Sodium boiling detection by acoustic method

not registered; not registered; not registered ; Haga, Kazuo*; not registered; not registered

Sodium boiling experiments were conducted with the out-of-core sodium loop in order to establish the acoustic detection method of sodium boiling in FBR reactor core. The following results, which are informative to the design of the sodium boiling boiling acoustic detection system were obtained concerned about the characteristic of sodium boiling sound, the method of signal processing and the change of acoustic sensor performance. (1)Acoustic pressure by sodium boiling increases according to the boiling grade, but boiling period becomes longer conversely. The maximum acoustic pressure reached about 1000 Pascal, and the period decreased until about 0.7 second. (2)Acoustic spectrum extends from a few kHz to a few tens kHz, but by in-sodium sensor, lower frequency components and by on-wraper tube sensor, higher frequency components were obtained mainly. And the latter sensor had peculiar acoustic signals which didn't appear in the former sensor. (3)Smooting processing of acoustic signals was found to be necessary for the cross correlation method in order to obtain the time lag between the signals of two sensors. (4)Detecting sensitivity of piezo electric acoustic sensors (LiNbO) decreased about 20 dB and recovered to 5 dB after used in sodium for long time. But the resistance between electrodes of sensors continued to decrease with the operation time in sodium due to lack of oxygen. (5)On the detection of early stage sodium boiling, some methods which utilizes the boiling periodicity and cross-correlation between two sensors would be necessary in order to distinguish that was caused by boiling from the flow noise. Some studies are still necessary in future for the establishment of the detection method of early stage boiling under the real level of flow noise, and the localization method of boiling sourse. Besides these efforts, the development of magnetic distortion probe which doesn't need oxygen is also expected.