Automated service tool for moving instrumentation thimbles in PWRs during refueling outages

During the refueling outage period of PWR nuclear power plants, the in-core movable detector thimbles located inside fuel assemblies are withdrawn from the seal table, and inserted again as the refueling is finished. The thimble handling process has been commonly performed manually. However, the manual handling process can give many drawbacks including unsatisfactory labor efficiency due to the narrow and high radiation working environment around the seal table, and the possibility of giving serious damage to the delicate thimbles caused by uneven force exerted on the thimbles. In order to minimize radiation exposure to the workers and maintain the thimbles safely, an easy-to-use and robust thimble service tool has been developed. The performance of the tool was verified at the test facility and Kori #3 unit (Westinghouse design, 1000 MWe).