FLAW DETECTION ABILITY OF NDT TECHNIQUES ON CLAD SURFACES OF REACTOR PRESSURE-VESSELS

The flaw detection ability of non-destructive testing (NDT) methods (u ltrasonic and eddy-current testing) during in-service inspections of t he inner surface of PWR vessels is evaluated, especially for the area of the core weld and the coolant nozzles. A great variety of test flaw s (cracks under the cladding, surface notches and underclad notches) i n different clad test blocks is examined. This paper describes the res ults and the methods used to quantify the reliability of NDT assessmen ts. The ultrasonic technique (70-degrees-SEL) is capable of detecting underclad flaws with through-wall dimensions from 2 mm upwards and sur face flaws which reach 2 mm into the ferritic material with the same h igh degree of reliability. Surface flaws within the cladding, 2 mm to 3 mm deep, can be detected and interpreted clearly with a combined ult rasonic (US) and eddy-current inspection.