Application of the relative power contribution methodology to the analysis of a control system failure

The Relative Power Contribution methodology has been applied to delineate the initiating event leading to a BWR transient. Diverse reactor signals were analyzed to calculate the coefficients required on the relative power contribution method. Those coefficients were computed from an autoregressive multivariable model. Among the signals used in the analysis of the transient event are total flow through the core, pressure drop across the core, feedwater flow, and reactor power. Analyses of the same type of transient event showed a resonance of the main event frequency on the range within which it has been considered and observed frequencies related to some failures of certain control systems of a nuclear power plant. Those analyses employed the short-time Fourier transform or the power spectral density, for time-frequency and frequency-only domains, respectively. In this work, the same value of the frequency of the resonance mentioned above was obtained through the relative power contribution analysis, but, furthermore it was found that the feedwater flow behavior had an important impact on the transient event, and also that the transient event was not initiated by a reactivity-related instability.