SAN LUIS OBISPO, Calif. (AP) — An overwhelming number of jellyfish-like creatures clogging seawater intake screens forced operators on Thursday to shut down the Unit 2 reactor at the Diablo Canyon nuclear power plant, Pacific Gas & Electric officials said.
Both reactors at the central coast plant are now offline.
Unit 1 was shut down earlier this month for scheduled refueling. The twin-reactor San Luis Obispo County nuclear plant provides enough power for more than 3 million homes in Central and Northern California.
Grid managers at the California Independent System Operator say electricity shortages aren't expected because of ample reserves and cool weather.
The Unit 2 reactor was reduced to about 25 percent earlier this week because of salps entering the beach intake structure.
Salps are small barrel-shaped plankton tunicates similar to jellyfish. They can grow up to 4 inches long and often link together and float in the water in long ropelike formations.
Southerly winds began blowing salps into the plant's cooling water intake cove on Tuesday and plant operators noticed water pressure changes, indicating the creatures were beginning to clog the rolling screens in front of the intake.
Power was then drawn down.
"I've been very pleased with how staff has reacted to this by putting safety first," Pacific Gas & Electric Co. chief nuclear officer Ed Halpin said.
The Unit 2 reactor at the plant was shut down Thursday night because of the clogged screens, the utility's plant spokesman Tom Cuddy said Friday.