Performance of Ontario’s CANDU nuclear generating stations in 2013

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2014 July

At the end of 2013 Darlington had a four unit average lifetime capacity factor of 84.3 percent and an annual capacity factor of 82.2 percent. Bruce B had a four unit average lifetime capacity factor of 83.4 percent and an annual capacity factor of 86.5 percent. Pickering B had a four unit average lifetime capacity factor of 76.8 percent and an annual capacity factor also of 76.8 percent. Very respectable performances.
The raw performance data (assumed to be capacity factor data), in-service dates, and MWe capacity used in this article are taken from the Nuclear Canada Yearbook 2014 (reference 1).
The performance of the CANDU 6 reactors is described in, Pedigree of the Enhanced CANDU 6 (EC6) proposed for Darlington B (reference 2).

The performance of some of Ontario’s nuclear generating stations is affected by the surplus of (unreliable) generation in the province (reference 3). The surplus usually arises because of intermittent wind generation coming in at times of low demand and wind generation is expected to increase even more over the next several years. Some nuclear units saw electricity output reductions during periods of surplus baseload generation (SBG). This means the capacity factors are lower than they could have been for those units. A better metric of performance in these cases would be the capability factor, used by Ontario Power Generation (OPG) for Darlington and Pickering and by Bruce Power for the Bruce A and B stations. The capability factor adjusts for external events beyond the control of the plant operators that reduce the energy output of the plant, like SBG and transmission constraints. However it makes little environmental, economic or technical sense to reduce output from low cost zero greenhouse gas emitting nuclear stations to accommodate expensive wind generation on the grid.

All manoeuvred reductions in electrical output from Ontario’s nuclear stations to accommodate the much more expensive wind generation are done by the flexible Bruce A and Bruce B stations using turbine steam bypass to condenser and they get paid for the lost revenue. The provincially owned Darlington and Pickering stations do not manoeuvre but would have to come off line to accommodate wind and they would not get paid for the lost revenue. While the Bruce electricity output reductions are easily seen from the hourly Generator Output and Capability Report on the website of Ontario’s Independent Electricity System Operator (IESO) it is more difficult to know if nuclear unit shutdowns are to mitigate SBG or are due to forced outages. Maybe an outage was extended, or a planned outage was rescheduled, to accommodate anticipated SBG. However a review of the power history graphs of the Ontario nuclear units in Appendix F, of CNSC Staff Integrated Safety Assessment of Canadian Nuclear Power Plants for 2013 (DRAFT – June 2014), by the Canadian Nuclear Safety Commission, shows that there were no unit shutdowns specifically attributed to SBG although there were some forced outages on Bruce units attributed to external problems/events with electrical grid.

From 2013 September wind generation can be curtailed when flexible nuclear manoeuvring reaches its limit and before any nuclear unit has to be shutdown and go off line. Wind operators will get paid for the generation that they could have produced under the forecast wind conditions.

Darlington

The four Darlington units came in-service between 1990 and 1993. Each unit is 934 MWe gross. The design of the primary heat transport system basically follows CANDU 6 although the reactor itself is basically the Bruce A design. At the end of 2013 the units had an average lifetime capacity factor of 84.3 percent and an average annual capacity factor of 82.2 percent. Unit 1 had the station’s best annual capacity factor at 97.3 percent. The average annual capacity factor for 2013 of 82.2 percent was lower than the 92.5 percent for 2012 because of extensions to planned outages but mainly because of an additional planned outage in the third quarter.

Darlington units do not provide flexible operation like Bruce A and B units during periods of SBG, they are either on or off. Darlington units may or may not have been used to mitigate SBG. Darlington is preparing for a major refurbishment to start in 2016. The units had some early start up technical issues but quickly became reliable performers. In 2012 Darlington received a prestigious Award of Excellence from the Institute of Nuclear Power Operations (INPO) which recognizes achievements in safety, operations and management.

Bruce A

The four Bruce A units came in-service between 1977 and 1979. Each unit is 825 MWe gross. Bruce A design is many ways different from Pickering A, the first four unit nuclear station in Ontario. Bruce unit 2 was laid up in 1995 due to lead contamination and the rest of the units were were laid up between 1996 and 1998 as part of Ontario Power Generation’s nuclear improvement program so that operations could concentrate on Bruce B. Units 3 and 4 were returned to service in 2004 January and 2003 November respectively. Units 1 and 2 came back on line in late 2012 after being off line for 15 and 17 years respectively. Units 1 and 2 have been refurbished with new fuel channel assemblies, some new feeders, new steam generators, and other significant improvements were made.

Capacity factors for units 1 and 2 relate to the 2012 in-service date and not to the original in-service dates. At the end of 2013, the first full year of operation after refurbishment, units 1 and 2 had an average lifetime capacity factor of 81.3 percent and an average annual capacity factor of 84.9 percent. At the end of 2013 units 3 and 4 had an average lifetime capacity factor of 64.5 percent and an average annual capacity factor of 75.8 percent. Units 3 and 4 are scheduled for refurbishment starting with unit 4 in 2016 followed by unit 3 in 2019. Unit 2 had the station’s best annual capacity factor at 87.7 percent. The four units provide valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output without coming off line. Bruce A units may or may not have been shutdown to mitigate SBG.

Bruce B

The four Bruce B units came in-service between 1984 and 1987. Each unit is 872 MWe gross. The Bruce B design is basically the Bruce A design with improvements. At the end of 2013 the units had an average lifetime capacity factor of 83.4 percent and an average annual capacity factor of 86.5 percent. Unit 7 had the station’s best annual capacity factor at 97.9 percent. The four units provide valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output without coming off line. Bruce B units may or may not have been shutdown to mitigate SBG. These units are scheduled for refurbishment starting with unit 5 in 2022 and ending with unit 8 that starts its refurbishment in 2028. This means unit 8 would have been operating for 41 years before going into its mid-life refurbishment.

Pickering A (units 1 and 4)

The four Pickering A units came in-service between 1971 and 1973. Each unit is 542 MWe gross. Pickering A was really the first commercial nuclear station in Ontario. The feasibility of the CANDU design had been proved earlier with the 25 MWe gross Nuclear Power Demonstration (NPD) unit at Rolphton (in-service 1962) and the larger 220 MWe gross unit at Douglas Point (in-service 1968). The Pickering A station was voluntarily laid up in 1997 as part of Ontario Power Generation’s nuclear improvement program so that operations could concentrate on Pickering B. The intention was to bring the units into conformance with the latest regulatory standards so that they could be retuned to service. In the end only units 1 and 4 were returned to service, in 2005 November and 2003 September respectively, and units 2 and 3 were permanently shutdown. Pickering A and B are operated as one station.

At the end of 2013 units 1 and 4 had an average lifetime performance factor of 65 percent and an average annual capacity factor of 66.2 percent. Unit 4 had the better annual capacity factor at 86.2 percent. The capacity factors for 2013 at Pickering A and Pickering B were affected by extensions to planned outages.These units do not provide flexible operation like Bruce A and B units during periods of SBG, they are either on or off. Units 1 and 4 may or may not have been used to mitigate SBG. As well as being laid up these units have had long periods of shutdown including one for the replacement of pressure tubes in all four units over the period 1985 – 1992 and one in 2007 to improve safety related electrical connections between the Pickering A and B stations. The two units are scheduled to be permanently shutdown by 2020 after nearly 50 years of operation.

Pickering B

The four Pickering B units came in-service between 1983 and 1986. Each unit is 540 MWe gross. The Pickering B design was based on Pickering A, that was designed in the 1960s, but with much improved safety systems. At the end of 2013 the units had an average lifetime capacity factor of 76.8 percent and an average annual capacity factor of 76.8 percent. The capacity factors for 2013 at Pickering A and Pickering B were affected by extensions to planned outages. Unit 7 had the station’s best annual capacity factor at 95.1 percent. This same unit set a world record for continuous power production with a run of 894 days (2.45 years) back in 1994. These units are scheduled to be permanently shutdown by 2020. Pickering B units do not provide flexible operation like Bruce A and B units during periods of SBG, they are either on or off. Pickering B units may or may not have been used to mitigate SBG. Pickering A and B are operated as one station.

References

1. Nuclear Canada Yearbook 2014, published by the Canadian Nuclear Society (CNS),
http://media.cns-snc.ca/yearbook/CNS_Yearbook_2014_front.pdf

2. Pedigree of the Enhanced CANDU 6 (EC6) proposed for Darlington B, Don Jones, 2014 June, https://thedonjonesarticles.wordpress.com/2014/06/09/pedigree-of-the-enhanced-candu-6-ec6-proposed-for-darlington-b/

3. Wind and nuclear and the increasing irrelevance of capacity factor in Ontario, Don Jones, 2014 February, https://thedonjonesarticles.wordpress.com/2014/02/22/wind-and-nuclear-and-the-i
ncreasing-irrelevance-of-capacity-factor-in-ontario-2014-february/

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