Heat and drought force nuclear plants to cut power

Heat and drought have forced nuclear power plants in Europe to reduce output, including in Switzerland, but the reasons differ depending on the technology, SRF reported.

In Switzerland, the temperature of the Aare River determines operations at Axpo’s Beznau I and II nuclear power plants. When the water reaches 25 degrees Celsius, Axpo reduces their output or shuts them down completely. This has happened several times since June.

The plants are cooled directly with river water. The water is warmed during the process before being returned to the Aare. Further heating could harm animals and plants in the already warm river, so electricity production is reduced for environmental protection reasons.

In Hungary, the Paks nuclear power plant recently also reduced its electricity production. The plant is cooled with water from the Danube, which is currently at a record low level. The reduced water supply means there is not enough water to maintain cooling, so output has been cut for safety reasons.

Different technology, different risks

Critics of nuclear power see the examples of Beznau and Paks as further evidence that nuclear energy is not a reliable source of electricity. They argue that heat and drought expose the limits of the technology.

Political and scientific supporters of nuclear power reject that argument. For them, the issue is primarily a question of using the appropriate technology. The debate has also appeared in social media comments by Nils Epprecht, managing director of the Swiss Energy Foundation, which opposes nuclear power, and Annalisa Manera, a professor of nuclear safety at ETH Zurich.

The type of plant determines whether operations must be reduced during heat and drought. Beznau’s reactors belong to the first generation of nuclear power plants and are cooled with river water. At full operation, they require around 40,000 litres of river water per second for cooling.

Newer plants in Gösgen and Leibstadt, by contrast, are cooled by the surrounding air and are far less dependent on water temperature or water levels. They still use river water for cooling, but in significantly smaller quantities than the Beznau plants. Leibstadt currently takes around 2,900 litres per second from the Rhine, according to its operator. Most of that water is returned, with only evaporation reducing the amount.

The technological difference is visible in the plants’ cooling towers, which release heat as a prominent plume of water vapour at Leibstadt and Gösgen.

A scenario similar to the one at Paks is therefore unlikely at Leibstadt or Gösgen. The Rhine currently carries around 400,000 litres per second at the Rheinfelden monitoring station downstream from Leibstadt. That is well below the long-term August average of 1.2 million litres per second, but even at this exceptionally low water level, Leibstadt is still far from having to stop operations because of a lack of water. The plant operator says the power station has never had to do so because of the water level.