Oskarshamn nuclear power plant cleared of jellyfish cluster but biologists warn closures of this kind are becoming more common

This article is more than 6 years old

This article is more than 6 years old

A huge cluster of jellyfish forced the Oskarshamn plant, the site of one of the world's largest nuclear reactors, to shut down by clogging the pipes conducting cool water to the turbines.

Operators of the plant on the Baltic coast in south-east Sweden had to scramble reactor No 3 on Sunday after tons of jellyfish were caught in the pipes.

By Tuesday, the pipes were cleared of the jellyfish and engineers were preparing to restart the 1,400MWe boiling water reactor, said Anders Osterberg, a spokesman for OKG, the plant operator.

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

Jellyfish are not a new problem for nuclear power plants. Last year, the Diablo Canyon facility in California had to shut its reactor 2 after sea salp, a gelatinous, jellyfish-like organism, clogged intake pipes. In 2005, the first unit at Oskarshamn was turned off temporarily due to a sudden influx of jellyfish.

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

Marine biologists said they would not be surprised if more jellyfish shutdowns occurred 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 the Oskarshamn shutdown is known as the common moon jellyfish.

"It's one of the species that can bloom in extreme areas that … are over-fished or have bad conditions," said 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."

Moller said the biggest problem was that there was no monitoring of jellyfish in the Baltic sea to produce the data scientists needed for decisions on tackling the issue.