High Helium Content Research Articles

IMPROVING THE ACCURACY OF CALCULATING THE SUPER-COMPRESSIBILITY COEFFICIENT OF HELIUM BASED ON STATE EQUATIONS

To date, the Russian gas industry is developing a large number of deposits with a high helium content in the composition of the extracted gas, such as Chayandinskoye, Kovyktinskoye, Yaraktinskoye oil and gas condensate fields. Helium has never before been the object of detailed study during gathering and treatment, but today helium is an important resource that is used in many fields: military industry, medicine, shipbuilding, laser technology, space technology. The high demand for the component of the extracted gas has created requirements for the creation of a technology for separating it from gas. In addition, helium is a «cold» gas due to the weak interaction of its molecules, so it is difficult to model phase equilibrium at extremely low temperatures. As a result, improving the simulation of condensation of a helium mixture is undoubtedly an urgent task of the industry today. The purpose of the study is to increase the accuracy of calculating the thermodynamic properties of helium based on one of the modifications of the Peng-Robinson equation of state for thermobaric conditions corresponding to helium liquefaction processes.As the methods used in this work, a software module for calculating the selection of the Peneloux correction in the Java programming language was implemented. The results are tested on known experimental data, as well as a specialized software product for calculating the thermodynamic properties of fluids.The features of calculating the superconductivity coefficient of helium based on the cubic equation of state are presented. The optimal range of the Peneloux correction for the Peng-Robinson equation of state has been found, as well as an approximation formula that allows us to find the correction in the low temperature region. The results obtained will allow us to calculate the thermodynamic properties of helium with high accuracy. This will allow us to predict the volume of production and condensation of helium from natural gas, which is certainly an important task for the development of the country's economy.

Mantle noble gas abundance ratios inferred from oceanic basalts and model estimates

We investigated mantle noble gas abundance ratios using a global compilation of data from mid-ocean ridge basalts (MORB) and high 3He/4He ocean island basalts (OIB), coupled with calculated abundances based on closed-system evolution models. Assuming that the mantle sources of MORB and high 3He/4He OIB are derived from the same early Earth parental material, variations in their noble gas abundance ratios are useful to ascertain which source is more depleted or degassed, or if the mantle noble gases might be a hybrid of different parental materials. Therefore, noble gas compositions of mantle sources can be a key to elucidating mantle evolution and structure. We calculated the noble gas abundance patterns using a Monte Carlo approach with validated end-members, which provides new estimates for the abundance ratios and their uncertainties. The adequacy of the calculated values was confirmed by existing data. We compiled all published noble gas data extracted by total heating of glassy oceanic basalts, which enables estimation of the pristine abundance patterns of noble gases including Kr for both sources of MORB and OIB. The pristine abundance ratios of the mantle sources for oceanic basalts are estimated by correcting measured values for atmospheric influences and elemental fractionation. The corrected abundance ratios resemble mantle values calculated using the proposed end-members for MORB and high 3He/4He OIB. The estimated relative abundance ratios in the high 3He/4He OIB source are similar to those of C1 chondrites in the range of He to Kr, supporting the hypothesis that a less degassed primitive OIB source can exist in the Earth's mantle. By contrast, the MORB source shows depletion of lighter noble gases, but with high relative helium content compared to the OIB source. The contrast in He/Ne abundance ratios between MORB and OIB, is a key constraint on mantle evolution models, andis expected to reflect several stages of diffusive fractionation during Earth history, or different initial mantle sources, which would require heterogeneous Earth accretion.

Genetic Types, Distribution Patterns and Enrichment Mechanisms of Helium in China’s Petroliferous Basins

Helium is a strategic resource with many scientific, technical and industrial applications. However, despite its importance and scarcity, there is a lack of understanding on its origin, migration and accumulation processes. In view of this, the distribution patterns and enrichment mechanisms of helium are studied based on systematic analysis of the genetic types of helium in petroliferous basins in China. The helium in the petroliferous basins in China is mainly radiogenic, which involves the decay of U and Th. As expected, we found that, in one gas field, the helium content in natural gas increases with the age of reservoir rock, and in the same layer of the same structure within one reservoir, the helium content in natural gas in high altitude part of the structure is higher than that in the lower part. Enrichment of helium is closely related to old deep groundwater. The helium produced by radioactive decay in old strata is dissolved in water and transported and enriched through water migration. Due to large uplift of the structure during the Himalayan period, the helium dissolved in water was exsolved and accumulated with natural gas in the trap above the water. And thus, the helium-rich natural gas reservoirs formed. So, the helium contents in natural gas fields increase gradually along the flow direction of groundwater. The area with large range of uplift often shows higher helium content. This study not only provides a basis for the study of helium enrichment research, but also provides a new idea for industrial helium resource exploration.

A condensation heat transfer model with light gas effects in non-condensable gas mixtures

In this study, the condensation heat transfer on a vertical tube in a steam-air‑helium mixture was investigated. The effect of helium on condensation heat transfer was analyzed using a heat and mass transfer analogy model and a new effective diffusivity which was proposed based on the Maxwell-Stefan diffusion model. The condensation heat transfer was increased at a low helium content and decreased at a high helium content, which could be explained by the competition induced by the increasing diffusivity due to helium and reduction in density difference between the bulk conditions and wall. In addition, the vapor content and wall subcooling influenced the effect of helium. An experimental investigation was conducted to analyze the helium effect on condensation heat transfer. The helium content was measured using a gas analyzer, while the vapor content was obtained under the assumption that the gas was saturated. The results of the experiment were consistent with the theoretical analyses, although the helium effect at a low helium content was stronger than that predicted by the theoretical model. An improved helium effect factor was proposed after fitting the theoretical model to the experimental data, and the model predicted the effect of helium reasonably well.

Tritium embrittlement of austenitic stainless-steel tubing at low helium contents

Austenitic stainless steels are the standard materials for containment of hydrogen and tritium because of their resistance to mechanical property degradation in those environments. The mechanical performance of the primary containment material is critical for tritium handling, processing, and storage, thus comprehensive understanding of the processes of tritium embrittlement is an enabling capability for fusion energy. This work describes the investigation of the effects of low levels of tritium-decay-helium ingrowth on 304 L tubes. Long-term aging with tritium leads to high helium contents in austenitic stainless steels and can reduce fracture toughness by 95 %, but the details of behavior at low helium contents are not as well characterized. Here, we present results from tensile testing of tritium pre-charged 304 L tube specimens with a variety of starting microstructures that all contain a low level of helium. The results of the tritium exposed-and-aged materials are compared to previously reported results on similar specimens tested in an unexposed condition as well as the hydrogen precharged condition. Tritium precharging and aging for a short duration resulted in increased yield strengths, ultimate tensile strengths and slightly increased elongation to failure, comparable to higher concentrations of hydrogen precharging.

Underground storage facilities for helium concentrate in porous medium

The gas of many fields in Eastern Siberia (Chayandinskoye, Kovyktinskoye, Sobinskoye, Chikanskoye, etc.) has a complex component composition with a high helium content. In order to realize the advantage of a unique raw material base, it is necessary to put into practice solutions for the industrial implementation of technologies for the extraction of helium, storage and transportation. One of the directions for the solution of these problems is the creation of temporary underground storage of helium concentrate in a porous medium next to gas chemical plants. This will ensure supply flexibility and reduce helium losses. The global demand for helium is continuously increasing from year to year and in the long term, a favorable situation will emerge on the global helium market for Russia, a positive effect from which can be achieved, provided the benefits of the raw material base are realized. A positive effect means not only the monetary effect, but also takes into account the formation of prerequisites for the development of new spheres of influence: access to new trading platforms and sales markets, the development of high-tech industries, basic and applied sciences, etc. In order to realize the advantage of the raw material base, Russia needs in a fairly short period of time to put into practice the decisions on the industrial introduction of gas separation technologies and underground helium storage.

Basic design and thermodynamic analysis of a high helium content natural gas-fuel cell power plant

In this paper, a new developed integrated process for the production of power, helium, and liquefied natural gas (LNG) is proposed and analyzed. The proposed integrated process is composed of the following subsystems: helium recovery and LNG production unit, molten carbonate fuel cell (MCFC), absorption refrigeration system (ARS), as well as the steam power plant. Natural gas enters the helium recovery unit, in which crude helium and LNG are produced, and then, methane-rich natural gas with a higher heating value enters the MCFC cycle, which is responsible for generating power and supplying required heat duty of the system. The produced cooling in the ARS unit is also introduced to the helium recovery cycle to provide its necessary cooling. A comprehensive comparative study is employed to assess process performance. In addition, a sensitivity analysis is performed to investigate the effect of the main operating parameters such as current density, fuel utilization factor, fuel cell temperature, and feed flow rate on process efficiency. Based on the energy analysis results, the electrical efficiency of MCFC and the overall thermal efficiency of the process are 42.01% and 94.91%, respectively. Also, the integrated system produces helium and LNG, with helium extraction rate of 91.42% and specific power consumption (SPC) of 0.2086 kWh/kg LNG, respectively, in conjunction with 4793 MW net power.

Distribution law of helium in Leshan-Longnvsi paleo-uplift in Sichuan Basin, China

The Weiyuan and Anyue large gas fields discovered on the Leshan-Longnvsi paleo-uplift in Sichuan Basin have the oldest marine gas reservoir discovered in China so far, and Weiyuan is also the first gas field to utilize helium resources in China. The Helium in natural gas of Leshan-Longnvsi paleo-uplift belongs to crust-derived helium formed by radioactivity, and its content distribution shows obvious regularity. The content of helium is highly correlated with the age of reservoir in the same gas field, and the helium content is gradually increased from the top to the bottom. However, the content of helium in natural gas presents significantly different in various tectonic units. The content of helium in Anyue gas field developed on Gaoshiti-Moxi structure is very low. The average contents of Sinian and Cambrian are 0.0356% and 0.0078%, respectively. The content of helium in Weiyuan gas field developed on Weiyuan structure is relatively higher, and the average contents of Sinian and Cambrian are 0.28% and 0.18% respectively. The high helium content of natural gas in Weiyuan gas field is related to the large-scale granite body developed on the basement on the one hand and the water-soluble gas accumulation on the other hand. The main gas reservoirs in the Weiyuan gas field and adjacent areas are located in the Sinian system. From the slope area to the high point of the Weiyuan structure, the helium content has increased significantly. With the tectonic movement of the Himalayan period, the Weiyuan area is greatly uplifted, causing structural traps. Natural gas dissolved in the water, including helium gas, is decomposed by decompression, and the released gas is trapped, then released gases accumulated in traps and thus formed Weiyuan gas field with high content of helium.

A flammability limit model for hydrogen-air-diluent mixtures based on heat transfer characteristics in flame propagation

Abstract Predicting lower flammability limits (LFL) of hydrogen has become an ever-important task for safety of nuclear industry. While numerous experimental studies have been conducted, LFL results applicable for the harsh environment are still lack of information. Our aim is to develop a calculated non-adiabatic flame temperature (CNAFT) model to better predict LFL of hydrogen mixtures in nuclear power plant. The developed model is unique for incorporating radiative heat loss during flame propagation using the CNAFT coefficient derived through previous studies of flame propagation. Our new model is more consistent with the experimental results for various mixtures compared to the previous model, which relied on calculated adiabatic flame temperature (CAFT) to predict the LFL without any consideration of heat loss. Limitation of the previous model could be explained clearly based on the CNAFT coefficient magnitude. The prediction accuracy for hydrogen mixtures at elevated initial temperatures and high helium content was improved substantially. The model reliability was confirmed for H2-air mixtures up to 300 °C and H2-air-He mixtures up to 50 vol % helium concentration. Therefore, the CNAFT model developed based on radiation heat loss is expected as the practical method for predicting LFL in hydrogen risk analysis.

Nanoindentation and TEM to Study the Cavity Fate after Post-Irradiation Annealing of He Implanted EUROFER97 and EU-ODS EUROFER.

The effect of post-helium irradiation annealing on bubbles and nanoindentation hardness of two reduced activation ferritic martensitic steels for nuclear fusion applications (EUROFER97 and EU-ODS EUROFER) has been studied. Helium-irradiated EUROFER97 and EU-ODS EUROFER were annealed at 450 °C for 100 h in an argon atmosphere. The samples were tested by nanoindentation and studied by transmission electron microscopy extracting some focused ion beam lamellae containing the whole implanted zone (≈50 µm). A substantial increment in nanoindentation hardness was measured in the area with higher helium content, which was larger in the case of EUROFER97 than in EU-ODS EUROFER. In terms of microstructure defects, while EU-ODS EUROFER showed larger helium bubbles, EUROFER97 experienced the formation of a great population density of them, which means that the mechanism that condition the evolution of cavities for these two materials are different and completely dependent on the microstructure.

Micro-structural effects of irradiation temperature and helium content in neutron irradiated B-alloyed Eurofer97-1 steel

The micro-structural effects of different neutron irradiation temperatures and helium contents, for 16 dpa dose, have been investigated by means of small-angle neutron scattering (SANS) in B-alloyed ferritic/martensitic steel Eurofer97-1 (0.12 C, 9 Cr, 0.2 V, 1.08 W wt%, B concentrations up to 1000 ppm); due to B transmutations, fusion relevant He/dpa values are expected to be produced under neutron irradiation. SANS measurements have been carried out on a sample irradiated at 350 °C, with estimated helium content of 5600 appm, and compared to previous SANS results, obtained on two other irradiated samples of this same B-alloyed steel. These new measurements confirm that for such high helium contents the SANS cross-section increases in order of magnitude and the magnetic SANS component is strongly reduced, compared to lower helium content (400 appm). Such effects are attributed to increase in helium bubbles density and to the presence of micro-cavities, produced after dissolution of large B-carbides. The SANS data analysis procedure has been improved, also thanks to the additional information provided by the new measurements, and more accurate helium bubble size distributions have been obtained for all the investigated samples. For 5600 appm helium content, bubble volume fractions are found of 0.025 for the sample irradiated at 350 °C and of 0.041 for the previously investigated sample irradiated at 400 °C, significantly increasing with the irradiation temperature. These values are approximately one order of magnitude larger than the value of 0.003 previously found for the sample with 400 appm helium. The size distributions are compared with electron microscopy observations of these same samples. It appears that the occurrence of complex micro-structural changes in irradiated Eurofer97-1 steel should be taken in due account when considering its application under high He/dpa ratio values.

Exploring the sub-salt play in the frontier Amadeus Basin - Insights from regional 2D seismic and potential field data

Early exploration of the frontier Amadeus Basin in the Northern Territory has been limited due to its size and remoteness, along with complexity of structuring and limited early success. The primary exploration targets of the southern Amadeus are the sub-salt and intra-salt plays of the Neoproterozoic lower Gillen-Heavitree petroleum system. Two wells have tested the sub-salt play, both flowing gas with high helium content, confirming the sealing capacity of the Gillen evaporates despite two significant orogenic events.In 2013, the first regional framework of 2D seismic was acquired over the southern Amadeus. In areas where seismic coverage is sparse, or of poor quality due to halotectonics, higher spatial density magnetic and gravity surveys have been used to interpolate trends between seismic and well control and create a high resolution depth-to-basement model. Alternate methods of seismic processing have also been trialled to improve sub-salt imaging.The newly acquired seismic and depth-to-basement model are revealing the architecture of the basin and provide a regional perspective of the sub-salt and intra-salt plays. With improved seismic imaging large sub-salt structures are emerging beneath the complex folds resulting from thin-skinned deformation.Learnings from the challenges associated with acquisition and processing, along with a better understanding of the complex halotectonics, will have significant implications for future exploration in the region.

On the age of Galactic bulge microlensed dwarf and subgiant stars

Recent results by Bensby and collaborators on the ages of microlensed stars in the Galactic bulge have challenged the picture of an exclusively old stellar population. However, these age estimates have not been independently confirmed. In this paper we verify these results by means of a grid-based method and quantify the systematic biases that might be induced by some assumptions adopted to compute stellar models. We explore the impact of increasing the initial helium abundance, neglecting the element microscopic diffusion, and changing the mixing-length calibration in theoretical stellar track computations. We adopt the SCEPtER pipeline with a novel stellar model grid for metallicities [Fe/H] from -2.00 to 0.55 dex, and masses in the range [0.60; 1.60] Msun from the ZAMS to the helium flash at the red giant branch tip. We show for the considered evolutionary phases that our technique provides unbiased age estimates. Our age results are in good agreement with Bensby and collaborators findings and show 16 stars younger than 5 Gyr and 28 younger than 9 Gyr over a sample of 58. The effect of a helium enhancement as large as Delta Y/Delta Z = 5 is quite modest, resulting in a mean age increase of metal rich stars of 0.6 Gyr. Even simultaneously adopting a high helium content and the upper values of age estimates, there is evidence of 4 stars younger than 5 Gyr and 15 younger than 9 Gyr. For stars younger than 5 Gyr, the use of stellar models computed by neglecting microscopic diffusion or by assuming a super-solar mixing-length value leads to a mean increase in the age estimates of about 0.4 Gyr and 0.5 Gyr respectively. Even considering the upper values for the age estimates, there are four stars estimated younger than 5 Gyr is in both cases. Thus, the assessment of a sizeable fraction of young stars among the microlensed sample in the Galactic bulge appears robust.

Feasibility of high-helium natural gas exploration in the Presinian strata, Sichuan Basin

Helium in China highly depends on import at present, so the most practical way to change the situation is searching for medium-to-large natural gas fields with high helium content. Therefore, the hydrocarbon accumulation mechanism and the helium origin of the Weiyuan high-helium natural gas reservoir have been analyzed to find out the feasibility of finding natural gas field with high helium content in the Presinian strata of the Sichuan Basin. Based on twelve outcrop sections and drilling data of four wells encountering the Presinian strata, the petrological features, sedimentary facies and source rocks of Presinian strata were systematically analyzed, which shows that the sedimentary formation developed in the Presinian is the Nanhua system, and the stratigraphic sequence revealed by outcrop section in the eastern margin includes the Nantuo, Datangpo, Gucheng and Liantuo Fms, and it is inferred that the same stratigraphic sequence may occur inside the basin. The Nantuo, Gucheng and Liantuo Fms are mainly glacial deposits of glutenite interbedded with mudstone; the Datangpo Fm is interglacial deposits of sandstone and shale, the lower part shale, rich in organic matter, is fairly good source rock. Further study showed that the Nantuo coarse-grained clastic reservoir, Datangpo source rock and the intruded granite “helium source rock” make up a good high-helium gas system. Controlled by the early rift, the thick Presinian sedimentary rocks occur primarily inside the rift. The distribution of sedimentary rocks and granite in the basin was predicted by use of the seismic data, which shows that the feasibility of finding high-helium gas reservoirs in Ziyang area of the Sichuan Basin is great.

Theoretical Study on the Structure and Properties of Helium-Containing Zirconium Hydrides

The structure and properties of CaF2-type δ structure of helium-containing zirconium hydrides were investigated using density functional theory. The properties of this material vary with hydrogen and helium concentrations. Hydrogen has a significant effect on the behavior of helium. The occupied sites of He atoms strongly depend on the hydrogen concentration. The structures and formation mechanisms of helium clusters vary with hydrogen concentration at a high helium content. The embedding energies of He atoms mainly result from interactions between helium and zirconium atoms. However, H-He interactions significantly contribute to the embedding energies. Variations in lattice volume expansion and bulk modulus were also investigated.

Deuterium retention in the carbon co-deposition layers deposited by magnetron sputtering in D2/He atmosphere

Carbon was deposited on Si and W substrates using a D2/He plasma in a radio frequency magnetron sputtering system. The deposited layers were examined with ion beam analysis (IBA), Raman spectra analysis (RS) and scanning electron microscopy (SEM). The growth rate of the layers deposited at 2.5Pa total pressure and 300K decreased with increasing He fraction in the D2/He gas mixture. The deuterium concentration in the layers deposited on the Si substrate increased from 14% to 28% when the flow rate of the He gas relative to the D2 gas was varied from 0.125 to 0.5, but the deuterium concentration in the layers on a W substrate decreased from 24% to 14%. Deuterium or helium retention and the layer thickness all significantly decreased when the substrate temperature was increased from 423K to 773K. Raman analysis showed that the deposited layers were amorphous deuterated-carbon layers (named a-C: D layer) and the extent of bond disorder increased dramatically with the increasing helium content in the film. Blisters and bubbles occurred in the films for high helium content in the films, and surface cracking and exfoliation were also observed.

DOUBLE HORIZONTAL BRANCHES IN NGC 6440 AND NGC 6569 UNVEILED BY THE VVV SURVEY

We report the discovery of a peculiar horizontal branch (HB) in NGC 6440 and NGC 6569, two massive and metal-rich Galactic globular clusters (GGCs) located in the Galactic bulge, within 4 kpc from the Galactic Center. In both clusters, two distinct clumps are detected at the level of the cluster HB, separated by only ~ 0.1 magnitudes in the Ks band. They were detected with IR photometric data collected with the "VISTA Variables in the Via Lactea" (VVV) Survey, and confirmed in independent IR catalogs available in the literature, and HST optical photometry. Our analysis demonstrates that these clumps are real cluster features, not a product of field contamination or interstellar reddening. The observed split HBs could be a signature of two stellar sub-populations with different chemical composition and/or age, as recently found in Terzan 5, but it cannot be excluded that they are caused by evolutionary effects, in particular for NGC 6440. This interpretation, however, requires an anomalously high helium content (Y > 0.30). Our discovery suggests that such a peculiar HB morphology could be a common feature of massive, metal-rich bulge GGCs.

Surface Blistering and Flaking of Sintered Uranium Dioxide Samples under High Dose Gas Implantation and Annealing

High helium contents will be generated within minor actinide doped uranium dioxide blankets which could be used in fourth generation reactors. In this framework, it is essential to improve our understanding of the type of damage which a pellet could incur as a result of extensive helium build-up. This paper is an attempt at tackling this issue. Sintered uranium dioxide disks have been implanted with helium ions then annealed at various temperatures. Above a concentration of 0.4 at.% and above 1000°C, optical images of the sample surface revealed swollen grains and extensive areas which have exfoliated. Nuclear reaction microanalyses and atomic force microscopy observations were performed to demonstrate that helium has substantially precipitated within the swollen grains. Massive precipitation of the gas leads under these conditions to sample surface blistering which appears to precede flaking. Deuterium ion irradiations have also been performed at ambient and a direct flaking of the sample surface was observed, but for this phenomenon to be observed required much higher doses than in the He study, indicating that temperature could be an essential ingredient for gas to migrate and cause extensive precipitation. Such phenomena could possibly lead to degradation of the fuel.

Noble gas isotopes in corundum and peridotite xenoliths from the eastern North China Craton: Implication for comprehensive refertilization of lithospheric mantle

Noble gas isotopic ratios provide unique and important constraints for the evolution of the subcontinental mantle. We present one-step crushing noble gas isotope data from corundum and co-existing mantle xenoliths and megacrystals from the Changle volcanic fields in the middle part of the Tan-Lu Fault Zone, eastern North China Craton. The 3He/ 4He ratio is 7.6–8.3 times the atmospheric ratio (Ra) in corundum, indicating contributions of fluids from convective asthenosphere. The 3He/ 4He ratio in titanomagnetite megacrystals ranges from 5.8 to 6.5 Ra, suggesting possible U–Th contamination in the crystal lattice, with the 3He/ 4He ratio of host magma being higher than 6.5 Ra. The olivine and opx in lherzolite show high helium contents and homogeneous isotopic helium ratios (6.9–7.0 Ra). The cpx in wehrlite show significantly higher helium contents and slightly higher helium ratio (7.6 Ra) than co-existing olivine (7.0–7.5 Ra). Combined with isotope correlation diagrams, the systematic difference in 4He abundance, the 3He/ 4He and 4He/ 40Ar ∗ ratios of cpx, opx and olivine in pyroxenite, lherzolite and wehrlite suggest comprehensive refertilization of lithospheric mantle in the eastern North China Craton.

X-SHOOTER OBSERVATIONS OF MAIN-SEQUENCE STARS IN THE GLOBULAR CLUSTER NGC 2808: FIRST CHEMICAL TAGGING OF A He-NORMAL AND A He-RICH DWARF

We present the first chemical composition study of two unevolved stars in the globular cluster NGC 2808, obtained with the spectrograph X-shooter@VLT. NGC 2808 shows three discrete, well separated main sequences. The most accepted explanation for this phenomenon is that their stars have different helium contents. We observed one star on the bluest main sequence, (bMS, claimed to have high helium content, Y~0.4), and one on the reddest main sequence (rMS, consistent with a canonical helium content, Y=0.245). We analyzed features of NH, CH, Na, Mg, Al, and Fe. While Fe, Ca, and other elements have the same abundances in the two stars, the bMS star shows a huge enhancement of N, a depletion of C, an enhancement of Na and Al, and small depletion of Mg with respect to the rMS star. This is exactly what is expected if stars on the bMS formed from the ejecta produced by an earlier stellar generation in the complete CNO and MgAl cycles whose main product is helium. The elemental abundance pattern differences in these two stars are consistent with the differences in helium content suggested by the color-magnitude diagram positions of the stars.