摘要:

AbstractHauser-Feshbach calculations of the cross sections for producing selected excited states of27Al,56Fe, and90Zr are compared with experiment. It is found that, in addition to the usual width fluctuation correction factor, modified optical model transmission coefficients are necessary. A simple approximate formula, due to Feshbach, for the modified transmission coefficient is found to give good overall agreement with experiment.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19534

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractExperiments in a large zero-power graphite reactor indicate that simple-point reactor kinetics adequately describe the neutron fluctuation spectra everywhere except near the edges of the reactor. Near the edges, the break frequencies and rolloff slopes differ significantly, and anomalous irregularities in the distribution are observed. Computations explicitly for the large reactor, based on recently proposed theories, also agree excellently away from the edges, and fail to predict the measured spectra near the boundary.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19535

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractCalculations are presented of the thermal-neutron flux as a function of position in a water moderator surrounding a variety of thick targets which are bombarded by protons in the energy range 540 to 2000 MeV. The calculated results are compared with experimental values, and very good agreement is obtained. Results are also given for the thermal-neutron flux as a function of position in a D2O moderator and for the energy deposition in the targets and the moderators.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19536

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractNeutron total cross sections in the energy range from 1 to 11 MeV have been experimentally evaluated for several shielding materials by comparing calculations and measurements of the spectra of the uncollided flux transmitted through thick samples. This technique provides a critical test of the minima in the cross sections but yields little information about the resonance regions. Special emphasis has been placed on evaluating the total cross sections in the Evaluated Nuclear Data File (ENDF/B), which, in most cases, are the best available, the exceptions being for iron and tungsten.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19537

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThejNmethod is applied within the context of a multigroup model to solve neutron transport problems for an infinite homogeneous slab with finite thickness under the assumption that the scattering of neutrons is spherically symmetric in the laboratory system. Stationary space-angle energy-dependent problems are treated as a special case of time-dependent problems. The numerical results for the vector flux generated by a stationary boundary source show that thej5approximation gives an accuracy comparable to theS8approximation in Carlson's theory, regardless of the size of the system. The transient time behavior of leakage neutrons is calculated on the basis of a one-group model and compared with Monte Carlo results. Thej7approximation gives values which agree well with those of the Monte Carlo calculation. In addition, the leakage neutron fluxes from copper blocks are obtained by the use of a 7 groupj7approximation as a function of time and the decay constants are compared with the experimentally observed values.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19538

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractApproximate solutions to the one-velocity neutron transport equation for an infinite cylinder with isotropic scattering and spatially piecewise constant cross sections are obtained by Fourier expansion of the neutron distribution function in one of the angular variables. An infinite coupled set of equations for the expansion coefficients is derived and general properties of the solutions to the truncated set of equations are discussed. A scheme for solving these equations by Gauss quadratures is given, and, as an example, the solution to the bare infinite cylinder critical problem is given in three orders of approximation. Excellent accuracy is obtained with a fairly small investment of analytical effort. The extension of the method to include the effects of anisotropic scattering is sketched.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19539

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractLocal and weighted transient temperatures in a cylindrical, cladded fuel rod and a single-phase compressible coolant are determined by a linear analytical model applying Laplace transformation. All independent variables determining the channel temperatures and the interaction between fuel, canning, and coolant temperatures are taken into account. Assuming constant material properties in the fuel rod, the calculation of fuel and clad temperature is shown to require four functions defined such that one argument is real and depends on geometry only. Material properties affect only the other (imaginary) argument, and different properties result in parallel displacement of the functions. These features enable a relative general presentation of the functions for various geometries and material properties. The functions determining coolant temperature may be given in an integral-free form if, essentially, the can-to-coolant heat transfer coefficient is space independent. The model was originally developed for use in steam cooled fast reactor analysis. It may be applied to other fast or thermal systems with single-phase coolants. Furthermore, it may serve as a means for evaluating numerical approximations of nonanalytical finite difference methods (e.g., to establish the necessary number of subregions).

ISSN:0029-5639    

DOI:10.13182/NSE68-A19540

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe ability to obtain accurate solutions to time-dependent group diffusion problems by simultaneously synthesizing in both thezandtdimensions is demonstrated numerically. The potential of the combined space-time synthesis method becomes apparent from several comparisons of synthesis solutions with exact (in a finite difference sense) two-group, two-dimensional, time-dependent diffusion solutions for two different reactor geometries.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19541

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractMeasurements of the pulse-height distribution of gamma rays observed as a function of position and angle in the water shield of the Bulk Shielding Reactor II, a water-moderated and water-cooled pool-type reactor with stainless steel clad fuel plates, have been transformed to gamma-ray energy flux spectra by a computer program which removed the effects of the spectrometer's nonunique pulse-height response and accounted for the energy variation of the spectrometer's efficiency. The results show that the photons above 5 MeV originate primarily from thermal-neutron capture in the components of the stainless steel. Gamma rays due to the57Fe component were identified as those known to be at 5.91, 6.02, and 7.6 MeV. Others were due to58Fe at 10.16 MeV, to54Cr at 8.88 and 9.72 MeV, and to59Ni at 8.53 and 8.99 MeV. Below 5 MeV the spectra consist of a strong contribution at 2.2 MeV from thermal-neutron capture in the hydrogen of the pool water, combined with a continuum presumably composed of prompt and delayed gamma rays following fission, lower energy components in the capture spectra from the stainless steel, scattering in the reactor or shield, and other lesser sources.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19542

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe statistical method for calculating neutron cross sections in the unresolved resonance region has been extended to permit the construction of ladders for higher angular momentum neutrons and for all accessible spin states (and substates) of the compound nucleus. The new method is an improvement over existing methods in that a fitting procedure is adopted to ensure that the constructed sequence of resonances reproduces resonance integrals inferred from low-resolution experimental results. Thes- andp-wave components of the capture cross section of238U have been computed between 4 and 80 keV using a sequence of resonances obtained by fitting over the energy range 4 to 15 keV. The calculated238U capture cross section is in excellent agreement with published data in the energy range 25 to 60 keV.

ISSN:0029-5639    

DOI:10.13182/NSE68-A19543

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor