Heatwave Threatens Beznau Nuclear Plant

Switzerland is experiencing an intense heatwave that has raised the temperature of the Aare River, the primary source of cooling water for the Beznau nuclear power plant. When river temperatures remain above 25 °C for three consecutive days, the plant must be shut down to protect local wildlife and vegetation.

The Beznau facility, operating two reactors that began service in 1969 and 1971, is one of Europe’s oldest nuclear sites. In response to the rising river temperatures, the operator Axpo already reduced the output of both reactors by half on Tuesday, limiting the plant’s contribution to the national power mix.

Water drawn from the Aare River is used to cool the reactors, and after passing through the plant, it returns to the river several degrees warmer. This additional heat further elevates river temperatures, creating a feedback loop that can exacerbate the environmental impact.

Axpo has indicated that exceptions to the shutdown rule may be considered if continued operation is essential for maintaining electricity supplies, ensuring grid stability, or meeting nuclear safety requirements. However, any decision to keep the reactors online must weigh the urgent need for power against the potential harm to the river ecosystem.

If the river’s temperature falls below the critical threshold or forecasts predict sufficient cooling, the plant can be restarted after receiving approval from the relevant authorities. The situation underscores the growing challenges that extreme weather poses to aging energy infrastructure and the importance of resilient, climate‑aware operating plans.

As temperatures continue to climb across western Europe, the Beznau case highlights how heatwaves can directly affect energy production, environmental protection, and public safety, prompting operators and regulators to balance immediate power needs with long‑term ecological stewardship.