摘要:

AbstractThe theory of a new methodology for quantifying and then reducing the uncertainties in the pressure vessel fluences (or fluxes) of a pressurized water reactor (PWR) is described. The theory involves combining the results of calculated and measured dosimetry integral experiments along with differential data used in the calculations, together with covariances, into a generalized linear least-squares adjustment code named LEPRICON. The procedure solves the translation problem necessitated by the use of ex situ PWR dosimetry, and its covariance reducing potential is further enhanced by simultaneously combining the PWR data with a data base consisting of the results of analysis of simpler benchmark experiments. Development of this data base and a demonstration of the uncertainty reduction with application to one of the benchmark experiments are also described. For the example chosen, covariances of the calculated fluxes were reduced by factors of between 4 and 8.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18355

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe boron injection tank (BIT) of a pressurized water reactor safety system is filled with borated water and pressurized by a nitrogen blanket. Accurate evaluation of the gas poly tropic index (n) during the injection process is important to assure required flow from such tanks. An experimental setup simulating a typical BIT system was built and used to evaluate n of the gas under different test conditions.When the N2regulator valve was left open, n at the end of the injection process was much lower than 1.0. For the conservative situation with a closed N2regulator valve, however, n was close to 1.0 under all test conditions.Test duration, which was a strong function of initial gas properties and gas expansion rate, had a noticeable effect on n at the endpoint. Although heat transfer from tank walls had a minor effect at the endpoint, its effect on n after time t from starting injection was noticeable.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18356

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA dryout model, based on the drift-flux approach to the separated two-phase countercurrent flow system with interfacial momentum transfer due to interphase friction, is derived in terms of a zero-dimensional and quasi-equilibrium form. The predictions of dryout heat flux in a large-particle debris bed within an overlying pool of saturated water and with complete blockage underneath are compared with various models and with the experimental results, which are available from the literature. The comparisons demonstrate the adequacy of the presented methodology.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18357

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractNew extrapolation techniques are presented based on the inverse power method to facilitate solution of the multigroup neutron diffusion equation. Unlike the usual acceleration approaches, no estimate of the dominance ratio is required to calculate optimal extrapolation factors. At each outer iteration, the extrapolation factors that correspond to a stationary point of an appropriate functional have been calculated. This technique has been used successfully in the calculation of direct, direct/adjoint, and fixed-source eigenvalue problems for a multigroup formulation of the neutron diffusion equation discretized by finite elements. Numerical tests allow the performance of the variational method to be compared with that of the Chebyshev method.

ISSN:0029-5639    

DOI:10.13182/NSE85-6

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractFast neutron inelastic scattering cross sections for levels between 700- and 1400-keV excitation energy in232Th have been measured using the (n,n′) time-of-flight (TOF) technique. Measurements of 125-deg differential cross sections were made using neutrons with a typical energy spread of 8 to 10 keV, generated by the7Li(p,n)7Be reaction. The incident neutron energies covered three regions: (a) 950 to 1550 keV in 50-keV intervals with the TOF spectrometer optimized to detect 200- to 600-keV scattered neutrons, (b) 1200 to 2000 keV in 100-keV intervals with the spectrometer optimized to detect 400- to 800-keV scattered neutrons, and (c) 1700 to 2100 keV in 100-keV steps with the spectrometer optimized for 800- to 1300-keV scattered neutrons. Throughout the experiment, an overall energy resolution of<15 keV was maintained. Level cross sections were deduced from the 125-deg differential scattering cross sections and are compared with (n,n′λ) measurements and the ENDF/B-V evaluation. Angular distributions for states in the 700- to 900- keV region have been measured at 1.2, 1.5, and 2.0 MeV.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18359

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe neutron capture cross section of243Am was measured from 258 eV to 92 keV. The relative capture cross sections were normalized to 74.8 b at 0.0253 eV from ENDF/B-V. Agreement with the one previous measurement in the kilo-electron-volt neutron energy range is reasonably good (∼8%). These results are needed for calculating the buildup of higher actinides in operating reactors.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18360

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractNeutron scattering cross sections were measured for14N and9Be at incident neutron energies of 11, 14, and 17 MeV using time-of-flight methods. Angular distributions for14N and9Be elastic scattering and9Be inelastic scattering to the 2.429-MeV excited state were obtained between 20 and 160 deg in 5-deg increments. The data were corrected for finite geometry effects using a Monte Carlo simulation code. Legendre polynomial coefficients deduced by fitting the experimental data are tabulated. The results of a spherical optical model analysis for the14N data are reported. Coulomb correction terms are obtained from a comparison of neutron and proton elastic scattering data for14N.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18361

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA set of equations that describes the diffusion of thermal neutrons is obtained from the energy-dependent Boltzmann equation. These equations are analogous to the phenomenological laws of the thermodynamic theory of irreversible processes and show, for instance, that as a temperature gradient produces a neutron current (Soret effect), a density gradient yields an energy flow (Dufour effect). The method is applied to the“two-temperature problem”in order to gain better insight into the thermal diffusion phenomenon. The thermal diffusion of neutrons is shown to strongly depend on the scattering law of the two media where neutrons diffuse, and it is determined that some of the conclusions previously obtained are valid only for the case of a heavy gas moderator with the scattering cross section independent of the energy.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18362

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractRecently a detailed theory analyzing the dependence of the second moment and calculational time upon geometrical splitting was developed based on the direct statistical approach (DSA). The extended model refers to the application of the DSA to the case in which splitting and Russian roulette are used depending on the direction in which the particle crosses the surface, but with the limitation that any source particle reaching the detector must have crossed the surface. The results of a first attempt to use the theoretical results for the optimization of the splitting parameter on one surface in a practical problem are reported. The feasibility of the method in predicting a near optimum splitting parameter is demonstrated, and the application of the method to multiple surface problems is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE85-A18363

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE85-A18364

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor