摘要:

AbstractLarge dynamic stresses are induced in the fuel components of fast-burst, or pulse, reactors because of rapid fission heating. These stresses increase more than linearly with burst energy yield and, at some yield, will cause fuel failure. Despite many attempts, no one has yet succeeded in predicting a fuel damage threshold with useful certainty in the reactor design stage, nor has the maximum fuel stress for a given power pulse in an operating reactor been calculated satisfactorily. Some analytic solutions for the burst dynamic behavior of typical fuel components that are consistent with available fuel displacement measurements are discussed. In particular, an analytic function is introduced for stress-vibration excitation of fuel components by the bell-shaped power pulse of a reactor burst. These solutions can be employed to determine fuel damage thresholds with useful certainty. Also, a new approach is presented for the analysis of prompt burst power transients by employing fuel displacement solutions to derive dynamic reactivity quench for use in power calculations.

ISSN:0029-5639    

DOI:10.13182/NSE90-149

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe sensitivity of a neutron detector to parametric fluctuations in the core of a reactor depends on the position and the frequency of the perturbation. The basic neutron diffusion model for the calculation of this so-called field of view (FOV) of the detector is extended with respect to the dimensionality of the problem and the number of energy groups involved. The physical meaning of the FOV concept is illustrated by means of some simple examples, which can be handled analytically. The possibility of calculating the FOV by a conventional neutron diffusion code is demonstrated. In that case, the calculation in n neutron energy groups leads to 2n modified neutron diffusion equations.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23896

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractHistorically, Monte Carlo variance reduction techniques have been developed one at a time in response to calculational needs. The theoretical basis is provided for obtaining unbiased Monte Carlo estimates from all possible combinations of variance reduction techniques. Hitherto, the techniques have not been proven to be unbiased in arbitrary combinations. The authors are unaware of any Monte Carlo techniques (in any linear process) that are not treated by the theorem herein.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23897

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTo exclude the reflector region during core calculations, the relationship between group currents and fluxes is investigated in a 60-deg homogeneous sector. With given normal currents on the boundary, a two-dimensional analytical solution to the four-energy-group diffusion equation is derived. Furthermore, a numerical procedure is presented to calculate the flux distribution on the boundary, with a given normal current distribution there. Numerical results are presented to illustrate the coupling between fine-mesh cell edges and between energy groups, as well as to illustrate the impact of the current distribution on the flux distribution.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23898

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA novel application of the numerical Laplace transform inversion to the solution of the one-group neutron transport equation in a half-space with a distributed source is presented. Embedded isotropic sources are considered as well as distributed beam sources. The simplicity of the method in generating numerical results is demonstrated.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23899

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe cross section of the reaction238U(n,γ)239U is measured at neutron energies of 23 and 964 keV. Photoneutron sources Sb-Be and Na-Be are calibrated using a manganese bath traceable to the National Bureau of Standards neutron source NBS-I and are provided nearly monoenergetic neutron irradiation. Neptunium-239 from the decay of239U is chemically separated from the uranium target and is counted to determine the reaction rate. An242Am foil is used as an absolute gamma-ray calibration standard in the determination of the induced activity. The resulting cross-section values are 491±11 and 138±5 mb at 23 and 967 keV, respectively.

ISSN:0029-5639    

DOI:10.13182/NSE90-99

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractDifferential (p,xn) cross sections, d2σ/dΩdEn, from thin targets of beryllium, carbon, oxygen, aluminum, iron, lead, and238U for 256-MeV protons are measured. Time-of-flight techniques are used to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental data with intranuclear-cascade evaporation-model calculations using the HETC code showed discrepancies of as much as a factor of 7, notably at 7.5 and 150 deg.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23901

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAbsolute neutron yields from stopping-length targets at angles of 7.5, 30, 60, and 150 deg for the 256-MeV proton bombardment of elemental beryllium, carbon, aluminum, and iron are measured. Time-of-flight techniques are used to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental data with intranuclear-cascade evaporation-model calculations using the HETC code showed good agreement, indicating that transport probably dominates production effects in the calculations.

ISSN:0029-5639    

DOI:10.13182/NSE92-A23902

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE92-A23903

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor