Decay Ratio estimation in BWRs based on the improved complete ensemble empirical mode decomposition with adaptive noise

In this paper a new method based on the improved complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), was developed to estimate the Decay Ratio (DR) in boiling water reactors (BWR). The proposed method mitigates the so-called mode mixing phenomenon, a common problem that may appear when neutronic signals are analyzed through the standard empirical decomposition (EMD), a data driven method to decompose non-stationary signals that may stem from non-linear systems. The EMD decomposes the signals of interest in different levels called intrinsic mode functions (IMFs). When applying the EMD to real data, the mode mixing problem often appears, this means that the EMD method has a very high sensitivity towards noise fluctuations that might lead to a biased IMF extraction. In our case, the presence of mode mixing in the IMFs extracted through EMD decomposition of BWR real signals might hinder the estimation of the proposed DR. The methodology was validated with an artificial signal, and was applied to a specific case from the Forsmark stability benchmark.