摘要:

AbstractThe equivalence relation for the calculation of resonance capture employs a modified rod radius to account for inaccuracies in the Wigner rational approximation of the probability of escape from the rod. In this paper we extend older work to derive a correction to the mean chord length which depends on the peak resonance cross section, the potential scattering, and the rod radius. Such a formula represents a useful compromise between use of the less accurate but computationally convenient equivalence relation and accurate but computationally complex methods.By fitting the radius modifier over a wide range of values, the following representation is found:

ISSN:0029-5639    

DOI:10.13182/NSE70-A21214

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA class of resonant absorbing cross sections was found for which there are simple exact solutions of the neutron moderation equation. Some of these solutions are compared with corresponding numerical solutions obtained by the methods of Rowlands, Nordheim, and Finkelstein. The first two methods are accurate for narrow and intermediate absorption resonances but develop instability when relatively strong (with respect to scattering) absorption extends for a few or more collision intervals. Then only the third method may be used with confidence.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21215

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA multigroup, collision-probability, order-of-scattering approach is made to the slowing down solution of the neutron transport equation in a heterogeneous, non-multiplying medium with sources. Introducing first-collision probabilities in the Liouville-Neumann series solution of the neutron flux, the series may be summed and a transport matrix defined. If a flat source distribution in the region is assumed, this matrix is typical of the medium and of the geometrical configuration only and links, in an explicit way, sources and resultant fluxes. In a multiplying system without external sources it is also possible to use the above transport model when determining the effective neutron multiplication factor by the fission probability matrix method.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21216

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe effect of the errors in presently available delayed-neutron data on various calculations and measurements in reactor physics is analyzed. It is shown that these errors have very little influence on static calculations but may cause an error of 5 to 9% in reactivity calculations and measurements; this is a third of the discrepancy between presently observed measurements and calculations. Very large errors in predicting the dynamic behavior of large fast reactors resulted when uncertainties in the delayed-neutron spectra were considered.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21217

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA numerical investigation of space-time effects in the dynamic behavior of fast breeder reactors is presented. The basic approach is to compare results from point kinetics and time-dependent diffusion theory. The accuracy of point kinetics is determined for different approximations to the shape function used in calculating the initiating reactivity and feedback coefficients. Several space-dependent feedback models are studied.The importance of considering spatial effects that arise from two sources is shown. The first type consists of those induced by local reactivity perturbations. Usually, these can be adequately accounted for through the proper selection of a shape function. For example, it is found that when calculating rapid, localized ramp insertions, a good choice is the flux shape at prompt critical. The second type consists of those induced by feedback with strong space dependence. Spatial effects of this type are shown to be difficult to cope with when applying point kinetics.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21218

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA method for studying systems of differential equations employing an interactive computer system with a display screen is presented and applied to three nonlinear problems in reactor kinetics. Interactively it is possible to construct phase space solutions of second- and third-order systems of equations. It is also possible to project from the three-dimensional space and to consider the solutions of the equations as explicit functions of the independent variable. The method is demonstrated on three different nonlinear problems of interest to nuclear reactor kinetics. A second-order problem with temperature-dependent reactivity is considered. Two third-order problems with reactivity a function of two effective temperatures and135Xe concentration, respectively, are also considered. The method of analysis makes it possible to efficiently study the effect of various parameter values on the solutions of the equations. Limit cycle behavior is investigated and the effect of the parameters of the model on the limit cycles is studied with greater effectiveness than can be achieved by an analytical study.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21219

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe application of the Monte Carlo method to the solution of deep-penetration radiation transport problems requires the use of“importance sampling.”A systematic approach to obtaining an importance function is to calculate the solution of the inhomogeneous adjoint transport equation (using the Monte Carlo estimator of the answer of interest as the source term) and to use this adjoint flux (or value function) as the importance function. The adjoint flux is calculated for simplified geometries using one-dimensional discrete ordinates methods.In three-dimensional deep-penetration Monte Carlo calculations the alteration of both the transport and the collision kernel is desirable. The exponential transform is quite useful for altering the transport kernel. However, selection from the altered collision kernel is much more difficult. The approach taken here is to introduce an angular grid with 30 discrete directions fixed in the laboratory coordinate system, along which particles are required to travel. After determining appropriate scattering probabilities and values of the importance function for each of the discrete directions, the selection of the outgoing direction and, hence, energy from the resulting discrete distribution is easily performed.The effects of the discrete angular grid and the capability of angular-biased Monte Carlo have been investigated for neutron transport by comparison with standard Monte Carlo and discrete ordinates calculations, experiment, and exact analytic solutions for several configurations. In all cases the discrete grid alone (no angular biasing) was observed to have no significant effect on the results. Monte Carlo calculations were performed utilizing the exponential transform, nonleakage, source energy biasing, Russian roulette, and splitting plus the angular biasing. The results of these calculations illustrate the general usefulness of this discrete grid approach to angular biasing in several ways. First, meaningful results were obtained with angular biasing at much greater distances from the source than were practically possible with the earlier biasing techniques. The answers, variances, and computer times were all on the same order or better than those obtained with the earlier biasing techniques. Finally, this method utilizing the discrete grid to incorporate angular biasing requires very little human interaction once the adjoint configuration is selected.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21220

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractHigh resolution measurements have been made of the gamma-ray spectrum produced in liquid nitrogen by a 14-MeV neutron source. The spectra of gamma rays from neutron inelastic scattering were measured to a distance of six feet by pulsing the source. Comparison of the inelastic photon flux with discrete ordinates calculations using ENDF/B neutron cross sections and recent gamma-ray production cross sections shows good agreement for the strong well-resolved lines. The results of unfolding the continuum part of the spectrum reveal a flux of high energy lines that is a sizable fraction of the total flux of resolved lines. These normally unresolved gamma rays account for part of the gap in the nitrogen nonelastic cross section.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21221

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractMeasurements have been made at the Tower Shielding Facility of the spectra of secondary gamma rays arising from fast-neutron interactions in samples of natural iron, aluminum, copper, zinc, titanium, potassium, calcium, sodium, silicon, nickel, barium, sulfur, and a type-321 stainless steel. The absolute spectra are expressed as values of (ΔEγ) = 4πd/dΩ(ΔEγ, 90 deg), where(ΔEγ) is the production cross section in millibarns averaged over an incident neutron spectrum from 1 to 14 MeV for 0.5-MeV wide gamma-ray intervals lying between approximately 1 and 6.5 MeV in gamma-ray energy. These data are intended primarily as integral checks on existing and future production cross-section sets which are differential in both the gamma-ray and neutron energy. Agreement with existing sets of data is adequate for iron, nickel, chromium, calcium, and aluminum. The agreement is fair to poor for the remaining elements where comparisons could be made.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21222

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractGamma-ray production cross sections were measured for the16O(n, xγ) reaction from 6.35- to 16.52-MeV neutron energy. The Gulf General Atomic LINAC was used to produce a pulsed source of neutrons having a continuous distribution of neutron energies. A 30-cm3Ge(Li) detector, placed at 125 deg to the incident neutron beam, was used to measure theγ-ray spectra. The corresponding neutron energy was determined by the time-of-flight technique. The two-parameter data (γ-ray energy, neutron energy) were processed with an on-line computer and sorted into 10γ-ray spectra spanning the range 6.35 MeV≤En≤16.52 MeV. From these data we obtained average differential gamma-ray production cross sections for 9 gamma rays from the16O(n, xγ) reaction. The cross sections are in good agreement with other recent measurements, but show rather large disagreement with some earlier measurements. The total nonelastic cross section obtained by summing the partial cross sections is consistent with the nonelastic cross section obtained from the difference between the total cross section and the total elastic cross section forEn

ISSN:0029-5639    

DOI:10.13182/NSE70-A21223

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor