Jellyfish Cluster Shuts Down Nuclear Reactor

A huge cluster of jellyfish has forced one of the world's largest nuclear reactors to shut down.

Operators of the Oskarshamn nuclear plant in Sweden had to scramble reactor number three on Sunday after tons of jellyfish clogged the pipes that bring in cool water to the plant's turbines.

By Tuesday, the pipes had been cleaned of the jellyfish and engineers were preparing to restart the reactor, which at 1,400 megawatts of output is the largest boiling-water reactor in the world.

All three Oskharshamn reactors are boiling-water types, the same technology used at Japan's Fukushima Daiichi plant, which suffered a catastrophic failure in 2011 after a tsunami breached the facility's walls and flooded its equipment.

Jellyfish are not a new problem for nuclear power plants. Last year the California-based Diablo Canyon facility had to shut its number two reactor after sea salp - a gelatinous, jellyfish-like organism - clogged intake pipes.

In 2005, the first unit at Oskarshamn was temporarily turned off due to a sudden jellyfish influx.

Nuclear power plants need a constant flow of water to cool their reactor and turbine systems, which is why many such plants are built near large bodies of water.

Marine biologists, meanwhile, say they would not be surprised if more jellyfish shutdowns occur in the future.

"It's true that there seems to be more and more of these extreme cases of blooming jellyfish," said Lene Moller, a researcher at the Swedish Institute for the Marine Environment. "But it's very difficult to say if there are more jellyfish, because there is no historical data."

The species that caused this shutdown is known as the common moon jellyfish.

"It's one of the species that can bloom in extreme areas that ... are overfished or have bad conditions," said Ms Moller.

"The moon jelly likes these types of waters. They don't care if there are algae blooms, they don't care if the oxygen concentration is low. The fish leave ... and the moon jelly can really take over the ecosystem."

Ms Moller said the biggest problem was that there is no monitoring of jellyfish in the Baltic Sea to produce the data that scientists need to figure out how to tackle the issue.