摘要:

AbstractDecomposition of the energy-dependent neutron transport equation in plane geometry into simpler coupled one-speed and slowing down equations offers a relatively simple way of approximately solving the transport problem. This paper demonstrates how this decomposition can be made and illustrates the solution of the transport equation in the TPNapproximation. Using the methods developed, the infinite medium Green’s function and albedo problems are solved in the age diffusion approximation.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21451

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThe expression for the average energy of the two interacting particles undergoing a thermonuclear reaction is developed, and results are presented for selected reactions between light isotopes. It is shown that the assumption that the average energy is equal to 3kT is only valid for a 1/υrelative cross-section dependence.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21452

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractDifferential cross sections are reported for elastic scattering of neutrons from16O. Source neutrons were provided by the D(d,n)3He reaction with average neutron energies of 9.21, 9.71, 10.21, 10.70, 10.95, 11.15, 11.95, 12.45, 12.94, 13.94, and 14.93 MeV. Time-of-flight spectra were obtained for neutrons scattered by a BeO sample at 28 angles from 25 to 160 deg in 5-deg increments. Flight paths of 4 and 6 m were used. Spectra obtained with a separate beryllium sample were subtracted to remove the beryllium scattering contribution. The angular distribution data were corrected for finite source and finite sample-size effects. Legendre polynomial coefficients and total elastic scattering cross sections are reported for oxygen. The data are not well reproduced by the spherical optical model because of the many resonances in the total neutron cross section. Inclusion of resonances together with an optical model background improves the fits to the angular distribution and total cross-section data.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21453

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractPrompt neutron capture from highly enriched samples of the stable silver isotopes was measured at the Oak Ridge Electron Linear Accelerator neutron time-of-flight facility. Resonance peaks were parameterized from 2.65 to 7 keV, and average capture cross sections were derived as a function of energy up to 2000 keV. The average values for the109Ag(n,γ) cross section are a few percent smaller than for107Ag up to 700 keV, above which energy they drop more rapidly, falling to∼60% of the107Ag(n,γ) cross section at 2000 keV Average radiation widths found for spin 1 resonances were 152±7 meV for107Ag and 146±6 meV for109Ag. Maxwellian average cross sections for kT = 30 keV are 801 mb for107Ag and 778 mb for109Ag with estimated uncertainties of 3%.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21454

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractNeutron total cross sections of natural chromium were measured from 1.0 to 4.5 MeV with intermediate energy resolution at intervals of≲50 keV. Elastic and inelastic differential scattering cross sections were determined over the energy and angular range of 1.5 to 4.0 MeV and 20 to 160 deg, respectively. Scattered neutron groups were observed corresponding to average inelastic excitation energies of 1.433±0.009, 2.377±0.008, 2.665±0.005, 2.778±0.007, and 2.970±0.006 MeV. The experimental results were examined in terms of the spherical optical statistical model with additional consideration of the vibrational direct excitation of the 1.433 first-excited level.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21455

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractWe present algorithms, describe a computer program, and give a computational procedure for the statistical consistency analysis of neutron cross-section data, SNcalculations, and measured tritium production in 14-MeV neutron-driven integral assemblies. Algorithms presented include a reduced matrix manipulation technique suitable for many-group, 14-MeV neutron transport calculations. The computer program incorporates these algorithms and is expanded and improved to facilitate analysis of such integral experiments. Details of the computational procedure are given for a natural lithium deuteride experiment performed at the Los Alamos National Laboratory. Results are explained in terms of calculated cross-section sensitivities and uncertainty estimates. They include a downward adjustment of the7Li(n,xt) 14-MeV cross section from 328±22 to 284±24 mb, which is supported by the trend of recent differential and integral measurements. It is concluded that with appropriate refinements, the techniques of consistency analysis can be usefully applied to the analysis of 14-MeV neutron-driven tritium production integral experiments.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21456

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractThis paper describes current analysis and modeling results of large-scale steam explosion experiments. For the large-scale experiments, a transient one-dimensional explosion model was developed that can qualitatively predict the trends in the experimental data. The model employs a description of vapor film collapse and subsequent fuel fragmentation by thermal and mechanical means. In addition, a simple empirical explosion model was developed and incorporated into a two-dimensional hydrodynamic computer program. This combination can be used to investigate the two-dimensional characteristics of the propagation and expansion phases for large-scale explosions.

ISSN:0029-5639    

DOI:10.13182/NSE82-429

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractAn evaluation of the computational efficiency of some spatial discretization schemes has been carried out on a number of slab geometry problems of interest in the shielding field. The achievable accuracy for a given cost of the calculation was compared, taking into account that the actual cost depends on both the computing time and the storage required and using as an error measure the ratio to the“reference solution”for a global quantity like the dose rate or the fast flux. The examined cases include neutron calculations in water, concrete, and steel slabs and, in a pressurized water reactor system, the photon calculations in a lead slab.The main conclusion of the study is that, for a given cost, the exponential scheme supplies solutions more accurate than those of the linear characteristic scheme or, at least, of the same quality.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21458

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractIn this Note a new iterative method for solving the monoenergetic diffusion equation is presented. Experience has shown that the usual iterative methods used to solve the resulting equations either do not converge at all or the number of inner iterations becomes too large when a high-order approximation is used for the spatial flux. Our aim therefore has been to develop a new iterative method that leads to a small number of iterations even for a high order of spatial flux approximation. The present method is additionally expedited using Chebyshev or Wagner and Andrzejewski procedures, which are compared.The SAPHIR benchmark test case with a fixed volume source was used for calculations because it is difficult to converge. It is shown that the present method needs almost the same number of iterations for Lagrangian flux approximation of first to fourth order. This number is smaller than 53. The Chebyshev procedure, which was the most effective, halved the number of inner iterations.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21459

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor

摘要:

AbstractA rigorous formalism is presented for sensitivity analysis of functional-type responses associated with the well-posed system of quasi-linear partial differential equations (PDEs) of hyperbolic type that describe one-dimensional, two-phase flows. The rigor and generality of this formalism stem from the use of G differentials. In particular, it is possible to treat discontinuities and parameters that are functions rather than scalars. This formalism uses adjoint functions to determine efficiently sensitivities to many parameter variations. The adjoint system satisfied by these adjoint functions is explicitly determined and shown to be solvable as a well-posed system of linear first-order PDEs possessing the same characteristics as the original quasi-linear PDEs. For completeness, a general solution of this adjoint system is obtained by using the method of characteristics. The physical meaning of this sensitivity analysis formalism is illustrated by an application to the homogeneous equilibrium model for two-phase flow. Although this formalism does not address transition phenomena between single- and two-phase flow regimes and ignores higher order effects of parameter variations, it provides a complete theoretical framework for implementing an efficient sensitivity analysis capability into one-dimensional, two-phase flow models.

ISSN:0029-5639    

DOI:10.13182/NSE82-A21460

出版商:Taylor&Francis    

年代:1982

数据来源: Taylor