摘要:

AbstractA general Monte Carlo-discrete ordinates radiation transport coupling procedure has been created to study effects of the radiation environment in Hiroshima and Nagasaki due to the bombing of these two cities. The forward two-dimensional, free-field, air-over-ground flux is coupled with an adjoint Monte Carlo calculation. The size, orientation, or translation of the Monte Carlo geometry is unrestricted. The radiation effects calculated are the dose in the interior of a large concrete building in Nagasaki and the activation production of60Co and32P in Hiroshima.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24009

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractIt was recently demonstrated that in planar geometry, the classic PNequations are an asymptotic limit of the transport equation. A corresponding boundary layer analysis established the asymptotically consistent boundary conditions. These boundary conditions were evaluated variationally, and it was conjectured that these variational approximations are quite accurate for all values of N. Here, we evaluate these boundary conditions exactly (numerically) and show that the previous variational results are indeed accurate to a few percent. The exact results were computed using numerical methods previously developed for solving Chandrasekhar’s H equations.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24010

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractAn upwind nodal solution method is developed for the steady, two-dimensional flow of an incompressible fluid. The formulation is based on the nodal integral method, which uses transverse integrations, analytical solutions of the one-dimensional averaged equations, and node-averaged uniqueness constraints to derive the discretized nodal equations. The derivation introduces an exponential upwind bias by retaining the streamwise convection term in the homogeneous part of the transverse-integrated convection-diffusion equation. The method is adapted to the stream function-vorticity form of the Navier-Stokes equations, which are solved over a nonstaggered nodal mesh. A special nodal scheme is used for the Poisson stream function equation to properly account for the exponentially varying vorticity source. Rigorous expressions for the velocity components and the no-slip vorticity boundary condition are derived from the stream function formulation.The method is validated with several benchmark problems. An idealized purely convective flow of a scalar step function indicates that the nodal approximation errors are primarily dispersive, not dissipative, in nature. Results for idealized and actual recirculating driven-cavity flows reveal a significant reduction in false diffusion compared with conventional finite difference techniques.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24011

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractSevere accident codes, i.e., codes that model core meltdown and accident progression in light water reactors, do not currently make use of parallel processing technology. Previous efforts to parallelize severe accident codes using DO-loop or data partitioning have resulted in speedup factors of<2.0 because of large serial code sections. Severe accident codes are more amenable to the functional partitioning approach, which splits a code into parallel tasks each representing a separate physical model. When combined, the two methods are able to partition 95% of the HECTR containment analysis code. Overall speedups of 2.6 and 3.2 on four and eight processors are obtained with the parallel HECTR code on an Alliant FX/80 parallel computer when modeling a moderately sized accident scenario. Speedups are expected to increase for larger severe accident codes, such as MELCOR, which contain more functional parallelism than the HECTR code.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24012

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractIn the design and operation of nuclear reactors, safety-related goals must be embedded in complex multivariate control strategies. It is often the case that the goals exist only as mental models in the mind of the designer or the operator. In order to effect control that is risk averse, the goals must be translated into an effective control strategy that can be both verified and validated. The relation that these safety goals have to a particular architecture of artificial neural network, the Barto-Sutton architecture, is examined and the capability of the network to embed safety goals in nontrivial control tasks is demonstrated. To realize these goals, the network was extended to encompass a multiple-input/multiple-output control structure.The network synthesizes a control schedule through the construction of artificial precursors to failure; these serve as an additional, virtual layer in the defenses against fission product release. The synthesized schedule can be visually inspected for anomalies and inconsistencies and is validated during training.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24013

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe master equation theory of precompound and compound nuclear reactions has been generalized to include the conservation of angular momentum and parity. Based on this improved semi-classical theory, the UNF code has been developed as a tool for calculating nucleon-induced reaction cross sections and double-differential cross sections at incident neutron energies below 20 MeV. It is demonstrated that the code contains the Hauser-Feshbach model and the exciton models as the limiting cases. The unified treatment of equilibrium and pre-equilibrium reaction processes includes the introduction of composite particle formation factors in calculations of pickup-type composite particle emissions. A method to calculate the double-differential cross sections for all kinds of particles is proposed based on the leading particle model.

ISSN:0029-5639    

DOI:10.13182/NSE93-3

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractA formula for the uncertainty of core performance parameters based on a combination of the cross-section adjustment and bias factor methods has been derived. The formula is compared with those derived from the cross-section adjustment method and the bias factor method used separately. When the method error correlation is strong between the critical assemblies and a target core, the combined method is superior to the cross-section adjustment method used alone. The combined method is, in general, superior to the bias factor method used alone. Numerical results are presented for the uncertainties of keff, the control rod worth, and the power distribution of a large fast reactor. The combined method yields a smaller uncertainty for the control rod worth calculated in dollar units than the cross-section adjustment method used alone.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24015

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractBuildup factors are reported for the absorbed dose in air resulting from point isotropic sources of monoenergetic photons with energies from 10 to 100 MeV. Factors were calculated from photon fluences computed by the EGS4 code for coupled photon and electron transport. Comparisons are made with results of moments method calculations and with buildup factors computed directly from localized energy absorption.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24016

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractIntranodal pin power distributions calculated by the CASMO-3/SIMULATE-3 code have been compared with pin gamma scan measurements. These data were obtained from the depleted core of an operating boiling water reactor (BWR), which is more complicated than a pressurized water reactor to calculate because of the existence of coolant void distributions and cruciform control blades. Furthermore, measured bundles include mixed-oxide (MOX) bundles in which steep thermal flux gradients occur. Both UO2and MOX bundles have been calculated in the same manner based on the standard CASMO-3/SIMULATES methods. The total pin power root-mean-square (rms) error is 2.7%, which includes measurement error, from an 896-point comparison. There is no obvious dependency on axial elevations (void fractions) and no significant difference between fuel types (UO2or MOX), although the errors in a peripheral bundle, which is less important from the standpoint of core design, are somewhat larger than those in the internal bundles. If the peripheral bundle is excluded, the total rms error is reduced to 2.2%. From these results, it is concluded that excellent agreement has been obtained between the calculations and measurements and that the calculational capability of CASMO-3/SIMULATES for the intranodal pin power distribution is quite satisfactory and useful for BWR core design.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24017

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE93-A24018

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor