摘要:

AbstractThe deposition of suspended iron oxide in boiling water at atmospheric pressure on a heated Zircaloy surface has been studied. The effects of various factors, including heat flux of the heated surface, concentration of iron oxide, and flow rate of boiling water, on the deposition rate during the initial period have been investigated.A model based on the microlayer evaporation and drying out phenomena that occur in the nucleate boiling bubble is proposed for an interpretation of the deposition rate. Close agreement is obtained between calculations using that model and the experimental results.

ISSN:0029-5639    

DOI:10.13182/NSE78-6

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe problem of rapid detection of an unexpected reactivity insertion into a nuclear reactor is studied assuming a stochastic point reactor model and noisy measurements of neutron density. The fundamental assumption is that the time dependence of the reactivity is given as in a ramp function with unknown coefficients. Thereupon, the present method applies a likelihood ratio test to the innovation sequence obtained by using a discrete Kalman filter, which is designed for the steady-state condition of reactor operation. By numerical experiment, the mean delay time for detection has been obtained under the condition that the mean time between false alarms takes on a prescribed constant. A comparative study with some typical existing methods shows that the proposed method is remarkably effective except for extremely large or small inputs of reactivity.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27233

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractOne-dimensional, one-energy-group diffusion theory is applied to a coupled-core slab reactor to derive kinetic equations for the system, with different modes of formulation taken for moderator regions and for core regions. For the former, the diffusion equation is exactly solved to obtain the time-dependent neutron currents from moderator to core (the moderator response function) in response to the neutron incident current in the form of a unit impulse on the boundary. For the core regions, the neutron fluxψ(x,t) is written as a product of a shape function,ϕ(x,t), and a time function, P(t), as suggested by Henry, with P(t) chosen to represent the time variation of total importance over the respective core. The boundary terms that arise in the equations for P(t) are combined with incoming neutron currents at the boundaries, which in turn are expressed in terms of the moderator region response functions above. The equations for P(t) derived by such procedures include the coupling effect between the two cores, without a need for the conventional,a prioriassumption of coupling coefficient.For the Argonaut two-slab core, the transfer functions are obtained and compared with existing values. The value of the conventional coupling coefficient is also inferred by reducing the present form of coupling terms by approximation. From the approximation needed in the procedure, the limitation of the coupling coefficient approach is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27234

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractAbsolute 125-deg differential gamma-ray production cross sections have been measured for 21 gamma rays produced in natural chromium by the (n,n′γ) reaction in the incident neutron energy range from 0.84 to 3.97 MeV. The pulsed beam time-of-flight technique was employed for background reduction. The data were corrected for neutron multiple scattering and neutron and gamma-ray attenuations in the scattering sample. Angle-integrated gamma-ray production cross sections were inferred from the differential measurements using gamma-ray angular distributions obtained from compound nucleus statistical model calculations. On the basis of the angle-integrated cross sections and measured branching ratios, neutron inelastic scattering cross sections were deduced for 22 energy levels in the four naturally occurring isotopes of chromium. These results are compared to previous measurements and the Evaluated Nuclear Data File (ENDF/B-IV, MAT 1191). The present measurements suggest that in the threshold energy region for inelastic neutron scattering to each of the first excited 2+-states in50,52,54Cr, the cross sections are significantly overestimated in ENDF/B-IV.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27235

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractNeutron capture and transmission measurements were made on a sample of fission product palladium. The level parameters were obtained for 34107Pd resonances below 700 eV. The observed average level spacing was〈D〉= (10.7±1.5) eV, and the s-wave neutron strength function was determined to be 104S0=. The capture widthΓγfor the 6.834-eV107Pd resonance was deduced to be (125±15) meV. Assuming that all107Pd resonances have the same radiation width as the 6.834-eV resonance, the resonance capture integral for all 34 resonances is 87 b.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27236

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe Lewins variational functional was employed to formulate approximations to the neutron detection efficiency, which is a parameter required in the measurement of reactivity by the modified source multiplication technique. In particular, a conventional variational method, a variational extrapolation method, a variational interpolation method, and a multi-reference-state variational method were developed for estimating neutron detection efficiency. Results obtained using the various approximate techniques in one and two dimensions were compared with results from exact formulations. The results obtained using the multi-reference-state variational method in all cases and the variational interpolation method in most cases compared very favorably (discrepancies<5%) with results from the exact calculations. The approximate techniques can be cast in a form where very simple calculational capabilities are all that are required to obtain detection efficiency for any given (but arbitrary) subcritical state. Therefore, we conclude that the methodology developed herein would be applicable to on-line applications using minimal computer capabilities.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27237

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractMeasured and calculated neutron spectra from a sphere of lithium metal with natural isotopic composition are compared. In the calculations, the investigation is concentrated on the SNmethod with nuclear data from ENDF/B-III for lithium and from KEDAK 3 for iron. A special partition of the angular coordinate, S19, was introduced to allow for the strong anisotropy of the neutron flux in the radial direction. For the proper treatment of the anisotropic elastic scattering, a new technique for improved, extended, and consistent transport approximation up to T5is used. These ameliorations being introduced, it is shown that the nonelastic scattering is treated inadequately with respect to the angular and energetic distribution of the outcoming neutrons. The investigation is completed by a comparison of the measured and calculated space-dependent tritium production rate, in which the discrepancy is found consistent with the discrepancy in the neutron spectra. Furthermore, we propose that the7Li(n,n′α) cross section should be reduced by 15 to 20% with respect to the ENDF/B-III value.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27238

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe various definitions of lattice cell diffusion coefficients are discussed within the context of a one-dimensional slab lattice in one energy group. It is shown how each definition, although originally derived in its own particular way, can be derived from a single approach. This makes clear the differences between, and the advantages of, the various definitions.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27239

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractThe time-dependent generalized perturbation theory is applied to the neutron and the nuclide fields to obtain a general perturbative formulation of the type of the Maclaurin expansion for functionals linear with the neutron or nuclide densities. Such functionals may represent, typically, activation detections or quantitative measurements of built-up or decayed higher isotopes of fuel materials. An alternative procedure is shown by which perturbation first- and higher order expansions of the neutron or nuclide density changes can also be obtained. Two simple but representative examples confirm the validity of the formulations.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27240

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor

摘要:

AbstractA unified definition of a wide class of Monte Carlo reaction rate estimators is presented, since most commonly used estimators belong to that class. The definition is given through an integral transformation of an arbitrary estimator of the class. Since the transformation contains an arbitrary function, in principle an infinite number of new estimators can be defined on the basis of one known estimator. It is shown that the most common estimators belonging to the class, such as the track-length and expectation estimators, are special cases of transformation, corresponding to the simplest transformation kernels when transforming the usual collision estimator.A pair of new estimators is defined and their variances are compared to the variance of the expectation estimator. One of the new estimators, called the trexpectation estimator, seems to be appropriate for flux-integral estimation in moderator regions. The other one, which uses an intermediate estimation of the final result and is therefore called the self-improving estimator, always yields a lower variance than the expectation estimator. As is shown, this estimator approximates well to possibly the best estimator of the class.Numerical results are presented for the simplest geometries, and these results indicate that for absorbers that are not too strong, in practical cases the standard deviation of the self-improving estimator is less than that of the expectation estimator by more than 10%. The experiments also suggest that the self-improving estimator is always superior to the track-length estimator as well, i.e., that it is the best of all known estimators belonging to the class.In the Appendices, for simplified cases, approximate conditions are given for which the trexpectation and track-length estimators show a higher efficiency than the expectation estimator.

ISSN:0029-5639    

DOI:10.13182/NSE78-A27241

出版商:Taylor&Francis    

年代:1978

数据来源: Taylor