摘要:

AbstractThe equilibrium phase diagram of the plutonium-cerium-copper system is presented, based on data obtained by differential thermal analysis, metallography and electron-microprobe x-ray analysis. Liquid-solid phase transitions were found between 419 and 1083°C. Ten crystalline phases solidify as primary phases from molten plutonium-cerium-copper solutions. No ternary compounds occur in the system. The ternary system is divided into two subsystems by the quasibinary section, CeCu2-PuCu2. Continuous solid solubility occurs along this join with neither a maximum nor a minimum. Solid solubility also occurs between the congruent compound, CeCu6, and the incongruent compound, Pu2Cu11. The ternary system is characterized by a single eutectic (4at.%Pu-68at.%Ce-28at.%Cu at 419°C), four peritectics, and two inversion points.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19253

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractEnergy spectra were obtained experimentally for fission fragments escaping from backed films of enriched uranium dioxide that were less than 11µm thick. The data were reduced to give values for the relative average escape energies (R), escape fractions (S) and energy deposition efficiencies (D). A mathematical model was developed to synthesize these results using a Monte-Carlo-type computer code. This code included the fission-fragment masses, yields, and initial energies, the experimental source-detector geometry, a range-energy relationship, an energy-loss relationship and a function for the pulse-height defect in surface-barrier detectors. Various functions for these last three parameters were used in combination to obtain results that duplicated the experimental spectra andR, SandDvalues. The agreement was obtained with range proportional to (energy)1/2, the square energy-loss function, and pulse-height defect =A(E) (M-B), whereAandBare constants andEandMare energy and mass, respectively. The experimental detection functions were removed from the code, and the spectra andR, SandDvalues were calculated for a 2πgeometry. These values agreed well with those calculated using weighted averages for range and initial energy.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19254

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThis study was undertaken to evaluate radiometric techniques for sensing atomic hydrogen in trace quantities at low pressure, for possible application to satellite measurements. A reaction utilizing radioactive As74metallic surfaces demonsrated quantitative evolution of As74H3vapor in linear relationship with the impingent flux of atomic hydrogen. Equivalent partial pressures of atomic hydrogen below 10−8torr were quantitatively measured.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19255

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractTo perform fast-neutron penetration calculations, a new method is described, which offers some of the advantages of the Monte Carlo method and other highly sophisticated methods, yet retains some of the features of the line-of-sight kernel methods. The method includes the use of effective flux-removal cross sections to predict a distribution of‘last-collision’centers in a shield and uses statistical estimation to obtain the flux at the receiver from each last collision. The chief advantage of the method is that it provides an approximate angular distribution of the neutron flux at the receiver and includes the effects of boundaries, but is much less costly to apply than Monte Carlo. The principal limitation to the accuracy of the method stems from the assumption of no change in neutron direction and energy prior to the last collision. Detailed formulations for slab and for cylindrical geometries are given, along with results of an initial evaluation based on comparisons with Monte Carlo and with measured data for lithium hydride shields.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19256

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractSpatially dependent neutron-spectrum measurements have been made in both light and heavy water, using the General Atomic Linear Accelerator Facility and standard time-of-flight techniques. The measurements were made with varying geometrical arrangements, and both 1/vand resonance absorbers were utilized to simulate reactor poisons. The measurements were compared to calculations performed with anSNtransport code utilizing the bound scattering models proposed for these moderators. The agreement between theory and experiment for the Nelkin model for H2O and Honeck’s extension of this model to D2O is shown to be very satisfactory for the cases studied.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19257

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe ratio of the neutron capture cross section to the fission cross section,α, for U235has been measured for incident neutron energies from 3.25 eV to 1.8 keV. A pulsed and collimated neutron beam was passed through a U235fission chamber placed at the center of a large liquid scintillator, and both capture and fission events in the chamber were detected in the scintillator by means of their prompt gamma rays. A fission event was distinguished from a capture event by a coincidence of the scintillator signal with a signal from the fission chamber. The values ofαobtained, after various efficiency and background corrections were applied, are in good agreement with data derived from other experiments.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19258

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA procedure for calculating the neutron multiplication factor and few-group constants for water-moderated reactors has been developed. The intent of this development was to produce a calculational procedure which could be used with confidence in the engineering design of water-moderated reactors. Analytic procedures that require large amounts of computer time were excluded from consideration. The proposed procedure includes a heterogeneous treatment of the fast-fission effect, resonance absorptions and the thermal utilization. The results of the procedure agree well with more rigorous calculations requiring orders of magnitude more computer time. The procedures have been applied to 116 U-metal and UO2experimental lattices covering a wide range of parameters. The multiplication factor is calculated for all cases with a standard deviation about the mean of 0.86%.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19259

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractMeasurements of the shape of the fundamental mode of a thermalized neutron pulse in graphite for rectangular stacks has yielded a value of the extrapolation length,d= 1.825±0.025 cm. The pulsed-neutron decay constants in graphite have been measured over a buckling range from 1.946×10−3to 1.230×10−2cm−2and fitted to three- and four-term power series in the buckling. To fit points at bucklings greater than 6.0×10−3cm−2, a cubic fit is necessary. An iterative method of fitting the decay constants results in an extrapolation length of 1.78±0.01 cm. The diffusion constant was (2.0896±0.0093)×105cm2/sec, and the diffusion cooling constant was (3.77±0.35)×106cm4/sec at a density of 1.689 g/cm3. A technique of correcting the decay constants for the effect of spectral cooling has been developed. The decay constants corrected to room temperature can be fitted as a linear function of the buckling. This method interates on the heat-transfer coefficient,γ, and gives a value ofγ= 1633±89 sec−1for graphite. The heat-transfer coefficient relates the rate of energy transfer from a moderator to a cooled-neutron spectrum. With this approach the entire buckling range can be fitted with three parameters.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19260

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractIn a previous paper Leslie, Hill and Jonsson put forward a method for the rapid evaluation of the Dancoff factor in regular arrays of fuel rods. They also showed how extended rational approximations to the fuel nonescape probability could be used to improve the form of the equivalence theorem based on Wigner's rational approximation. This form of equivalence asserts that the resonance integral is a function of the geometry through the excess potential scattering 1/Nonly, whereNis the number density of the absorber andis the mean chord. In the modification proposed by Leslie, Hill and Jonsson, this function is generalized toa/N; the Bell factorais found to vary with coolant density. By making use of an approximate analytic method for the calculation of collision probabilities in geometries more general than regular arrays, the present authors extend this work to cluster-type fuel elements. The basic procedure is the same as in the work referred to above. An analytic expression for the fuel-to-fuel collision probability is derived using arguments about its behavior in the black and white limits (i.e. in the limits of high and low cross sections). The Dancoff factor is derived from the behavior in the black limit. It is shown, by comparison with exact calculations, that for two types of cluster geometry of current interest in fuel element design, the proposed Dancoff factor is in error by at most 2%. Improved equivalence relations for cluster geometry are also considered. It has been customary to assume that the cluster is equivalent to an isolated rod of diameterdp/Γ, wheredpis the diameter of a single pin in the cluster andΓis the Dancoff factor. Such a procedure implies that the Bell factor of the cluster is constant and equal to its value for an isolated rod. It is shown in this paper that the Bell factor is a function of coolant density and that, in a particular case, the cluster is almost equivalent to an isolated rod at low density. As the density increases, the Bell factor drops rapidly by 6% and then increases slowly.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19261

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractFor the heavy-gas model, the stationary space-dependent neutron spectrum in one- and two-dimensional heterogeneous thermal reactors is determined in the diffusion approximation. The fuel elements, which are not necessarily identical, and absorbing slabs or rods are arranged arbitrarily. However, absorption in all of them is assumed to follow a l/vlaw. The neutron flux is represented as a linear combination of the lowest eigenfunction of the Laplace operator for the geometry considered and a finite set of Green's functions for the stationary-wave equation for various, usually imaginary, wave numbers. The energy-dependent coefficients are determined by the author's method, developed in an earlier paper. The lowest eigenfunctions of the Laplace operator and Green's functions for the stationary-wave equation are given for some geometries of practical interest. Solutions found earlier for simple geometries may now be regarded as special representations of these Green's functions. But in these cases, too, other representations can be found which are to be preferred for numerical reasons.

ISSN:0029-5639    

DOI:10.13182/NSE65-A19262

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor