South Korea’s first CANDU 6, Wolsong unit 1, is cleared to restart

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2015 February

Wolsong unit 1, a CANDU 6 unit in South Korea operated by the Korea Hydro and Nuclear Power (KHNP) Company, was cleared for continued operation on 2015 February 27 by the Korean nuclear regulator (the Nuclear Safety and Security Commission – NSSC) after being out of service since 2012 November. Wolsong 1 was the first CANDU 6 unit in South Korea (reference 1) and went into commercial operation in 1983 April. The unit was taken out of service for refurbishment in 2009 April. At the end of 2008, the last full year of operation before the shutdown for refurbishment, the annual capacity factor was 93.2 percent and the lifetime capacity factor was 87.0 percent. The capacity factors are taken from the Power Reactor Information System (PRIS) database of the International Atomic Energy Agency (IAEA). Note that the Load Factor term used in the PRIS database has the same meaning as capacity factor. Capacity factors are based on the (net) Reference Unit Power and on the (net) Electricity Supplied, as defined in the PRIS database. For the 5 years prior to the refurbishment outage the average annual capacity factor was 89.4 percent.

The unit returned to service in 2011 July after the 839 day (2.3 years) refurbishment outage making it the first CANDU 6 unit, ahead of Point Lepreau, to be refurbished for life extension and lessons learned will undoubtedly reduce the refurbishment outage time on future projects. However the operating licence expired 2012 November at the end of the unit’s original 30 year design life so it had to be taken offline for its second Periodic Safety Review (PSR) and, in this case, to meet additional requirements for operation beyond design life. Like all reactors in Korea, whether they have a 30 or 40 year design life, these additional requirements have to be met in order to obtain approval from the nuclear regulator for continued operation. The safety review was to demonstrate continued safe operation with an operational life time horizon of 40 years. The annual capacity factor at the end of 2012 (less than a full year of operation) was 71.6 percent.

The Fukushima Daiichi event in 2011 had resulted in additional safety assessments by the Korean nuclear regulator on all reactors in South Korea including Wolsong 1 and had identified improvement that had to be implemented. Since Wolsong 1 was to operate beyond its original design life the International Atomic Energy Agency (IAEA) was invited to perform a ” Peer Review Service on Safe Long Term Operation (SALTO Peer Review Service)”. This was conducted on Wolsong 1 by the IAEA in 2012 May/June so the safety related ageing and plant life management issues raised by this comprehensive review had to be resolved. This optional SALTO review was in addition to the latest Intensive PSR for Wolsong 1. A SALTO follow-up was scheduled to happen 18 to 24 months after initial SALTO and this occurred 2014 April. Another nuclear unit in Korea, Kori unit 1 a Westinghouse pressurized light water reactor that came into service six years before Wolsong 1 and was the first nuclear power unit in Korea, has also undergone a SALTO review previously in July 2007 with a SALTO follow-up in 2010 May and that unit is now operating beyond its original design life.

An application for continued operation had been submitted to the Korean nuclear regulator on 2009 December. On 2014 October inspectors (the Korea Institute of Nuclear Safety – KINS) for the nuclear regulator concluded that the operation of the unit could be safely extended for another 10 year term and the Korean nuclear regulator finally approved the application for continued operation on 2015 February 27. The unit is now licensed to operate for another 10 years, to the time of its next PSR in 2022.


1. CANDU 6 shares the load with light water reactors in China and South Korea, Don Jones, 2014 July,

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