摘要:

AbstractA practical formula for sensitivity coefficients of burnup properties has been derived by means of a generalized perturbation theory. A differential method is employed. The resultant formula corresponds to an extension of the Williams formula, which is based on a variational method. The applicability of the proposed formula is investigated by calculating sensitivity coefficients in a typical fast breeder reactor and by comparing the results with those from the direct subtraction calculations. The physical meanings of components of the coefficients are discussed.

ISSN:0029-5639    

DOI:10.13182/NSE85-5

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe prediction accuracy of the burnup characteristics of large liquid-metal fast breeder reactors (LMFBRs) is very hard to evaluate because of the unavailability of the direct experimental information. A quantitative evaluation was performed on the accuracy of the burnup property by use of the sensitivity coefficients in a large LMFBR and the covariance matrix of nuclear data. Also evaluated was the decrease in prediction error when the cross-section set was adjusted by the use of experimental data, such as criticality, reaction rate ratios, and others.It was concluded that accuracy with the direct use of current nuclear data is±30% for burnup reactivity loss and±5% for breeding ratio. On the other hand, the accuracy would be improved to±18% and±2.5% by utilizing the experimental data obtained on the zero-power plutonium reactor assembly.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17126

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA number of improvements have been made to the Hermite method in order to obtain a high order finite element method capable of solving the neutron diffusion equation. First, a variational formulation of the equation is used to obtain a Weierstrass-Erdmann-type coupling relation valid at all points in the domain, singular and nonsingular. The basic solution yielded by this type of discretization is obtained by the inverse power method with variational acceleration of outer iterations. The linear systems appearing in the inverse power method are solved using a one-way dissection algorithm followed by asymmetric block factorization. These procedures were programmed in the BIVAC code for a treatment of the neutron diffusion equation with a two-dimensional reactor representation. The Hermite method was then compared with alternative approaches to a solution. The tests correspond to two-dimensional configurations of pressurized water reactors and CANDU reactors.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17127

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractMonte Carlo techniques for the calculation of the effective multiplication factor Keffof a nuclear reactor are discussed. A source iteration procedure based on a fixed number of fission points per generation is rigorously analyzed in the framework of the Markov chain corresponding to that procedure. It is shown that the estimated eigenvalue converges asymptotically to the correct eigenvalue of the transport equation and the bias in Keffis bounded by an expression of the form C·N1/2, where N is the number of fission points in each generation and C is a constant depending on the bulk properties of the reactor.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17128

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractRecently a Markov chain process corresponding to a source iteration procedure was proposed and analyzed. The properties of this process are further analyzed, yielding an integral equation for the first-order bias in the eigenmode and an explicit first-order expression for the bias in the eigenvalue.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17129

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractUsing thermal neutron scattering kernels suggested for crystalline and noncrystalline polyethylene (PE) various thermal neutron transport processes, such as pulsed neutron, temperature-dependent diffusion length, and temperature- and absorption-dependent steady-state spectra have been studied.The calculated values of the fundamental decay mode in pulsed neutron problems in crystalline PE at 293 K agree with the experimental results of Sjöstrand et al. and Graham and Carpenter for a large buckling range B2= 0 to∼1.5 cm-2. The time-dependent neutron density for crystalline and amorphous PE is essentially the same and agrees well with the experimental results of Fullwood et al. The propagation of a neutron pulse is therefore independent of the degree of crystallinity of PE. The thermalization time for B2<1.0 cm-2is almost constant at≃12.5µs.The calculated values of the temperature-dependent diffusion length in crystalline PE in the temperature range from 293 to 400 K agree well with the experimental results of Esch. The computed diffusion lengths in amorphous PE are the same as those in crystalline PE. The space-dependent spectra for different absorptions have also been reported.Steady-state spectra calculations for crystalline PE at 293 K for natural absorption and for absorptions corresponding to 5.74 and 10.45 b/H atom agree well with the experimental results of Young et al. A somewhat detailed study at lower temperatures down to 4 K shows that the effective temperatures of neutron spectra are the same as those at 21K and correspond to 46 K. Thus PE can be a good source of cold neutrons down to 21K, and it is unprofitable to cool it below this temperature to obtain a still larger flux of cold neutrons. The above studies have also been performed on amorphous PE and yield almost the same results as those obtained in crystalline PE. Thus the transport of thermal neutrons is more or less independent of the degree of crystallinity of PE.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17130

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA thermal neutron inelastic scattering kernel for polyethylene (PE) of any degree of crystallinity based on a recently proposed dynamic model is suggested. The dynamic model takes proper account of the anisotropic linear chain structure of PE that gives rise to an acoustic phonon frequency distribution function, which is quite different from the usual Debye type, and that has been successful in explaining the observed temperature variation of the specific heat of PE of different degrees of crystallinity. The expressions for zero-phonon and one-phonon neutron scattering cross sections are derived by making use of the frequency distribution function. The kernel incorporates the contribution of two-phonon acoustic modes and also that of optical modes. The kernel has been used to calculate the total scattering cross sections of thermal neutrons from crystalline and noncrystalline PE, including amorphous PE. The calculated values of total scattering cross sections are in reasonable agreement with the experimental results of 60 and 98% crystalline PE. The calculated values for amorphous PE are not very different from those for crystalline PE. Thus the total scattering cross sections are found to be independent of the degree of crystallinity in agreement with the experimental results. The details of the contribution of various scattering processes to the total scattering cross section for crystalline and amorphous PE are reported.The kernel has also been used to study theγij-neutron condensed system energy exchange observable for both crystalline and amorphous PE and has been compared with the equivalent isotropic Debye kernel. Theγijvalues are found to be almost independent of the degree of PE crystallinity. Also, theγijvalues, as determined using the suggested scattering kernel, are quite different from those calculated using the Debye kernel, showing thereby the importance of the linear chain structure of three-dimensional PE crystal.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17131

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractUsing results of experiments simulating hydrodynamic aspects of countercurrent flow in particulate beds, it is shown that most of the existing dryout heat flux data exhibit an influence of the overlying liquid layer. If the experiments are conducted in beds of sufficient depth such that the overlying liquid layer has little or no effect, the dryout heat flux in bottom- and volume-heated beds of large diameter particles should be the same.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17132

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractAccurate neutron emission probability distributions (Pv) associated with spontaneous and induced fission are necessary in correcting for neutron multiplication in neutron coincidence counting. A reanalysis of previously published Pvdistributions is presented as well as recent measurements. All data were obtained using a large liquid scintillator tank.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17133

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractAn analysis of the excitation of neutron flux waves in reactor core transients has been performed. A perturbation theory solution has been developed for the time-dependent thermal diffusion equation in which the absorption cross section undergoes a rapid change, as in a pressurized water reactor rod ejection accident. In this analysis the unperturbed reactor flux states provide the basis for the spatial representation of the flux solution. Using a simplified space-time representation for the cross-section change, the temporal integrations have been carried out and analytic expressions for the modal flux amplitudes determined. The first-order modal excitation strength is determined by the spatial overlap between the initial and final flux states and the cross-section perturbation. The flux wave amplitudes are found to be largest for rapid transients involving large reactivity perturbations.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17134

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor