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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The Role of Co-injected Helium on Swelling and Cavity Evolution at High Damage Levels in Ferritic-Martensitic Steels

The influence of helium co-injection at rates from 0 to 4 appm He/dpa on swelling in ferritic-martensitic alloys T91 and HT9 was explored. Irradiations with 5.0 MeV Fe++ ions and degraded He++ ions were performed at 445°C up to damage levels of 150 dpa and helium co-injection rates of 0, 0.02, 0.2 and 4 appm He/dpa in T91, and at 460°C to a damage level of 188 dpa and helium co-injection rates of 0, 0.06 and 4 appm He/dpa in HT9. Helium was observed to enhance cavity nucleation at low damage levels, resulting in the maximum swelling at the highest helium co-injection rate. As the damage level was increased, the helium content at which swelling was maximized shifted to lower helium concentrations, ultimately resulting in the highest swelling occurring with zero helium by 150 dpa. Finally, this behavior was due to the helium-stabilized bubble microstructure that increased the cavity sink strength and reduced both cavity growth rate and swelling relative to the helium-free condition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Detection of circumstellar helium in Type Iax progenitor systems

ABSTRACT We present direct spectroscopic modelling of 44 Type Iax supernovae (SNe Iax) using spectral synthesis code SYNAPPS. We confirm detections of helium emission in the early-time spectra of two SNe Iax: SNe 2004cs and 2007J. These He i features are better fit by a pure-emission Gaussian than by a P-Cygni profile, indicating that the helium emission originates from the circumstellar environment rather than the SN ejecta. Based on the modelling of the remaining 42 SNe Iax, we find no obvious helium features in other SN Iax spectra. However, ${\approx } 76{{\ \rm per\ cent}}$ of our sample lack sufficiently deep luminosity limits to detect helium emission with a luminosity of that seen in SNe 2004cs and 2007J. Using the objects with constraining luminosity limits, we calculate that 33 per cent of SNe Iax have detectable helium in their spectra. We examine 11 SNe Iax with late-time spectra and find no hydrogen or helium emission from swept-up material. For late-time spectra, we calculate typical upper limits of stripped hydrogen and helium to be 2 × 10−3 M⊙ and 10−2 M⊙, respectively. While detections of helium in SNe Iax support a white dwarf–He star binary progenitor system (i.e. a single-degenerate [SD] channel), non-detections may be explained by variations in the explosion and ejecta material. The lack of helium in the majority of our sample demonstrates the complexity of SN Iax progenitor systems and the need for further modelling. With strong independent evidence indicating that SNe Iax arise from an SD channel, we caution the common interpretation that the lack of helium or hydrogen emission at late-time in SN Ia spectra rules out SD progenitor scenarios for this class.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Probing thermodynamics of radiogenic helium and defects in $δ$-plutonium alloys and interactions with adsorbed environmental gases

Differential scanning calorimetry coupled with simultaneous evolved gas analysis (DSC-EGA) on aged δ-Pu samples shows that most radiogenic helium remains trapped within the Pu matrix at temperatures very close to, or slightly above, the melting temperature. Our results indicate that helium release from 50-year-old δ-Pu occurs as a burst just below the melting temperature (>0.994 T m ), with subsequent pressure oscillations as temperature increases. Subordinate quantities of H 2 were also released along with helium. Here, the helium emission tails off and ceases above ~720 – 750°C. In a δ-Pu alloy aged 6 years, the initial helium burst occurs slightly above melting (~1.015 – 1.042 T m ), with a discrete, larger helium spike occurring between 670 and 686°C. The proximity of helium release to the liquidus transition presented challenges in the deconvolution of overlapping process enthalpies, the liquidus endotherm, and the exotherm resulting from bubble collapse, annealing and gas expulsion. Helium’s strong affinity for vacancy binding in a 2He-vac configuration is predicted by Density Functional Theory (DFT) modeling. The measured stored energy associated with the He release events in a 50-year-old δ alloy is on the order of ~ 10–11 J/g, which is significantly higher than stored energies measured in the sub-solidus regimes (~2 J/g) that are related to the solid-state annealing of processing- and radiation-induced defects. This implies that aged δ Pu alloys have a remarkable resilience to accommodate the lattice strain produced by the internal pressure of the helium bubbles and provides further insight into the thermodynamic behavior of aged δ Pu.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An Experimental Reversed Heat Flux Investigation of the Helium-Cooled Modular Divertor with Multiple Jets

The Georgia Institute of Technology group has performed studies to characterize the thermal hydraulics of a single “finger” module of the helium-cooled modular divertor with multiple jets (HEMJ) proposed for long-pulse magnetic fusion reactors in a helium (He) loop designed with maximum mass flow rate of 10 g/s. However, testing divertor modules at prototypical heat fluxes and temperatures remains an engineering challenge. A new larger helium loop with a maximum mass flow rate of 100 g/s, suitable for evaluating helium-cooled divertors with larger surface areas such as a nine-finger HEMJ module, is currently being constructed. This work presents an experimental validation of a numerical model exploring the applicability of the “reversed heat flux approach,” which cools (versus heats) the plasma-facing surface of the divertor module to evaluate the helium-side heat transfer coefficient (HTC). The approach is to be used for performance evaluation of single and multiple modules of HEMJ in existing and future large helium loops. A cooling facility for producing a jet of water with a maximum mass flow rate of 1.4 kg/s at a maximum pressure of 0.4 MPa and temperature of 295 K (Re = 2.2 × 10 5 ) is described. Numerical and experimental results are presented for the heat flux and average helium impingement surface temperature over a range of water flow rates (0.5 to 1.4 kg/s) for heat fluxes as high as 5 MW/m 2 . The numerical model suggests that the HTC of the water impingement surface is comparable to or greater than that of the helium impingement surface. For given helium and water temperatures, the heat flux values are generally limited by conduction across the outer shell. These initial studies provide guidance on extending this approach to estimating the thermal-hydraulic performance of larger divertor module designs while reducing the challenges associated with studying such designs in the normal heating configuration at their extremely high prototypical temperatures and incident heat fluxes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Helium flux effects on bubble growth and surface morphology in plasma-facing tungsten from large-scale molecular dynamics simulations

We investigate helium flux effects on helium transport and surface evolution in plasma-facing tungsten using molecular dynamics. The simulations span two orders of magnitude, from ITER-relevant levels to those more typical of simulations published to date. Simulation times of up to 2.5 µs (corresponding to actual fluences of 1.4 x 10 21 m -2 ) are achieved, revealing concerted bubble-bursting events that are responsible for significant and very sudden changes in surface morphology. The depth distribution of helium depends very strongly on helium flux: helium self-trapping becomes more probable near the surface at high flux, and a layer of near-surface bubbles forms. Helium retention prior to the onset of bubble bursting is also substantially lower at low flux than it is at high flux. Surface features at low fluence are correlated with the positions of bubbles, but at high fluence, bubbles tend to coalesce, venting to the surface at one or more locations and leaving large interconnected cavities below the surface. Ruptured bubbles may serve as pathways deeper into the material, allowing helium to bypass the layer of near-surface bubbles and fill deeper, potentially much larger, bubbles that can produce more substantial surface features. Deeper bubbles also emit prismatic dislocation loops that can fill in cavities closer to the surface. Our results suggest that nearly all molecular dynamics simulations published to date are hampered by finite-size effects, and that helium flux is a very important parameter in determining the behavior of helium in plasma-facing components.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Modeling and Design Parameter Optimization to Improve the Sensitivity of a Bimorph Polysilicon-Based MEMS Sensor for Helium Detection

Helium is integral in several industries, including nuclear waste management and semiconductors. Thus, developing a sensing method for detecting helium is essential to ensure the proper operation of such facilities. Several approaches can be used for helium detection, including based on the high thermal conductivity of helium, which is several times higher than air. This work utilizes the high thermal conductivity of helium to design and analyze a bimorph MEMS sensor for helium sensing applications. COMSOL Multiphysics software (version 6.2) is used to carry out this investigation. The sensor is constructed from poly-silicon and SiO 2 materials with a trenched cantilever beam configuration. The sensor is electrically heated, and its morphed displacement depends on the surrounding gas’s composition, which decreases in the presence of helium. Several factors were investigated to probe their effect on the sensor’s sensitivity to helium, including the thickness of the poly-silicon layer, the configuration of the trench, and the thickness and location of SiO 2 layer. The simulations showed that the best performance, up to 2 ppm helium detection level, can be achieved with thinner beams and medium trench lengths.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Helium Brayton Cycle Design for Advanced High Temperature Reactor System

Gen-IV reactors have many advantages over current generation reactors. Higher outlet temperatures in these next generation reactors allow for other power cycles to be considered, such as the helium Brayton cycle. Additionally, the higher temperatures allow the energy to be utilized in other industrial applications. The advanced high temperature reactor concept utilizes the helium Brayton cycle for electricity production. The system consists of four components shown in Fig. 1. This includes a turbine, recuperator, precooler, and compressor. The helium coolant exits the secondary heat exchanger (SHX) at a high temperature and enters the turbine. Helium spins the turbine causing the generator to spin producing electricity. The pressure and temperature drop as the coolant travels through the turbine. The helium enters a recuperator where the cold side stream exiting the compressor is heated up. Helium then travels through a precooler where water is used to cool down the helium before entering the compressor. Helium enters the compressor where the temperature and pressure of the coolant increase. Compressed helium travels through the recuperator heating up to the desired temperature before entering the SHX again. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2022

Creating two-dimensional solid helium via diamond lattice confinement

The universe abounds with solid helium in polymorphic forms. Therefore, exploring the allotropes of helium remains vital to our understanding of nature. However, it is challenging to produce, observe and utilize solid helium on the earth because high-pressure techniques are required to solidify helium. Here we report the discovery of room-temperature two-dimensional solid helium through the diamond lattice confinement effect. Controllable ion implantation enables the self-assembly of monolayer helium atoms between {100} diamond lattice planes. Using state-of-the-art integrated differential phase contrast microscopy, we decipher the buckled tetragonal arrangement of solid helium monolayers with an anisotropic nature compressed by the robust diamond lattice. These distinctive helium monolayers, in turn, produce substantial compressive strains to the surrounded diamond lattice, resulting in a large-scale bandgap narrowing up to ~2.2 electron volts. This approach opens up new avenues for steerable manipulation of solid helium for achieving intrinsic strain doping with profound applications.

42 ENGINEERING↗
DOE OSTI2025

Helium recovery system at IB3a

The increasing need for optimal and sustainable use of cryogenic resources to support Fermilab’s scientific mission has highlighted the necessity of improving the Laboratory’s helium management practices. An assessment of cryogenic test facilities identified the Technical Division’s Industrial Building 3a (IB3A) as a key site requiring upgrades to integrate a helium recovery system. The IB3A facility is essential for characterizing and testing superconductors, cables, and coils for various R&D projects, including the US High-Luminosity LHC Accelerator Upgrade Project (AUP), Mu2e, and other external collaborations. Currently, the facility relies on 500 L helium Dewars and vents the vaporized helium directly into the atmosphere, leading to significant helium loss. Given the non-renewable nature of helium, recovering and reusing this resource is critical for the sustainability of Fermilab’s operations. To address this challenge, a project has been initiated to connect IB3A to an existing helium purification station and refrigeration system located in another building via a dedicated pipeline pass over the roof of several buildings. This solution will enable the efficient capture of vented helium, its transfer to the purification station, and subsequent liquefaction for reuse in future operations. The project includes a detailed design phase, specifying the pipeline route, flow control mechanisms, and integration with the existing cryogenic infrastructure, followed by phased implementation and commissioning. By implementing this pipeline connection and upgrading IB3A, Fermilab aims to significantly reduce helium waste, lower operational costs, and align with its commitment to sustainability. This initiative provides a model for resource-efficient cryogenic operations and reinforces the Laboratory’s capacity to support its science mission for the long term.

Porwisiak, D. [Fermilab]↗
DOE OSTI2015

Exploring the isopycnal mixing and helium–heat paradoxes in a suite of Earth system models

This paper uses a suite of Earth system models which simulate the distribution of He isotopes and radiocarbon to examine two paradoxes in Earth science, each of which results from an inconsistency between theoretically motivated global energy balances and direct observations. The helium–heat paradox refers to the fact that helium emissions to the deep ocean are far lower than would be expected given the rate of geothermal heating, since both are thought to be the result of radioactive decay in Earth's interior. The isopycnal mixing paradox comes from the fact that many theoretical parameterizations of the isopycnal mixing coefficient A Redi that link it to baroclinic instability project it to be small (of order a few hundred m 2 s −1 ) in the ocean interior away from boundary currents. However, direct observations using tracers and floats (largely in the upper ocean) suggest that values of this coefficient are an order of magnitude higher. Helium isotopes equilibrate rapidly with the atmosphere and thus exhibit large gradients along isopycnals while radiocarbon equilibrates slowly and thus exhibits smaller gradients along isopycnals. Thus it might be thought that resolving the isopycnal mixing paradox in favor of the higher observational estimates of A Redi might also solve the helium paradox, by increasing the transport of mantle helium to the surface more than it would radiocarbon. In this paper we show that this is not the case. In a suite of models with different spatially constant and spatially varying values of A Redi the distribution of radiocarbon and helium isotopes is sensitive to the value of A Redi . However, away from strong helium sources in the southeastern Pacific, the relationship between the two is not sensitive, indicating that large-scale advection is the limiting process for removing helium and radiocarbon from the deep ocean. The helium isotopes, in turn, suggest a higher value of A Redi below the thermocline than is seen in theoretical parameterizations based on baroclinic growth rates. We argue that a key part of resolving the isopycnal mixing paradox is to abandon the idea that A Redi has a direct relationship to local baroclinic instability and to the so-called "thickness" mixing coefficient A GM .

58 GEOSCIENCES↗
NASA NTRS1981

Observations of solar-wind helium

It is pointed out that the concentration of helium in the solar wind relative to hydrogen fluctuates wildly. Under certain circumstances, the helium to hydrogen abundance ratio is strongly enhanced over probable solar values; at other times, the amount of helium in the solar wind is immeasurably small. In spite of the fact that helium is heavier than hydrogen, solar-wind helium often leaves the solar gravitational field with a higher velocity than does the hydrogen. It is thought that the mechanisms responsible for helium behavior may contain clues to unanswered questions concerning the acceleration and energy exchange processes of the entire solar wind. A brief review is given of the principal features and theories of the solar wind as a whole. In addition, measurement techniques are discussed. Emphasis throughout is on the experimental data concerning the dynamics of solar-wind helium. On the basis of coronal temperatures, it is shown that helium in the solar wind is almost always doubly ionized. It is also shown that the average abundance of helium ions in the solar wind is usually in the range of 3 to 6% by number.

Neugebauer, M.↗
NASA NTRS2008

Affect of Air Leakage into a Thermal-Vacuum Chamber on Helium Refrigeration Heat Load

NASA s Johnson Space Center (JSC) Building 32 houses two large thermal-vacuum chambers (Chamber A and Chamber B). Within these chambers are liquid nitrogen shrouds to provide a thermal environment and helium panels which operate at 20K to provide cryopumping. Some amount of air leakage into the chambers during tests is inevitable. This causes "air fouling" of the helium panel surfaces due to the components of the air that adhere to the panels. The air fouling causes the emittance of the helium panels to increase during tests. The increase in helium panel emittance increases the heat load on the helium refrigerator that supplies the 20K helium for those panels. Planning for thermal-vacuum tests should account for this increase to make sure that the helium refrigerator capacity will not be exceeded over the duration of a test. During a recent test conducted in Chamber B a known-size air leak was introduced to the chamber. Emittance change of the helium panels and the affect on the helium refrigerator was characterized. A description of the test and the results will be presented.

Garcia, Sam↗
DOE OSTI2024

Microstructure and mechanical properties of friction stir weld performed on neutron-irradiated 304L steel with helium

As nuclear power plants (NPPs) approach or exceed 40–60 years of service, it may become necessary to repair damaged neutron-irradiated components to prolong longevity. However, fusion welding repair of irradiated steels and metallic materials is challenging because of helium-induced cracking. This study used friction stir welding (FSW) to address helium-related issues, such as helium bubble formation and grain boundary cracking. The microstructure, helium-induced degradation, and mechanical properties of a friction stir weld produced on neutron-irradiated 304L stainless steel with approximately 5.2 appm of helium were characterized. The analysis focused on variations in grain size, texture, and the morphology of helium-induced damage in the friction stir weld. Mechanical properties were characterized on the irradiated base metal (BM) and metallurgical zones of the friction stir weld: the stir zone (SZ), the thermo-mechanically affected zone (TMAZ), and the heat affected zone (HAZ). Only minor scattered porosity in the SZ and TMAZ and a few short microcracks (below 20 μm in length) in the TMAZ were observed, indicating limited helium-induced degradation. Tensile tests revealed good mechanical properties and fractography analysis demonstrated predominantly ductile fracture. In conclusion, the results highlight the immediate and substantial benefits of the FSW approach for repairing or joining helium-containing irradiated materials in NPPs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of break geometry and orientation on helium-air mixing in simulated reactor cavities of high temperature gas reactors

Here, this study experimentally examined the spatial and temporal variations in air and helium concentrations and temperature fields within simulated reactor cavities of a High Temperature Gas Reactor (HTGR) following helium discharge into an initially air-filled reactor cavity system. Detailed temperature maps were generated using a combination of fiber optics temperature sensor and multiple thermocouple probes within the simulated reactor cavities. The research scenario involved a hypothetical small pipe break in the Reactor Pressure Vessel, resulting in the release of high-temperature helium into the surrounding cavity. A scaled multi-compartment experimental facility, modeled after the General Atomics Modular High Temperature Gas Reactor (GA-MHTGR) design, was constructed for helium and air mixing experiments. Oxygen sensors and thermocouple probes were installed in all five cavities to measure the concentrations of oxygen (or helium) and the temperature distributions of the gas mixture. The experimental findings highlighted the significant impact of the injected helium jet velocity on the gas mixing process and demonstrated how the direction of the helium jet influences the air-helium temperature profiles within the cavities.

Air-ingress↗
DOE OSTI2021

Helium Bubbles and Blistering in a Nanolayered Metal/Hydride Composite

Helium is insoluble in most metals and precipitates out to form nanoscale bubbles when the concentration is greater than 1 at.%, which can alter the material properties. Introducing controlled defects such as multilayer interfaces may offer some level of helium bubble management. This study investigates the effects of multilayered composites on helium behavior in ion-implanted, multilayered ErD 2 /Mo thin film composites. Following in-situ and ex-situ helium implantation, scanning and transmission electron microscopy showed the development of spherical helium bubbles within the matrix, but primarily at the layer interfaces. Bubble linkage and surface blistering is observed after high fluence ex-situ helium implantation. These results show the ability of metallic multilayers to alter helium bubble distributions even in the presence of a hydride layer, increasing the lifetime of materials in helium environments.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Helium release during shale deformation: Experimental validation

This paper describes initial experimental results of helium tracer release monitoring during deformation of shale. Naturally occurring radiogenic 4 He is present in high concentration in most shales. During rock deformation, accumulated helium could be released as fractures are created and new transport pathways are created. We present the results of an experimental study in which confined reservoir shale samples, cored parallel and perpendicular to bedding, which were initially saturated with helium to simulate reservoir conditions, are subjected to triaxial compressive deformation. During the deformation experiment, differential stress, axial, and radial strains are systematically tracked. Release of helium is dynamically measured using a helium mass spectrometer leak detector. Helium released during deformation is observable at the laboratory scale and the release is tightly coupled to the shale deformation. These first measurements of dynamic helium release from rocks undergoing deformation show that helium provides information on the evolution of microstructure as a function of changes in stress and strain.

58 GEOSCIENCES↗
DOE OSTI2022

Microstructure analysis of laser beam weldments performed on neutron-irradiated 304L steel containing 3 and 8 appm helium

We report that AISI 304 L austenitic stainless steel is one of the major structural materials used in light water reactors (LWRs). In the future, 304 L components may require repair, and several welding techniques have been proposed as candidates. In this study, laser beam welding using the low-energy contribution approach was performed in ~2016 on neutron-irradiated AISI 304 L steel with nominal values of 3 and 8 appm helium (He). The goal was to investigate the impact of helium on the irradiated material weldability and evaluate helium-associated damage. The weld and heat-affected zone (HAZ) microstructure was studied using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Analysis of the weldment cross-sections did not reveal severe cracking. Still, evidence of incipient helium-associated damage was observed in the HAZ, manifesting as degraded grain boundaries (GBs) “decorated” by pore chains and mostly small (i.e., ≤ 25-30 µm) scattered cracks. The largest observed crack was ~50 µm in length. Helium-associated damage was localized within ~200-300 µm of the weld pool boundary, and the fraction of the compromised GBs, as a rule, was below ~9-11% of the total GB network. TEM analysis showed significant annealing of the radiation-induced defects at distances up to ~300 µm from the weld pool boundary. Inside the HAZ, the cavities (likely, helium bubbles) tended to form at GBs and inclusions, such as manganese sulfide precipitates in the grain interior. Crystallography analysis of the HAZ damage showed that random high-angle boundaries were most susceptible to helium-associated damage. In contrast, low-angle random boundaries and twin boundaries appeared to be strongly resistant to degradation from the combined effects of helium and welding.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of helium bubbles on the mobility of edge dislocations in copper

Abstract Helium bubbles can form in materials upon exposure to irradiation. It is well known that the presence of helium bubbles can cause changes in the mechanical behavior of materials. To improve the lifetime of nuclear components, it is important to understand deformation mechanisms in helium-containing materials. In this work, we investigate the interactions between edge dislocations and helium bubbles in copper using molecular dynamics (MD) simulations. We focus on the effect of helium bubble pressure (equivalently, the helium-to-vacancy ratio) on the obstacle strength of helium bubbles and their interaction with dislocations. Our simulations predict significant differences in the interaction mechanisms as a function of helium bubble pressure. Specifically, bubbles with high internal pressure are found to exhibit weaker obstacle strength as compared to low-pressure bubbles of the same size due to the formation of super-jogs in the dislocation. Activation energies and rate constants extracted from the MD data confirm this transition in mechanism and enable upscaling of these phenomena to higher length-scale models.

36 MATERIALS SCIENCE↗