Automated sizing and classification of defects in CANDU pressure tubes

Pressure tubes within CANDU reactors are subject to frequent ultrasonic non-destructive examination to identify and characterize any defects that pose a risk of initiating Delayed Hydride Cracking (DHC), a well-known problem that occurs in zirconium components that are subject to high mechanical and thermal stresses. The analysis of the ultrasonic data gathered from the pressure tubes is often a long and repetitive process on the critical path to the restart of the reactor. Motivations for developing an automated system include saving time on the critical path, minimising human subjectivity from the process and increasing repeatability of measurements. An automated system providing decision support to analysts also reduces the risk of operator fatigue by minimising time spent processing routine defects. This paper describes a novel system for the automated analysis of CANDU pressure tube inspection data. The system automates the entire initial examination process including the complex decision-making procedures by implementing an expert system with an associated rule-base. Results from this system are detailed, illustrating the location and characterisation of defects and key features within the pressure tube with a high degree of accuracy while increasing repeatability through the removal of subjectivity in measurements.