NUCLEAR REACTOR NOISE ANALYSIS USING A DECONVOLUTION METHOD

An investigation has been made to obtain the true amplitude modulation of the resonant signal from the ex-core neutron sensors of a pressurized water reactor (PWR).;A power-spectral-density curve of the fluctuating signal from an excore neutron sensor of the H. B. Robinson II PWR shows a resonant peak centered at 6.64 Hz. The modulation of an oscillatory signal within a selected frequency band carries information which is not present in the frequency itself. The extraction of the signal of interest in the presence of noise is generally performed by a band-pass filter, but the signal is distorted by this filtering process and a deconvolution method is developed to restore the true amplitude modulation of the signal after this distortion. The amplitude of the band-pass filtered signal is generated by the Hilbert transform, this amplitude is deconvolved with the amplitude of the impulse response of the band-pass filter and a successive approximation technique is employed for a deconvolution procedure.;Lateral core barrel motion and the response of the ex-core neutron sensors were simulated to study the correlation between the signals of ex-core neutron sensors located 90 degrees apart around the core. From the analysis of the simulated signal it was demonstrated that the Lissajous curve derived from the band-pass filtered signal may not represent the true core barrel motion, and it is suggested that the use of the deconvolution procedure provides a closer approximation of the true core barrel motion.;Results indicate that, from the analysis of the deconvolved amplitude of neutron fluctuation of the H. B. Robinson II PWR, the core barrel motion shows short bursts of resonance.