Drought pressures European nuclear plants

Record-low river levels have left Hungary struggling to keep its nuclear power plant running, while Romania has been forced to shut down its last active reactor, raising the question of how to adapt nuclear power to an increasingly extreme climate.

Reliance on river water to cool nuclear reactors has long been a problem and has repeatedly led to reduced electricity production during the summer months, especially in France, which depends more on nuclear energy than any other country.

However, the scale of this year's drought and heatwave in Europe, a continent that is warming faster than any other, has given added urgency to the debate on adaptation.

Hungary was forced earlier this month to reduce the output of its two-gigawatt Paks nuclear power plant to just over 10 percent, narrowly avoiding a complete shutdown for the first time in 44 years. The plant is now operating at 25 percent of capacity.

Romanian state-owned company Nuclearelectrica shut down its last operating reactor on Thursday after attempts to divert additional cooling water to the power plant were not enough.

Part of the solution, but also part of the problem

Nuclear power plants have the advantage of producing stable electricity without carbon dioxide emissions, which means they play an important role in reducing the use of fossil fuels and combating climate change.

Both Romania and Hungary are committed to expanding nuclear power generation as an abundant domestic source of electricity, but that means finding ways to cool reactors that are less dependent on river levels.

Diana Irge-Vorsac, a professor at the Central European University in Vienna, told Reuters that scientific models show that central and eastern Europe will become an increasingly drier region.

"This is not only a consequence of lower rainfall, but also the fact that soil moisture and groundwater levels have been decreasing in recent years, while less rainfall and more frequent heat waves are further drying out the soil," she said.

At last year's conference of the Hungarian Hydrological Society, water experts already warned that "flow patterns could become more extreme and unstable" on the Danube, one of Europe's longest rivers.

Governments are now under pressure to find solutions, as emergency cuts in production at Hungarian and Romanian nuclear power plants have forced authorities to call on companies and households to reduce electricity consumption.

Among the proposed measures, Hungarian Prime Minister Péter Magyar said on Wednesday that his government would build a so-called weir in the riverbed - a submerged dam-like structure - to raise the water level. Two barges were also sunk yesterday to raise the water level further and try to prevent the power plant from shutting down, as the water level is expected to fall further in the coming days.

The country is also reviewing plans for a planned expansion of the Paks 2 nuclear power plant, which relies on the Danube for cooling. The former government of Viktor Orban selected Russia's Rosatom to carry out the work without a tender in 2014.

Different technologies, but water is still essential

Romania's Nuclearelectrica operates two 706-megawatt reactors, which together produce a fifth of the country's electricity. They use Canadian CANDU technology, which relies on heavy water, in which hydrogen is replaced with a heavier isotope to slow down neutrons.

The four reactors at Hungary's Paks power plant, which produce about half of the country's electricity, are Russian-made and belong to the pressurized water reactor type.

Both technologies use water from the Danube for cooling, after which the water is returned to the river.

In contrast, nuclear power plants in the Czech Republic and Slovakia use wet cooling towers, which require less water, while the steam generated during the process is released into the atmosphere.

Scientists have also proposed the possibility of hybrid cooling, which would supplement river cooling with cooling towers.

Attila Asodi, a professor and nuclear energy expert at the Budapest University of Technology and Economics, said, however, that it would probably not be economically viable to retrofit a cooling tower to the existing reactors of the Paks power plant.

"I don't think it would be economical to install a large cooling tower for the remaining 20-plus years that Paks 1 is expected to operate," Asodi told Reuters. "A new assessment of the available cooling methods at that site is certainly necessary."

Romania plans intervention on the Danube

In neighboring Romania, the country's only nuclear power plant is located along a river arm called the Old Danube, which intersects with another arm, the Bala.

In 2024, the government approved a project worth 1,02 billion lei, or about $225 million, that would raise the riverbed of the Bala Arm to better manage water flow.

The proposed solution includes moving the point where the branches cross upstream, as well as raising the riverbed threshold on the deeper Bala branch.

The project is delayed, and the government has not said when it might be completed.

When asked how the low level of the Danube affects plans to build two more reactors, Nuclearelectrica told Reuters that studies show that the project on the Bala branch would allow all four reactors to operate at full capacity.

Eugenija Gusilov, director of the Romania Energy Center think tank, agreed that this was feasible, adding that alternative cooling methods should be considered before work begins.

“The construction of units 3 and 4 still makes sense if the necessary hydraulic works are carried out,” she said.