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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Current Practices in Distribution Utility Resilience Planning for Winter Storms

This report is part of a series of hazard-focused case studies examining common practices in electric utility resilience planning. We use standard terminology defining resilience as the ability to anticipate, withstand, absorb, and recover from hazards that cause long duration outages. We distinguish between reliability and resilience using Institute of Electrical and Electronics Engineers (IEEE) 1366-2022, which defines major events as an event that exceeds reasonable design and/or operational limits of the electric power system. Resilience planning is focused on major event days and reliability planning is focused on nonmajor event days. Utility resilience plans are assessed according to common resilience components identified in existing resilience frameworks. The focus of this report is on winter storms in which the primary hazards are heavy snowfall, freezing rain, ice, extreme cold, severe wind, and flooding. These hazards can also contribute to generation shortages, resulting in bulk power system impacts that have consequences for the distribution system, such as load shedding. Stand-alone reports focusing on wildfires and nonwinter storms have been published in parallel with this report. This report can be used as a starting point for understanding potential investment prioritization processes and investment options. This report is intended to improve utility resilience planning by supporting constructive dialogue among utilities, regulators, and other stakeholders.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1994

Coronal temperature, density, and magnetic field maps of a solar acitve region using the Owens Valley Solar Array

We present the first results of solar active region observations with the recently completed five-element Owens Valley Solar Array. On 1991 October 24, maps of Active Region AR 6891 were obtained at 22 frequencies from 1.2-7.0 GHz to provide brightness temperature spectra at each point. This is the first time that both high spatial and frequency-resolution brightness temperature spectra have been available over such a broad radio-frequency range. We find that over most of the region the spectra fall into one of the two well-defined categories: thermal free-free or thermal gyroresonance. In these cases, we use the spectra to deduce the spatial variation of physical parameters-electron temperature, column emission measure (intergral n(sup 2)(sub e) dl), and the coronal magnetic field strength-in and around the active region. Over a limited area of the region, the spectra resemble neither of the simple types, and alternative interpretations are required. The possibilties include the presence of fine structure that is unresolved at low frequencies; the presence of a small number of nonthermal electrons; or the presence of overlying, cooler 10(exp 6) K material which at low frequencies absorbs the hot (3 x 10(exp 6) K) thermal emission generated below.

Gary, Dale E.↗
DOE OSTI2020

Test of the Dynamic-Domain and Critical Scattering Hypotheses in Cubic Methylammonium Lead Triiodide

We investigate the hypothesis of dynamic tetragonal domains occurring in cubic CH 3 NH 3 PbI 3 using high-resolution neutron spectroscopy to study a fully deuterated single crystal. The R-point scattering above the 327.5 K cubic-tetragonal phase transition is always resolution limited in energy and therefore inconsistent with dynamic-domain predictions. This behavior is instead consistent with the central peak phenomenon observed in other perovskites. Here, the scattering may originate from small, static, tetragonal-phase domains nucleating about crystal defects, and the temperature dependence demonstrates the transition is first order.

14 SOLAR ENERGY↗
NASA NTRS2012

Fabrication of a Kilopixel Array of Superconducting Microcalorimeters with Microstripline Wiring

A document describes the fabrication of a two-dimensional microcalorimeter array that uses microstrip wiring and integrated heat sinking to enable use of high-performance pixel designs at kilopixel scales (32 X 32). Each pixel is the high-resolution design employed in small-array test devices, which consist of a Mo/Au TES (transition edge sensor) on a silicon nitride membrane and an electroplated Bi/Au absorber. The pixel pitch within the array is 300 microns, where absorbers 290 microns on a side are cantilevered over a silicon support grid with 100-micron-wide beams. The high-density wiring and heat sinking are both carried by the silicon beams to the edge of the array. All pixels are wired out to the array edge. ECR (electron cyclotron resonance) oxide underlayer is deposited underneath the sensor layer. The sensor (TES) layer consists of a superconducting underlayer and a normal metal top layer. If the sensor is deposited at high temperature, the ECR oxide can be vacuum annealed to improve film smoothness and etch characteristics. This process is designed to recover high-resolution, single-pixel x-ray microcalorimeter performance within arrays of arbitrarily large format. The critical current limiting parts of the circuit are designed to have simple interfaces that can be independently verified. The lead-to-TES interface is entirely determined in a single layer that has multiple points of interface to maximize critical current. The lead rails that overlap the TES sensor element contact both the superconducting underlayer and the TES normal metal

Chervenak, James↗
NASA NTRS2010

Effect of Anatomical Modeling on Space Radiation Dose Estimates: A Comparison of Doses for NASA Phantoms and 5th, 50th, and 95th Percentile UF Hybrid Phantoms

The estimate of absorbed dose to individual organs of a space crewmember is affected by the geometry of the anatomical model of the astronaut used in the radiation transport calculation. For astronaut dosimetry, NASA currently uses the computerized anatomical male (CAM) and computerized anatomical female (CAF) stylized phantoms to represent astronauts in its operational radiation dose analyses. These phantoms are available in one size and in two body positions. In contrast, the UF Hybrid Adult Male and Female (UFHADM and UFHADF) phantoms have organ shapes based on actual CT data. The surfaces of these phantoms are defined by non-uniform rational B-spline surfaces, and are thus flexible in terms of body morphometry and extremity positioning. In this study, UFHADM and UFHADF are scaled to dimensions corresponding to 5th, 50th, and 95th percentile (PCTL) male and female astronauts. A ray-tracing program is written in Visual Basic 2008, which is then used to create areal density maps for dose points corresponding to various organs within the phantoms. The areal density maps, along with appropriate space radiation spectra, are input into the NASA program couplet HZETRN/BRYNTRN, and organ doses are calculated. The areal density maps selected tissues and organs of the 5th, 50th, and 95th PCTL male and female phantoms are presented and compared. In addition, the organ doses for the 5th, 50th, and 95th PCTL male and female phantoms are presented and compared to organ doses for CAM and CAF.

Bahadori, A.↗
DOE OSTI2021

Undersizing of aged African biomass burning aerosol by an ultra-high-sensitivity aerosol spectrometer

The ultra-high-sensitivity aerosol spectrometer (UHSAS) differs from most other optical particle spectrometers by using a high-power infrared (IR) laser to detect small particles and reduce the sizing ambiguity due to the non-monotonicity of scattering with particle size. During the NASA ORACLES project (ObseRvations of Aerosols above CLouds and their intEractionS) over the southeast Atlantic Ocean, the UHSAS clearly undersized particles in the biomass burning plume extending from southern Africa. Since the horizontal and vertical extent of the plume was vast, the NASA P-3B research aircraft often flew through a fairly uniform biomass burning plume for periods exceeding 30 min, sufficient time to explore the details of the UHSAS response by selecting single particle sizes with a differential mobility analyzer (DMA) and passing them to the UHSAS. This was essentially an in-flight calibration of the UHSAS using the particles of interest. Two modes of responses appeared. Most particles were undersized by moderate amounts, ranging from not at all for 70 nm aerosols to 15 % for 280 nm particles. Mie scattering calculations show that composition-dependent refractive index of the particles cannot explain the pattern. Heating of brown carbon or tarballs in the beam causing evaporation and shrinking of the particles is the most plausible explanation, though mis-sizing due to non-sphericity cannot be ruled out. A small fraction (10 %–30 %) of the particles were undersized by 25 % to 35 %. Those were apparently the particles containing refractory black carbon. Laboratory calibrations confirm that black carbon is drastically undersized by the UHSAS, because particles heat to their vaporization point and shrink. A simple empirical correction equation was implemented that dramatically improves agreement with DMA distributions between 100 and 500 nm. It raised the median particle diameter by 18 nm, from 163 to 181 nm, during the August 2017 deployment and by smaller amounts during deployments with less intense pollution. Calculated scattering from UHSAS size distributions increased by about 130 %, dramatically improving agreement with scattering measured by nephelometers. The correction is only valid in polluted instances; clean marine boundary layer and free troposphere aerosols behaved more like the calibration spheres. We were unable to directly test the correction between 500 and 1000 nm, though aerodynamic particle sizer (APS) data appear to show that the correction is poor at the largest diameters, which is no surprise as the composition of those particles is likely to be quite different than that of the accumulation mode. This adds to the evidence that UHSAS data must be treated cautiously whenever the aerosol may absorb infrared light. Similar corrections may be required whenever brown carbon aerosol is present.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Experimental validation of an organic rankine-vapor compression cooling cycle using low GWP refrigerant R1234ze(E)

There is a significant global opportunity to capture and utilize low grade waste heat to reduce fossil fuel consumption, greenhouse gas emissions, and improve energy efficiency across a wide range of industries. In this work, an advanced type of thermally activated cooling system, an organic Rankine-vapor compression cycle (ORVC) with novel heat integration strategies, was designed and tested at a relevant scale for industrial waste heat recovery (300 kW th cooling capacity). The ORVC linked an organic Rankine power cycle and a vapor compression cooling cycle using a turbine and compressor that shared a single shaft. The ORVC test facility absorbed waste heat from a liquid stream at 91 °C to simulate engine coolant in diesel generator sets, rejected heat to a glycol stream at 30 °C, and generated chilled water at 7 °C. A cooling capacity of 264 kW ± 3.5 kW was experimentally validated with a COP of 0.56 ± 0.01 during steady-state operation at the design temperatures. The thermal efficiency, accounting for pump work, of the Rankine cycle was 7.7% ± 0.22% and the COP of the vapor compression cycle was 5.25 ± 0.09. The centrifugal turbo-compressor operated at 31.5 kRPM ± 0.3 kRPM, with a turbine and compressor isentropic efficiencies of 76.7% ± 0.90% and 84.8% ± 0.54%, respectively, with near-perfect power transmission between these components. The pressure drop in the piping and heat exchangers were significantly larger than expected which had a detrimental impact on the performance of the ORVC. In addition, the condenser on the cooling cycle could not deliver the subcooling as specified from the design point modeling. Furthermore, the results from the sensitivity analysis showed that the higher condenser glycol outlet temperature had the largest impact on performance, which is consistent with other analytical models in the literature. When the ORVC simulations were updated with experimental values for isentropic efficiencies of the turbomachinery, the thermal COP was 0.66 which represents an estimate of the predicted performance if test facility limitations are overcome.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Optical properties of Mo and amorphous MoOx, and application to antireflection coatings for metals

To form antireflection (AR) coatings to hide metal architecture in display technologies, we deposited thin films of metal Mo and oxide MoOx by sputtering targets of various compositions using pure Ar sputter gas. The optical constants [n,k] of these samples were measured by the direct numerical solution of reflectance and transmittance at each wavelength point measured. We find that 50 nm films are uniform in the growth direction, but for thicker 100 nm samples, evidence exists for nonuniform growth, where the top 20 nm appears to be metal rich. From these [n,k], negative Tauc bandgap energies show these oxides are semi-metals. We then identified the specific composition (x) that optimizes the AR response for a host of metals (Al, Cu, Ag, Au). Finally, two methods were used to understand why these MoOx materials function well as AR media, including (i) using phasor rays and (ii) developing a universal expression for the AR condition that applies to both dielectric and metal substrates. In (i), we find two characteristics for AR of metals: (a) its optical thickness should be roughly π3, not the π2 for dielectrics, since for MoOx, their [r^ij,t^ij] Fresnel phases differ from the usual [180°, 0°] of dielectrics; and (b) the medium incorporates a k-dominant strategy whose function is to absorb the energy that is reflected at the AR/metal interface. In (ii), the universal AR condition is found to be r^01+r^12z^=0. For dielectrics, this reduces to the well-known nAR=nairnsub condition. However, for metals, a concise analytic expression is lacking since this expression is highly nonlinear but is easily solved by numerical methods.

Tsu, David V. (ORCID:0000000295903418)↗
NASA NTRS2005

Seeing Red and Shooting Blanks: Study of Red Quasars and Blank X-Ray Sources

A major paper describing the technique and providing a list of 'blanks' was published in the Astrophysical Journal (abstract below). The results revealed a fascinating trove of novel X-ray sources: high redshift clusters of galaxies found efficiently; X-ray absorbed, optically clean AGN, which may be the bright prototypes of Chandra Deep Survey sources; and several with a still unknown nature. Recent XMM-Newton results confirm the existence of this class of X-ray source with much refined positions. During the first year of this project we have made a major discovery. The second 'blanks' X-ray source observed with Chandra was found to be extended. Using Chandra data and ground-based R and K band imaging we estimated this to be a high redshift cluster of galaxies with z approx. 0.85. Spectroscopy agrees with this estimate (z=0.89). This success shows that our method of hunting down 'blank' field X-ray sources is a highly efficient method of finding the otherwise elusive high redshift clusters. With extensive follow-up we should be able to use 'blanks' to make cosmological tests. The paper is now in press in the Astrophysical Journal (abstract below.) The other Chandra source is point-like, showing that there are a variety of 'blank' source types. Other follow-up observations with XMM-Newton, and (newly approved in cycle 2) with Chandra are eagerly awaited. A follow-up paper uses a large amount of supporting data for the remaining blanks. A combination of ROSAT, Chandra and ground based data convincingly identified one of the blanks as a Ultra-luminous X-ray source (ULX) in a spiral galaxy (abstract below). This program resulted in 3 refereed papers in major journals, 4 conference proceedings and a significant fraction of the PhD thesis of Dr. Ilaria Cagnoni. Details of the publications are given.

Oliversen, Ronald↗
DOE OSTI2022

Gamma Spectrometry Code Rodeo for Uranium Enrichment—FY 2021 Report

In FY22, the participating Department of Energy (DOE) laboratories continued the work on the project “Gamma Spectrometry Code Rodeo for Uranium Enrichment”. Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) continued their efforts to acquire spectra using uranium sources. A collimator (with side and back shields) was custom designed and constructed at ORNL. Spectra were acquired at ORNL using the uranium enrichment standards supplied by New Brunswick Laboratory (NBL) and the collimated M400 detector. Spectra were also acquired using steel absorbers of different thickness placed between the source and the collimated M400 detector. The plan was to ship the collimator to LLNL so that spectra could be acquired using the LLNL detector in collimated geometries. This activity was suspended since problems were noticed with the performance of the LLNL M400 detector. Also, it was brought to light to the project team that some of the aspects of the M400 detector had been updated by the vendor H3D in response to requests by the IAEA. In February 2021, the ORNL and LLNL M400 detectors were returned to the H3D factory in order to resolve the problems with the LLNL detector and to update ORNL and LLNL detectors to the same configuration as the M400 supplied to the IAEA. H3D repaired the LLNL M400 and performed the IAEA updates on both the ORNL and LLNL detectors. ORNL and LLNL received the detectors in April 2021. Data acquisition was continued using the upgraded detectors. ORNL re-collected the spectra using point sources and the NBL standards in uncollimated and collimated geometries. The collimator was shipped from ORNL to LLNL. Spectra were acquired at LLNL through Q4 of FY22. When the ORNL spectra were examined closely, it became apparent that there were spurious artifacts present in some of the spectra. This rendered suspect the ORNL spectra collected in June/July 2021 time frame. ORNL contacted H3D and per H3D’s advice, the M400 detector was returned to H3D for repairs in mid-August 2021. H3D diagnosed the problem and established that the root cause was the extra tight packaging that created a strain on the CZT crystals, causing one of them to break down. The repaired M400 was returned to ORNL in early September 2021. ORNL re-started data acquisition for the third time. Data was continued to be acquired at ORNL and LLNL through September 2021. The ORNL and LLNL data will be shared with the principal investigators from the analyzing laboratories. The GADRAS code and FRAM have been developed to have the capability to analyze the M400 spectra. Good quality spectra from FY21 have been analyzed using modified versions of GADRAS and FRAM. The spectra have also been analyzed using the GEM code. The analysis results from GADRAS, FRAM and GEM codes are presented and discussed in this report. Some preliminary results from FRAM and GEM analysis were presented in February 2021 at the U-Pu Isotopics Workshop sponsored by the IAEA. CZTU code is being modified to analyze M400 spectra. Data collection, code development and analysis will be continued in FY22 as per the FY22 Project Work Plan (PWP).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Investigating the Impact of Absorbed Surface Impurities (CO, CO 2 , CH 4 , and H 2 O) on Getter Rate Performance

This report provides an overview of engineering and experimental efforts to establish a new capability for measuring H2 uptake rates for Tritium Producing Abosrber Rod (TPBAR) getter materials. This new system was used to gain a better understanding of the impact of contaminant species (CO 2 , CO, CH 4 , and H 2 O) on getter performance under relevant hydrogen uptake conditions (350 °C, 20 torr). Herein, we successfully established a high-resolution gravimetric sorption (HRGS) system in a flow through configuration that can measure sample mass changes with high resolution (1 µg or 10 µg) over long experiment times (days), high temperature, and varying pressures. We coupled this capability with an in-line universal gas analyzer (UGA) system to characterize potential surface chemistry side reactions occurring after contaminant gas exposure. The major findings of this study suggest that methane and CO have the most detrimental effects on getter H 2 uptake performance showing large changes in rate after exposure compared to CO 2 and water. The effect of these contaminant species did not influence getter sample capacity (~ 1.8 wt% H 2 ). After CO and methane exposure, changes in getter rate were accompanied by observable Ni-surface defects and pinholes via SEM imaging suggesting possible Ni- layer corrosion. Additionally, the increase in C and O signal in the zircaloy layer, observed via EDX, point to C and O species transport through the getter sample resulting in the formation of carbides and oxide species. Thus, co-exposure studies where mixed gases or water vapor are introduced together will be important to further understand what mechanisms are contributing to Ni-layer corrosion and changes in getter performance.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Solar Thermal Propulsion Improvements at Marshall Space Flight Center

Solar Thermal Propulsion (STP) is a concept which operates by transferring solar energy to a propellant, which thermally expands through a nozzle. The specific impulse performance is about twice that of chemical combustions engines, since there is no need for an oxidizer. In orbit, an inflatable concentrator mirror captures sunlight and focuses it inside an engine absorber cavity/heat exchanger, which then heats the propellant. The primary application of STP is with upperstages taking payloads from low earth orbit to geosynchronous earth orbit or earth escape velocities. STP engines are made of high temperature materials since heat exchanger operation requires temperatures greater than 2500K. Refractory metals such as tungsten and rhenium have been examined. The materials must also be compatible with hot hydrogen propellant. MSFC has three different engine designs, made of different refractory metal materials ready to test. Future engines will be made of high temperature carbide materials, which can withstand temperatures greater than 3000K, hot hydrogen, and provide higher performance. A specific impulse greater than 1000 seconds greatly reduces the amount of required propellant. A special 1 OkW solar ground test facility was made at MSFC to test various STP engine designs. The heliostat mirror, with dual-axis gear drive, tracks and reflects sunlight to the 18 ft. diameter concentrator mirror. The concentrator then focuses sunlight through a vacuum chamber window to a small focal point inside the STP engine. The facility closely simulates how the STP engine would function in orbit. The flux intensity at the focal point is equivalent to the intensity at a distance of 7 solar radii from the sun.

Gerrish, Harold P.↗
NASA NTRS2015

Comparison and Validation of FLUKA and HZETRN as Tools for Investigating the Secondary Neutron Production in Large Space Vehicles

NASA's exploration goals are focused on deep space travel and Mars surface operations. To accomplish these goals, large structures will be necessary to transport crew and logistics in the initial stages, and NASA will need to keep the crew and the vehicle safe during transport and any surface activities. One of the major challenges of deep space travel is the space radiation environment and its impacts on the crew, the electronics, and the vehicle materials. The primary radiation from the sun (solar particle events) and from outside the solar system (galactic cosmic rays) interact with materials of the vehicle. These interactions lead to some of the primary radiation being absorbed, being modified, or producing secondary radiation (primarily neutrons). With all vehicles, the high energy primary radiation is of most concern. However, with larger vehicles that have large shielding masses, there is more opportunity for secondary radiation production, and this secondary radiation can be significant enough to cause concern. When considering surface operations, there is also a secondary radiation source from the surface of the planet, known as albedo, with neutrons being one of the most significant species. Given new vehicle designs for deep space and Mars missions, the secondary radiation environment and the implications of that environment is currently not well understood. Thus, several studies are necessary to fill the knowledge gaps of this secondary radiation environment. In this paper, we put forth the initial steps to increasing our understanding of neutron production from large vehicles by comparing the neutron production resulting from our radiation transport codes and providing a preliminary validation of our results against flight data. This paper will review the details of these results and discuss the finer points of the analysis.

Rojdev, Kristina↗
DOE OSTI2021

Evaluation of riverbed magnetic susceptibility for mapping biogeochemical hot spots in groundwater‐impacted rivers

Abstract Redox hot spots occurring as metal‐rich anoxic groundwater discharges through oxic wetland and river sediments commonly result in the formation of iron (Fe) oxide precipitates. These redox‐sensitive precipitates influence the release of nutrients and metals to surface water and can act as ‘contaminant sponges’ by absorbing toxic compounds. We explore the feasibility of a non‐invasive, high‐resolution magnetic susceptibility (MS) technique to efficiently map the spatial variations of magnetic Fe oxide precipitates in the shallow bed of three rivers impacted by anoxic groundwater discharge. Laboratory analyses on Mashpee River (MA, USA) sediments demonstrate the sensitivity of MS to sediment Fe concentrations. Field surveys in the Mashpee and Quashnet rivers (MA, USA) reveal several discrete high MS zones, which are associated with likely anoxic groundwater discharge as evaluated by riverbed temperature, vertical head gradient, and groundwater chemistry measurements. In the East River (CO, USA), widespread cobbles/rocks exhibit high background MS from geological ferrimagnetic minerals, thereby obscuring the relatively small enhancement of MS from groundwater induced Fe oxide precipitates. Our study suggests that, in settings with low geological sources of magnetic minerals such as lowland rivers and wetlands, MS may serve as a complementary tool to temperature methods for efficiently mapping Fe oxide accumulation zones due to anoxic groundwater discharges that may function as biogeochemical hot spots and water quality control points in gaining systems.

Wang, Chen↗
DOE OSTI2026

Optimization of Annealing for WZ-Phase Removal and Densification in Sb-Doped CdSexTe1-x Solar Cells

The impact of high temperature annealing (HTA) treatments on the performance of Sb-doped CdSeTe solar cells containing a CdSe0.25Te0.75/CdTe front stack and a vapor transport (VT) deposited CdTe:Sb absorber was studied. The HTA treatment of the thermally evaporated CdSe0.25Te0.75/CdTe front stack converts the mixed-phase film into a single zinc blende structure through recrystallization of the photo-inactive wurtzite phase. Subsequently, HTA treatment of the full device stack after vapor transport deposition of CdTe:Sb absorber promotes Se-Te intermixing, reduces voids, densifies the full stack and enhances CdTe:Sb grain growth. Comprehensive characterizations revealed that the combined HTA treatments significantly improved film crystallinity, removed the WZ phase in the front stack, enhanced full-stack densification, reduced defect densities, and enhanced carrier dynamics. With HTA treatments, the open-circuit voltage (VOC) of CdSeTe:Sb devices increased from ~ 400 mV to >= 600 mV, and when combined with optimized CdCl2 treatment, VOC reached 849 mV. The net carrier concentrations (NA-ND) of representative devices were NA-ND = 1.5 x 10^15, 1.1 x 10^15, and 3.5 x 10^14 cm-3 for the no-HTA, moderate-HTA, and optimized high-VOC conditions, respectively. Since the highest VOC corresponds to the lowest apparent NA-ND, , which is similar to a Cu-doped-only CdSeTe solar cell (NA-ND ~= 2 x 10^14 cm-3), the data indicate that improved device performance does not result from increased electrically active Sb; instead, it points to structural improvement as the dominant effect of HTA. The findings demonstrate the potential of HTA treatments to improve the structural and electrical properties of CdSeXTe1-X solar cells.

14 SOLAR ENERGY↗
DOE OSTI2025

Band Gap Engineering and Metastable Phase Discovery in Cu 2 BaSnS 4– x Se x Nanocrystals via Topotactic Anion Exchange

Earth-abundant multinary inorganic chalcogenides, such as Cu 2 BaSnS 4–x Se x (CBTSSe), have emerged as promising absorbers for next-generation solar cells. However, accessing colloidal CBTSSe nanocrystals, including metastable polymorphs with more favorable optoelectronic properties, remains a critical synthetic challenge. Herein, we report the first use of topotactic anion exchange to access metastable crystal structures in soft chemistry syntheses. By varying the stoichiometry of selenium precursors, we directly synthesize Cu 2 BaSnS 4–x Se x (0 ≤ x ≤ 4) nanocrystals with a broad band gap tunability of 1.51–2.04 eV. At x = 4, a new metastable trigonal phase of Cu 2 BaSnSe 4 is isolated. This phase arises via an in-situ topotactic anion exchange from sulfur-rich Cu 2 BaSnS 4–x Se x intermediates, while retaining both the cation sublattice and overall nanocrystal morphology. The trigonal Cu 2 BaSnSe 4 exhibits a nearly direct band gap that is 280 meV lower than its thermodynamically stable orthorhombic counterpart, aligning more closely with the optimal band gap for single-junction solar cells. In contrast, a post-synthetic anion exchange route leads to the thermodynamically preferred orthorhombic polymorph, pointing to the critical nature of the in-situ transformation. Our findings open a versatile pathway for both polymorphic and morphological control in colloidal nanocrystals, expanding the synthetic design space for new optoelectronic materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Sulfur speciation in dacitic melts using X-ray absorption near-edge structure spectroscopy of the S K -edge (S-XANES): Consideration of radiation-induced changes and the implications for sulfur in natural arc systems

Abstract The synchrotron technique of micro X-ray absorption near-edge structure spectroscopy at the sulfur K-edge (S-XANES) provides a unique opportunity to measure the proportion of different oxidation states of sulfur (S) in silicate glasses. Although applied extensively in the analysis of basaltic silicate glasses, few S-XANES studies have investigated variations in S oxidation states with fO2 in felsic silicate glasses. In addition, no study has systematically compared the S-XANES results obtained from the same samples at different photon flux densities to quantify the relationship between exposure time and changes in S speciation in silicate glass, as has been done for Fe and V. This study evaluates observed differences in S speciation measured in experimentally produced H2O-saturated dacitic glasses over a range of reducing to oxidizing conditions (from log fO2 = ΔFMQ-0.7 to ΔFMQ+3.3; FMQ is the fayalite-magnetite-quartz mineral redox buffer) and equilibrated at 1000 °C and 300 MPa. S-XANES spectra were collected at three different photon flux densities using three microspectroscopy beamlines. As is observed in S-XANES analyses of basaltic silicate glasses, beam-induced changes to the S6+/ΣS are observed as a function of photon flux density and beam exposure time. Our results demonstrate that silicate glasses of dacitic composition undergo beam-induced photo-reduction in samples equilibrated at ΔFMQ > +1.75 and photo-oxidation if equilibrated at ΔFMQ < +1. The time required to observe beam-induced changes in the spectra varies as a function of flux density, and our study establishes an upper photon density limit at ~1.0 × 1012 photons/µm2. The S6+/ΣS calculated from spectra collected below this absorbed photon limit at intermediate flux densities (~1–4 × 109 photons/s per µm2) are affected by beam damage, as no conditions were found to be completely free of beam-induced changes. However, the S6+/ΣS ratios calculated below the limit at intermediate flux densities are consistent with thermodynamic constraints, demonstrating that S6+/ΣS ratios calculated from S-XANES spectra can be considered reliable for estimating the oxygen fugacity. Our results carry important implications for the S budget of felsic magmas and dissolution mechanisms in evolved melts. While our results from all three flux densities show the presence of S4+ dissolved in relatively oxidized (ΔFMQ > +1.75) dacitic glass, even in the spectra exposed to the lowest photon densities, we are unable to rule out the possibility that the S4+ signal is the result of instantaneous X-ray irradiation induced beam damage using S-XANES alone. When our spectra are compared to S-XANES spectra from basaltic silicate glasses, important differences exist in the solubility of S2– and S6+ between dacitic silicate melts, pointing to differences in solubility mechanisms as melt composition changes. This study highlights the need for further investigation into beam damage systematics, presence of S4+, and the solubility mechanisms of different oxidation states of S as silicate melt composition changes.

Geochemistry & Geophysics↗
DOE OSTI2021

Technical Documents for Gateway for Accelerated Innovation in Nuclear (GAIN)

The Gateway for Accelerated Innovation in Nuclear (GAIN) provides the nuclear energy community with access to the technical, regulatory, and financial support necessary to move new or advanced nuclear reactor designs toward commercialization. GAIN provides the nuclear community with a single point of access to the broad range of capabilities (i.e., people, facilities, materials, and data) across the U.S. Department of Energy (DOE) complex and its National Lab capabilities. The Fast Flux Test Facility (FFTF) is the most recent liquid metal reactor (LMR) to be designed, constructed, and operated by DOE. The 400-MWt sodium-cooled, fast-neutron flux reactor plant was designed for irradiation testing of nuclear reactor fuels and materials for liquid metal fast breeder reactors. Following the demise of the breeder reactor program in the United States, FFTF continued to play a key role in providing a test bed for demonstrating performance of advanced fuel designs and demonstrating operation, maintenance, and safety of advanced liquid metal reactors. The FFTF Program provides valuable information for potential follow-on reactor projects in the areas of plant system and component design, component fabrication, fuel design and performance, reactor control, prototype testing, and site construction. This report provides documents related to three important aspects of FFTF design and operation: 1) irradiation behavior of structural alloys and absorber materials, 2) thermohydraulics of rod bundles (i.e., coolant mixing), and 3) natural circulation heat transfer in the areas of modeling and validation. These technical documents are believed to be of interest to the nuclear industry and in particular to designers of new liquid metal reactors.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗