摘要:

AbstractExperiments performed with two coupled uranium (93.16 wt%235U) metal cylinders (17.77-cm o.d., 5.08 cm thick) are the first application to coupled systems of the252Cf-source-driven neutron noise analysis method for obtaining the subcritical neutron multiplication factor. These coaxial cylinders were separated axially by various thicknesses of either air or borated plaster between the flat surfaces. In all measurements, the252Cf neutron source was located at the center of the outer flat surface of one cylinder, and the two detectors were located in three configurations: (a) both adjacent to the radial surface of the cylinder with the source, (b) both detectors adjacent to the radial surface of the cylinder without the source, and (c) one detector adjacent to the radial surface of each cylinder. A ratio of spectral densities obtained with the source and detectors adjacent to the cylinder with the source can be interpreted using point kinetics to obtain the subcritical neutron multiplication factor. However, when the source and detectors are placed on different cylinders, a coupled kinetics model is required to interpret the ratio of spectral densities. The cross-power spectral densities between detector and source positioned on different cylinders depend on the neutronic coupling and approach zero as the coupling does. By comparing the subcriticality from the measurements performed with borated plaster separating the uranium cylinders to those separated by air, it was found that the neutron multiplication factor was always increased by the insertion of borated plaster between the cylinders, regardless of their separation.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20428

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA new technique, based on the noise analysis of neutron detector and core-exit coolant temperature signals, is developed for monitoring the moderator temperature coefficient of reactivity in pressurized water reactors (PWRs). A detailed multinodal model is developed and evaluated for the reactor core subsystem of the loss-of-fluid test (LOFT) reactor. This model is used to study the effect of changing the sign of the moderator temperature coefficient of reactivity on the low-frequency phase angle relationship between the neutron detector and the core-exit temperature noise signals. Results show that the phase angle near zero frequency approaches -180 deg for negative coefficients and 0 deg for positive coefficients when the perturbation source for the noise signals is core coolant flow, inlet coolant temperature, or random heat transfer. Operational data from the LOFT reactor and two different commercial PWRs all show -180-deg phase lag at zero frequency. Furthermore, both the model study and data analysis indicate that the dominant noise perturbation source in the LOFT reactor is the core coolant flow fluctuations.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20429

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractAn electron transport solver has been developed based on a streaming ray (SR) solution to the Spencer-Lewis equation. Several special numerical techniques were used to make the algorithm fast and accurate. These include1.an efficient routine for simulating energy loss straggling2.use of extended-transport-corrected and Fokker-Planck equivalent cross sections, which speed convergence and reduce both angular and spatial differencing errors3.a discrete transport correction, which further speeds convergence and further reduces spatial differencing errors4.the method of numerical shoves and countershoves, which attempts to estimate and correct the remaining spatial differencing errors.The extended transport correction and the Fokker-Planck equivalent cross sections were originally developed for SNcomputations. The remaining techniques are new. The use of all these techniques together with the SR method has led to a complicated but highly efficient electron transport algorithm. Its efficiency is especially evident in energy spectrum calculations for which other fast algorithms such as the SNmethod often yield poor results. Several sample calculations involving electron transport in aluminum slabs are presented.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20430

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA singular perturbation method for the analysis of large power oscillations in nuclear reactors is applied to obtain phase-plane solutions of the Ergen- Weinberg model. The system equations, recast in an appropriate form, directly give a first approximation to the closed trajectory in which the system behavior is idealized as relaxation oscillations. Further approximations in the phase plane are determined using separate perturbation series on individual parts of the oscillation, with variations in the assignment of dependent and independent variables to consistently obtain convergent series. The accuracy of each order of the phase-plane solution increases with the magnitude of the power pulse in the actual physical situation. For realistic reactor conditions, both the trajectory and period of oscillation are well predicted using the first two terms of each perturbation series.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20431

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractCross sections and spectra for (n,xp) and (n,xα) reactions on58Ni and60Ni at energies of 9.4 and 11 MeV and for58Ni at 8 MeV have been measured. This energy range spans the threshold for the (n,n’p) reaction. Based on comparison of Hauser-Feshbach calculations with the measured spectra, this reaction provides a large fraction of the proton spectrum at 11 MeV for58Ni. Both (n,xp) and (n,xα) processes appear to be due largely to compound nuclear processes. Comparison of the measurements obtained here and those previously published at 15 MeV with calculations allows us to infer information about the nuclear level densities. Cross sections for (n,d) reactions are sufficiently small that only upper limits can be derived for them.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20432

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractImprovements have been made to an existing method for implementing realistic pairing corrections in particle-hole state densities. The threshold energy for the pairing“single particle”states is used to replace the usual equispacing model Pauli energy, resulting in an improvement in the calculated state densities for low exciton numbers. Remaining discrepancies between the simple state densities and the results of a detailed pairing calculation are attributable to deficiencies in the original equispacing model state density formula. An ad hoc improvment to this formula is proposed. The method is extended to state densities for two types of fermions, and questions associated with its practical implementation are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20433

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe sum of the9Be(n, t0)7Li and9Be(n, t1)7Li reaction cross sections was measured at an incident neutron energy of 14.6 MeV using a counter telescope for triton detection. The angular distribution of these reactions was obtained for the center of mass angles up to 90 deg. It is nearly isotropic. Assuming a forward-backward symmetry of the angular distribution, the total cross section for the (n, t) reaction on9Be is found to be 24±2 mb. This result compares favorably with the data from the tritium beta-counting experiments.

ISSN:0029-5639    

DOI:10.13182/NSE87-A20434

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor