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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

BISON Simulated and Experimental Fission Product Release Comparisons from Reradiated AGR-3/4 Compacts During High Temperature Heating Tests

The fuel performance modeling code BISON was used to predict the release of fission products iodine-131 (131I), xenon-133 (133Xe), and krypton-85 (85Kr) from four re-irradiated AGR-3/4 fuel compacts containing tristructural isotropic (TRISO) coated particles during high-temperature isothermal heating tests. The AGR-3/4 fuel compacts were irradiated in the Advanced Test Reactor (ATR) as part of the third and fourth series of planned experiments to support the Advanced Gas Reactor (AGR) Program. They were subsequently stored and re-irradiated in the Neutron Radiography (NRAD) reactor for approximately five days and then stored for another five to eight days before being subjected to isothermal heating tests in the Fuel Accident Condition Simulation (FACS furnace) for 200 to 300 hours at temperatures between 1000°C and 1600°C to evaluate fission product release at elevated temperatures. New nuclide-specific fission product source term models for the three nuclides of interest were developed using the reactor multiphysics code Griffin and implemented into BISON to support this work. The new source term models were incorporated into coupled compact- and particle-scale BISON simulations, which predict spatially- and temporally-resolved radionuclide generation, radioactive decay, transport, and release throughout the entire irradiation history, including the initial ATR irradiation, NRAD re-irradiations, FACS heating tests, and intermediate periods spent in storage. The experimentally measured fission product release from the heating tests were compared to modeling release predictions calculated by BISON to evaluate how well the code compares to experimental results. Overall, the experimental measured and BISON predicted comparative release results varied but generally agreed to within 5 particle equivalents. Comparative release results identified general observations to take into consideration to help refine future models and reduce uncertainties associated with both the measurement results and predictive results. This includes developing new uranium oxycarbide (UCO) specific kernel diffusivities for the three isotopes examined to more accurately reflect the material properties of the fuel form. Deriving new diffusivities will aid in producing a more informed BISON model

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

AGR-5/6/7 Thermal Model with Non-uniform Gas Gaps

The daily as-run thermal analysis for the Advanced Gas Reactor (AGR)-5/6/7 experiment was documented in ECAR-5633 (Hawkes 2021). A finite element model was created for the entire test train, which consisted of five capsules. The fuel compacts, graphite holders, stainless-steel capsule walls, and all other major components were individually modeled, including all thermocouples (TCs). Daily heat rates for each compact and component in the model were input from daily as-run physics analyses. Daily gas compositions for each capsule were also input. The thermal conductivity of the compacts and graphite holders varied with fast neutron fluence. Gas mixture thermal conductivity was implemented using experimentally attained values from the literature. Fluence and temperature-dependent thermal conductivity was used for the graphite components and the fuel compacts. Radiation heat transfer was implemented. The model was tuned in an attempt to match the TC readings during the first cycle by adjusting the Neolube (graphite lubricant) thickness.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1989

Disk-instability model for soft-X-ray transients containing black holes

Consideration is given to the time-dependent behavior of the accretion disks in low-mass X-ray binaries as a model for soft X-ray transients. The thermal stability and vertical structure properties of the disk are studied in the range between 10 to the 7th and 10 to the 8th cm. An Eulerian time-dependent thin disk model is used to show that, for relevant accretion rates, the disk suffers a thermal instability leading to intermittent accretion onto the central compact object. The disk instability model reproduces the basic features of outbursts of soft X-ray transients. Also, the physical state of quiescence of the binary A0620-00 is examined, focusing on the possible existence of a black hole. It is suggested that the modulation of the accretion flow in the inner disk may be responsible for the bimodal behavior observed in the spectra of black hole candidates such as Cyg X-1, GX 339-4, and A0620-00.

Mineshige, Shin↗
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 NTRS1989

Target signature modeling and bistatic scattering measurement studies

An annual report that summarizes the work done on Grant No. NAG2-542 is presented. There are four areas of study to be summarized: (1) bistatic scattering measurement studies for a compact range; (2) target signature modeling for test and evaluation hardware in the loop situations; (3) aircraft code modification study; and (4) SATCOM antenna studies on aircraft.

Burnside, W. D.↗
NASA NTRS2023

A New Model of Dry Firn Densification Constrained By Continuous Strain Measurements Near South Pole

Converting measurements of ice-sheet surface elevation change to mass change requires measurements of accumulation and knowledge of the evolution of the density profile in the firn. Most firn-densification models are tuned using measured depth-density profiles, a method which is based on an assumption that the density profile in the firn is invariant through time. Here we present continuous measurements of firn-compaction rates in 12 boreholes near the South Pole over a two-year period. To our knowledge, these are the first continuous measurements of firn compaction on the Antarctic Plateau. We use the data to derive a new firn-densification algorithm framed as a constitutive relationship. We also compare our measurements to compaction rates predicted by several existing firn densification models. Results indicate that an activation energy of 60 kJ mol (−1), a value within the range used by current models, best predicts the seasonal cycle in compaction rates on the Antarctic Plateau. Our results suggest models can predict firn-compaction rates with at best 7% uncertainty and cumulative firn compaction on a two year timescale with at best 8% uncertainty.

C. Max Stevens↗
NASA NTRS1999

The Circumstellar Environment of Low Mass Star Forming Regions

The final technical report of the NASA grant project is presented. The goals of the grant were to: (1) analyze the data from the Far-Infrared (FIR) Camera on board the Kuiper Airborne Observatory (KAO); (2) acquire additional data at other wavelengths for models and (4) to develop source models for the Young stellar objects (YSOs)under study. The complete Spectral Energy Distribution (SED) from 10 microns out to 1.3 mm for all sources being studied have been obtained. The FIR imaging data was processed to reveal the maximum angular resolution possible, which allows us to model the disk. To model the disk we have the high resolution millimeter interferometry data. In summary the results to date are: (1) the vast majority of embedded YSOs in Taurus are compact at 100 microns. The models mos consistent with our data and other observations are either dominated by disk emissions, or envelopes that have relatively steep density gradients; (2) the submillimeter/millimeter photometer suggests that models are very successful. Disk emission plays an important role and must be considered when predicting the overall emission. (3) in the two cases, where we seem to have extended emission, we have to investigate other possible source models than a Shu collapse.

Butner, Harold M.↗
DOE OSTI2025

More about the lattice Hamiltonian for Adjoint QCD 2

In our earlier work [1], we introduced a lattice Hamiltonian for Adjoint QCD 2 using staggered Majorana fermions. We found the gauge invariant space of states explicitly for the gauge group SU(2) and used them for numerical calculations of observables, such as the spectrum and the expectation value of the fermion bilinear. In this paper, we carry out a more in-depth study of our lattice model, extending it to any compact and simply-connected gauge group G. We show how to find the gauge invariant space of states and use it to study various observables. We also use the lattice model to calculate the mixed ’t Hooft anomalies of Adjoint QCD 2 for arbitrary G. We show that the matrix elements of the lattice Hamiltonian can be expressed in terms of the Wigner 6j-symbols of G. For G = SU(3), we perform exact diagonalization for lattices of up to six sites and study the low-lying spectrum, the fermion bilinear condensate, and the string tension. We also show how to write the lattice strong coupling expansion for ground state energies and operator expectation values in terms of the Wigner 6j-symbols. For SU(3) we carry this out explicitly and find good agreement with the exact diagonalizations, and for SU(4) we give expansions that can be compared with future numerical studies.

confinement↗
NASA NTRS2004

Iron K Lines from Accretion Disks: Models for Line Production and Spectroscopic Constraints

Measured profiles of the iron K lines provide important dynamical information about emitting matrial in compact objects. However, much of the modeling work which has been used to infer the location and origin of line observed from AGN and galactic black hole sources is based on highly simplified assumptions about the microphysics of K line emission. In particular, many of the intrinsic line energies, widths and emissivities are based on central-field atomic calculations. We present the results of new calculations of the quantities for the entire iron isonuclear sequence, and demonstrate that the intrinsic K line spectra contain considerably more complexity than has been previously considered. We also present calculations of iron K emission and absorption spectra which include the new data, including the local spectrum radiated from an X-ray illuminated accretion disk. The implications for the interpretation of observed iron K lines from black hole sources will be discussed.

Kallman, Timothy↗
DOE OSTI2020

A geospatial model for the analysis of time-dependent land subsidence induced by reservoir depletion

Land subsidence due to fluid depletion is an outcome of physical processes operating across a wide range of time and length scales. Although geomechanical models are crucial to simulate reservoir compaction and predict its long-term fate, their use across large regions often bears prohibitive computational costs. To overcome this obstacle, this paper proposes a simplified modelling framework consisting of (i) a near-field numerical solver simulating the coupling between fluid flow and rock deformation with reference to a simplified one-dimensional geometry and (ii) a far-field geospatial algorithm mapping ground settlements across a region through the superposition of poroelastic computations at multiple wells. The model computes the delay between depletion history and reservoir compaction in proximity of a producing well by assuming basal depletion of a fluid-saturated deformable disk, while the Geertsma solution of nucleus of strain is used to extrapolate the impact of such time-varying reservoir compaction around the well. This approach has been used to back-analyze the spatio-temporal progression of subsidence at the Groningen gas field. The results are compared against measurements collected over 50 year of production at 25 benchmark locations scattered over an area of 900 km 2 . It is shown that coupled simulations based on average values of rock compressibility and permeability lead to nonlinear trends of subsidence evolution in good agreement with field measurements, while uncoupled analyses overpredict settlements by more than 70%. Lastly, synthetic forecasts based on different rates of depletion were provided. The results suggest that slower depletion rates lead to lower subsidence at a given time, and that residual subsidence may continue to develop for several decades after interruption of production activities.

58 GEOSCIENCES↗
DOE OSTI2024

KOMPASS-II: Compaction of Crushed salt for Safe Containment – Phase 2

Long-term stable sealing elements are a basic component in the safety concept for a possible repository for heat-emitting radioactive waste in rock salt. The sealing elements will be part of the closure concept for drifts and shafts. They will be made from a welldefinied crushed salt in employ a specific manufacturing process. The use of crushed salt as geotechnical barrier as required by the German Site Selection Act from 2017 /STA 17/ represents a paradigm change in the safety function of crushed salt, since this material was formerly only considered as stabilizing backfill for the host rock. The demonstration of the long-term stability and impermeability of crushed salt is crucial for its use as a geotechnical barrier. The KOMPASS-II project, is a follow-up of the KOMPASS-I project and continues the work with focus on improving the understanding of the thermal-hydraulic-mechanical (THM) coupled processes in crushed salt compaction with the objective to enhance the scientific competence for using crushed salt for the long-term isolation of high-level nuclear waste within rock salt repositories. The project strives for an adequate characterization of the compaction process and the essential influencing parameters, as well as a robust and reliable long-term prognosis using validated constitutive models. For this purpose, experimental studies on long-term compaction tests are combined with microstructural investigations and numerical modeling. The long-term compaction tests in this project focused on the effect of mean stress, deviatoric stress and temperature on the compaction behavior of crushed salt. A laboratory benchmark was performed identifying a variability in compaction behavior. Microstructural investigations were executed with the objective to characterize the influence of pre-compaction procedure, humidity content and grain size/grain size distribution on the overall compaction process of crushed salt with respect to the deformation mechanisms. The created database was used for benchmark calculations aiming for improvement and optimization of a large number of constitutive models available for crushed salt. The models were calibrated, and the improvement process was made visible applying the virtual demonstrator.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2024

Comparison of Geant4-DNA and RITRACKS/RITCARD: Microdosimetry, Nanodosimetry and DNA Damage Predictions for Low to High LET Ions

Low linear energy transfer (LET) ionizing radiations induce homogeneously distributed DNA damage at the cellular scale, while high LET ionizing radiations are well known to create complex biological damage including clustered double strand breaks (DSB). Clustered DSB are critical events that are difficult to repair, leading to increased biological outcomes compared to low LET radiation exposure. Recent studies have shown that DNA compaction, which can be actively modified by the cell to allow DNA repair, influences the yield of DSB [1]. The goal of this work is to determine the impact of DNA compaction on chromosome aberration formation, a biomarker of radiation-induced cancer risk. The RITRACKS track structure code [2], together with the RITCARD code [3], allow one to simulate the transport of high LET ions, calculate DNA damage and repair, and chromosome aberration formation, but does not include detailed geometrical models of DNA. The Geant4-DNA toolkit provides such detailed models with different levels of DNA compaction [1,4], but does not model chromosome aberration formation. In this work, these highly detailed DNA geometries are used to compute DNA breaks with Geant4-DNA and combine the results with the RITCARD tool to compute chromosome aberrations. As a first step, we compared the transport models used in RITRACKS and Geant4-DNA and newly released heavy ion model transport (G4DNARuddIonisationExtendedModel Geant4 v11.2) to ensure consistency between the physical stage of the two radiation transport codes. We compared energy deposition at the micrometric and nanometric scales for different ions (H 250 MeV, H 150 Me, He 250 MeV/n, C 290 MeV/n, O 350 MeV/n, O 55 MeV/n, Si 170MeV/n, Ti 300 MeV/n, Ti 300 MeV/n, Fe 600 MeV/n, Fe 450 MeV/n and Fe 300 MeV/n) with LET ranging from ~0.4 keV/μm up to 235 keV/μm. Excellent agreement is found for both microdosimetric and nanodosimetric spectra for all ion types and energies. The calculation of DNA breaks and their complexity with the Geant4-DNA is an ongoing work, and comparison with RITCARD will be presented based on result availability at the time of the conference. [1] Tang et al. (2019). Med. Phys., 46(3), 1501-1511. [2] Plante et al. (2008). NJP, 10(12), 125020. [3] Plante et al. (2019). Rad. Res., 192(3), 282-298. [4] Incerti et al. (2018). Med. Phys., 45(8), e722-e739.

Floriane Poignant↗
NASA NTRS1976

A spinar model of Cygnus A

It is proposed that a gravitationally bound supermassive object is located in the 'core' of each of the Cyg A radio clouds and that these objects are responsible for the prolonged ejection of magnetic plasma which produces the synchrotron radio emission. The objects are considered to be analogous to the massive rotators, or spinars, which have been used to model the central radio and optical activity of quasars. The formation of Cyg A is described in terms of the breakup of such an object in the central optical galaxy, and the physical properties of both the compact and the giant clouds are discussed, including the effects of intergalactic drag. It is shown that the spinars are capable of effectively replenishing the extended radio clouds with relativistic electrons, even if they are embedded within the compact clouds. The spinars are modeled quantitatively, and their possible detection is considered. The requirements of the proposed model are compared with those of several other models for bright double radio galaxies.

Flasar, F. M.↗
DOE OSTI2023

Magnetic frame-dragging correction to the electromagnetic solution of a compact neutron star

ABSTRACT Neutron stars are usually modelled as spherical, rotating perfect conductors with a predominant intrinsic dipolar magnetic field anchored to their stellar crust. Due to their compactness, General Relativity corrections must be accounted for in Maxwell’s equations, leading to modified interior and exterior electromagnetic solutions. We present analytical solutions for slowly rotating magnetized neutron stars, taking into account the magnetic frame-dragging correction. For typical compactness values, i.e. Rs ∼ 0.5 [R*], we show that the new terms lead to a per cent order correction in the magnetic field orientation and strength compared to the case, with no magnetic frame-dragging correction. Also, we obtain a self-consistent redistribution of the surface azimuthal current. We verify the validity of the derived solution through two-dimensional particle-in-cell simulations of an isolated neutron star. Defining the azimuthal electric and magnetic field amplitudes during the transient phase as observables, we prove that the magnetic frame-dragging correction reduces the transient wave amplitude, as expected from the analytical solution. We show that simulations are more accurate and stable, when we include all first-order terms. The increased accuracy at lower spatiotemporal resolutions translates into a reduction in simulation runtimes.

Torres, R. (ORCID:0000000291820228)↗
DOE OSTI2025

Gas and dust dynamics in γ Cephei-type disks

Context. Giant planets are observed orbiting the primary stars of close binary systems. Such planets may have formed in compact circumprimary disks, which once surrounded these stars, under conditions much different than those encountered around single stars. Aims. In order to quantify the effects of the strong gravitational perturbations exerted on circumprimary disk material, the three-dimensional (3D) dynamics of gas and dust in orbit around the primary star of a compact and eccentric binary system was modeled by applying the stellar and orbital parameters of γ Cephei, a well-known system that can be representative of a class of close binaries. Methods. Circumprimary gas was approximated as an Eulerian viscous and compressible fluid and modeled by means of 3D hydrodynamical simulations, assuming locally isothermal conditions in the medium around the primary star. Dust grains were modeled as Lagrangean particles, subjected to gravity and aerodynamic drag forces. Models that include a giant planet were also considered. Results. Models indicate that spiral density waves excited around pericenter passage propagate toward the inner boundary of the disk, through at least a few pressure scale-heights from the mid-plane, inducing radial and vertical mixing in the gas. However, perturbations imparted to gas, both in terms of eccentricity and precession, are far weaker than previously estimated by two-dimensional (2D) simulations. Models predict small eccentricities, ≲0.03, and slow retrograde precession. The addition of a giant planet does not change the low eccentricity state of the disk. The parameters applied to the disk would lead to the formation of a massive planet, many times the mass of Jupiter, in agreement with some observations. Micron to mm-size dust grains are well coupled to the gas, resulting in similar dynamics and statistically similar distributions of orbital elements. The planet only affects the dust distributions locally. In agreement with outcomes of recent 2D models, the lifetime of an isolated circumprimary disk would be brief, ~10 5 years, because of its compact nature, requiring a long-term external supply of mass to allow for the in situ formation of a giant planet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Extending the Gutowski model to kidney-bean and elliptically shaped fibers

Efforts by manufacturers to produce more cost-effective carbon fibers have resulted in fibers with irregular cross-section often referred to as kidney-bean shaped fibers. In this research, compaction experiments were performed with a modified laser light section method to evaluate the compaction behavior of kidney-bean shaped carbon fibers. The kidney-bean shaped fibers followed a different compaction behavior compared to the Gutowski model for circular fibers. Additionally, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which has implications in infiltration and consolidation efficiency for composites manufacturing. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the Gutowski model to fibers with irregular cross-sectional shapes. The modified Gutowski model provided an appropriate order of magnitude fit for the kidney-bean fibers. Furthermore, this modification to the Gutowski model recovered the original solution for circular fibers (cross-sectional aspect ratio = 1).

Materials Science↗
NASA NTRS1977

Econ's optimal decision model of wheat production and distribution-documentation

The report documents the computer programs written to implement the ECON optical decision model. The programs were written in APL, an extremely compact and powerful language particularly well suited to this model, which makes extensive use of matrix manipulations. The algorithms used are presented and listings of and descriptive information on the APL programs used are given. Possible changes in input data are also given.

Source record↗