Three cracks assumed to be caused by Stress Corrosion Cracking (SCC) were detected on shroud support of Tokai Daini Nuclear Power Plant (Tokai-2) in 2005. Additional inspections were performed in 2009 and 2011, and additional initiation and propagation of cracks were observed on core shroud and shroud support. Flaw evaluation was performed at each time. The results showed that these structures were allowed to use without repair.
There has been a few inspection experiences in Japan, of successive SCC behavior in operating plants. In this paper, the change of crack shape and crack growth rate (CGR) was investigated. The result showed that cracks tend to change its shape as they grow and crack growth rate in an operating plant was below the crack growth disposition line of Japan Society of Mechanical Engineers (JSME) Code.
Water Jet Peening for core shroud with cracks was performed in 2011 and Noble Metal Chemical Addition is planned in next cycle to mitigate crack initiation and growth. These preventive maintenances are effective also in cracked surface. It is important to confirm that crack behavior and effect of preventive maintenances in successive inspections.