The Attack of the Jellyfish

An influx of tiny, jellyfish-like creatures last week forced the shutdown of one of the reactors at the Diablo Canyon nuclear power plant in California. The creatures are called “Salp” and they can be held in the palm of a hand, although they can grow up to four inches in length. They maneuver in the water just like squid by pumping water through their gelatinous bodies and ejecting it in a stream.

Because of an influx of the photoplankton they feed off, millions of the little critters were swarming in the waters at Diablo Canyon, which sits on an 85-foot cliff overlooking the Pacific Ocean. Some hapless Salp were getting sucked into the plant’s intake structure and pulled up against screens that protect the condensers and heat exchangers from marine debris.

Some of creatures passed right through the screens within the intake structure and passed right through the plant; but others got caught up against the metal mesh, clogging the screens. The plant’s Unit 1 has been shut down since April 22 for a refueling outage that is expected to last several weeks. On April 23, operators reduced power in the Unit 2 reactor to 15 percent as a protective measure. The Salp don’t pose a danger to any of the plant’s safety systems, but operating at lower power minimizes the impact of a shutdown, if one becomes necessary.

On April 25, it did. The buildup of Salp in the intake prompted operators to manually shutdown the reactor. All systems functioned as designed and no unexpected equipment issues were encountered. Unit 2 restarted last weekend.

Victor Dricks
Public Affairs Officer, Region IV

Author: Moderator

Public Affairs Officer for the U.S. Nuclear Regulatory Commission

3 thoughts on “The Attack of the Jellyfish”

  1. In Australia the jellyfish can be fatal .. Interesting to see they cause problems all over the world.

  2. I wondered why these were so intrusive. I searched on <<>> and it became obvious. These organizms chain up and stick together.

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