Abstract: In ultrasonic flaw inspection for determining the size of a flaw by emitting an ultrasonic wave to a subject via a probe and receiving an ultrasonic echo from said flaw existing inside said subject, changes in the propagation distances of the ultrasonic echoes before and after movement of said probe through a micro-small distance are compared with each other and the ultrasonic echoes are determined to result from the same flaw if the change width falls within a predetermined value determined by the angle of incidence of the ultrasonic wave and the directional angle.

Abstract: An ultrasonic flaw detector device including axial and circumferential fixed tracks located in a space defined between a pressure vessel of a nuclear reactor and a heat insulating wall surrounding the vessel and arranged axially and circumferentially respectively of the pressure vessel of the nuclear reactor. A rotary track is located at a junction of the axial fixed track and the circumferential fixed track and moved in rotary movement by a chain and has its angle of rotation restricted by a pair of stoppers. A carrier member supporting an ultrasonic probe is moved on the tracks to effect ultrasonic flaw detection to detect any flow that might be present in the pressure vessel. To transfer the carrier member from the axial fixed track to the circumferential fixed track, the carrier member is first transferred from the axial fixed track to the rotatable track, and after the rotary track is rotated, the carrier member is transferred from the rotatable track to the circumferential fixed track.

Abstract: A number of sound detectors are provided on an external enclosure of a pressure vessel of a nuclear reactor. Output signals produced from the individual detectors are combined into a pattern in terms of time difference of the detector output signals relative to the time point at which the detected signal is first produced in response to the sound signal and relative peak values of the detector output signals relative to the magnitude of the output signal produced by the detector which detects the sound signal with the highest sensitivity. The pattern thus obtained is then compared with patterns which have been previously prepared by intentionally producing the sound signals at locations in interest within the pressure vessel, to thereby estimate the location within the pressure vessel at which the sound is produced.