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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Comparative post-irradiation examination of high burnup U-19Pu-10Zr: Assessing steady-state irradiation behavior against historical and modeled fuel performance

Here, the development of next-generation sodium-cooled fast reactors necessitates comprehensive research on metallic fuels to maximize economic performance while ensuring safe operation. In this study, we investigated the steady-state irradiation behavior of two high burnup U-19Pu-10Zr fuel pins, DP-36 and DP-40, in preparation for planned safety testing. Post-irradiation examination (PIE) was performed to quantify fuel column elongation, regions of low-density at the top of the fuel column, pin deformation, fission product distribution, fractional fission gas release, microstructural evolution, and fuel constituent redistribution. Benchmarking against existing PIE data from U-19Pu-10Zr fuel pins irradiated in EBR-II revealed consistent patterns in fuel column elongation and cladding diametral strain. However, both pins exhibited longer low-density structures, and destructive examination of DP-36 revealed more complex constituent redistribution patterns compared to previously reported data for ternary fuel pins. The steady-state irradiation of both pins was also modeled using BISON. Comparisons of PIE results with modeled predictions showed overall agreement in fractional fission gas release but consistent overestimation of axial and radial swelling due to gaseous and solid swelling models. These findings underscore the critical importance of pre-test characterization on test and sibling pins to accurately capture steady-state fuel behavior ahead of transient testing, thus establishing a baseline for post-test comparison. Additionally, these analyses identified key data gaps that warrant further investigation to improve the understanding and prediction of fuel swelling, thereby enhancing the synergy between modeling and experimental efforts in supporting accident testing.

BISON↗
DOE OSTI2026

Effects of ZrN Coating and Heat Treatment on U-Mo Dispersion Fuel under Irradiation

The stability of U-Mo fuel particles in Al matrix can be improved using ZrN coating and heat treatment. This study investigated irradiation behaviors of fuel plates containing U-Mo fuel particles fabricated with different conditions including heat treatment and the thickness of ZrN coating. Additionally, different fission densities were applied to each fuel plate to understand how varying fission densities affect its irradiation behaviors. This study showed that more recrystallization of grains and development of high burnup structure (HBS) occurred in irradiated fuel particles with higher fission densities. Heat treatment reduced the accumulation of fission gas bubbles in the fuel particles by coarsening their grains. The fuel particles with a ZrN coating thickness of 1.2-1.8 µm showed less significant development of U-Mo/Al interaction layers than the particles with a coating thickness of 0.5 µm after irradiation. This might indicate the existence of a critical thickness of ZrN coating to minimize the formation of the interaction layers. Fission gas bubbles were observed at grain boundaries of irradiated U-Mo fuel particles at low fission densities, and the formation of dendritic features with a darker contrast was identified in backscattered electron images. These features stemmed from grain boundaries with fission gas bubbles or HBS, and some of them contained the bubbles, indicating that they might represent an early stage of HBS propagation in the fuel particles.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Effect of secondary gas-phase reactions (SGR) in pyrolysis of carbon feedstocks for anisotropic carbon materials production – 3: Modifying non-coking coal tar through co-pyrolysis of coal with linear low-density polyethylene and high-impact polystyrene

Herein, this work focuses on co-pyrolysis experiments of Utah Sufco coal with linear low-density polyethylene (LLDPE) and high-impact polystyrene (HIPS). These two plastic types have differing pyrolysis chemistries and have different hydrogen transfer behavior. Similar to earlier work in this series of papers, controlled secondary gas-phase reactions during pyrolysis were used to induce cracking and condensation reactions among the pyrolytic tar species. Co-pyrolysis tests were performed with feed plastic percentages ranging from 10-20 wt% and pyrolysis SGR temperatures ranging from 800-900°C. Analyses of the intermediate tar products showed that oxygen contents and aromaticity were substantially different, depending on the plastic, and resulting pitch softening points and mesophase contents also varied greatly depending on the starting plastic feedstock used. Most of the synergies observed in the co-pyrolysis results were negative, except for the oxygen content. Oxygen contents were higher than expected when LLDPE was used, resulting in reactive pitches with softening points > 350°C. On the other hand, oxygen contents were lower than expected when HIPS was used, resulting in less reactive pitches. Ultimately, only the HIPS/coal samples created at the SGR temperature of 900°C had reasonable softening points at or under 350°C, making them the only samples created in this work potentially suitable for mesophase pitch-based carbon fiber production. The success in creating fusible mesophase pitches from co-pyrolyzing HIPS with Utah Sufco coal is likely attributed to the fact that polystyrene is a stronger hydrogen acceptor rather than donor, which should facilitate more cracking rather than stabilizing tar oxygen functional groups, making the tar species ultimately less reactive during thermal conversion to mesophase pitch.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2022

Validation of the Porous Medium Approximation for Hydrodynamics Analysis in Compact Heat Exchangers

Compact heat exchangers (HXs) have gained attention in recent years in various fields such as solar and nuclear power generation, oil and gas, and refrigeration due to their low cost, high power density, and robustness in high-pressure and/or high-temperature environments. However, the large difference between a compact HX's overall dimensions (~m) and the much smaller scale of its channels (~mm) makes it challenging to model the entire HX at once, due to computational limitations. In this work, we treat the channeled region of a compact HX as a porous medium (PM) to circumvent the need to model/mesh each individual channel. This allows us to simulate the entire HX, including both the header and channeled regions while maintaining the computational cost at a practical level. Although the porous medium approach has been used to model heat exchangers, its validity is still questionable because (1) the resistance coefficients are heavily data-based and thus difficult to be applied to new heat exchangers and (2) the validation has been focused on matching the overall pressure drop in the channel region, which does not address whether such model can predict detailed pressure and velocity field. For the first time, this work addresses under what circumstances and with what uncertainty does the PM approach work for hydrodynamics modeling in compact HXs. By answering these questions, we introduce the PM approach as a powerful tool for HX hydrodynamics modeling that can predict not only the overall pressure drop but also the detailed pressure and velocity distributions.

Engineering↗
NASA NTRS1982

Molecular clouds in Orion and Monoceros

Attention is given to a fairly homogeneous and nearly complete inventory of the molecular clouds in Orion and Monoceros, to a peak CO intensity of 0.5 K and a velocity resolution of 0.6 km/sec, from which a contour map of velocity-intergrated CO intensity is derived and presented with a schematic key. It is noted that, with the exception of Mon R2, the main areas of star formation in this survey lie on the forward surface of a large blunt cone or wedge of molecular clouds pointing towards the center of Barnard's Loop and the older subassociations of OB stars in Orion. This is a region which the present negative CO results, 21-cm observations, and galaxy counts, despite the currently low density, show to have once contained the dense molecular gas from which older OB stars formed.

Thaddeus, P.↗
NASA NTRS2015

Propulsion System Development for the Iodine Satellite (iSAT) Demonstration Mission

The development and testing of a 200-W iodine-fed Hall thruster propulsion system that will be flown on a 12-U CubeSat is described. The switch in propellant from more traditional xenon gas to solid iodine yields the advantage of high density, low pressure propellant storage but introduces new requirements that must be addressed in the design and operation of the propulsion system. The thruster materials have been modified from a previously-flown xenon Hall thruster to make it compatible with iodine vapor. The cathode incorporated into this design additionally requires little or no heating to initiate the discharge, reducing the power needed to start the thruster. The feed system produces iodine vapor in the propellant reservoir through sublimation and then controls the flow to the anode and cathode of the thruster using a pair of proportional flow control valves. The propellant feeding process is controlled by the power processing unit, with feedback control on the anode flow rate provided through a measure of the thruster discharge current. Thermal modeling indicates that it may be difficult to sufficiently heat the iodine if it loses contact with the propellant reservoir walls, serving to motivate future testing of that scenario to verify the modeling result and develop potential mitigation strategies. Preliminary, short-duration materials testing has thus-far indicated that several materials may be acceptable for prolonged contact with iodine vapor, motivating longer-duration testing. A propellant loading procedure is presented that aims to minimize the contaminants in the feed system and propellant reservoir. Finally, an 80-hour duration test being performed to gain experience operating the thruster over long durations and multiple restarts is discussed.

Polzin, Kurt A.↗
NASA NTRS1985

The effect of a weak shock on interstellar gas toward the Rho Ophiuchi cloud

The effect of a low-velocity shock on depletion in interstellar clouds is studied. High-resolution Copernicus observations of interstellar absorption lines toward four stars in the Rho Ophiuchi cloud complex were used to measure differential depletion in interstellar clouds separated by velocities of 10-15 km/s. Optical observations of CH and CH(+) were used as indicators of shock strength and direction of propagation. Observations indicate the presence of a shock with velocity about 10 km/s expanding away from the sun into the Rho Oph cloud. The existence of this shock is supported by the other observations quoted in the literature. Two distinct regions in the lines of sight have been found. A low-density, less depleted, predominantly atomic region is associated with preshock gas, while postshock gas accounts for a predominantly molecular, more highly depleted region. Apparently a weak shock, has the effect of enhancing grain formation or grain growth as a result of increased density in the postshock gas. It is possible for grain growth by accretion to occur in the shocked gas on time scales short compared with the cloud-crossing time of the shock.

Meyers, K. A.↗
NASA NTRS1994

Cosmic bullets as particle accelerators and radio sources

We have simulated in two dimensions the dynamical evolution of dense gas clouds(`cosmic bullets') moving supersonically through a uniform low-density medium. The diffusive shock acceleration of relativistic protons (cosmic rays) and their dynamical feedback on the background flow are included by the two-fluid model for this process. The acceleration of relativistic electrons is approximated by a test-particle model, and a passive magnetic field is followed by a simple advection scheme. Strong bow shocks, with Mach numbers similar to that of a bullet's motion, are the most important particle accelerators in the flow, while tail shocks and shocks inside the bullets do not play generally significant roles in this regard. For our simulation parameters, approximately greater than 10% of the initial bullet kinetic energy is converted to a combination of internal energy of gas and cosmic-ray protons by the time the bullets begin to be disrupted. Characteristically, the cosmic rays gain several percent of the available kinetic energy. Bullet destruction on timescales only a little larger than the ram pressure bullet crushing time begins in response to Kelvin-Helmholtz and especially to Rayleigh-Taylor instabilities along the forward bullet surface. For dense bullets this happens before the bullet is stopped by ram pressure. According to our simple model for synchrotron emission from relativistic electrons accelerated and transported within the flows, that emission increases rapidly as the bullet begins to fragment, when it is strongly dominated by field enhancement in sheared flows. Synchrotron emission from the acceleration region within the bow shock is, by contrast, much weaker.

Jones, T. W.↗
DOE OSTI2022

Computational Identification and Experimental Demonstration of High‐Performance Methane Sorbents

Abstract Remarkable methane uptake is demonstrated experimentally in three metal‐organic frameworks (MOFs) identified by computational screening: UTSA‐76, UMCM‐152 and DUT‐23‐Cu. These MOFs outperform the benchmark sorbent, HKUST‐1, both volumetrically and gravimetrically, under a pressure swing of 80 to 5 bar at 298 K. Although high uptake at elevated pressure is critical for achieving this performance, a low density of high‐affinity sites (coordinatively unsaturated metal centers) also contributes to a more complete release of stored gas at low pressure. The identification of these MOFs facilitates the efficient storage of natural gas via adsorption and provides further evidence of the utility of computational screening in identifying overlooked sorbents.

Nath, Karabi↗
DOE OSTI2022

Computational Identification and Experimental Demonstration of High‐Performance Methane Sorbents

Abstract Remarkable methane uptake is demonstrated experimentally in three metal‐organic frameworks (MOFs) identified by computational screening: UTSA‐76, UMCM‐152 and DUT‐23‐Cu. These MOFs outperform the benchmark sorbent, HKUST‐1, both volumetrically and gravimetrically, under a pressure swing of 80 to 5 bar at 298 K. Although high uptake at elevated pressure is critical for achieving this performance, a low density of high‐affinity sites (coordinatively unsaturated metal centers) also contributes to a more complete release of stored gas at low pressure. The identification of these MOFs facilitates the efficient storage of natural gas via adsorption and provides further evidence of the utility of computational screening in identifying overlooked sorbents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Thin shell formation in radiative shocks. 1: Supernova remnants in low-density media

This paper explores the onset of thin-shell formation in interstellar shocks associated with supernova explosions. We outline a simple but useful scheme that indicates the time at which thin shell formation begins for supernova remnants (SNRs) evolving in a range of interstellar environments, extending the previous analytical models to arbitrary power-law density media. The result depends on the gas cooling properties and the shock velocity and radius. This is then applied to the specific case of SNRs in low-density media. The procedure for defining the time for the onset of shell formation, t(sub sf), equates the value of the adiabat, kappa = p/rho(exp gamma), to zero using the known time dependence of the shock radius and velocity. For the case of a power-law density ambient medium of the form rho(r) = Br(exp -omega), it is found that shell formation can be prevented when the ambient density drops faster than a critical rate. For a cooling function of the form Lambda = Lambda(sub 0) tau(exp beta), with beta = -0.5 (appropriate for line cooling), shell formation never occurs for omega greater than or equal to 9/5. The shell formation time is then computed for spherical shocks in a power-law density medium. For omega = 0, the onset of shell formation is found to be at t(sub sf) approx. equal to 2.87 x 10(exp 4) E51(exp 3/14) n(sub 0 exp -4.7) yr, which agrees well with previous estimates derived by other means. We compare the analytical shell formation time with the results of detailed numerical models for omega = 0 and three different ambient densities and find good agreement. The extension of the criterion for the onset of thin shell formation using the ratio of cooling to swept-up column density is also described. This method provides a useful approximation for cases when the exact solution is not known.

Franco, Jose↗
NASA NTRS1990

Interaction of planetary nebulae with the interstellar medium

The interaction of a moving planetary nebula (PN) with the interstellar medium is considered. The PN shell is compressed first in the direction of the stellar motion. This produces a dipole asymmetry in the surface brightness of the nebula, typically at a nebular density of about 40/cu cm if the nebula is located in the Galactic plane. In the later stages of the interaction, this part of the shell is significantly decelerated with respect to the central star, and the PN becomes strongly asymmetric in shape. This distortion and the subsequent stripping of the nebular gas away from the central star typically occurs at a low nebular density of about 6/cu cm. The morphology of PNs with central stars whose proper motions exceed 0.015 arcsec/yr was examined, and it was found that many of the extended nebulae are interacting with the interstellar medium (ISM). The sample doubles the number of known PNs interacting with the ISM. The morphology of nearby PNs was examined, and a number of strongly asymmetric nebuale were found.

Borkowski, Kazimierz J.↗
NASA NTRS1998

A Coupled Plasma Dynamics and Gas Flow Model for Semiconductor Processing

A continuum modeling approach by self-consistently coupling plasma dynamics and gas flow will be presented for the analysis of high density plasma reactors. Experimental data shows that gas flow distribution affects the etch rate uniformity even at low pressures (6-20 mTorr) and flow rates (20-70 sccm). This study will investigate the effects of gas flow and gas energy on bulk plasma densities and temperatures using a continuum model. The model solves multidimensional equations of mass balance for neutrals and ions, gas momentum, separate energy equations for electrons and neutrals and Maxwell's equations for power coupling. A test case of N2 plasma in a 300mm TCP etch reactor, for which hybrid model and Langmuir probe data are available, is chosen for this analysis. Our preliminary results show that modeling gas flow and energy improves the predictions of electron density and its spatial variation in the reactor when compared with the experimental data. The aim of this study is to identify the operating conditions for the TCP reactor when a self-consistent modeling of gas flow is important.

Bose, Deepak↗
DOE OSTI2023

Grey Galaxies’ as an endpoint of the Kerr-AdS superradiant instability

Kerr-AdS d+1 black holes for d ≥ 3 suffer from classical superradiant instabilities over a range of masses above extremality. We conjecture that these instabilities settle down into Grey Galaxies (GGs) — a new class of coarse-grained solutions to Einstein’s equations which we construct in d = 3. Grey Galaxies are made up of a black hole with critical angular velocity ω = 1 in the ‘centre’ of AdS, surrounded by a large flat disk of thermal bulk gas that revolves around the centre of AdS at the speed of light. The gas carries a finite fraction of the total energy, as its parametrically low energy density and large radius are inversely related. GGs exist at masses that extend all the way down to the unitarity bound. Their thermodynamics is that of a weakly interacting mix of Kerr-AdS black holes and the bulk gas. Their boundary stress tensor is the sum of a smooth ‘black hole’ contribution and a peaked gas contribution that is delta function localized around the equator of the boundary sphere in the large N limit. We also construct another class of solutions with the same charges; ‘Revolving Black Holes (RBHs)’. RBHs are macroscopically charged SO(d, 2) descendants of AdS-Kerr solutions, and consist of ω = 1 black holes revolving around the centre of AdS at a fixed radial location but in a quantum wave function in the angular directions. RBH solutions are marginally entropically subdominant to GG solutions and do not constitute the endpoint of the superradiant instability. Nonetheless, we argue that supersymmetric versions of these solutions have interesting implications for the spectrum of supersymmetric states in, e.g. N = 4 Yang-Mills theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1990

Self-similar perturbations of a Friedmann universe

The present analysis of spherically symmetric self-similar solutions to the Einstein equations gives attention to those solutions that are asymptotically k = 0 Friedmann at large z values, and possess finite but perturbed density at the origin. Such solutions represent nonlinear density fluctuations which grow at the same rate as the universe's particle horizon. The overdense solutions span only a narrow range of parameters, and resemble static isothermal gas spheres just within the sonic point; the underdense solutions may have arbitrarily low density at the origin while exhibiting a unique relationship between amplitude and scale. Their relevance to large-scale void formation is considered.

Carr, Bernard J.↗
NASA NTRS1983

Gas flow through rotameters

Using data available for small rotameters that use spherical floats in gas flow, a linear relationship is derived. It is noted that the relationship provides a good fit for variable volumetric flow, density, and viscosity at constant flow height. With low Reynolds numbers (Re being less than 1), the product of the variable volumetric flow and the viscosity becomes constant; at high Reynolds numbers (Re being greater than 2000), the product of the variable volumetric flow and the square root of the density becomes constant. It is pointed out that the equation given here can be used to obtain an indirect calibration with any gas of known density and viscosity. The constancy of the product of the variable volumetric flow and viscosity at low variable volumetric flows is seen as suggesting the development of simple, inexpensive gas viscometers using rotameter technology.

Levin, H.↗
NASA NTRS1991

Transverse conductivity of a relativistic plasma in oblique electric and magnetic fields

Resistive tearing in a primary candidate for flares occurring in stressed magnetic fields. Its possible application to the strongly magnetized environments (Hz about 10 to the 12th G) near the surface of neutron stars, particularly as a mechanism for generating the plasma heating and particle acceleration leading to gamma-ray bursts, has motivated a quantum treatment of this process, which requires knowledge of the electrical conductivity sigma of a relativistic gas in a new domain (i.e., that of a low-density n/e/) plasma in oblique electric and magnetic fields. This paper discusses the mathematical formalism for calculating sigma and present numerical results for a wide range of parameter values. The results indicate that sigma depends very strongly on both the applied electric and magnetic fields.

Melia, Fulvio↗
NASA NTRS1995

The detection of molecular gas in the ring galaxy Arp 143

We have used the NRAO 12 m telescope to map the inner 10 kpc of NGC 2445, the ring galaxy in Arp 143, in CO-12(J = 1-0). Emission is peaked near the ring galaxy nucleus, but we find evidence for an additional asymmetric and extended CO component. This extended CO distribution is consistent with an approximately 8 kpc diameter crescent-shaped ring of molecular gas, similar to the one seen in H I, accounting for approximately half of the total CO flux. Assuming this distribution, we derive a total H2 mass for NGC 2445 of 0.4-2.4 x 10(exp 10) solar mass, depending on whether a Galactic or low-metallicity Large Magellanic Cloud (LMC) conversion factor is used, and an H2/H I mass ratio between 0.9 and 5. The ring is experiencing low rates of massive star formation despite very high gas column densities. We find that the gas surface density exceeds the critical threshold for star formation throughout the ring, even without a possible contribution from a significant molecular component. The absence of vigorous star formation is most simply understood in terms of its youth (approximately 30 Myr): massive stars have not had time to form in large numbers. Our results support the interpretation that NGC 2445 is a nascent ring galaxy, seen prior to its ring starburst phase.

Higdon, James L.↗