Beznau nuclear plant returns to full operation after heatwave shutdowns

Beznau is fully operational again after a summer of forced interruptions. Axpo said on Friday that Reactor 2 at the nuclear power plant in northern Switzerland returned to the grid on Thursday and should reach full capacity within approximately two days. Reactor 1 had already resumed operations on August 21.

The restart restores both of Switzerland's oldest operating reactors at a moment when heatwaves have exposed a practical vulnerability in Europe's nuclear fleet. The Aare River, which supplies cooling water to Beznau, reached unusually high temperatures during the summer. Operators shut the plant in June and again in July as the heat affected operating conditions.

Reactor 2 also spent part of the period offline for planned refuelling. The outage began on August 4, and technicians replaced 20 of the reactor's 121 fuel assemblies. That work was completed before the unit was reconnected.

For Switzerland, the return matters beyond one site in the canton of Aargau. Nuclear power produces just over one third of the country's electricity, and Beznau's two reactors cover around one tenth of Swiss electricity demand. Their return adds capacity to a system that has had to manage both extreme weather and scheduled maintenance.

A hotter Aare forced operators to interrupt production twice. Nuclear reactors generate heat through fission, then use that heat to produce steam and electricity. The plant must continuously remove residual heat through its cooling system. Beznau draws on the Aare River, a major waterway that drains nearly half of Switzerland before flowing into the Rhine.

During the June and July heatwaves, the river became unusually warm. That reduced the margin available for cooling operations and led to temporary shutdowns. The same pressure affected several nuclear power plants elsewhere in Europe, where operators either reduced output or stopped units during the hot weather.

The interruptions show how river-based nuclear facilities are tied to local environmental conditions. A reactor can remain technically ready while the surrounding water system limits how much heat the plant can safely manage. High temperatures can therefore affect electricity production even when demand is rising because households and businesses use more power for cooling.

Beznau's experience also gives Switzerland a concrete example of climate-related operational risk. The source report does not identify a permanent change to the plant's operating limits, and Axpo has not announced a new long-term cooling system. For now, the reactors have returned as the Aare has cooled enough to support normal operations.

Reactor 2 combined a planned maintenance outage with an unplanned summer challenge. Axpo took the unit offline on August 4 for refuelling, a routine part of nuclear plant operation. Workers replaced 20 of 121 fuel assemblies in the reactor core, then carried out the work needed to return the unit to service.

Reactor 1 came back online on August 21. Reactor 2 followed on Thursday, after the refuelling outage and the heat-related interruptions that had affected the site earlier in the summer. Axpo said the unit would gradually increase output and reach full capacity in about two days, rather than instantly returning to maximum generation.

That staged restart reflects the demands of bringing a nuclear reactor back to power. Operators reconnect the unit to the grid, raise output progressively and monitor the plant as it transitions into normal operation. The process also gives the electricity system a predictable flow of additional supply.

The timing matters for the national grid. Switzerland is restoring a significant source of low-carbon generation while Europe continues to manage hotter summers and more volatile energy conditions. Beznau's return does not erase the need for other forms of generation or cross-border electricity trade, but it removes one major source of uncertainty created by the summer outages.