摘要:

AbstractThe classical Rayleigh-Ritz procedure is applied to the variational formulation of the one-dimensional diffusion equation. By minimizing the corresponding functional over finite dimensional piecewise cubic and quintic spaces, generalizations of the classical finite difference schemes are derived in the domain of continuous variables. Error estimates in the continuous norm are established which compare very favorably with corresponding ones in the discrete norm.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28971

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractIn this paper a new definition is given of the diffusion coefficient as a second-order tensor fully describing the anisotropic character of neutron diffusion in a homogeneous convex body. Numerical values for the diffusion coefficient tensor are reported for some typical geometries.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28972

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe delayed neutron precursor decay curves which result from a pulse of fissions of the isotopes233U,235U,238U,232Th,239Pu,240Pu,241Pu, and242Pu are consistently fit to a single set of six isotope-independent decay constants. When delayed neutron yields based on a single set of group decay constants are employed in reactor transient analysis, it becomes possible to introduce macroscopic precursor production cross sections for each of the delayed neutron groups. The newly fitted data are tested by the analysis of a typical fast reactor transient; the analysis shows that the utilization of the new data in comparison to the use of original data results in an insignificantly small deviation, while permitting a considerable reduction of calculational effort.The new technique developed for the fitting is shown to preserve important integral kinetics parameters. The fitting technique also allows the recasting of original five group data into the more conventional six group structure.Recent measurements on the energy dependence of delayed neutron yields and emission spectra are briefly discussed. The lack of energy dependence of the total delayed neutron yield in the range of interest for fast reactor analysis leads to a modification of the definition of the effective delayed neutron fraction.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28973

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractOne usually assumes that Sjöstrand’s area method for determination of reactivity by the pulsed-neutron technique is only valid in case of exponential prompt-neutron decay and no kinetic distortion. In this paper the method is shown to be valid more generally. Namely, for all systems satisfying multigroup multinode reactor equations, with only one fissioning node, the method holds true exactly when reactivity is understood to be the static reactivity, whileβeffis defined as the relative difference between the static prompt and total multiplication factors, provided the sensitivity of the detector has the same energy dependence as the fission cross section of the fuel of the active zone. It follows, e.g., that Sjöstrand’s method with a suitable fission counter is very well suited for measurement of subcriticality in small reflected subcritical fast cores. Some general recommendations are given.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28974

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe bilinear method of cell averaging of the neutron cross sections developed by Nicholson from the variational principle has been explained and supported by a perturbation theory derivation. By introducing further approximations, a form of the method is derived which involves only the scalar fluxes and adjoints and the currents. The scalar form differs from that used previously by others. A physical explanation is given for the flux gradient term which leads to a pseudoabsorption effect.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28975

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe methods for nonresonant cell homogenization in plate-type fast reactor critical assemblies are discussed and tested against high orderSntransport calculations in one-dimensional geometry. The methods tested show satisfactory agreement with transport calculations. The TESS calculations with bilinear flux-adjoint weighting are slightly preferred over flux weighting with either TESS or CALHET fluxes. Two different treatments of the leakage in the cell calculation lead to slightly different heterogeneity effects when calculated by flux weighting, but very little difference when calculated by bilinear weighting. A two-dimen-sional test problem gave some surprising results (negative heterogeneity factor) and has raised some unanswered questions.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28976

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractA measurement of the total neutron cross sections of238U was made using the Rensselaer Polytechnic Institute electron LINAC. The operating electron energy was about 60 MeV, and the beam burst width was 20 nsec. The neutron energies were determined using the time-of-f light technique with an overall resolution of 0.1 nsec/m. The cross sections are presented from 0.8 to 30.0 MeV; the cross-section curve is smooth in this region, and the averaged data have a statistical precision of 1%. The data reported here have been compared with the ENDF/B-III file. The disagreements are within 2% over the energy range 0.8 to 15 MeV. In addition, the experimental cross sections were fit using coupled channel code JUPITOR to obtain optical model and deformation parameters.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28977

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractA new method of determining photon energy spectra has been developed with the activities induced by various photonuclear reactions. Test calculations by the orthonormal expansion method show that this method is applicable to the determination of the bremsstrahlung spectra above about 5 MeV when the activation rates and the cross-section data are given as error-free. The experiments were performed for iron and tungsten targets bombarded by 15-MeV electrons from a linear accelerator and the bremsstrahlung spectra obtained were in agreement with those of approximate calculation. This activation method has the advantage of being available for measuring the spectrum of a bremsstrahlung burst and being suitable for determining the distribution of the photon energy spectrum in the medium.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28978

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe252Cf prompt-fission-neutron spectrum has been measured by time-of-flight techniques over the energy range 0.5 to 13 MeV. Significant analytical and experimental improvements over earlier measurements were employed. The data were simultaneously analyzed with the angular pattern data of Bowman et al., using a model which includes anisotropy of emission in the neutron fragment coordinate system and a stationary source. Based on this analysis, the mean energy is found to be 2.105±0.014 MeV. It is also concluded that the fragment emission spectra are highly anisotropic. The anisotropy is dictated by the data presented here, rather than by angular patterns. The existence of the stationary source is supported by both data types. A Maxwellian fit to the data provided a temperature parameter of 1.406±0.015 MeV. While the spectrum clearly deviates from a Maxwellian, this simple representation was found to be adequate to±5% from 0.7 to 8.0 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28979

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThis paper reports a study of bubble nucleation by fission fragments in superheated water. The experimental work was conducted using a small bubble chamber especially built for the program. The minimum superheat necessary for nucleation of visible bubbles by fission fragments (the threshold) was measured at temperatures between 380 and 440°F.Predictions of the threshold are based on comparison of the energy and linear energy transfer (LET) of fission fragments with the values required for bubble nucleation. Because of the variation in fission-fragment energy, the comparison is made on the basis of the median, 80’th percentile, and maximum energy and LET of the fragments present in the experiment.The data indicate that the LET comparison is the appropriate basis for prediction of the threshold. Using an empirically adjusted value of the LET required for nucleation, the calculated threshold agrees reasonably well with the data but becomes increasingly discrepant with increasing temperature. Reasons for deviation of the data from predictions are discussed, but a definitive determination cannot be made on the basis of the available data.

ISSN:0029-5639    

DOI:10.13182/NSE73-A28980

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor