Flaw evaluation on an indication at the weld joint of pressurizer spray line of Ohi Nuclear Power Station Unit-3

Onizawa, Kunio ; Lu, K. ; Mano, Akihiro ; Katsuyama, Jinya  ; Li, Y. 

In KEPCO's Ohi Nuclear Power Station Unit-3, an indication was detected from ultrasonic test on the weld joint in the pipe. To ensure the structural integrity of the weld joint, crack growth and allowable applied bending stress were calculated by the KEPCO. In this document, the calculated results by KEPCO were checked by JAEA. In addition, as the sensitivity analysis of the influential factor, the crack growth and allowable applied bending stress were also calculated with consideration of the hardened layer at the inner surface of the pipe. Moreover, according to the alternative rule required by the regulation, allowable crack depth was calculated. As the results, the following items were clarified: (1) as for the crack growth calculation, the results of KEPCO are consistent with those of JAEA, (2) as for the calculation of allowable applied bending stress, there are differences between the KEPCO results and the JAEA results. The differences are due to the fact that KEPCO used the logarithmic function in Z factor formula as a natural logarithm function, (3) the hardened layer at the inner surface of the pipe has a significant effect on calculation results of crack growth, allowable applied bending stress, and allowable crack depth.