摘要:

AbstractThis paper considers a system that involves the attack of water vapor on a graphite cylinder such as occurs in gas-cooled nuclear reactors. Its purpose is to describe such a system, develop a mathematical model for it, and provide a means of solving the model. This is accomplished by first discussing the transport and rate mechanisms of the system: convective transport of reactants by an inert flowing stream, solid-state diffusion into a porous conduit, and chemical reaction with the conduit material. Based on these mechanisms, mass balance equations are written which give a mathematical description of the system. This mathematical model is then solved by two essentially different numerical techniques.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20911

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractFlow boiling crisis can be categorized into at least two types: Departure from Nucleate Boiling (DNB) in the subcooled and low-quality region and dry-out in the high-quality region. To analyze the DNB flux in a rod bundle, the flow conditions should be evaluated by a subchannel analysis and a single-channel DNB correlation can be used for predictions. Rod-bundle DNB data have been presented to verify the above statement.The uncertainties in the measured DNB heat fluxes are listed as: statistical nature of flow turbulences and surface conditions,±3% fabrication tolerances of test sections,±5% imperfectness of correlation in handling the parameter effects,±5% and random and systematic instrumentation errors and various loop system characteristics,±10%. The probability of a rod bundle reaching DNB for a given DNB ratio predicted by W-3 correlation has been evaluated and demonstrated for its use.The effect of a DNB rod in a rod bundle is considered as not detrimental and not contagious. The above statement is demonstrated and evidenced by a photograph of the bird's-eye view of DNB and two sets of experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20912

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe total neutron cross section of182Ta has been measured from 0.01 to 1000 eV using the MTR fast chopper. The observed total neutron cross section at 0.0253 eV is 8200±600 b. Parameters of individual resonances below 30 eV and average parameters at higher energies give a resonance absorption integral of 943±50 b and a neutrons-wave strength functionof (1±0.1)×10−4(eV)1/2. The possible use of182Ta as a neutron temperature monitor is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20913

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe capture cross section of238U has been measured absolutely at a neutron energy of 30 keV using kinematically collimated neutrons from the7Li(p, n)7Be reaction near threshold. Activation techniques were used to determine both the number of capture events and the number of neutrons that occurred during the irradiation. The result of the238U capture cross section measurement is 479±14 mb at 30 keV. In addition, the shape of the238U capture cross section has been measured for neutron energies from 25 to 500 keV using neutrons from the7Li(p, n)7Be reaction. The capture reactions in the238U target were detected using a large liquid scintillator tank and time-of-flight techniques. The relative neutron flux was measured using a flat response neutron detector. The cross-section shape measurement was normalized to the present absolute measurement at 30 keV. The present measurement has been compared with several measured values, theoretical calculations, and compiled values of the238U capture cross section as given by other authors.

ISSN:0029-5639    

DOI:10.13182/NSE68-2

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe General Atomic Neutron Velocity Selector has been used to study the details of neutron scattering in reactor-grade graphite. The scattering into various angular directions between 30 and 120°has been studied for incident neutrons with energies ranging up to 0.611 eV. The energy-transfer cross sections, corrected for plural scattering effects, have been evaluated to provide data in regions of large energy and momentum transfers not previously available and not readily accessible to experimenters using a reactor as a source of neutrons. The results are quite definitive and, when compared to the best available theory, indicate some regions of good agreement and some regions where a more complete theoretical treatment would be useful.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20915

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe results of an extensive slow-neutron inelastic scattering study of heavy water at 299°K are reported. High-energy resolution measurements were made on thin D2O samples to obtain the double-differential scattering cross sections for energy transfers to 7kTand momentumtransfers to 9.5Å−1. A spectral density for the modes of motion in D2O has been obtained by an extrapolation technique. Experimental results are presented in the form of the Egelstaff scattering function and are compared with calculations based on the McMurry-Russell modification of the Nelkin model for water and the Egelstaff-Schofield theory for an incoherent scatterer with a Gaussian self-correlation function.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20916

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractCentral reactivity contributions of gram-sized samples of244Cm,239Pu, and235U have been obtained in a fast critical assembly of bare239Pu in a spherical geometry. Resulting values are:244Cm = (1276±5%) cents/g at.;239Pu = (1393±3%) cents/g at.;235U = (701±2%) cents/g at. From these data, the critical mass of a bare sphere of244Cm is estimated to be (27.7±2.5) kg at a density of 13.5 g/cm3.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20917

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractFluctuation spectra of the current from a neutron-sensitive ionization chamber located in a reactor have been determined experimentally with increased precision. The cold and clean Bulk Shielding Reactor core was held critical and at various subcritical reactivities up toρ=−10β. The amplified current fluctuations were processed on-line in a ten-channel spectrum analyzer utilizing analog-computer components. The shapes of the spectra, and the values of neutron generation time and reactivity inferred therefrom, were in good agreement with theoretical predictions and with values measured using the pulsed-neutron technique. The results were the same for the two detector locations investigated.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20918

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe pulsed-neutron experiment discrete time-decay constants are examined in slab and spherical geometries using a one-term degenerate isotropic scattering kernel. The integral form of the space-, energy-, and time-dependent neutron-transport equation is considered in the proof of four theorems that determine the nature of the decay constants as a function of system size. The theorems are verified by actual calculation of the decay constants for the simpler of the two degenerate-kernel models considered. The spatial eigenfunctions that become flatter as system size is decreased are also computed. The one-velocity problem is solved as a special case.Pulsed-neutron experiment size-dependent extrapolation distances are defined and calculated in such a way as to bring exp (iB·r) theory decay constant results into agreement with those obtained by a more rigorous treatment of the spatial dependence, even for vanishingly small systems. Again, the monoenergetic problem is included as a special case. The variable extrapolation distances approach the Milne problem value as system size is increased. The variation of the extrapolation distance with system dimension is discussed in terms of opposing effects of the thermalization and transport phenomena.Estimates of leakage angular distributions and energy spectra in slabs are calculated from single iterations (performed analytically) on spatial functions synthesized from asymptotic solutions using the size-dependent extrapolation distances. The nature of the singularity in the angular distributions within extremely small systems is investigated. Finally, physical explanations for the changes in the leakage angular distributions and energy spectra (which are diffusion cooled) with slab dimensions are proffered.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20919

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe pulsed-neutron experiment fundamental mode discrete time-decay constant has been calculated as a function of system size for spherical light water assemblies using realistic H2O scattering models by the discrete-ordinates method. Comparison with experiment shows agreement to be good. The computed energy spectra and angular distributions of the fundamental mode neutron fluxes are discussed and physical interpretations of their behavior are proffered. The effect of including various orders of anisotropy in the scattering kernel is examined. Decay-constant calculations were also performed for a model that neglects chemical binding. The results are compared with those based on models that include binding (and are in good agreement with experiment). The effects of chemical binding in neutron thermalization are shown to be significant by this comparison.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20920

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor