摘要:

AbstractIn many types of nuclear-reactor-pumped lasers, the fission fragments that are used to excite gaseous lasing species heat the gas in a spatially nonuniform manner. This heating nonuniformity induces transient gas motion, which results in density and refractive-index gradients that affect the laser’s optical behavior. A computational model of the transient gas motion is developed using the acoustic filtering methodology, which neglects the spatial variation of the pressure. This model incorporates the effect of spatially varying gas density onfission-fragment heating. Gas motion out of the laser cell into small, rapidly cooled regions is treated as a volumetric mass loss distributed over the laser cell. Although these regions have a relatively small fraction of the total volume, a large amount of gas can flow into them during the heating because of the rapid cooling therein. This gas removal from the cell during pumping, neglected in previous analyses, is important because fission-fragment heating is strongly dependent on local gas density. To quantify the laser’s optical behavior, experiments are performed in which a probe laser beam is passed through the laser cell This probe beam acquires a wavefront distortion from the refractive-index gradients and is imaged onto a wavefront slope sensor, which yields temporally and spatially resolved measurements of the angular deflection (wavefront slope) of the probe laser beam. Experimental and computed results for this quantity exhibit reasonable agreement over a wide range of pressures and heating amplitudes.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24488

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe solubility of NiO and CoO in high-temperature water is measured at temperatures between 373 and 523 K in a special batch autoclave system. Great importance has been given to deriving reliable thermodynamical data for the related ionic species at elevated temperatures. The experimental results for NiO seem to be consistent with the previously proposed free-energy data set for Ni2+. Because of the lack of experimental information on the free energy of formation (ΔG°f) for Co2+, the Criss-Cobble approach is used to calculate the values. The estimates are compared with the experimental results. It is concluded that the application of the Criss-Cobble procedure to Co2+ions is not correct above 423 K. Based on the experiments, a new set ofΔG°fvalues for Co2+is proposed.

ISSN:0029-5639    

DOI:10.13182/NSE92-36

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThermal and epithermal neutron sensitivities are calculated for cobalt self-powered neutron detectors (SPNDs). Using a reformulation of the analytical model for the calculation of the electric charge produced per neutron captured, a multiple-collision treatment for the calculation of the neutron capture rate is introduced. The calculated values for thermal sensitivities are in excellent agreement with experimental results.,Taking neutron multiple scattering into account, significant differences are found in epithermal sensitivities of cobalt SPNDs with respect to the usual single-collision approximation. It is concluded that the prompt electric current produced in cobalt SPNDs is mainly determined by epithermal neutrons forratios>1.3.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24490

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractProposals are made for improving the heterogeneous diffusion procedure for reactor design and operating calculations. The procedure is based on the use of pin-by-pin properties for the assemblies and on low-order discretization for the reactor diffusion calculation. It proposes the introduction of a second-generation superhomogénéisation equivalence technique between the flux and cross-section edit calculations to yield heterogeneous diffusion properties consistent with exact control rod worth calculations. This equivalence technique is designed to preserve the pin-cell reaction rates and the assembly integrated fluxes. Two-group colorset benchmarks are proposed to validate the new procedures. Numerical results are also given for typical fine-group test cases.

ISSN:0029-5639    

DOI:10.13182/NSE92-10

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe ENDF/B-V nuclear data are validated for use in light water reactor criticality calculations. This is done by using the continuous energy Monte Carlo code MCNP to simulate critical experiments with two distinct core configurations typical of those of boiling water reactors. By varying parameters such as temperature, burnable absorber content, and the amount of control poison, a set of 12 experiments is selected. Eigenvalue and local fission density results from the Monte Carlo simulations are found to be in good agreement with the measurements.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24492

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractPart of the reactor design process is performance evaluation according to predefined criteria, including reactor stability behavior under different conditions. This work focuses on the stability characterization of a reactor system with feedback under low reactor power, low reactor coolant flow conditions. Such conditions might be encountered, for example, after a loss of flow without scram in some passively safe reactor designs. Algebraic and frequency stability-criteria-based methods are developed to find stability regions, stability boundary surface in system parameter space, and frequency of oscillation at oscillatory instability boundaries. Models are developed for the reactor, its detailed thermal-hydraulic reactivity feedback path associated with coolant outlet temperature, and decay heat. Developed stability analysis tools are applied to the system model. A unique aspect is the assessment of the influence of decay heat on stability. Other selected parameters are the following: temperature coefficient of reactivity, reactor coolant flow, and natural-circulation flow. The result is a stability boundary surface in four-dimensional system parameter space and its associated frequency of oscillation surface. Adopting model parameter values from two reactors results in system parameters within the stable region. Conditions for system parameters to remain in the stable region are identified.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24493

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractAn accurate and computationally efficient numerical method for solving the two-group, multidimensional transient neutron diffusion equations with feedback is discussed. The method employs an approximation for the spatial shape of the thermal fluxes. The results of the test problems demonstrate that the convergence of the iteration scheme can be accelerated, and the resulting computing time can be greatly reduced while maintaining computational accuracy.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24494

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractA technique for calculating an approximation to the time-dependent power of a boiling water reactor (BWR) during steady-state, low-amplitude limit-cycle oscillations is described. An approximate solution is obtained from the application of Galerkin’s method to a BWR dynamic model consisting of the point-kinetics equations and the power-to-reactivity feedback transfer function; such a feedback transfer function can be obtained from linear frequency domain stability codes, such as the LAPUR code. The approximate solution technique is described, and comparisons of approximate solutions with numerical results and measured data are given. It is concluded from these comparisons that the application of Galerkin’s method to the equations obtained from this particular BWR dynamic model can be used to extend results from a linear frequency domain stability code to calculate nonlinear, time-dependent reactor parameters during low-amplitude limit-cycle oscillations.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24495

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThe problem of determining neutron yield from the (α, n) reaction has been the subject of much investigation, mainly experimental, for a number of years. Calculated values depend on cross sections and other nuclear data, which are not available for all isotopes. As a compromise, using the experimental data as a basis, an expression has been derived to provide a simple computation of the neutron yield in any given mixture containing actinides. This has been successfully tested with known (α,n) neutron source strengths in compounds of plutonium.

ISSN:0029-5639    

DOI:10.13182/NSE93-A24496

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor