The Oskarshamn Nuclear Power Plant in Kalmar County on Sweden's southeast coast was forced to close one of its reactors on Sunday 29 October 2013, after a bloom of Jellyfish blocked one of its intake pipes, preventing cold water from entering the turbine. The Oskarshamn Plant is a boiling water reactor, in which heat from the nuclear fuel is used to boil water, which then drives a steam turbine. The water is then cooled down by heat exchange with seawater that is pumped into the plant and then recycled. The intake which was blocked was used to bring in water for this cooling process, which is then returned to the sea; this water is never brought into direct contact with the nuclear fuel. This is essentially the same type of nuclear reactor as the Fukushima Daiichi Plant in Japan, which was destroyed by a tsunami in 2011, though the Oskarshamn Plant is in a rather more stable geological setting.
The Oskarshamn Nuclear Power Plant. Wikimedia Commons.
This is not the first time that Oskarshamn has been closed down by a Jellyfish bloom, it was previously forced to close one of its reactors for similar reasons in 2005. Other reactors dependent on external water for cooling have suffered similar problems, for example the Diablo Canyon Power Plant in California was forced to close a reactor in 2012 due to a bloom of Salps (gelatinous macroplankton superficially resembling Jellyfish, but more closely related to Vertebrates) blocked its intake pipes and a number of hydroelectric and nuclear plants with freshwater intakes in the US have been forced to make repeated shutdowns due to pipes being blocked by the invasive Zebra Mussel (Dreissena polymorpha).
Jellyfish blooms have been linked to overfishing and marine pollution, which eliminate potential predators of Jellyfish allowing their numbers to explode. While this is undoubtably a factor in these events, Jellyfish do reproduce extremely rapidly under the correct conditions, and explosive population blooms are a part of their natural population cycle, so it is unlikely that such incidents could ever be completely eliminated.
The approximate location of the Oskarshamn Nuclear Power Plant. Google Maps.
The Oskarsham Reactor reopened on Tuesday 1 October, after several tonnes of Jellyfish had been removed from its intake pipes.
See also Punctatus emeiensis, not a Cnidarian after all? A new species of Hydrozoans from British Columbia and The mysterious ebb and flow of Jellyfish populations.
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