Sensitivity of power spectral density techniques to numerical parameters in analyzing neutron noise experiments

Abstract

Power spectral density methods (Cohn-α methods) are well-known and widely used for the analysis of neutron noise experiments and obtaining the reactor core integral kinetic parameters, i.e., the effective delayed neutron fraction β eff and the prompt neutron generation time Λ. The Cohn-α methods are considered as the standard data processing procedure in the case of a current acquisition system that works at high fission rates. Many uncertainties are usually considered in the Cohn-α method, e.g., statistical fluctuations in the neutron count, power drifts, uncertainties in the Diven factor, the integral fission rate, and in the reactivity value. However, the uncertainty associated with the numerical parameters used in the power spectra calculation procedure, e.g., time bin size and buffer size, is hardly discussed in the literature and generally overlooked. In this paper, The Cohn-α method is implemented to analyze critical and subcritical configurations of the MAESTRO core in the MINERVE zero power reactor in order to measure its β eff and Λ integral kinetic parameters. Both cross-correlation and auto-correlation power spectral densities are calculated and the kinetic parameters are obtained via Lorentzian curve fitting over the calculated spectra. The sensitivity of the obtained kinetic parameters to the choice of numerical parameters used for spectrum calculations is studied and found to be pronounced and comparable with other uncertainties. A novel methodology is proposed for analyzing the kinetic parameters' sensitivity to the power spectra calculations and for quantifying the associated uncertainties.

Determinação experimental e análise dos tempos de geração de nêutrons do núcleo e do refletor e da fração de retorno do refletor em várias configurações do reator IPEN/MB-01 e seus impactos na determinação da reatividade do sistema

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