. Enrichment of Sn and Fe, and small amounts of Cr and Ni, was observed at grain boundaries after both exposure times. After three cycles, a partially dissolved second phase particle of Zr(Fe,Cr)(2) type that contained about ten times more Cr than Fe was observed. (C)& nbsp;2022 The Author(s). Published by Elsevier B.V.& nbsp;
查看更多>>摘要：W-Y2O3-ZrO2 composite materials were fabricated by a combination of wet chemical method and spark plasma sintering. We systematically studied the W-Y2O3-ZrO2 composite materials at different Y and Zr doping atomic ratios. The ultrafine tungsten-based composites with a dispersed distribution of Y2Zr2O7 particles can be prepared by appropriate Y and Zr doping atomic ratios for this experiment. The surface evolution behavior of W-5Y-5Zr composites induced by high temperature annealing and helium ion irradiation was investigated. The nano-Y2Zr2O7 second-phase particles greatly increased the resistance of the material to grain growth. The dispersed and fine of Y2Zr2O7 particles in the tungsten-based composites effectively improved the resistance to helium ion irradiation. These findings can serve as a reference for the fabrication of tungsten-based materials in fusion engineering. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Gibb, Logan D.Allen, Elijah W.McDonald, Luther W., IVAbbott, Erik C....
8页
查看更多>>摘要：Understanding the mechanisms controlling the morphology of uranium ore concentrates (UOCs) is impactful for both the nuclear forensics and nuclear fuels communities. In forensics, this understanding enables predicting the morphology of materials to help determine provenance and processing history. In fuels, this understanding aids in optimizing the morphology for higher fuel efficiency. To elucidate the influence of thermodynamics on the morphology of UOCs, uranyl peroxide, specifically metastudtite (UO2O2 center dot 2H(2)O), was precipitated from solutions of varying complexing strength to the uranyl ion. Specifically, metastudtite was precipitated from solutions of equal ionic strength of uranyl nitrate and uranyl chloride, where the nitrate ion has greater complexing strength with the uranyl ion. Following precipitation, the metastudtite was calcined to U3O8, and the phase purity of each sample was confirmed by powder X-ray diffraction (p-XRD). The surface features were characterized using scanning electron microscopy (SEM), and the morphology was quantified using the Morphological Analysis for Materials (MAMA) software. Nanoparticles of metastudtite precipitated from uranyl nitrate, which has the higher complexing strength, were larger, more angular, and more elongated than nanoparticles produced by precipitation from uranyl chloride. Overall, a more rigid morphology was produced when replacing the nitrate with the peroxide while more rounded particles were produced when replacing a chloride with the peroxide. Even after sintering at high temperatures, differences in morphology between the two routes were still present in the U3O8. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Leclerc, A.Champenois, J. B.Bleyen, N.Smets, S....
14页
查看更多>>摘要：& nbsp;Water uptake and salt leaching of two simulated French Bituminized Waste Products (BWP) have been investigated under nearly constant volume conditions. The resulting pressure development was monitored during 5 to 6 years for two simulated BWP samples, varying one from the other by their inorganic load and composition. Pressure development induced by water uptake is mainly the result of two processes: (1) an osmotic phenomenon due to the presence of soluble and hygroscopic salts (NaNO3 and Na2SO4) embedded in the bitumen matrix and (2) recrystallization of anhydrous Na2SO4 into its decahydrate form, leading to an important volumetric expansion. After a certain hydration period, the pressure exerted by the hydrating BWP stabilizes when the pressure generating phenomena are fully counteracted by the leaching of soluble salts via out-diffusion, reconsolidation of pores in highly leached parts of the BWP, and/or some creep of the BWP into the technical voids of the water uptake cells. For one of the French BWP, this already occurred after 1 year of hydration. Differences are found in the pressure evolution and increase rate of the two studied BWP, though a much larger difference is observed when comparing the results of the French BWP to a Belgian BWP, i.e. Eurobitum. The faster pressure development observed for the French BWPs can be attributed to the differences in the soluble salt content, the inorganic load, the content of recrystallizing salts, but also to the presence of insoluble salts such as BaSO4, which seems to facilitate the water uptake rate in the French BWP. The faster hydration in French BWP results in a larger fraction of salts becoming available for osmosis and recrystallization within a relatively short time frame, thereby explaining the faster pressure build-up. On the other hand, BaSO4 does not seem to affect the leaching of soluble salts from BWP directly. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
Gurovich, B. A.Frolov, A. S.Kuleshova, E. A.Maltsev, D. A....
16页
查看更多>>摘要：The paper presents the investigation results using TEM and SEM methods of alloy 42XNM after irradiation as a part of the absorbing element (the control rod cladding) of the VVER-10 0 0 reactor control system (to the damaging dose of similar to 12 dpa at a temperature of similar to 350 C) and after isothermal annealing in the temperature range of (50 0-110 0) C simulating LOCA-parameters and corresponding to a sharp decrease in plastic properties. It was shown that during such annealing, a change in the alloy's phase composition and porosity evolution was observed, dislocation loops and grain boundary segregations were completely annealed. The probable reasons for the decrease in the plasticity of the 42XNM alloy in the specified temperature range were found: the formation of alpha-Cr particles along grain boundaries and the pore formation on interfacial and grain boundaries. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
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