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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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Scalable algorithms for domain decomposition of Monte Carlo neutral particle transport simulations on unstructured mesh

Monte Carlo simulations are the gold standard in particle transport simulations, for shielding and nuclear reactor simulations Full core simulations can require terabytes of memory for tracking pin-resolved (up to 50k pins), nuclide (200 tracked), axial (20-200 zones) reaction rates Domain decomposition, splitting the calculation and the memory storage, among several nodes is challenging as it involves communication of particles across domain boundaries We created a new MOOSE application, MaCaw, to study this problem Algorithms developed for ray tracing in MOOSE were adapted for simulating neutral particle transport Physics and tally routines in OpenMC, dynamically linked, are called from the application

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Embedding Neural Thermal Scattering (NeTS) Modules in SERPENT for Higher Fidelity Advanced Reactor Analysis

When a neutron born in fission thermalizes to the order of $k$ $B$ $T$, it’s de-Broglie wavelength and energy approach the order of inter-atomic spacing and elementary lattice oscillations, respectively. $S$($a,β,t$) or the scattering law, uuantify these temperature-dependent crystallographic contributions to total cross section (or reaction rate). In a Monte Carlo analysis, cumulative distribution functions (CDFs) of $S$($a,β,t$) are loaded to memory from “A Compact ENDF” (ACE) files for stochastically selecting thermal scattered neutron trajectories. In this work, novel neural thermal scattering (NeTS) modules for $S$($a,β,t$) CDFs are designed, trained, serialized and embedded within SERPENT using Python’s limited C-API for on-the-fly deployment of crystalline graphite $S$($a,β,t$) sampling. Torchscript tracing and Numba just-in-time (JIT) compilation streamline neural inference on NVIDIA GPUs with CUDA libraries. Demonstrations of bare sphere thermalization of fast and thermal sources show excellent agreement between embedded NeTS in SERPENT and MCNP. With an explicit model of the reactor, NeTS can predict on-the-fly changes in TREAT neutron spectra as a function of local temperature, which can serve to improve transient and accident predictions in a multiphysics analysis framework. This framework can be further extended to account on-the-fly for changes in local graphitic microstructure to scattering cross sections, and outlines a novel coupling of modern machine learning with state-of-the-art reactor physics methods.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Investigation of Ring-heterogeneous Geometry Approximation for Efficient and Practical SFR Analysis

A novel geometry approximation scheme named ring-heterogeneous approximation for intermediate resolution multiphysics analysis of SFRs is presented. This approach particularly targets neutronics coupled with thermo-mechanics feedback, which dominate the passive safety of SFR designs. The ring-heterogeneous approximation casts an array of pins into volume-preserving bands of materials that constitute the pins. It allows to efficiently simulate SFRs with an unstructured mesh and also to explicitly consider the deformation of each material by retaining their heterogeneity. Verification results with single assembly and core problems of the ABTR benchmark demonstrated that the ring-heterogeneous approximation is a reasonable approximation for SFRs. For a 2D full core problem, the ring-heterogeneous approximation significantly reduced the number of elements by at least a factor of 70 from a fully-heterogeneous mesh while almost exactly preserving the reference fully-heterogeneous solutions with the RMS error of only 0.02% in the ring-wise fission reaction rate.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Analysis of SPND Material Candidates for Real-Time Neutron Spectrum Monitoring Poster

The future of the nuclear industry will be shaped by advanced reactor designs requiring innovative instrumentation for safe operation. A key area of innovation is the ability to accurately and reliably monitor the neutron energy spectrum during operations, which would also enhance the experimental capabilities of existing research reactors. To address this need, our research focuses on the potential use of Self-Powered Neutron Detectors (SPNDs) for real-time neutron spectrum monitoring. We investigated various candidate materials for SPNDs by evaluating their energy-dependent reaction rates. Promising materials were further modeled using MCNP to determine the free electron production per neutron across the neutron energy spectrum, approximating their energy-dependent signal sensitivity. Our findings identified Samarium (Sm) and Gadolinium (Gd) as top candidates for thermal neutrons, Hafnium (Hf) and Thulium (Tm) for epithermal neutrons, and Tantalum (Ta) for fast neutrons. These materials will undergo future experimental validation to confirm the modeled responses and assess their feasibility for real-time neutron spectrum measurements.

46 - INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AN↗
DOE OSTI2025

The CO2 mineralization potential of New Mexico basalts and associated critical element behavior and mobility.

This presentation reports on laboratory experiments assessing the carbon dioxide (CO₂) mineralization potential of New Mexico basalts, including trachybasalt and basalt lithologies. Using simulated groundwater and controlled conditions, the study evaluates the kinetics of CO₂ sequestration, mineral saturation indices, and secondary mineral formation. It also investigates the mobility of critical and trace elements such as Ni, Zn, Cu, and Li during basalt dissolution. Results indicate that New Mexico basalts can effectively sequester CO₂ through carbonate formation, with grain size and mineral composition influencing reaction rates and elemental behavior. These findings support the viability of geologic carbon storage in mafic volcanic terrains and inform strategies for critical element recovery.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High-fidelity Pebble Bed Reactor Depletion Based on Pebble Tracking Transport in Griffin

The pebble tracking transport (PTT) method is a high-fidelity, heterogeneous deterministic transport technique for pebble bed reactor analysis. It discretizes the broad-group neutron transport equation in space and angle with the discontinuous finite element and the discrete ordinates method, and utilizes various solving techniques, including mesh sweeping and diffusion acceleration, to provide pebble- wise reaction rates. This work presents the extension of the PTT method to enable fuel depletion capability in the Griffin code. We discuss the implementation details of the PTT-based high-fidelity depletion where isotope inventory of all individual pebbles is tracked through pre-determined pebble flow paths in the core. The implementation is verified with a generic pebble bed reactor model. Some preliminary equilibrium core results are included. Future works are also discussed.

97 - MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Kinetic Plasma Simulation Capabilities in the MOOSE Framework: Verification of Particle-Particle Collisions

High-fidelity simulations of complex plasma systems allow researchers to gain key insights into and understanding of these systems. To facilitate massively parallel high-fidelity plasma simulations, finite-element-based particle-in-cell capabilities are being developed within the open-source Multiphysics Object-Oriented Simulation Environment (MOOSE) based framework called Software for Advanced Large-scale Analysis of MAgnetic confinement for Numerical Design, Engineering & Research (SALAMANDER). While SALAMANDER’s primary objective is modeling edge plasmas and plasma-facing components in fusion devices, the particle-in-cell capabilities being developed are general and will support modeling low-temperature plasmas as well. Previously, collisionless magnetostatic simulation capabilities have been verified with the two-stream and Dorey-Guest-Harris instabilities, and single particle motion. Collisions were implemented using the direct simulation Monte Carlo method, and verification of this capability will be presented here several verification problems: relaxation of a randomly initialized gas to a Maxwellian distribution, Fourier heat flow, and comparison of reaction rates to both analytic calculations and those calculated using a multi-term Boltzmann solver.

70 - PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1988

Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

Gokoglu, Suleyman A.↗
NASA NTRS1994

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH3CHF2) and (for CH2Cl2) HFC-161 (CH3CH2F). Using absolute rate constants for HFC-152a and HFC-161, which we have determined relative to those for CH4, CH3CCl3, and C2H6, temperature dependent rate constants of both compounds were derived. The derived rate constant for CH3Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH2Cl2 where the present rate constant is about a factor of 1.6 below the JPL 92-20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates.

Hsu, K.-J.↗
DOE OSTI2022

Shock tube/laser absorption measurement of the rate constant of the reaction: H 2 O 2 + CO 2 2OH + CO 2

We address the role of the linear mixing rule in the kinetics of the H 2 O 2 decomposition system by reporting the rate constant for H 2 O 2 + M = 2OH + M (M = Ar and CO 2 ) in the temperature range of 1087-1234 K at low pressures in a mixture of 20% CO 2 in Argon. The reaction rate constant was inferred from H 2 O concentrations monitored by using a laser-absorption spectroscopy-based water diagnostic. To the best of our knowledge, this is the first measurement of the rate constant of this reaction in a mixture to be reported in literature. A significant discrepancy was found between the rate constants derived using the traditional linear mixing rule and the reduced pressure linear mixing rule. Furthermore, this discrepancy can have serious implications on the predictive accuracy of these kinetic models, especially under conditions relevant to the operation of supercritical CO 2 (sCO 2 ) power cycles that rely on oxy-fuel combustion in a working fluid comprised almost entirely of CO 2 .

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1976

Absolute rate of the reaction of O/3-P/ with hydrogen sulfide over the temperature range 263 to 495 K

The technique of flash photolysis coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction of O(3-P) with H2S at temperatures from 263 to 495 K and at pressures in the range 10-400 torr. Under conditions where secondary reactions are avoided, the measured rate constants for the primary step obey the Arrhenius equation k = (7.24 plus or minus 1.07) x 10 to the -12th exp(-3300 plus or minus 100/1.987 T) cu cm/molecules/s. Experiments with D2S show that the reaction exhibits a primary isotope effect, in support of a hydrogen abstraction mechanism.

Whytock, D. A.↗
DOE OSTI2020

Methods and compositions to increase the rate of ligation reactions catalyzed by a sortase

In various embodiments methods and compositions to increase the rate and/or activity of ligation reactions catalyzed by a sortase. In certain embodiments reagents are provided that comprises, inter alia, a polypeptide comprising an amino terminal polyglycine sequence comprising at least three contiguous Gly residues (e.g., a triglycine sequence, a tetraglycine sequence, a pentaglycine sequence, etc.) followed by a peptide that is to be ligated to a moiety followed by a sequence comprising the catalytic domain of a Sortase A enzyme.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Rates of hydroxyl radical reactions with some HFCs

Relative rate constants for OH reactions with some HFCs have been determined at 298 K by a technique which measures the loss of HFC greater than OH. The following ratios were determine: k(152a)/k(CH4) = 5.2 +/- 0.5, k(CH4)/k(125) = 3.9 +/- 0.5, k(CH4)/k(134a) = 2.1 +/- 0.2, k(134a)/k(125) = 2.0 +/- 0.2, and k(C2H6)/k(152a) = 6.2 +/- 1.0. These results are in good agreement with literature values for the absolute rate constants except for HFC 134a, where a slower rate constant is indicated.

Demore, William B.↗
NASA NTRS1978

Absolute rate of the reaction of atomic hydrogen with ethylene from 198 to 320 K at high pressure

The rate constant for the H+C2H4 reaction has been measured as a function of temperature. Experiments were performed with high pressures of Ar heat bath gas at seven temperatures from 198 to 320 K with the flash photolysis-resonance fluorescence (FP-RF) technique. Pressures were chosen so as to isolate the addition rate constant k1. The results are well represented by an Arrhenius expression. The results are compared with other studies and are theoretically discussed.

Lee, J. H.↗
NASA NTRS1977

Photochemistry of the Martian atmosphere

A critical analysis is carried out for models which may be fine tuned to give agreement with observational constraints for O2, CO, and O3 in the Martian lower atmosphere and which are in accord also with upper atmospheric data for O and CO. The models have a number of features in common: dynamic mixing must be exceedingly rapid at heights above 90 km; if heterogeneous processes are not assumed to play a major role in the removal of atmospheric CO and O2, mixing must be rapid at heights between 30 and 40 km. The value implied for the diffusion coefficient in this region depends on the assumptions made regarding the rates for reaction of OH with HO2 to form H2O and the rate of reaction of HO2 with itself to form H2O2. If these reaction rates are taken to have values similar to those used in current models of the earth's stratosphere, the eddy diffusion coefficient at 40 km above the Martian surface should be about 5 by 10 to the seventh power sq cm/sec.

Kong, T. Y.↗
NASA NTRS1984

The rate of the reaction of OH with HCl

Using the techniques of laser/flash photolysis-resonance fluorescence, the absolute rate constant for the OH + HCl reaction is measured from 240 to 295 K. Ultraviolet and infrared spectrophotometry are used to continuously monitor the HCl concentrations. It is shown that the rate constant values obtained in the study are 20-30 percent larger than those recommended by Smith and Zellner (1974) and Ravishankara et al. (1977) for modeling of stratospheric chemistry.

Molina, M. J.↗
NASA NTRS1985

Rate constant for the reaction Cl + HO2NO2 yielding products

The rates for the reaction of Cl atoms iwth HO2NO2 were calculated from data obtained by the use of the discharge flow/resonance fluorescence (DF/RF) and the discharge flow/mass spectrometric (DF/MS) techniques. The total rate constant, k1, for the overall reaction: 1a (Cl + HO2NO2 yielding HCl + NO2 +O2), 1b (yielding HO2 + ClNO2), and the two possible additional channels was found to be less than 1.0 x 10 to the -13th cu cm/s at 296 K. The value of (k1a + k1b) was found to be 3.4 + or - 1.4) x 10 to the -14th cu cm/s. Thus, the reaction of Cl with peroxynitric acid is too slow, by a factor of 100, to contribute significantly to the hydrogen abstraction by Cl in the stratosphere.

Simonaitis, R.↗