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Heat, water shortages, jellyfish: nuclear energy is becoming uncontrollable

Heatwaves, droughts, rivers that are too hot or too low: since June, European nuclear power plants have been experiencing numerous power reductions and shutdowns. One question is becoming increasingly difficult to avoid: is nuclear power still manageable in a warming world ?

By 

Laure Noualhat, August 14, 2026 , https://reporterre.net/Le-climat-met-le-nucleaire-europeen-a-sec-Le-nucleaire-rattrape-par-la-question-du

On August 12, shortly before 10 a.m., a fifth of France’s nuclear power plants were offline. Exactly 20.4  % of their production capacity was unavailable due to ” 
 environmental constraints “ or ”  external environmental causes , “ a record since 2015, calculated by AFP using data from EDF .

Thirteen reactors were affected: eight completely shut down, and five operating at reduced capacity. On one hand, rivers were either too hot or too low after five heat waves ; on the other, at Gravelines (Nord), several tons of jellyfish had clogged the water intakes of Western Europe’s largest nuclear power plant. Nuclear power can be controlled, certainly, but it still needs to be cooled.

In Golfech, on the banks of a sweltering Garonne River, the situation has taken on the air of a summer ritual. On August 8, at 9 p.m., 
EDF once again shut down reactor number 2. The Garonne threatened to reach 28°C the following day, the threshold beyond which the power plant must reduce its production or shut down to comply with environmental regulations and avoid harming aquatic life. Since reactor number 1 was already undergoing maintenance, the plant was no longer producing any electricity. The same scenario, to varying degrees, played out at Bugey (Ain), Saint-Alban (Isère), and Tricastin (Drôme), where the Rhône River’s waters, having become too warm, led  EDF to adjust its production.

Because while a reactor needs water to dissipate its heat, it cannot turn rivers into scalding baths. Discharges from power plants are regulated by the Nuclear Safety and Radiation Protection Authority ( 
ASNR ), which sets, for each site, limits on the temperature increase of the watercourse between upstream and downstream, as well as a maximum temperature that must not be exceeded.

What uses will be prioritized as droughts occur ?

This summer, the Bugey nuclear power plant 
was the only French plant to request a temporary modification of its thermal regulations , the  ASNR (  French Nuclear Safety Authority) told Reporterre .  The  Rhône River was already very hot upstream, while  RTE (the Frenchelectricity transmission network operator) demanded that a minimum power output be maintained to guarantee grid security. The Authority therefore agreed to temporarily raise certain limits, but only between July 
10 and 20. This compromise aptly summarizes the dilemma ahead: protecting a river already suffering from the heatwave while preventing the electrical grid from overheating as well.

In Chooz, in the Ardennes region, the problem isn’t the temperature but the amount of water. The Meuse River’s flow rate dropped drastically at the beginning of August. The two reactors were shut down, not because there wasn’t enough water to safely cool the facilities, but to comply with the Franco-Belgian agreement guaranteeing a minimum flow for the various river users. Thus, nuclear power is confronted with a question already familiar to farmers, industrialists, and river conservationists: who has the right to water when it becomes scarce  ? Which uses will be prioritized as droughts continue to occur  ?

Controllable… but not climate-insensitive

Taken separately, each of these episodes seems almost commonplace. 
EDF has long adjusted its power plants’ output during heat waves. In 2003, the utility even sprayed the Fessenheim reactor building with water jets! 
 But their repetition, and especially their simultaneity, changes the landscape. Up to 7.3 gigawatts of French nuclear power were unavailable on August 12 or constrained by the heat and low flow rates. ” This is a record peak in environmental unavailability , 
 “ according to AFP . At the same time, there was a lack of wind in Germany, and air conditioners were running more frequently, which drove up electricity prices.

However, it would be wrong to claim that the nuclear fleet is faltering; it’s simply overheating. It’s actually producing significantly more than during the major crisis of 2022 when 32 reactors were unavailable due to stress corrosion cracking. The real issue lies elsewhere. A nuclear power plant is an enormous thermal machine that must dissipate some of its heat. It can produce electricity without wind or sun, but not without cold water. And this resource, too, is caught up in the whirlwind of climate change.

The Danube is offering a much more stark demonstration this summer. In Hungary, the Paks power plant, which supplies nearly half of the country’s electricity, saw 
its production plummet in early August due to the river’s exceptionally low water level. 

 “A temporary rise in water levels then allowed for the recovery of some production, but the government has announced its intention to re-examine the cooling requirements of the Paks 
II project ,” explains András Kéri of the climate policy institute Energiaklub. ” 
A power plant built today will only be operating at full capacity in the second half of this century… 
 “ What will the state of the Danube be in 2050, 2070, or even 2100 ?
 It’s difficult to say.
 

Further downstream, Romania faces an even more critical situation. The country will shut down its only nuclear power plant on August 13th, for the first time since the 2003 drought, as the Danube’s flow has dropped too low. As early as July 28th, the operator of the Cernavodă site shut down Unit 1 due to a Danube level described as ”  very low and unprecedented” . 
 The intake canal had to be dredged and the riprap blasted to redirect the flow. When the river needs to be reshaped locally to maintain electricity production, climate adaptation is no longer just a chapter in an annual report. Switzerland also experienced this very real future firsthand by reducing the two reactors at Beznau to 50% of their capacity when the Aare River reached the critical temperature of 25°C.

In France and Switzerland, most of these power reductions do not signal a loss of safety and are precisely intended to comply with environmental regulations. In Hungary and Romania, the extreme low water level of the Danube more directly impacts operating conditions. But for the electrical grid, the result is comparable: megawatts considered readily available on demand become slightly less so at the very moment when heat increases certain needs.

And as the Anthropocene knows how to keep things interesting, the Gravelines nuclear power plant has added jellyfish to the mix. On August 10, their massive arrival in the water intakes triggered the automatic shutdown of 3 of the 6 reactors. EDF insisted there was no safety issue . And besides, is this becoming a regular occurrence  ? A similar incident had already happened in August 2025 .

European nuclear power is therefore not collapsing under the heatwave. But this summer is challenging a simplistic way of speaking: ”  controllable  “ nuclear power does not mean ”  insensitive to climate .  “ It depends on it, like everything else.

What about EPR2s

The issue becomes considerably more serious when we look at the reactors currently in the design phase. EDF asserts that it has sized the future EPR2 reactors ”  with regard to heatwave risks  “ by taking into account the IPCC climate scenarios for 2070 and 2100, ASNR told Reporterre . EDF has allocated €8.7 billion by 2040 to adapt its nuclear, hydroelectric, and island activities to climate change , notably through the Adapt project, which aims to assess, plant by plant, their vulnerability to rising temperatures, droughts, and changes in water resources.

In 2023, the Court of Auditors still estimated investments directly attributable to climate adaptation of the nuclear fleet at around €600 million for the following fifteen years. Going from €600 million to €8.7 billion in three years is a gigantic leap  !
The ASNR (French National Agency for Radioactive Waste Management) emphasizes the need to maintain ” margins , “ as tomorrow’s climate may diverge fromprojections. Every ten years,” safety standards must therefore be reassessed, 
 “ and facilities may need to be adapted to higher temperatures. But how, specifically ?
  What technological advancements are needed to secure water supplies when a river runs dry ?
  No one is saying.

To date, nuclear power plants evaporate 833 million cubic meters 
^of fresh water per year. While this water is reintroduced into the water cycle, it remains unavailable for other needs (domestic consumption, agriculture, industry, etc.). With the future EPR2 reactors —particularly those located along rivers—this will increase the amount of water drawn from rivers to 
1,232 million cubic meters ^per year and from the seas to 575 million cubic meters 
^per year, according to figures from Global Chance.

August 15, 2026 - Posted by Christina Macpherson | climate change, France, Reference