Performance of Ontario’s CANDU nuclear generating stations in 2016

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2017 March 31

At the end of 2016 Darlington had a four unit average lifetime Capacity Factor (CF) of 83.6 percent and an average annual CF of 83.6 percent. Bruce A had a four unit average lifetime CF of 69.4 percent and an average annual CF of 81.9 percent. Bruce B had a four unit average lifetime CF of 83.5 percent and an average annual CF of 82.3 percent. The six unit Pickering station had a six unit average lifetime CF of 72.5 percent and an average annual CF of 73.6 percent. More information, and performance data for 2015 are in reference 1.

The raw performance data for 2016 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 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 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). 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 5 has a 2016 annual CF of 94 percent and an EAF of 97.4 percent. However based on what was just said above this EAF of 97.4 percent must really be a UCF of 97.4 percent and this anomaly may 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 increase 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. However, according to the Bruce Site Updates website there appeared to be be just one overnight shutdown, on unit 2, caused by 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 2016 unit 1 had a lifetime CF of 84.5 percent; unit 2, 78.9 percent; unit 3, 85.9 percent and unit 4, 85.2 percent, for an average lifetime CF of 83.6 percent. The annual CF for unit 1 was 98.2 percent (EAF 98.6 percent); unit 2, 74.3 percent (EAF 74.4 percent); unit 3, 87.1 percent (EAF 87 percent) and unit 4, 74.9 percent (EAF 74.7 percent) , for an average annual CF of 83.6 percent. Average annual EAF, 83.6 percent. Darlington units do not provide flexible operation like Bruce A and B units during periods of SBG.

Unit 2 was shutdown on 2016 October 15 to commence a refurbishment outage.

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 2016 units 1 and 2 had lifetime CFs of 67.8 percent and 63.9 percent respectively and annual CFs of 91.7 percent (EAF 90.4 percent) and 73.2 percent (EAF 73.2 percent).

At the end of 2016 units 3 and 4 had lifetime CFs (from original in-service date and do not include the effect of the mandated lay-up) of 73.2 percent and 72.7 percent respectively and annual CFs of 75.8 percent (EAF 75.5 percent) and 87 percent (EAF 85.2 percent).

Bruce A had a four unit average annual CF of 81.9 percent and an average lifetime CF of 69.4 percent. The average four unit annual EAF for Bruce A was 81 percent. Bruce A units seem to have done very little steam bypass power manoeuvring in 2016.

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 2016 unit 5 had a lifetime CF of 85 percent; unit 6, 82 percent; unit 7, 84.2 percent and unit 8, 82.7 percent, for an average lifetime CF of 83.5 percent. The annual CF for unit 5 was 94 percent (EAF 97.4 percent); unit 6, 95.8 percent (EAF 97.1 percent); unit 7, 69.4 percent (EAF 71.9 percent) and unit 8 , 70.2 percent (EAF 71.4 percent), for an average annual CF of 82.3 percent. At the end of 2016 the annual average EAF for the four units was 84.5 percent so it looks as if Bruce B did most of the steam bypass power manoeuvring in 2016. To get some ballpark idea of the amount of electricity being curtailed by load cycling see Addendum, below, where a detailed curtailment calculation is done for Bruce B unit 5 using available PRIS data.

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 2016 the lifetime CF for unit 1 was 64.4 percent; unit 4, 66.4 percent; unit 5, 73.9 percent; unit 6, 77.9 percent; unit 7, 77.2 percent and unit 8, 75.2 percent for an average lifetime CF of 72.5 percent. The annual CF for unit 1 was 93.1 percent (EAF 93.4 percent); unit 4, 54.3 percent (EAF 54.3 percent); unit 5, 96 percent (EAF 96.6 percent); unit 6, 88.2 percent (EAF 88.2 percent); unit 7, 61.8 percent (EAF 62 percent) and unit 8, 48.5 percent (EAF 48.4 percent), for an average annual CF of 73.6 percent. Average annual EAF, 73.8 percent.

Performance Summary

For 2016 Darlington had a four unit average annual CF of 83.6 percent (average annual EAF, 83.6 percent).
For 2016 Bruce A had a four unit average annual CF of 81.9 percent (average annual EAF, 81 percent).
For 2016 Bruce B had a four unit average annual CF of 82.3 percent (average annual EAF, 84.5 percent).
For 2016 Pickering had a six unit average annual CF of 73.6 percent (average annual EAF, 73.8 percent).

 

Addendum

Worked example of nuclear curtailment using PRIS data

Reference Energy Generation, and Capable (or Available) Energy Generation, below, are determined relative to reference ambient temperature while Electricity Supplied (or Net Energy Generation) depends on actual ambient temperature. This means there is an external energy loss if cooling water temperature rises above the reference temperature. Of course there will will be an external energy gain if cooling water temperature falls below reference temperature so there will be some cancelling out. External energy losses are beyond the control of plant management. External energy losses beyond the control of plant management are included in the calculation of Energy Availability Factor (EAF) but not in the calculation of Unit Capability Factor (UCF). OPG and Bruce Power use UCF not Capacity Factor (CF) or EAF. Other external energy losses can be due to, load cycling/following, grid failures, earthquakes, lightning strikes, labour disputes etc.

For example take Bruce B unit 5 for 2016

From PRIS data, https://www.iaea.org/pris/ , Energy Availability Factor = 97.4%; Reference Unit Power = 817 MW; Electricity Supplied (or Net Energy Generation) = 6742400 MWh

From what was discussed earlier the EAF number of 97.4 percent must really be the UCF. Except for load cycling the other external energy losses would be close to zero so any difference between the CF and the UCF will be due to load cycling curtailment only.

The definition of UCF is,

UCF = (Reference Energy Generation) – (planned and unplanned energy losses attributed to plant management) * 100%

Reference Energy Generation

So, UCF = 97.4 = (817*24*366) – (planned and unplanned energy losses attributed to plant management) * 100%

817*24*366

Solving gives, (planned and unplanned energy losses attributed to plant management) = 186,590 MWh
So, Capable (or Available) Energy Generation = (817*24*366) – 186,590 = 6989938 MWh

Therefore, Curtailed Energy for Bruce B unit 5 in 2016 = 6989938 – 6742400 = 247,538 MWh
This is equivalent to a unit derating of 28 MWe for the entire year.

 

References

1. Performance of Ontario’s CANDU nuclear generating stations in 2015, Don Jones, 2016 March 19,
https://thedonjonesarticles.wordpress.com/2016/03/18/performance-of-ontarios-candu-nuclear-generating-stations-in-2015/

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/