The improvement of residual stress in component surface by shot peening was applied mainly to the core shroud for the purpose of preventing stress corrosion cracking (SCC) in BWR Nuclear Power Plants (NPP’s) in the late 1990’s. Subsequently, advanced peening techniques using pressure shock wave impact, such as Water Jet Peening (WJP) and Laser Peening (LP), were developed. Subsequently, PWR NPP’s also adopted these techniques to prevent Primary Water Stress Corrosion Cracking (PWSCC) in Japan.

These peening techniques were implemented with performance demonstration tests conducted in advance by JAPEIC (Japan Power Engineering and Inspection Corporation). Operators also planned on-site applications, including risk management. This risk refers to the risk that components integrity or outage schedule may be affected by peening. In fact, Tsuruga-2 faced a difficult situation, despite the preparation for the risk that cracks might be detected during pre-peening inspection. It was beyond anything that could have been expected.

This paper presents the experiences of peening technique applications at Tokai-2 (2 loop, 1,100 MWe BWR) and Tsuruga-2 (4 loop, 1,160 MWe PWR), analyzing common risk factors present in general application cases based on specific experiences. As a result, high-risk possibilities are indicated depending on risk management, and the necessity is shown for controls that take into consideration materials, design, operation time and other factors. Additionally, the relationship between the risk management and Codes & Standards is also referenced.

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