摘要:

AbstractBeam source problems are difficult to treat numerically because of the associated singularities in angle and space. For electrons, conventional first collision source techniques offer little help because the cross sections are so large and anisotropic that the first collision source and original source are not very different. By extending the definition of the uncollided flux to include particles that have not deviated significantly from the original beam direction, an extended first collision source is obtained that is smooth enough for use in SNcodes. Through the use of effective cross sections, the extended first collision source is determined using standard first collision source techniques. The effective cross sections model electron transport with a reduced number of collisions, but larger deflections per collision. These qross sections are generated using a brute-force SNsolution of the space-independent Spencer-Lewis equation on a restricted cone of directions, centered about the beam direction. Several sample calculations are given.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23947

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractIn HELIOS, a two-dimensional program for fuel assembly calculations, the geometric system can be partitioned into heterogeneous space elements. The transport of neutrons and gammas is treated by the CCCP method: current coupling (CC) of the space elements, which are internally treated by collision probabilities (CPs). The region-to-region, region-to-surface, surface-to-region, and surface-to-surface probabilities are evaluated. They are numerically integrated according to Carlvik’s method. It is illustrated that elaborate ray tracing and careful normalization prevent the instabilities that the CPs would otherwise suffer. The angular dependence of the interface currents introduces angular dependence into the last three of these probabilities. A reciprocity relation between region-to-surface and surface-to-region probabilities is derived for the individual angular sectors at the surfaces. Also, a new integral function is introduced, the partial Bickley function. An efficient evaluation method for both normal and partial Bickley functions is presented that reduces the computational time for the CPs by∼20%.

ISSN:0029-5639    

DOI:10.13182/NSE112-16

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractGeometric domain decomposition methods are described for solving x-y geometry discrete ordinates (SN) problems on parallel architecture computers. First, a parallel source iteration scheme is developed; here, one subdivides the spatial domain of the problem, performs transport sweeps independently in each subdomain, and iterates on the scattering source and the interface fluxes between each subdomain. Second, a parallel diffusion synthetic acceleration (DSA) scheme is developed to speed up the convergence of the parallel source iteration. These schemes have been implemented on the IBM RP3, a shared/distributed memory parallel computer. The numerical results show that the parallel source iteration and DSA methods both exhibit significant speedups over their scalar counterparts, but that a degradation in parallel efficiency occurs due to the geometric domain decomposition (iteration on interface fluxes) and the overhead time required for the communication of data between processors. However, the degradation due to geometric domain decomposition is unimportant if the subdomains are not optically thin or do not contain a small number of cells.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23949

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA WIMS-based calculational route for pebble-bed fuel has been established. An outstanding advantage of the WIMS code is its integrated route from basic lattice data to burnup-dependent lattice cross sections. The problem in applying WIMS to pebble-bed fuel is that it lacks spherical geometry. This problem is solved by establishing a number of practical equivalences enabling the replacement of a lattice of spherical fuels by a lattice of cylindrical fuels. A special program was written to convert physical data into WIMS input files, including the Dan-coff factor required for resonance shielding in the multilayer multicell pebble lattice. This capacity provides all that is necessary to generate core-homogenized cross sections directly applicable to core studies. Also generated are zone-homogenized cross sections; in some cases, their use in a transport code results in more accurate core-homogenized cross sections. In terms of the fuel infinite criticality factor, this added accuracy is in the range of 1 to 3 mk for fuel free of absorbers or fuel carrying boron-only absorbers; it is in the range of 3 to 12 mk for fuel carrying hafnium absorbers.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23950

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe HYBRID method is used in the calculations of the iron benchmark experiment at the EURACOS-II device. The saturation activities of the32S(n,p)32P reaction at different depths in an iron block are computed with ENDF/B-IVdata to compare with the measurements. At the outer layers of the iron block, the HYBRID calculation gives increasingly higher results than the VITAMIN-C multigroup calculation. With the adjustment of the two- to one-dimensional ratios, the HYBRID results agree with the measurements to within 10% at most penetration depths, a considerable improvement over the VITAMIN-C multigroup results. The development of a collapsing method for the HYBRID cross sections provides a more direct and practical way of using the HYBRID method in the two-dimensional calculations. It is observed that half of the window effect is smeared in the collapsing treatment, but it still provides a better cross-section set than the VITAMIN-C cross sections for the deep-penetration calculations.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23951

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSurveillance of a nuclear reactor core involves determination of the power or temperature distribution of the assemblies. Derived from other assemblies’measured temperatures, the temperature of a nonmeasured assembly is calculated for every assembly with the help of the principal components method (PCM). The basis of this method is presented, and the measured values are interpolated for various geometrical coverings of the WWER-440 core. A number of procedures have been elaborated and investigated, the most successful of which are introduced. Each method offers self-consistent means for determining the numerical errors of the interpolated values. The procedure based on the PCM can be utilized for any reactor type and is fairly accurate.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23952

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractDifferential (p,xn) cross sections are measured for 800-MeV protons incident on thin targets of depleted uranium and of natural beryllium, boron, carbon, nitrogen, oxygen, aluminum, iron, cadmium, tungsten, and lead. Measurements for neutron energies from 0.3 to 800 MeV are made at angles of30, 60, 120, and 150 deg. Time-of-flight techniques are used to determine the neutron energy spectra, and particular effort is made to identify and discriminate against background contributions. Comparisons of the experimental data with calculations using the high-energy transport code (HETC) intranuclear-cascade evaporation model show good agreement for the heaviest elements (tungsten, lead, and uranium), but significant discrepancies exist for the light elements, especially in the evaporation region.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23953

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAbsolute neutron capture cross sections for natural elements of scandium, titanium, rubidium, molybdenum, iodine, cesium, cerium, praseodymium, holmium, lutetium, and gold, and separated isotopes of190Os,192Os,194Pt, and238U are measured in the 0.5- to 3.0-MeV energy range. For most of these nuclides and isotopes, experimental data are scarce and discrepant, especially for rubidium,133Cs, cerium, lutetium, and194Pt, where no data are available above 0.6 MeV. Gamma-ray spectra emitted in the capture of 0.5-MeV neutrons, as well as the multiplicity of the gamma-ray transitions, are presented.

ISSN:0029-5639    

DOI:10.13182/NSE91-92N

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe absorption probability of neutrons in a cylindrical sample is considered. The neutron beam is monochromatic and collimated, and its intensity is uniform across the beam. A uniform (one-region) sample and a nonuniform (concentric two-region) sample are considered. An exact solution in an analytic form is found for the uniform case. In the nonuniform case, the exact solution is given in the form of an integral (which should be numerically integrated). In the nonuniform sample, concave (i.e., low in the center) and convex distributions of absorber are considered. Some symmetry in the change in the absorption probability due to the absorber nonuniformity with respect to these types of absorber distributions is pointed out and discussed. The applicability and limitations of the solutions are discussed, and an application example is given.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23955

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE92-A23957

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor