Abstract:
A special apparatus was developed for the ultrasonic inspection of a research reactor tank wall, from inside, without removal of the vessel top cover. The inspection is performed by the immersion technique using the coolant / moderator water as a medium for ultrasound transmission. A manipulator, carrying an ultrasonic search-unit is inserted into the tank through a central 70 mm diameter hole. The compact search unit carries up to 16 ultrasonic transducers, positioned at angular and straight orientations and operating both in pulse-echo and pitch-catch modes. The ultrasonic system is designed to scan the entire area of the tank wall with high resolution, to store the entire acquired data (full A-Scan) and to analyse it. It is capable of detecting 0.2 mm thickness variations, of corrosion pits of diameters greater than 3 mm and depths greater than 1 mm, and linear (crack-like) flaws in any orientation. The validation of the newly developed system, as well as of the inspection techniques, were carried out using a full-scale mock-up of a reactor tank, containing flaws unknown to the inspectors.