Reliability of Ultrasonic In-Service Inspection of Welds in Reactor Internals of Boiling Water Reactors

Instances of stress corrosion cracking in reactor pressure vessel internal components have been found, especially in the boiling water reactor (BWR) core shroud. Results from in-service inspection are an important aspect of integrity evaluations. One of the major goals of the work described in this report is to quantify the crack detection reliability and sizing error of ultrasonic inspection methods for reactor internals. A mockup is described, along with its application to the assessment on nondestructive evaluation reliability for in-service inspection of reactor internals. The mockup of a BWR core shroud includes cracks in some of the 40 welded assemblies selected to represent field conditions. The selected material and geometry include most conditions and alloys used in the core shroud and its support structure. This report provides an overview of the work being performed and focuses on the parametric study results relating ultrasonic response and its variance to inspection effectiveness. Results of a blind test of an in-service inspection vendor's phased array technique are also provided in this report.