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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enabling high resolution strain mapping in zirconium alloys

Highlights: • Optimisation of speckle patterns suitable for high resolution digital image correlation in a zirconium alloy • Evidence of distinct strain patterning at the macro and micro scale • Analysis of strain heterogeneity in a neighbouring low and high strain band • Paved the way for future studies on strain localization in zirconium alloys subjected to hydriding and irradiation damage - Abstract: High Resolution Digital Image Correlation (HRDIC) has been established recently as a novel displacement mapping technique during mechanical loading experiments to quantify strain localisation down to the level of individual slip traces. This is achieved by the creation of a nano-scale gold pattern naturally formed during remodelling of a thin gold layer that was sputtered onto the region of interest. To date, the gold remodelling is carried out in a water vapourisation environment, which excludes the technique to be applied to materials that readily form noticeable oxide layers in such environments. The current paper describes a recently developed gold remodelling technique using a styrene-argon environment at substantially lower temperatures than the water-vapour based technique. The material used in the present work is a zirconium alloy where we first demonstrate the problem of oxide formation during remodelling in water vapour and the benefit of the modified remodelling procedure. The error associated with the spatial drift was assessed for different interrogation window sizes followed by detailed analysis of the subsequent strain maps produced using the styrene remodelled patterns after tensile deformation to nominal applied strains of ~3.5% and ~7.0%. The level of detail captured demonstrate the suitability of styrene-argon-based remodelling for materials like Zr alloys with the strain maps showing clear strain patterning on both a transgranular and single grain scale with the possibility of quantifying strain across a single slip trace.

36 MATERIALS SCIENCE↗
DOE OSTI2025

GMFOLD: Subgraph matching for high-throughput DNA-aptamer secondary structure classification and machine learning interpretability

Aptamers are oligonucleotide receptors that bind to their targets with high affinity. Here, we consider aptamers comprised of single-stranded DNA that undergo target-binding-induced conformational changes, giving rise to unique secondary and tertiary structures. Given a specific aptamer primary sequence, there are well-established computational tools (notably mfold) to predict the secondary structure via free energy minimization algorithms. While mfold generates secondary structures for individual sequences, there is a need for a high-throughput process whereby thousands of DNA structures can be predicted in real-time for use in an interactive setting, when combined with aptamer selections that generate candidate pools that are too large to be experimentally interrogated. We developed a new Python code for high-throughput aptamer secondary structure determination (GMfold). GMfold uses subgraph matching methods to group aptamer candidates by secondary structure similarities. We also improve an open-source code, SeqFold, to incorporate subgraph matching concepts. We represent each secondary structure as a lowest-energy bipartite subgraph matching of the DNA graph to itself. These new tools enable thousands of DNA sequences to be compared based on their secondary structures, using machine-learning algorithms. This process is advantageous when analyzing sequences that arise from aptamer selections via systematic evolution of ligands by exponential enrichment (SELEX). This work is a building block for future machine-learning-informed DNA-aptamer selection processes to identify aptamers with improved target affinity and selectivity and advance aptamer biosensors and therapeutics.

Aptamer↗
DOE OSTI2020

Atomic scale understanding of organic anion separations using ion-exchange resins

A combination of ab initio and classical molecular dynamic simulations was used to explore the adsorption/desorption and diffusion characteristics of ion-exchange resins for extraction of organic anions in electrically-driven separation processes. We considered two classes of carboxylate mixtures that are commonly encountered in bioprocessing separations: a short chain fatty acid mixture (acetate/butyrate) and an aromatic mixture (ferulate/coumarate). The suitability of several resin materials including PFC100E, IRC86, PFA444 and IRA67 was interrogated. The decomposition of the interaction energies by the symmetry-adapted perturbation theory and the classical molecular dynamic simulations of organic diffusion together reveal that the geometries of the organic anions and the functional groups of the resins, as well as their Columbic interactions, are the controlling factors in the diffusion process of the organic compounds in these resins. Additionally, classical simulations also show that modifying the functionality of resin beads, the magnitude of electric fields, and the ratio of organic mixtures may provide an effective way to control the diffusion rate and obtain selective separation of these organic mixtures. Finally, a general suggestion for favorable separation conditions is summarized.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microbial metaproteomics: Identifying the repertoire of proteins that microorganisms use to compete and cooperate in complex environmental communities

The availability of genome information for microbial consortia, including unculturable species, from environmental samples has enabled systems-biology interrogation by providing a means to access genomic, transcriptomic, and proteomic information. This provides a unique opportunity to characterize the molecular activities and interactions of these microbial systems at a comprehensive level never before possible. Such information not only provides details about the organizational, functional, and metabolic activities of such systems, but also the untapped reserve of molecular activities that might be invoked and exploited under certain environmental conditions. Since bacteria naturally exist in complex ecosystems, it is imperative to develop and utilize analytical approaches that can provide molecular level details on systems consisting of mixed microbial membership. This is the realm of metaproteomics - the characterization of the complement of proteins expressed by a microbial community in an environmental sample

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Uncultivated thermophiles: current status and spotlight on ‘Aigarchaeota’

Meta-analysis of cultivation-independent sequence data shows that geothermal systems host an abundance of novel organisms, representing a vast unexplored phylogenetic and functional diversity among yet-uncultivated thermophiles. There are a number of thermophiles that were recently interrogated using metagenomic and/or single-cell genomic approaches, including members of taxonomic groups that inhabit both thermal and non-thermal environments, such as 'Acetothermia' (OP1) and 'Atribacteria' (OP9/JS1), as well as the exclusively thermophilic lineages 'Korarchaeota', 'Calescamantes' (EM19), 'Fervidibacteria' (OctSpA1-106), and 'Aigarchaeota' (HWCG-I). The 'Aigarchaeota', a sister lineage to the Thaumarchaeota, likely includes both hyperthermophiles and moderate thermophiles. Furthermore, they inhabit terrestrial, marine, and subsurface thermal environments and comprise at least nine genus-level lineages, several of which are globally distributed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Evolutionary relationships among shell proteins of carboxysomes and metabolosomes

Bacterial microcompartments (BMCs) are self-assembling prokaryotic organelles which encapsulate enzymes within a polyhedral protein shell. Additionally, the shells are comprised of only two structural modules, distinct domains that form pentagonal and hexagonal building blocks, which occupy the vertices and facets, respectively. As all BMC loci encode at least one hexamer-forming and one pentamer-forming protein, the evolutionary history of BMCs can be interrogated from the perspective of their shells. Here, we discuss how structures of intact shells and detailed phylogenies of their building blocks from a recent phylogenomic survey distinguish families of these domains and reveal clade-specific structural features. These features suggest distinct functional roles that recur across diverse BMCs. For example, it is clear that carboxysomes independently arose twice from metabolosomes, yet the principles of shell assembly are remarkably conserved.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Biaxial deformation in high purity aluminum

The convergence of multiple characterization tools has been applied to investigate the relationship of microstructure on damage evolution in high purity aluminum. The extremely coarse grain size of the disc-shaped sample provided a quasi-two dimensional structure from which the location of surface-measured features could be inferred. In particular, the role of pre-existing defects on damage growth was accessible due to the presence of casting porosity in the aluminum. Micro tomography, electron backscatter diffraction, and digital image correlation were applied to interrogate the sample in three dimensions. Recently micro-bulge testing apparatus was used to deform the pre-characterized disc of aluminum in biaxial tension, and related analysis techniques were applied to map local strain fields. Subsequent post-mortem characterization of the failed sample was performed to correlate structure to damaged regions. We determined that strain localization and associated damage was most strongly correlated with grain boundary intersections and plastic anisotropy gradients between grains. Pre-existing voids played less of an apparent role than was perhaps initially expected. Finally, these combined techniques provide insight to the mechanism of damage initiation, propagation, and failure, along with a test bed for predictive damage models incorporating anisotropic microstructural effects.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High-throughput experimentation for microstructural design in additively manufactured 316L stainless steel

In the present study, a combination of high-throughput (HT) and low-throughput (LT) techniques was used to rapidly determine the processing window and generate processing maps for Selective Laser Melting (SLM) of 316L stainless steel. The HT method includes the fabrication of hundreds of hex nut-shaped specimens, each processed with a unique combination of laser power, scanning speed, and hatch spacing. An easily removable scaffolding permitted rapid sample extraction from the base plate, thus saving machining cost and time. Hardness and immersion density measurements were used for HT characterization to identify a processing window for maximum strength and density. Within the defined processing window, a low-throughput (LT) microstructural interrogation of specimens were performed. The microstructural analysis included quantification at various length scales (i.e., grains size and morphology, texture, primary dendrite arm spacing, and melt pool geometry analysis). Microstructure-based processing maps as a function of volumetric energy density were generated. The combination of HT and LT methods produced a predictive relationship between hardness and primary dendrite arm spacing using a Hall-Petch relationship. A model is proposed to explain the dependence of microstructure on the melt pool geometry. Here, the HT method can be applied for the microstructural design of SLM-fabricated components in other alloys.

316L stainless steel↗
DOE OSTI2026

Conceptual design study of neutron detectors for safeguards measurement of an irradiated pebble

Nuclear material control and accounting (MC&A) of pebble-bed reactors (PBRs) is challenging because a PBR utilizes hundreds of thousands of identical, unmarked pebbles that are continuously recirculated through the core. To develop tools that enable the implementation of international safeguards, especially in the context of MC&A of spent pebbles, we designed and simulated three neutron detection concepts to determine fissile content in individual pebbles: a differential die-away (DDA) detector, a californium interrogation prompt neutron (CIPN) detector, and a passive neutron albedo reactivity (PNAR) detector using Monte Carlo calculations. Burnup calculations were performed on the spent pebbles from the PBMR-400 classic PBR. The varying neutron and gamma source terms, and isotopic compositions in the spent pebbles calculated at various burnup levels were used in the neutron detector models. DDA was found to be sensitive to the number of passes a pebble has had through the core and to the fissile content contained in a spent pebble. Optimization in the DDA design further increased the neutron count rates and thus reduced counting uncertainty. Meanwhile, passive neutron counting using the same detector body could distinguish pebbles with different numbers of passes, but its response was dominated by neutron-emitting actinides and was not sensitive to fissile content. On the other hand, the PNAR technique was not viable for a single pebble but performed reasonably for a 27-pebble array, which suggested potential use for verification measurements of containers filled with 27 or more spent pebbles.

CIPN↗
DOE OSTI2026

Enhancers that direct gene expression to central nervous system vascular endothelial cells in vivo

CNS vascular endothelial cells (ECs) exhibit a distinctive gene expression program that is foundational for the blood-brain barrier (BBB). Previous research identified candidate cis-regulatory elements (CREs) that were hypothesized to control this program. In this work, transgenic mice and recombinant adeno-associated virus (rAAV) vectors have been used to interrogate these candidate CREs in vivo. These experiments show that an 850 bp genomic DNA segment ∼60 kb 5′ of Slc2a1 possesses enhancer activity that is (1) specific for BBB+ CNS ECs and (2) both necessary and sufficient for BBB+ EC gene expression. A screen of >8,000 genomic DNA segments from CNS EC-specific CRE candidates reveals several hundred with enhancer activity. Transcription factors ERG and LEF1 are shown to occupy sites in brain ECs that are highly enriched in candidate and experimentally validated CREs, lending strong support to a model in which canonical Wnt signaling activates the BBB program via LEF1.

CUT&RUN↗
DOE OSTI2016

Experimental verification of a method to create a variable energy neutron beam from a monoenergetic, isotropic source using neutron elastic scatter and time of flight

An experiment was performed to determine the neutron energy of near-monoergetic deuterium–deu-terium (D–D) neutrons that elastically scatter in a hydrogenous target. The experiment used two liquid scintillators to perform time of flight (TOF) measurements to determine neutron energy, with the start detector also serving as the scatter target. The stop detector was placed 1.0 m away and at scatter angles of π/6, π/4, and π/3 rad, and 1.5 m at a scatter angle of π/4 rad. When discrete 1 ns increments were implemented, the TOF peaks had estimated errors between 21.2 and 3.6% relative to their expected locations. Full widths at half-maximum (FWHM) ranged between 9.6 and 20.9 ns, or approximately 0.56–0.66 MeV. Monte Carlo simulations were also conducted that approximated the experimental setup and had both D–D and deuterium–tritium (DT) neutrons. The simulated results had errors between -17.2 and 0.0% relative to their expected TOF peaks when 1 ns increments were applied. The largest D–D and D–T FWHMs were 26.7 and 13.7 ns, or approximately 0.85 and 4.98 MeV, respectively. These values, however, can be reduced through manipulation of the dimensions of the system components. Lastly, the results encourage further study of the neutron elastic scatter TOF system with particular interest in application to active neutron interrogation to search for conventional explosives.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Improved lithium iodide neutron scintillator with Eu 2+ activation: The elimination of Suzuki-Phase precipitates

Monovalent alkali halides such as NaI, CsI, and LiI are widely used as inorganic scintillators for radiation detection due to their light yield, the capability for the growth of large single crystals, relatively low cost, and other favorable characteristics. These materials are frequently activated through the addition of small amounts (e.g., a few hundred ppm) of elements such as thallium - or sodium in the case of CsI. The monovalent alkali halide scintillators can also be activated with low concentrations of Eu 2+ , however Eu activation has previously not been widely employed due to the non-uniform segregation of the divalent Eu dopant that leads to the formation of unwanted phases during Bridgman or other solidification crystal-growth methods. Specifically, for Eu concentrations near and above ~0.5%, Suzuki Phase precipitates form in the course of the melt-growth process, and these Suzuki Phase particles scatter the scintillation light. This adversely affects the scintillator performance via reduction in the optical transmission of the material, and depending on the crystal thickness and precipitated-particle concentration, this reduction can occur up to the point of opacity. Here we describe a post-growth process for the removal of Suzuki Phase precipitates from single crystals of the neutron scintillator LiI activated with Eu 2+ at concentrations up to and in excess of 3 wt.%, and we correlate the resulting neutron-detection performance with the thermal processing methods used to remove the Suzuki Phase particles. Furthermore, the resulting improved scintillator properties using increased Eu activator levels are applicable to neutron imaging and active interrogation systems, and pulse-height gamma-ray spectroscopy rather than pulse-shape discrimination can be used to discriminate between gamma ray and neutron interaction events.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Estimating the Effective System Dead Time Parameter for Correlated Neutron Counting

We present that neutron time correlation analysis is one of the main technical nuclear safeguards techniques used to verify declarations of, or to independently assay, special nuclear materials. Quantitative information is generally extracted from the neutron-event pulse train, collected from moderated assemblies of 3 He proportional counters, in the form of correlated count rates that are derived from event-triggered coincidence gates. These count rates, most commonly referred to as singles, doubles and triples rates etc., when extracted using shift-register autocorrelation logic, are related to the reduced factorial moments of the time correlated clusters of neutrons emerging from the measurement items. Correcting these various rates for dead time losses has received considerable attention recently. The dead time losses for the higher moments in particular, and especially for large mass (high rate and highly multiplying) items, can be significant. Consequently, even in thoughtfully designed systems, accurate dead time treatments are needed if biased mass determinations are to be avoided. In support of this effort, in this paper we discuss a new approach to experimentally estimate the effective system dead time of neutron coincidence counting systems. It involves counting a random neutron source (e.g. AmLi is a good approximation to a source without correlated emission) and relating the second and higher moments of the neutron number distribution recorded in random triggered interrogation coincidence gates to the effective value of dead time parameter. We develop the theoretical basis of the method and apply it to the Oak Ridge Large Volume Active Well Coincidence Counter using sealed AmLi radionuclide neutron sources and standard multiplicity shift register electronics. The method is simple to apply compared to the predominant present approach which involves using a set of 252 Cf sources of wide emission rate, it gives excellent precision in a conveniently short time, and it yields consistent results as a function of the order of the moment used to extract the dead time parameter. In addition, this latter observation is reassuring in that it suggests the assumptions underpinning the theoretical analysis are fit for practical application purposes. However, we found that the effective dead time parameter obtained is not constant, as might be expected for a parameter that in the dead time model is characteristic of the detector system, but rather, varies systematically with gate width.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2018

Low-cost, multi-mode detector solutions

Low-cost radiation detectors capable of providing efficient gamma-ray and neutron detection are essential in passive nuclear monitoring systems such as radiation portal monitors (RPMs) and detection of Special Nuclear Materials (SNM) through Active Interrogation (AI). Here, three low-cost detector solutions are discussed—(1) Large-area polystyrene-based plastic scintillators for AI (2) Pulse Shape Discrimination (PSD) capable plastic scintillators doped with heavy-metals for imparting gamma-ray spectroscopy (3) Composite detector technology based on inorganic scintillator submerged into the plastic scintillator, for detection of thermal and fast neutrons in addition to gamma-ray spectroscopy. Composite detectors using inorganic component such as Cs 2 LiYCl 6 (CLYC), Cs 2 LiLaBr x Cl 6-x (CLLBC), or CsI:Tl have been developed up to 4” sizes. Neutron and gamma efficiencies are compared for samples with different inorganic loading.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Nondestructive measurements of residual 235 U mass of Israeli Research Reactor-1 fuel using the Advanced Experimental Fuel Counter

In 2018, a measurement campaign took place with participants from Los Alamos National Laboratory (LANL), the Nuclear Research Centre-Negev (NRCN) and Soreq Nuclear Research Center (SNRC) at the Israeli Research Reactor-1 (IRR-1) in which 14 of the reactor’s used fuel assemblies (FAs) with varied amount of depletion were measured with the nondestructive assay instrument Advanced Experimental Fuel Counter (AEFC). Designed for safeguards purposes, the AEFC measures both neutrons emitted from the FA (passive neutrons) and fission neutrons induced by an external neutron source (in this experiment, 252 Cf). Signals recorded with the AEFC include total neutron count rates (Singles), time-correlated neutron count rates (Doubles), and total gamma-ray count rates. The 235 U content of the FAs was previously assessed by two independent methods: (1) measurement of the transparency of the FA to low-energy gamma rays from an activated rhenium source (rhenium gamma transmission, or the RGT method) and (2) calculation of the 30-year burnup history of the core using detailed three-dimensional Monte-Carlo core depletion calculations. The results from the FAs that had been measured via the RGT method were used to construct the calibration curves, which translate the AEFC count rates to 235 U mass. Then, the calibration was evaluated using AEFC measurements of six additional FAs that were not measured via the RGT method. From the results, it was determined the Doubles calibration curve was more reliable than that of the Singles and follows a simple second-order polynomial fit for the whole range of residual 235 U mass content, albeit with larger statistical uncertainty. Detailed uncertainties quantification was conducted for both the AEFC Singles and Doubles. This includes the analysis of statistical uncertainties, calibration uncertainty, and random uncertainties due to the sensitivity of the AEFC to several sources of uncertainty, namely the FA position, FA orientation, interrogation source position, and ambient pool temperature. Finally, an overall total uncertainty of 6 g of 235 U is estimated for the Singles and Doubles, which is mainly due to calibration uncertainty (for the Singles) and statistical uncertainty (for the Doubles), and which constitutes 3%–6% of the 235 U total mass in the FAs, depending on their level of depletion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Configuration and impurity quantification of AmLi sources using radiography and gamma spectroscopy

This paper presents the non-destructive assay of two AmLi sources used for detector characterization and active interrogation at PNNL, identified as MRC-101 and MRC-103. First, a detailed description of the internal configuration of 2724-BT encapsulated MRC sources is established. X-ray radiographs of the AmLi sources are reported for the first time to verify the dimensions and orientation of the encapsulation. Notably, a density variation was observed as a contrast change across the height of the source cavities. Contrary to commonly made assumptions in literature, it is indirectly observed that the AmLi source/target material only occupies a portion of the source cavity. The intensity of the prompt gamma-rays resulting from the inelastic scatter of alpha particles on 7Li was used to calculate the mass ratios of LiH:AmO2. The gamma-ray spectra revealed the presence of numerous impurities in both source and target material (243Am, 237Np, 154Eu, 23Na, and 9Be). Neutron-gamma production ratios were applied to the intensity of the Doppler-broadened peaks from alpha-induced reactions with 7Li, 9Be, and 23Na to calculate neutron rates for both sources. A neutron/alpha production yield (derived in this work) was then related to the atomic concentration of these isotopes to find the approximate masses within each source. Ultimately, the AmLi source density was estimated with prompt gamma analysis based on partial source volumes as 0.45±0.08 g/cm^3.

DTRA, AmLi, neutron↗
DOE OSTI2021

Sensitivity of the active neutron coincidence collar response during simulated and experimental fresh fuel assay

Verification of the fissile (and fertile) content in fresh nuclear fuel assemblies is conducted by the IAEA to enforce the Nuclear Non-Proliferation Treaty using the UNCL (Uranium Neutron Collar — Light Water Reactor Fuel). The UNCL uses an uncorrelated AmLi neutron source to interrogate the fuel, producing a signal of coincident fission neutrons (Doubles rate) used to assay 235 U content of the fuel. The cost of producing calibration assemblies and limited availability of diverse commercial assemblies at any one time historically restricted the ability to explore the full parameter space experimentally. Monte Carlo simulations can overcome this, but introduce additional sources of uncertainty. In this work, the sensitivity of simulations and measurements to various parameters is assessed for a reference 1616 PWR assembly of uniform 3.2% enrichment. Uncertainty contributions in this evaluation include: simulated AmLi neutron source spectrum, AmLi neutron emission rate, AmLi anisotropicity, high density polyethylene (HDPE) density, the precise position of the fuel assembly within the detector, and experimentally the statistical uncertainty. The overall total systematic uncertainty estimate for the simulation of the absolute/relative Doubles rates responses are estimated to be approximately 2.0%/1.5%, and for experimental measurements systematic uncertainty reduces to 1.1%. This analysis supports further work using the relative Doubles rates in place of measurements for updating and extending the UNCL analysis methodology as systematic uncertainty is reasonably small.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Evaluation of gamma-ray transmission through rectangular collimator slits for application in nuclear fuel spectrometry

Gamma-ray spectrometry is widely applied in several science fields, and in particular in non-destructive gamma scanning and gamma emission tomography of irradiated nuclear fuel. Usually, a collimator is used in the experimental setup, to selectively interrogate a region of interest in the fuel. For the optimization of instrument design, as well as for planning measurement campaigns, predictive models for the transmitted gamma-ray intensity through the collimator are needed. Commonly, Monte Carlo Radiation Transport tools are used for accurate prediction of gamma-ray transport, however, the long computation time requirements when used in low-efficiency experimental setups present challenges. Here, the full-energy peak intensity transmitted through a rectangular collimator slit was examined. A uniform planar surface source emitting isotropically was considered, and the rate of photons reaching an ideal counter plane on the opposite side of the collimator was evaluated by analytical integration. To find a closed-form primitive function, some idealizations were required, and thereby parametric models were obtained for the optical field of view, dependent on slit dimensions (length, height and width) and source-to-collimator distance. For contributions from outside the optical field of view, where a closed-form expression cannot be found, fast numerical integral methods were instead used. The results were validated using the Monte Carlo code MCNP6 and show an agreement within three percent for the numerical method. For the analytical method, deviations up to tens of percent were obtained, which is deemed to still be sufficient for instrument design and measurement planning, where often the order of magnitude of the count rate is not a priori known. The method is planned for use in iterative optimization routines in the design of Gamma Emission Tomography devices, as well as for the prediction of gamma spectra obtained in the planning of fuel inspections. An application of the proposed method was demonstrated in spectrum prediction for a short cooling-time fuel rod test from the Halden reactor.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗