DÖTTINGEN, SWITZERLAND / EuroWire / – Switzerland’s Beznau nuclear power station shut down both reactor units after high temperatures in the Aare River limited cooling at the site. The river reached about 25 degrees Celsius during a heatwave, a level that does not allow normal cooling conditions. The shutdown followed an earlier output cut to 50 percent for both units. Operators took the reactors off the grid on Friday.
The Beznau plant uses water from the Aare River for cooling. Heated cooling water returns to the river after use. During hot weather, that process can add stress to the river system. The measure aims to protect the Aare ecosystem and keep the plant within environmental rules. The shutdown did not stem from a reported nuclear safety incident.
Axpo, the plant operator, had reduced production earlier in the week as river temperatures rose. The company said both Beznau units entered a shutdown state once the Aare reached the temperature threshold. The site sits in northern Switzerland in the canton of Aargau. It remains one of the country’s key nuclear power facilities.
River cooling limits
Beznau has two reactor units, each with a capacity of 365 megawatts. The units began operation in 1969 and 1971. The plant produces about 6,000 gigawatt hours of electricity in a normal year. That output makes Beznau an important part of Swiss power supply. Its operation also depends on river conditions during periods of high heat.
The Swiss Federal Office of Energy issued environmental rules for heated cooling water discharge in 2019. Those rules cover how the plant handles warm water returned to the Aare. They require operators to limit the river’s temperature increase after cooling water mixes downstream. Load cuts or temporary shutdowns can follow when the limit becomes hard to meet.
Heat affects power operations
The latest shutdown came during a period of intense heat across Switzerland and parts of Europe. Basel recorded 38 degrees Celsius this week, according to Swiss weather data. Warm air and lower cooling margins can affect power plants that rely on rivers. Nuclear, hydroelectric and thermal plants can all face operating limits when water temperatures rise.
Beznau also cut output during high river temperatures in summer 2025. One unit shut down on July 2 last year, and the second followed on July 3. Both units returned to full operation after the river cooled. The 2026 shutdown again shows how high river temperatures can affect Swiss nuclear power generation and environmental compliance.