Flux Distortion Research Articles

The Effect of Local Flux Distortions on the Doppler Effect of Small Fissile Samples

Samples used in Doppler-effect measurements in fast critical assemblies distort the flux in their vicinity. For fissile samples whose Doppler effect depends strongly on spectrum, this distortion ma...

Power Reactor Flux-Tilt Protection Instrument

An instrument has been developed as part of a flux-tilt protective system for the light-water-cooled, heavy-water-moderated power reactor (CANDU-BLW) at Gentilly, Quebec. This system is independent of the normal over-power protection instrumentation and is designed to prevent overheating of fuel that could result from spatial flux distortions (or tilts). Three identical instruments are used in the system, each comparing currents from ion chambers located at three positions around the reactor. If flux differences become greater than a preset level a trip signal is generated. The reactor is shut down by dumping heavy water if any two instruments generate simultaneous trip signals. Each instrument contains three linear-logarithmic amplifiers, comparators to sense high flux-tilt levels and logic circuits that combine the comparator signals to produce the final output in the form of relay contact closures. A mixed linear-logarithmic signal is developed from the measured ion chamber current to provide a fluxtilt signal that is non-linear with respect to reactor power.

Neutron flux perturbations due to infinite plane absorbers III. Cosine flux

This work was conducted with the aim of gaining some insight into the problem of neutron flux perturbations due to absorbing materials placed in a flux gradient. A hybrid theory is developed, which combines the advantage of the conventional asymptotic reactor theory approximation with the virtues of an exact solution by the Wiener-Hopf technique. The theory is able to provide information about the effect of neutron leakage on the angular distribution at the surface of a purely absorbing foil or control plate embedded in a finite moderator in which the unperturbed shape is a cosine function. Single and multivelocity calculations of the angular distribution at the surface of the absorber, the flux distortion factor, the flux depression factor and the self-shielding factor have been carried out. The effect of flux distortion on the locus of the depression in a single foil as it is moved across the system is shown to be very small indeed, and one can confidently neglect this effect when calculating errors in buckling measurements by foil activation. However, the effect of flux curvature on foil activation in cells requires further examination if such experiments are to be interpreted with confidence.

Remedies for Ray Effects

Remedies are considered for the ray effect, a flux distortion producing defect of the discrete ordinates approximation to the transport equation. The partially effective remedies of increasing the number of directions, selecting quadrature sets invariant under discrete rotations, and introducing coupling terms into the representation of the transport divergence operator are considered. Numerical results are presented showing the effectiveness of these remedies in a standard test problem. Remedies that eliminate the ray effect are also considered. We show how to formulate multidimensional discrete ordinate equations equivalent to spherical harmonic equations and relate the order of the equivalent spherical harmonic equations to the degree of precision of the numerical quadrature. We give numerical results for this kind of remedy in three test problems, including one with material discontinuities. We show how the use of orthonormal polynomials permits the formulation of discrete ordinates approximations which have properties “like” those of the highest order spherical harmonic equations consistent with the number of directions in the discrete ordinates approximation. We find that these formulations also eliminate ray effects. We conclude that the partially effective remedy of using more, specially chosen, directions is the most practical remedy for most applications, but that for especially difficult situations or for reference calculations, the defect-eliminating spherical harmonic-like formulations should be available for use.

Neutron flux perturbations due to infinite plane absorbers II: Exponential flux

The problem considered is that of the activation of a non-scattering foil placed in an exponential flux. A pair of coupled, non-singular, integral equations for the surface angular distributions have been obtained by the Wiener-Hopf method. These have been solved numerically. Our results indicate that the angular distributions incident on the two faces of the foil are very different from those which exist in the constant source problem. Nevertheless, we find that prvided C, the ratio of scattering to total cross section, lies within the range 09 < C < 10, then the flux distortion factors for the two problems are practically identical. An explanation of this is given.

Measurement of the total loss of cold-rolled nonoriented 3% silicon iron using an Epstein square

Cold-rolled nonoriented magnetic sheet steel has better magnetic properties when magnetised along the rolling direction than when magnetised across it. For example, losses along the rolling direction are 15–20% below the mean. Owing to this difference in properties, values of core loss obtained when testing in an Epstein square may differ by as much as 4.5% according to the arrangement in the limbs of pieces cut along and pieces cut across the rolling direction. These differences have been investigated, and some of them have been explained on the basis of nonuniform flux and flux-waveform distortion. The best arrangement of the sample for testing is shown to correspond with that recommended in BS 601: Part 1: 1959.

A Continuous-Current Generator for High Voltage

Of all electro-dynamic machines, the direct-current machine probably is the best understood. It was the first machine to be commercially utilized and it is an interesting matter from an engineering standpoint to follow the evolution which this type of machine has passed through. The first great improvement to be incorporated in this type of machine was the application of commutating poles. As is the case in any radical development, engineering opinion was much divided as to the usefulness of such a construction. At first it was held that commutating poles were only useful where the service was severe, as, for example, in adjustable speed motors covering a large speed range. Today, however, it is well realized that commutating poles are advantageous in all kinds of direct-current machines, except in very small machines of fractional horse power output. It is well understood in the art that commutating poles alone do not offer a perfect solution of the direct-current problem, since there exists in such machines troublesome flux distortions. Many attempts have been made to overcome this by aid of distributed windings, and in this paper is described a form of such windings, which have given excellent results both from an operating and an economical standpoint. This distributed winding consists of two parts, one of which may be considered a counterpart of the armature, and is called a compensating winding. This winding opposes the armature reaction in every point around the circumference and effectively prevents any distortion of the flux. There is also a second winding for supplying the excitation and as is described in the paper, this winding is also distributed. By aid of such field windings, it is possible to meet very extreme conditions of service, for example, as is met with in high-voltage machines. In the machine that is described, the voltage between bars runs up to about 100 volts, or nearly four times the conventional value; nevertheless, the commutation is perfect. Machines rated 15 kw. have been built successfully up to 15,000 volts. One of the mechanical difficulties in building high-voltage, direct-current machines lies in the building of the commutator. A novel type of commutator is described in the paper. This commutator construction provides simple means for holding the segments together, and at the same time secures high insulation qualities.

Iron losses in direct-current machines

The term iron loss, as used in connection with rotating machinery, is shown to cover a large number of losses, some of which actually do not lie in the iron itself. The term core loss should be used except when the losses are actually located in the iron itself. It is shown that no great accuracy is practicable in the calculation of the actual iron losses, except in special instances, due to the fact that the ordinary treatment of materials in manufacture is such that large discrepancies are almost sure to occur, in certain types of apparatus. A brief explanation of several causes of variation in losses is given. In the treatment of core losses in direct-current machines, the four principal sources of losses are considered, namely — armature ring loss, armature tooth loss, eddy currents in buried conductors, and pole face losses. Under eddy current losses is given an explanation of certain losses not usually taken into account, and a crude method of calculation is given, with some tabulated results. Under pole face losses an empirical formula is given, also some tabulated results. The effect of load on losses is discussed, but no calculated results are given. Some of the effects of flux distortion on the losses are shown. A principal object of the paper is to show the impracticability of calculating all the core losses with any great accuracy at no-load, and the still greater difficulty in predetermining them with load.

Iron Losses in Direct-Current Machines

The term iron loss, as used in connection with rotating machinery, is shown to cover a large number of losses, some of which actually do not lie in the iron itself. The term core loss should be used except when the losses are actually located in the iron itself. It is shown that no great accuracy is practicable in the calculation of the actual iron losses, except in special instances, due to the fact that the ordinary treatment of materials in manufacture is such that large discrepancies are almost sure to occur, in certain types of apparatus. A brief explanation of several causes of variation in losses is given. In the treatment of core losses in direct-current machines, the four principal sources of losses are considered, namely-armature ring loss, armature tooth loss, eddy currents in buried condtuctors, and pole face losses. Under eddy current losses is given an explanation of certain losses not usually taken into account, and a crude method of calculation is given, with some tabulated results. Under pole face losses an empirical formula is given, also some tabulated results. The effect of load on losses is discussed, but no calculated results are given. Some of the effects of flux distortion on the losses are shown. A principal object of the paper is to show the impracticability of calculating all the core losses with any great accuracy at noload, and the still greater difficulty in predetermining them with load.