Linear or non-linear stability monitor in BWRs? Introducing a new non-linear monitor based on the fractal spectrum

The stability phenomenon in nuclear boiling water reactors (BWRs) continues to be of scientific and technological interest contributing to the development of advanced stability monitors. The Mexican scientific community over the course of more than two decades (in the world more than four decades) has developed innovative techniques for stability analysis in BWRs, both online and offline; inspired in the first instance by the Laguna Verde NPP instability event occurred on January 24, 1995. Under this perspective, an extensive discussion of linear and non-linear techniques for stability analysis of BWRs is included in this work as well a novel method of stability analysis in BWR based on a Higuchi Fractal Spectrum for the design of a non-linear monitor. This methodology, based on a generalization of the Higuchi Fractal Dimension (HFD), permits to determine in real-time, the stability of a BWR. Hence, real challenging cases in which the instability of the reactor is not evident, were used to test this proposed stability indicator. In general, this proposal gives a better forecast than that based on the simple HFD.