Investigation after one cycle on DOEL 3 tubes sleeved by Westinghouse

At DOEL 3, 55 steam generator tubes cracked at the roll transition were repaired by Westinghouse in 1988 by CO2 laser welded sleeving, with post weld stress relieving. After one cycle, two sleeved tubes were pulled out for examination. The main purpose of this examination was the correlation with the on-site ultrasonic inspection performed after sleeving, because surface irregularities of the weld had interfered with the determination of weld penetration in the case of several sleeves. Good correlation between the ultrasonic results and the direct examination was found for the two tubes, which are both affected by surface irregularities on the majority of the circumference. Another important goal of the examination is the verification of the resistance to primary water stress corrosion cracking of the upper joint of the sleeve. After one year's service, no degradation was observed so that it was decided to keep all the other sleeves in service. This examination also shows the differences between the pulled-out tubes and the laboratory models examined beforehand, which highlights the problem of the reproducibility of such a process. (author)