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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Late-time Cooling of Neutron Star Transients and the Physics of the Inner Crust

An accretion outburst onto a neutron star transient heats the neutron star’s crust out of thermal equilibrium with the core. After the outburst, the crust thermally relaxes toward equilibrium with the neutron star core, and the surface thermal emission powers the quiescent X-ray light curve. Crust cooling models predict that thermal equilibrium of the crust will be established ≈1000 days into quiescence. Recent observations of the cooling neutron star transient MXB 1659-29, however, suggest that the crust did not reach thermal equilibrium with the core on the predicted timescale and continued to cool after ≈2500 days into quiescence. Because the quiescent light curve reveals successively deeper layers of the crust, the observed late-time cooling of MXB 1659-29 depends on the thermal transport in the inner crust. In particular, the observed late-time cooling is consistent with a low thermal conductivity layer near the depth predicted for nuclear pasta that maintains a temperature gradient between the neutron star’s inner crust and core for thousands of days into quiescence. As a result, the temperature near the crust–core boundary remains above the critical temperature for neutron superfluidity, and a layer of normal neutrons forms in the inner crust. We find that the late-time cooling of MXB 1659-29 is consistent with heat release from a normal neutron layer near the crust–core boundary with a long thermal time. We also investigate the effect of inner crust physics on the predicted cooling curves of the accreting transient KS 1731-260 and the magnetar SGR 1627-41.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Effect of Inter-layer Cooling Time on Distortion and Mechanical Properties in Metal Additive Manufacturing (AM)

Laser Metal Deposition with wire (LMD-w) is one of the novel Direct Energy Deposition (DED) processes that is gaining attention in aerospace industry due to the potential cost and lead time reductions for large-scale components. However, improving process parameters (for example, laser power, wire feed rate, robotic travel speed, inter-layer cooling time, etc.) is still under development. These parameters affect thermal gradients that cause residual stresses that in-turn influence distortion. These parameters also affect mechanical properties. Inter-layer cooling time, specifically, is one of the main factors for total production time, and it is used to help mitigate distortion. Therefore, this paper investigated the effects of different inter-layer cooling times on both distortion and mechanical properties. Distortion of deposited Ti-6Al-4V walls was measured automatically using a laser scanner. Finally, suitable recommendations are discussed to optimize the inter-layer cooling time to fabricate components with desired mechanical properties.

Bandari, Yashwanth Kumar↗
DOE OSTI2016

Determining initial enrichment, burnup, and cooling time of pressurized-water reactor spent fuel assemblies by analyzing passive gamma spectra measured at the Clab interim-fuel storage facility in Sweden

The purpose of the Next Generation Safeguards Initiative (NGSI)–Spent Fuel (SF) project is to strengthen the technical toolkit of safeguards inspectors and/or other interested parties. The NGSI–SF team is working to achieve the following technical goals more easily and efficiently than in the past using nondestructive assay measurements of spent fuel assemblies: (1) verify the initial enrichment, burnup, and cooling time of facility declaration; (2) detect the diversion or replacement of pins; (3) estimate the plutonium mass [which is also a function of the variables in (1)]; (4) estimate the decay heat; and (5) determine the reactivity of spent fuel assemblies. Since August 2013, a set of measurement campaigns has been conducted at the Central Interim Storage Facility for Spent Nuclear Fuel (Clab), in collaboration with Swedish Nuclear Fuel and Waste Management Company (SKB). One purpose of the measurement campaigns was to acquire passive gamma spectra with high-purity germanium and lanthanum bromide scintillation detectors from Pressurized Water Reactor and Boiling Water Reactor spent fuel assemblies. The absolute 137 Cs count rate and the 154 Eu/ 137 Cs, 134 Cs/ 137 Cs, 106 Ru/ 137 Cs, and 144 Ce/ 137 Cs isotopic ratios were extracted; these values were used to construct corresponding model functions (which describe each measured quantity’s behavior over various combinations of burnup, cooling time, and initial enrichment) and then were used to determine those same quantities in each measured spent fuel assembly. Furthermore, the results obtained in comparison with the operator declared values, as well as the methodology developed, are discussed in detail in the paper.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

COOLING TIME, FREEFALL TIME, AND PRECIPITATION IN THE CORES OF ACCEPT GALAXY CLUSTERS

Star formation in the universe's largest galaxies—the ones at the centers of galaxy clusters—depends critically on the thermodynamic state of their hot gaseous atmospheres. Central galaxies with low-entropy, high-density atmospheres frequently contain multiphase star-forming gas, while those with high-entropy, low-density atmospheres never do. The dividing line between these two populations in central entropy, and therefore central cooling time, is amazingly sharp. Two hypotheses have been proposed to explain the dichotomy. One points out that thermal conduction can prevent radiative cooling of cluster cores above the dividing line. The other holds that cores below the dividing line are subject to thermal instability that fuels the central active galactic nucleus (AGN) through a cold-feedback mechanism. Here we explore those hypotheses with an analysis of the Hα properties of ACCEPT galaxy clusters. We find that the two hypotheses are likely to be complementary. Our results support a picture in which cold clouds inevitably precipitate out of cluster cores in which cooling outcompetes thermal conduction and rain down on the central black hole, causing AGN feedback that stabilizes the cluster core. In particular, the observed distribution of the cooling-time to freefall-time ratio is nearly identical to that seen in simulations of this cold-feedback process, implying that cold-phase accretion, and not Bondi-like accretion of hot-phase gas, is responsible for the AGN feedback that regulates star formation in large galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Effect of Interlayer Cooling Time, Constraint and Tool Path Strategy on Deformation of Large Components Made by Laser Metal Deposition with Wire

Laser metal deposition with wire (LMD-w) is a developing additive manufacturing (AM) technology that has a high deposition material rate and efficiency and is suitable for fabrication of large aerospace components. However, control of material properties, geometry, and residual stresses is needed before LMD-w technology can be widely adopted for the construction of critical structural components. In this study, we investigated the effect of interlayer cooling time, clamp constraints, and tool path strategy on part distortion and residual stresses in large-scale laser additive manufactured Ti-6Al-4V components using finite element method (FEM). The simulations were validated with the temperature and the distortion measurements obtained from a real LMD-w process. We found that a shorter interlayer cooling time, full clamping constraints on the build plates, and a bidirectional tool path with 180° rotation minimized part distortion and residual stresses and resulted in symmetric stress distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Data Mining Techniques to Estimate Plutonium, Initial Enrichment, Burnup, and Cooling Time in Spent Fuel Assemblies

The Next Generation Safeguards Initiative (NGSI), Office of Nonproliferation and Arms Control (NPAC), National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE) has sponsored a multi-laboratory, university, international partner collaboration to (1) detect replaced or missing pins from spent fuel assemblies (SFA) to confirm item integrity and deter diversion, (2) determine plutonium mass and related plutonium and uranium fissile mass parameters in SFAs, and (3) verify initial enrichment (IE), burnup (BU), and cooling time (CT) of facility declaration for SFAs. A wide variety of nondestructive assay (NDA) techniques were researched to achieve these goals [Veal, 2010 and Humphrey, 2012]. In addition, the project includes two related activities with facility-specific benefits: (1) determination of heat content and (2) determination of reactivity (multiplication). In this research, a subset of 11 integrated NDA techniques was researched using data mining solutions at Los Alamos National Laboratory (LANL) for their ability to achieve the above goals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Data Mining Techniques to Estimate Plutonium, Initial Enrichment, Burnup, and Cooling Time in Spent Fuel Assemblies

The Next Generation Safeguards Initiative (NGSI), Office of Nonproliferation and Arms Control (NPAC), National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE) has sponsored a multi-laboratory, university, international partner collaboration to (1) detect replaced or missing pins from spent fuel assemblies (SFA) to confirm item integrity and deter diversion, (2) determine plutonium mass and related plutonium and uranium fissile mass parameters in SFAs, and (3) verify initial enrichment (IE), burnup (BU), and cooling time (CT) of facility declaration for SFAs. A wide variety of nondestructive assay (NDA) techniques were researched to achieve these goals [Veal, 2010 and Humphrey, 2012]. In addition, the project includes two related activities with facility-specific benefits: (1) determination of heat content and (2) determination of reactivity (multiplication). In this research, a subset of 11 integrated NDA techniques was researched using data mining solutions at Los Alamos National Laboratory (LANL) for their ability to achieve the above goals.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

The Effect of Protoplanetary Disk Cooling Times on the Formation of Gas Giant Planets by Gravitational Instability

Observational evidence exists for the formation of gas giant planets on wide orbits around young stars by disk gravitational instability, but the roles of disk instability and core accretion for forming gas giants on shorter period orbits are less clear. The controversy extends to population synthesis models of exoplanet demographics and to hydrodynamical models of the fragmentation process. The latter refers largely to the handling of radiative transfer in three-dimensional (3D) hydrodynamical models, which controls heating and cooling processes in gravitationally unstable disks, and hence dense clump formation. A suite of models using the β cooling approximation is presented here. The initial disks have masses of 0.091 M {sub ⊙} and extend from 4 to 20 au around a 1 M {sub ⊙} protostar. The initial minimum Toomre Qi values range from 1.3 to 2.7, while β ranges from 1 to 100. We show that the choice of Q {sub i} is equal in importance to the β value assumed: high Q{sub i} disks can be stable for small β , when the initial disk temperature is taken as a lower bound, while low Q{sub i} disks can fragment for high β . These results imply that the evolution of disks toward low Q{sub i} must be taken into account in assessing disk fragmentation possibilities, at least in the inner disk, i.e., inside about 20 au. The models suggest that if low Q{sub i} disks can form, there should be an as yet largely undetected population of gas giants orbiting G dwarfs between about 6 au and 16 au.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Determination of initial fuel state and number of reactor shutdowns in archived low-burnup uranium targets

This article presents a method for destructive analysis of irradiated uranium (U) targets, with a focus on collection and measurement of long-lived (t 1/2 > ~10 years) and stable fission product isotopes of ruthenium and cesium. Long-lived and stable isotopes of these elements can provide information on reactor conditions (e.g. flux, irradiation time, cooling time) in old samples (> 5–10 years) whose short-lived fission products have decayed away. The separation and analytical procedures were tested on archived U reactor targets at Los Alamos National Laboratory as part of an effort to evaluate reactor models at low-burnup.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Growth and evolution of thermal instabilities in idealized galaxy cluster cores

Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times ≲1 Gyr. Both observations and theoretical models have linked the condensation of cold gas with heating by an active galactic nucleus (AGN) through a cycle in which cooling gas fuels the AGN and drives energetic outbursts that reheat the ICM and maintain a state of approximate thermal balance. In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio t{sub cool}/t{sub ff}≲10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. We find that instability leads to convection and that perturbations continue to grow while the gas convects. Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below t{sub cool}/t{sub ff}≲3, even if the volume-averaged timescale ratio is substantially greater. In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. Finally, we find that if condensation is powering feedback, a conversion efficiency of around 10{sup −3} for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Process Variability Effects on Tensile Response in Injection Molded, Fluorinated Thermoplastics

The mechanical properties of fluorinated thermoplastics (i.e., tensile strength and elongation) can vary with changes in injection molding processing parameters. Four fluoropolymers are examined: poly(vinylidene fluoride) (PVDF) and random poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) with three CTFE concentrations. Dog bones were manufactured with various cylinder dwell times and mold cooling times to assess the manufacturing sensitivity to the tensile response. Dwell and cooling times increasingly impact mechanical performance as CTFE concentration increases. Specimens exhibit higher tensile strength as a function of injection order. The first injected specimen exhibits the lowest tensile strength and highest elongation in all copolymers. This trend becomes more pronounced among fluoropolymers with higher CTFE concentration and lower weight-averaged molecular weight. Parallel plate rheology was used to obtain the zero-shear viscosity as a function of material type, process, and injection order. We found that in the copolymers, the first injected sample exhibited a lower zero-shear viscosity than the next, which indicates a lower molecular weight in the first injected specimen. This phenomenon was not presented for the PVDF homopolymer. Copolymer mechanical uncertainties are hypothesized to result from the shorter molecular weight chains extruding out of the specimens' sides as a flash due to higher mobility with CTFE segments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Process Variability Effects on Tensile Response in Injection Molded, Fluorinated Thermoplastics

The mechanical properties of fluorinated thermoplastics (i.e., tensile strength and elongation) can vary with changes in injection molding processing parameters. Four fluoropolymers are examined: poly(vinylidene fluoride) (PVDF) and random poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) with three CTFE concentrations. Dog bones were manufactured with various cylinder dwell times and mold cooling times to assess the manufacturing sensitivity to the tensile response. Dwell and cooling times increasingly impact mechanical performance as CTFE concentration increases. Specimens exhibit higher tensile strength as a function of injection order. The first injected specimen exhibits the lowest tensile strength and highest elongation in all copolymers. This trend becomes more pronounced among fluoropolymers with higher CTFE concentration and lower weight-averaged molecular weight. Parallel plate rheology was used to obtain the zero-shear viscosity as a function of material type, process, and injection order. We found that in the copolymers, the first injected sample exhibited a lower zero-shear viscosity than the next, which indicates a lower molecular weight in the first injected specimen. This phenomenon was not present for the PVDF homopolymer. Copolymer mechanical uncertainties are hypothesized to result from the shorter molecular weight chains extruding out of the specimens’ sides as a flash due to higher mobility with CTFE segments.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Chandra and XMM-Newton observations of the merging cluster of galaxies PLCK G036.7+14.9

We present Chandra and XMM-Newton observations of PLCK G036.7+14.9 from the Chandra–Planck Legacy Program. The high resolution X-ray observations reveal two close (∼72″ = 193 kpc in projection) subclusters, G036N and G036S, which were not resolved by previous ROSAT, optical, or recent Planck observations. We perform detailed imaging and spectral analyses and use a simplified model to study the kinematics of this system. The basic picture is that PLCK G036.7+14.9 is undergoing a major merger (mass ratio close to unity) between the two massive subclusters, with the merger largely along the line of sight (∼80° between the merger axis and the plane of the sky from the simplified model) and probably at an early stage (less than ∼0.4–0.7 Gyr since the merger began). G036N hosts a small (∼27 kpc), moderate cool core (cooling time t{sub cool}∼2.6–4.7 Gyr), while G036S has at most a very weak cool core (t{sub cool}∼5.7–10.3 Gyr) in the central ∼40 kpc region. The difference in core cooling times is unlikely to be caused by the ongoing merger disrupting a pre-existing cool core in G036S. G036N also hosts an unresolved radio source in the center, which may be heating the gas if the radio source is extended. The total mass of the whole cluster determined from XMM-Newton is ∼(5.9−8.0)×10{sup 14} M{sub ⊙}, and is ∼(6.7−9.9)×10{sup 14} M{sub ⊙} from Chandra. The Planck derived mass, ∼(5.1−6.0)×10{sup 14} M{sub ⊙}, is higher than the X-ray measured mass of either subcluster, but is lower than the X-ray measured mass of the whole cluster, due to the fact that Planck does not resolve PLCK G036.7+14.9 into subclusters and interprets it as a single cluster. This mass discrepancy could induce significant bias to the mass function if such previously unresolved systems are common in the Planck cluster sample. High resolution X-ray observations are necessary to identify the fraction of such systems and correct such a bias for the purpose of precision cosmological studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Characterization of coarse bainite transformation in low carbon steel during simulated welding thermal cycles

Coarse austenite to bainite transformation in low carbon steel under simulated welding thermal cycles was morphologically and crystallographically characterized by means of optical microscope, transmission electron microscope and electron backscattered diffraction technology. The results showed that the main microstructure changes from a mixture of lath martensite and bainitic ferrite to granular bainite with the increase in cooling time. The width of bainitic laths also increases gradually with the cooling time. For a welding thermal cycle with relatively short cooling time (e.g. t{sub 8/5} is 30 s), the main mode of variant grouping at the scale of individual prior austenite grains changes from Bain grouping to close-packed plane grouping with the progress of phase transformation, which results in inhomogeneous distribution of high angle boundaries. As the cooling time is increased, the Bain grouping of variants becomes predominant mode, which enlarges the effective grain size of product phase. - Highlights: • Main microstructure changes and the width of lath structure increases with cooling time. • Variant grouping changes from Bain zone to close-packed plane grouping with the transformation. • The change of variant grouping results in uneven distribution of high angle grain boundary. • Bain grouping is main mode for large heat input, which lowers the density of high angle boundary.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Cool core cycles: cold gas and AGN jet feedback in cluster cores

Using high-resolution 3D and 2D (axisymmetric) hydrodynamic simulations in spherical geometry, we study the evolution of cool cluster cores heated by feedback-driven bipolar active galactic nuclei (AGNs) jets. Condensation of cold gas, and the consequent enhanced accretion, is required for AGN feedback to balance radiative cooling with reasonable efficiencies, and to match the observed cool core properties. A feedback efficiency (mechanical luminosity ≈ ϵ M-dot {sub acc}c{sup 2}; where M-dot {sub acc} is the mass accretion rate at 1 kpc) as small as 6 × 10{sup −5} is sufficient to reduce the cooling/accretion rate by ∼10 compared to a pure cooling flow in clusters (with M{sub 200}≲7×10{sup 14} M{sub ⊙}). This value is much smaller compared to the ones considered earlier, and is consistent with the jet efficiency and the fact that only a small fraction of gas at 1 kpc is accreted onto the supermassive black hole (SMBH). The feedback efficiency in earlier works was so high that the cluster core reached equilibrium in a hot state without much precipitation, unlike what is observed in cool-core clusters. We find hysteresis cycles in all our simulations with cold mode feedback: condensation of cold gas when the ratio of the cooling-time to the free-fall time (t{sub cool}/t{sub ff}) is ≲10 leads to a sudden enhancement in the accretion rate; a large accretion rate causes strong jets and overheating of the hot intracluster medium such that t{sub cool}/t{sub ff}>10; further condensation of cold gas is suppressed and the accretion rate falls, leading to slow cooling of the core and condensation of cold gas, restarting the cycle. Therefore, there is a spread in core properties, such as the jet power, accretion rate, for the same value of core entropy or t{sub cool}/t{sub ff}. A smaller number of cycles is observed for higher efficiencies and for lower mass halos because the core is overheated to a longer cooling time. The 3D simulations show the formation of a few-kpc scale, rotationally supported, massive (∼10{sup 11} M{sub ⊙}) cold gas torus. Since the torus gas is not accreted onto the SMBH, it is largely decoupled from the feedback cycle. The radially dominant cold gas (T < 5 × 10{sup 4} K; |v{sub r}|>|v{sub ϕ}|) consists of fast cold gas uplifted by AGN jets and freely infalling cold gas condensing out of the core. The radially dominant cold gas extends out to 25 kpc for the fiducial run (halo mass 7×10{sup 14} M{sub ⊙} and feedback efficiency 6 × 10{sup −5}), with the average mass inflow rate dominating the outflow rate by a factor of ≈2. We compare our simulation results with recent observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Methodology and Software for Gross Defect Detection of Spent Nuclear Fuel at the Atucha-I Reactor [Novel Methodology and Software for Spent Fuel Gross Defect Detection at the Atucha-I Reactor]

Here, fuel assemblies in the spent fuel pool are stored by suspending them in two vertically stacked layers at the Atucha Unit 1 nuclear power plant (Atucha-I). This introduces the unique problem of verifying the presence of fuel in either layer without physically moving the fuel assemblies. Given that the facility uses both natural uranium and slightly enriched uranium at 0.85 wt% 235 U and has been in operation since 1974, a wide range of burnups and cooling times can exist in any given pool. A gross defect detection tool, the spent fuel neutron counter (SFNC), has been used at the site to verify the presence of fuel up to burnups of 8000 MWd/t. At higher discharge burnups, the existing signal processing software of the tool was found to fail due to nonlinearity of the source term with burnup.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

The Relationship Between Brightest Cluster Galaxy Star Formation and the Intracluster Medium in CLASH

We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates (SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far-IR. By comparing these quantities to intracluster medium (ICM) cooling times and freefall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR and the ICM cooling time to freefall time ratio, t{sub cool}/t{sub ff}, with an upper limit on the intrinsic scatter of 0.15 dex. Furthermore, starburst durations may correlate with ICM cooling times at a radius of 0.025 R{sub 500}, and the two quantities converge upon reaching the gigayear regime. Our results provide a direct observational link between the thermodynamical state of the ICM and the intensity and duration of BCG star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable ICM overdensities that fuel long-duration (>1 Gyr) BCG starbursts. This scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between SFR and t{sub cool}/t{sub ff}. We also find that the scaling relation between SFR and dust mass in BCGs with SFRs <100 M{sub ⊙} yr{sup −1} is similar to that in star-forming field galaxies; BCGs with large (>100 M{sub ⊙} yr{sup −1}) SFRs have dust masses comparable to extreme starbursts.

79 ASTRONOMY AND ASTROPHYSICS↗