High Levels Of Helium Research Articles

Helium Suicide, a Rapid and Painless Asphyxia: Toxicological Findings

Suicide by helium inhalation has become increasingly common in the last few decades in Europe and the US because it produces a quick and painless death. Inhaled-gas suicides can easily be assessed through death scene investigation and autopsy. However, helium is a colorless and odorless inert gas that unfortunately cannot be detected using standard toxicological analysis. A successful gas analysis was performed following the suicide of a 17-year-old female. For the detection of helium, central/peripheral blood samples and gaseous samples from the esophagus, stomach, and upper and lower respiratory airways (from the trachea and the primary left and right bronchia) were collected with a gastight syringe, ensuring minimal dilution. Qualitative analyses were positive in all gaseous samples. Quantitative analyses were performed using a special gas-inlet system with a vacuum by which the sample can be transferred to a mass spectrometer, reducing the risk of contamination. Helium concentrations were 20.16% from the trachea, 12.33% from the right lung, and 1.5% from the stomach. Based on the high levels of helium, the cause and manner of death were assessed as asphyxia suicide by inhalation of helium. Therefore, toxicological analyses should always be applied in order to gain evidence of inhaled gas in gaseous samples.

Radiogenic helium concentration and isotope variations in crustal gas pools from Sichuan Basin, China

Helium is an exhaustible natural resource and the main commercial helium was separated from helium-rich natural gas. The helium in the sedimentary basin is mainly the radiogenic origin of crustal rocks with high level of uranium and thorium. Data from 242 natural gas samples were used to investigate the distribution and formation mechanism of helium-rich gases in the Sichuan Basin of China. All gas samples show remarkably low 3He/4He ratios with ranging from 0.002 to 0.05 Ra, which represent typical crustal helium. The Weiyuan gas pool in the southern Sichuan Basin possesses high levels of helium (1500–18770 ppm, average 2785.7 ppm) in Precambrian and Cambrian strata. A positive relationship were observed in the helium and nitrogen contents increased with reservoir layer age for all Weiyuan gas samples. Presinian granite was considered as the main helium source for the Weiyuan gas pool. Gaoshiti–Moxi and Weiyuan gas pools belonged to the same ancient gas pool before the Late Cretaceous, but the helium abundance of Gaoshiti–Moxi gas pool is relatively low (200–891 ppm). The change of pressure and fracture system caused by the uplift of Weiyuan structure in the Himalayan orogenesis led to the helium accumulation and enrichment of Weiyuan gas pool. The shale of the Silurian Longmaxi Formation has high contents of uranium and thorium and generated a large amount of helium while forming large quantities of hydrocarbon gases. Generally, the helium abundance of shale gases and conventional gases generated from the Longmaxi Formation ranges from 63 to 1500 ppm and some of the gas pool are sufficient for commercial helium resource exploitation. Therefore, the relative quantities of helium and hydrocarbon gases are act as a key factor influencing the formation of helium-rich natural gas reservoirs.

The influence of carbon on cavity evolution in ion-irradiated ferritic-martensitic steels

Beam-induced carbon uptake has been discovered to occur excessively in high damage ion irradiation experiments. This uptake of carbon has the potential to compromise experiments which aim to emulate the effects of radiation damage. In this study, the effect of carbon on cavity evolution in ion-irradiated ferritic-martensitic steels T91 and HT9 was evaluated. Irradiations were performed with 5.0 MeV Fe2+ ions at 460 °C to damage levels up to 450 dpa. Some samples utilized a 100 nm alumina coating to prevent beam-induced carbon uptake. The T91 samples were pre-implanted with helium concentrations of 0, 1, 10, 100, and 1000 appm and the HT9 samples were irradiated in a dual-beam configuration with 5.0 MeV Fe2+ ions and energy-degraded helium up to 188 dpa, with He/dpa ratios of 0, 0.0006, 0.003, 0.015, and 0.2 appm He/dpa. Cavity evolution and carbide formation was characterized using TEM. The effect of carbon uptake on swelling and cavity evolution was evaluated by comparing the results of the samples which experienced excess carbon uptake to irradiated samples which experienced no carbon uptake. It was found that excess carbon suppressed swelling and distorted the role of helium on cavity evolution, regardless of helium injection method. The dissociation of helium bubbles led to a dramatic loss of bubble density at high helium levels by 450 dpa. Significant carbide formation contributed to the dissociation of helium bubbles by providing an alternate sink for emitted helium atoms.

Chlorine Stable Isotope and Helium Isotope Studies Contributing to the Understanding of the Hydrogeochemical Characteristics of Old Groundwater

Chlorine stable isotope and helium isotope data were integrated in order to study the chemical and isotopic characteristics of old groundwater in the Pannonian Basin. Former studies showed groundwater is of meteoric origin, based on oxygen and deuterium isotopes, which have isotopic signatures of formation waters from the deeper part of the basin. Depletion of the heavier 37Cl isotope can be observed along the flow paths. Despite the fact that most of the sampled groundwater contains high helium levels, indicating a crustal helium origin, their 3He content is also high. The 3He/4He ratios (expressed in R/Rac) with values between 0.4 and 1.2 shows that helium of mantle origin must also be a component in the groundwater along the flow paths. The presence of mantle origin helium could be detected not just in the deeper part of the basin, but even in the Quaternary sediments.

Use of double and triple-ion irradiation to study the influence of high levels of helium and hydrogen on void swelling of 8–12% Cr ferritic-martensitic steels

In accelerator-driven spallation (ADS) devices, some of the structural materials will be exposed to intense fluxes of very high energy protons and neutrons, producing not only displacement damage, but very high levels of helium and hydrogen. Unlike fission flux-spectra where most helium and hydrogen are generated by transmutation in nickel and only secondarily in iron or chromium, gas production in ADS flux-spectra are rather insensitive to alloy composition, such that Fe–Cr base ferritic alloys also generate very large gas levels. While ferritic alloys are known to swell less than austenitic alloys in fission spectra, there is a concern that high gas levels in fusion and especially ADS facilities may strongly accelerate void swelling in ferritic alloys. In this study of void swelling in response to helium and hydrogen generation, irradiation was conducted on three ferritic-martensitic steels using the Electrostatic Accelerator with External Injector (ESUVI) facility that can easily produce any combination of helium to dpa and/or hydrogen to dpa ratios. Irradiation was conducted under single, dual and triple beam modes using 1.8 MeV Cr+3, 40 keV He+, and 20 keV H+. In the first part of this study we investigated the response of dual-phase EP-450 to variations in He/dpa and H/dpa ratio, focusing first on dual ion studies and then triple ion studies, showing that there is a diminishing influence on swelling with increasing total gas content. In the second part we investigated the relative response of three alloys spanning a range of starting microstructure and composition. In addition to observing various synergisms between He and H, the most important conclusion was that the tempered martensite phase, known to lag behind the ferrite phase in swelling in the absence of gases, loses much of its resistance to void nucleation when irradiated at large gas/dpa levels.

Molecular dynamics simulation of cascade-induced ballistic helium resolutioning from bubbles in iron

Molecular dynamics simulations have been used to assess the ability of atomic displacement cascades to eject helium from small bubbles in iron. This study of the ballistic resolutioning mechanism employed a recently-developed Fe–He interatomic potential in concert with an iron potential developed by Ackland and co-workers. The primary variables examined were: irradiation temperature (100 and 600K), cascade energy (5 and 20keV), bubble radius (0.5 and 1.0nm), and He-to-vacancy ratio in the bubble (0.25, 0.5 and 1.0). Systematic trends were observed for each of these variables. For example, ballistic resolutioning leads to a greater number of helium atoms being displaced from larger bubbles and from bubbles that have a higher He/vacancy ratio (bubble pressure). He resolutioning was reduced at 600K relative to 100K, and for 20keV cascades relative to 5keV cascades. Overall, the results indicate a modest level of He removal by ballistic resolutioning. The results may be particularly relevant to fusion irradiation conditions which produces high levels of helium by transmutation. They can be used to provide initial guidance in selection of a “resolution parameter” that can be employed in kinetic models to predict the bubble size distribution that evolves under irradiation.

Helium transport, fate and management in nanostructured ferritic alloys: In situ helium implanter studies

High helium levels produced in fusion neutron spectra may lead to severe increases in the brittle fast fracture temperature, enhanced void swelling and degradation of creep rupture properties at lower, intermediate and higher irradiation temperatures, respectively. Thus it is important to develop structural alloys with stable microstructures that can manage helium based on understanding of its transport, fate and consequences. We report on the initial results of a study of helium in a nanostructured ferritic alloy (NFA), MA957, that is dispersion strengthened by an ultra-high density of nm-scale Y–Ti–O nanofeatures (NFs). An in situ helium implanter technique uniformly deposited ≈380appm helium to ≈6μm in MA957 irradiated in the High Flux Isotope Reactor (HFIR) to ≈9 dpa at 500°C. Through focus transmission electron microscopy (TEM) showed that helium is in extremely fine bubbles that often appear to coincide with bright field features taken as a NF.

Response of electrochemical oxygen sensors to inert gas–air and carbon dioxide–air mixtures: Measurements and mathematical modelling

Electrochemical oxygen gas sensors are widely used for monitoring the state of inertisation of flammable atmospheres and to warn of asphyxiation risks. It is well established but not widely known by users of such oxygen sensors that the response of the sensor is affected by the nature of the diluent gas responsible for the decrease in ambient oxygen concentration. The present work investigates the response of electrochemical sensors, with either acid or alkaline electrolytes, to gas mixtures comprising air with enhanced levels of nitrogen, carbon dioxide, argon or helium. The measurements indicate that both types of sensors over-read the oxygen concentrations when atmospheres contain high levels of helium. Sensors with alkaline electrolytes are also shown to underestimate the severity of the hazard in atmospheres containing high levels of carbon dioxide. This deviation is greater for alkaline electrolyte sensors compared to acid electrolyte sensors. A Computational Fluid Dynamics (CFD) model is developed to predict the response of an alkaline electrolyte, electrochemical gas sensor. Differences between predicted and measured sensor responses are less than 10% in relative terms for nearly all of the gas mixtures tested, and in many cases less than 5%. Extending the model to simulate responses of sensors with acid electrolytes would be straightforward.

Nano-cavities observed in a 316SS PWR flux thimble tube irradiated to 33 and 70 dpa

The radiation-induced microstructure of a cold-worked 316SS flux thimble tube from an operating pressurized water reactor (PWR) was examined. Two irradiated conditions, 33 dpa at 290 °C and 70 dpa at 315 °C were examined by transmission electron microscopy. The original dislocation network had completely disappeared and was replaced by fine dispersions of Frank loops and small nano-cavities at high densities. The latter appear to be bubbles containing high levels of helium and hydrogen. An enhanced distribution of these nano-cavities was found at grain boundaries and may play a role in the increased susceptibility of the irradiated 316SS to intergranular failure of specimens from this tube during post-irradiation slow strain rate testing in PWR water conditions.

Experimental simulation of the effect of transmuted helium on the mechanical properties of silicon carbide

Experimental results simulating the effects of transmuted helium on the mechanical properties of SiC are presented. High-purity, stoichiometric chemically vapor-deposited SiC bend bars were cyclotron implanted using 37.7 MeV α particles at 590 °C. A uniform implantation to 100 and 1000 appm was carried out, with a maximum implantation depth of ≃0.46 mm. Samples were then neutron irradiated to a dose of ≃8 dpa at 800 °C, thereby simulating atomic displacements at dose rates and temperatures similar to those of a fusion blanket, while in the presence of high helium levels of (≃125 appm He/dpa). Results on as-implanted SiC yield statistically significant changes in bend strength, indent fracture toughness and density. It is clear that these changes are in part due to the ≃0.1 dpa dose coincident with the helium implantation. Following neutron irradiation a larger change in properties occurs, though the difference between the helium pre-injected SiC, and the irradiated control samples was not statistically significant.

High-sensitivity quadrupole mass spectometry system for the determination of hydrogen in irradiated materials

High levels of helium and hydrogen are generated in metals in fusion reactors, and fusion simulations in mixed-spectrum fission reactors, spallation neutron sources, and high-energy charged particle environments. Although hydrogen generation rates are generally higher than those of helium, hydrogen is thought to quickly diffuse out of metals, especially at elevated temperatures. There appear to be some conditions, however, where significant hydrogen retention can occur. To assess this potential, a high-sensitivity analysis system has been developed for the measurement of hydrogen in small samples of irradiated materials. The system is based on a low-volume extraction furnace in combination with a quadrupole mass spectrometer, and has a detection limit of ∼1 appm for steel. Hydrogen levels have been measured in high-energy proton-irradiated tungsten and Inconel 718, in iron-based alloys and vanadium alloys from fusion materials programs, and in stainless steels and pure metals irradiated in light water reactors. Details of the system and typical results are presented.

Simulation of transport in the ignited ITER with 1.5-D predictive code

The confinement in the bulk and scrape-off layer plasmas of the ITER EDA and CDA is investigated with special versions of the 1.5-D BALDUR predictive transport code for the case of peaked density profiles (Cu=1.0). The code self-consistently computes 2-D equilibria and solves 1-D transport equations with empirical transport coefficients for the ohmic, L and ELMy H mode regimes. Self-sustained steady state thermonuclear burn is demonstrated for up to 500 s. It is shown to be compatible with the strong radiation losses for divertor heat load reduction caused by the seeded impurities iron, neon and argon. The corresponding global and local energy and particle transport are presented. The required radiation corrected energy confinement times of the EDA and CDA are found to be close to 4 s, which is attainable according to the ITER ELMy H mode scalings. In the reference cases, the steady state helium fraction is 7%, which already causes significant dilution of the DT fuel. The fractions of iron, neon and argon needed for the prescribed radiative power loss are given. It is shown that high radiative losses from the confinement zone, mainly by bremsstrahlung, cannot be avoided. The radiation profiles of iron and argon are found to be the same, with two thirds of the total radiation being emitted from closed flux surfaces. Fuel dilution due to iron and argon is small. The neon radiation is more peripheral, since only half of the total radiative power is lost within the separatrix. But neon is found to cause high fuel. Dilution. The combined dilution effect by helium and neon conflicts with burn control, self-sustained burn and divertor power reduction. Raising the helium fraction above 10% leads to the same difficulties owing to fuel dilution. The high helium levels of the present EDA design are thus unacceptable. For the reference EDA case, the self-consistent electron density and temperature at the separatrix are 5.6*1019 m-3 and 130 eV, respectively. The bootstrap current of 2.4 MA is much lower tha

Microstructural evolution of neutron-irradiated Fe-Cr-Ni ternary alloys at high helium generation rates

A series of Fe-Cr-Ni ternary alloys were irradiated to 12–14 dpa in the Oak Ridge Research Reactor (ORR). In this experiment, most of the helium atoms were produced by the 58Ni(n, γ) 59Ni(n, α) 56Fe sequential reaction, and, therefore, the helium generation rate was almost proportional to the nickel content, ranging from 27 to 58 appm He/dpa in 20 to 45 wt% Ni alloys. Irradiation temperatures were 330, 400, 500 and 600°C, and the specimen variables were the nickel level, the chromium level and cold-working. The high levels of helium, combined with details of the temperature history, were found to have dominated to microstructural development, sometimes overwhelming and even reversing the action of a given material variable. Microscopy examination showed that there was an unprecedented refinement of cavity microstructure at all temperatures, which accounts for the substantial alterations in both swelling and mechanical properties observed in earlier studies.

The effect of helium on microstructural evolution and mechanical properties of austenitic steels as determined by spectral tailoring experiments

Fe15Cr xNi alloys irradiated at both low (0.66 to 1.2) and very high (27 to 58) helium/dpa levels exhibit significantly different levels of strengthening due to an unprecedented refinement of cavity microstructure at the very high helium levels. When compounded with the nickel dependence of helium generation, the cavity distribution for some irradiation conditions and alloy compositions can be driven below the critical radius for bubble-to-void conversion, leading to a delay in swelling. The critical radius also appears to be dependent on the nickel level. The refinement may not have resulted from the high helium levels alone, however, but may also have been influenced by differences in displacement rate and temperature history in the two experiments.

Helium embrittlement in Fe-Ni-Cr austenitic alloys and ferritic MA 956 alloy

The helium embrittlement with helium injection by cyclotron and the irradiation embrittlement with neutrons by JMTR were compared in Fe-25% Ni-15% Cr alloys and Fe-40% Ni-15% Cr alloys with and without intermetallic compound strengthening, and in the MA 956 alloy. The results are summarized as follows: 1. (1) For helium-injected austenitic alloys precipitation-hardened by γ′ or γ″ to their highest strength, the total elongation almost becomes zero even for a very low helium level of 5–10 at ppm. 2. (2) For neutron-irradiation specimens, the embrittlement is also prominent for the specimens with highest tensile strength. The embrittlement may be caused primarily by helium from 10B(n, α) reactions. 3. (3) Addition of 0.25% Ti to the Fe-25Ni-15Cr alloy slightly suppresses the helium embrittlement in the case of neutron irradiation, but not in the He-injected case. 4. (4) The MA 956 alloy is found quite resistant to helium embrittlement even for high helium levels of 670 atppm.

Helium effects on the creep and fatigue resistance of austenitic stainless steels at high temperatures

The effects of helium on the high temperature mechanical properties of austenitic stainless steel, also known as high temperature helium embrittlement, are reviewed. Special emphasis is given to such experimental data which simulate a fusion reactor environment best, i.e., to creep and low frequency fatigue experiments at high helium levels (≥ 100 appm He). Correlations between mechanical properties data and microstructural data are presented and compared to recently developed models for helium embrittlement. The presented data are critically assessed in the light of fusion reactor materials needs and some suggestions for future work are made.

Helium effects on the creep and fatigue resistance of austenitic stainless steels at high temperatures

The effects of helium on the high temperature mechanical properties of austenitic stainless steel, also known as high temperature helium embrittlement, are reviewed. Special emphasis is given to such experimental data which simulate a fusion reactor environment best, i.e., to creep and low frequency fatigue experiments at high helium levels (≥ 100 appm He). Correlations between mechanical properties data and microstructural data are presented and compared to recently developed models for helium embrittlement. The presented data are critically assessed in the light of fusion reactor materials needs and some suggestions for future work are made.

A comparison of measured and calculated helium production in nickel using newly evaluated neutron cross sections for 59Ni

Fusion reactors will produce high levels of helium in surrounding materials with a helium (appm)-to-displacement ratio of about 10-to-1 in stainless steel. This high ratio can be obtained in mixed-spectrum reactors, which are used for fusion materials testing, due to unusually high thermal neutron cross sections for the sequential reactions 58Ni(n,γ) 59Ni(n,α) 56Fe. The highenergy (∼340 keV) 56Fe recoils also add significantly to the displacement damage at the rate of one DPA per 567 appm helium. Until now, the calculation of helium production in nickel has been done in a semi-empirical manner due to a lack of evaluated cross sections for 59Ni. However, this approach cannot be readily transferred between different reactors since we do not know the contributions from epithermal neutrons in different neutron spectra. A new evaluation of the 59Ni cross sections has recently been completed, permitting us to calculate all of the required reaction rates for any given neutron spectrum. Radiometric dosimetry and helium measurements have recently been completed for several different mixed-spectrum reactors. Precise comparisons of the helium production cross sections and measurements can thus be made in well-characterized neutron spectra. Data are presented for several recent fusion materials irradiations in the Oak Ridge Research Reactor and High Flux Isotope Reactor at Oak Ridge National Laboratory and for the Experimental Breeder Reactor II at Argonne National Laboratory. Procedures are recommended for calculating helium production for nickel-bearing materials in any neutron spectrum.

A new calculation of thermal neutron damage and helium production in nickel

It has long been recognized that thermal neutron irradiations of nickel-bearing materials generate high levels of helium from the sequential 58Ni(n,γ) 59Ni(n, α) 56Fe nuclear reactions. This process is used to simulate fusion reactor helium-to-displacement damage rates in stainless steel during fission reactor irradiations. However, it has not previously been recognized that the 56Fe recoils will also cause significant displacement damage. At thermal neutron energies the 340 keV 56Fe recoil event will displace 1762 atoms in nickel. The helium (appm)-to-displacement ratio from this process will be 567, a value that can be used to correct previous displacement calculations in nickel-bearing materials. This effect can nearly double the displacement damage in nickel in HFIR at high neutron fluences.