Laser peening systems for preventive maintenance against stress corrosion cracking in nuclear power reactors

Laser peening is a surface enhancement process that introduces compressive residual stress on materials by irradiating laser pulses under aqueous environment. The process utilizes the impulsive effect of high-pressure plasma generated by ablative interaction of each laser pulse. Around a decade ago, the authors invented a new process of laser peening without any surface preparation, while the conventional types required coating that prevented the surface from melting. Taking advantage of the new process without surface preparation, we have applied laser peening without coating (LPwC) to nuclear power plants (NPPs) as a preventive maintenance against stress corrosion cracking (SCC). Toshiba released the first LPwC system in 1999, which delivered laser pulses through waterproof pipes with mirrors. In 2002, fiber-delivery was attained and significantly extended the applicability. Now, the development of the third generation system has been just accomplished, which is extremely simple, reliable and easy-handled.