摘要:

AbstractSurface depletion was investigated in laboratory- and plant-scale distillation units with mixing by natural convection or by mechanical surface agitation. During the distillation of210Po, Zn, Cd, Te, and Mg from bismuth at 650 to 750°C, surface depletion was significant for the more volatile components:210Po, Zn, and Cd. The extent of surface depletion was decreased by relatively intense agitation of the entire liquid-metal surface. A model was developed for predicting the degree of surface depletion during the distillation of metals from bismuth as a function of temperature, still pot dimensions, and degree of agitation.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21131

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractIf the coolant mass flow were constant across the core, the coolant temperature rise would be proportional to the channel power. But, without orificing, the coolant mass flow in the hot channel is smaller than the average flow while the outlet temperature is hotter than the mixed mean temperature. The approximate radial distributions of coolant mass flow (M/M0) and temperature rise (ΔT/ΔT0) are shown to depend only upon the (arbitrary) radial flux distribution (H/H0) and upon a single lumped core parameter (δ), proportional to the product of the pressure by the pressure drop. For simple radial flux distributions and whenδgoes from zero to infinity, (M0/Mav) increases approximately from (Hav/H0) to one, while (ΔT0/ΔTav) decreases approximately from (H0/Hav)2to (H0/Hav). The relationships between hot channel parameters, maximum clad or fuel temperatures, and thermal power are derived in the Appendix for a“chopped cosine”axial flux distribution.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21132

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA linear analytical dynamic model is developed for steam cooled fast power reactors. All main components of such a plant are investigated on a general, though relatively simple, basis. The model is distributed in those parts concerning the core but lumped as to the external plant components. Coolant is considered as compressible and treated by the actual steam law.Combined use of analog and digital computer seems most attractive.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21133

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractModeling of two-phase hydrodynamic phenomena with a refrigerant (Freon) has been carried out for several years because of the lower cost of experimentation with this working fluid. Freon-12amodeling of the critical-heat-flux condition, a coupled hydrodynamic thermal phenomenon, has recently been reported. The effort described here represents an extension of the critical-heat-flux modeling work using Freon-22.bA recently proposed correlation method, comparing Freon and water data, has been modified, and good agreement is shown between water and Freon-22 test results in a round tube with and without a twisted ribbon insert. The modeling technique is also extended to cover inlet subcooling and the operating pressure effect. In addition, some liquid-metal and water critical-heat-flux data are compared.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21134

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe present paper deals with the problem of self-sustained hydrodynamic oscillations of a two-phase fluid traveling in a single heated channel.The aim of the work described has been to establish a physically adequate analytical model of this often discussed phenomenon that is simple enough to provide some understanding of the driving mechanisms and to permit immediate conclusions as to the bearing on system stability of several important design and operational parameters. For this reason, it was decided to avoid conventional transfer-function description, which could have provided somewhat greater accuracy.It has been shown that a pure density effect is capable of explaining the oscillatory behavior under the boundary condition of a constant pressure drop over the system. An instructive stability plot that permits a quick survey over the stability properties of a given system is introduced.However, it has also been shown that the integrated or point model is not adequate for all cases. Hence, a modification, called the“long channel correction,”that successfully substitutes a spatial analysis whenever necessary is introduced. Stability plots are obtained that clearly display the difference between the predictions of the model without the long channel correction (the simple model) and the model with the long channel correction.Comparisons have been made to experimental data as well as to the predictions of a stability code with a detailed spatial description. Good agreement has been demonstrated for the model with the long channel correction.The existence of a crucial boiling length or point of minimum stability is confirmed by the corrected model but not by the simple model. Moreover, it appears that the point of minimum stability is closely related to the point where the long channel correction becomes important. In other words, as subcooling is decreased, the increasing importance of the time delays in the system gives rise to an inversion of the stability trend and, at the same time, the point-model description becomes insufficient.The present model is expected to find application in cases where a quick survey of the stability trends of a group of systems is more important than accurate predictions for one particular situation.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21135

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA general method is presented for determining the bounds on allowable disturbances, in linearly stable systems, for which the system remains asymptotically stable. It is based on transforming a set of nonlinear differential equations to a single equation that is valid within a given region of equilibrium. It is applicable to systems with a fairly general nonlinear feedback as well as to systems that exhibit finite escape time, thus extending previous methods. The physics enters through the linear characteristic roots, and provision is made for both real and complex roots. The method is also of use in determining the range of validity of space-independent reactor models. Applications are given to three examples of reactor systems, including the determination of reactor excursions.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21136

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe angular distribution, yield, spectra, and attenuation of fast neutrons from the alpha-particle bombardment of a thick elemental tantalum target have been measured.Data obtained by using threshold energy detectors and thermal-neutron detectors were reduced to neutron spectra with the computer program FLUXPOS. Thermal-neutron activation foils were placed in the shielding at 6-in. intervals to determine the neutron attenuation profiles at 0, 75, and 90°from the target.Data show that the neutron spectral slope becomes steeper and the relaxation length (1/eattenuation thickness) decreases with increasing angle.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21137

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractNeutrons emitted from pulsed spheres have been measured as a function of time in order to stringently test input parameters and computational assumptions in neutron transport calculations. Using the sphere transmission technique in conjunction with the time-of-flight facilities at Livermore, measurements have been made for 0.5, 1.3, and 3.0 mfp of carbon, and for 1.0 mfp of nitrogen, using a 15.3-MeV pulsed neutron beam. The measured neutron time spectra have proved to be sensitive, not only to the magnitude of the elastic and inelastic neutron cross sections, but also to the shapes of their angular distributions. The analysis of the data has been done using the Livermore Monte Carlo Neutron Transport Program (SORS). To obtain agreement with the data, a revision of some of the cross sections and respective angular distributions was required, which resulted in a dramatic improvement in the quality of the fits to the measured time spectra.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21138

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractThe time-dependent neutron transport equation is treated as a problem in singular perturbation theory. The method of matched asymptotic expansions is used to find equations yielding approximate solutions that are uniformly valid in time. The long-time solutions resulting from this method are those of the prompt-jump approximation. Although best suited for fast subcritical systems, numerical results from diffusion theory calculations indicate that very good accuracy is obtained for thermal systems as well.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21139

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor

摘要:

AbstractA method is proposed for measuring the prompt decay eigenvalue of the neutron population. It is based on the determination of the covariance of the integrated outputs from two neutron detectors placed in a nuclear reactor, for different values of the integration time interval. The covariance is measured by an analysis of the four types of combined outputs which can occur if only the sign of the signal with respect to its mean is recorded from each detector. In fact, the frequence of every combination ++,−+,−−, +−assumes a different value according to the degree of coherence between the two detector counting outputs.The method allows experiments to be made with low-detection efficiency and can be applied also to fast reactor-noise analysis, unlike all the other variance-type procedures.Since the detection of only the sign of the variables is needed, a pulse counter is not indispensable and, therefore, the technique is expected to be applicable even to nonzero power reactors.

ISSN:0029-5639    

DOI:10.13182/NSE69-A21140

出版商:Taylor&Francis    

年代:1969

数据来源: Taylor