DEVELOPMENT OF REPAIR SYSTEM FOR CRDM WELDS IN KOREA STANDARD TYPE RPV HEAD

摘要

Control rod drive mechanism (CRDM) nozzles and their welds fabricated with Alloy 600 and alloy 82 have been experiencing primary water stress corrosion cracking (PWSCC). In this study, Doosan presents the development an auto-repair system for the OPR-1000 (Korea standard system) to repair damaged CRDM nozzle welds. The repair system consists of machining, welding & inspection equipment and a robot to deliver this equipment. The machining equipment is used to remove defects in CRDM welds. The process adopts the electro discharge machining (EDM) due to the allowable load requirements of the GENESIS robot. The welding equipment is designed for the machined J-groove in the CRDM welds. Auto-welding equipment incorporates a laser vision sensor that measures the 3-dimensional shape of the groove and a welding pass generation program that calculates the weld path parameters. Dye-penetrant inspection equipment with auto-spraying, developed by Doosan, is used to examine CRDM nozzle welds after the repair. The robot for delivering this equipment is GENESIS, which was originally used for repair of a steam generator, with a guidance system that can move in both the horizontal and vertical directions. The repair equipment is installed in the GENESIS arm. Doosan successfully completed a Mock-up test of the Korea standard type CRDM nozzle weld. In addition, dye-penetrant equipment is being prepared for pre-service inspection (PSI) of replacement RPV heads.