"JOYO" Start-up test report; In-core acoustic monitoring (1)

not registered; Muramatsu, Toshiharu; Yamamoto, Hisashi*; Sanda, Toshio*; not registered; not registered; Tamura, Seiji*

A great interest exists in developing the reliable rapid malfunction detection system for the safe and economic operation of LMFBR. In the experimental fast reactor "Joyo", the acoustic detection technique was adopted to monitor the reactor core as one of malfunction detection techniques. According to this technique, power spectral density and rms value of the signal from the in-core acoustic detector are monitored. If they vary greatly rrom their normal pattern and value, the inspection is held to assure the failure part. Two in-core acoustic detectors are inserted above the reactor core (address [5A2] and [5C2]). The data from them at normal reactor condition were collected during the low power test and the power up test up to 50MW. Some conclusions were derived from the analysis of the data. (1)The characteristies of [5A2] and [5C2] in-core acoustic monitoring systems are different. The [5C2] in-core acoustie monitoring system is affected by acoustic noises of the rotating plug. While the signal amplitude or [5A2] in-core acoustic signal was reduced by half at high sodium temperature. (2)A S/N ratio or this system is poor quality, therefore the amount of information detected from sodium by the in-core acoustic detectors is not known yet. (3)CRD housing acoustic detector is more sensitive to the impact sound caused by control rod vibration than the in-core acoustic detectors. (4)Abnormal condition has not been found until now according to this monitoring system.