摘要:

AbstractThe singular perturbation method is applied to the stiff system of differential equations representing the one-point reactor kinetics model and is shown to be a higher order generalization of the prompt-jump approximation. The numerical tests show that a sufficient accuracy can be achieved even in low-order approximations for reasonable reactivity inputs for both fast and thermal reactors.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27212

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe time-dependent Boltzmann equation for neutron transport is transformed into eigenvalue equations in k,λ,γ, andα, whose general properties are stated as hypotheses. Numerical solutions are obtained with the discrete-ordinates code DTF, where a directλeigenvalue calculation has been added. Eigenvalues and eigenfunctions are analyzed for idealized fast and thermal systems in both bare and reflected configurations. The differences found in these idealized cases provide some useful bases for estimating the behavior of the different eigenvalue solutions in specific applications.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27213

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe singular differential equations of arbitrary order, derived in a tensorial approximation to the integral transport for monoenergetic neutrons in slab and sphere geometries, are solved by a power series expansion without imposing any boundary condition. The relation to the exact integral transport approach is theoretically studied, and numerical calculations for the tensorial differential approach are worked out.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27214

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThis paper presents the first results of a comprehensive application of the sensitivity theory developed for the FORSS code system to the analysis of fast reactor integral experiments. A variety of assemblies and performance parameters were studied to determine the nuclear data sensitivity as a function of nuclide, reaction type, and energy. Comprehensive libraries of energy-dependent sensitivity coefficients were developed in a computer retrievable format for several critical assemblies. Uncertainties induced by nuclear data were quantified using preliminary energy-dependent relative covariance matrices evaluated with ENDF/B-IV cross sections and processed for238U(n,f),238U(n,γ),239Pu(n,f),239Pu(n,γ), and. Calculational results, cross-section covariances, and integral results and their covariances were used in a consistent fashion to improve uncertainty estimates of fast reactor core performance. A first attempt was made to quantify specifications for new cross-section measurements required to satisfy specific design goals at minimum experimental cost.An analysis of several critical experiments indicated that design accuracy goals of 0.5% in k and 2% in the central238U capture:239Pu fission ratio (28c/49f) ratio in mixed oxide liquid-metal fast breeder reactor cores are unlikely to be attained in the near future. This assumes that the nuclear data are based only on microscopic measurements, and the current cross-section measurement program is not changed dramatically. Current estimates are 2.3% in k and 7.3% in central reaction ratio using only differential covariance information. Using the measurements in ZPR-6/7 for k and central28c/49f in a cross-section adjustment scheme with assigned uncorrected standard deviations of 1 and 2%, respectively, standard deviations of the same parameters were computed to be 0.7 and 1.8%. Results of integral experiments, therefore, are needed to improve uncertainty estimates of reactor performance for current fast reactor design work.

ISSN:0029-5639    

DOI:10.13182/NSE78-3

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractNuclear state and level densities as a function of excitation energy, angular momentum, and parity have been calculated by a combinatorial method for56Fe,59Co,60Ni,61Cu,62Ni,63Cu, and65Cu. Single-particle states for both Woods-Saxon and Nilsson potentials were used. These calculations were done with zero and nonzero pairing energy.State densities as a function of excitation energy have been calculated by an approximate inversion of exact partition functions; they agree well with state densities calculated by the combinatorial method. Average excitation energy as a function of temperature has been calculated from the partition function for each of the nuclei.Level densities as a function of energy, calculated by the combinatorial method, are compared with measured level densities. The agreement is either good or very good for most, but not all, of the nuclei. No evidence was found that must be interpreted as indicating a failure of the independent-particle model at higher excitation energies. For level density calculations with zero pairing energy, there is a suggestion, but no clear indication, that Woods-Saxon single-particle states are better than Nilsson single-particle states. Calculated and measured spin cutoff parameters are compared for56Fe and61Cu.Single-particle states for Nilsson-type potentials tend to give higher state and level densities than single-particle states for Woods-Saxon-type potentials. This tendency is not due to the larger number of single-particle states for Nilsson-type potentials, and it can be compensated for by using a nonzero pairing energy. The calculated fraction of negative-parity states is about one-half as expected, but this fraction varies much more than expected from one energy interval to another. The calculated M-value distribution is approximately Gaussian as expected.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27216

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractNeutron scattering cross-section measurements were performed with a very thin238U sample. From an area analysis of the data, a value of 24.2±0.8 meV was obtained for the capture width of the 6.6 7-eV resonance.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27217

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe252Cf fission neutron-induced gamma fields in iron have been investigated experimentally and theoretically. The gamma leakage spectra from a series of relatively small iron spheres (15 to 35 cm in diameter) and the space-dependent gamma spectra within a relatively large (∼100-×100-×100-cm) steel pile have been measured with an absolutely calibrated Si(Li). Compton spectrometer in the energy range from 0.3 to 3 MeV. In addition, neutron spectra (with a spherical proton recoil proportional counter and a3He semiconductor spectrometer) and235U fission rates have been measured within the steel pile. The measurements are compared with calculations. For the calculation of the neutron spectra, we used the one-dimensional neutron transport code DTK (208 energy groups), and for the calculation of the gamma spectra, an extended version (51 energy groups) of the gamma transport code BIGGI 4T and an (n-γ) production cross-section matrix constructed from published data were used. The gamma flux induced by inelastic neutron scattering is well reproduced by the calculations, whereas that induced by capture processes is somewhat underestimated (∼20%).

ISSN:0029-5639    

DOI:10.13182/NSE78-A27218

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe neutron capture cross sections of240Pu and242Pu were measured in the energy range from 10 to 90 keV. The capture cross sections of both197Au and238U were chosen as standards. Neutrons were produced via the7Li(p,n) reaction with the Karlsruhe 3-MV pulsed Van de Graaff accelerator. Capture events were detected by a Moxon-Rae detector. The high neutron flux available at flight paths as short as∼10 cm offers a signal-to-background ratio one order of magnitude better than obtained in previous experiments. The cross-section ratios could therefore be determined with a total statistical and systematic uncertainty of 4 to 10% for240Pu and 6 to 10% for242Pu. The results agree with previous data, while discrepancies to the evaluated files ENDF/B-IV and KEDAK 3 were found (up to 30% for240Pu and up to 50% for242Pu).

ISSN:0029-5639    

DOI:10.13182/NSE78-A27219

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractEquation systems describing one-dimensional, transient, two-phase flow with separate continuity, momentum, and energy equations for each phase are classified by use of the method of characteristics. The main purpose of this paper is to study the mathematical nature of these equations, not their physics, although it is realized that these two problems are not entirely independent. Many of the equation systems possess complex-valued characteristics and hence, according to well-known mathematical theorems, are not well-posed as initial-value problems (IVPs). Real-valued characteristics are necessary but not sufficient to ensure well-posedness. In the absence of lower order source or sink terms, that can affect the well-posedness of IVPs, the complex characteristics associated with these two-phase flow equations imply unbounded exponential growth for disturbances of all wavelengths.Analytical and numerical examples show that the ill posedness of IVPs for the two-phase flow partial differential equations that possess complex characteristics produce unstable numerical schemes. These unstable numerical schemes can produce apparently stable and even accurate results if the growth rate resulting from the complex characteristics remains small throughout the time span of the numerical experiment or if sufficient numerical damping is present for the increment size used. Other examples show that clearly nonphysical numerical instabilities resulting from the complex characteristics can be produced. These latter types of numerical instabilities are shown to be removed by the addition of physically motivated differential terms that eliminate the complex characteristics. These terms should not destroy long-wavelength physical instabilities that arise and that may sometimes be calculated approximately using ill-posed equation systems.

ISSN:0029-5639    

DOI:10.13182/NSE78-4

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe effects of internal circulation velocity and the presence of noncondensable gas on vapor removal rate by condensation from a rising large vapor-gas bubble produced in a hypothetical core disruptive accident are investigated by solving the resulting transient heat and mass transfer problem of turbulent flow. Sample calculations are performed for the condensation of UO2and sodium vapors containing noncondensable fission gases. The time-averaged condensation heat transfer coefficients are presented for the condensation of UO2and sodium vapors for different internal circulation velocities and the concentration of noncondensable gas.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27221

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor