Maintenance PWR vessel head - CRDM canopy seal repair - abs31

The COMEX Nucleaire Engineering and Intervention departments have developed and performed a metallurgic maintenance operation on the adapter lip of the Canopy seal welded with reactor control rod drive mechanisms in an Electricite de France (French Electrical Utility) PWR plant. This involved removing in-situ stress corrosion cracks and rebuilding an adapter lip with the exact original geometry. High dose rates in the repair zone necessitated the development of automated machines requiring very little human intervention. The method consists in removing the cracked lip on 360 deg. and rebuilding it with a weld build-up deposited by orbital TIG welding around the adapter. This deposit is then machined by orbital milling to the initial dimensions of a new lip, and controlled. The entire operation was qualified in France and was implemented on the Bugey 5 plant unit in 2001. (authors)