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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Technetium and iodine aqueous species immobilization and transformations in the presence of strong reductants and calcite-forming solutions: Remedial action implications

At the Hanford Site in southeastern Washington State, radionuclide (Tc-99/I-129) laden liquid wastes have been discharged to ground, resulting in vadose zone contamination, which provides a continuous source of these contaminants to groundwater. The presence of multiple contaminants increases the complexity of finding viable remediation technologies to sequester vadose zone contaminants in situ and protect groundwater. Although previous studies have shown the efficiency of zero valent iron (ZVI) and sulfur modified iron (SMI) in reducing mobile Tc(VII) to immobile Tc(IV) and iodate incorporation into calcite, the coupled effects from simultaneously using these remedial technologies have not been previously studied. In this first-of-a-kind laboratory study, we used two efficient reductants (i.e., ZVI and SMI) and calcite-forming solutions to simultaneously remove aqueous Tc(VII) and iodate via reduction and incorporation, respectively. The results confirmed that Tc(VII) was rapidly removed from the aqueous phase via reduction to Tc(IV). ZVI removed Tc(VII) faster than SMI, although both had removed the same amount by the end of the experiments. Most of the aqueous iodate was rapidly transformed to iodide, and therefore was not incorporated into calcite, but instead remained in the aqueous phase. The iodate reduction to iodide was much faster than iodate incorporation into calcite, suggesting that this remedial pathway is not efficient in removing aqueous iodate when strong reductants are present. Other experiments suggested that iodate removal via calcite precipitation should occur first and then reductants should be added for Tc(VII) removal. Although ZVI can negatively impact microbial populations and thereby inhibit natural attenuation mechanisms, only changes in the makeup of the microbial community were observed. However, these changes in the microbial community may have an impact on remediation efforts in the long term that could not be seen in a short-term study. The results underscore the importance of identifying interactions between natural attenuation pathways and remediation technologies that only target individual contaminants.

Keywords: Tc removal, groundwater remediation, nuc↗
DOE OSTI2014

Highly Textured Tin(II) Sulfide Thin Films Formed from Sheetlike Nanocrystal Inks

Highly textured tin(II) sulfide thin films are prepared from a nanocrystal ink comprised of high-aspect-ratio nanosheets. The orthorhombic nanosheets are synthesized colloidally to isolate lateral growth and minimize the presence of alternate crystal phases. The tin sulfide films deposited from the nanosheets exhibit pure elemental composition, micrometer-sized grains, and a remarkable degree of texturing. The films consist of lamellar stacking of nanosheets with some intercalation, and the average sheet thickness is ~30 nm. The SnS films have an indirect band gap of 1.23 eV, and density functional theory calculations indicate minimal quantum confinement contributions. The anisotropic electronic properties of tin sulfide are greatly intensified in films formed by this process, yielding an in-plane mobility of 5.7 cm 2 /(V s) but an out-of-plane resistivity as high as 30 kΩ cm. This work represents a new strategy for nanocrystal inks in which the nanocrystal morphology is tailored to direct film orientation, grain size, and transport properties. The method provides a route for the deposition of high-quality, layered semiconductor thin films with applications in photovoltaics and two-dimensional (2-D) electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

{sup 13}C ISOTOPIC FRACTIONATION OF HC{sub 3}N IN STAR-FORMING REGIONS: LOW-MASS STAR-FORMING REGION L1527 AND HIGH-MASS STAR-FORMING REGION G28.28-0.36

We observed the J = 9–8 and 10–9 rotational lines of three {sup 13}C isotopologues of HC{sub 3}N in L1527 and G28.28-0.36, with the 45 m radio telescope of the Nobeyama Radio Observatory, in order to constrain the main formation mechanisms of HC{sub 3}N in each source. The abundance ratios of the three {sup 13}C isotopologues of HC{sub 3}N are found to be 0.9 (±0.2) : 1.00 : 1.29 (±0.19) (1 σ ), and 1.0 (±0.2) : 1.00 : 1.47 (±0.17) (1 σ ), for [H{sup 13}CCCN : HC{sup 13}CCN : HCC{sup 13}CN] in L1527 and G28.28-0.36, respectively. We recognize, from a similar {sup 13}C isotopic fractionation pattern, that the abundances of H{sup 13}CCCN and HC{sup 13}CCN are comparable, and HCC{sup 13}CN is more abundant than the others. Based on the results, we discuss the main formation pathway of HC{sub 3}N. The {sup 13}C isotopic fractionation pattern derived from our observations can be explained by the neutral-neutral reaction between C{sub 2}H{sub 2} and CN in both the low-mass (L1527) and high-mass (G28.28-0.36) star-forming regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Use of Grid-Forming Medium-Voltage Power Electronics Hub in a Microgrid Setting

This paper presents the application of a new design of a multiport, modular, medium-voltage power electronics hub (M3PE-HUB) in a microgrid setting. The M3PE-HUB system was modeled in a digital real-time simulator (DRTS) and integrated into the Banshee microgrid test system. This paper presents the preliminary DRTS simulation-based results of the M3PE-HUB system connected in a test microgrid system. Verification and validation of the M3PE-HUB architecture and controls in the test microgrid setting are the primary contributions of this work. The results of the operation during the islanding and resynchronization process indicate the feasibility of the proposed architecture in a microgrid setting. This paper also presents results for a system reconfiguration use case where the M3PE-HUB was used to reconfigure the system under a fault condition.

grid forming↗
DOE OSTI2017

Glass binder development for a glass-bonded sodalite ceramic waste form

This paper discusses work to develop Na2O-B2O3-SiO2 glass binders for immobilizing LiCl-KCl eutectic salt waste in a glass-bonded sodalite waste form following electrochemical reprocessing of used metallic nuclear fuel. Here, five new glasses with high Na2O contents were designed to generate waste forms having higher sodalite contents and fewer stress fractures. The structural, mechanical, and thermal properties of the new glasses were measured using variety of analytical techniques. The glasses were then used to produce ceramic waste forms with surrogate salt waste. The materials made using the glasses developed during this study were formulated to generate more sodalite than materials made with previous baseline glasses used. The coefficients of thermal expansion for the glass phase in the glass-bonded sodalite waste forms made with the new binder glasses were closer to the sodalite phase in the critical temperature region near and below the glass transition temperature. These improvements should result in lower probability of cracking in the full-scale monolithic ceramic waste form, leading to better long-term chemical durability. Additionally, a model generated during this study for predicting softening temperature of silicate binder glasses is presented.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

The proton form factor measurements at Jefferson Lab, past and future

Use of the double-polarization technique to obtain the elastic nucleon form factors has resulted in a dramatic improvement of the quality of two of the four nucleon electromagnetic form factors, G{sub Ep} and G{sub En}. It has also changed our understanding of the proton structure, having resulted in a distinctly different Q{sup 2}-dependence for both G{sub Ep} and G{sub Mp}, contradicting the prevailing wisdom of the 1990’s based on cross section measurements, namely that G{sub Ep} and G{sub Mp} obey a “scaling” relation μG{sub Ep} ∼ G{sub Mp}. A related consequence of the faster decrease of G{sub Ep} revealed by the Jefferson Lab (JLab) polarization results was the disappearance of the early scaling F{sub 2}/F{sub 1} ∼ 1/Q{sup 2} predicted by perturbative QCD. In three experiments, GEp(1), GEp(2) and GEp(3), in Halls A and C at JLab, the ratio of the proton’s electromagnetic elastic form factors, G{sub Ep}/G{sub Mp}, was measured up to four momentum transfer Q{sup 2} of 8.5 GeV{sup 2} with high precision, using the recoil polarization technique. The initial discovery that the proton form factor ratio measured in these three experiments decreases approximately linearly with four-momentum transfer, Q{sup 2}, for values above ∼ 1 GeV{sup 2}, was modified by the GEp(3) results, which suggests a slowing down of this decrease. There is an approved experiment, GEp(5), to continue these measurements to 15 GeV{sup 2}. A dedicated experimental setup, the super bigbite spectrometer (SBS), will be built for this purpose. It will be equipped with a new focal plane polarimeter to measure the polarization of the recoil protons. In this presentation, I will review the status of the proton elastic electromagnetic form factors, mention succinctly a number of theoretical approaches to describe results and show some features required for the future GEp(5) experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Clean measurements of the nucleon axial-vector and free-neutron magnetic form factors

We discuss the feasibility of a weak charged current experiment using a low energy electron beam. A first goal is to measure the Q{sup 2} dependence of the axial-vector form factor g{sub a}(Q{sup 2}). It can be measured model-independently and as robustly as for electromagnetic form factors from typical electron scattering experiments, in contrast to the methods used so far to measure g{sub a}(Q{sup 2}). If g{sub a}(Q{sup 2}) follows a dipole form, the axial mass can be extracted with a better accuracy than the world data altogether. The most important detection equipment would be a segmented neutron detector with good momentum and angular resolution that is symmetric about the beam direction, and covers a moderate angular range. A high intensity beam (100 uA) is necessary. Beam polarization is highly desirable as it provides a clean measurement of the backgrounds. Beam energies between 70 and 110 MeV are ideal. This range would provide a Q{sup 2} mapping of g{sub a} between 0.01 <Q{sup 2}< 0.04 GeV{sup 2}. 60 days of beam can yield 14 data points with a subpercent statistical and point to point uncorrelated uncertainties on each point. Such an experiment may also allow to measure the free-neutron magnetic form factor G{sub M}{sup n}. The experiment employs the usual techniques of electron-nucleon scattering and presents no special difficulty. Higher energy extensions are possible. They could yield measurements of g{sub a}(Q{sup 2}) up to Q{sup 2}=3 GeV{sup 2} and the possibility to access other form factors, such as the almost unknown pseudoscalar form factor g{sub P}. However, the experiments become much more challenging as soon as beam energies pass the pion production threshold.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Optical flashes from internal pairs formed in gamma-ray burst afterglows

We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts (R<10) lasting for up to one hundred seconds. The number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The evolution of the fractions of quiescent and star-forming galaxies as a function of stellar mass since z = 3: increasing importance of massive, dusty star-forming galaxies in the early universe

Using the UltraVISTA DR1 and 3D-HST catalogs, we construct a stellar-mass-complete sample, unique for its combination of surveyed volume and depth, to study the evolution of the fractions of quiescent galaxies, moderately unobscured star-forming galaxies, and dusty star-forming galaxies as a function of stellar mass over the redshift interval 0.2 ≤ z ≤ 3.0. We show that the role of dusty star-forming galaxies within the overall galaxy population becomes more important with increasing stellar mass and grows rapidly with increasing redshift. Specifically, dusty star-forming galaxies dominate the galaxy population with log(M{sub star}/M{sub ⊙})≳10.3 at z ≳ 2. The ratio of dusty and non-dusty star-forming galaxies as a function of stellar mass changes little with redshift. Dusty star-forming galaxies dominate the star-forming population at log(M{sub star}/M{sub ⊙})≳10.0--10.5, being a factor of ∼3–5 more common, while unobscured star-forming galaxies dominate at log(M{sub star}/M{sub ⊙})≲10. At log(M{sub star}/M{sub ⊙})>10.5, red galaxies dominate the galaxy population at all redshift z < 3, either because they are quiescent (at late times) or dusty star-forming (in the early universe).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Densified waste form and method for forming

Materials and methods of making densified waste forms for temperature sensitive waste material, such as nuclear waste, formed with low temperature processing using metallic powder that forms the matrix that encapsulates the temperature sensitive waste material. The densified waste form includes a temperature sensitive waste material in a physically densified matrix, the matrix is a compacted metallic powder. The method for forming the densified waste form includes mixing a metallic powder and a temperature sensitive waste material to form a waste form precursor. The waste form precursor is compacted with sufficient pressure to densify the waste precursor and encapsulate the temperature sensitive waste material in a physically densified matrix.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Densified waste form and method for forming

Materials and methods of making densified waste forms for temperature sensitive waste material, such as nuclear waste, formed with low temperature processing using metallic powder that forms the matrix that encapsulates the temperature sensitive waste material. The densified waste form includes a temperature sensitive waste material in a physically densified matrix, the matrix is a compacted metallic powder. The method for forming the densified waste form includes mixing a metallic powder and a temperature sensitive waste material to form a waste form precursor. The waste form precursor is compacted with sufficient pressure to densify the waste precursor and encapsulate the temperature sensitive waste material in a physically densified matrix.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Epsilon Metal: A Waste Form for Noble Metals from Used Nuclear Fuel

Epsilon metal (e-metal) is the metallic phase that forms as inclusions at the grain boundaries in the UO2 fuel during reactor operation. This metal is composed of Pd, Mo, Rh, Ru, and Tc. These metallic inclusions are insoluble in strong acid and remnants of these metallic inclusions have been found in the UO2 matrix that remains from the natural reactors in Gabon that were active 1.8 billion years ago, therefore e-metal should be an excellent waste form for the immobilization of the long-lived isotopes 107Pd (6.5 ? 106 a) and 99Tc (2.13 ? 105 a), with 99Tc being the isotope of interest for repository performance. Therefore, the chemical durability of this potential waste form is assessed in this study. Typically, corrosion rates for metallic materials are measured electrochemically because they are quick, inexpensive, and can reveal the mechanism by which a metal corrodes, at least initially. However, in a repository the waste form would be subjected to slowly flowing water without an applied electrical potential over long time periods. Therefore, the corrosion rates of e-metal specimens were measured with both electrochemical tests and the single-pass flow-through test (SPFT). Potentiodynamic and potentiostatic polarization results suggest that a thin passive film exists on the alloy surface, which seems to be responsible for its high corrosion resistance. Additionally, X-Ray photoelectron spectroscopic results suggest that Pd oxides are significantly enriched in the passive film Results from the SPFT show that the dissolution rates were weakly dependent on pH. Only Mo and Re were found in solution and were used for the calculation of the dissolution rates. In general, the electrochemically determined corrosion rates agree reasonably well with the initial dissolution rate measured with the SPFT test, but they are about one or two orders of magnitude higher than the steady state rates. The causes for this discrepancy are discussed.

epsilon-metal, nuclear waste form, corrosion, sing↗