Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Nuclear Modeling”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Engine Cycle Comparison for Alternative Propellant Nuclear Thermal Propulsion Engines

A modular Nuclear Thermal Propulsion (NTP) engine modeling suite was coded in Simulink to analyze various engine cycle configurations and propellants. This model was validated and used for previous studies involving alternative propellants for NTP engines. The current study compared hydrogen-based NTP (H-NTP) with ammonia-based Alternative propellant NTP (A-NTP) engines with expander and bleed cycle configurations. Based on prior work, the bleed cycle configuration was modified to yield a feasible result. The assumption that was made was that the Testing Reference Design (TRD) reactor will be used for all cases and that the difference in fuel loading fractions will be enough to offset any differences in the neutronics caused by switching the propellant. This work provided and compared propellant state points throughout the cycles as well as the key performance parameters. The conclusion was that bleed cycles for H-NTP engines are advantageous over expander cycles in terms of maximum system pressure, cycle simplicity, and potentially engine mass. Conversely, expander cycles are more advantageous for A-NTP engines according to the same scope of parameters. Future work will analyze reactor designs that are different from the TRD and use neutronics software integrated with the X-NTP model to provide higher fidelity results.

Nuclear↗
NASA NTRS1972

Common radiation analysis model for 75,000 pound thrust NERVA engine (1137400E)

The mathematical model and sources of radiation used for the radiation analysis and shielding activities in support of the design of the 1137400E version of the 75,000 lbs thrust NERVA engine are presented. The nuclear subsystem (NSS) and non-nuclear components are discussed. The geometrical model for the NSS is two dimensional as required for the DOT discrete ordinates computer code or for an azimuthally symetrical three dimensional Point Kernel or Monte Carlo code. The geometrical model for the non-nuclear components is three dimensional in the FASTER geometry format. This geometry routine is inherent in the ANSC versions of the QAD and GGG Point Kernal programs and the COHORT Monte Carlo program. Data are included pertaining to a pressure vessel surface radiation source data tape which has been used as the basis for starting ANSC analyses with the DASH code to bridge into the COHORT Monte Carlo code using the WANL supplied DOT angular flux leakage data. In addition to the model descriptions and sources of radiation, the methods of analyses are briefly described.

Warman, E. A.↗
NASA NTRS1971

Comets and nongravitational forces. IV.

Orbital elements and nongravitational parameters are derived from observations at every apparition of the periodic comets Honda-Mrkos-Pajdusakova, Faye, Tempel 2, Biela, Brorsen, and Tempel-Swift. For all except the first comet, the observations go back a century and more, although the last three comets have failed to reappear for some considerable time. The circumstances of the splitting of P/Biela are studied, and it is shown that the motion of the primary component was scarcely affected; it is also demonstrated that, if the primary still exists, it may pass only 0.05 AU from the earth in November 1971. An up-to-date list of mass-loss rates from comets is presented. It is found that, while most of the reliable determinations indicate that the cometary nongravitational effects decrease with time, there are a few cases where the effects increase slightly. The former situation is discussed in terms of a nuclear core-mantle model, implying that these comets will eventually evolve into inert, asteroidal objects, while the nuclei of the other comets are interpreted as coreless, eventually to disappear completely (or almost completely).

Marsden, B. G.↗
NASA NTRS1978

Planetary gamma-ray spectroscopy

The measured intensities of certain gamma rays of specific energies escaping from a planetary surface can be used to determine the abundances of a number of elements. The fluxes of the more intense gamma-ray lines emitted from 32 elements were calculated using current nuclear data and existing models for the source processes. The source strengths for neutron-capture reactions were modified from those previously used. The fluxes emitted form a surface of average lunar composition are reported for 292 gamma-ray lines. These theoretical fluxes were used elsewhere to convert the data from the Apollo gamma-ray spectrometers to elemental abundances and can be used with measurements from future missions to map the concentrations of a number of elements over a planet's surface. Detection sensitivities for these elements are examined and applications of gamma-ray spectroscopy for future orbiters to Mars and other solar-system objects are discussed.

Reedy, R. C.↗
NASA NTRS1978

Gamma ray lines from novae

Activities identify the mechanisms responsible for the eruptions characterizing cataclysmic variables are concerned with close binary systems, the properties of which are dominated by the presence of mass transfer from a late-type star onto a white dwarf via an accretion disk. Theories for the outbursts vary in their identification of the eruption mechanism with either gravitational or nuclear energy sources. Existing models for the dwarf novae invoke a dynamical instability in the envelope of the red star which triggers episodic Roche lobe overflow and a concomitant increase in the rate of mass transfer and the outbursts are associated with an increase in the accretion luminosity liberated in the disk. The most successful theoretical models for common nova events involve thermonuclear runaways proceeding in accreted hydrogen envelopes on the white dwarf components of these systems. The characteristics of such runaway events, which can give rise to detectable gamma ray fluxes are discussed. Salient features of existing runaway models are reviewed. Gamma fluxes from Na-22 decay, positron annihilation, and shock induction are predicted.

Truran, J. W.↗
NASA NTRS1978

Planetary gamma-ray spectroscopy

The measured intensities of certain gamma rays of specific energies escaping from a planetary surface can be used to determine the abundances of a number of elements. The fluxes of the more intense gamma ray lines emitted from 32 elements have been calculated using current nuclear data and existing models for the source processes. The fluxes emitted from a surface of average lunar composition are reported for 292 gamma ray lines. Detection sensitivities for various elements are examined and applications of gamma ray spectroscopy for future orbiters to Mars and other solar system objects are discussed.

Reedy, R. C.↗
NASA NTRS1986

Comparison of abrasion model differences in heavy ion fragmentation - Optical versus geometric models

Two different abrasion formalisms, one based on an energy-independent geometric model and the other based on a quantum-mechanical optical model, are shown to yield comparable fragmentation cross section predictions when used as input to an abrasion-ablation frictional-spectator interaction fragmentation calculation which includes electromagnetic dissociation contributions. The results suggest that any dependence upon the incident ion's kinetic energy above 200 MeV/nucleon is weak. It is also noted that the larger surface diffusiveness of the optical model densities only affects nuclear cross sections for near-projectile-mass fragments, while for heavier nuclei, the sizable cross-section contributions from electromagnetic dissociation negate these differences.

Townsend, L. W.↗
NASA NTRS1989

Charged particle radiation exposure of geocentric satellites

The near-earth radiation environment is characterized, summarizing published data on trapped and transient charged particles and their potential effects on hardware systems and the crews of manned missions. Topics examined include the role of the magnetosphere, the five radiation domains, cyclic and sporadic variations in the radiation environment, the potential effect of a high-altitude nuclear explosion, NASA empirical models for predicting trapped proton and electron fluxes, and the South Atlantic anomaly and the estimation of flux-free periods. Consideration is given to solar cosmic rays and heavy ions, Galactic cosmic rays, geomagnetic shielding, secondary radiation, the design of shielding systems, variables affecting dose evaluations, and ionizing-radiation doses. Extensive diagrams, graphs, and tables of numerical data are provided.

Stassinopoulos, E. G.↗
NASA NTRS1990

Rationalization of Comet Halley's periods

The sense of long axis orientation of Comet Halley during the Vega 1 encounter must be reversed from that deduced by Sagdeev et al. (1986) in order to harmonize the comet nucleus' Vega/Giotto-observed orientations with periodicities extracted from time-series brightness data. It is also demonstrated that Vega/Giotto observations can be satisfied by either a 2.2- or 3.7-day long-axis free precession period. A novel Fourier algorithm is used to reanalyze five independent data sets; strong evidence is adduced for periods harmonically related to a 7.4-day period. The preferred candidate models for Halley's nuclear rotation are characterized by a long-axis precession period of 3.7 days.

Belton, Michael J. S.↗
NASA NTRS1987

Stochastic acceleration in the transrelativistic region and pion production in solar flares

The stochastic Fermi acceleration spectrum in the transrelativistic region obtained from a Monte-Carlo simulation for an energy-independent alpha(T) is much harder than the extension of the nonrelativistic analytic spectrum to this energy range for the same alpha(T). The latter, with alpha(T) = 0.043, was used to model the pion and nuclear line emissions for the impulsive phase of the 3 Jun. 1982 flare, as well as the 2.223 MeV emission from this flare. We find that the ratios of these three emissions for the Monte-Carlo spectrum with alpha(T) = 0.028 are essentially the same as those for the analytical spectrum with alpha(T) = 0.043. We also find that the acceleration time from approximately 30 MeV to approximately 1 GeV is less than or approximately = 10 s, consistent with the observations of the 3 Jun. 1982 flare.

Miller, James A.↗
NASA NTRS1993

Innovative electric propulsion thruster modeling

The objective of this program is to model and evaluate advanced nuclear electric propulsion (NEP) system concepts as an aid to the performance of NEP mission benefits studies. The two primary goals are as follows: (1) provide scaling relationships for mass, power, and efficiency, as functions of Isp, propellant type, and other important quantities. The discussion is presented in vugraph form.

Frisbee, Robert H.↗
NASA NTRS1993

GPS system simulation methodology

The following topics are presented: background; Global Positioning System (GPS) methodology overview; the graphical user interface (GUI); current models; application to space nuclear power/propulsion; and interfacing requirements. The discussion is presented in vugraph form.

Ewing, Thomas F.↗
NASA NTRS1993

Development of deterministic transport methods for low energy neutrons for shielding in space

Transport of low energy neutrons associated with the galactic cosmic ray cascade is analyzed in this dissertation. A benchmark quality analytical algorithm is demonstrated for use with BRYNTRN, a computer program written by the High Energy Physics Division of NASA Langley Research Center, which is used to design and analyze shielding against the radiation created by the cascade. BRYNTRN uses numerical methods to solve the integral transport equations for baryons with the straight-ahead approximation, and numerical and empirical methods to generate the interaction probabilities. The straight-ahead approximation is adequate for charged particles, but not for neutrons. As NASA Langley improves BRYNTRN to include low energy neutrons, a benchmark quality solution is needed for comparison. The neutron transport algorithm demonstrated in this dissertation uses the closed-form Green's function solution to the galactic cosmic ray cascade transport equations to generate a source of neutrons. A basis function expansion for finite heterogeneous and semi-infinite homogeneous slabs with multiple energy groups and isotropic scattering is used to generate neutron fluxes resulting from the cascade. This method, called the FN method, is used to solve the neutral particle linear Boltzmann transport equation. As a demonstration of the algorithm coded in the programs MGSLAB and MGSEMI, neutron and ion fluxes are shown for a beam of fluorine ions at 1000 MeV per nucleon incident on semi-infinite and finite aluminum slabs. Also, to demonstrate that the shielding effectiveness against the radiation from the galactic cosmic ray cascade is not directly proportional to shield thickness, a graph of transmitted total neutron scalar flux versus slab thickness is shown. A simple model based on the nuclear liquid drop assumption is used to generate cross sections for the galactic cosmic ray cascade. The ENDF/B V database is used to generate the total and scattering cross sections for neutrons in aluminum. As an external verification, the results from MGSLAB and MGSEMI were compared to ANISN/PC, a routinely used neutron transport code, showing excellent agreement. In an application to an aluminum shield, the FN method seems to generate reasonable results.

Ganapol, Barry↗
NASA NTRS1999

Accurate Universal Parameterization of Absorption Cross Sections: Light Systems - 3

Our prior nuclear absorption cross sections model is extended for light systems (A less than or equal to 4) where either both projectile and target are light particles or one is light particle and the other is medium or heavy nucleus. The agreement with experiment is excellent for these cases as well. Present work in combination with our original model provides a comprehensive picture of absorption cross sections for light, medium and heavy systems. As a result the extended model can reliably be used in all studies "where there is a need for absorption cross sections.

Tripathi, R. K.↗
NASA NTRS1999

Universal Parameterization of Absorption Cross Sections

Our prior nuclear absorption cross sections model is extended for light systems (A less than or equal to 4) where either both projectile and target are light particles or one is a light particle and the other is a medium or heavy nucleus. The agreement with experiment is excellent for these cases as well. Present work in combination with our original model provides a comprehensive picture of absorption cross sections for light, medium, and heavy systems, a very valuable input for radiation protection studies.

Tripathi, R. K.↗