摘要:

AbstractA theoretical study of fully developed heat transfer for in-line slug flow through unbaffled equilateral triangular bundles is reported. Results are given for the pitch: diameter range 1.05 to 2.00. Two sets of thermal boundary conditions have been considered: (a) uniform wall heat flux in all directions and (b) uniform wall heat flux in the axial direction and uniform wall temperature in the circumferential direction. For the first set, results on the circumferential variation of the wall temperature are given; and for the second, those on the circumferential variation of the wall heat flux are given. For both sets, average Nusselt numbers and circumferential variations of the local heat-transfer coefficients are also given. In all cases, the results are presented in the form of convenient dimensionless groups, and it is shown that they apply to, or can be used for, the estimation of the same dependent variables for turbulent flow of liquid metals through rod bundles.It has also been shown that for theP/Dratios and Peclet numbers normally employed in liquid-metal-cooled reactor cores, the ratio of the maximum temperature variation around a rod to the average wall-to-bulk temperature drop, in the case of uniform wall heat flux in all directions, is not greatly different for both slug and turbulent flows.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21194

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe problem of determining neutron flux spectra through detector activation is of wide and continued interest in the nuclear industry. Analysis of this problem has historically been divided into two areas of concern. The first area is the evaluation of the perturbation introduced into the flux field by the detector. The second area is the determination of the unperturbed energy-dependent neutron flux from the integral relationship of neutron flux to detector activity.An expression was derived which relates detector activity to the unperturbed neutron flux and the adjoint difference flux through the use of a variational approach and a transport theory description of the system. The equation was cast in discrete ordinates formalism to permit numerical solution. The self-contained adjoint problem was solved using standard techniques. The unperturbed flux was expanded as a series of Laguerre polynomials, the coefficients of which were determined through inversion of the resulting rectangular matrix.The theoretical model was examined through application to several synthetic problems. A water-moderated spectrum was examined with both perturbed and unperturbed calculations. Direct calculation of perturbed activities showed good agreement with standard activity calculations. Comparable calculations of flux spectra with perturbed and unperturbed activities showed close agreement. The flux spectrum calculations yielded good results in the thermal energy range, and analysis showed that difficulties encountered in the epithermal range were due to the polynomial expansion scheme, as has been previously observed.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21195

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe time behavior of delayed neutrons from the photofission of238U and235U was measured for bremsstrahlung endpoint energies of 8- and 10-MeV. The data were analyzed to determine the relative abundances (βi) of the delayed-neutron groups assuming the observed time distribution can be adequately described by six groups. A comparison of the238U results at 8- and 10-MeV, and other results at 15-MeV show no strong dependence of theβion endpoint energy. In the case of235U, no large differences were observed between theβiat 8- and 10-MeV, however there are marked variations for several groups at 15 MeV. Possible causes for the observed differences in theβiwith endpoint energy are discussed. No evidence was found for the existence of a delayed-neutron group with a half-life in the 10 to 100 msec region

ISSN:0029-5639    

DOI:10.13182/NSE70-A21196

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractEnergy-dependent diffusion theory with a modified one-term degenerate kernel is employed to derive an expression for the detector response in neutron-wave experiments performed in a slab and a cylinder of crystalline moderator. The Watson transform and the Laplace transform modified to finite systems are used and different mathematical representations of the detector output are discussed.From the derived expressions, various decaying modes, including the continuum mode, are calculated for a 100-cm graphite slab. The condition for the existence of the discrete mode is studied, and the maximum frequencies obtained are 7440 cps for graphite and 9300 cps for beryllium.The experiment reported by Utsuro et al. is interpreted and the observed interference pattern is reproduced analytically with a slight discrepancy in the resonance frequency. The potential of this experiment for measuring moderator properties is also discussed.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21197

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA subcritical assembly (29×38×29 cm) built of TRIGA-type fuel elements was pulsed by coupling it with the Illinois TRIGA reactor through a graphite thermal column (2 ft square by 4 ft long). Flux measurements were made at seven locations in four different fuel loadings—9, 16, 25, and 49 fuel elements—withkeffvarying from∼0.4 to 0.92. A polynomial expansion method is used to provide a continuous representation of pulse shapes. Derivatives appearing in a diffusion-theory model, evaluated using this expansion, are then used to determine the propagation velocity and the neutronic parameters. The maximum“asymptotic”velocity (removed from the boundaries) varied from∼4×104cm/sec atkeff= 0.60 to 2.54×104cm/sec atkeff= 0.92. The theoretical model involves an expansion which, depending on the number of terms retained, bounds the experimental data. However, differences of as much as 40% in absolute values are observed and they are attributed to inadequacies in the model for this small heterogeneous assembly. Uncertainties in the neutronic parameters, as well as nonlinearities in the instrumentation, may also contribute.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21198

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractCalculations on the decay of a neutron pulse in H2O ice assemblies of various bucklings and at various temperatures in the range 273 to 21°K are reported. The scattering kernel is based on the Debye frequency distribution function of lattice vibrations, with a suitably chosen Debye temperature. Contributions from one- and two-phonon processes have been considered. The Boltzmann equation in the diffusion approximation has been solved both by an iterative procedure to obtain the fundamental mode of decay, and by a matrix diagonalization method. This latter method enables us to calculate neutron spectra at various times after the introduction of the neutron pulse. These time-dependent spectra have been compared with available experimental results with considerable success. By studying the time variation of the mean energy of the neutron distribution, we have calculated the slowing down relaxation timesτthin ice at various temperatures and compared these with the measured values. We have also studied the heating up of a low-energy neutron pulse in ice assemblies at a few temperatures and find that, unlike the case of beryllium (Grover and Kothari) the heating up relaxation timeτHcomes out to be nearly the same asτth.The calculated values of diffusion coefficientD0, and diffusion cooling coefficientCat various temperatures have been compared with the experimental results. The agreement between the two sets of values is very good forD0, but not so good forC.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21199

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA set of fundamental equations for fluctuations about the mean neutron density is studied for a reactor-detector system in which the detector is treated as an integral part of the system. The reactor-detector system is described, mathematically, as a general Markov process, and expressions for various descriptive parameters are derived in a consistent manner within the context of the basic equations.The role of the general adjoint neutron density is discussed with special emphasis on the mean and second-moment functions, and a relationship between the second-moment equations similar to the relationship between first-moments (mean and its adjoint) is observed. The extension to higher moments is also noted.A reduction of the second-moment equations is carried out, without approximation, using a variational principle. This consistent reduction allows a definition of the parameters involved, especially a definition of the detector efficiency, through a comparison of this reduced form with the usual point-reactor equations. The parameters defined contain weighting functions dependent upon the number of detectors used in the experiment.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21200

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractTransport theory (Sn) calculations of the Ultra High Temperature Reactor Experiment (UHTREX) are compared with results obtained in clean cold critical experiments. These experiments are characterized by a high (43% of all neutrons produced) fast neutron leakage from the core, a hardened thermal neutron spectrum (a reactivity effect of−9.5% compared to a Maxwellian spectrum at the same temperature) and two spatial self-shielding effects. The smaller of the self-shielding effects,−2% in reactivity, occurs in the coated fuel particles contained in the fuel elements. A larger spatial self-shielding effect,−3.6% in reactivity, results from the heterogeneous arrangement of fuel elements and core moderator. The radial fuel channel design and radially graduated fuel loading complicate the calculation of the fuel element self-shielding because the entire core cannot be represented by one simple unit cell. However, conventional cell homogenization techniques are adequate when applied to subregions of the core. In spite of the geometrical complexities, the calculated multiplication factors and fission distributions agree well with experiment.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21201

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe methods of variational synthesis, which are derived from the direct method of the calculus of variations, are applied to the problem of computing the optimal control for spatially dependent reactor models. By this means, the optimal control problem is reduced to the solution of coupled algebraic equations. A general formalism is developed which is specialized to the case of one-group neutron diffusion theory, with and without delayed neutrons, and with thermal feedback.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21202

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe development of a concept for the control of a boiling water reactor by an on-line digital computer is described. The concept is based on the principles of Modern Control Theory.Experimental results are presented which compare digital control and analog control for equivalent perturbations. It appears that the digital control, which uses more process information than the analog control, handles perturbations more effectively.

ISSN:0029-5639    

DOI:10.13182/NSE70-A21203

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor