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Sweden faces its own shutdown: Cause? Jellyfish

Revenge of the sea? Thousands of moon jellyfish take down the world's largest nuclear reactor.

Found in most ocean waters, moon jellyfish feed on plankton and can grow to be up to 16 inches across.
Luc Viatour/Wikimedia

As government Web sites in the US go dark, the National Zoo panda cam shuts off, and NASA's AsteroidWatch tweets fall silent, spare a thought for poor Sweden.

It's grappling with its own shutdown, one that's threatening its electricity supply. A nuclear power plant that provides 10 percent of the county's power has been operating at reduced capacity.

The culprit? Not bickering politicians, but waves of jellyfish that flooded the plant's water intake pipes.

Specifically, tons of moon jellyfish besieged the Oskarshamn nuclear plant in southeastern Sweden on Sunday, forcing a shutdown of its unit 3 reactor.

The 1,400-megawatt boiling-water reactor is the largest in the world, according to operator OKG. It's similar to the ones that suffered catastrophic meltdowns at the tsunami-hit Fukushima Daiichi plant in Japan in 2011.

By Tuesday, workers at the Oskarshamn plant had removed the jellyfish from the pipes, which take in water to cool the turbines. A restart of the reactor was expected.

A real-time display of output from the plant's three reactors shows 385 megawatts from unit 1, zero at unit 2 while it undergoes regular maintenance, and zero at unit 3 due to the jellyfish.

"The function of the cooling water in the condenser is to cool down the steam so that it is reformed in to water again, and subsequently brought in to the reactor vessel," OKG said in a release. "This cooling water has no connection to the cooling of the reactor vessel."

"It's true that there seems to be more and more of these extreme cases of blooming jellyfish," Lene Moller, a of the Swedish Institute for the Marine Environment, was quoted as saying by

"But it's very difficult to say if there are more jellyfish, because there is no historical data."

This isn't the first time that Oskarshamn has been sidelined by jellyfish. But they're only the latest woe at the plant. Unit 3 has experienced a number of problems recently, including leaking cooling water in the generator.

"On 1 September, a control valve in the conventional turbine system caused the initial shutdown of the operation at O3," OKG said. "This was followed by problems with another control valve in the turbine plant and a failure in the protective equipment of the facility's transformers."

Jellyfish don't mix well with nuclear power plants, but they do make for relaxing viewing. Check out the tranquil dance of these marine creatures in the vid below.

(Via Popular Science)