Washington — Exelon Generation reduced output Thursday night and Friday morning at four of its nuclear units in Illinois. At least three of ramped down because of low power prices in the PJM Interconnection market and transmission grid congestion, the company said. Two of those units have since returned to full-power operation, Exelon said.
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The 1,268-MW Byron-1 in Byron, Illinois, reduced output beginning at 2 am CDT (0700 GMT) Friday "in coordination with PJM due to pricing signals and transmission line constraints," Exelon spokesman Paul Dempsey said in an email. The unit was operating at 86% of capacity as of 7 am CDT (1200 GMT), Dempsey said. He did not say when Byron-1 is expected to return to full-power operation.
The adjacent 1,241-MW Byron-2 was operating at 100% early Friday morning, the US Nuclear Regulatory Commission said in its daily reactor status report.
Output was reduced at the 912-MW Quad Cities-1 in Cordova, Illinois, beginning at 10:33 pm CDT Thursday (0333 GMT Friday), and at the 994-MW Quad Cities-2 beginning at 10:30 pm CDT Thursday (0330 GMT Friday), "in coordination with PJM due to pricing signals and transmission line constraints," Exelon spokeswoman Brandy Donaldson said in an email.
Quad Cities-1 was operating at 87% capacity, and Quad Cities-2 at 98% of capacity early Friday morning, down from 100% at both units early Thursday, according to NRC's daily report.
Both Quad Cities units were operating at 100% as of noon CDT (1700 GMT) Friday, Donaldson said.
The 1,320-MW Braidwood-1 in Braceville, Illinois, was operating at 92% early Friday, down from 100% Thursday, according to NRC's report. An Exelon spokesman did not immediately reply to questions on the status of that unit and the reason for the output reduction.
Since 2015, Exelon has temporarily reduced off-peak output at one or more of its nuclear plants in Illinois numerous times because of low power prices in PJM and/or grid constraints. The company has previously said intermittent grid congestion and periods of negative prices have been occurring in the region around those plants because of transmission line outages for scheduled maintenance, large influxes of wind-generated power into the grid during off-peak hours, or a combination of those factors.
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