A maintenance strategy to repair or modify the dissimilar weld on the branch connection of the steam generator hot leg in CANDU6 was developed. The repair method is to add a carbon steel pipe spool as a transition fitting to transfer the dissimilar weld to shop welding, and the modification method is to use the backup tap fabricated during plant installation, so that the weld quality would be superior comparing with field welding, and the quantity of argon gas getting into the primary heat transport system would be reduced simultaneously. A gasbag is used to isolate the branch connection for welding performance when the primary heat transport system is drained to low level state during the prolonged shutdown. If the gasbag could not work, a nonstandard pipe fitting with O-ring should be used to isolate the branch connection.

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