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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Multi-Physics System-level Simulations of a Generic Pebble Bed High-Temperature Gas Cooled Reactor with Coupled SAM/Griffin Model

A SAM model for a 200 MWth generic pebble bed high-temperature gas-cooled reactor (PBHTGR) is presented in this work. As an extension to the modeling effort from FY-22 (Ooi et al. (2022)), an improved core channel approach is used to model the pebble bed of the reactor. The improvement greatly simplifies the model and reduces the run time of the model. Furthermore, the SAM model is coupled to the Griffin reactor physics model from Stewart et al. (2021) using the MOOSE MultiApp system where neutronics calculations are performed by the Griffin model and thermal hydraulics calculations by the SAM model. Favorable predictions are produced by the SAM/Griffin coupled model for steady-state normal operating condition. A load-following transient is also simulated with the coupled model where the neutronics and thermal hydraulics responses of the core are predicted correctly by the model. A protected Pressurized Loss of Forced Cooling (PLOFC) accident is simulated with the SAM model, in which the reactor power is determined using the decay heat curve, and therefore the Griffin model is not needed and thus decoupled. A simplified RCCS (Reactor Cavity Cooling System) loop is added to the model to remove decay heat from the core during the transient. Qualitatively, the prediction by the SAM model matches the expected behavior of a PB-HTGR during a PLOFC accident.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2018

NICER Detection of Strong Photospheric Expansion during a Thermonuclear X-Ray Burst from 4U 1820–30

The Neutron Star Interior Composition Explorer (NICER) on the International Space Station (ISS) observed strong photospheric expansion of the neutron star in 4U1820–30 during a Type I X-ray burst. A thermonuclear helium flash in the star’s envelope powered a burst that reached the Eddington limit. Radiation pressure pushed the photosphere out to ∼200 km, while the blackbody temperature dropped to 0.45 keV. Previous observations of similar bursts were performed with instruments that are sensitive only above 3 keV, and the burst signal was weak at low temperatures. NICERʼs 0.2–12 keV passband enables the first complete detailed observation of strong expansion bursts. The strong expansion lasted only 0.6 s, and was followed by moderate expansion with a 20 km apparent radius, before the photosphere finally settled back down at 3 s after the burst onset. In addition to thermal emission from the neutron star, the NICER spectra reveal a second component that is well fit by optically thick Comptonization. During the strong expansion, this component is six times brighter than prior to the burst, and it accounts for 71% of the flux. In the moderate expansion phase, the Comptonization flux drops, while the thermal component brightens, and the total flux remains constant at the Eddington limit. We speculate that the thermal emission is reprocessed in the accretion environment to form the Comptonization component, and that changes in the covering fraction of the star explain the evolution of the relative contributions to the total flux.

Keek, L.↗
DOE OSTI2024

Critical response to M. Worrall et al. Published in Annals of Nuclear Energy 207 (2024) 110731

M. Worrall et al. recently published a manuscript titled “Fast neutron irradiation capability in existing thermal test reactors” (Worrall, 2024) that summarizes an irradiation vehicle design that would boost the fast neutron flux in the Advanced Test Reactor (ATR) for testing of nonfuel materials in a neutron flux energy spectrum that is more representative of fast reactors. Here, the authors compare their design with a separate vehicle design that they conceived of that would be implemented within the High Flux Isotope Reactor (HFIR). They analyzed both designs and drew conclusions on the most realistic near-term options for shielded nonfuel material irradiations.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2022

Thermal expansion and phonon anharmonicity of cuprite studied by inelastic neutron scattering and ab initio calculations

Inelastic neutron scattering measurements were performed with a time-of-flight chopper spectrometer to observe phonons in all parts of the Brillouin zone of a single crystal of cuprite Cu 2 O. We reduced the experimental data to phonon dispersions in the high-symmetry directions, and changes between 10 and 300 K are reported. In this paper, we show ab initio quasiharmonic (QH) and anharmonic (AH) calculations of phonon dispersions. We performed all AH calculations with a temperature-dependent effective potential method. Both QH and AH calculations account for the small negative thermal expansion of cuprite at low temperatures. However, the measured temperature-dependent phonon behavior was predicted more accurately with the AH calculations than the QH ones. Nevertheless, at 300 K, the cubic AH used in this paper did not entirely account for the experimental phonon dispersions in cuprite.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Comparison of Zirconium Redistribution in BISON EBR-II Models Using FIPD and IMIS Databases with Experimental Post Irradiation Examination

Metallic fuels have seen increased interest for future sodium fast reactors due to their material properties: high thermal conductivities and advantageous neutronic properties allow for greater fission densities. One drawback to typical metallic fuels is zirconium redistribution, which impacts this advantageous material and its neutronic properties. Unfortunately, the processes behind zirconium migration behavior are understood using first principles, so before these fuels are implemented in future fast reactors, characterization and fuel qualification regimes must be completed. These activities can be supported through the use of robust modeling using the most accurate empirical models currently available to fuel researchers around the world. The tool that allows researchers to model this complex coupled thermo-mechanical behavior and nuclear properties is BISON. Additionally, BISON model parameters need to be compared against PIE measurements. The current work utilizes two fuel pins from EBR-II experiment X441 to optimize various model parameters, including porosity correction factor, thermal conductivity, phase transition temperature, and diffusion coefficient multipliers, before implementing the final model for seven fuel pins with differing characteristics. To properly evaluate the BISON simulations, the results are compared to PIE metallography data for each fuel pin, to ensure the zirconium redistribution is properly reflected in the simulation results. Six out of seven analyzed fuel pins demonstrate good agreement between the metallography images and BISON results, showing alignment of the Zr-rich, Zr-depleted, and moderately Zr-enriched zones at various axial heights along the fuel pins. Further work is needed to refine the model parameters for general pin use.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2017

X-Ray Reflection and an Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143

Thermonuclear X-ray bursts from accreting neutron stars power brief but strong irradiation of their surroundings, providing a unique way to study accretion physics. We analyze MAXI/Gas Slit Camera and Swift/XRT spectra of a day-long flash observed from IGR J17062-6143 in 2015. It is a rare case of recurring bursts at a low accretion luminosity of 0.15% Eddington. Spectra from MAXI, Chandra, and NuSTAR observations taken between the 2015 burst and the previous one in 2012 are used to determine the accretion column. We find it to be consistent with the burst ignition column of 5x10(exp 10) g cm (exp −2), which indicates that it is likely powered by burning in a deep helium layer. The burst flux is observed for over a day, and decays as a straight power law: F gamma t (exp −1.15). The burst and persistent spectra are well described by thermal emission from the neutron star, Comptonization of this emission in a hot optically thin medium surrounding the star, and reflection off the photoionized accretion disk. At the burst peak, the Comptonized component disappears, when the burst may dissipate the Comptonizing gas, and it returns in the burst tail. The reflection signal suggests that the inner disk is truncated at approximately 102 gravitational radii before the burst, but may move closer to the star during the burst. At the end of the burst, the flux drops below the burst cooling trend for 2 days, before returning to the pre-burst level.

ccretion↗
DOE OSTI2020

NS 1987A in SN 1987A

The possible detection of a compact object in the remnant of SN 1987A presents an unprecedented opportunity to follow its early evolution. The suspected detection stems from an excess of infrared emission from a dust blob near the compact object’s predicted position. The infrared excess could be due to the decay of isotopes like 44 Ti, accretion luminosity from a neutron star or black hole, magnetospheric emission or a wind originating from the spin down of a pulsar, or to thermal emission from an embedded, cooling neutron star. In this work it is shown that the last possibility is the most plausible as the other explanations are disfavored by other observations and/or require fine-tuning of parameters. Not only are there indications that the dust blob overlaps the predicted location of a kicked compact remnant, but its excess luminosity also matches the expected thermal power of a 30 yr old neutron star. Furthermore, models of cooling neutron stars within the minimal cooling paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron star. If correct, a long heat transport timescale in the crust and a large effective stellar temperature are favored, implying relatively limited crustal n- 1 S 0 superfluidity and an envelope with a thick layer of light elements, respectively. If the locations do not overlap, then pulsar spin down or accretion might be more likely, but the pulsar’s period and magnetic field or the accretion rate must be rather finely tuned. In this case, NS 1987A may have enhanced cooling and/or a heavy-element envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

PheniX: A New Vision for the Hard X-ray Sky

We are proposing a mission devoted to high energy X-ray astronomy that is based on a focusing telescope operating in the 1-200 keV energy range but optimized for the hard X-ray range. The main scientific topics concern: Physics of compact objects: The proximity of compact objects provides a unique laboratory to study matter and radiation in extreme conditions of temperature and density in strong gravitational environment. The emission of high energy photons from these objects is far from being understood. The unprecedented sensitivity in the high energy domain will allow a precise determination of the non-thermal processes at work in the vicinity of compact objects. The full 1-200 keV energy coverage will be ideal to disentangle the emission processes produced in the spacetime regions most affected by strong-gravity, as well as the physical links: disk-thermal emission-iron line-comptonisation-reflection-non-thermal emission-jets. Neutron stars-magnetic field-cyclotron lines: Time resolved spectroscopy (and polarimetry) at ultra-high sensitivity of AXP, milliseconds pulsars and magnetars will give new tools to study the role of the synchrotron processes at work in these objects. Cyclotron lines-direct measurement of magnetic filed-equation of state constraints-short bursts-giant flares could all be studied with great details. AGN: The large sensitivity improvement will provide detailed spectral properties of the high energy emission of AGN's. This will give a fresh look to the connection between accretion and jet emission and will provide a new understanding of the physical processes at work. Detection of high-redshift active nuclei in this energy range will allow to introduce an evolutionary aspect to high-energy studies of AGN, probing directly the origin of the Cosmic X-ray Background also in the non-thermal range (> 20 keV). Element formation-Supernovae: The energy resolution achievable for this mission (<0.5 keV) and a large high energy effective area are ideally suited for the 44Ti line study (68 and 78 keV). This radioactive nuclei emission will give an estimate of their quantities and speed in their environment. In addition the study of the spatial structure and spectral emission of SNR will advance our knowledge of the dynamics of supernovae explosions, of particles acceleration mechanisms and how the elements are released in the interstellar medium. Instrumental design: The progress of X-ray focusing optics techniques allows a major step in the instrumental design: the collecting area becomes independent of the detection area. This drastically reduces the instrumental background and will open a new era. The optics will be based on depth-graded multi-layer mirrors in a Wolter I configuration. To obtain a significant effective area in the hundred of keV range a focal length in the 40-50 meters range (attainable with a deployable mast) is needed. In addition such a mission could benefit from recent progress made on mirror coating. We propose to cover the 1-200 keV energy range with a single detector, a double-sided Germanium strip detector operating at 80 K. The main features will be: (a) good energy resolution (.150 keV at 5 keV and <.5 keV at 100 keV), (b) 3 dimensional event localization with a low number of electronic chains, (c) background rejection by the 3D localization, (d) polarisation capabilities in the Compton regime.

PHENIX↗
DOE OSTI2020

PARAMETRIC EVALUATION OF ALTNERNATIVE NUCLEAR PROPULSION CORES USING CURVED FUEL PLATES

Nuclear Thermal Propulsion (NTP) holds the potential of reducing travel times for deep space missions (e.g. to Mars). Previous reactor core designs considered by the Rover/NERVA program relied on highly enriched uranium (HEU) fuel contained within a hexagonal graphite matrix. An alternative layout is investigated in this paper. It consists of a circular assembly containing concentric curved plates of UN fuel. These fuel assemblies are placed within a beryllium block and reflector. Preliminary results indicate that many variations of this design are viable, with high power to mass ratio and outlet temperatures.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1984

Neutron and X-ray diffraction of plasma-sprayed zirconia-yttria thermal barrier coatings

ZrO2-7.8mol. pct. YO1.5, a fused powder, and ZrO2-8.7mol. pct. YO1.5, a prereacted powder, were plasma-sprayed onto steel substrates. Neutron diffraction and X-ray diffraction of the as-received powder, the powder plasma sprayed into water, as-sprayed coatings, and coatings heat-treated for 10 and 100 h were carried out to study phase transformations and ordering of the oxygen ions on the oxygen sublattice. The as-received fused powder has a much lower monoclinic percentage than does the pre-reacted powder, this resulting in a much lower monoclinic percentage in the coating. Heat treatment increases the percentages of the cubic and monoclinic phases, while decreasing the tetragonal content. An ordered tetragonal phase is detected by the presence of extra neutron diffraction peaks. These phase transformations and ordering will result in volume changes. The implications of these transformations on the performance of partially stabilized zirconia thermal barrier coatings is discussed.

Shankar, N. R.↗
DOE OSTI2025

Improvement and Verification of Online Cross Section Generation Capability of Griffin for TRISO-fueled Reactors

Griffin, a MOOSE-based reactor multiphysics code jointly developed by Idaho National Laboratory and Argonne National Laboratory under the DOE Office of Nuclear Energy’s NEAMS program, has pursued the development of an online multigroup cross section generation capability for a few years to enable high-fidelity, problem-dependent neutronics analyses of advanced thermal reactors. Recent advancements in Griffin’s online multigroup cross section generation capability have significantly improved the accuracy, robustness, and efficiency of self-shielding calculations for both prismatic and pebble-bed TRISO-fueled reactor applications. Key developments include a unified fuel self-shielding method applicable to both TRISO and annular compact/spherical shell fuel zone geometries; an advanced Dancoff Category-based Equivalence Theory using a bell function for non-fuel resonance treatment, achieving more than an order-of-magnitude speedup compared to the Tone method; an on-the-fly multigroup equivalence approach to mitigate group condensation errors; and a streaming correction method for pebble-bed homogenization. A proof-of-concept demonstration of on-the-fly group condensation with consistent P0 transport correction was also achieved. The method reproduced direct fine-group solutions with excellent accuracy (eigenvalue errors within 10 pcm and pin-power differences within 0.5%), but due to performance limitations of the current fixed-source solver, improvements to solver efficiency will be addressed in future work. Verification tests were performed on graphite-moderated TRISO-fueled two-dimensional core benchmark problems representing gas-cooled microreactors, heat pipe-cooled microreactors, gas-cooled pebble-bed reactors, and fluoride salt-cooled high-temperature reactors. Across all cases, Griffin showed excellent agreement with Serpent2 continuous energy Monte Carlo solutions: eigenvalue errors within 200 pcm, pin-power root-mean-square errors within 2%, and control rod and drum worth errors less than 2%. It should be noted that, for the benchmark problem, cross section generation contributed less than 3% of the total simulation times. These results demonstrate that Griffin’s online cross section generation capability delivers accurate and efficient reactor physics solutions across a wide spectrum of TRISO-fueled advanced reactor designs. With further improvements to the fine-group fixed-source solver and planned extensions to depletion, transients, and coupled neutron–gamma transport, Griffin will be well-positioned to become a powerful and comprehensive tool for advanced reactor analysis.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1992

Cooling of neutron stars

It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

Pethick, C. J.↗
DOE OSTI2022

Accelerated coupled Monte Carlo-Thermal hydraulic calculations using a hybrid GTF-diffusion-based prediction block: first results

Accurate predictions of spatial power and temperature distributions require the coupling of a neutron transport solver with a thermal-hydraulic (TH) feedback. Nowadays, Monte Carlo (MC) codes are widely coupled to TH solvers, typically via a Picard iteration (PI) method, due to the higher fidelity that such frameworks can produce. To speed up a PI, a prediction step can produce an improved initial guess for a source distribution and feed it to the MC code. Recent work investigated a prediction step that uses generalized transfer functions (GTFs) to predict the macroscopic cross sections' variations following a perturbation in TH properties, such as coolant density. The previous method also relied on first order perturbation (FOP) theory to predict perturbed power profiles, rather than using an expensive MC iterate. The implemented FOP method relied on generating a fission matrix from which the forward and adjoint Eigenmodes were extracted and later used to for power calculations. The generation of the fission matrix can introduce a significant computational overhead, therefore undermining the performance of the proposed hybrid technique when applied to high-dimensional problems, e.g., full core calculations. This work attempts to improve the GTF-FOP prediction step by replacing the FOP solver with a nodal diffusion solver, thus eliminating the need to calculate a fission matrix. The GTF-diffusion step was tested for various moderator density perturbations. In each case, the predicted power distribution showed good agreement with the reference case. The latter is attributed to the generally good prediction of most spatially distributed macroscopic cross sections, except the transport cross section, which will become the focus of future work. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

Investigation of neutron noise in a micro-scale, natural circulation molten salt fission battery system

The Molten Salt Reactor (MSR) concept is a rapidly evolving Generation IV design that has recently attracted favorable attention due to the potential for reducing waste generation, realizing passive safety features, and seizing on the opportunity for cost effective economics. A specific novel micro-MSR, natural circulation, battery design concept involves placing all primary components within a single reactor vessel containment without the need of primary forced pumping. This small modular, integral design presents potential cost savings while producing safety, reliable, and transportable carbon-free power for decades. This investigation evaluates the neutron noise induced by density and flow fluctuations in a natural circulation MSR battery concept being developed at the University of Idaho. This study finds numerical solutions to the one-dimensional, one-group, coupled diffusion equations for a bare, homogeneous core, and evaluates neutron flux and delayed neutron precursor concentration noise due to core flow and fuel salt density perturbation sources. Noise analysis shows both point kinetic and space-dependent behavior is present despite the small size, low-flow, closely-coupled nature of the natural circulation MSR concept. Analysis shows that the low flow of the convective system results in noise behavior typically representative of a larger forced-circulation MSR system. Finally, noise techniques may also be useful in MSR core diagnostics as a non-invasive, low-cost radiological option to traditional monitoring schemes.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Reactor physics characterization of triply periodic minimal surface-based nuclear fuel lattices

Triply periodic minimal surface (TPMS) lattices are receiving substantial attention in numerous engineering fields due to their impressive topology-driven physical characteristics. TPMS lattices are periodic structures of two distinct intertwined volume domains separated by an area-minimizing surface or wall. TPMS lattices have been observed in nature, such as biological membranes, skeletons, block copolymers, sea urchins, butterfly wings, and equipotential surfaces in crystals. Intriguingly, the topology of TPMS lattices can be easily parametrized via level-set equations and thus are heavily numerically and experimentally studied. Here, a significant research effort is currently applying TPMS lattices for heat exchangers and sinks. This paper extends TPMS lattice applications to nuclear reactor fuel designs, with a focus on identifying relevant TPMS geometric parameters controlling neutronics characteristics, such as reactivity, neutron spectrum, and heat removal properties. We found that fuel surface-area-to-volume ratios for TPMS lattices can be two orders of magnitude larger than current cylindrical fuel rods. Further, the selected TPMS lattice and its implicit equation, the unit cell pitch, wall thickness, and structure porosity are design parameters enabling neutronics optimization for both thermal and fast spectrum configurations, paving the way for exceptionally compact and dense nuclear core concepts.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

Transforming Thermal Expansion from Positive to Negative: The Case of Cubic Magnetic Compounds of (Zr,Nb)Fe 2

Negative thermal expansion (NTE) is an intriguing property for not only fundamental studies but also technological applications. However, few NTE materials are available compared with the huge amount of positive thermal expansion materials. The discovery of new NTE materials remains challenging. In this paper, we report a chemical modification strategy to transform thermal expansion from positive to negative in cubic magnetic compounds of (Zr,Nb)Fe 2 by tuning the magnetic exchange interaction. Furthermore, an isotropic zero thermal expansion can be established in Zr 0.8 Nb 0.2 Fe 2 (α 1 = 1.4 x 10 -6 K -1 , 3-470 K) over a broad temperature range that is even wider than that of the prototype Invar alloy of Fe 0.64 Ni 0.36 . The NTE of (Zr,Nb)Fe 2 is originated from the weakened magnetic exchange interaction and the increased d electrons of Fe by the Nb chemical substitution, so that the magnetovolume effect overwhelms the contribution of anharmonic lattice vibration.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Data transfers for full core heterogeneous reactor high- fidelity multiphysics studies

Multiphysics simulations for nuclear reactor analysis are usually performed by resorting to operator splitting and fixed point iterations between single-physics solvers. This enables the separate solution of each physics, such as neutronics, fuel performance, and thermal hydraulics, on meshes tailored to the requirements of the respective numerical discretizations of the equations. As the equations are coupled, several fields must be transferred between single-physics solves. Projecting fields between meshes while preserving order of accuracy, conservation properties, and mapping non-overlapping geometries is a complex endeavor. This conference paper will present the transfers as implemented in MOOSE, which can handle arbitrary meshes, arbitrary mappings, conservation of integral quantities, and are made to scale with distributed simulations on both ends of the transfers. Their adequacy for advanced nuclear reactor multiphysics coupling is shown through examples and numerical studies.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

Cost Drivers for a Tokamak-Based Compact Pilot Plant

A comprehensive systems code that includes a range of physics and engineering considerations along with a simplified costing model has been utilized to evaluate the primary cost drivers for a compact tokamak pilot plant. The systems code has been benchmarked against several tokamak reactor designs and is utilized with sophisticated optimization algorithms to develop optimal solutions for a set of user-specified assumptions and design constraints. Here, in contrast to previous models that have focused on the cost of electricity as the key cost metric, this study uses the estimated capital cost of the facility. The analysis suggests that a pilot plant with the following features may offer potential for a cost-attractive pilot plant: A ~ 3, H 98y2 > 1.5, P net = 200 MW, 𝜏 𝑝⁢𝑢⁢𝑙⁢𝑠⁢𝑒 ~ 1 to 2 h utilizing rare-earth barium copper oxide (REBCO) magnet technology and a plug-bucked central solenoid/toroidal field (CS/TF) magnet support structure. While REBCO magnets offer some advantages relative to Nb 3 Sn magnets in all cases, the most gain is obtained when combined with the plug-bucked CS/TF bucking solution. Pulsed operation reduces capital cost requirements relative to steady-state operation, especially at low confinement. Cost sensitivity studies indicate that there are significant cost uncertainties associated with the achievable confinement quality, tritium breeding capability, attainable thermal efficiency, and achievable neutron wall loading, suggesting that these areas are the most critical areas in reducing the cost risk for a compact tokamak pilot plant. Further cost sensitivity studies indicate that the estimated cost is most sensitive to the underlying cost of the magnetic coils, providing further impetus to better establish cost-effective means for producing fusion magnets.

Compact pilot plant↗