No abstract available

No abstract available

No abstract available

[en] Exact solutions are obtained to the time-dependent one-speed neutron diffusion equation in one-dimensional multiregion Cartesian and spherical geometries with multiplication and without delayed neutrons. These solutions enable the study of the one-speed space-time behavior of prompt neutrons in an arbitrary number of neutronically dissimilar material regions. Parametric benchmark calculations are presented. (author)

[en] We have calculated the effective delayed neutron fraction βeff for 32 benchmark configurations for which measurements have been reported. We use these results to test the delayed neutron data of JEFF-3.0, ENDF/B-VI.8, and JENDL-3.3

[en] The singularly perturbed linear equations describing the time behavior of neutrons and delayed neutron precursors in a reactor system, are considered. The asymptotic solution of an arbitrary fixed order in the perturbation parameter is given as the sum of the inner and outer asymptotic solutions. The inner asymptotic solution differs significantly from zero only across the initial layer. The comparison is made with the matched asymptotic expansion method previously introduced into reactor physics calculations and the practical advantages of the approach proposed in this paper are demonstrated. (author)

[en] The purpose of this work is to present the experimental results of the in-pile experiments performed at the IPEN/MB-01 Reactor for the determination of the effective delayed neutron parameters and reactivity. The methodologies employed were the macroscopic noise in the frequency domain, where the very low frequency range (< 1.0 Hz) was also exploited and analyzed, and the microscopic noise, which is based on the measurement of Rossi-α and Feynmann-α distributions at several subcritical levels. In this last case, a Two- Region Model was developed. The main advantage of these methodologies is to obtain the effective delayed neutron parameters in a purely experimental way, eliminating all parameters that are difficult to measure or calculate. Consequently, the uncertainties associated with these parameters are eliminated and the accuracy in the effective delayed neutron parameters is improved. Both techniques are claimed to be well defined and produce experimental data of very high quality. Finally, it is proposed to assign benchmark-values to β_eff (the effective delayed neutron fraction), to Λ (the prompt neutron generation time), to their ratio (β_eff/Λ) and also for the first time to the reactivity by means of the in-hour equation. It is concluded that the experiments are acceptable benchmarks. (authors)

[en] The prompt supercritical process of a nuclear reactor with temperature feedback and initial power while inserting large step reactivity (ρ > β) is analyzed. The new analytic expressions of reactivity and output power as well as reactor's temperature increase during the course of the prompt supercritical are derived. The maximal power and the related reactivity and time are obtained. The effects of the inserted step reactivity and initial power on the prompt supercritical process are analyzed and discussed. It is found that for considering only the effect of prompt neutron the reactivity, power and temperature vary much more quickly and the power peak value and the increase values of temperature are larger than those for considering the effect of both prompt neutron and delayed neutron

[en] Highlights: • The count-loss effect in the two-detector neutron correlation methods is discussed. • A robustness against the count-loss effect of these methods were re-confirmed. • New formulae of these methods were proposed for extremely high counting rate cases. - Abstract: The count-loss effect often produces serious problems for the neutron correlation methods that employ a single neutron counting system, since this effect deteriorates the information extracted from subcritical reactor systems. On the other hand, it has been considered that the neutron correlation methods that employ two sets of neutron counting systems, e.g., the covariance-to-mean and the cross-correlation methods, are inherently robust against the count-loss effect in determining the prompt neutron decay constant. The present study investigated this virtue of the latter methods on the basis of a rigorous theoretical approach for treating the count-loss process. The investigation clarified that they indeed show the robustness against the count-loss effect except for extremely high counting rate cases. In the present study, new and alternative formulae of these methods with an explicit correction of the count-loss effect were hence proposed for such extreme cases.

[en] In this paper, the concept of information divergence, based on Kullback's information measure, is introduced into reactor noise analysis. Information divergence, as introduced by Kullback, is the total average information measuring the separation or dissimilarity between two classes of statistical populations. A new species of information divergence is proposed that applies information divergence theory to stochastic processes in general and the reactor noise process in particular. Using this information divergence, the pattern discrimination of reactor noise for a subcritical reactor is studied. 18 refs