Bugey 3

Bugey 3 is a 910 MW pressurised water reactor (PWR) operated by EDF at the Bugey nuclear power station near Saint-Vulbas on the Rhône river in eastern France. On 30 June 2026, EDF took Bugey 3 offline as summer heat pushed Rhône water temperatures above the permitted cooling-water discharge threshold, a regulatory limit designed to protect the river's ecology from thermal pollution. EDF took the unit offline again on 12 July 2026 during a second heat dome, alongside Chooz and Golfech, and this time secured a government exemption allowing Bugey to discharge above the standard Rhône-temperature ceiling, valid to 20 July 2026.

French nuclear capacity is routinely curtailed in hot summers when river temperatures rise above environmental thresholds. The 30 June outage came alongside output reductions at Golfech and Nogent-sur-Seine, together cutting roughly 12% of EDF's nuclear fleet on the day; the 12 July outage repeated that pattern with Chooz and Golfech fully offline and eight further reactors reduced. Bugey 3 is one of four PWR units at the Bugey site; all draw cooling water from the Rhône. River-temperature curtailments are ordinarily temporary, restored once ambient temperatures fall, but the July exemption shows regulators can also relax the discharge limit itself rather than wait for the heat to pass.

For European power markets, the June curtailment compounded an already tight supply picture but did not flip the France-Germany spread as traders expected; France cleared day-ahead power at EUR 123.50/MWh against Germany's EUR 195.00/MWh on 30 June. The July repeat briefly did flip the spread, with France clearing roughly EUR 7/MWh above Germany before settling back to a EUR 3/MWh France-cheaper gap by 13 July. Bugey 3 has now been curtailed by river heat twice in a single summer, underlining that Rhône temperature limits are becoming a recurring, not one-off, constraint on the unit's output.