PREVENTION OF SCC OCCURRING IN A EXPANSION TRANSITION REGION OF STEAM GENERATOR TUBING BY Ni-PLATING IN PWRS

Applicability of a nickel-plating technique was investigated for a possible proactive method to prevent stress corrosion cracking in the expansion transition region of prerssurized water reactor steam generator tubing around the top of the tubesheet. The surface of steam generator tubes is plated with nickel in the region from the bottom ends of the U-tubes up to above the location where the tube is to be expanded, before the expansion process. The nickel-plated regions of the tubes are then inserted into the holes of the tube sheet and expanded to build up a steam generator. In order to verify the applicability and the effectiveness of the tequnique, mockup tests were performed for nickel-plated Alloy 600 HTMA tubes with hydraulic expansions. Integrity of the expanded nickel plating layers was examined and susceptibility to SCC was evaluated by using the C-ring and the slow strain rate tests in simulated pressurized water reactor environments.