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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Design of the Fifth-Generation Target-Moderator-Reflector-Shield Assembly

The facilities at the Los Alamos Neutron Science Center are described first. The target is being redesigned so that the Flight Paths (FP) in the upper tier provide a higher intensity in the epithermal and medium energy range. It is found that a 3-piece design looks promising: intensity in epithermal and medium energy range in upper tier is an order of magnitude higher than current Mark III, and intensity in the thermal energy range is higher in the lower tier than current Mark III. Time emission spectra show a bump due to the scattering of fast neutrons. Other investigations such as the addition of wings around the upper target will be conducted.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Energy Efficiency Financing for Low- and Moderate-Income Households: Current State of the Market, Issues, and Opportunities

Although the need is great, many LMI households may not be able to afford efficiency improvements or may be inhibited from adopting efficiency for other reasons. Decision-makers across the country are currently exploring the challenges and potential solutions to ramping up adoption of efficiency in LMI households, including the use of financing.

energy efficiency↗
DOE OSTI2018

Criticality Safety Evaluation for 700 and 350 Gram Moderated Fissionable Equivalent (MFE) Criticality Control Areas (CCAs)

This evaluation is intended to generically apply to facilities and/or areas designated as CCAs that store and/or handle greater than 15 grams of fissionable material but no more than 700 grams of MFE. This evaluation includes facilities and/or areas designated as CCAs limited to no more than 350 grams of MFE. Activities performed in these CCAs may include general laboratory activities to include work in radiological areas, chemical procurement, material handling, sampling, imaging, non-destructive analysis, and disposing of nuclear and radiological materials. Materials included in these activities may include radioactive-contaminated oil, polychlorinated biphenyls (PCBs), and/or equipment. Fissionable materials may consist of transuranic (TRU) waste, sources containing fissionable material, uranium in various forms such as metal, oxide and silicide, however other forms of uranium and plutonium may be present. Fissionable materials may consist of fines from cutting, be solid forms mounted on a ring and embedded in epoxy or be in small volumes of dilute solutions resulting from cleaning or other processes. Major equipment located in these CCAs may include inert gas environment gloveboxes, fume hoods, ultrasonic testing equipment, hot presses, rolling mills, furnaces, gamma irradiators, autoclaves, machining equipment, tensile testing equipment, shears, forklifts and cranes.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2013

Annular seed-blanket thorium fuel core concepts for heavy water moderated reactors

New reactor concepts to implement thorium-based fuel cycles have been explored to achieve maximum resource utilization. Pressure tube heavy water reactors (PT-HWR) are highly advantageous for implementing the use of thorium-based fuels because of their high neutron economy and on-line re-fuelling capability. The use of heterogeneous seed-blanket core concepts in a PT-HWR where higher-fissile-content seed fuel bundles are physically separate from lower-fissile-content blanket bundles allows more flexibility and control in fuel management to maximize the fissile utilization and conversion of fertile fuel. The lattice concept chosen is a 35-element bundle made with a homogeneous mixture of reactor grade Pu and Th, and with a central zirconia rod to help reduce coolant void reactivity. Several annular heterogeneous seed-blanket core concepts with plutonium-thorium-based fuels in a 700-MWe-class PT-HWR were analyzed, using a once-through thorium (OTT) cycle. Different combinations of seed and blanket fuel were tested to determine the impact on core-average burnup, fissile utilization, power distributions, and other performance parameters. It was found that the various core concepts can achieve a fissile utilization that is up to 30% higher than is currently achieved in a PT-HWR using conventional natural uranium fuel bundles. Up to 67% of the Pu is consumed; up to 43% of the energy is produced from thorium, and up to 363 kg/year of U-233 is produced. Seed-blanket cores with ∼50% content of low-power blanket bundles may require power de-rating (∼58% to 65%) to avoid exceeding maximum limits for peak channel power, bundle power and linear element ratings. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Checkerboard seed-blanket thorium fuel core concepts for heavy water moderated reactors

New reactor concepts to implement thorium-based fuel cycles have been explored to achieve maximum resource utilization. Pressure tube heavy water reactors (PT-HWR) are highly advantageous for implementing the use of thorium-based fuels because of their high neutron economy and on-line re-fuelling capability. The use of heterogeneous seed-blanket core concepts in a PT-HWR where higher-fissile-content seed fuel bundles are physically separate from lower-fissile-content blanket bundles allows more flexibility and control in fuel management to maximize the fissile utilization and conversion of fertile fuel. The lattice concept chosen was a 35-element bundle made with a homogeneous mixture of reactor grade Pu (about 67 wt% fissile) and Th, and with a central zirconia rod to help reduce coolant void reactivity. Several checkerboard heterogeneous seed-blanket core concepts with plutonium-thorium-based fuels in a 700-MWe-class PT-HWR were analyzed, using a once-through thorium (OTT) cycle. Different combinations of seed and blanket fuel were tested to determine the impact on core-average burnup, fissile utilization, power distributions, and other performance parameters. It was found that various checkerboard core concepts can achieve a fissile utilization that is up to 26% higher than that achieved in a PT-HWR using more conventional natural uranium fuel bundles. Up to 60% of the Pu is consumed; up to 43% of the energy is produced from thorium, and up to 303 kg/year of Pa-233/U-233/U-235 are produced. Checkerboard cores with about 50% of low-power blanket bundles may require power de-rating (65% to 74%) to avoid exceeding maximum limits for channel and bundle powers and linear element ratings. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Lattice cell and full core physics of internally cooled annular fuel in heavy water moderated reactors

A program is underway at Atomic Energy of Canada Limited (AECL) to develop a new fuel bundle concept to enable greater burnups for PT-HWR (pressure tube heavy water reactor) cores. One option that AECL is investigating is an internally cooled annular fuel (ICAF) element concept. ICAF contains annular cylindrical pellets with cladding on the inner and outer diameters. Coolant flows along the outside of the element and through the centre. With such a concept, the maximum fuel temperature as a function of linear element rating is significantly reduced compared to conventional, solid-rod type fuel. The preliminary ICAF bundle concept considered in this study contains 24 half-metre long internally cooled annular fuel elements and one non-fuelled centre pin. The introduction of the non-fuelled centre pin reduces the coolant void reactivity (CVR), which is the increase in reactivity that occurs on voiding the coolant in accident scenarios. Lattice cell and full core physics calculations of the preliminary ICAF fuel bundle concept have been performed for medium burnups of approximately 18 GWd/tU using WIMS-AECL and reactor fuel simulation program (RFSP). The results will be used to assist in concept configuration optimization. The effects of radial and axial core power distributions, linear element power ratings, refuelling rates and operational power ramps have been analyzed. The results suggest that burnups of greater than 18 GWd/tU can be achieved in current reactor designs. At approximately 18 GWd/tU, expected maximum linear element ratings in a PT-HWR with online-refuelling are approximately 90 kW/m. These conditions would be prohibitive for solid-rod fuel, but may be possible in ICAF fuel given the reduced maximum fuel temperature as a function of linear element rating. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Heavy Water Moderated, Molten Uranium Cooled Reactor MCNP Model

Two of the major challenges facing the nuclear industry are the large amounts of nuclear waste produced by the current light water reactors and the risk of nuclear proliferation. Most proposed solutions for the waste problem involve fast breeder reactors, but that doesn't help with the nuclear proliferation problem. It is generally understood that a uranium fueled (U-238 + U-235) thermal reactor cannot be a breeder because there aren't enough neutrons. That analysis does not include the effects of fast fission of U-238. This is not surprising because the percentage of fast fissions in existing thermal reactor designs is low, around 3% (in Candu reactors) or less. Table I shows the neutrons involved in 1,000 fissions in a thermal reactor for a conversion ratio of 1.000 when the fuel is mostly U-238 and the fissile content is low enough so that most fast fissions are of U-238. The top section of the table is for U-235 in U-238, the bottom section is for Pu-239 in U-238. The bottom line in each section shows the number of neutrons available for all other losses (escape from the reactor, absorption in non fuel components, and absorption in xenon, samarium, and other fission products). If the percentage of fast fissions of U-238 is 10 or 15 % a thermal breeder may be feasible. This is largely independent of the percentage of fissile content of the fuel. If the reactor starting fissile content is mostly U-235, as the U-235 is replaced with Pu-239 the number of available neutrons increases even if the conversion ratio is only 1.000. The percentage of fast fissions in a reactor is a question of reactor geometry, as the minimum dimension of the fuel elements increases the average distance a fast neutron travels in the fuel before exiting increases and with it the probability of fast fission of U-238.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Hierarchically Controlled Inside-Out Doping of Mg Nanocomposites for Moderate Temperature Hydrogen Storage

Demand for pragmatic alternatives to carbon–intensive fossil fuels is growing more strident. Hydrogen represents an ideal zero–carbon clean energy carrier with high energy density. For hydrogen fuel to compete with alternatives, safe and high capacity storage materials that are readily cycled are imperative. Here, development of such a material, comprised of nickel–doped Mg nanocrystals encapsulated by molecular–sieving reduced graphene oxide (rGO) layers, is reported. While most work on advanced hydrogen storage composites to date endeavor to explore either nanosizing or addition of carbon materials as secondary additives individually, methods to enable both are pioneered: “dual–channel” doping combines the benefits of two different modalities of enhancement. Specifically, both external (rGO strain) and internal (Ni doping) mechanisms are used to efficiently promote both hydriding and dehydriding processes of Mg nanocrystals, simultaneously achieving high hydrogen storage capacity (6.5 wt% in the total composite) and excellent kinetics while maintaining robustness. Furthermore, hydrogen uptake is remarkably accomplished at room temperature and also under 1 bar—as observed during in situ measurements—which is a substantial advance for a reversible metal hydride material. In conclusion, the realization of three complementary functional components in one material breaks new ground in metal hydrides and makes solid–state materials viable candidates for hydrogen–fueled applications.

08 HYDROGEN↗
DOE OSTI2024

Deconvoluting Effects of Lithium Morphology and SEI Stability at Moderate Current Density Using Interface Engineering

Lithium (Li)-morphology and solid electrolyte interphase (SEI) are among the most significant performance regulators in Li-metal batteries (LMBs). While both Li-morphology and SEI composition play key roles in the cyclability of LMBs, less is understood about the individual contributions of each factor to overall Li reversibility, particularly at a practical current density (1 mA cm −2 ) at which the kinetics of both factors are not naturally separated. Herein, an interface engineering approach is introduced to deconvolute the impacts of Li-morphology and SEI composition on battery performance. By using interfacial nanofilms with differing resistivity (resistive HfO 2 versus conductive ZnO), the morphology of Li is varied, and by virtue of similar acidic character of the nanofilms, the formation of anion-rich SEIs is maintained. It is established that although the surface acidity of the thin films enables preformation of a more anion-rich SEI, it is not preserved after Li plating. It is further shown that resistance-controlled, low-surface-area Li-morphology exhibits up to threefold increase in stable cycle life when tested in multiple electrolytes. Overall, these findings explain why Li-morphological control is more advantageous for performance improvement than preformed SEI modulation due to the inherent challenges in SEI preservation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Marine phytoplankton resilience may moderate oligotrophic ecosystem responses and biogeochemical feedbacks to climate change

Are the oceans turning into deserts? Rising temperature, increasing surface stratification, and decreasing vertical inputs of nutrients are expected to cause an expansion of warm, nutrient deplete ecosystems. Such an expansion is predicted to negatively affect a trio of key ocean biogeochemical features: phytoplankton biomass, primary productivity, and carbon export. However, phytoplankton communities are complex adaptive systems with immense diversity that could render them at least partially resilient to global changes. This can be illustrated by the biology of the Prochlorococcus “collective.” Adaptations to counter stress, use of alternative nutrient sources, and frugal resource allocation can allow Prochlorococcus to buffer climate-driven changes in nutrient availability. In contrast, cell physiology is more sensitive to temperature changes. We argue that biogeochemical models need to consider the adaptive potential of diverse phytoplankton communities. However, a full understanding of phytoplankton resilience to future ocean changes is hampered by a lack of global biogeographic observations to test theories. We propose that the resilience may in fact be greater in oligotrophic waters than currently considered with implications for future predictions of phytoplankton biomass, primary productivity, and carbon export.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Moderate Velocity Ball Impact of a Mock High-Explosive

Modeling of thermal and mechanical events in high-explosive materials is complicated by the composite nature of the material, which experiences viscoelastic and plastic deformations and sustains damage in the form of microcracks that can dominate its overall behavior. A mechanical event of interest is projectile interaction with the material, which leads to extreme local deformation and adiabatic heating, which can potentially lead to adverse outcomes in an energetic material. Simulations of such an event predicted large local temperature rises near the path of a spherical projectile, but these were experimentally unconfirmed and hence potentially non-physical. This work concerns the experimental verification of local temperatures both at the surface and in the wake of a spherical projectile penetrating a mock (unreactive) high-explosive at {approx}700 m/s. Fast response thermocouples were embedded radially in a mid-plane of a cylindrical target, which was bonded around the thermocouples with epoxy and recorded by an oscilloscope through a low-pass filter with a bandwidth of 500 Hz. A peak temperature rise of 70 K was measured both at the equator of the projectile and in its wake, in good agreement with the temperature predicted in the minimally distorted elements at those locations by a finite element model in ABAQUS employing the ViscoSCRAM constitutive model. Further work is needed to elucidate the extreme temperature rises in material undergoing crushing or fragmentation, which is difficult to predict with meshed finite element methods due to element distortion, and also challenging to quantify experimentally.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Low and moderate x gluon contribution to exclusive Compton scattering processes

We revisit the high energy semi-classical description of the exclusive processes DVCS, TCS, and Double DVCS by explicitly keeping track of the Feynman x dependence in both the hard and the hadronic matrix elements. This is achieved by a modification of the standard shock wave approximation to derive the effective Feynman rules, which leads to a generic expression on which we then perform a partial twist expansion to get rid of quantities suppressed by the proper physical scales. We obtain a compact factorized master formula that can be used to investigate the Bjorken limit at leading twist. In particular, we recover the full one-loop result in the collinear limit for pure gluon exchange with the target. Finally, we discuss the subtleties in taking the simultaneous collinear and small x limit.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Assessing microbial residues in soil as a potential carbon sink and moderator of carbon use efficiency

Abstract A longstanding assumption of glucose tracing experiments is that all glucose is microbially utilized during short incubations of ≤2 days to become microbial biomass or carbon dioxide. Carbon use efficiency (CUE) estimates have consequently ignored the formation of residues (non-living microbial products) although such materials could represent an important sink of glucose that is prone to stabilization as soil organic matter. We examined the dynamics of microbial residue formation from a short tracer experiment with frequent samplings over 72 h, and conducted a meta-analysis of previously published glucose tracing studies to assess the generality of these experimental results. Both our experiment and meta-analysis indicated 30–34% of amended glucose-C ( 13 C or 14 C) was in the form of residues within the first 6 h of substrate addition. We expand the conventional efficiency calculation to include residues in both the numerator and denominator of efficiency, thereby deriving a novel metric of the potential persistence of glucose-C in soil as living microbial biomass plus residues (‘carbon stabilization efficiency’). This new metric indicates nearly 40% of amended glucose-C persists in soil 180 days after amendment, the majority as non-biomass residues. Starting microbial biomass and clay content emerge as critical factors that positively promote such long term stabilization of labile C. Rapid residue production supports the conclusion that non-growth maintenance activity can illicit high demands for C in soil, perhaps equaling that directed towards growth, and that residues may have an underestimated role in the cycling and sequestration potential of C in soil.

Geyer, Kevin (ORCID:0000000252182745)↗
DOE OSTI2015

Cumulative fission yields of short-lived isotopes under natural-abundance-boron-carbide-moderated neutron spectrum

The availability of gamma spectroscopy data on samples containing mixed fission products at short times after irradiation is limited. Due to this limitation, data interpretation methods for gamma spectra of mixed fission product samples, where the individual fission products have not been chemically isolated from interferences, are not well-developed. The limitation is particularly pronounced for fast pooled neutron spectra because of the lack of available fast reactors in the United States. Samples containing the actinide isotopes 233, 235, 238U, 237Np, and 239Pu individually were subjected to a 2$ pulse in the Washington State University 1 MW TRIGA reactor. To achieve a fission-energy neutron spectrum, the spectrum was tailored using a natural abundance boron carbide capsule to absorb neutrons in the thermal and epithermal region of the spectrum. Our tailored neutron spectrum is unique to the WSU reactor facility, consisting of a soft fission spectrum that contains some measurable flux in the resonance region. This results in a neutron spectrum at greater than 0.1 keV with an average energy of 70 keV, similar to fast reactor spectra and approaching that of 235U fission. Unique fission product gamma spectra were collected from 4 minutes to 1 week after fission using single-crystal high purity germanium detectors. Cumulative fission product yields measured in the current work generally agree with published fast pooled fission product yield values from ENDF/B-VII, though a bias was noted for 239Pu. The present work contributes to the compilation of energy-resolved fission product yield nuclear data for nuclear forensic purposes.

Finn, Erin C.↗
DOE OSTI2017

The amorphization of 3C-SiC irradiated at moderately elevated temperatures as revealed by X-ray diffraction

Mechanisms of radiation damage buildup in 3C-SiC remain poorly understood. Here, we use X-ray diffraction in combination with numerical simulations to study depth profiles of radiation-produced strain and lattice damage in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal increased defect recombination with increasing temperature, with a critical amorphization fluence increasing from 0.17 to 0.44 displacements per atom. The amorphization process is found to be correlated with the evolution of lattice strain. We find that, at fluences corresponding to the onset of amorphization, lattice strain is ~2% and is independent of temperature. With continuing bombardment above the onset of amorphization, the strain in the crystal bulk increases and reaches a saturation value that decreases from 7% to 5% with increasing temperature. Based on strain profiles, we compute depth profiles of the effective concentration of point defect clusters in the crystalline phase. Bombardment at higher temperatures results in lower maximum defect concentrations pointing to enhanced defect mobility.

36 MATERIALS SCIENCE↗