A Swedish nuclear reactor was restarted on Wednesday following a three-day closure caused by a build-up of jellyfish in a cooling system, according to the operators.
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The incident occurred in reactor 3 at Oskarshamn power station on the Baltic Sea coast, which is run by OKG, a subsidiary of the German electricity company EON.
"It was a larger amount than we had ever seen. Every autumn we have to get rid of jellyfish, but not that many," OKG spokeswoman Emmy Davidsson told AFP.
The company announced on Sunday that the reactor -- Sweden's largest with a 1400 MW output and the world's largest boiling water reactor -- was "manually shut down due to a large amount of jellyfish present at the cooling water intake".
The closure did not lead to power outages.
On Wednesday the company said in a statement that the reactor was restarted once the jellyfish had been cleared from the system and the numbers of new arrivals had subsided.
"Furthermore we have reinforced our clearing system to deal with any future jellyfish invasions," wrote OKG.Ironies abound: Jellyfish are proliferating largely thanks to climate change, and nuclear power is supposed to be a good way to slow the release of CO2. It's a little unsettling to think that something as negligible as a jellyfish could put a reactor at risk. Earthquakes and tsunamis, OK, we see the threat. But jellyfish?