Frequent Nuclear Plant Shutdowns as France’s Output Drops Nearly 10%
In July 2026, temperatures across much of Europe soared past 40°C, hitting France’s nuclear fleet first. Of the country’s 57 nuclear reactors, three were forced to shut down due to extreme heat, while another seven reduced output, leading to a nearly 9% drop in total nuclear power generation. Michael Tadrous, a researcher at McMaster University, explained that the primary impact of high temperatures on nuclear power stems from rising river water temperatures used for cooling, which reduces reactor efficiency. For instance, a 15°C increase in water temperature can cut the output of a large reactor by about 6%.
However, regulatory constraints proved to be an even greater obstacle. Nuclear plants discharge cooling water at elevated temperatures, which can harm aquatic ecosystems, prompting many countries to mandate automatic reactor shutdowns when river temperatures exceed legal limits. Henry Preston, a spokesperson for the World Nuclear Association, noted that such shutdowns are “typically to comply with ecological protection regulations, rather than technical failures.” During extreme heatwaves, some countries temporarily relax these rules to ensure power supply. France, for example, waived certain restrictions in July 2026.
Drought further exacerbated the challenges facing nuclear plants. On 3 August 2026, persistently low water levels in the Danube River forced multiple reactors in Romania and Hungary to shut down or reduce output, taking nearly 40% of southeast Europe’s nuclear capacity—approximately 2.44 GW—offline. Romania’s Cernavodă nuclear plant, which supplies 20% of the country’s electricity, saw its shutdown deal a severe blow to energy security. With no significant rainfall forecast in the near term, the Danube’s water levels were expected to take days or even weeks to recover, leaving several eastern European countries facing an energy emergency.
Despite the severe short-term impact, Tadrous’s research found that heatwaves reduced annual nuclear generation by just 0.6% on average between 2003 and 2022. The sole exception was France in 2003, when heatwaves caused a 1.3% drop in output. EDF, France’s nuclear operator, has since begun installing additional cooling towers at high-risk plants and adjusting maintenance schedules. Tadrous highlighted that river-cooled nuclear plants in France lost 5.5 TWh of output during the 2003 heatwave, but by 2022, such losses had fallen to 0.5 TWh—a 90% reduction.
Gas Plant Efficiency Declines as Wind Power Generation Plummets
Gas-fired power plants were also hit hard by the extreme heat. Iain Staffell, an associate professor at Imperial College London, noted that at 40°C, gas plants experience a 13% drop in capacity and a 7% decline in efficiency. Combined cycle gas turbines (CCGTs) and other water-cooled units suffered further efficiency losses as hotter air reduced combustion performance. In August 2020, gas plants accounted for 79% of the offline capacity during California’s rolling blackouts amid a heatwave. Similar reductions were observed in the UK and France during the summer of 2026.