Effects of Residual Stress on the UT Detectability of Surface Cracks in Feedwater Nozzles. Final Report

摘要

This report describes the results of a study of the effects of service induced residual stresses due to high amplitude thermal loading on the UT detectability of surface cracks in BWR feedwater nozzles. The objective of the study is to determine the conditions under which shallow surface cracks would escape ultrasonic detection due to the presence of compressive residual stress fields. Two-dimensional transient temperature analyses coupled in time with elastic-plastic analyses of a reference BWR nozzle design were performed over a wide range of loading and geometric variables. As the study will show, crack closure behavior is governed, to varying degrees, by such variables as crack length, service history and unloading sequence. It may be possible to make use of these results, in combination with crack growth analysis, to develop inspection schedules which periodically coincide with normally scheduled shutdowns. (ERA citation 08:017798)