Development of portable laser peening systems for practical application

Stress corrosion cracking (SCC) is the major factor to reduce the reliability of aged reactor components. Laser Peening (LP) technology was developed and applied to reactor components in operating Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR). Bottom mounted nozzles are made from Alloy 600 tubing and attached with Alloy 82/182 welds, which are known to be susceptible to Primary Water Stress Corrosion Cracking (PWSCC). Ultra-compact laser peening systems, which integrates laser oscillator and positioning robotics into a unit, were developed and applied for both inside and outside surface of BMI nozzles in the U.S. Small irradiation head with aspherical mirror was attached to optical fiber in order to perform LP inside surface of BMI nozzles. On the other hand, mirror-delivery type of LP tool was employed for outside surface of BMI nozzles. Magnitude of compression induced by the LP process was verified prior to application at the plant using mockups of BMI nozzles and effectiveness were proved.