Swiss nuclear power plant shuts down reactors due to heatwave

The water temperature of the river used to cool the Beznau nuclear power plant reached 25 degrees Celsius, forcing the operating company to shut down its reactors.

Swiss energy company Axpo announced on 26/6 that the Aare river's temperature reached 25 degrees Celsius for two consecutive days and showed "no sign of cooling sufficiently". As a result, the Beznau nuclear power plant in northern Switzerland, near the German border, ceased operations, shutting down both reactors.

Nuclear power plants typically use river water for their secondary cooling systems. River water is pumped through a filtration system and circulated through pipes in a condenser to absorb excess heat from the ultrapure water that cools the reactor. The warmed water is then discharged back into the river. While the river water does not directly contact the radioactive core during this process, legal regulations require that the temperature of the discharged water does not exceed permitted limits to prevent thermal shock to aquatic life.

"We are monitoring the Aare river's temperature", Axpo stated. "When the river water temperature cools or is forecast to drop to an acceptable level, the Beznau plant can plan to restart its reactors."

The Beznau nuclear power plant in northern Switzerland. Photo: AFP

This announcement comes as an extreme heatwave is affecting 150 million people across Western Europe, with temperatures exceeding 35 degrees Celsius. Temperatures in Switzerland on 26/6 broke June heat records for two consecutive days, reaching 38,8 degrees Celsius in Basel, near Beznau. On 25/6, the area also recorded 38 degrees Celsius, breaking an 80-year record.

Nuclear energy accounts for over one-third of Switzerland's electricity production. The nation has four old nuclear reactors, including two at Beznau. Reactor one began operations in 1969, and reactor two in 1971, making it one of the world's oldest operating nuclear power plants.

The heatwave's impact extends to other European countries: France also shut down two nuclear reactors on 25/6 for environmental protection, to avoid discharging excessive hot water into warming rivers. The country has recorded at least 55 drownings since the heatwave began. Germany recorded its highest temperature ever on 26/6 at 41,3 degrees Celsius in the western city of Saarbruecken, breaking the previous June record of 39,6 degrees Celsius. On the same day, the UK meteorological agency reported that the country continued to record a temperature of 37,3 degrees Celsius in the village of Santon Downham, Suffolk, marking the highest June temperature for the third consecutive day.

Data indicates that 45% of the 854 cities in Western Europe have broken or are forecast to break their historical high-temperature records from 18/6 to 30/6. Graphic: World Weather Analysis Organization

This heatwave has broken many temperature records and is causing major impacts on human health, ecosystems, agriculture, and labor productivity, according to Clare Nullis, spokesperson for the United Nations' World Meteorological Organization. Meteorological experts forecast that the heatwave is moving from Western Europe to the Balkan region, with temperatures potentially reaching 39 degrees Celsius in parts of Serbia, Bosnia, Croatia, Kosovo, North Macedonia, and Montenegro.