In Paks, Hungary’s only nuclear station idled all but one of its eight turbines in August as the Danube fell to levels not seen since the river’s record began. Workers monitored the gauge as Prime Minister Péter Magyar admitted, “We are in uncharted territory.” Nuclear reactors draw river or sea water to cool their cores. 

Operators must throttle output once the water grows too warm or too scarce, protecting safety margins and aquatic life downstream. Hungary’s near closure stands alongside curbs at French, Swiss and Romanian stations, each trimming output across the continent over the summer. 

The trend raises an honest question, whether heat will become a lasting block on nuclear power or only its most stubborn seasonal toll. The evidence gathered so far points toward the latter, and the capital now pouring into new reactors backs the reading.

A Summer of Reactors Idled

The Danube’s low point capped a season of comparable curbs at stations on the Rhône and the Aare. France’s state utility, Électricité de France, known as EDF, shut down three reactors on a single Sunday in July. The company cited rules against discharging overheated water into rivers already pressed by drought. 

Swiss operator Axpo idled both units at its Beznau plant after the Aare reached 25 degrees Celsius, past the point where operators could no longer guarantee sufficient cooling. Downstream, Romanian naval engineers blasted rock formations near Izvoarele to redirect Danube water toward the Cernavodă plant’s intake. 

The country had already idled both of the plant’s reactors, cutting output to a fraction of normal levels. Budapest has since begun raising the Danube itself, tipping some 145,000 cubic metres of rock into the riverbed to lift water levels near Paks by roughly a metre.

Physics, Not Politics, Sets The Limit

None of these curbs arise from safety concerns inside the reactors themselves. EDF’s own accounting puts the average annual loss from heat and low flow at 0.3% of the French fleet’s output over the past quarter-century. It has recorded the total across eight separate hot summers. 

The utility has committed roughly €8.7 billion over 15 years to harden its stations against warmer rivers, including options to cool discharge water before release. Reactors cooled directly by rivers make up only 14% of the world’s nuclear fleet, so the exposure, real as it is, is not universal. 

Gas stations lose efficiency in the same heat, and hydropower dries up alongside the rivers, so nuclear’s troubles form only part of a wider seasonal squeeze on Europe’s supply.

Investors Back Reactors Regardless

Capital markets have priced the curbs into routine upkeep. Dealmaking in Europe’s nuclear sector climbed to a seven-year high last year. Data-centre demand for constant, low-carbon electricity drove much of the rise, alongside a renewed hunger for energy security after the Ukraine and Middle Eastern shocks. 

Belgium’s parliament recently reversed its decades-old phase-out law, extending the lives of its Doel and Tihange units a decade past their scheduled retirement. In Slovakia, the fourth reactor at the Mochovce plant is set to push the country’s nuclear share to 77.5%, overtaking France as the highest proportion of any country’s electricity supply. 

Chancellor Friedrich Merz has called Germany’s exit from nuclear power a strategic mistake, one he now hopes to redress through smaller reactors.

Price Buffer Worth Keeping

The steadier case for nuclear rests in prices. France’s nuclear fleet, supplying about 70% of the country’s electricity, holds prices below levels seen in gas-fired Italy or coal-fired Germany, insulating households and industry from combustible-driven spikes. 

European Union officials attribute an added €25 billion import bill to oil and gas purchases made since the year’s disruptions began. Nuclear-heavy France has largely avoided passing the levy to its own consumers. A power source able to soften such swings earns its keep even in the summers its output briefly dips.

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