Huge Nuclear Reactor Shut Down by Jellyfish Swedish plant is back in business after massive clog By John Johnson, Newser Staff Posted Oct 1, 2013 5:15 PM CDT 18 comments Comments File photo of moon jellyfish. (AP Photo/Lionel Cironneau, File) (Newser) – The Oskarshamn power plant in Sweden has one of the biggest nuclear reactors in the world, but it's apparently no match for tiny jellyfish. Tons of moon jellyfish clogged the reactor's intake pipes from the ocean over the weekend, forcing the plant to shut down, reports Popular Science. (Not so comforting tidbit: It's a "boiling-water" type reactor, same as at Fukushima.) All was back to normal by today, however. The jellyfish were in a "bloom" cycle, a phenomenon that produces huge numbers at once, and a marine biologist tells Phys.org that "more and more of these extreme cases of blooming jellyfish" are cropping up. Moon jellyfish in particular thrive in areas that have been overfished and consequently overrun by algae blooms. "They don't care if the oxygen concentration is low," said the biologist. The fish move out, and the jellyfish move in. A similar clog happened last year at California's Diablo Canyon plant, though the culprit then was technically sea salp.