Analysis of a signal during bistable flow events in Laguna Verde Nuclear Power Station with wavelets techniques

This paper is concerned about bistable flow, which is manifested by a small and spontaneous change in the recirculation loop flow that has been reported in some Boiling Water Reactors. Here some real time series of the bistable flow from the Laguna Verde Nuclear Power Plant (LVNPP) are analyzed using a methodology based on wavelet transform. This methodology involves the decomposition of the original signal using the Continuous Wavelet Transform (CWT) and the application of the Discrete Wavelet Transform (DWT) based on the Multiresolution Analysis (MRA). The CWT provides information about ruptures, discontinuities and fractal behavior. The MRA allows a fast implementation of the Discrete Wavelet Transform providing information about frequencies, discontinuities and transients that can be detected with analysis at different levels of details coefficients. The combination of both techniques allows the definition of an integral methodology for the study of reactor signals. We found that the associated frequencies for the singularities observed due to bistable flow for the case of LVNPP, correspond to the interval 0.01-0.1 Hz.