France generates about 70% of its electricity from nuclear power. This year, output has been disrupted by repeated heatwaves and droughts.
France recorded on Wednesday a shortfall of more than 20% of its nuclear power generation capacity, a new record for outages due to "environmental constraints" or "external causes linked to the environment": drought, extreme heat and a jellyfish invasion.
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Nuclear power provides around 70% of France's electricity. This year, output has been disrupted by multiple heatwaves and periods of drought.
According to AFP calculations based on data published by energy group EDF since 2015, 20.4% of generating capacity was unavailable.
Between 9:45 and 10:00, EDF's nuclear fleet hit a new peak in unavailability for reasons described as "environmental constraints" or "external environmental causes", both in terms of the number of reactors shut down or operating at reduced power and in terms of lost generating capacity.
In total, 13 of the 57 reactors in the French nuclear fleet were affected. Eight were completely shut down (Bugey 3, Cattenom 1, Chooz 1 and 2, Golfech 2, Gravelines 2, 3 and 4) and five were running below capacity (Saint-Alban 2, Tricastin 1 and 4, Gravelines 1 and 6).
Eight reactors were completely offline, while five were operating at reduced power.
A large share of the lost nuclear capacity was due to full or partial shutdowns of five of the six reactors at the Gravelines power plant, western Europe's largest, after a mass of jellyfish clogged the pumps used to cool the facilities.
"Several tonnes of jellyfish" surged into the seawater pumping stations, clogging the filter drums, an EDF spokeswoman said.
Units 1 and 6 have since returned to full power at around 10 am on Wednesday, while reactor 5 is in a scheduled maintenance shutdown. Currently offline, Gravelines 2 is due to be reconnected to the grid at 11 pm on Wednesday.
Gravelines, which draws water from the North Sea to cool its installations, had already faced the same problem exactly one year earlier.
According to experts, overfishing, plastic pollution and warmer waters linked to climate change have created conditions favourable to the proliferation and reproduction of jellyfish.
Apart from the Gravelines plant, the largest in western Europe, shutdowns or reduced output at other reactors are linked to extreme heat and drought, which deprive power stations of the water they need for cooling.
In periods of drought or heatwave, lower river flows and higher water temperatures can force EDF to cut back or even halt production in order to protect the environment and biodiversity. In such cases the operator cannot discharge chemical or radioactive effluents, nor further warm rivers with its cooling water, which is returned at a higher temperature.
"But there is enough leeway for this not to cause supply problems" in the short term, stressed Nicolas Goldberg, an energy expert at consultancy Colombus Consulting, quoted by CNews. In August, a month when electricity consumption is lower, France was still on Tuesday a significant net exporter of electricity, after posting a record net export balance of 51 TWh in the first half of the year.
In the longer term, however, "particularly if the lifespan of reactors is extended to 70 or 80 years, adapting them to climate change will be a real stress test over the next 20 to 30 years, in a warmer climate," the expert said.
