French Nuclear Curtailments Head Back to 12% of Fleet After Latest Heatwave Spikes Day-Ahead Prices
France's day-ahead power prices hit 142.5 euros/MWh on Tuesday (2026-08-11) as EDF projected heat-linked reactor cuts to ease toward 12% of installed capacity by Thursday (2026-08-13).
France's day-ahead power prices rose as much as 21.8% to 142.5 euros per megawatt hour on Tuesday (2026-08-11), per LSEG data cited by Reuters. EDF data pointed to nuclear generation cuts of 7.3 gigawatts, equal to 12% of total installed capacity, at the mid-day peak on Wednesday (2026-08-12), with river cooling systems under pressure across multiple catchments. Montel reported on Tuesday (2026-08-11) that heat-linked curtailments were expected to ease to 12% of the fleet by Thursday (2026-08-13), signalling the peak disruption had begun rolling off.6,5
Nuclear energy covers around 70% of France's electricity supply. Curtailments of that scale shift the day-ahead balance quickly, and river-cooled reactors face discharge temperature limits set by environmental regulation: when ambient water temperatures rise, those limits constrain output before extreme heat is required. France's river-dependent fleet has few short-term workarounds when temperatures are high and water levels are low.6
This was at least the fifth heatwave to curtail French nuclear output this summer. On July 8 (2026-07-08), EDF disconnected the 1.3 GW Golfech 2 reactor on the Garonne river in southwestern France and imposed 3 GW of cuts in total, equal to 4.6% of installed capacity, as temperatures peaked at 42 degrees Celsius, per Montel citing EDF Remit data. Output curbs widened to 6.4 GW in mid-July 2026 during a prolonged and intense wave.3,6
August 3 (2026-08-03) produced the deepest cut since the wave beginning the week of July 27 (2026-07-27): 7.6 GW, or 12% of the fleet, per Montel citing EDF data. EDF then projected reductions falling to 4.3 GW, or 7% of capacity, on August 4 (2026-08-04) and settling near 3 GW, around 5%, through August 13 (2026-08-13). That settling did not hold; the week of August 10 (2026-08-10) brought a fresh escalation back to the same 12% band.4
The repeated convergence around 12% of capacity, touched on August 3 (2026-08-03), forecast again for Wednesday (2026-08-12), and targeted as the post-peak level for Thursday (2026-08-13), reflects how consistently this summer's heat has pushed France's river-cooled fleet to its thermal limits.5,6,4
The price response on Tuesday (2026-08-11) was direct. A move of as much as 21.8% in French day-ahead power concentrates cost for unhedged industrial and commercial buyers, and spot prices at 142.5 euros/MWh press against the forward curve if traders expect heat to persist into late August.6
EDF's structural answer to summer vulnerability is the EPR2 programme — three pairs of 1.7 GW reactors totalling 10 GW of new capacity at a projected cost of €72.8bn, per EDF's half-year report. The utility is targeting a final investment decision on that programme by end-2026. But the European Commission launched a state-aid investigation in May 2026 (2026-05-19) into France's proposed €73bn subsidy scheme for the six reactors, creating uncertainty over both timeline and financing structure. New capacity would not remove the river-cooling constraint, though a larger fleet absorbs forced outages on individual units without the same aggregate effect on the day-ahead market.2,1
River temperatures across France's catchments remain the immediate variable. If another heat intrusion arrives in late August before river levels recover, the easing that Montel projected for Thursday (2026-08-13) would prove temporary and curtailments could return above 12%. EDF updates its outage forecasts as conditions change. The next revision will say whether the summer's fifth heatwave was the last one that mattered.5