摘要:

The most general linear truncation relation for the spherical harmonic representation of the transport equation in three dimensions is shown in any order to be a partial differential equation. This equation is uniquely determined up to two independent scalar parameters in the time-dependent case and one scalar parameter in the time-independent case. In the time-dependent situation, one of the parameters may be related to the other parameter, which is pertinent to the time-independent limit, in such a way as to give correct retardation in all orders.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17326

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

This paper presents an operator-type perturbation method which may be used to solve perturbation problems associated with the neutron diffusion equation. The method is related to the hybrid Schrodinger-Heisenberg operator methods used in quantum mechanics. The operators are derived from the variational principles associated with the neutron diffusion equation; therefore, the method includes the advantages of the variational method. Two applications in one-dimensional, one-group diffusion theory are illustrated. The first example illustrates how a plane source of neutrons can be treated as a perturbation. The solution to this problem is exact. In the second example, the solution to a simplified time-independent problem involving fission-product poisoning is presented. The solution to this example is in open form as expected. It is found by way of comparison that this operator method gives a better result in this particular example than the more familiar method of approximating the perturbed solution by an expansion in terms of eigenfunctions of the unperturbed solution.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17327

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Epithermal absorption by control rods in nuclear reactors is taken into account by replacing the black-grey-transparent rod by a black-transparent model. The lethargy boundary, in the model, is determined for 1/νabsorbers by the prescription that, at the boundary, half the incident partial current is absorbed by the rod. Application of the model to space-independent spectrum calculations improves the calculation to the extent that, provided the black-transparent boundary is the boundary between the groups, two-group methods can be used for control rods in bare reactors. For control rods in reflected reactors, three groups are indicated. Calculations are presented to demonstrate the accuracies of the black-transparent model and the small number of neutron energy groups.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17328

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

From an empirical choice of the shadowing of one control-plate element by another, expressions are derived for the reactivity worth of systems of circumferential control plates. The expressions contain three parameters which are determined when independent calculations of three control systems have been made. The parameters can be expressed in terms of the worth of the complete control plate, the increase in reactivity due to unshadowing of an end of a control plate and the decay constant of the assumed exponentially decaying shadowing function. Application of the expressions to a particular reactor design, where circumferential control plates separate core from radial reflector, shows that the analysis is accurate for those situations where the number of control plates is not large. The analysis neglects neutron absorption by the edge of a control plate so that it underestimates reactivity worth in situations involving large numbers of control plates where the surface area of the plate edges becomes significant.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17329

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

A formalism based upon the source-sink method of Horning, Feinberg, and Galanin has been developed which predicts the neutron noise spectrum, and time-dependent correlation function, in heterogeneous reactor systems. The method is applied to two problems in infinite plane geometry: the infinite lattice, and detector perturbations. In the lattice problem, it is shown that the simple, homogeneous theory will only be valid when the lattice spacing is very much less than the attenuation length of a neutron wave in the pure moderator. The flux depression in the neighborhood of a neutron detector is found to introduce significant corrections to the noise spectrum.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17330

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

Methods of correcting double-differential slow-neutron scattering data for multiple scattering have been investigated and applied to three important experimental studies of room-temperature water. The corrections obtained are very significant, particularly for low-momentum transfer data, which in some cases require corrections of 50% or more. However, uncertainties are introduced into the correction process by sensitivity to theoretical models, which must be used to calculate the multiple scattering. The choice of the correction method and interpretation of the corrected results in the presence of these uncertainties is considered in detail.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17331

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

The distributions in water of indium resonance and115In(n,n′)115mIn neutrons from a 2.85-MeVT(ρ,n)3He source have been measured. The values of the integrated plane activities perpendicular to the proton beam direction (including the extrapolated region beyond the range of measurement in each plane) are presented. The experimental results are in agreement with Monte Carlo calculations utilizing two oxygen elastic-scattering descriptions and agree within quoted standard deviations in both cases.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17332

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

The graded exposure of 4 plutonium-aluminum alloy, 19-rod clustered fuel elements, and the subsequent destructive sampling of the elements have provided experimental data showing the variation of plutonium isotopes with irradiation. Irradiations were conducted in the heavy-water-moderated and -cooled Plutonium Recycle Test Reactor at Pacific Northwest Laboratory of the Battelle Memorial Institute. Using137Cs as a fission indicator, the depletion of the initial plutonium to 50.4±1.1% is determined. Reactor effective cross-section ratios for the plutonium isotopes are derived from the data, and results show that the capture-to-fission cross-section ratio for239Pu (239) is 0.426±0.019.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17333

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

The space-dependent ion production rate by fission fragments escaping from a fuel plate is studied using: 1) the Bohr stopping equation with the Thomas-Fermi approximation of the effective charge Zeff; 2) the Alexander-Gazdik (A-G) semiempirical velocity-distance relationship for fission fragments. The assumptions are: a) no scattering during slowing down; b) the nonionizing energy loss in nuclear recoils can be taken into account by increasing thewvalue for fission fragments over that forαparticles; c) a delta-function mass distribution for the light and heavy group; and d) a monoenergetic source. The energy current carried by the fragments at a point in the outer medium is first derived, and the energy deposition per unit volume per second is obtained by taking the gradient of the energy current. Dividing the energy deposition by thewvalue for the medium yields the ion production rate by fission fragments in that medium. The results show that the semiempirical velocity-distance relationship gives a higher ion production rate than that given by the velocity-distance relationship derived from the Bohr stopping equation with the Thomas-Fermi approximation of the effective charge Zeff. The volumetric, spatial average ion production rate is also obtained. For a fuel plate containing 20%235U and 80% Pt and for a flux of 6×1010n/(cm2sec), the velocity-distance relationship based on the Bohr stopping equation gives an average ion production rate of 2.0×1013ion pairs/(cm3sec) in a mixture Ne + 0.1% Ag. Using the same values for the fragment ranges, the semiempirical velocity-distance relationship yields an average volumetric ion production rate in neon higher by about 18% for the light fragment and by about 20% for the heavy fragment. According to existing experimental results on plasmas induced by fission fragments, an ion source of 2.0×1013ion pairs/(cm3sec) would yield a conductivity of about 1×10−3(Ωm)−1in the gas mixture Ne + 0.1% Ag, at 200-mm Hg and 400°K and at an electric field of 560V/m.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17334

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

The behavior of thermal neutrons in a water shield containing ducts was studied experimentally and compared with theoretical models. In addition to measuring the total flux, a source separation technique was used to isolate the various flux components, which are:1)direct flux, uncollided neutrons which enter the duct mouth2)scattered flux, collided neutrons which enter the duct mouth3)penetration flux, collided neutrons which originally enter the shield. Duct diameters from 1to 4 in. were considered. The shield absorption properties were altered by dissolving various amounts of boric acid in the water. The duct cross-sectional shape was changed by partially flooding the interior of the duct.The experimental results indicated that the direct flux is inversely proportional to distance squared. For sufficiently long ducts, the direct flux is nearly the total flux. For shorter ducts, either the scattered flux or penetration flux may produce the largest contribution to the total flux. Each of these components peak near the duct mouth and then attenuate more rapidly than the direct flux.Successful calculational models were developed for each of the flux components. These permitted determination of the total flux to within a factor of 1.3 at distances greater than two or three duct diameters from the mouth.

ISSN:0029-5639    

DOI:10.13182/NSE67-A17335

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor