Drought and high river temperatures have curtailed nuclear power output at plants in France and Hungary during summer 2026, reducing France's electricity exports and contributing to brief price spikes in France and Germany, according to grid operators and a French government audit report.
Heat and low river levels force cutbacks at nuclear plants in France and Hungary
Drought and high river temperatures have curtailed nuclear power output at plants in France and Hungary during summer 2026, reducing France's electricity exports and contributing to brief price spikes in France and Germany, according to grid operators and a French government audit report.
At Hungary's Paks nuclear station, which normally supplies around 40% of the country's electricity, only one of four turbine units was still operating as of the time of reporting, after record-low water levels in the Danube briefly put the plant at risk of a complete shutdown.
In France, which relies on nuclear power more heavily than any other European country, heat-related production losses across all reactors averaged less than 1% of annual nuclear output in any given year between 2000 and 2022, according to a 2023 report by France's official audit office. Even during the extreme heat of summer 2003, annual losses reached only about 1.5%.
Short-term fluctuations can be considerably larger, however. During the summer of 2003, French nuclear plants temporarily reduced output by more than six gigawatts. During heat waves at the end of June and in mid-July 2026, maximum available capacity was temporarily limited by eight to nine gigawatts, equivalent to up to one-fifth of France's normal summer nuclear capacity.
Grid operators stated that France retained sufficient reserves even during the 2026 heat waves and remained a net electricity exporter on balance. The distinction between capacity curtailment and an equivalent overall shortfall is significant because some reactors would not have been running at full capacity regardless, owing to lower summer demand, high solar output, or grid bottlenecks.
On June 24, 2026, capacity was reduced by approximately 4.1 gigawatts due to high river temperatures, and France's electricity exports fell to about three gigawatts, down from 10 to 12 gigawatts the previous week. Combined with higher consumption, low wind output, and increased gas-fired generation, this contributed to electricity prices in France and Germany briefly reaching their highest levels since January 2025.
During subsequent July heat waves, curtailments were more extensive. On July 13, eight reactors with a combined capacity of 6.3 gigawatts were affected and two were taken fully offline, though France still intermittently exported more than 10 gigawatts and imported solar and wind power from Spain.
Nuclear plants are particularly sensitive to river conditions because only about one-third of the heat a reactor generates is converted into electricity; the remainder is released into the environment, often via rivers. When river levels are low, waste heat is distributed across a smaller volume of water, raising temperatures more quickly. Legal temperature limits exist to protect aquatic life, and it is compliance with these limits — rather than reactor safety concerns — that typically prompts summer throttling.
French authorities have occasionally granted exemptions to those temperature limits in critical situations, allowing closer monitoring of water bodies and enabling state-owned utility EdF to produce additional electricity in the short term.
Cooling towers reduce the direct thermal load on rivers but do not fully insulate a plant from weather-related constraints. The Golfech plant on the Garonne River — which experiences warm temperatures and low water levels in summer — remains one of France's most vulnerable sites despite having cooling towers. At Chooz on the Meuse River, reactors were throttled in 2020 to avoid threatening Belgium's drinking water supply, even though cooling towers were in use there as well.
Four years before the time of reporting, France's reactors generated nearly 82 terawatt-hours less electricity than in 2021, a decline attributed primarily to stress corrosion cracking and deferred maintenance rather than climate factors.
France's audit office projects that climate-related reactor downtime could triple or quadruple by 2050. French authorities plan to factor climate change into an upcoming modernization program: four of six planned EPR2 reactors are to be built on the coast at Penly and Gravelines, while a third pair will be built on the Rhone near Bugey, where cooling towers are intended to limit the thermal load on the river.
- No response or comment from EdF, the state-owned operator of French nuclear plants, is included beyond contextual references to its operations.
- No response from Hungarian authorities or Paks plant operators is included regarding their situation or recovery plans.
- The article does not specify the exact dates when Hungary's Paks plant was most severely affected or when it returned to fuller operation.
- The precise legal temperature thresholds that trigger curtailments in France are not specified.
- The cost estimates for heat-resistant upgrades to French nuclear plants are not quantified.
Read the original at Deutsche Welle