摘要:

AbstractThe extraction of65Zn from falling liquid-metal drops of pure zinc and dilute zinc in lead alloys by fused-salt solutions of lead chloride and zinc chloride in the potassium chloride-lithium chloride eutectic has been investigated. Both chemical and isotopic exchange processes were found to be controlled by external mass transfer in the salt phase. The measured external resistances were comparable to those predicted by models based upon a rigid drop. Extraction in the pure zinc metal-lead chloride system appeared to proceed by a mechanism involving subchlorides as intermediates in the interfacial reaction.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18003

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe microparameters including the thermal-neutron disadvantage factor, DF, the epi- to sub-Cd neutron capture ratio in238U,ρ28, the epi- to sub-Cd fission ratio in235U,δ25, and the ratio of the epi-Cd238U fission to the sub-Cd235U fission,δ28, were measured in the Ozenji Critical Facility for a seven-rod clustered nuclear superheat fuel element. The factorsf, p, andϵwere derived therefrom and the effect of235U epithermal fissions on the neutron multiplication factor was observed to be 1.5%Δk/k. Flooding changed the individual factorsf, p, andϵby amounts corresponding to−6.8%Δk/k, +4.7%Δk/k, and−2.9%Δk/k, respectively, yielding an overall change of−5.1%Δk/k. The maximum discrepancies between measurement and calculation are 1 to 3% for DF,ρ28,δ25, andδ28; 0.3%Δk/kforf, p, andϵ; and 0.4%Δk/kfor the infinite multiplication factor. The calculation of the effects of flooding onf, p,ϵ, and the infinite multiplication factor agrees with the experiment to within 0.3 to 0.4%Δk/k. When performing the cell calculations, care was taken to determine how to cylinderize the unit cell to perform the one-dimensional calculations with the THERMOS code, how to select the value of theLfactor to be used in the JUPITER code (modified MUFT) and how to incorporate the heterogeneous effect of fast fissions.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18004

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractA computational analysis was made for the large number of available critical experiments with hydrogenous mixtures. The calculations were made using both multigroup S4and diffusion theory with 18 energy groups obtained with the GAMTEC-II code. Resonance capture by the isotope240Pu was treated in the NR and NRIA approximations. Rather good agreement was found between experiment and theory. The results are given as a parametric survey for Pu densities ranging from 0.015 to 1.0 g/cm3. The calculated minimum critical mass of239Pu is 547 g for water-reflected aqueous Pu(NO3)4solutions and 531 g for similar mixtures of239Pu and water.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18005

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractExperimental data to establish criticality control specifications for enriched uranium rods undergoing dissolution are extremely limited. A principal difficulty in treating the problem theoretically is that the resonance absorbing238U is admixed in the aqueous solution in which the rods are immersed. The“narrow resonance”and“infinite mass”approximations are applied; and from this application, expressions are developed for treating resonance capture by an absorbing lump embedded in a moderator admixed with the absorber. The computed change in the critical buckling of a heterogeneous array on replacing the water moderator by a uranyl nitrate solution is in good agreement with experiment. Results from survey calculations for 3 and 5 wt%238U rods latticed in uranium-water mixtures are given. It was concluded that for enrichments up to 5 wt% 235 U, dissolver vessels designed geometrically safe for water-moderated arrays of uranium rods will remain safe during the dissolution process.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18006

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe ages to the indium 1.46-eV resonance, of“point source”235U thermal-fission neutrons in mixtures of ThO2-D2O-H2O have been measured in a lattice in which the volume ratio of moderator-to-aluminum-clad thoria pellets was 1.00 and the square pitch was 0.548 in. The results areWithin the experimental uncertainty, no difference was found between measurements made parallel rather than perpendicular to the thoria axis, nor were differences found when the detector foils were located inside the aluminum tubes among the pellets rather than in the moderator surrounding the tubes. However, it was found that the size and composition of the stringer which held and positioned the foils in the moderator could perturb the results. Analysis indicated that corrections ranging from +0.4% for 0% D2O to−0.4% for 90% D2O arise from considerations of absorption in other than the main indium resonance, detector foil shielding, and the lattice discontinuity required for source irradiation.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18007

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractSource-sink methods of calculation are compared with a set of experiments with mixed-fuel lattices in a heavy-water moderator. The theoretical model used was C. N. Klahr's modification of the Feinberg-Galanin theory. A comparison of calculation and experiment was made both for thermal-neutron density ratios within the lattice components, and for critical geometric bucklings (radial and vertical separately). Agreement was good in the case of thermal-neutron density ratios and rather good for radial bucklings. The moderate disagreements between calculated and experimental critical vertical bucklings were ascribed primarily to errors in the cell codes used to generate input for the mixed lattice calculations.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18008

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe spatial and temporal behavior of neutron distributions governed by the nonlinear diffusion equation approximation to neutron transport theory are considered in this paper. Stability criteria for the equilibrium states of various reactor feedback models are determined by the method of comparison functions. The comparison functions are used to construct simple solutions with error bounds to the equations considered. The two reactor models considered are the prompt feedback and the adiabatic model. The stability of the equilibrium state was found to be governed by the generalized bucklingand its relationship toμthe lowest eigenvalue of the associated linear Helmholtz equation. Negative feedback is considered in both cases. Since the comparison functions bound the true solution from above and below, one can determine absolute errors of the approximations involved when constructing solutions. In a similar fashion, a bound on the maximum value of the excursion can also be obtained with little extra effort.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18009

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractAn exploration is made into a method for using reciprocal variational problems to develop figures of merit for approximate solutions of diffusion problems. The theory of the reciprocal problems is described in both a continuous and discrete context. Connections with the method of Slobodyansky are discussed. A strategem is presented for extending the method to the (non-self-adjoint) group-diffusion case. Limitations of the method are discussed and numerical examples given. It is concluded that the method is useful in one-, two-, and perhaps in small three- dimensional problems but is probably computationally not practical for full-blown, detailed, three-dimensional calculations.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18010

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractThe group diffusion equations in two dimensions are solved by assuming the separation of variables sectionally. Using one-dimensional Green's functions, the two-dimensional diffusion equations are transformed into two sets of one-dimensional three-point difference equations at fine-mesh points. Assuming that the separation of variables ofxandycoordinates is possible in a coarse mesh in a reactor, the two sets of one-dimensional difference equations are solved by the alternating direction iteration method. Sample calculations for235U-H2O thermal reactors show that this method gives fairly good results with few coarse and fine meshes and the computation time can be considerably reduced compared with the usual finite difference method.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18011

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor

摘要:

AbstractA nonabsorbing heavy-gas model is used to study neutron thermalization in a moderator with a nonuniform temperature distribution. The method of Williams is first extended to arbitrary temperature distributions. The method is then applied to spherical geometry and numerical results are given for the mean energy of the neutrons. In the case where the radius of curvature of the temperature discontinuity is of the same order of magnitude as the rethermalization length, new transport-theoretical corrections are required to diffusion-theoretical results. In plane geometry, theP3approximation is used to solve the Boltzmann equation and the mean energy of neutrons is calculated. Results are compared with diffusion-theoretical and exact calculations and agreement with the latter is found to be very satisfactory. Some neutron spectra are also plotted in theP3approximation.

ISSN:0029-5639    

DOI:10.13182/NSE68-A18012

出版商:Taylor&Francis    

年代:1968

数据来源: Taylor