摘要:

AbstractReactor physics parameters were measured in three heavy water lattices consisting of 0.250-in.-diam, 1.03 wt%235U metal fuel rods in triangular arrays spaced at 1.25, 1.75, and 2.50 in. The following quantities were measured in each lattice: the ratio of epicadmium to subcadmium radiative captures in238U (ρ28); the ratio of epicadmium to subcadmium fissions in235U (δ25); the ratio of radiative captures in238U to fissions in235U (C); and the fissions in238U to fissions in235U (δ28). These experimental results were used to calculate the following reactor physics parameters for each lattice: the resonance escape probabilityp, the fast fission factorϵ, the multiplication factor for an infinite systemk∞, and the initial conversion ratioC. Analytical results obtained by using THERMOS and GAM-I are in fair agreement with the experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20210

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractPrompt-neutron decay constants have been determined for unreflected and unmoderated subcritical cylinders of enriched uranium (93.15 wt%235U) by the Rossi-αtechnique. The cylinder diameters were 17.77, 27.93, and 38.09 cm and the heights varied from 10.184 to 2.548, 8.431 to 5.399, and 7.502 to 4.780 cm, respectively. The decay constants agreed to within 4% with those measured by the pulsed-neutron method; the comparison with the results ofSntransport theory calculations showed disagreements as large as 20%. The ratio of the prompt-neutron decay constant of a cylinder at delayed criticality to that of a subcritical cylinder and the ratio of the corresponding prompt-neutron lifetimes were used to obtain subcritical reactivities as great as 33 dollars. The lifetimes were calculated using neutron fluxes fromS8transport theory. These reactivities agreed favorably with values determined by an analog computer whose input was the response of an ionization chamber to power changes when an assembly was disassembled from delayed criticality to a given reactivity.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20211

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractMeasurements have been made of the anisotropy of neutron slowing down in Al-H2O plate lattices. The moments of the slowing down distribution from fission to 1.46 eV were determined in the two characteristic directions at two volume ratios using the point-source, point-detector method. For the 1:1 case, with an Al plate thickness of 0.25 in., the ages parallel and perpendicular to the plates were 65.4±0.8 and 60.8±0.8 cm2, respectively, giving an anisotropy of 1.076±0.02. In the 2:1 (A1:H2O) case, with an Al thickness of 0.50 in., the corresponding values are 100.3±1.5 and 92.5±1.3 cm2, giving an anisotropy of 1.085±0.02. The higher moments were characterized by higher anisotropics.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20212

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE68-A20213

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe feasibility of using Monte Carlo methods to compute the criticality of thermal reactors is investigated by analyzing three simple critical assemblies with the 05R Monte Carlo neutron transport code. Results indicate that a precision of 0.5 to 0.8% in the eigenvalue is obtainable for these cores in less than one hour on the CDC-6600 computer. Further time reductions are foreseeable pending refinements in the operating system and more effective utilization of variance-reduction techniques. Several aspects of problem strategy and variance estimation are examined, leading to increased understanding of criticality estimators and correlation of data.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20214

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractAn artificial neutron source located within a subcritical reactor at a position that is asymmetric with respect to a line or a plane of symmetry will give rise to a neutron flux shape that is itself asymmetric. The ratio of counting rates from two counters at different locations will then depend on the degree of subcriticality of the reactor, and this ratio can be used to infer the effective multiplication constant (λ0) of the system provided certain auxiliary parameters, which must be either computed or obtained by experimental calibration, are known. This situation is analyzed theoretically and some simple numerical experiments are presented which suggest that the auxiliary parameters (which themselves depend on the degree of shutdown) may be taken as constants in some cases.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20215

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractA transport calculation of the lattice diffusion length, yielding the“gross”decay of the asymptotic flux in a lattice, is made using the method of K. M. Case. Refinements over the diffusion calculation are shown to be 1) slight adjustments in the slab widths due to boundary effects, and 2) the appearance of exact homogeneous diffusion lengths as calculated by transport theory. The extension to“asymptotic”time-dependent problems is also given. For the neutron-wave problem, the complex-valued diffusion length is derived as a function of frequency, and the relation between the time decay constant and the buckling is given for the pulsed-neutron problem. Limiting cases involving very wide slabs are discussed. Finally, some experiments are briefly described for which the analysis of this paper might be applicable.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20216

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe Milne problem for thermal neutrons is studied with an arbitrary scattering kernel, using concepts derived from the invariant imbedding method. An eigen-value equation for the Milne leakage current is given and an expression for the flux inside the medium expressed in terms of the Milne leakage current and the reflection operator is found. Though no unique definition of the extrapolation length exists in the general case, a very simple expression for the extrapolation length of the scattering rate is given.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20217

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe nature of anomalous computational effects due to the discretization of the angular variable in transport theory discrete ordinates approximations is described and analyzed. The origin of these effects within the derivation of theSndiscrete ordinates equations is shown, and the effects are related to the non-equivalence of the general geometry discrete ordinates equations and the corresponding spherical harmonics equations. Procedures are given for the definition of two-dimensional discrete ordinates equations that are equivalent to the spherical harmonics equations. Elimination of ray effects from the two-dimensionalS2equations by reduction to the diffusion theory equations is verified in a numerical example. Recipes for the elimination of ray effects are analyzed in the analytic solution of the infinite medium, isotropic line-source problem in the rectangular geometry,S2approximation. Optimum magnitudes for corrective source terms are indicated by the analysis. It is concluded that ray effects may be eliminated by modification of the discrete ordinates formulation, but that the extra computational effort may be more expensive than the alternative of increasing the order of angular quadrature and that the presence of discretization effects may serve as an indicator of the adequacy of the angular quadrature used.

ISSN:0029-5639    

DOI:10.13182/NSE68-4

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractSome optical properties of neutron diffusion waves are discussed. Expressions are given for the change in the direction of propagation of the wave components reflected and refracted at the interface between two semi-infinite media by using appropriate formulae for the refraction of the electromagnetic waves in conducting media.It was found that the phase speed of the refracted asymptotic wave depends upon the direction of propagation. This dependence is especially noticeable in graphite/light-water systems. The phase speed is practically constant in graphite/ heavy-water systems. The results predict the existence of the total reflection of the asymptotic wave on the graphite/vacuum interface, providing the incidence angle is larger than∼23°.Experimental verification of the diffusion wave refraction is suggested.

ISSN:0029-5639    

DOI:10.13182/NSE68-A20219

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor