摘要:

Cross sections for production of gamma rays due to neutron interactions with iron have been measured as a function of both neutron and gamma-ray energy. Two experimental configurations were used to obtain the data: a NaI-spectrometer system using the Oak Ridge Linear Accelerator as the neutron source and a Ge(Li)-spectrometer system using a pulsed Van de Graaff and the D(d, n) reaction as the neutron source. The NaI-spectrometer system, described completely in this report, was used to acquire data for 0.8≤En≤20 MeV andθγ= 125 deg, which were unfolded to obtaind2σ/dωdEvalues for gamma-ray energies between 0.7 and 10 MeV. The Ge(Li) system was used to obtain high resolution information on the production of discrete-linedσ/dωvalues for 4.85≤En≤9.0 MeV andθγ= 55, 75, and 90 deg. Our data are compared with previously reported experimental data and with the current ENDF/B evaluation. Although there is generally reasonable (20%) agreement, important differences among these data are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26567

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

A theoretical study of the pulsed neutron problem and of steady-state neutron spectra has been made in mixtures of H2O and D2O in the temperature range 253 to 4°K. Mixtures with D2O content of 0, 5, 10, 15, and 20 wt% have been considered. For the pulsed neutron problem the multigroup Boltzmann equation in the diffusion approximation has been diagonalized to obtain asymptotic and transient spectra in assemblies with buckling values ranging from 0 to 0.6 cm-2at 253, 77, and 21°K. The calculated values of the fundamental mode decay constant in various assemblies of ice at 253°K containing 20% D2O are found to agree very well with the experimental values reported by Salaita.For the steady-state problem, the multigroup inhomogeneous Boltzmann equation in the diffusion approximation has been solved by the matrix inversion method for different mixtures at 253, 77, 21, and 4°K. We show that there is an enhancement of cold neutron flux as the D2O content in ice is gradually increased. As in the case of H2O ice, we find that the mean energy of the neutron distribution goes on decreasing with decrease in ice temperature only as long as the temperature is above about 20°K. No further reduction in the mean energy of the neutron distribution is obtained when the temperature of the mixture is reduced below 21°K. It is shown that at 21°K, ice containing about 10 to 20% D2O is a better cold neutron source than pure H2O ice.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26568

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The benchmark experiments, performed in a plutonium-fueled critical assembly (ZPR-6 Assembly 7) in support of the fast reactor demonstration plant program, were used, in conjunction with a statistical method of correlation, as a source of suggestions for possible modifications to multigroup neutron cross-section sets based on ENDF/B files. Version 1 of these files was a starting point in the correlation procedure. The general trends of the results (lower238U capture cross section and235U fission cross section, higher239Pu capture to fission ratio, with respect to ENDF/B Version 1 data) are discussed, and the suggested multigroup cross-section adjustments are compared with recent evaluations. Calculations of keff, and of the ratios of238U and235U fission rate and of238U capture rate to239Pu fission rate, using the proposed adjusted set, give results in good agreement with the experiments.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26569

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The neutron energy spectrum of fast reactors in the energy range from several keV to several tens of keV is influenced by a multitude of resonances of the fertile and fissile elements. A single elastic scattering in this range distributes the neutrons across many resonances. Since the resonance parameters are randomly distributed about average values, the collision rate below any energy point is the sum of many, uncorrelated, resonant scattering rates above the point. Hence the collision density, as a function of energy, is a smooth curve dominating over small local fluctuations. It is demonstrated, both analytically for simplified cases and numerically for realistic cases, that the deviations from a smooth curve are negligible.In lethargy units, the smooth collision density is [a(u)/v(u)] exp[-v(u)]. The definitions of the parametersa(u) andv(u) involve only average properties of the resonance population, namely the averages over many resonances of the scattering probabilitiessi≡∑(scattering, element)/∑(total, mixture). The average absorption probability isa(u);v(u) is given implicitly by the transcendental equation 1−v=∑i[〈si〉/αi] [1−(1−αi)1−v], whereαiis the maximum relative energy loss per scattering in thei’th element. An accurate solution of the transcendental equation is found most essential for an accurate prediction of integral reaction rates. For this purpose a series solution forvin terms of〈si〉is developed.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26570

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The partial 2200-m/sec equivalent neutron capture cross sections (σ2200)andneutron capture resonance integrals (Ic) of 432.7-yr241Am to produce 152-yr242mAm and 16.01-h242gAm were measured relative to59Co standards. The number of242mAm atoms produced per241Am target atom was determined by high precision mass spectrometry after chemical purification of americium. The number of242gAm atoms produced per241Am target atom was determined by measuring the alpha activity of its 164.4-day242Cm daughter. The measured values for241Am are as follows:σ2200(to242mAm) = 83.8±2.6 b,Ic(to242mAm) = 208±18 b (0.369-eV cutoff),σ2200(to242gAm)= 748±20 b, andIc(to242gAm)= 1330±117 b (0.369-eV cutoff). Measured values are compared with those calculated from the ENDF/B-III neutron cross-section library.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26571

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

The stability of a nuclear reactor with prompt feedback is examined when its eigenvalue (size, material buckling) is increased or decreased. Two models describing the temperature dependence of the Doppler coefficientsT−1andT−3/2are used in the analysis, and their relative effectiveness in maintaining stability is compared. Both the eigenvalue and neutron flux of the nonlinear reactor are expanded in the perturbation parameter∈, defined as the spatially weighted average of the change in neutron flux relative to the flux of the linear reactor. For a change in reactor eigenvalue, the equilibrium states of the neutron flux are obtained, accurate to the first order of feedback, but to an arbitrary order of perturbation. The stability of each state is examined.It is found that even for an overall negative prompt feedback, there exists a limit to the increase in reactor eigenvalue (or in neutron flux), beyond which instability may result. This limit depends on the initial conditions of the perturbed reactor. The neutron flux is shown to be more sensitive to a changeεthan the reactor eigenvalue, and this sensitivity depends on the temperature variation of feedback. It is also shown that theT−1variation of the negative Doppler coefficient is more effective than theT−3/2variation in maintaining reactor stability when the reactor eigenvalue is increased.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26572

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractTurbulent mixing rates between adjacent subchannels were obtained at 50 psia for annular flow of air-water mixtures in a simulated square-square rod bundle geometrical array using a tracer technique. The gap spacing was varied by a factor of 5. Mixing rates were found to be flow regime dependent, decreasing exponentially with subchannel mass flux and quality and increasing with gap spacing. Enhanced liquid interchange was measured in the low quality bubble flow regime and high quality annular flow regime. The results presented here are in qualitative agreement with data obtained by other investigators using steam-water at elevated pressures.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26573

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe Wiener-Hopf technique is applied to obtain the solution for the extrapolated endpoint for an infinite half-space problem containing a uniform isotropic source, and this endpoint is compared to the Milne extrapolated endpoint. Another definition of extrapolated endpoint for use in diffusion theory based on the interior flux for the uniform source half-space problem is given and compared to the equivalent uniform source diffusion theory endpoint.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26574

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe consequences of using three different interpolation methods for tabular neutron and photon energy distribution data are investigated. The three methods are linear interpolation on energy, linear interpolation on energy after the secondary energy ranges are transformed to unit base, and linear interpolation on energy after the initial distributions are converted to cumulative probability distributions by integration over the secondary neutron or photon energy. The latter two methods may subsequently be reconverted to differential probabilities. Linear interpolation on energy without transformation or conversion is shown to be the least desirable for most applications.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26575

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe neutron spectrum and criticality of ZPR-3 Assembly 11 have been calculated using estimated cross sections for the238U(n,γn’) reaction. Inclusion of this reaction markedly improves agreement between the measured and calculated spectra, and it also decreases the calculated criticality by 0.62%. This change in criticality can be compensated for by lowering the238U capture cross section from the ENDF/B-III values to those of a recent microscopic measurement. These and other ramifications of the (n,γn’) reaction in fast reactor assemblies are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26576

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor