Multivariate Empirical Mode Decomposition applied to the estimation of the decay ratio and out-of-phase oscillations in BWRs

• We applied Multivariate Empirical Mode Decomposition (MEMD) to BWR data.
• We found a common oscillatory mode (density wave) with MEMD considering all LPRMs.
• With MEMD we can estimate the Decay Ratio (DR) in each local LPRM.
• MEMD can estimate the phase of the density wave from measurements of two LPRMs.
• This method detects BWR instabilities (DR increase and out-of phase oscillations).

This work presents a novel method based on the Multivariate Empirical Mode Decomposition (MEMD) to estimate the Decay Ratio (DR) and the apparition of a possible out-of-phase oscillation in Boiling Water Reactors (BWRs). The MEMD algorithm, have the potential to find common oscillatory modes within multivariate data called Intrisic Mode Functions (IMF). Based on this fact, we implement the MEMD technique to find the common oscillatory mode (density wave) in BWRs considering the measurements obtained in each Local Power Range Monitor (LPRM) through the entire core. These IMFs, analyzed simultaneously in time, permit to obtain an estimation of the DR and; also give some considerations about an incipient out-of-phase oscillation through the phase measured between two specific LPRMs. Effectiveness of the proposed method is demonstrated on a specific challenging case from the Forsmark stability benchmark.