摘要:

AbstractA second-order generalized perturbation theory (GPT) for the effect of multiple system variations on a general flux functional in source-driven systems is derived. The derivation is based on a functional Taylor series in which second-order derivatives are retained. The resulting formulation accounts for the nonlinear effect of a given variation accurate to third order in the flux and adjoint perturbations. It also accounts for the effect of interaction between any number of variations. The new formulation is compared with exact perturbation theory as well as with perturbation theory for altered systems. The usefulness of the second-order GPT formulation is illustrated by applying it to optimization problems. Its applicability to areas of cross-section sensitivity analysis and system design and evaluation is also discussed.

ISSN:0029-5639    

DOI:10.13182/NSE68-1-1

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe probability table method (PTM), used in unresolved resonance region calculations, assumes that cross sections are not energy correlated. Strong cross-section energy auto-correlations are noted for some heavy nuclides that could affect the use of the PTM in the unresolved resonance region or its extension to the resolved resonance region. Uranium-238 has strong cross-section auto-correlations and is considered a severe test material for the PTM. Monte Carlo calculations of capture rates in238U at 500, 1000, and 2000 eV do not show differences between the PTM and exact methods within an∼1% calculational uncertainty. These results show that strong auto-correlations do not interfere with the use of the PTM in the resolved and unresolved resonance regions.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27265

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA method to calculate volumetric distributions of contributon flux and contributon current is developed utilizing only the forward Monte Carlo approach. Various aspects of tracking contributons are discussed. Basically, the new method consists of sampling secondary particles at collision points occurring within a prespecified volume. A simple connection between integrals over that volume and surface integrals of contributon current is derived, thus providing a means of calculating integral detector responses via a volume integration of the contributon current. This leads to a considerable improvement of the effectiveness with which deep penetration radiation transport problems can be solved relative to analog Monte Carlo. A theoretical and numerical comparison of the performance of this new method with the performance of analog Monte Carlo techniques is carried out. Numerical results are discussed, and a theoretical model to predict the relative advantage of the new method was found to give satisfactory answers. If no biasing techniques are employed in either method, our sample problems show that the contributon method can save up to 90% of computing time over the conventional Monte Carlo method in deep penetration problems when computing an integral response with the same target accuracy.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27266

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractSome very simple relations between classical problems of one-speed transport theory are established. These relations exist in the three one-dimensional geometries—plane, cylindrical, and spherical—whatever the scattering law might be.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27267

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractDifferential cross sections are reported for elastic and inelastic scattering of neutrons from beryllium. Source neutrons were provided by the D(d,n)3He reaction at energies from 7 to 15 MeV in 1-MeV steps. Scattered neutrons were observed over a flight path of 4 m at angles ranging from 25 to 160 deg in 5-deg increments. The integrated elastic scattering cross sections agree well with the ENDF/BIV cross-section set. The inelastic scattering cross sections are for the sum of the 1.69-, 2.43-, 2.8-, and 3.06-MeV-state cross sections and fall below the ENDF/B-IV predictions. Inelastic scattering to the 2.43-MeV state in9Be accounts for less than half of the total9Be(n,2n) cross sections above 8 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27268

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe238U to235U fission cross-section ratio has been measured for incident neutrons from 0.1 to 25.0 MeV. A ratio shape measurement was normalized by the threshold cross-section method. A fission cross-section ratio from 0.436±0.004 was found averaged over neutron energies from 2.35 to 2.95 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27269

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractMeasured neutron emission spectra from 14-MeV neutron-induced reactions in a wide range of nuclei are analyzed by precompound nuclear model calculations. The nuclear model code parameters are adjusted using a least-squares fitting procedure to optimize the agreement between calculation and experiment, but the parameters are constrained to physically reasonable values. A single set of input nuclear constants produces calculated spectra that agree to within 30% of experimental values in over 70% of the cases.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27270

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe Canadian Deuterium-Uranium (CANDU) pressurized heavy water reactor is fueled continuously at power, with alternate channels being fueled in opposite directions (continuous bidirectional fueling). The rate at which channels are refueled in various regions of the core determines the burnup distribution in the core. The burnup distribution in the core determines the power distribution. In present practice, the core is divided radially into two burnup regions having constant average discharge burnup. The limit on maximum neutron flux and the requirement for a critical system determine the size of the inner burnup region and the values of the burnups in the two regions.We can increase the core average exit burnup if we allow the burnup distribution to vary continuously rather than being regionwise constant. The purpose of this analysis is to derive an optimum burnup distribution that will maximize core average discharge burnup subject to a limit on maximum flux. This is equivalent to minimizing the total fuel feed rate.A set of equations describing the optimum distribution of burnup has been derived using calculus of variations techniques. These equations have been solved numerically in one-dimensional cylindrical geometry for homogeneous cores of approximately the size of current generation CANDU reactors.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27271

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA model has been developed to describe the transient pressure field within the interconnected porosity of solid mixed-oxide fast reactor fuel during a reactor transient. The pore gas may be composed of up to two distinct chemical species, so that gas released from fuel grains may differ chemically from the fill gas originally present within the porosity of the fuel. The volume expansion of fuel upon melting is accounted for, but mechanical deformation of the solid fuel is not modeled. Results are presented for a hypothetical unprotected transient over-power accident in a gas-cooled fast reactor with ramp rates of 0.10, 1.0, and 10.0 dollar/s. In these calculations, fuel cladding failure is computed from a linear accumulative damage law and a Larson-Miller parameter correlation.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27272

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractWigner-Wilkins scattering kernel computation is reexamined from the viewpoint of a novel mapping. The benefits of this transformation are (a) a stream-lined integrand, (b) a simple, half-strip integration domain, and (c) manifest detailed balance symmetry relative to the equilibrium Maxwellian.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27273

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor