Hough Transform Method for Determining the Fuel Sub-Assembly's In-Situ 'Bow' in Breeder Reactor Using Its Sparsely Scanned Ultrasonic Image

An Ultrasonic under-sodium scanner has been developed for use in Prototype Fast Breeder Reactor (PFBR), Kalpakkam, India. An ultrasonic scanning technique already developed enables us to determine the in-situ 'bow', if any, of the Fuel Sub-Assembly (FSA) in reactor by two methods viz 'circle-fitting' and 'data-based'. This paper proposes another method viz Hough Transform by which we are able to determine the center of the circular top surface of a mock-up FSA head using its under-water image obtained in an earlier scanning experiment. A program written in MATLAB script carries out Hough transformation of four sparsely scanned images of the head kept at distances of 135 to 165 mm from the scanner-axis. We have devised a 'composite' Hough Transform algorithm to obtain the 'true' center coordinates and hence the scanner axis-FSA head distance values to an accuracy of 3 mm for distances up to 155 mm, and 5 mm for 165 mm distance.