Performance of Ontario’s CANDU nuclear generating stations in 2017

By: Donald Jones, retired nuclear industry engineer, 2018 March 29

The raw performance data for 2017 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 (CF). CFs are based on the (net) Reference Unit Power and on the (net) Electricity Supplied, as defined in the PRIS database. For Ontario, at least, the Energy Availability Factor in the PRIS database can be read as the Unit Capability Factor, see later. More information and performance data for 2016 are in references 1 and 2.

The performance of some of Ontario’s nuclear generating stations is affected by the surplus baseload generation (SBG) 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 3). A better metric of performance in these cases would be the Unit Capability Factor (UCF – used by Ontario Power Generation and by Bruce Power). The Energy Availability Factor (EAF) is another performance indicator and is shown in the PRIS database. The EAF adjusts the available energy generation for energy losses attributed to plant management, planned and unplanned, 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 beyond control of plant management like load cycling/load following, grid failures, earthquakes, cooling water temperature higher than reference temperature, floods, lightning strikes, labour disputes outside the plant etc.

For Ontario there should be little significant difference between CF,  UCF and EAF for units that do not load cycle (an external energy loss) since other external energy losses will be close to zero. For units that load cycle the UCF will be higher than the EAF and higher than the CF but the EAF should  not be significantly different from the CF. For example, from PRIS data, Bruce B unit 7 has a 2017 annual CF of 92.8 percent and an EAF of 96.3 percent. However based on what was just said above this EAF of 96.3 percent must really be a UCF of 96.3 percent and this anomaly will apply to all EAFs given in this article.The UCF and the EAF are based on reference ambient conditions so, unlike the CF, they cannot exceed 100 percent. In some cases the CF can be more than the EAF because the cooling water temperature is lower than the reference temperature and that increases the electrical output of the unit.

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.

From 2013 September wind generation was curtailed when flexible nuclear manoeuvring reached its limit and before any nuclear unit had to be shutdown and go off line. Starting early 2016 the rules changed again allowing flexible wind generation and solar generation to be curtailed before manoeuvring down nuclear units. Wind operators get paid for the generation that they could have produced under the forecast wind conditions.

Darlington

At the end of 2017 unit 1 had a lifetime CF of 83.6 percent; unit 2, 76.0 percent; unit 3, 86.2 percent and unit 4, 85.8 percent, for an average lifetime CF of 82.9 percent. The annual CF for unit 1 was 60.3 percent (EAF 60.3 percent); unit 2, 0 percent (EAF 0 percent); unit 3, 93.9 percent (EAF 94.3 percent) and unit 4, 98.7 percent (EAF 98.1 percent) , for an average annual CF of 63.2 percent. Darlington units do not provide flexible operation like Bruce A and B units during periods of SBG.  No significant difference between CF and EAF numbers. The three operating units had an average annual CF of 84.3 percent and were likely affected by the refurbishment work on unit 2.

Unit 1 had a major planned maintenance and inspection outage in 2017. Unit 2 was shutdown on 2016 October 15 to commence a refurbishment outage and was shutdown for all of 2017.

Bruce A

The four units are capable of providing valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output, using steam bypass, 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 2017 units 1 and 2 had lifetime CFs of 68.9 percent and 65.3 percent respectively and annual CFs of 96.6 percent (EAF 95.5 percent) and 97.4 percent (EAF 97.4 percent).

At the end of 2017 units 3 and 4 had lifetime CFs (from original in-service date and do not include the effect of the mandated lay-up) of 73.5 percent and 73.3 percent respectively and annual CFs of 83.8 percent (EAF 83.2 percent) and 94.2 percent (EAF 93.8 percent).

Bruce A had a four unit average annual CF of 93.0 percent and an average lifetime CF of 70.2 percent. The average four unit annual EAF for Bruce A was 92.5 percent. Bruce A units seem to have done very little power manoeuvring in 2017.

Bruce B

The four units are capable of providing valuable flexibility to the Ontario power grid during SBG periods by reducing electrical output, using steam bypass, without coming off line.

At the end of 2017 unit 5 had a lifetime CF of 84.6 percent; unit 6,  81.9 percent; unit 7, 84.5 percent and unit 8, 83.2 percent, for an average lifetime CF of 83.5 percent. The annual CF for unit 5 was 70.3 percent (EAF 72.4 percent); unit 6, 80.2 percent (EAF 81.0 percent); unit 7, 92.8 percent (EAF 96.3 percent) and unit 8 , 97.7 percent (EAF 99.7 percent), for an average annual CF of 85.2 percent. At the end of 2017 the annual average EAF for the four units was 87.3 percent. Significant difference between CF and EAF (really the UCF for Ontario units – reference 2) numbers showing that Bruce B did power manoeuvring.

Pickering (6 units)

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. Pickering units do not provide flexible operation like Bruce A and B units during periods of SBG.

At the end of 2017 the lifetime CF for unit 1 was 64.2 percent; unit 4, 66.9 percent; unit 5, 73.6 percent; unit 6, 78.5 percent; unit 7, 77.3 percent and unit 8, 75.5 percent for an average lifetime CF of 72.7 percent. The annual CF for unit 1 was 57.8 percent (EAF 57.9 percent); unit 4, 87.8 percent  (EAF 87.9 percent); unit 5, 63.8 percent (EAF 64.1 percent); unit 6, 98.1 percent (EAF 98.3 percent); unit 7, 83.0 percent (EAF 83.1 percent) and unit 8, 85.6 percent (EAF 85.7 percent), for an average annual CF of 79.3 percent. No significant difference between CF and EAF numbers.

Performance Summary

The EAF given in the PRIS database is really the UCF for Ontario units.
For 2017 Darlington had a four unit average annual CF of 63.2 percent and lifetime CF of 82.9 percent.
For 2017 Bruce A had a four unit average annual CF of 93.0 percent  (EAF, 92.5 percent) and lifetime CF of 70.2 percent.
For 2017 Bruce B had a four unit average annual CF of 85.2 percent (EAF, 87.3 percent) and lifetime CF of 83.5 percent.
For 2017 Pickering had a six unit average annual CF of 79.3 percent and lifetime CF of 72.7 percent.

References

1. Performance of Ontario’s CANDU nuclear generating stations in 2016, Don Jones, 2017 March 31,
https://thedonjonesarticles. wordpress.com/2017/04/03/ performance-of-ontarios-candu- nuclear-generating-stations- in-2016/

2. Confusion with the IAEA reactor performance data in the PRIS, Don Jones, 2017 July 28,      https://thedonjonesarticles. wordpress.com/2017/07/30/ confusion-with-the-iaea- reactor-performance-data-in- the-pris/

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- increasing-irrelevance-of- capacity-factor-in-ontario- 2014-february/

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