摘要:

Prolonged exposure of the hydrogen form of a cation-exchange resin—a sulfonated copolymer of polystyrene crosslinked with divinylbenzene—to gamma radiation and flowing water caused more drastic changes in the chemical and physical properties of the material than has been reported by other investigators for resin exposed to like dosage in a static system. After a dose of 0.75×109rads in a dynamic system, the rate of loss of strong-acid capacity was 20 to 25%/(W-h g) of dry resin, compared with the 4% and the 10 to 20% found by others for the static system. Also, de-crosslinking of more than 4% of the resin matrix accompanied this loss of capacity, compared with the more moderate de-crosslinking or even additional crosslinking reported for the static system. Gamma radiation also caused gas evolution, bead swelling, and produced a weak-acid capacity in the resin equivalent to 3 to 5% of the original strong-acid capacity. Decomposition products included soluble sulfuric, sulfonic, and oxalic acids and insoluble bits of resin. The average rate of loss of sulfur during exposure was estimated to represent 1.0 to 1.2 atoms lost per 100 eV of energy absorbed.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18118

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

A method for calculating effective cadmium cutoff energies to be applied to measured resonance integrals of Doppler-broadened-resonance absorbers, as well as 1/υabsorbers, is described. The method is applied to infinite slab, infinite cylinder, and sphere configurations in which the absorber, at some uniform concentration, occupies all the space within the cadmium cover. It is pointed out that the effective cutoff value applying to an activation measurement of a resonance integral differs from that applying to a reactivity measurement under otherwise identical conditions. The development of calculations for both cases is presented. Some results are given for gold, indium-115, plutonium-240, and the l/υabsorbers, boron and vanadium, as a function of sample configuration, cadmium thickness, absorber density, temperature, and neutron spectrum. Many of these values differ significantly from the nominal 0.5 eV.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18119

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

The theory of Lane, Nordheim, and Sampson for the calculation of the effective resonance integral in media containing absorber in the form of small particles was tested by comparison with experiment. Measurements were made on samples containing gold particles in a range of volume fractions from 0.1 to 30%. Two diluent materials, lead and graphite, were used to test the effect of the type of material admixed with the absorber particles in the samples. Comparison of the theory and experiments was made on the basis of the calculated and measured decrease in effective resonance integral of the particle case relative to the corresponding homogeneous case with the same average absorber and diluent density. The results show that, for small absorber volume fractions, there is good agreement between theory and experiment, if the theory is suitably modified to describe the experiment. This agreement also extends to volume fractions above 10%, although the results of the theory are in question in this range.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18120

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

A new activation technique has been developed for the measurement of the ratio of the capture cross section of238U and the fission cross section of235U in zero-energy fast reactors. This work was initiated because of the long-standing discrepancy between calculated values of this ratio and radio-chemically measured values. The new technique is a direct counting method that does not involve chemical separation in any way. Measurements have been made in fourZPR-III fast reactor assemblies, two with hard spectra and two with soft spectra. In all four cases the measured ratio was slightly higher than the calculated value being, on the average, 4% higher than calculation. This is in strong contrast with the past radiochemical measurements inZPR-U3 assemblies that gave values 16% less than calculation. The present measurements, therefore, support the general correctness of the calculated ratio and, hence, indicate that there are no gross errors in the assumed average microscopic values of the238U capture cross section and the235U fission cross section.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18121

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

Within the framework of a simplified one-dimensional model, the following problem is considered. Given a segment of some fissionable material with a length less than its natural critical length, construct, if possible, reflectors that provide albedos sufficient to make the segment critical (or achieve a prescribed degree of supercriticality) and do this in an optimal way (i.e. with minimum weight or cost). It is shown via asymptotic solutions to the one-dimensional Boltzmann equations that the appropriate left and right albedos lie on a segment of a hyperbola. For any pair of these albedos and for a wide class of optimization criteria, the optimal reflectors can be designed using the technique of dynamic programming. The solution to the problem is then found by a simple minimization along an arc of the hyperbola which relates the left and right albedos. Numerical examples are provided to illustrate the method when the optimization criterion is minimum weight.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18122

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

The one-velocity time-independent neutron integro-differential transport equation is converted into an integral equation by the use of a homogeneous Green's function. The neutron flux, Green's function, and source are expanded in spherical harmonics. The integrations over the angles are carried out by the use of the spherical harmonic orthogonality relation. The net result is a set of coupled integral equations in the flux angular moments. Relations that give the Green's function angular moments are derived for any nonreentrant geometry and all boundary conditions applicable to the neutron transport equation. The conditions for which the scalar flux and some of the flux higher moments can be calculated exactly are discussed. Sample problems of unit slab cells that meet these conditions, are solved. The results are found to be in excellent agreement with those of the DS16 and the TRANVAR codes. A method to estimate the effect of the flux non-zeroth angular moments and the spatial truncation errors on the scalar flux is introduced. A sample problem of a heterogeneous unit slab cell is presented. It is found that the errors in the scalar flux due to neglecting the flux non-zeroth angular moments and the spatial truncation error are each of the order of 0.03% for this problem.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18123

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

The method of first-flight collision probabilities in an isotropic scattering medium is developed for an anisotropic scattering medium, and a closed form of the expression for the circularly cylindricalized cell is formulated. A reciprocity relation and neutron conservation for the generalized first-flight collision probability are discussed. As an application, the thermal-neutron spectrum in the uranium light-water lattice, which was studied in Brookhaven National Laboratory, is calculated using the FIRST II code, and numerical results for the disadvantage factor of dysprosium activation are compared with results calculated by Honeck using the transport approximation. It is shown that the transport approximation gives fairly good results.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18124

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

It is shown that it is possible to recast the usual canonical conditions for predicting stability-in-the-large for reactor-kinetics systems into terms of the parameters characteristic of the physical system, thus permitting direct qualitative examination of the stability of a given system. For systems with more than one reactivity coefficient, it is found as a direct consequence of the physical formulation that if the prompt coefficient is negative then a delayed positive coefficient can be more stabilizing than a delayed negative coefficient.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18125

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

摘要:

The digital computer algorithm produced by the methods of dynamic programming, generates optimal reactor-shutdown programs that (i) minimize the post-shutdown xenon concentration maximum, or that (ii) minimize the xenon concentration itself at a given post-shutdown time. Such shutdown programs are found to consist of pulsing the reactor at specified intervals. The number and duration of the pulses depend on the parameters involved, especially the magnitude of the flux constraints, and the constraints on the xenon override reactivity available in a given fuel loading.

ISSN:0029-5639    

DOI:10.13182/NSE66-A18126

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE66-A18127

出版商:Taylor&Francis    

年代:1966

数据来源: Taylor