Measurement of Acoustic Background Noise and Simulated Impact Sound in BWR

In order to develop a method for detecting and locating metallic loose parts in BWRs, sound properties were studied. Five acoustic sensors were attached to the BWR pressure vessel and simulated impacts were given to the vessel by hitting it with a hammer. Background noise during the actual plant operation and the impact sound were measured and analyzed. The following results were obtained: (1) Signals with S/N of five or more for impacts with an energy of 0.2 J at full power plant operation were obtained by accelerometers located within 6m from the impact positions. (2) Arrival time and amplitude of the impact signals showed a good reproducibility for the same impact position. On the other hand, there was a poor relationship between time or amplitude information and acoustic path length. This fact suggested that there is little chance for impact sound location into reality by analytical methods such as triangulation. It will be one of the solution for the acculate location to make use of data for reference impacts.