Application of ultra-high pressure cavitation peening on reactor vessel head penetration, BMN and primary nozzles

Abstract

Cavitation Peening (CP) is achieved by delivery of Ultra-High Pressure (UHP) water through a nozzle, the pressure drop through the orifice creating cavitation bubbles, and delivering these bubbles to the target metal surfaces. Collapse of the bubbles on the surface generates a shock wave resulting in compressive stresses. Complex or regular geometric surfaces can be treated by “coating” them with cavitation bubbles through this simple, robust, and forgiving process. Laboratory tests have demonstrated that the compressive stresses due to UHP CP prevent PWSCC crack initiation of Alloy 600. UHP CP additionally does not significantly affect roughness and hardness in depth of the mitigated surfaces nor risk to damage the component. UHP CP can be applied cost effectively to the remaining Alloy 600 primary components in order to prevent expensive repairs or replacements. Process parameter development and a tooling qualification program for the application of the UHP CP process on Alloy 600 RPV head penetration nozzles was completed, and this process was successfully implemented in several PWRs.