Nuclear Power’s Green Claim Tested by Europe’s Heatwaves

The June-July 2026 heatwave that dried Europe’s major rivers forced temporary shutdowns or output reductions at nuclear sites in France, Hungary and Romania. Nuclear reactors need large cooling supplies—The Nuclear Energy Institute estimates 1,514–2,725 litres of water per MWh, amounting to hundreds of gigalitres annually. Without reliable water, reactors risk overheating and possible core damage, a risk that prompted the recent curtailments.

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While nuclear generation emits little CO2 at the point of production, experts note that the “bulky concrete structures” of reactors embed substantial carbon, and uranium mining adds further emissions. Dr Bettina Wittneben, a lecturer at Oxford’s Saïd Business School, stresses that waste disposal and decommissioning must also be counted in the carbon budget.

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In 2025 the EU generated 652 TWh of electricity from nuclear—23.3 % of the bloc’s total, outpacing solar (13.1 %) and wind (17.1 %). France supplied 392 TWh, with 68.8 % of its domestic electricity from nuclear. Other contributors included Spain (54.1 TWh) and Sweden (46.7 TWh). By contrast, Germany ceased nuclear generation on April 15, 2023, after shutting its last three reactors, a move described by Chancellor Friedrich Merz as a “grave strategic mistake.” In 2025 wind and solar together provided 44 % of Germany’s electricity, while coal fell to 21 %.

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EU Climate Action Commissioner Wopke Hoekstra has urged member states to lean on nuclear as part of the bloc’s energy transition. Dr Wittneben counters that the real challenge in high-renewables systems is not generation capacity but timely access to electricity, and that nuclear’s inflexibility can exacerbate “Hellbrise” – periods of excess renewable output and negative prices.

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• “In the high-renewables systems of Europe, the problem is increasingly not how to generate more electricity but how to access it when and where it’s needed,” — Dr Bettina Wittneben

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• “The bulky concrete structures mean that it has a large amount of embodied carbon and, of course, it is not a renewable energy as it requires the mining of uranium, bringing with it carbon costs in terms of extraction and transport,” — Dr Bettina

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• “This is also the narrative of fossil fuel advocates, who present fossil gas as the saviour of the baseload, or the electricity that is available when renewables fall short,” — Dr Wittneben

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