How a Shrinking Danube Threatened Nuclear Power in Hungary and Romania

Record-low water levels on the Danube turned cooling water into a critical constraint for nuclear power in Central and Southeastern Europe. Hungary’s Paks plant came close to an automatic shutdown, while Romania’s Cernavodă station was forced to take both reactors off the grid. This was not a fuel problem or a reactor malfunction. It was a water-supply crisis unfolding as extreme heat pushed electricity demand higher.

Paks: centimetres from an automatic shutdown

Paks uses Danube water to cool its reactors and other essential equipment. As the river fell, the plant’s intake system risked losing the conditions needed for safe operation. Even after a reactor stops generating electricity, the plant still needs water to remove residual heat, so shutting down does not immediately eliminate the cooling challenge.

Reports published on 17 August said Paks was only 9 centimetres from its automatic shutdown threshold. One specialist report described just one of the plant’s eight turbines as operating, with output at roughly 10% of its usual 2 GW capacity. However, the more specific figures of 480 MW and eight operating turbines were not independently confirmed by the higher-authority sources in the supplied material. They should therefore be treated as figures reported at the time, rather than as uniformly verified measurements.

Hungary urged households and businesses to conserve electricity to reduce pressure on the grid. The government also sought to manage water flows and preserve the conditions around Paks’s water intake. Before rain was forecast upstream, the key question was whether inflows from the upper basin and water-management measures could raise the Danube quickly enough. If the river continued to fall, more generating units would have to be taken offline.

Rain later improved the outlook. Hungary expected to restart one Paks turbine as the river rose, although officials warned that the improvement could be temporary without further rainfall. The plant could therefore recover part of its output as hydrological conditions changed, but the episode did not remove its fundamental dependence on the river.

Cernavodă: Romania loses both reactors

Romania’s Cernavodă plant has two reactors, each rated at about 706 MW. The first had already been taken offline; the second was disconnected from the grid as the Danube continued to fall, leaving the entire 1,400 MW station shut down. According to the supplied reports, it was the first drought-forced full shutdown at the plant since 2003.

Cernavodă normally supplies roughly one-fifth of Romania’s electricity. Losing both reactors therefore removed a substantial block of firm generation while the country was already under pressure to maintain supply. Romania declared an energy emergency in August and asked households and businesses to voluntarily reduce consumption.

Authorities tried extraordinary measures to direct more water toward the plant’s intake. Reported actions included using explosives to remove an underwater obstruction, dredging the riverbed and sinking stone-filled barges to redirect the flow. Such measures could buy time, but they could not replace a stable cooling-water source. Restarting the reactors still depended on the river’s level and flow recovering enough to meet safety conditions.

Why heat makes the problem worse

Extreme heat stresses the electricity system in two opposing ways. Higher temperatures drive up demand for air conditioning, while drought reduces the water available to cool power plants. When river water is both scarce and warmer than usual, operators may need to cut generation or limit the amount of heated water discharged back into the environment.

Copernicus reported that worsening drought in July and August pushed the Danube, Loire, Po and Rhine to record-low levels. These rivers support far more than nuclear cooling: they are also important for hydropower, freight transport and industrial activity. One climate shock can therefore produce several simultaneous pressures—less electricity supply, higher demand, disrupted fuel and goods transport, and increased economic costs.

A wider European energy warning

Nuclear plants in France were also affected by high river temperatures and low water levels. An ICIS analysis cited in the supplied material estimated that around 7 GW of nuclear capacity in France, Hungary and Romania was offline because of prolonged heat and unusual river conditions, with France accounting for about 5 GW. This was a market analysis, not a single official statistic covering all of Europe.

Hydropower also suffers when river flows weaken. At the same time, low levels on the Danube and Rhine reduce the loads that ships can carry, disrupting freight and affecting company revenues. CNBC cited a Triodos estimate that heat-related disruptions could cost the European Union €180 billion, or about 1% of GDP. That figure is an estimate from a cited organisation, not confirmed damage already recorded.

Water is now an energy-security issue

Paks and Cernavodă show why water must be treated as a crucial input to the power system, alongside fuel, transmission lines and generating capacity. Nuclear power can provide steady electricity, but river-based plants remain dependent on water levels, flow rates and temperatures for safe operation.

When heatwaves and drought arrive together, the risk extends beyond any single facility. Nuclear and hydropower generation can decline at the same time that cooling demand surges. River transport can also falter, making it harder and more expensive to move fuel and other goods.

The Danube crisis is therefore a warning about the climate resilience of Europe’s energy infrastructure. Rain may help Paks restore part of its capacity, but one wet spell cannot eliminate the long-term risks facing power plants that depend on rivers under growing water stress.