Europe heat wave: nuclear, gas and hydro plants shut

Europe’s heat wave has forced at least one French nuclear reactor offline and prompted output limits at others this week. On June 22 unit two at the Golfech nuclear power plant shut down at about 11:45 p.m. when the Garonne River used for cooling got too warm; a spokesperson for EDF called the move “a precautionary measure.”

What happened this week?

The short answer: extreme temperatures and warm river water forced nuclear operators to pause or limit production, while other generation sources also lost capacity. France recorded its hottest day since national records began in 1947 on June 23, with temperatures climbing to over 44 °C and overnight temperatures remaining unusually high. EDF said Golfech’s unit two stopped after return-stream temperatures were expected to reach 28 °C, which exceeds regulatory limits. EDF is also limiting output at other reactors; one reactor at Nogent-sur-Seine was ramped down as of Tuesday, and more limits were expected later in the week, EDF spokesperson Brid Nelligan told the operator.

RTE, the national grid operator, said these outages and limits are not expected to prevent France from meeting electricity demand this week. Still, the timing is sensitive: unit one at Golfech was already offline for planned maintenance and refueling when unit two shut, according to a follow-up account of the plant’s status.

How is heat affecting different types of power plants?

Heat is squeezing supply and raising demand at the same time, affecting multiple generation types. Hydropower output in Europe fell 13 percent in the first five months of 2025 compared with the year before, as high temperatures and low water reduced available generation. Thermal and nuclear plants that rely on river cooling have to cut output when intake or return temperatures exceed regulatory or equipment limits. Ember Energy data show at least seven gigawatts of nuclear capacity were forced offline across France during a heat wave in July 2025. In the UK five gas plants have reported output reductions that together removed about 2.5 gigawatts from the supply.

Demand is rising because of cooling. The number of UK homes using air-conditioning has roughly doubled since 2022, and Europe-wide adoption remains lower than in the United States, where nearly 90 percent of homes have air-conditioning. The International Energy Agency projects global energy use for cooling will double by 2050 relative to 2023 levels, a long-term driver of higher summer peaks.

Why it matters

Utilities and grid operators face a triple squeeze: cooling demand spikes, some plants lose efficiency or must cut output, and seasonal maintenance schedules can leave capacity thin. That combination raises risk for tighter markets and higher prices and forces cross-border power trading at scale. Preparing generators and grids for hotter summers has a cost: EDF’s climate-change vulnerability assessment estimates upgrades will cost about €600 million per year over the next 15 years, a figure the company published as part of planning for its nuclear and hydropower assets.

What to watch

High temperatures were expected to continue across much of Europe through the end of the week; watch RTE grid notices and EDF statements for new output limits or unplanned outages. Also monitor hydrological reports for river intake temperatures and reservoir levels and Ember Energy or operator bulletins for rolling tallies of forced outages and gigawatts lost to heat.