By: Donald Jones, P.Eng., retired nuclear industry engineer, 2015 March 24
Following on from some early conceptual work by Canadian General Electric (CGE), Atomic Energy of Canada Limited (AECL) based the CANDU 6 design on the four unit Pickering A station (that was brought into service 1971-1973) but as a single unit station with a significant power increase, major equipment simplifications, improvements in shutdown and emergency core cooling systems, extensive use of digital computers for control and safety systems etc. In fact the CANDU 6 is unrecognizable as being based on Pickering except maybe for the fuel channel sizing, even though fewer channels are in CANDU 6, and the two loop primary heat transport system that were retained. Since Ontario Hydro was enamored by multi-unit stations CANDU 6 was intended as a single unit for out of province build including off shore. The two lead CANDU 6 projects were Gentilly 2 in Quebec and Point Lepreau in New Brunswick and these were quickly followed by Embalse in Argentina and Wolsong, now Wolsong 1, in South Korea and all came into service in the early to mid 1980s. These can be regarded as the first tranche of CANDU 6 build.
The second tranche of CANDU 6 units came with Wolsong 2, 3 and 4 in South Korea, Cernavoda 1 and 2 in Romania, and Qinshan 4 and 5 in China (the other units at Qinshan site are not CANDU), all entering service between 1996 to 2007. Each of the second tranche CANDU 6 units incorporate lessons learned from operation of the earlier units with changes to meet latest regulatory codes and standards. All three Wolsong units came in on budget and on schedule and the two Qinshan units came in under budget and ahead of schedule. In fact the total project schedule for the CANDU 6 units at the Qinshan site in China was 81 months from contract effective date to in-service.
Unlike the 2013 CANDU 6 performance figures (reference 1) 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 figures, as defined in the PRIS database.
CANDU 6 Units
Point Lepreau, New Brunswick, Canada. Unit came into commercial operation in 1983 February. It was the first CANDU 6 to be licensed and go into commercial operation. The unit was taken out of service in 2008 March for refurbishment, the complete replacement of all fuel channel assemblies, inlet/outlet feeder pipes and significant other work. At the end of 2007, its last full year of operation and the end of its first life before the refurbishment outage, the unit had a respectable lifetime Capacity Factor of 81.8 percent and an annual Capacity Factor for 2007 of 74.1 percent. The unit was back in commercial operation in 2012 November. Lessons learned in the Point Lepreau refurbishment proved useful for Wolsong 1 and will prove useful for future refurbishments of other CANDU 6 units. The unit achieved full power output 2013 November. At the end of 2014, just over two years after refurbishment, the “refurbished lifetime” Capacity Factor was 76.5 percent and the annual Capacity Factor for 2014 was 81.7 percent. The lifetime Capacity Factor since start of commercial operation in 1983 was 69.5 percent, including the refurbishment outage
Gentilly 2, Quebec, Canada. Unit came into commercial operation in 1983 October. The unit was permanently shutdown at the end of 2012 by Hydro-Quebec after election of the short lived Parti Quebecois government earlier in the year. At the end of 2012, when it was shutdown, it had a lifetime Capacity Factor of 76.2 percent with an annual Capacity Factor for 2012 of 70.7 percent.
Wolsong 1, South Korea. Unit came into commercial operation in 1983 April. 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. 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 30 year design life so it had to be taken offline. The Capacity Factor for 2012 (less than a full year of operation) was 71.6 percent.
A “Peer Review Service on Safe Long Term Operation (SALTO Peer Review Service)” was conducted on Wolsong 1 by the International Atomic Energy Agency in 2012 May/June so the safety related ageing and plant life management issues raised by this comprehensive review had to be resolved and recommendations acted upon and this took time. The Fukushima Daiichi event in 2011 had resulted in safety assessments by the Korean nuclear regulator on all reactors in South Korea including Wolsong 1 and had identified short and long-term measures for improvement. An application for continued operation had been submitted to the Korean nuclear regulator in 2009 December. The unit was approved for continued operation for another 10 years by the nuclear regulator on 2015 February 26 (reference 2), to the time of its next Periodic Safety Review in 2022.
Wolsong 2, South Korea. Unit came into commercial operation in 1997 July. This unit and its two sister units, units 3 and 4, came in on budget and on schedule. Basically same as Wolsong 1 but with significant design updates and advancements and incorporates operating experience from earlier CANDU 6 units. At the end of 2014 it had an excellent lifetime Capacity Factor of 93.6 percent and an annual Capacity Factor for 2014 of 90.8 percent.
Wolsong 3, South Korea. Unit came into commercial operation in 1998 July. Basically same as Wolsong 2. At the end of 2014 it had an excellent lifetime Capacity Factor of 94.0 percent and an annual Capacity Factor for 2014 of 85.3 percent.
Wolsong 4, South Korea. Unit came into commercial operation in 1999 October. Basically same as Wolsong 2. At the end of 2014 it had an excellent lifetime Capacity Factor of 95.3 percent and an annual Capacity Factor for 2014 of 84.8 percent.
Embalse, Argentina. Unit came into commercial operation in 1984 January. At the end of 2014 it had a respectable lifetime Capacity Factor of 80.8 percent despite operating for several years at reduced power because of low demand in the early years and some ageing issues in later years. The lifetime Energy Availability Factor at end of 2014 was 85.3 percent. PRIS defines the Energy Availability Factor as the ratio of the available energy generation (net) over a given time period to the reference energy generation (net) over the same period, expressed as a percentage. Both of these energy generation terms are determined relative to reference ambient conditions. The Energy Availability Factor is discussed in more detail in the article on performance of Ontario’s CANDUs (reference 3).
It had an annual Capacity Factor for 2014 of only 29.2 percent. However the PRIS data also shows an annual Energy Availability Factor for 2014 of 99.8 percent which means the unit appeared to be fully available for energy generation. The unit is expected to be taken out of service in 2015 February for refurbishment for life extension. For the 5 years prior to the expected start of the refurbishment outage the average annual Capacity Factor was 60 percent. The refurbishment work involves the replacement of fuel channel assemblies, inlet/outlet feeders, the four steam generators, and obsolete control system equipment together with other changes in the balance of plant to improve thermal efficiency and increase power output. The whole project will take about five years but the unit is expected to be offline for about 20 months.
Cernavoda 1, Romania. Unit came into commercial operation in 1996 December. At the end of 2014 it had an excellent lifetime Capacity Factor of 89.8 percent and an annual Capacity Factor for 2014 of 90.7 percent. Unit 1 had its planned bi-yearly maintenance outage in 2014 which reduced its CF.
Cernavoda 2, Romania. Unit came into commercial operation in 2007 October. Basically same as Cernavoda 1 but with updates based on experience with Cernavoda 1 and other CANDU 6 units. At the end of 2014 it had an excellent lifetime Capacity Factor of 94.4 percent and an annual Capacity Factor for 2014 of 98.2 percent. Unit 2 had its planned bi-yearly maintenance outage in 2013.
Qinshan 4, China. Unit came into commercial operation in 2003 January. This unit and its sister unit came in under budget and ahead of schedule. The design was based on that of Wolsong 3/4 and used advanced electronic engineering design tools including 3-D visualization for interferences and a data base for tracking drawings and documents and material usage. Open top construction and very heavy lift cranes reduced the construction schedule together with modularization and prefabrication. At the end of 2014 it had an excellent lifetime Capacity Factor of 91.2 percent and an annual Capacity Factor for 2014 of 94.3 percent. The annual Energy Availability Factor for 2014 was 96.3 percent.
Qinshan 5, China. Unit came into commercial operation in 2003 July. The design is based on that of Wolsong 3/4 and used advanced electronic engineering design tools including 3-D visualization for interferences and a data base for tracking drawings and documents and material usage. Open top construction and very heavy lift cranes reduced the construction schedule. At the end of 2014 it had an excellent lifetime Capacity Factor of 92.0 percent and an annual Capacity Factor for 2014 of 88.1 percent. The annual Energy Availability Factor for 2014 was 91.7 percent.
CANDU 6 summary
Gentilly 2 was permanently shutdown on orders from the Quebec government instead of being refurbished for extended operation. Wolsong unit 1, which was off-line in 2014, has had its application for continued operation approved after being refurbished and will likely be back on-line 2015 April. Embalse is expected to begin its refurbishment outage early in 2015 and Point Lepreau has been operating for just over two years after being refurbished. The average lifetime Capacity Factor for Embalse and Point Lepreau, in the first tranche of CANDU 6 build and the only two of the four operating in 2014, was 75.2 percent. The seven CANDU 6 units in the second tranche of build are amongst the world’s best performers. The average lifetime Capacity Factor for the seven CANDU 6 units in the second tranche of build was 92.9 percent up to end of 2014 and their average annual Capacity Factor for 2014 was 90.3 percent. They make an excellent reference design for the Enhanced CANDU 6 units at Darlington B, when the time comes.
1. Pedigree of the Enhanced CANDU 6 (EC6) proposed for Darlington B, Don Jones, 2014 June,
2. South Korea’s first CANDU 6, Wolsong unit 1, is cleared to restart, Don Jones, 2015 February,
3. Performance of Ontario’s CANDU nuclear generating stations in 2014, Don Jones, 2015 March, https://thedonjonesarticles.wordpress.com/2015/03/24/performance-of-ontarios-candu-nuclear-generating-stations-in-2014/