摘要:

AbstractA simplified method based on an extension of the rigorous pole representation of cross sections has been developed to facilitate the utilization of the newly released Reich-Moore parameters in reactor applications. By using the analytical properties of each pole term with energy-independent parameters, it is possible to cast the original representation into the Humblet-Rosenfeld form in which the“background”term can be explicitly identified with pole terms attributed to outlying poles and poles with wide“width.”The computational efficiency and its amenability to existing reactor codes can be enhanced significantly when the background term is replaced by a low-order rational function via nonlinear least-squares fitting. Codes have been developed to compute all pertinent parameters from any given set of Reich-Moore parameters. The method, which preserves both the rigor of the Reich-Moore cross section and the desirable features of the traditional formalisms, is readily amenable to all ENDF/B format based codes. Extensive calculations have been carried out to demonstrate the viability of the proposed method for treating theRmatrix data for major nuclides given in the ENDF/B-VI files, and the results are presented.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23928

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe experimental data on the interactions of I- to 20-MeV neutrons with238U are summarized, together with the theoretical analyses. Particular attention is devoted to the elastic and inelastic scattering cross sections because of their practical importance. Functional forms for the surface and volume imaginary terms of the optical potential are chosen so that the dispersion relation, by means of which these terms generate additional contributions to the real part of the optical potential, can be evaluated analytically. The fission and capture cross sections are not included as they have been extensively reviewed elsewhere.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23929

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractWe present a discretization of the diffusion equation that can be used to accelerate transport iterations when the transport equation is spatially differenced by a discontinuous finite element (DFE) method. That is, we present a prescription for diffusion synthetic acceleration of DFE transport iterations. (The well-known linear discontinuous and bilinear discontinuous schemes are examples of DFE transport differencings.) We demonstrate that our diffusion discretization can be obtained in any coordinate system on any grid. We show that our diffusion discretization is not strictly consistent with the transport discretization in the usual sense. Nevertheless, we find that it yields a scheme with unconditional stability and rapid convergence. Further, we find that as the optical thickness of spatial cells becomes large, the spectral radius of the iteration scheme approaches zero (i.e., instant convergence). We give analysis results for one- and two-dimensional Cartesian geometries and numerical results for one-dimensional Cartesian and spherical geometries.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23930

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe variational nodal transport method is generalized for the effective treatment of multigroup criticality problems in two and three dimensions. A symbolic manipulation procedure is developed to achieve the fully automated generation of nodal response matrices in three-dimensional and non-Cartesian geometries. A red-black partitioned matrix algorithm for accelerating the solutions of the resulting within-group equations is presented, and its efficacy demonstrated. The methods are implemented as an option of the Argonne National Laboratory code DIF3D and applied to a series of five benchmark problems in x-y-z and hexagonal-z geometries. For reactors with large transport effects, the variational P3calculations agree with accurate Monte Carlo eigenvalues to within a few hundredths to a few tenths of a percent while requiring Cray X-MP computing times ranging from tens to hundreds of seconds.

ISSN:0029-5639    

DOI:10.13182/NSE92-1

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSeveral vector and parallel processing algorithms for the inherently recursive Snmethod are developed for two-dimensional curvilinear geometries. The iterative sweeps through the spatial and directional meshes are decomposed into various independent subdomains suitable for multiprocessing on shared memory architectures. Both spatial decomposition (using both axial and radial groups) and angular decomposition (using directional groups) are used. The new algorithms are implemented on the six-processor Cornell National Supercomputing Facility IBM 3090/600J computer using the IBM parallel Fortran compiler. The algorithm behaviors are investigated using a series of r-z cylindrical geometry fixed-source problems. In addition, to verify the algorithm performance for realistic problems, a two-group, r-θgeometry, pressurized water reactor (PWR) source calculation is performed. Total speedups as high as 5.86 are observed for the PWR model compared with the one-processor solution. The suitability of these algorithms for highly parallel architectures is also discussed.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23932

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractFor high-accuracy criticality calculations, one should take into account the difference in the energy distributions between prompt and delayed fission neutrons. In steady-state reactor calculations, it is usually assumed that delayed and prompt neutrons are emitted with the same energy distribution. This approximation may lead to systematic deviations in keffof between−0.2 and +0.05%. While for typical cores of liquid-metal-cooled fast reactors and corresponding critical assemblies the effect is usually fairly small, it may become more important for low-enriched k∞experiments and for highly enriched, high-leakage cores. For group cross-section adjustment procedures usually covering a wide range of critical assemblies with fairly different nuclear characteristics, a proper treatment of the energy distributions of delayed neutrons could be particularly important for excluding systematic differences as far as possible.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23933

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractDepletion perturbation theory has been extended to the closed nuclear fuel cycle, and methods have been developed for computing the constrained sensitivities that account for fuel reprocessing and fabrication. An iterative method was developed to solve the sensitivity equations and applied to the closed fuel cycle of the Integral Fast Reactor (IFR). The sensitivities computed using the method were in good agreement with sensitivities from direct subtraction of perturbed and unperturbed depletion calculations. The closed fuel cycle sensitivities were also compared with the sensitivities for the open fuel cycle without reprocessing. The closed fuel cycle sensitivities were found to be larger, particularly for isotopes higher up the burnup chain. These results indicate this work would have particular importance for the analysis of advanced reactor designs with closed fuel cycles, such as the IFR. The methods developed here will facilitate accurate and efficient sensitivity studies of such reactors.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23934

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor