Cernavoda, Paks, Gravelines plants suffer as European heat wave impacts water sources

Romania has taken its last operating reactor off line due to the record-low water levels of the Danube River, in what is the latest example of how the historic heat wave gripping Europe has impacted the river levels and water temperatures needed to operate nuclear power plants across the continent. The situation is not isolated to Romania, however, as power plants in Hungary and France are also facing challenges.

Cernavoda shuts down: Romania's Ministry of Energy announced that at 10:53 a.m. local time on Thursday, Cernavoda nuclear power plant's Unit 2 was shut down.

One day earlier, the Ministry of Energy announced Unit 2 would be shut down in a controlled manner, and that at that moment there were no risks to the supply of electricity nationally, the agency said. The plan was for Romania to offset the loss of the 1,300 MW provided by Cernavoda through hydroelectric, wind, coal, and electricity imports.

This outage comes after Cernavoda-1 was shut down on July 28. Together, the two reactors generate about 20 percent of Romania's electricity.

How long will the shutdown last? Plant director Romeo Urjan told Romanian news outlet Digi24 that Cernavoda will not be restarted for at least 10 days. The Ministry of Energy said it has alerted the European Commission of its crisis.

Previously, the Romanian government attempted to stave off the shutdown by conducting controlled blasts along the Danube to divert river flow toward the power plant.

Paks holds on: Elsewhere along the Danube, Hungary's Paks power plant continues to operate, but at reduced capacity due to low river levels. To combat this, Hungary has transported two 80-meter-long barges to the site, where they could be submerged to raise water levels, Prime Minister Péter Magyar said in a Facebook post Wednesday. NBC News reported the plan is to build a bed sill upriver from the plant to slow the current and raise water levels.

Further continuation of record-low water levels along the Danube could prompt the shutdown of Paks for the first time in its 44 years of service. The 1,916-MWe, four-unit Paks is Hungary's only nuclear power plant and, according to the International Energy Agency, generates 42 percent of the country's electricity.

Jellyfish swarm Gravelines: France's fleet of nuclear reactors has been impacted by the scorching summer, too, with production cuts at Golfech in late July due to high water temperatures.

On August 10, Électricité de France shut down three of the six reactors at the Gravelines plant because of a "massive influx" of jellyfish. The swarm also prompted a reduction of power in another reactor by 50 percent. Jellyfish populations have been known to grow and swarm along the coasts in warming water.

By Thursday, EDF said two of the affected reactors were still shut down because of the incident earlier in the week, with plans to power them back up over the next few days.

Coincidentally, multiple reactors at the six-unit Gravelines shut down on August 10 and 11, 2025, for the same reason.

"These stations provide the seawater supply essential for cooling the steam circuits. The exceptional scale of the phenomenon, exceeding the usual forecasts, led to a partial clogging of the filtration devices, in particular the pre-grids and the filter drums. Faced with this situation, the reactors in operation have successively put themselves under protection, in accordance with the operating rules," EDF wrote earlier this summer recapping the 2025 jellyfish swarm.