Jellyfish jam forces reactor shutdown

Nearly 1,000 jellies swarm a system designed to keep debris from entering the cooling water at a nuclear power plant, surprising operators

David Sneed
San Luis Obispo Tribune
10/23/2008

A swarm of nearly 1,000 jellyfish floated into the cooling water cove at Diablo Canyon nuclear power plant Tuesday evening, forcing operators to take one reactor offline and reduce the other to half power.

Plant operators shut the unit down at 8:51 p. m. Tuesday after the mass of moon jellies clogged the plant’s cooling water intake screens, impairing the ability of pumps to circulate enough cooling water through the system.

Plant operators planned to begin returning the unit at half power to full power Wednesday night.

However, the other unit will stay shut down into today as plant workers perform more maintenance and tests.

Divers inspected the intake structure early Wednesday morning and removed the jellies from a rack of bars and a rolling screen that prevent debris from entering the cooling water system.

Plant workers are also inspecting equipment to see if the jellyfish caused any damage, said Sharon Gavin, plant spokeswoman.

Plant operators often ramp the plant down in the fall when the first large swells of the season clog the intake structure with kelp.

But there were no large swells and the mass of jellyfish took operators by surprise, Gavin said.

Other plants that use ocean water for cooling have had problems with jellyfish, but this is the first time jellies have caused a shutdown at Diablo Canyon, which dates to the mid-1980s, Gavin said.

Moon jellies have been unusually prolific off the Central

Coast this year.

Hundreds have washed up on local beaches. Moon jellies look like gelatinous, translucent blobs when they wash up on the beach.

Jellyfish were still coming into the intake cove on Wednesday, but not nearly in the numbers they were Tuesday night, Gavin said.

Marine biologists say conditions in the ocean this year have been conducive for jellyfish.

When conditions such as water temperature and currents combine with enough food in the water in the form of algae, jellyfish populations can explode.

The nuclear plant circulates billions of gallons of seawater daily through its cooling system in order to condense steam that has powered the plant’s two huge electrical generators...

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Reach David Sneed at 781- 7930.