Understanding of fission products evaporation and retention behaviour in liquid lead is crucial for estimating mechanistic radioactive source term of Lead-cooled Fast Reactors during accident scenarios. An experimental setup was designed and built at the University of New Mexico, to demonstrate the evaporation rate evaluation process of molten lead under oxygen-controlled and oxygen-saturated conditions. Measurements were conducted at a range of liquid lead temperatures between 550 and 700 degrees C, resulting in a highly turbulent argon cover gas of Rayleigh number of approximately 10(8). Measured lead's evaporation rates under oxygen-controlled conditions were consistently higher than predictions from conventional evaporation models, suggesting the presence of localized fog formation near the molten surface. This fog enhances mass transport by steepening the lead vapor concentration gradient within the boundary layer. The evaporation rate increased with increased temperature up to a maximum value of 1.1x10(-6) kg/m(2).sec for oxygen-controlled (similar to 3x10(-6) wt%) and 1.96x10(-7)kg/m(2).sec for oxygen-saturated lead at 700 degrees C. The reduced lead's evaporation rate in the oxygen-saturated lead is attributed to the formation of a surface lead oxide layer, which has lower vapor pressure and inhibits evaporation. The developed experimental platform will support future studies on the evaporation and retention behavior of representative fission product isotopes in molten lead.

This study investigates the effects of external magnetic fields (0–9 T) applied during a 30 min tempering treatment on the microstructure and mechanical properties of HT-9 ferritic/martensitic steels. Electron backscatter diffraction (EBSD) analysis reveals no significant changes in grain size, crystallographic texture, or grain boundary character distribution following magnetic-field-assisted tempering. However, grain orientation spread and kernel average misorientation analyses indicate a reduction in local lattice distortion and residual strain with increasing magnetic field strength. Transmission electron microscopy (TEM) observations show that carbides at grain boundaries become finer and more spherical after tempering under magnetic field, while carbides within the matrix exhibit minimal changes. Thermodynamic estimations suggest that the applied magnetic field increases the ferrite/carbide interfacial energy by up to approximately 7%, promoting carbide refinement and morphological evolution. Magnetic-field-assisted tempering results in an increase in yield strength, reaching a maximum value of 959 MPa at 6 T. No further increase in strength is observed at 9 T, suggesting a possible saturation of the magnetic-field-induced strengthening effect. These results demonstrate that magnetic-field-assisted tempering can modify carbide precipitation behavior and local strain distribution in HT-9 steel without significantly altering its grain structure.

Bulk Cu/Nb nanolayered composites fabricated by accumulative roll bonding (ARB) have attracted considerable interest as potential radiation-tolerant structural materials because of their high density of heterophase interfaces. However, their irradiation stability under high dose irradiation and the relationship with layer thickness remain to be explored. In this study, ARB Cu/Nb multilayers with individual layer thicknesses of 18, 90, and 650 nm were irradiated with 5 MeV Cu²⁺ ions at 400°C to doses up to 550 dpa. Transmission electron microscopy (TEM), energy-filtered TEM (EFTEM), and energy-dispersive X-ray spectroscopy (EDS) were employed to characterize the irradiation-induced microstructural evolution and interfacial mixing. The 90 and 650 nm multilayers retained their layered architecture without significant interface merging, void formation, or large-scale radiation-induced mixing, demonstrating excellent irradiation tolerance. In contrast, the 18 nm multilayer exhibited pronounced layer dissolution and interfacial degradation after irradiation to 500 dpa. Analysis of the irradiation response indicates that the high interface sink strength of the Cu/Nb interfaces effectively suppresses defect accumulation in the thicker multilayers. Furthermore, the positive heat of mixing of the Cu–Nb system limits element mixing through thermodynamically driven chemical de-mixing, contributing to the preservation of the multilayer structure in the thicker specimens. However, when the estimated thermal-spike diameter (3 -10 nm) becomes comparable to the layer thickness in the 18 nm multilayer sample, the ballistic mixing inside the thermal spike promotes cascade overlaps and enhances interfacial mixing. These results demonstrate the excellent irradiation tolerance of ARB Cu/Nb multilayers and the potential critical layer thickness preventing radiation-induced degradation within the thermal spike, providing guidance for the design of radiation-resistant nanolayered composites for advanced nuclear applications.

The electrical conductivity of nanolayered copper/niobium composites fabricated using accumulative roll bonding was investigated as a function of layer thickness. Cu/Nb was used as a model system to evaluate the processing-structure–property relationship stemming from the accumulative roll bonding process. The physical properties were compared against samples of individual average layer heights ranging from 193 to 25 nm. The electrical resistivity was measured over a temperature range of ∼3–300 K. Analysis on the role of interfaces on temperature dependence is conducted including the residual resistivity ratio and temperature coefficient of resistivity. It was found that electrical resistivity increases with decreasing layer height.

This study presents the shape memory behavior of Ni-rich NiTi shape memory alloy fabricated by Laser Powder Bed Fusion Additive Manufacturing (L-PBF-AM) before and after post-processing heat treatment. The microstructural features and thermo-mechanical responses were systematically investigated to understand the effects of processing on the behavior of the specimens. It was shown that the L-PBF-AM process improves the functionality of NiTi components by illustrating perfect superelastic behavior at higher-temperature windows compared to the casted ingot. In addition, it was revealed that shape memory responses were tailored by altering hatch distance, which significantly controls the texture formation along the building direction. After post-processing treatments, transformation temperatures were increased, hysteresis was decreased, and the strength of the samples was significantly improved. The aged L-PBF-AM sample with a smaller hatch distance (80 µm) and intense [001] texture illustrated perfect superelastic behavior with a recoverable strain of 7

Accumulative roll-bonded Cu/Nb nanolaminates (ARB Cu/Nb) possess high strength, thermal stability, and radiation tolerance arising from a high content of heterophase interfaces at fine layer thicknesses. These properties can be tailored by processing parameters used in the ARB Cu/Nb fabrication process, in which layer thickness, thermal history, and strain pathway determine the interface types and resultant properties found in the material. In this work, we subject ARB Cu/Nb to annealing, and then two different rolling pathways - one where rolling direction is held constant (longitudinal rolling, or LR), and one where rolling direction is rotated by 90 degrees and held constant thereafter (cross rolling, or CR). Rolling is performed on ARB Cu/Nb over a targeted range of layer thicknesses from 193 to 25 nm and resultant bulk textures measured by neutron diffraction are correlated with mechanical properties measured by miniaturized tensile tests. The annealing procedure sharpens texture in both phases. We find that Cu mostly develops the same texture in LR and CR. In contrast, Nb develops a distinct texture along the CR pathway that is distinct from the LR texture. The composite texture of Cu/Nb is thus distinct between LR and CR pathways. This difference in texture development between Cu and Nb as a function of strain after change in rolling direction demonstrates the viability for deliberate pairing of Cu LR and Nb CR textures at a desired layer thickness. For mechanical properties, we find that differences in texture do not result in yield or flow stress differences above a layer thickness of 25 nm. Below a layer thickness of 25 nm, despite similar Taylor factors, yield and flow stress and are significantly different. This indicates texture only influences mechanical behavior at low layer thickness, where interface structure dominates mechanical properties.

The increasing demand for customized products and rapid prototyping triggers the development of dieless forming process where the need of part-specific dies is eliminated compared to conventional forming processes. This paper presents a heat-assisted three-roll incremental rolling system capable of producing rods and tubes of various diameters without the need for die/tool replacement. The system incorporates two possible heating mechanisms, namely, an induction heater and a high-current power supply for electrically assisted forming. Due to its high flexibility and hot forming ability, this rolling system is ideal for low volume production or scientific research. The newly fabricated rolling machine was initially evaluated using low carbon steel rods. The experiments have shown that the machine can produce metallic rods down to 6 mm in diameter without apparent spiral marks on the outer surface of the rolled product using multiple passes. The finite element method (FEM) was used to analyze the reaction moment, depth of the spiral marks, and the effect of axial feeding speed on the spiral marks. The simulation model predicted the results of the experiments with less than a 10% error. The work established a flexible rolling platform for possible future research, which can include the study of interface behavior in the thermo-mechanical rolling processes, and the study of material behavior in this multi-axial multi-physics environment.

Accumulative Roll Bonding was used to process nanolayered Cu/Nb and Zr/Nb composites with varying individual layer thickness. Mechanical tests show remarkable strength as the average layer thickness decreases. Relatively high strength is preserved even at elevated temperatures. Despite differences in texture between rolling paths (longitudinally rolled-RL and cross rolled-CR) Cu/Nb, flow stresses between the resultant materials were similar. In addition, thermal conductivity does not change significantly as the interface density increases. The alloys show remarkable resistance to irradiation damage at very high doses due to stability of the interfaces. The results on Zr/Nb indicate that liquid phase chemistry resulting from thermal spikes play an important role and should be taken into account when designing alloys for extreme environments.

This paper seeks to introduce the latest design of the Extended Length Test Assembly-Cartridge Lead (ELTA-CL) with associated thermal-hydraulic (TH) assessment and related experiment activities to support the critical component development performed by the ELTA-CL team (Los Alamos National Laboratory, Westinghouse Electric Company, and the University of New Mexico). The goal of the ELTA-CL program is to develop and validate an experimental capability to perform irradiation experiments in the Versatile Test Reactor (VTR) addressing Lead Fast Reactor (LFR) technology gaps, in support of the commercial development of advanced lead-cooled fast reactor concepts. Through a design maturation process and parametric study, a conceptual design is proposed to meet the requirements for material and corrosion testing. Thermal-hydraulic characteristics for the conceptual design at desired operating conditions are assessed with systems-level (one-dimensional) and computational fluid dynamics (three-dimensional) simulations. Along with the conceptual design work, experimental activities for the development of critical components such as the pump and flowmeter are undertaken. From both the modeling study and the experimental results, the design requirements of the Phase 1 ELTA-CL (e.g., 500 degrees C and 2 m/s) are achievable with the current conceptual design. Additional design improvements and safety assessments at both steady-state and transient conditions for the final ELTA-CL design will be pursued.

Mass transfer is the dominant mode of structural material corrosion in energy systems employing heavy liquid metal coolant such as lead-cooled reactors. Modeling efforts in the literature have focused on materials science aspects, such as diffusive transport of alloying elements in structural materials and oxide layers, oxide layer growth and erosion, and species dissolution at the interface, but they have overlooked convective transport which is often represented by simplified one-dimensional models with no transverse convection. Here, within a Lagrangian framework, we particularly study the convective transport of dissolved elements at specimen boundaries in a flowing molten lead loop. Three-dimensional transient Reynolds-averaged Navier-Stokes simulations coupled with particle transport are carried out to compare convective transport in lead and other coolants, such as lead-bismuth eutectic, pressurized water, and sodium. Transverse convection in the narrow test section is observed to occur at a timescale comparable to longitudinal (downstream) transport and removal of particles from the test section, which highlights the need for three-dimensional modeling in the present setup. The effects of temperature, surface roughness, and mean flow velocity on convective transport in lead are investigated. While mean flow velocity is the dominant variable affecting convective mass transfer, increased surface roughness and reduced temperature are also shown herein to moderately enhance convective transfer.

The heavy-ion irradiation behavior of bulk zirconium-niobium multilayered composites was investigated up to large doses. Multilayers with an average individual layer thicknesses ranging between 15 and 80 nm were synthesized by accumulative roll bonding technique. The irradiation was performed with a defocused 7 MeV Zr2+ ion beam at 500 degrees C. The maximum dose achieved was similar to 145 dpa at the depth of similar to 1.5 mu m from the irradiated surface. Sub-surface microstructural damage and the chemical redistribution were characterized by transmission electron microscopy and energy dispersive spectroscopy, respectively. Irrespective of the layer thicknesses, the irradiation condition caused layer instability and the extent of damage varied with the dose levels. Doses lesser than similar to 60 dpa caused layer fragmentation and greater than similar to 60 dpa resulted in layer dissolution. The chemical mixing of layers occur to a depth of -1 mu m, consuming multiple bi-layer periods. Despite the elevated irradiation temperature (500 degrees C) and a slightly positive heat of mixing (+6 kJ/mol), no phase separation was observed and single-phase was retained in the mixed region. The results demonstrate that chemical mixing was facilitated by the liquid phase miscibility of Zr and Nb, which propelled the interdiffusion within the thermal spikes towards mixing. (C) 2021 Elsevier B.V. All rights reserved.

12Cr-1MoWV (wt.%) ferritic/martensitic (F/M) steel is a candidate material for fuel cladding in advanced nuclear reactors. As such, understanding the relationship between microstructure and mechanical properties in the context of irradiation environments for these steels is critical. Here we reveal the presence of ultrafine scale (2-5 nm), intralath V(C,N) precipitates in conventionally heat treated 12Cr-1MoWV steel for the first time. Lower N content results in finer intralath precipitates, whereas higher N content results in larger, elongated disks or needles. N content significantly alters the strength, but not the strain hardening behavior, by its impact on precipitate characteristics. Finer precipitates could have an impact on irradiated behavior, specifically their capacity as defect sinks. The presence of ultrafine scale V(C,N) precipitates in conventionally heat treated 12Cr-1MoWV steel, controlled by N variations, provides a new means for tailoring the strength and irradiation response of F/M steels for nuclear applications.

A material corrosion test loop ("Lobo Lead Loop") has been established at the University of New Mexico to investigate the compatibility of structural materials with flowing molten lead. The project aims to prequalify materials for Versatile Test Reactor (VTR) testing and support the development of computational models of flow accelerated corrosion in molten lead. The Lobo Lead Loop is designed to operate at high temperatures up to 700 degrees C and high mean flow velocities reaching 3 m/s within the specimen holder channels. Numerical simulations are utilized to design loop components with performance that allows for achieving the operation targets. Specimen holders are designed for (a) multi-material testing at 3 m/sec, (b) multi-velocity testing, (c) shear stress testing, and (d) high temperature (>= 600 degrees C) testing at low mass flow rates. The computational fluid dynamics models used are shown to produce results in agreement with experimental data for flow in pipes. The models are then used in parametric analyses to identify parameters of importance to specimen holder design and computation of pressure losses for flows along smooth and rough specimen walls. Specimen holder designs for the purposes outlined are presented along with performance curves. The maximum achievable flow rate is estimated based on the intersection of the pump performance curve with the system curve.

Spark plasma joining of nanostructured ferritic 14YWT alloys has been carried out at 800°C, 1020 °C and 1030 °C in vacuum. The characteristics of joining as a function of temperatures were investigated using bulk density, nanoindentation and electron backscattered diffraction techniques. Joining performed at 1020 °C and 1030 °C shows a complete, uniform bonding of the samples, whereas the samples joined at 800 °C showed a visible crack that runs along the entire sample length. Bulk density measurements indicate that the reduction in density of samples joined at 800 °C is due to the presence of voids at the interface. The presence of columnar grains only close to the interface at 800 °C suggests the possibility of a steep temperature rise locally at the interface that is attributed to high electrical contact resistance at the interface.

Titanium/Titanium Carbide (Ti/TiC) composites with 20, 40 and 60 vol% of TiC powders were deposited on Ti-6Al-4V substrates using a laser-directed energy deposition method. The bulk relative densities exceeding 99% were achieved in the deposits. The evolution of microstructures and local chemical compositions in the deposits under rapid melting and solidification were analyzed using X-ray diffraction, electron probe micro-analyzer and scanning electron microscopy. Assessment of mechanical integrity of the deposits involved microhardness, tensile testing and fractography. The deposition process resulted in defect-free deposits with 20% TiC. However, cracks were observed originating from the substrate/deposit interface in the 40% and 60% TiC deposit. The L-DED process caused only partial dissolution of the initial TiC particles and the amount of undissolved particles in the deposited matrix increased with increasing TiC volume fraction in the initial powder feedstock mixture. A non-stoichiometric TiC0.55 compound was found to form during solidification. The solidified product in the deposits included dendritic and equiaxed TiC0.55 precipitates homogeneously distributed in the matrix. Micro-hardness measurements indicated that hardness values increased monotonically with TiC content in the deposit. On the other hand, a gradient Ti/TiC composite with composition ranging between 20% and 60% TiC did not develop any growth cracks suggesting an efficient processing route for synthesizing MMCs with high volume fraction of brittle ceramic reinforcements. It was found that pre-existing cracks in the TiC used in the starting feedstock played a key role in the mechanical integrity of the deposits. This observation suggests that the mechanical performance of the Ti/TiC composite deposits can be improved using techniques that promote complete dissolution of the original TiC.

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Identifying economically viable intervention measures to reduce COVID-19 transmission on aircraft is of critical importance especially as new SARS-CoV2 variants emerge. Computational fluid-particle dynamic simulations are employed to investigate aerosol transmission and intervention measures on a Boeing 737 cabin zone. The present study compares aerosol transmission in three models: (a) a model at full passenger capacity (60 passengers), (b) a model at reduced capacity (40 passengers), and (c) a model at full capacity with sneeze guards/shields between passengers. Lagrangian simulations are used to model aerosol transport using particle sizes in the 1-50 μm range, which spans aerosols emitted during breathing, speech, and coughing. Sneeze shields placed between passengers redirect the local air flow and transfer part of the lateral momentum of the air to longitudinal momentum. This mechanism is exploited to direct more particles to the back of the seats in front of the index patient (aerosol source) and reduce lateral transfer of aerosol particles to other passengers. It is demonstrated that using sneeze shields on full capacity flights can reduce aerosol transmission to levels below that of reduced capacity flights without sneeze shields.