摘要:

An explanation is given of an apparent discrepancy between two methods for determining the collision density at epithermal energies. This explanation is based on a result from renewal theory.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26433

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

A series of experimental measurements has been made on the Experimental Gas Cooled Reactor (EGCR) lattice in the Physical Constants Test Reactor (PCTR). The measurements provide a broad basis for normalization of reactor calculations for lattices of this type. The fuel assembly is a cluster of seven uranium oxide rods, enriched in the U235isotope and clad with stainless steel. The fuel is spaced on an eight-inch square pitch in a graphite moderator. Values of the lattice parametersk∞, f,p,andεhave been obtained for 1.8% enrichment of the uranium oxide fuel. The values ofk∞and f have also been obtained for 2.6% enrichment fuel. The techniques of using the PCTR have been extended so that supercell measurements may be made. The values of the strength of a boron carbide control rod and a stainless steel loop tube have been obtained in this way. The strength of such an inhomogeneous poison in the lattice is expressed as the difference in the supercell multiplication factork∞with and without the poison in the supercell. This difference is the same quantity which is obtained in the usual reactor cell calculation. The fuel temperature coefficient of for this cluster has also been measured between 50 and 500°C. The coefficient obtained is temperature dependent. The more important of the lattice parameters for the 1.8% enriched fuel are = 1.146±0.004,f = 0.809±0.005, p28= 0.824±0.006,ε= 1.019±0.002,Δk(control rod -16 cell supercell) = -0.157±0.012,Δk(empty loop tube -9 cell supercell) = -0.117±0.011, and (l/k∞)(dk∞/dT) = -(0.68±0.05) X 10-3T-1/2(oK)-1For the 2.6% enriched fuel, results arek∞= 1.256±0.009 and f = 0.845±0.006.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26434

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

This review deals exclusively with the theoretical task of interpreting the measurement of a thermal neutron absorption rate in terms of the neutron density that existed at the probe location prior to probe insertion. Successful accomplishment of this task is fairly obviously of considerable practical importance, since activation measurements of thermal fluxes are an important adjunct to many reactor experiments and are also frequently employed to obtain thermal flux maps in reactor cores and reflectors. Because of its importance, the problem has received extensive and varied (but usually piecemeal and semi-intuitive) theoretical attention over the past twenty years. Many experiments have been performed concurrently. The net result has been to perpetuate a lively interest in the problem, since comparisons of experiment with experiment, experiment with theory, and theory with theory have been ragged and controversial.1It will be the purpose of this review to present an adequately precise and general statement of the problem and then attempt deductive comparisons of various theoretical attacks upon it. Attention will be focused primarily upon the task of obtaining operational descriptions of the diverse approximations explicit or implicit in the calculations considered.Throughout the review attention is persistently directed to an aspect of the problem that has received less than adequate attention so far, i.e., that of the effect of“flux-hardening”on the absorption rate. An attempt to obtain a qualitative estimate of the importance of this effect is presented, but the only conclusion drawn so far is that the effect is not obviously an ignorable one.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26435

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

The feasibility of applying the spherical harmonics technique to problems in gamma transport is investigated. The spherical harmonics procedure is described for one-dimensional slab geometry for plane monoenergetic sources. Energy spectra obtained by theP-3 approximation covering a wide range of source energies and materials are compared to moments results for penetrations up to fifteen mean free paths. The comparisons indicate that it is plausible to extend the method to multislab geometry for potential design applications.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26436

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

An experimental method of determining“initial conversion ratios,”the number of Pu239atoms produced for each U235atom destroyed, is described. The measurements are made relative to the conversion ratio that would be obtained for thin uranium in a thermal flux. The precision is about±%.The relative neptunium and fission product activities induced in a representative cross section of the fuel material (a thin foil of natural uranium) and in a foil in a thermal flux are compared. The neptunium is counted by a coincidence method which suppresses the counting rate due to fission products and natural background 10 times relative to the neptunium counting rate.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26437

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

The half-life of Cs137has been measured by observing the rate of growth of stable Ba137from a known quantity of Cs137by the use of isotope dilution mass spectrometry. The half-life thus obtained is 29.2±0.3 years

ISSN:0029-5639    

DOI:10.13182/NSE63-A26438

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

Experimental evidence indicates that diffusion through the porous matrix and evaporation from the geometric surface are the rate-limiting processes in the loss of some fission products from uranium-graphite fuel. The loss of other fission products is rate-limited by unidentified processes which do not include those macroscopic diffusion or evaporation processes, but which may include diffusion or evaporation on the microscopic or granular scale.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26439

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

A perturbation theory solution is given for the time-dependent, exp(—λt), neutron thermalization problem for a bare homogeneous multiplying medium. The model is based on diffusion theory with the heavy gas scattering kernel assuming 1/υcross sections with a constantD/(ξσυ). The fission spectrum is assumed to be a delta function at the mean fission energy,εf. The fundamental eigenfunction and eigenvalue are expressed in terms of infinite sums involving the Laguerre polynomials atεf. The sums were evaluated analytically and numerical results are given.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26440

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

An array of parallel flat plates is considered in which there are inlet deviations in the spacing. Analytic predictions are made of the effect of these deviations on the flow-induced deflections of the plates. It is shown that in the vicinity of Miller’s critical velocity, small deviations are sufficient to cause large deflections. Lesser deflections are predicted for lower flow rates.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26441

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor

摘要:

Flux perturbations due to indium disc foils exposed to an isotropic thermal neutron flux in a water medium were experimentally determined. The unperturbed flux, or the“zero thickness”activity, was determined using foils which matched the moderating ratio of the medium, thereby causing no flux perturbation. Comparison of the results with several modifications of the Ritchie and Eldridge theory gives excellent agreement for foil thickness from 0 to 0.025 in.

ISSN:0029-5639    

DOI:10.13182/NSE63-A26442

出版商:Taylor&Francis    

年代:1963

数据来源: Taylor