Application of noise analysis to boiling water reactor, (1)

As for reactor noise analysis, the analysis in low output conditions has been continued in the past. The analysis in the power developing range in large power plants is being investigated at present because theoretical solution is difficult. The authors have collected and analyzed the data on reactor noise in Tsuruga Nuclear Power Station (The Japan Atomic Power Co.) and Fukushima Station No.1 and No.2 plants (Tokyo Electric Power Co.) since about 6 years ago. Though many methods have been proposed for presenting the properties of the fluctuation in noise analysis, here power spectrum density, correlation function, and coherence function are described. Noise analysis at high power output is influenced by void and feedback. It has been confirmed that the noise in boiling water reactors includes the information on core stability in the frequency range below 1 Hz, and gives the information on void in the frequency range above 1 Hz, and the adjustment of pressure control system is possible on the basis of the noise analysis. Much investigations and developments still remain in the noise analysis at power operation, and further energetic studies are required. (Wakatsuki, Y.)