By: Donald Jones, P.Eng., retired nuclear industry engineer, 2015 March 23
At the end of 2014 Darlington had a four unit average lifetime Capacity Factor (CF) of 84.0 percent and an average annual CF of 91.1 percent. Bruce A had a four unit average lifetime CF of 68.2 percent and an average annual CF of 79.6 percent. Bruce B had a four unit average lifetime CF of 83.5 percent and an average annual CF of 87.3 percent. The six unit Pickering station had a six unit average lifetime CF of 74.5 percent and an average annual CF of 74.4 percent.
Unlike the 2013 performance figures (reference 1) the raw performance data for 2014 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 CF. CFs are based on the (net) Reference Unit Power and on the (net) Electricity Supplied, as defined in the PRIS database.
The performance of some of Ontario’s nuclear generating stations is affected by the surplus of generation in the province. The surplus usually arises because of unreliable 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 CFs are not a true performance indicator for those units (reference 2). A better metric of performance in these cases would be the Unit Capability Factor (UCF – used by Ontario Power Generation and by Bruce Power) or the Energy Availability Factors (EAF) that are shown in the PRIS database. The EAF adjusts the available energy generation for energy losses attributed to plant management and for external energy losses beyond the control of plant management while the UCF only includes energy losses attributed to plant management and excludes the external losses attributed to grid related unavailability and other things. This means that on unreliable grids, for example, UCF will be significantly higher that EAF but for Ontario there will be no significant difference. The UCF and the EAF take into account reductions in plant output due to load cycling and load following. For units that load cycle and/or load follow the CF will be significantly lower than the EAF. For example, Bruce A unit 4 has a 2014 annual CF of 94.3 percent and an EAF of 99.4 percent. The UCF and the EAF are based on reference ambient conditions so, unlike the CF, they cannot exceed 100 percent. The only reason for using the EAF here (see later for Bruce units) instead of the UCF is that EAFs are now available in PRIS and UCFs are not presently available (well, the author could not find them).
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. Of course it makes little environmental, economic or technical sense to reduce the low cost output from nuclear stations, with practically zero greenhouse gas emissions, to accommodate expensive unreliable wind generation on the grid that is not needed anyway. 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, according to the IESO there was just one nuclear shutdown caused by SBG in 2014 compared to six in 2013.
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.
The four Darlington units came in-service between 1990 and 1993. 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 2014 unit 1 had a lifetime CF of 84.5 percent; unit 2, 79 percent; unit 3, 86.8 percent and unit 4, 85.7 percent, for an average lifetime CF of 84 percent. The annual CF for unit 1 was 75.6 percent; unit 2, 96.4 percent; unit 3, 97.5 percent and unit 4, 95 percent, for an average annual CF of 91.1 percent. Unit 1 had a major planned maintenance outage in 2014.
Darlington units do not provide flexible operation like Bruce A and B units during periods of SBG, they are either on or off. Darlington is preparing for a major refurbishment to start in 2016 – hopefully this will include improvements to the station’s flexibility. 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.
The four Bruce A units came in-service between 1977 and 1979. 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 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 both came back to commercial operation in 2012 October 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 with other significant improvements. The four units provide valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output without coming off line.
Lifetime CFs in the IAEA database for units 1 and 2 relate to the original in-service dates and do not include the effect of the mandated lay-up that incorporated retubing. At the end of 2014 units 1 and 2 had lifetime CFs of 65.9 percent and 61.8 percent respectively and annual CFs of 83.3 percent and 76.4 percent. Bruce units are the only ones on the Ontario grid to supply significant output reductions when dispatched by the system operator. The annual EAFs (defined earlier) for units 1 and 2 at the end of 2014 were 85.5 percent and 81.7 percent respectively. Using the (net) electricity supplied figures and the reference power figure in the IAEA database gives the calculated “refurbished lifetime” CFs, since coming back into service after retubing, as 78.5 percent for unit 1 and 82.8 percent for unit 2.
At the end of 2014 units 3 and 4 had lifetime CFs (from original in-service date and do not include the effect of the mandated lay-up) of 72.7 percent and 72.4 percent respectively and annual CFs of 64.5 percent and 94.3 percent. The annual EAFs for units 3 and 4 at the end of 2014 were 64.6 percent and 99.4 percent respectively. Unit 3 had a planned major maintenance outage in 2014. Units 3 and 4 are scheduled for refurbishment, including retubing, starting with unit 4 in 2016 followed by unit 3 in 2019.
Bruce A had a four unit average annual CF of 79.6 percent and an average lifetime CF of 68.2 percent. The average four unit EAF was 82.8 percent.
The four Bruce B units came in-service between 1984 and 1987. The Bruce B design is basically the Bruce A design with improvements. At the end of 2014 unit 5 had a lifetime CF of 84.7; unit 6, 81.8 percent; unit 7, 84.6 percent and unit 8, 83.0 percent, for an average lifetime CF of 83.5 percent. The annual CF for unit 5 was 81.9 percent; unit 6, 94.6 percent; unit 7, 76.6 percent and unit 8 , 96.0 percent, for an average annual CF of 87.3 percent. Units 5 and 7 had planned maintenance outages in 2014. The four units provide valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output without coming off line. At the end of 2014 the annual EAF average for the four units was 90.7 percent. 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 first retubing outage.
Pickering A (units 1 and 4)
The four Pickering A units came in-service between 1971 and 1973. 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 returned to service. In the end only units 1 and 4 were refurbished and returned to service, in 2005 November and 2003 September respectively, and units 2 and 3 were permanently shutdown. Pickering A and B are now operated as one station.
At the end of 2014 units 1 and 4 had lifetime CFs of 63.8 percent and 65.9 percent respectively and annual CFs of 85.8 percent and 63.2 percent. Unit 4 had a planned maintenance outage in 2014. The lifetime CFs in the IAEA database include the effect of the retubing outages but ignores the mandated lay-up of the units for refurbishments. 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. These units do not provide flexible operation like Bruce A and B units during periods of SBG, they are either on or off. The two units are scheduled to be permanently shutdown by 2020 after nearly 50 years of operation.
The four Pickering B units came in-service between 1983 and 1986. 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 2014 the lifetime CF for unit 5 was 73.4 percent; unit 6, 77.9 percent; unit 7, 77.2 percent and unit 8, 75.4 percent, for an average lifetime CF of 76 percent. The annual CF for unit 5 was 94.1 percent; for unit 6, 88 percent; for unit 7, 61.6 percent and for unit 8, 53.4 percent, for an average annual CF of 74.3 percent. Pickering A and B are now operated as one station and all six units are scheduled to be permanently shutdown by 2020. The Pickering station six unit average annual CF was 74.4 percent and the average annual EAF was 74.5 percent.
Units 7 and 8 had planned maintenance outages in 2014. Unit 7 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.
For 2014 Darlington had a four unit average annual CF of 91.1 percent and an average annual EAF of 91.3 percent.
For 2014 Bruce A had a four unit average annual CF of 79.6 percent and an average annual EAF of 82.8 percent.
For 2014 Bruce B had a four unit average annual CF of 87.3 percent and an average annual EAF of 90.7 percent.
For 2014 Pickering had a six station average annual CF of 74.4 percent and an average annual AEF of 74.5 percent.
1. Performance of Ontario’s CANDU nuclear generating stations in 2013, Don Jones, 2014 July, https://thedonjonesarticles.wordpress.com/2014/07/03/performance-of-ontarios-candu-nuclear-generating-stations-in-2013/
2. 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-increasing-irrelevance-of-capacity-factor-in-ontario-2014-february/