Jellyfish Swarm Forces EON to Shut Sweden’s Biggest Reactor

EON SE shut down Sweden’s biggest nuclear reactor after a swarm of jellyfish blocked the cooling water inlet at the reactor on the Baltic coast.

It’s the first time the 1,400 megawatt Oskarshamn-3 unit has been closed by jellyfish, Anders Oesterberg, a spokesman for EON, said by e-mail today. The reactor, which makes up 5 percent of Sweden’s power, is scheduled to restart tomorrow and reach full power Oct. 3, EON said in a Nord Pool Spot AS filing.

“This situation is caused by a huge amount of jellyfish, just one is definitely not enough to cause problems,” Oesterberg said from Oskarshamn, Sweden. “The last time this happened was in August 2005, when we had to shut down Oskarshamn-1 because of a jellyfish invasion.”

Jellyfish have caused similar outages from Scotland, where the creatures forced Electricite de France SA to halt its Torness reactor in 2011, to Florida where NextEra Energy Inc. had to shut its Lucie 1 reactor in the same year. Global warming and overfishing has led to more plankton in the Baltic Sea, leading to a boom in jellyfish populations, according to German environment protection group BUND.

The marine creatures are part of the genus Aurelia, according to EON’s Oesterberg. Known as moon jellyfish, they have pale translucent bodies, are found mainly in coastal areas in Europe and North America and may grow as large as 40 centimeters (16 inches) in diameter, according to the online edition of the Encyclopaedia Britannica.

Output Halt

Oskarshamn-3, located about 340 kilometers (211 miles) south of Stockholm, was halted on Sept. 8 for maintenance and scheduled to resume output Sept. 27, according to a company filing. EON, Germany’s biggest utility, owns 55 percent of the plant, which was commissioned in 1985. Fortum Oyj of Finland owns the rest.

“The aim is to slowly start a couple of the cooling water pumps in order to drain the inlet pond of jellyfish and see that they are all distributed back to the sea,” Oesterberg said. “When the amount of jellyfish is reduced to an acceptable level, we will be able to restart production.”