A nuclear reactor at the Oskarshamn plant restarted on Wednesday morning, after engineers managed to clear out tonnes of jellyfish.
The reactor, based on the eastern shore of Sweden, near the island of Öland, will now produce about 1,400 megawatts of power.
About half of Sweden’s electricity comes from nuclear energy. The creatures that blocked the strainers to the cooling turbines for the reactor on Sunday were moon jellyfish, which can suddenly increase, or “bloom”, in the coastal Baltic waters.
It is not the first time that jellyfish have stopped nuclear output at Oskarshamn, back in 2005, the number 1 reactor was shutdown.
“This is something we monitor continuously and depending on the current around the plant, we might need to go down in power again, we hope not of course but this siuation with the jellyfish might be for a few more weeks until the Baltic cools down more for the winter,” says the Oskarshamn plant’s managing director Johan Sveningsson to Radio Sweden.
Gothenburg University marine biologist, Lene Friis Muller says that more research needs to be done into why the moon jellyfish gather in such numbers at this time of year.
“We can’t really say if there are more now than there used to be but there are more extreme cases like this one around the world and we don’t know why,” she tells Radio Sweden.
News agency AP reports that all three reactors at Oscarshamn are boiling-water types, the same as the ones that failed at Fukushima in 2011, but that the Oskarshamn reactor is the largest boiling-water reactor in the world.