摘要:

An analytical study was carried out to determine the effects of eccentricity on both local and average heat-transfer coefficients for turbulent flow of liquid metals through eccentric annuli. The study was based on the conditions of 1) heat transfer from the inner wall only, 2) heat flux, at a given circumferential angle, independent of length, 3) inner-wall temperature, at a given axial position, independent of circumferential angle, and 4) fully developed velocity and temperature profiles.This study is a sequel to an earlier one, which described a similar case, except that the heat flux in that case %as uniform in all directions. The scopes of the two studies were identical, as far as parameter ranges are concerned.In general, the effects of eccentricity were found to be much less in the present case. For a given radius ratior2/r1, and a given eccentricity, the circumferential variation of the local heat-transfer coefficient and the reduction in the average heat-transfer coefficient were both much less. Moreover, the reduction in the average heat-transfer coefficient, caused by a given degree of eccentricity, was found to be only slightly dependent on the radius ratio, in the present study. This is also in sharp contrast with the results of the previous study.It was further found that circumferential variation of the normalized local heat fluxq/q̄, and, therefore, that of the normalized local heat-transfer coefficient also, remained the same over the large range of Peclet numbers investigated, for a given radius ratio and a given degree of eccentricity.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18036

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Material bucklings and extrapolation distances were measured for several slightly enriched uranium-metal tube lattices and tube-in-tube assembly lattices in light water. The tubes measured were: 1.002 wt%235U enriched uranium (2.34-in. o. d.; 1.79-in. i. d.); 1.25 wt%235U enriched uranium (2.37-in. o. d.; 1.80-in. i. d.); and 1.95 wt%235U enriched uranium (2.28-in. o. d.; 1.41-in. i. d.). The tube-in-tube assemblies measured were: 1.002 wt%235U outer tubes (2.34-in. o. d.; 1.79-in. i. d.) containing 1.002 wt%235U inner tubes (1.18-in. o. d.; 0.49-in. i. d.); and 1.25 wt%235U outer tubes (2.37-in. o. d.; 1.80-in. i. d.) containing 0.95 wt%235U inner tubes (1.18-in. o. d.; 0.48-in. i. d.). Maximum bucklings for the tubes were found to be 25.00, 47.00, and 83.00 m-2, respectively; and for the tube-in-tube assemblies, 23.50 and 38.50 m-2, respectively. Based on the measurements, critical parameters for use in nuclear safety analyses were calculated.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18037

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Small proportional counters containing hydrogen and without collimation have measured reactor neutron spectra with resolution adequate for comparison with existing energy-group methods of calculation over the energy range from 1 keV to 1 MeV. The counters are efficient and operate satisfactorily at low (105/cm2sec) flux levels. Experimental methods currently in use for in-core measurements using proportional counters vary; the one described here makes use of an electronic pulse-shape discrimination to eliminate the background of gamma radiation. The nature of the numerical procedure required to extract neutron spectra from measured energy distributions of recoil protons bears upon the resolution and statistical precision of the result. Examples of measured neutron spectra are given where they illustrate the various points of experimental technique.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18038

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

A measurement of the neutron spectrum at the center of a large, dilute fast reactor is reported over the energy interval from 1 keV to 1 MeV. Resolution of the measurement was about 20% (FWHM) except at the lower energies. Errors in the measurement are described and a comparison made of the measured result with a multienergy-group calculation. There exists fair agreement between the measured spectrum and the multigroup calculation.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18039

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

An experimental method for the determination of the spectral average of the capture-to-fission ratioᾱfor materials inserted in a low-flux reactor is described. The procedure involves a comparison of reactor response to oscillated samples of a fissile material, an absorber, and a spontaneous fission neutron source, plus an experimental determination of fission rate for the fissile material and capture rate for the absorber. In addition, it is necessary that the neutron source be calibrated. These experimental results, combined with a knowledge of the number of neutrons per fission for the fissile material, yield a value of the quantity 1 +ᾱ. This method has been tested in Hi-C Core 10, a critical assembly of 3%-enriched-UO2fuel pins, moderated and reflected by light water, in a lattice spacing which yields a H-to-238U atom ratio of 2:91. The oscillator and absolute counting data yield a value of 0.217 for the central capture-to-fission ratio of235U, with a standard deviation of±0.015. This agrees well with values derived from a combination of measured235U fission cadmium ratios and calculated thermal and epithermal values forα.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18040

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

A method based on a power series expansion of the neutron spectrum in time is used to solve the space-independent Boltzmann equation. The coefficients are obtained from a relatively simple recursion formula well suited for numerical calculations. Assuming the atoms of a hydrogenous moderator free when the neutron energy is large, this formula is further simplified. Adopting the Einstein oscillator model and transforming the recursion formula into a matrix equation, the time-dependent energy spectrum of neutrons in zirconium hydride has been calculated with a small computer.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18041

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Measurements of the spectra of neutrons moderated in LiH were made in the energy range of about 0.01 to 600 eV, and the results were compared with calculated spectra obtained from a Monte Carlo calculation, a direct numerical integration of the Boltzmann equation (NIOBE code), a moments numerical calculation, and three infinite-medium thermalization calculations, each utilizing a different scattering kernel. The measurements were carried out by irradiating slabs of LiH with neutrons having a near-fission spectrum. The spectra of the leakage flux, of the forward-directed flux, and of the scalar flux within the slab were obtained at neutron penetrations of 2.5 to 10 cm. Below 30 eV, the leakage flux and scalar flux attained an asymptotic spectral shape at a penetration of 2.5 cm, and the forward-directed flux at about 5 cm. The shapes of the calculated spectra agree with the shapes of the measured spectra for all energy regions in which each calculation is valid. A large discrepancy between the NIOBE code predictions and the measurements below 0.08 eV is caused by upscattering and molecular binding effects, which are neglected by NIOBE. These effects were included in a neutron thermalization calculation for an infinite medium with a constant source density; however, good agreement with measurement was obtained only for the case in which the measurement had been made in a nearly gradient-free region. In a region of strong flux gradients, the spectrum of the forward-directed flux is shown to be related to that of the scalar flux with good accuracy by the Purohit expression, according to a NIOBE code calculation which yielded both spectra.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18042

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Experiments in which a wide range of scattering materials in the form of slabs were bombarded by reactor neutrons showed that the angular distribution of low-energy (<5-eV) neutrons leaking from the opposite side of a slab is independent of the source term and of the slab thickness for thicknesses greater than some minimum thickness zmin. In the case of pure lead, pure water, and mildly poisoned water, the resulting distributions are in agreement with the Fermi expression. The results for pure lead are also in excellent agreement with one-velocity calculations. An imperfect experiment with poisoned lead is in qualitative agreement with one-velocity calculations. The angular distribution for LiH is described byΦ(µ) = 1 +AµwhereAis less thanfor subcadmium neutrons and greater thanat 1.5 and 5 eV. For energies above 5 eV, a Monte Carlo calculation on LiH showed that A continues to rise to a peak value of about 2.5 at 30 eV, after which it decreases to a value ofabove 103eV, where the absorption cross section of lithium becomes negligible. The applicability of two neutron transport codes that numerically integrate the Boltzmann transport equation was tested in additional calculations for LiH and water. Although the two codes have been used successfully in other types of shielding calculations, they yielded angular distributions for the same material that disagreed with each other, as well as with some experimental data. This suggests that the development of neutron transport codes should include angular distribution tests.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18043

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

A pulse of monoenergetic fast neutrons of several nanoseconds duration is used to excite a lead assembly. The neutron decay is measured as a function of assembly size with conventional nanosecond time-of-flight equipment. The neutron detector is biased to eliminate all nonelasticly scattered neutrons. A theoretical relationship has been developed by Paik which relates the assembly size to the measured decay constant. The nonelastic cross section appears as a parameter in Paik's theory and can be chosen to give the best fit to the experimental data. Decay constants were measured at 2.1 and 1.7 MeV for lead assemblies 20-in. wide x 20-in. high and thicknesses from 1 to 8 in. Paik's theory assumes the establishment of an asymptotic spacial decay mode. This assumption was verified by measuring the neutron decay at various positions of the assembly. The results show that it takes the order of 10 to 15 nsec to establish a spacial mode. This method has been used to measure the total nonelastic cross section for lead at 2.1 and 1.7 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18044

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

The fast-fission cross section of233Pa has been determined for a fission-neutron spectrum originating from a233U source that was exposed to thermal reactor neutrons. The ofwas measured by comparing the fission rate of a known quantity of233Pa to that of a known thorium sample, using back-to-back fission counters. An average above-threshold value of 775±190 mb has been found, based on a fission cross section of 142 mb for232Th and an assumed threshold of 0.9 MeV for233Pa. This value is in very good agreement with published estimated values. The characteristics of the fission counter in the presence of the high beta background resulting from 0.3 to 1.8 Ci of233Pa were investigated and are presented in the paper.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18045

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor