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This paper describes the analysis of fluctuation signals from a nuclear reactor. The methods of analysis differ from the usual Fourier transform methods and include digital filtration, envelope generation by the use of Hilbert transforms, deconvolution, cepstrum analysis, autocovariances and simulation. These techniques are applied to an investigation of the characteristics of the envelope time-series of the signals from the SEQUOYAH reactor in the frequency range of 5.44–7.44 Hz—the core-barrel oscillation frequency. The results show that the core barrel oscillates with a high degree of damping and that the motion is caused by δ-function-like stimuli and that each stimulus consists of an initial stimulus followed by one or more subsequent stimuli (echoes) at defined time intervals. It is suggested that these stimuli are caused by contact between the core barrel and the pressure vessel. |
