摘要:

Experiments were performed on a large nuclear reactor to investigate the effects of detector placement and reflection on neutron noise spectra and space dependence of detector efficiency. The magnitudes, break frequencies, and rolloff slopes of the spectra were found to be affected by both detector placement and reflection. The space dependence of detector efficiency was found to be proportional to that of average detector count rates.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26603

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

Through the measurement of the kinetic distortion effect, defined as the modal shape and spectral difference between the fundamental prompt- and delayed-neutron modes, a spatial correction factor for the reactivity of the system, as determined by the Gozani and Garelis-Russell modified pulsed-source methods, is obtained. This factor is the ratio of the experimentally determined and properly normalized delayed- and prompt-neutron densities measured in a pulsed-neutron experiment. With this spatial correction factor the reactivity of the system is obtained as a true global parameter. The results of measurements in several235U enriched-uranium cores reflected by light water and by graphite and light water are presented.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26604

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe importance of the multiple reaction correction to cross sections above∼0.1 MeV is demonstrated by deriving a simple formula for a thin-slab sample utilizing a limited multigroup, spatially averaged, transport theory, and applying the formalism to a few examples. To illustrate the immediate relevance of the correction, we also apply it to revise an important cross section in current use, (238Uσnγ, ENDF/B-III). The correction can be large with thicker samples and at higher energies, especially for radiative capture (exceeding a factor of 10). Our examples indicate that multiple reaction effects must be checked in measuring or evaluating radiative capture, fission, reaction, and gamma production cross sections and their consequent spectra.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26605

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The neutron spectra emitted from 0.9, 2.9, and 4.8 mfp of iron for a 14-MeV neutron source have been measured between 14 MeV and 10 keV, using the sphere transmission and time-of-flight techniques. The spectra have also been calculated using the Monte Carlo neutron transport code TART. To reproduce the measurements, a revision of the Lawrence Livermore Laboratory neutron library was carried out. The cross sections were obtained from reported measurements, and a discussion of the revised neutron cross sections is presented. Very good agreement between measurements and calculations was obtained as a function of mean-free-path throughout the entire neutron energy spectrum. Calculations were also carried out with the ENDF/B-III neutron library and compared with the measurements.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26606

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The gamma-ray spectra produced by neutron-induced238U reactions are analyzed, primarily using the statistical model, to provide the data for gamma-ray heating and shielding in the nuclear reactor.The gamma-ray spectra in the low energy neutron capture were calculated by taking into account the discrete and the continuous energy levels, andE1,M1,E2, andM2 electromagnetic transitions. The transition probabilities for primary gamma rays were taken from the data of Price et al. The calculated data are compared with John’s experimental data and Yost’s calculations.To calculate the gamma-ray spectra due to inelastic neutron scattering, theE2 andM1 transitions of the lowest 13 discrete levels of238U were calculated by using the rotational vibrational model of Bohr-Mottelson.The gamma production cross section due to fast-neutron reactions (En>2 MeV) and the prompt gamma-ray spectrum due to fission were calculated by taking into account the yrast levels in the cascade process, as proposed by Thomas and Grover. The calculated prompt gamma-ray spectrum and the total gamma-ray production cross section are discussed in comparison with the experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26607

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

A method for determining narrow upper and lower bounds for the fundamental eigenvalue of a nuclear reactor in either multigroup diffusion theory or transport theory has been developed. This method is based on the Barta-Polya theorem. The Barta-Polya theorem has been extended to yield bounds for multigroup diffusion theory eigenvalue problems.The trial function is a linear sum of known modes and unknown amplitude parameters. Determination of the optimum values of the parameters is a max-min problem of the type that occurs in optimum control and economics. To facilitate numerical computation, a coarse mesh is introduced.A computational method has been developed which quickly yields narrow eigenvalue bounds. Classical methods cannot determine optimum bounds since the function which is to be optimized is not differentiable at the max-min point. The bounds are determined using an iterative method. On each iteration the function is linearized about the mesh points, and linear programming is used to find the optimum solution to the approximate problem. Bounds have been found for a two-region, one-group diffusion theory problem and for a one-group transport theory problem. The bounds are superior to previous results and approach the exact solution as the number of terms in the trial function increases.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26608

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The discrete ordinates algorithm in plane geometry is formulated within a mathematical framework which allows a detailed analysis of its convergence properties. The infinity norm of the iteration matrix is explicitly calculated for a slab geometry with a homogeneous isotropically scattering medium. This approach permits the calculation of a new convergence criterion which, along with the demonstrated convergence properties of theSNalgorithm, guarantees that the fractional iterative error is arbitrarily small.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26609

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractOperations are performed on the neutron transport equation in general form to obtain an exact multigroup Fick’s Law formalism consistent with the standard multigroup conservation equation. The inherent accuracy of the transport equation is maintained in the derived form of the spatially dependent“diffusion coefficient,”which is shown to be highly dependent on the angular flux spectra. Numerical investigations on fast reactor configurations substantiate the feasibility of incorporating a transport calculated diffusion coefficient in existing diffusion theory codes for reactor design and analysis with dual utility: (a) the errors in diffusion calculations due to incorrect diffusion coefficients can be separated from boundary-condition errors, and (b) the diffusion calculations of certain parametric design studies can be improved to accuracy approaching that of transport theory using spatially averaged diffusion coefficients obtained from a single transport calculation.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26610

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe multigroup diffusion equation has been solved by taking buckling to be energy dependent. This form of the solution has been justified in the paper. It has two distinct advantages: (a) the decay constant values so obtained are closer to the experimental results as compared to the ones obtained by taking constant buckling, and (b) it gives a decay constant dependent on the shape of the assembly.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26611

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe experimental total gamma-ray cross sections in the region 30 keV to 17.6 MeV are compared with the recent theoretical values and found to be in satisfactory agreement within 5% in general.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26612

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor