摘要:

AbstractA synthetic scheme for accelerating the convergence of the fission source in time-dependent multigroup even-parity Sncalculations with downscatter is described. The low-order operator associated with this scheme is a one-group diffusion operator. Thus, this scheme can be thought of as a variant of diffusion synthetic acceleration. A Fourier analysis of this scheme is performed, which indicates that it is unconditionally effective for a spatially infinite model problem. Computational results are presented that show excellent performance of the method in three-dimensional calculations. Although this method is derived for the even-parity Snequations, it can easily be generalized for application to the standard first-order Snequations. The accelerated iteration equations for both the even-parity and first-order Snequations are given, but only the even-parity algorithm is computationally tested.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21484

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA. Trkov, M. Ravnik

ISSN:0029-5639    

DOI:10.13182/NSE94-A21485

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe probability that reactivity feedbacks will fail to prevent damage is computed by propagating data and modeling uncertainties through transient calculations, with these uncertainties being constrained by experimental evidence. Screening processes are used to identify the most important parameters and accident initiators. The notion of treating an accident initiator in a probabilistic manner is introduced. The response surface method is used to facilitate the error propagation, and a Monte Carlo rejection technique is used to force the parameter variations to be consistent with the observed distribution of experimental quantities. The reliability of the failure probability estimates is evaluated. This method is illustrated by analyzing anticipated transients without scram for the Experimental Breeder Reactor II. The rod run-in initiator is represented by using a reactivity insertion magnitude distribution, a much less threatening and more realistic description than the technical specification limit on rod worths. Reactivity feedbacks are shown to reduce damage frequencies by orders of magnitude, and the experimental constraints are found to have a large effect.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21486

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractQuantities that depend on the collective effects of groups of particles cannot be obtained from the standard Boltzmann transport equation. Monte Carlo estimates of these quantities are called non-Boltzmann tallies and have become increasingly important recently. Standard Monte Carlo variance reduction techniques were designed for tallies based on individual particles rather than groups of particles. Experience with non-Boltzmann tallies and analog Monte Carlo has demonstrated the severe limitations of analog Monte Carlo for many non-Boltzmann tallies. In fact, many calculations absolutely require variance reduction methods to achieve practical computation times. A description is given of how variance reduction techniques can be applied when non-Boltzmann estimates are desired.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21487

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractCross sections were measured for the75As(n,p)75Ge,75As(n,α)72Ga,75As(n,2n)74As,74,76,78Se(n,p)74,76,78As,78,80Se(n,α)75,77Ge,72,73,74Ge(n,p)72,73,74Ga, and70,76Ge(n,2n)69,75Ge reactions over the 6.3- to 14.7-MeV neutron energy range. Samples of As2O3, selenium, and germanium or GeO2of natural isotopic abundance were used. The neutrons were produced via the D(d,n)3He reaction using a deuterium gas target at a variable energy cyclotron (En= 6.3 to 11.9 MeV) and via the T(d,n)4He reaction using a solid titanium-tritium target at a neutron generator (En= 14.7 MeV). The activation technique was used in combination with high-resolution gamma-ray spectroscopy. The experimental excitation functions are well reproduced by the nuclear model calculations, based on statistical multistep reaction theory.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21488

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe modified conversion ratio is defined as the ratio of238U captures to total fission. Gamma-ray spectrometry of irradiated fuel rods has been introduced to measure this quantity in two types of water-moderated low-enriched UO2cores: the standard core, called the 1.42S core, and a tight-lattice core, called the 0.56S core. The water moderator-to-fuel volume ratios Vm/Vfof the cores are 1.420 and 0.564, respectively.As no activation foil is used in this method, no corrections are needed for the neutron self-shielding and neutron flux depression that are caused by such a foil. Instead, the gamma-ray self-shielding effect due to the fuel rod must be corrected.The modified conversion ratio is measured by this method are 0.457 for the 1.42S core and 0.724 for the 0.56S core. The errors in the experimental results are estimated to be∼3%. Computer analyses using the VIM continuous-energy Monte Carlo code with the JENDL-2 library show that the calculated value is∼6% larger than the experimental one for the tight-lattice 0.56S core.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21489

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor