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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Neutron-induced capture-to-fission cross section ratio measured at LANSCE

Capture-to-fission cross section ratios are used as an alternative to absolute cross section measurements. This is due to the simplification on the calculations and the reduction of the uncertainties with respect to an absolute measurement of the cross section by eliminating experimental complications like self-absorption, beam/target overlap and non-uniformities. Different capture-to-fission reactions have been measured through the years at the Los Alamos Neutron Science Center (LANSCE) at Los Alamos National Laboratory (LANL) using the Detector for Advanced Neutron Capture Experiments (DANCE) combined with different fission detectors. Some of these are a Parallel Plate Avalanche Counter (PPAC) to detect fission fragments (FF), and the NEUtron detector array at DANCE (NEUANCE) to detect fission neutrons. As DANCE detects the γ-rays produced in capture and fission reactions, the fission instrument placed inside the DANCE cavity is used to tag the fission γ-rays for background identification and subtraction. Some examples of capture-to-fission ratio measurements performed with DANCE in the last years are the 233 U, 235 U and 239 Pu. The measurement technique, the different setups, and other potential applications of the instruments will be explained.

Nuclear Criticality Safety Program (NCSP)↗
DOE OSTI2025

Analyzing the Effects of the Interference between One- and Two-Body Currents on Neutrino-Nucleus Scattering in ACHILLES

Modeling improvements of neutrino–nucleus scattering are an essential aspect of reducing systematic uncertainties for current and future neutrino oscillation experiments. In particular, retaining quantum mechanical effects such as the interference between one-body (1p1h) and two-body (2p2h) currents in our cross-section models is an essential consideration. This work investigates the impact of this interference term on neutrino–argon scattering using the ACHILLES event generator, which directly implements the interference model developed by Lovato, Rocco, and Steinberg. Using fluxes relevant to SBND, the DUNE near detector, and MiniBooNE, charged- and neutral-current event samples are generated and predicted event rates are plotted against a variety of kinematic variables. For events simulated using the SBND flux, it is found that interference contributes approximately 10 \% to the total charged-current event rate, and serves to enhance the quasi-elastic peak. When considering events generated using the DUNE flux, resonance interactions contribute more to the predicted event rate, as the neutrino flux extends out to higher energies. The relative interference contribution subsequently decreases to roughly 7 \%. Neutral-current simulations show a higher rate of neutron knockout. Finally, a comparison of argon-to-carbon cross-section ratios is performed utilizing fluxes from SBND and MiniBooNE.

Pando, Nathan [Fermilab]↗
NASA NTRS1987

Comparison of theoretical and experimental thrust performance of a 1030:1 area ratio rocket nozzle at a chamber pressure of 2413 kN/sq m (350 psia)

The Joint Army, Navy, NASA, Air Force (JANNAF) rocket-engine performance-prediction procedure is based on the use of various reference computer programs. One of the reference programs for nozzle analysis is the Two-Dimensional Kinetics (TDK) Program. The purpose of this report is to calibrate the JANNAF procedure that has been incorporated into the December 1984 version of the TDK program for the high-area-ratio rocket-engine regime. The calibration was accomplished by modeling the performance of a 1030:1 rocket nozzle tested at NASA Lewis. A detailed description of the test conditions and TDK input parameters is given. The reuslts indicate that the computer code predicts delivered vacuum specific impulse to within 0.12 to 1.9 percent of the experimental data. Vacuum thrust coefficient predictions were within + or - 1.3 percent of experimental results. Predictions of wall static pressure were within approximately + or - 5 percent of the measured values.

Smith, Tamara A.↗
NASA NTRS1979

Effect of flight loads on turbofan engine performance deterioration

A significant percentage of high-bypass-ratio turbofan engine performance deterioration is caused by an increase in operating clearance between fan/compressor and turbine blades and their outer air seals. These increased clearances result from rubs induced by a combination of engine power transients and aircraft flight loads. An analytical technique for predicting the effect of quasi-steady state aircraft flight loads on engine performance deterioration has been developed and is presented. Thrust, aerodynamic and inertia loads are considered. Analytical results are shown and compared to actual engine test experience.

Stakolich, E. G.↗
DOE OSTI2018

Concomitant ion effects on isotope ratio measurements with liquid sampling – atmospheric pressure glow discharge ion source Orbitrap mass spectrometry

RATIONALE: The field of highly accurate and precise isotope ratio (IR) analysis has been dominated by inductively coupled plasma and thermal ionization mass spectrometers. While these instruments are considered the gold standard for IR analysis, the International Atomic Energy Agency desires a field deployable instrument capable of accurately and precisely measuring U isotope ratios. METHODS: The proposed system interfaces the liquid sampling – atmospheric pressure glow discharge (LS-APGD) ion source with a high resolution Exactive Orbitrap mass spectrometer. With this experimental setup certified U isotope standards and unknown samples were analyzed. The accuracy and precision of the system were then determined. RESULTS: The LS-APGD /Exactive instrument measures a certified reference material of natural U (235U/238U = 0.007258) as 0.007041 with a relative standard deviation of 0.158% meeting the International Target Values for Uncertainty for the destructive analysis of U. Additionally, when three unknowns measured and compared to the results from an ICP multi collector instrument, there is no statistical difference between the two instruments. CONCLUSIONS: The LS-APGD / Orbitrap system, while still in the preliminary stages of development, offers highly accurate and precise IR analysis that suggest a paradigm shift in the world of IR analysis. Furthermore, the portability of the LS-APGD as an elemental ion source combined with the low overhead and small size of the Orbitrap suggest that the instrumentation is capable of being field deployable. With liquid sampling glow discharge-Orbitrap MS, isotope ratio and precision performance improves with rejection of concomitant ion species.

atmospheric pressure sampling↗
NASA NTRS1994

Static investigation of two fluidic thrust-vectoring concepts on a two-dimensional convergent-divergent nozzle

A static investigation was conducted in the static test facility of the Langley 16-Foot Transonic Tunnel of two thrust-vectoring concepts which utilize fluidic mechanisms for deflecting the jet of a two-dimensional convergent-divergent nozzle. One concept involved using the Coanda effect to turn a sheet of injected secondary air along a curved sidewall flap and, through entrainment, draw the primary jet in the same direction to produce yaw thrust vectoring. The other concept involved deflecting the primary jet to produce pitch thrust vectoring by injecting secondary air through a transverse slot in the divergent flap, creating an oblique shock in the divergent channel. Utilizing the Coanda effect to produce yaw thrust vectoring was largely unsuccessful. Small vector angles were produced at low primary nozzle pressure ratios, probably because the momentum of the primary jet was low. Significant pitch thrust vector angles were produced by injecting secondary flow through a slot in the divergent flap. Thrust vector angle decreased with increasing nozzle pressure ratio but moderate levels were maintained at the highest nozzle pressure ratio tested. Thrust performance generally increased at low nozzle pressure ratios and decreased near the design pressure ratio with the addition of secondary flow.

Wing, David J.↗
NASA NTRS1940

Effect of wing loading, aspect ratio, and span loading of flight performances

An investigation is made of the possible improvements in maximum, cruising, and climbing speeds attainable through increase in the wing loading. The decrease in wing area was considered for the two cases of constant aspect ratio and constant span loading. For a definite flight condition, an investigation is made to determine what loss in flight performance must be sustained if, for given reasons, certain wing loadings are not to be exceeded. With the aid of these general investigations, the trend with respect to wing loading is indicated and the requirements to be imposed on the landing aids are discussed

Gothert, B↗
NASA NTRS1989

Effect of Propellant Flowrate and Purity on Carbon Deposition in LO2/Methane Gas Generators

The generation and deposition of carbon was studied in the Carbon Deposition Program using subscale hardware with LO2/Liquid Natural Gas (LNG) and LO2/Methane propellants at low mixture ratios. The purpose of the testing was to evaluate the effect of methane purity and full scale injection density on carbon deposition. The LO2/LNG gas generator/preburner testing was performed at mixture ratios between 0.24 and 0.58 and chamber pressures from 5.8 to 9.4 MPa (840 to 1370 psia). A total of seven 200 second duration tests were performed. The LNG testing occurred at low injection densities, similar to the previous LO2/RP-1, LO2/propane, and LO2/methane testing performed on the carbon deposition program. The current LO2/methane test series occurred at an injection density factor of approximately 10 times higher than the previous testing. The high injection density LO2/methane testing was performed at mixture ratios between from 0.23 to 0.81 and chamber pressures from 6.4 to 15.2 MPa (925 to 2210 psia). A total of nine high injection density tests were performed. The testing performed demonstrated that low purity methane (LNG) did not produce any detectable change in carbon deposition when compared to pure methane. In addition, the C* performance and the combustion gas temperatures measured were similar to those obtained for pure methane. Similar results were obtained testing pure methane at higher propellant injection densities with coarse injector elements.

Bossard, J. A.↗
DOE OSTI2018

Odor mitigation and bacterial community dynamics in on-site biocovers at a sanitary landfill in South Korea

Highlights: • On-site biocovers were evaluated to mitigate odors at a Korean sanitary landfill. • The biocover systems achieved above 80% removal of complex odor. • Removal efficiency of sulfur odor as significant contributor was greater than 90%. • The most abundant bacteria had little correlation with odor removability. • Bacteria increased in relative abundance contributed highly to odor removal. Unpleasant odors emitted from landfills have been caused environmental and societal problems. For odor abatement, two pilot-scale biocovers were installed at a sanitary landfill site in South Korea. Biocovers PBC1 and PBC2 comprised a soil mixture with different ratios of earthworm casts as an inoculum source and were operated for 240 days. Their odor removal efficiencies were evaluated, and their bacterial community structures were characterized using pyrosequencing. In addition, the correlation between odor removability and bacterial community dynamics was assessed using network analysis. The removal efficiency of complex odor intensity in the two biocovers ranged from 81.1% to 97.8%. Removal efficiencies of sulfur-containing odors (hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide), which contributed most to complex odor intensity, were greater than 91% in both biocovers. Despite the fluctuations in ambient temperature (−8.2 to 31.3 °C) and inlet complex odor intensity (10,000–42,748 of odor dilution ratio), biocovers PBC1 and PBC2 displayed stable deodorizing performance. A high ratio of earthworm casts as an inoculum source led to high odor removability during the first 25 days of operation, but different mixing ratios of earthworm casts did not significantly affect overall odor removability. A bacterial community analysis showed that Methylobacter, Arthrobacter, Acinetobacter, Rhodanobacter, and Pedobacter were the dominant genera in both biocovers. Network analysis results indicated that Steroidobacter, Cystobacter, Methylosarcina, Solirubrobacter, and Pseudoxanthomonas increased in relative abundance with time and were major contributors to odor removal, although these bacteria had a relatively low abundance compared to the overall bacterial community. These data contribute to a more comprehensive understanding of the relationship between bacterial community dynamics and deodorizing performance in biocovers.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Robustness to hydrodynamic instabilities in indirectly driven layered capsule implosions

Here, we report on a high convergence ratio liquid layer capsule implosion performed on the National Ignition Facility and contrast it to two previously reported layered implosions, in order to better understand how the capsule design impacts the hydrodynamic stability properties of implosions. Three implosions were performed with similar convergence ratios, fuel entropy, in-flight aspect ratios, and unablated shell mass; these qualities are important for determining hydrodynamic stability. Nevertheless, while two of these implosions exhibited robustness to asymmetries, including our recent experiment that had abnormally large amplitude long-wavelength capsule asymmetries, and produced more than 80% or the yield predicted by one-dimensional (1D) simulations, which do not account for the impacts of hydrodynamic instabilities, the third implosion produced only 14% of the yield from a 1D simulation. We perform a detailed computational analysis of these three shots, which suggests that the combination of several large asymmetry seeds result in the significantly degraded performance: a large 30 μm fill tube, the presence of a microstructure in the high density carbon ablator, and a higher level of drive asymmetry. This indicates that while it is possible to stabilize a high convergence ratio implosion through various means, the factors that determine stability cannot be considered independently. Furthermore, when these asymmetries are combined in 2D simulations, they can exhibit destructive interference and underpredict the yield degradation compared to experiment and three-dimensional simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2022

Preliminary Airfoil Design for Low Reynolds Numbers

Advances in the fields of electronics, batteries, and electric motors have enabled broad adoption of small-scale aircraft for various terrestrial applications. Numerous Micro Aerial Vehicles (MAVs) and small Unmanned Aerial Vehicles (UAVs), both civil and military, are in use today. Operation at their design flight condition often requires rotors, propellers, or wings to perform at Reynolds numbers significantly below 500,000 [1]. Airfoil performance at low Reynolds numbers is generally characterized by low aerodynamic performance (i.e. the attainable lift-to-drag ratio) compared to performance of airfoils at higher Reynolds numbers. The critical chord-based Reynolds number for conventional airfoils lies around Rec = 100,000 to Rec = 500,000 [2]. Below this critical Reynolds number, laminar separation of the boundary layer is usually the cause for poor performance. Researchers have found that below the critical Reynolds number, flat and cambered plates can outperform smooth airfoils. Circular-arc cambered plates especially have remarkable performance advantages compared to conventional airfoil shapes [3].

airfoil↗
DOE OSTI2019

Investigating the Effectiveness of P/S Amplitude Ratios for Local Distance Event Discrimination

The ability to discriminate between underground explosions and earthquakes is an important operation for global security and test-ban-treaty monitoring, and seismology plays a key role in this endeavor. The use of seismic P- to S-wave amplitude ratios has been demonstrated to be an effective discriminant at regional distances for a variety of emplacement conditions and test sites around the world. Increasing interest in detecting and discriminating smaller events, both for purposes of nuclear monitoring and seismic hazard estimation, requires the use of data with shorter event-to-station paths. At these local distances (≤ 200 km), the use of P/S ratios for event discrimination is poorly studied compared with regional distances (200-1500 km). The path averaging that allows for relatively simple corrections to P/S ratios to remove bias from along-path structural differences at regional distances may be insufficient to remove enough scatter from the ratios to allow for accurate event identification at local distances. We use data from a series of chemical explosions detonated as part of the Source Physics Experiment at the Nevada National Security Site in southern Nevada and surrounding seismicity to investigate the discrimination performance of P/S ratios at local distances. We find that discrimination at individual stations is highly variable, regardless of frequency. Network averaging of ratios improves discrimination performance above 6 Hz, as a result of the reduction of scatter among the earthquake ratios. Furthermore, azimuthal and distance–limited averaging suggests that explosion ratios are affected by a complicated source and path relationship that may lead to substantial variability in local P/S ratios at different locations.

58 GEOSCIENCES↗
NASA NTRS1980

Performance and noise of a low pressure ratio variable pitch fan designed for general aviation applications

A limited study has been conducted to establish the performance and noise characteristics of a low design tip speed (168 m/s, 550 ft/sec) low pressure ratio (1.04) variable pitch fan which was tested in the Langley 30 X 60 tunnel. This fan was designed for minimum noise when installed in the tail mount location of a twin engine aircraft which normally has both nose and tail mounted propulsors. Measurements showed the fan noise to be very close to predictions made during the design of the fan and extremely low in level (65 dBA at 1000 ft) with no acoustic treatment. This is about 8 dB lower than the unshrouded 2 blade propeller normally used in this installation. On the basis of tests conducted during this program, it appears that this level could be further reduced by 2 dBA if optimized acoustic treatments were installed in the fan duct. Even the best of the shrouded propellers tested previously were 7 dB higher in level than the Q-Fan without acoustic treatment. It was found that the cruise performance of this fan was within 5% of the predicted efficiency of 72%. Evaluation of the performance data indicated that disturbances in the inflow to the fan were the probable cause of the reduced performance.

Metzger, F. B.↗
NASA NTRS1953

Effect of Fuel-air Ratio Concentration in Combustion Zone on Combustion Performance of a 16-inch Ram-jet Engine

The results of fuel-air ratio and temperature surveys made in the flame stabilizing zone of a 16-inch ram-jet combustor indicated that the distribution of combustible mixture immediately downstream of a flame holder should be mechanically controlled if a preferred mixture composition is to be maintained in that zone. A sloping-baffle combustor configuration gave combustion efficiencies of 90 percent or greater over a range of fuel-air ratios from 0.010 to 0.045.

COMBUSTION - RAM-JET ENGINES↗
DOE OSTI2012

Qualification of JEFF3.1.1 library for high conversion reactor calculations using the ERASME/R experiment

With its low CO{sub 2} production, Nuclear Energy appears to be an efficient solution to the global warming due to green-house effect. However, current LWR reactors are poor uranium users and, pending the development of Fast Neutron Reactors, alternative concepts of PWR with higher conversion ratio (HCPWR) are being studied again at CEA, first studies dating from the middle 80's. In these French designs, low moderation ratio has been performed by tightening the lattice pitch, achieving a conversion ratio of 0.8-0.9 with a MOX fuel coming from PWR UOX recycling. Theses HCPWRs are characterized by a harder neutron spectrum and the calculation uncertainties on the fundamental neutronics parameters are increased by a factor 3 regarding a standard PWR lattice, due to the major contribution of the Plutonium isotopes and of the epithermal energy range to the reaction rates. In order to reduce these uncertainties, a 3-year experimental validation program called ERASME has been performed by CEA from 1984 to 1986 in the EOLE reactor. Monte Carlo analysis of the ERASME/R experiments with the Monte Carlo code TRIPOLI4 allowed the qualification of the recommended JEFF.3.1.1 library for major neutronics parameters. K{sub eff} of the MOX under-moderated lattice is over-predicted by 440 {+-} 830 pcm (2{sigma}); the conversion ratio, indicator of the good use of uranium, is also slightly over-predicted: 2 % {+-} 4 % (2{sigma}) and the same for B4C absorber rods worth and soluble boron worth, over-predicted by 2 %, both in the 2 standard deviations range. The radial fission maps of heterogeneities (water-holes, B4C and fertile rods) are well reproduced: maximal (C-E)/E dispersion is 1.3 %, maximal power peak error is 2.7 %. The void reactivity worth is the only parameter poorly calculated with an overprediction of +12.4% {+-} 1.5%. ERASME/R analysis of MOX reactivity, void effect and spectral indexes will contribute to the reevaluation of {sup 241}Am and Plutonium isotopes nuclear data for the next library JEFF3.2. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗