摘要:

AbstractA self-adjoint positive-definite variational principle is presented which leads to upper and lower bounds for, whereis an integral over position and angular direction of the product of the one-velocity neutron transport flux,ϕand an arbitrary adjoint source,S*. The Euler equation of the functional is a new form of the one-velocity Boltzmann neutron transport equation in which the dependent variable is one-half the sum ofϕandϕ*, whereϕ*is the adjoint flux. When a trial function consisting of an expansion in spherical harmonics is used, one obtains as a lower bound forthe quantity−, whereS1(r,Ω) = [S(r,Ω) + S*(r,−Ω)]/2, S2(r,Ω) = [S(r,Ω)−S*(r,−Ω)]/2,ϕ(P-N′;S1) is anodd P−Napproximation to a problem with the same cross sections as the original problem, but with sourceS1;ϕ(P−N″;S2) is aneven P−Napproximation to a problem with sourceS2, andUis the operator that takes a functionf(r,Ω) intof(r,−Ω).

ISSN:0029-5639    

DOI:10.13182/NSE69-A20009

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA new theoretical formalism of the space-time kinetics is developed for heterogeneous reactor models. The basic time-dependent diffusion equation, which contains terms representing localized absorption and fast-neutron production by fuel rods, has been analytically transformed into a convolution integral form. This enables computation of space- and time-dependent flux for heterogeneous reactors by considering the sizes and spacings of the fuel rods, their geometrical locations, and the nuclear properties of the material used. Although the basic idea and mathematical formalism developed in this paper can be applied for various other space-time kinetics problems, the final calculation is performed for the forced oscillation problem.Two computer codes, HERMITS-1 and HERMITS-2, are developed. By using these codes, it is shown that contour maps of the static flux, phase angles, and amplitudes of neutron waves around the fuel rods can be calculated in an extremely short amount of machine time.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20010

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractAn energy-dependent transport theory solution for the infinite medium neutron-wave propagation problem is obtained by applying a Laguerre polynomial expansion to represent the flux energy dependence. Integral transform methods are utilized to determine solutions appropriate for a general isotropic scattering kernel and general cross sections. Detailed calculations are performed for a two-term polynomial expansion and an energy-dependent cross-section model. Although the polynomial expansion approximation appears to be quite satisfactory for low modulation frequencies, serious inadequacies exist for higher frequencies where continuum effects are important. A critical frequency is not predicted, and the two-dimensional continuum of eigenvalues is approximated by a series of cuts, the number of which depends on the number of terms in the expansion.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20011

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA theoretical study of the axial propagation of plane-thermal-neutron waves in a heterogeneous system is performed in the framework of theP-1 approximation to the Boltzmann equation. The method is based on a modified form of heterogeneous reactor theory due to Feinberg and Galanin. The analysis predicts that the phase interference between the modes of propagation in the axial direction may give rise to resonances in the frequency response of the asymptotic moderator flux. A standing wave pattern is also predicted in the amplitude distribution of the oscillating part of the moderator flux in the axial direction. The relationships between the resonances and the system parameters are investigated. An experimental method that can be useful for the determination of the effective values of the diffusion parameters and the slowing down time is suggested.Numerical calculations for a heavy-water-moderated natural uranium system containing four identical fuel rods are presented in the frequency range from 0 to 1500 Hz. Two resonances are predicted in the transfer function of such a system in this frequency range. A comparison is made with the experimental results published in the literature for a similar system. The complex relaxation length for this system is also calculated numerically in order to study the effect of the resonances in the transfer function on the complex relaxation length. The results show existence of“loops”in the plot of the complex relaxation length.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20012

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA measurement has been made of the effects of flux depression upon the neutron-induced fission rate in235U using self-detection techniques. A thin235U fission detector was irradiated with neutrons from the LRL electron linear accelerator. The change in the fission counting rate was measured when absorber foils of235U were inserted into the neutron beam. The detector consisted of a parallel-plate fission chamber containing eight235U foils of thickness½mg/cm2each. The incident neutron energies were measured by time-of-flight within the energy range from 0.46 eV to 2.1 keV and with a timing resolution of 27 nsec/m. The effect of this relatively poor resolution of the energy-averaged fission rate is eliminated by the self-detection technique. The enriched uranium absorber foils varied in thickness from 0.14 to 19 g/cm2, with a235U content of 93%.In addition,235U fission and total cross sections were measured with comparable resolution.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20013

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractExponential and critical approach experiments have been performed to determine material bucklings and extrapolation distances for several hexagonal lattice arrays of 2.1 wt%235U enriched uranium tubes in light water. Tubes of two sizes were measured–2.33-in. o.d., 1.77-in. i.d.; and 1.38-in. o.d., 0.63-in. i.d. The arrays included clean lattices of uranium tubes; uranium tubes containing lithium aluminate target rods; uranium tubes with adjacent neutron absorbing columns; and two mixed lattices of 0.95 and 2.1 wt% enriched tubes–one with the 0.95 and 2.1 wt% tubes evenly distributed in the lattice, and the other with the 0.95 and 2.1 wt% tubes arranged in alternate rings. These experiments supplement data obtained in 1965 for 1.002, 1.25, and 1.95 wt% enriched uranium tubes. Critical parameters for these lattices, calculated with the HAMMER code, agree reasonably well with the measured results.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20014

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA study of the averages- andp-wave resonance parameters of115In and127I has been carried out by activation of samples in a10B filtered beam of epithermal neutrons from a reactor. Neutron strength functions were obtained that are comparable to recent values obtained by total-cross-section studies but somewhat lower than earlier capture measurements. Thes- andp-wave neutron strength functions for115In were found to be 0.09±0.03×10−4and 3.9±1.4×10−4, respectively, and for127I, the corresponding values were found to be 0.42×10−4and 0.83±0.20×10−4. The average energy-dependent neutron cross sections from 1 to 100 keV were computed for both isotopes from the experimentally determined resonance parameters.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20015

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractEffective removal cross sections for iron and lead that can be applied to fast-neutron dose rate calculations have been determined from calculated spatial-spectral neutron distributions as a function of succeeding polyethylene thickness. These cross sections increase with polyethylene thickness, and for large polyethylene thicknesses, they are in agreement with those derived from experiment. From the spatial-spectral neutron distributions, relative contributions of various neutron energy ranges to the neutron dose rate have been calculated as a function of succeeding polyethylene thickness. For polyethylene thicknesses>30 cm, fast (E>302 keV), epithermal (302 keV>E>0.625 eV), and thermal (E<0.625 eV) neutrons contribute 83, 6, and 11%, respectively, to the neutron dose rate.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20016

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe fast-neutron spectrum and dose rate were measured at various distances from a point fission-neutron source in water and in two aluminum and water mixtures using seven threshold reaction detectors and p-i-n silicon diode dosimeters. The experimental results were compared with calculations made using the ANISN computer code.The threshold reactions used were the115In(n, n′),32S(n, p),64Zn(n, p),27Al(n, p),56Fe(n, p),24Mg(n, p), and27Al(n,α). Using experimentally determined counting efficiencies, absolute saturation activities of the threshold reaction products were determined. A method of neutron-spectrum unfolding was devised which represented the fast-neutron spectrum by a group of successive exponentials, calculated from the saturation activities. The reported spectra generally agreed well with the results predicted by the ANISN code.The fast-neutron dose rate was measured directly using p-i-n junction dosimeters and indirectly by applying flux-to-dose conversion factors to the measured fast-neutron flux. Good agreement was obtained between these measurements and calculations

ISSN:0029-5639    

DOI:10.13182/NSE69-A20017

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe steady-state flux of matter of molecular size from a mixture of vapor and noncondensable gas to the walls of a large containment vessel during the condensation of vapor can be predicted with the present analysis. A boundary layer approach has been used in formulating the mass-transfer problem and the resulting equations are solved numerically. Charts are presented for the flux of molecular iodine from a steam-air mixture to the walls of the containment vessel during the condensation of steam. Knowing the total pressure and the temperature of the bulk mixture, the wall temperature, and the concentration of air and iodine in the bulk mixture, the rate of removal of iodine from the vessel can be predicted. The analysis is correlated with an experiment and close agreement is found.

ISSN:0029-5639    

DOI:10.13182/NSE69-A20018

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor