摘要:

Placzek proved that the collision density of neutrons coming from an energy point source and slowing down by isotropic elastic scattering in an infinite one-isotope nonabsorbing medium oscillates in a certain typical manner. It is proved in this paper that Placzek-type oscillations occur in one-isotope infinite media under the most general elastic scattering law and most general absorption law. In particular, the scattering need not be isotropic nor the absorption small or constant.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20652

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

The derivation of blackness boundary conditions is reviewed and generalized into a standard matrix formalism that is valid for any orderPNapproximation. It is then shown that for a finite slab effective diffusion and absorption matrices can be found which reproduce blackness boundary conditions at the interfaces. In the continuous or infinitely many mesh point description of the black region, the analysis leads to infinite series expressions for the equivalent matrices, which have been evaluated explicitly by means of the Caley-Hamilton theorem for the case of theP3approximation. Equivalent matrices have also been derived for two- and three-mesh-point descriptions of the black region. Numerical calculations for three model problems indicate thatP3blackness theory is a great improvement over conventionalP3theory and is roughly equivalent toP5theory in the prediction of both the exterior scalar flux and the absorption rate in the black region.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20653

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

The problem of controlling xenon-power spatial transients in a large thermal power reactor is formulated in terms of the dynamic programming formalism. This formulation results in a computing algorithm that can be used to select the control action that optimizes some performance index from among a predetermined set of allowable control sequences. An application of this formalism to a relatively detailed three-dimensional reactor model is presented.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20654

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

The linear extrapolation distance, extrapolated endpoint, and effective radius of grey and black cylindrical neutron absorbers imbedded in an infinite moderator have been calculated using Kofink's formulation of thePNmethod, withNodd up to 13. These parameters were determined as functions of the absorption of the moderator and of the linear anisotropic scattering component of the moderator, for two source distributions: 1) uniform isotropic sources; or 2) no sources with a current from infinity. The results are given both in tabular form and in simple formulas that are sufficiently accurate for most purposes. In addition, various kinds ofPNboundary conditions are compared and new calculations are given for the blackness of homogeneous grey rods.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20655

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

Neutrons of 0.05-eV energy were inelastically scattered from samples of water. The experiment was arranged so that a correction could be made for multiple scattering and so that the observed scattering law would be measured at momentum changeℏκsmaller than obtained in previous experiments. From the data, it is concluded that 1) at these lowκvalues the scattering law at fixedβis proportional toκas predicted by the McMurry-Russell model but by no other models, 2) discrete transitions are no more distinct at these smallerκ’s than at largerκ’s contrary to the predictions of the McMurry-Russell model, and 3) multiple scattering is important but not as large as predicted and that experimental corrections for it can be made.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20656

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

The General Atomic Neutron Velocity Selector was used to study the details of neutron scattering in liquid D2O maintained at 300°K. The scattering into various angular directions between 30 and 120°is studied for incident neutrons with energies ranging up to∼0.65 eV. The energy-transfer cross sections, corrected for plural scattering effects, are evaluated to provide data in regions of large energy and momentum transfers not previously available and not readily accessible to experimenters using a reactor as a source of neutrons. The present results agree satisfactorily with the previous results but indicate that the previous results contain effects due to plural scattering in the sample. The present results also are compared with theory. Although there are some regions of acceptable agreement, other regions of poorer agreement indicate that each of these theoretical treatments may need further attention.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20657

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

Thermal-neutron diffusion coefficients for H2O and D2O were determined from static measurements of the neutron relaxation length in boron poisoned H2O and D2O and pulsed measurements of the neutron die-away in different sized containers of these two moderators. The coefficients derived for H2O are:These results agree well with previously reported coefficients, fairly well with Honeck's calculations, and very well with Dorning's more recent calculations. The diffusion coefficients for D2O were derived from data in the range of (equivalent) poison concentrations,∑a(B) =−0.04 to +0.04/cm. Restricting the data to these limits avoids possible difficulties associated with the approach to the Corngold limits atκ= (∑t)minand. The coefficients derived for D2O are:Unlike previous experiments, these results indicate no discrepancy between pulsed and static determinations ofD0for D2O.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20658

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

Measurements have been made of the decay constant of thermal neutrons in water poisoned with boron and with the non-1/vabsorber cadmium. An experimental method has been used in which proper spatial integration of the neutron flux enables data that are representative of the infinite medium to be accumulated without waiting for the establishment of a fundamental mode distribution. The measurements yield effective absorption cross sections in good agreement with presently adopted values. The change in effective absorption cross section with concentration of the dissolved cadmium (dσeff)/(dN) has been determined for an infinite medium at 20°C. Two- and three-parameter fits of the decay constant yield−(0.32±0.09)·10−17b cm3and−(0.47±0.10)·10−17b cm3, respectively, for the coefficient (dσeff)/(dN). Earlier published measurements have resulted in two to five times larger values, whereas a published calculated value for Nelkin's model is−0.33·10−17b cm3.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20659

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

Fission rate fluctuations at low power in a reactor with a large fission-product inventory have been observed in the pool-type Ford Nuclear Reactor. A gaseous Cerenkov detector was used to sense the high-energy, prompt-fission gamma rays in the presence of a fission-product gamma field of 105to 106R/h. The ratioβ/lis determined from the cross power spectral density of the fluctuations in the signals from two of these detectors. Both this spectrum and the power spectral density of the output of a single detector show a large low-frequency component. This is attributed to moderator temperature fluctuations present when the fission-product decay heat is removed by natural circulation of the coolant. The temperature fluctuations as measured with a short-time-constant thermocouple are shown to be correlated to those in the fission rate.The detector is described, as well as a basis for calculating its performance and efficiency. A theory of the gamma noise experiment that reveals the effects of the detector on the measured spectrum is presented.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20660

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

Neutron spectra have been measured by the time-of-flight method from 1 eV to 2 keV at various positions across depleted uranium and borated polyethylene in slab geometry with an energy resolution of 0.9% at 6.68 eV. The observed behavior around the 6.68-eV resonance in238U has been compared with the predictions of the transport theory code 1DF in S4and S6approximations using different quadratures and spatial representations. The space-averaged flux has been calculated with the slowing down code GAROL. The 1DF calculations agree reasonably well with experiment and the GAROL values.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20661

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor