What were the causes, scale, and consequences of the record French nuclear shortfall in August 2026, including the roles of drought, extreme heat, and a jellyfish invasion at Gravelines, how many EDF reactors were affected, the simultaneous shutdown of Hungary's Paks plant due to

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Europe's fifth summer heatwave in 2026 triggered an unprecedented, multi-country collapse in nuclear generation from both heat-related cooling restrictions and biological disruptions, knocking roughly one-fifth of France's nuclear capacity offline while simultaneously forcing Hungary's sole nuclear plant to shut for the first time in 44 years, and sending wholesale power prices surging 20–100% across multiple markets.

Scale of the French shortfall

• 20.4% of capacity lost — By mid-August, France experienced a 20.4% shortfall in nuclear power capacity due to environmental causes .
• 13 of EDF's 57 reactors affected — Eight were fully shut down and five operated at reduced power .
• ~7.3 GW curtailed at peak — On August 11, French nuclear output was expected to be limited by 7.3 GW at the midday peak, about 15% of total fleet capacity . By August 13, output was the lowest since August 2023, with six reactors fully offline due to heat alone .
• Earlier waves — Output had already been cut by 4.1 GW (7% of demand) in late June and by 6.3 GW across eight reactors in mid-July .

Causes

Extreme heat and drought. France endured five successive summer heatwaves. High river temperatures forced EDF to throttle or shut reactors because environmental regulations limit the temperature of water returned to rivers. By early August, low water levels on the Meuse and Moselle rivers further reduced cooling-water availability, forcing shutdowns at Chooz and Cattenom . Three reactors (Golfech-2, Bugey-3, Chooz-2) were shut in July as temperatures pushed toward 40°C .

Jellyfish invasion at Gravelines. On August 10–11, a "massive influx" of jellyfish clogged the cooling-water intake pumps at France's largest nuclear plant (Gravelines, six reactors) . Three reactors were taken fully offline; a fourth was cut to 50% output — removing about 3.2 GW of capacity . This was the second consecutive August that jellyfish swarms disrupted Gravelines . EDF expected a quick restart once cleanup finished, as no new jellyfish were arriving .

Hungary's Paks shutdown

• First full shutdown in 44 years. Record-low water levels on the Danube River meant the plant's suction nozzles could no longer reach enough cooling water . Hungary's PM Péter Magyar announced the complete power-down on Sunday, August 2 .
• Paks supplies ~50% of Hungary's electricity and the plant was expected to remain offline for weeks as the Danube continued to recede .
• Romania also affected. Romania declared a state of emergency and raced to build a dike to divert Danube water to its only working nuclear reactor . Overall, about 7 GW of nuclear capacity was offline across France, Hungary, and Romania — roughly 10% of the EU's total installed nuclear capacity .

Electricity price surges

• France. French day-ahead baseload power spiked 21.8% to €142.50/MWh on August 11 . French spot prices rose 45.8% month-on-month into early August .
• Italy. Italian day-ahead prices hit their highest level in 3.5 years on August 4 as heatwave-driven cooling demand soared alongside supply constraints . July prices averaged €156.77/MWh, up 18.5% month-on-month .
• Southeastern Europe. Prices on regional exchanges surged 50–100% compared with prior weeks, exceeding €700/MWh in the most expensive 15-minute periods . Drought and heat reduced generation at both nuclear and hydroelectric plants across the Danube basin .
• Broader market. European spot power prices overall rose by more than 20%, with German wind speeds also slowing and compounding the supply squeeze . Summer power prices reached levels normally seen only in winter . Hungarian wholesale prices hit 3.5-year highs .

Broader outlook

The European Commission described the energy situation as "strained" on August 6, with power plants forced to shut across France, Italy, Poland, Hungary, Romania, and Slovenia due to low water levels or excessively high water temperatures . The cascading nuclear outages — from heat, drought, and biological disruptions — exposed the vulnerability of Europe's water-cooled thermal generation fleet to compounding climate shocks. Tighter grid conditions are expected to persist as long as heatwaves continue, accelerating investment in battery storage, solar, and demand-side flexibility as alternatives to weather-dependent nuclear and hydro capacity .