The first complete retubing and restart of a CANDU 6 reactor was performed on the Wolsong 1 facility in South Korea over 839 days between 2009 and 2011. Although many other CANDU reactors have been refurbished, this was the first on a CANDU 6, and was viewed by many as an advance indication of how well future refurbishments are likely to go. To the great pride of the Korean owners and the team at Candu Energy Inc. (then part of Atomic Energy of Canada Ltd.), by the time of the reactor’s return to service on July 18 2011, the refurbishment was judged a success. This is no small accomplishment considering that it was the first refurbishment of its type. The project team was extremely focused on studying the technical issues encountered in the process, and turning them into learnings that can be applied to improve future refurbishments.
The retubing phase of a CANDU 6 refurbishment project requires proceeding through a series of 35 distinct tasks each of which is precisely defined and controlled. The toolset for the Wolsong retubing included 5500 items. Retubing the reactor involves removing and replacing feeders, fuel channels and calandria tubes. Remotely-controlled tools and complex multi-task machines are required to conduct the retube work safely, due to the highly radioactive environment.
Within the project, teams were developed for each task series. Each team developed and tested processes so everything was ready and working when needed for on-face reactor work. A specialized tool testing and maintenance unit was established to make sure that tools worked properly even before testing and training on the mockup to ensure best use of time. That same team was available around the clock to repair tools on the reactor face, reducing downtime further. The project developed a ‘war room’ early on to ensure quality management decisions could be made quickly and with all needed input. This required all managers to work side-by-side in a single room.
Owned and operated by Korea Hydro and Nuclear Power (KHNP), the reactor has achieved a lifetime capacity factor of 86.2%, making it one of the top-performing reactors in Korea. Wolsong 1 is the first of a four-unit CANDU plant, the largest CANDU facility outside of Canada.
The Candu team is now working on preparations for a life extension project for Argentina’s Nucleoeléctrica Argentina Sociedad Anónima (NA-SA). The retube outage at NA-SA’s Embalse plant is currently scheduled to begin in late 2013.
For a full description of the refurbishment project please see this article on the APPrO magazine or Candu Energy Inc. websites , or Google “Wolsong_1_retubed.pdf”.