摘要:

AbstractThe theoretical study of time-varying two-phase flow problems in several space dimensions introduces such a complicated set of coupled nonlinear partial differential equations that numerical solution procedures for a high-speed computer are required in almost all but the simplest examples. Efficient attainment of realistic solutions for practical problems requires a finite difference formulation that is simultaneously implicit in the treatment of mass convection, equations-of-state, and the momentum coupling between phases. We describe such a method, discuss the equations on which it is based, and illustrate its properties by means of examples. In particular, we emphasize the capability for calculating physical instabilities and other time-varying dynamics, at the same time avoiding numerical instability. The computer code is applicable to problems in reactor safety analysis, the dynamics of fluidized dust beds, raindrops or aerosol transport, and a variety of similar circumstances, including the effects of phase transitions and the release of latent heat or chemical energy.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28455

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractDifferent decontamination factors for129I and131I are frequently invoked in environmental impact reports concerned with nuclear fuel recycle. Selected differences, or ratios, have not been justified on the basis of mathematical models or experimental data. This report presents a description of the origins of these differences in terms of isotopic exchange and material balance equations for the short- and long-lived (or stable) isotopes. The ratios of decontamination factors can be calculated when there is complete attainment of isotopic exchange between gas- or liquid-phase iodine and iodine sorbed by a solid or liquid. If there is no exchange, decontamination factors are isotope independent unless material recycle occurs within the system. Between these extremes, there can be decontamination factors whose explanation requires experimental determination of the extent of exchange. The model applies to other radioactive isotopes of iodine as well as to other elements with short- and long-lived (or stable) isotopes.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28456

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA data base of primary knock-on atom spectra and an analysis program have been created to assist experimentalists in studying, evaluating, and correlating radiation-damage effects in different neutron environments. Since experimentally obtained typical controlled thermonuclear reactor (CTR) neutron spectra are not presently available, the data base can be extremely useful in relating currently obtainable radiation damage to that anticipated in future fusion devices. However, the usefulness of the data base is not restricted to only CTR needs. Most of the elements of interest to the radiation-damage community and all neutron reactions of any significance for these elements have been processed, using available ENDF/B-IV cross-section data, and are included in the data base. Calculated data such as primary knock-on atom spectra, displacement rates, and gas production rates, obtained with the data base, for different radiation environments are presented and compared with previous calculations.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28457

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA benchmark measurement of the neutron leakage spectrum from a pulsed 38-kg uranium (93.5%235U) sphere has been made using time-of-flight techniques. The sphere had a multiplication of∼11 for 14-MeV neutrons, and a neutron hold-up time of∼40 nsec. The centrally located source of 14.1±0.8-MeV neutrons, produced by bombarding a tritium gas target with pulses of low-energy deuterons, was isotropic to±7.7%. Neutrons in the 0.180- to 16.0-MeV energy range were detected at the end of a 39-m flight path by an Ne-213 liquid scintillator employing pulse-shape discrimination. The detector efficiency was measured over this same energy range using monoenergetic neutrons from the T(p,n) T(d,n), and D(d,n) reactions. The measured neutron flux as a function of energy is compared with the results of Monte Carlo calculations performed with the MCN code. Uranium cross sections from ENDF/B-IV and an older set from Lawrence Livermore Laboratory were used in these calculations. The results calculated using the ENDF/B-IV cross sections are in good agreement with the measurements, especially in the 1- to 6-MeV energy region where the uncertainties in both the calculated and experimental results are the smallest.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28458

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractInformation on the production of high-energy photons, due to (n,γ) reactions for neutron energies up to∼20 MeV, may be useful in reactor technology. Use of theoretical estimates is required to make up for the lack of measured data. For this purpose, the semidirect capture model is used. The model is refined by introducing a volume form for both the real and the imaginary parts of the nucleon-nucleus coupling interaction and its validity checked on available experimental (n,γ) data. The effective cross sections for the production of 8- to 20-MeV photons are calculated for the140Ce(n,γ) and93Nb(n,γ) reactions considering three different distributions of 4- to 15-MeV incident neutrons.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28459

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractTo validate the neutronics analysis of hybrid fusion-fission reactor blankets, calculations were made of an experiment by Weale et al., where a 14-MeV neutron source was surrounded by a natural uranium metal pile. The evaluated nuclear data libraries, ENDL and ENDF/B, were used. The calculated parameters were found to be in closer agreement for present versions of these libraries than for preceding versions; however, there were still 15% differences in the235U(n,f) and238U(n,f) reaction rates. The present version of ENDL gives the results that are the closest to the experimental values for these reactions. For the238U(n,γ) reaction, the calculations with the ENDF/B libraries are closer to the measured values. Both the ENDL and ENDF/B evaluations, however, fail to calculate correctly the neutron leakage or derived values for the238U(n,2n) and238U(n,3n) reaction rates. The spatial variations of the235U(n,f),238U(n,y),238U(n,f), and239Pu(n,f) reaction rates show that the penetration of high-energy neutrons in the pile is better described by the calculation with ENDL, which gives a greater penetration. The effects of resonance self-shielding were investigated and found to require a much smaller correction than the differences between calculations with different data libraries.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28460

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractA model is developed to investigate the response of a coupled two-core reactor to a neutron pulse.Various coupled cores with symmetrical and asymmetrical configurations and compositions are studied. The fundamental spatial mode splits into two distinct decaying submodes. The reactivity of a coupled-core system is defined, and two methods are given for its measurement.The model is compared with results of pulsed-neutron experiments performed on a light-water-moderated, coupled, compact two-core reactor fueled with uranium of 90%235U content and reflected by both light water and graphite in either symmetrical or asymmetrical configurations

ISSN:0029-5639    

DOI:10.13182/NSE76-A28461

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe elementary solutions of the one-speed neutron-transport equation with linearly anisotropic scattering are used in conjunction with Chandrasekhar's invariance principles to solve in a concise manner the Milne problem for two adjoining half-spaces and the critical reactor problem for a reflected slab.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28462

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe results of a detailed and systematic study of time-dependent, space-dependent, and steady-state neutron spectra in different assemblies of various H2O-D2O mixtures in the temperature range of 253 to 21 K are reported.By the matrix diagonalization method, the multigroup Boltzmann diffusion equation was solved to obtain asymptotic and transient spectra in assemblies at 253 K, with buckling values ranging from 0 to 0.4 cm−2. Mixtures with D2O content of 20, 50, and 80 wt% are considered. The calculated values of the fundamental mode decay constant and the diffusion parameters are compared with the experimental values reported by Salaita and Robeson.The multigroup time-independent source-free Boltzmann equation was also diagonalized to obtain spatial eigenvalues and eigenfunctions. By using these eigenfunctions, neutron spectra and the effective diffusion length L(x), at different distances from the source plane, were calculated at 253 K. The asymptotic values of L(x) compare fairly well with those calculated by using the measured values of D0andin mixtures with a D2O content of 20, 50, and 80%.For the steady-state problem, the multigroup inhomogeneous Boltzmann diffusion equation was solved by the matrix inversion method for assemblies at 77 and 21 K with buckling values ranging from 0 to 0.1113 cm-2. Mixtures with D20 content of 0, 5, 10, 20, ... 90, 95, and 100% are considered. At 21 K, the relative usefulness of different assemblies as cold-neutron sources is discussed.For some selected assembly sizes, we determined the optimum H2O-D2O mixtures that would give maximum cold-neutron flux. The optimum mixtures for buckling values of 0.1113, 0.0158, and 0.001 cm-2are those with nearly 30, 70, and 90% D2O, respectively; the corresponding gain factors for graphite-filtered neutrons are 1.85, 4.17, and 13.57, respectively. We find that in mixtures, as in the cases of H2O and D2O ice, cooling an assembly below 21 K does not decrease the effective temperature of the neutron distribution below that obtained at 21 K.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28463

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor

摘要:

AbstractThe application of the linear Boltzmann equation as used in reactor and shielding problems to the transport of neutral atoms in a Tokamak-type plasma has been studied. The method was found to be generally valid with some limitations because of possible anisotropy of the plasma medium.Effective cross sections for the interaction of neutral atoms with an isotropic plasma were calculated and applied to the transport of hydrogen in a typical Oak Ridge Tokamak (ORMAK) plasma. The outer wall was found to have a significant effect on the hydrogen concentration.

ISSN:0029-5639    

DOI:10.13182/NSE76-A28464

出版商:Taylor&Francis    

年代:1976

数据来源: Taylor