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.
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