11th July 2026
The key point is that the French nuclear reactors are not being reduced because the reactors themselves cannot cope with heat.
The problem is the cooling system and environmental rules protecting rivers. Several French plants use river water for cooling.
When rivers become too warm, returning warmer water from the power station could damage fish and river ecosystems, so output has to be reduced or reactors temporarily shut down. EDF has recently reduced output at several sites, including Golfech, because river temperatures reached regulatory limits.
How does a nuclear power station need cooling water?
A nuclear reactor works by producing heat, which creates steam, which turns turbines to generate electricity.
The basic process is:
Nuclear fuel creates heat.
Water or another coolant carries that heat away.
Steam is produced.
The steam turns turbines.
The steam must then be cooled back into water so the cycle can continue.
That last stage is where rivers, seas or cooling towers come in.
Many French reactors were built beside rivers because rivers provided a convenient supply of cooling water. However, during severe heatwaves:
river temperatures rise;
river levels may fall;
environmental limits on water discharge can be reached;
reactors must reduce output to avoid overheating the river ecosystem.
France has previously experienced similar problems during major heatwaves.
Why does France matter so much to Europe?
France is unusual because it has historically produced a very large share of its electricity from nuclear power.
When its nuclear fleet is operating normally, France often produces more electricity than it needs and exports power to neighbours including:
Germany;
Belgium;
Italy;
Switzerland;
the United Kingdom.
The European electricity system works like a large interconnected network. Electricity does not stay within national borders. If France has surplus power, it can flow through cables to countries needing electricity.
The reverse also happens: if France loses generation, neighbouring countries may have to produce more of their own power or buy electricity elsewhere.
Recent figures show that France has been one of the UK's biggest electricity suppliers. In 2025, imports from France accounted for a significant part of Britain's imported electricity supply.
What could happen across Europe?
The effects depend on how severe and widespread the heatwave becomes.
Higher wholesale electricity prices
If France exports less electricity, countries that normally buy French power may need alternatives.
Those alternatives could include:
gas-fired power stations;
coal generation in some countries;
more expensive imports from other neighbours.
That can push wholesale electricity prices higher.
During previous periods of French nuclear problems, European electricity markets became much tighter because France moved from being a major exporter to needing more imports.
More pressure on gas supplies
Europe has reduced its dependence on Russian gas, but gas-fired power stations remain important when other sources are unavailable.
A hot summer can create a double problem:
people use more electricity for cooling;
some power stations produce less because of cooling difficulties.
That combination can increase demand for gas.
Possible impact on industry
Large industrial users are especially sensitive to electricity prices.
Higher prices can affect:
steel;
chemicals;
manufacturing;
data centres;
food processing.
Countries with already expensive energy systems would feel the pressure most.
What about the UK?
The UK is connected to Europe through several electricity interconnectors, including links to France.
This provides advantages:
Britain can import electricity when domestic supply is tight;
it can export when it has excess generation.
But interconnectors are not a guarantee of unlimited supply.
If France, Belgium, the Netherlands and other countries are all experiencing high demand at the same time, everyone is looking for the same limited spare capacity.
Britain has already experienced tighter margins during heatwaves, with the National Energy System Operator warning that extreme temperatures can put pressure on electricity supplies.
Would this affect electricity bills?
Not immediately in the way an oil price shock does.
Household electricity prices are usually based on longer-term costs, regulation and wholesale market movements rather than one day's power shortage.
However, prolonged periods of expensive wholesale electricity can eventually feed through into:
supplier costs;
future price caps;
industrial electricity prices.
The bigger lesson: climate risk affects all energy sources
This situation raises a wider energy debate.
Nuclear power is often described as reliable because it provides steady electricity regardless of whether the wind blows or the sun shines.
That remains true in many respects.
However, the French experience shows that all energy systems have vulnerabilities:
wind can be low during calm weather;
solar output falls at night;
gas depends on fuel supplies;
nuclear can be affected by heat and water availability;
hydro depends on rainfall.
The future electricity system therefore needs not just more generation, but also:
stronger grids;
more storage;
better interconnection;
flexible backup generation;
designs that cope better with extreme weather