MuhelebergThe heatwave across Europe in late July required some nuclear plants to reduce electricity after cooling water was affected by high temperatures.

Plants in Finland, Sweden, Germany, France and Switzerland have been affected. While air temperatures have been above 90 degrees Fahrenheit (32 degrees Celsius) in many parts, water temperatures have reached 75 degrees Fahrenheit (23.8 degrees Celsius) or more. 

The Loviisa nuclear plant, which produced 10% of Finland’s power in 2017, began reducing its output on 25 July, according to chief of operations, Timo Eurasto. He said customers were not affected, because other power plants were satisfying electricity demand. Loviisa previously reduced output in 2010 and 2011, due to warm water, but Eurasto said the current heatwave has been more severe. 

Reactors in Sweden and Germany also reduced production because of cooling problems, Reuters reported. A spokesperson for Sweden's nuclear energy regulator said the Forsmark had cut energy production "by a few percentage points”.

The Muehleberg nuclear power plant in Switzerland also cut output by 10% on 27 July, due to the rising water temperature in the nearby Aare River. By law, the 390MW boiling water reactor is must reduce production once water temperatures exceed 20.5 degrees Celsius.

In France,  EDF stopped production at unit 3 (900MWe) of its Bugey nuclear plant on 28 July and reported an unplanned outage at St Alban 1 (1300MWe) because of the heatwave. EDF operates the 58 nuclear reactors that account for more than 75% of France’s electricity. It discharges cooling water into surrounding rivers and canals. This is regulated by law to protect plant and animal life, which makes necessary cuts in output during prolonged hot weather. 

A report by the Union of Concerned Scientists in 2011 warned that warmer seas could affect nuclear plant efficiency explaining that during hot periods plants need to reduce output despite increased electricity demand from air conditioning use. 

Photo: Switzerland's Muehleberg nuclear plant cut production by 10% due to rising river temperatures