A non-linear stability monitor for boiling water reactors

In this work a novel boiling water reactor (BWR) stability monitor rooted in the Higuchi Fractal Dimension (Higuchi, 1988) is presented. This monitor detects incipient cyclic unstable oscillations related to density wave phenomenon through the analysis of irregularity or roughness of recorded signals from the local power range monitors using the Higuchi fractal dimension. The main goal of this work is to introduce to the BWR scientific community the potentialities of studying the roughness of local power range monitors time series through fractal analysis to detect core stability instead of relying on conventional power spectrum analysis techniques to achieve this important goal for this type of nuclear reactors, the detection of instabilities. This monitor is tested with real unstable signals that are provided by the Forsmark and Ringhals stability frameworks and with stable signals that stem from a typical BWR. The proposed monitor is capable of classifying stable states from unstable ones. (C) 2019 Elsevier Ltd. All rights reserved.