France's Nuclear Curtailments Reach 2026 Worst as Heat Forces 11.6 GW Offline
EDF constrained 13 reactors on Monday (2026-08-17), lifting heat-related losses to an 18.4% year high and tightening the margin on its annual output target.
EDF curtailed 11.6 GW of French nuclear capacity on Monday (2026-08-17), pushing heat-related losses to 18.4% of the reactor fleet, the highest point of the year, Montel reported. Thirteen reactors were affected, with high temperatures persisting in the south of France.7
By Tuesday (2026-08-18), EDF said the affected share had eased to 16.6% of the fleet. Ten reactors remained constrained, with cumulative cuts of 10.5 GW. The operator revises plans as the situation evolves, a caveat it has applied throughout a summer that has repeatedly set new records for heat-related generation loss.7
France generates roughly 70% of its electricity from nuclear and operates as a net exporter when its reactors run unimpeded. On Monday (2026-07-13), RTE data showed the country exporting more than 10 GW to neighboring countries despite 6.4 GW being constrained. With curtailments on Monday (2026-08-17) nearly double that July level, available data does not confirm whether France maintained its net export position.3
The progression since mid-July has been steep. Cuts stood at 6.4 GW on Monday (2026-07-13), equivalent to 14% of France's overall power demand at that point, according to OilPrice.com. Montel reported them climbing to 7.6 GW, or 12% of installed capacity, by August 3 (2026-08-03), the highest level since the heatwave began the week of 2026-07-27. The 11.6 GW recorded on Monday (2026-08-17) surpassed both prior peaks.3,5,7
The curtailment mechanism runs through river temperatures: when summer heat warms the waterways used for cooling, plants must reduce output to comply with environmental thermal discharge limits. EDF's data for Monday (2026-08-17) lists 13 constrained reactors without identifying the specific units, limiting assessments of how quickly the fleet might recover should temperatures in the south ease.3,4,7
The season's record has been reset at each successive wave of heat. Montel reported cuts of 4.6% on July 8 (2026-07-08), which grew to 6.4% by July 9 (2026-07-09), then climbed to 12% of installed capacity by August 3 (2026-08-03) before reaching 18.4% on Monday (2026-08-17). Each new high has been accompanied by EDF's standard caveat that forecasts are subject to revision, accurate as a statement of practice but offering little for those positioning in the forward market.1,2,5,7
EDF's annual guidance for French nuclear output stands at 350 to 370 TWh for 2026, with a longer-run target above 400 TWh. The company produced 189.9 TWh in the first half of the year. Each additional week of elevated curtailments narrows the buffer between actual output and the lower bound of the full-year range; EDF has not revised its guidance in the materials reviewed.6
The operator's August 5 (2026-08-05) half-year results recorded EBITDA of €14.1bn, net income of €5.2bn, and net financial debt of €51.5bn, alongside a confirmed 2027 target of net debt to EBITDA no higher than 2.5 times. Those figures predate the Monday (2026-08-17) peak curtailment and do not reflect any adjustment to the generation outlook that a prolonged heat tail might require.6
How quickly the 16.6% rate recorded on Tuesday (2026-08-18) recedes as southern temperatures moderate will shape cumulative summer losses against EDF's 350-370 TWh full-year range. A prolonged heat tail could eventually force a formal guidance revision.6,7