Historically low river levels have left Hungary struggling to keep its nuclear power plant running, and drought has now forced Romania to shut down its last operating reactor. The crisis is raising fresh questions about how nuclear power can adapt to increasingly extreme weather.
Cooling reactors with river water has long been a vulnerability, repeatedly forcing cuts to electricity production during the summer months, nowhere more so than in France, the country most dependent on nuclear power in the world.
This year, though, the extreme drought and heat waves sweeping Europe have lent the debate over adaptation new urgency.
Hungary was forced to cut output at its two-gigawatt Paks nuclear power plant to about 10% in early August, narrowly avoiding a complete shutdown for the first time in the facility's 44-year history. It is currently running at 25% of capacity.
Romanian state-owned company Nuclearelectrica shut down its last operating reactor on Thursday, after efforts to divert additional cooling water to the plant fell short.
Governments Scramble for Solutions
Nuclear power's advantage lies in its ability to generate electricity reliably without carbon emissions, giving it an important role in cutting fossil fuel use and fighting climate change.
Both Romania and Hungary plan to expand their nuclear capacity to secure enough energy from domestic sources. First, though, they must find ways to cool their reactors that rely less on river water levels.
Water management experts warned at last year's conference of the Hungarian Hydrological Society that "flow patterns may become more extreme and volatile" on the Danube, one of Europe's longest rivers.
Governments are now under pressure to find solutions. Emergency restrictions on nuclear output in Hungary and Romania have already forced them to call on businesses and households to cut electricity consumption.
Hungarian Prime Minister Peter Magyar announced on Wednesday that his government would build an underwater weir, a submerged structure resembling a dam, to raise the river's water level.
As a stopgap, two barges could be sunk as early as Friday to raise the water level and stave off a shutdown, since the Danube is expected to keep falling in the coming days.
Budapest is meanwhile reevaluating the planned Paks 2 expansion, which would also rely on Danube water for cooling. Viktor Orban's former government selected Russia's Rosatom to carry out the project in 2014.
Water Is Essential, Whatever the Technology
Romania's Nuclearelectrica operates two reactors, each with a capacity of 706 megawatts, together accounting for a fifth of the country's electricity production. They run on Canadian CANDU (CANada Deuterium-Uranium) technology, which relies on heavy water, in which ordinary hydrogen is replaced by its heavier isotope, to slow neutrons.
The four reactors at Hungary's Paks plant, which generate roughly half the country's electricity, are Russian-made pressurized water reactors.
Both technologies draw water from the Danube for cooling before discharging it back into the river.
Other nuclear plants, by contrast, use wet cooling towers, which need less water and release the resulting steam into the atmosphere.
Scientists have also proposed hybrid systems that would supplement river cooling with cooling towers.
Romania Bets on a Reshaped Riverbed
Romania's only nuclear power plant sits on a branch of the Danube known as the Old Danube, where it meets another branch, the Bala.
In 2024, the government approved a 1.02bn lei ($225m) project to raise the bed of the Bala branch and better regulate water flow.
The plan involves shifting the confluence of the two branches further upstream and raising the riverbed threshold on the deeper Bala arm. But the project has fallen behind schedule, and the government has given no indication of when it might be completed.
Asked how low Danube levels would affect plans for two additional reactors, Nuclearelectrica told Reuters that studies show the Bala branch project would let all four reactors run at full capacity.
Eugenia Gusilov, director of the Romania Energy Center, agrees the project is feasible, though she suggested it would be worth exploring alternative cooling methods before construction begins. "Building Units 3 and 4 still makes sense if the necessary hydrotechnical works are done", she said.