NEW YORK, Sept 27 (Reuters) - Storm Helene forced major U.S. electric utilities to shut or slow power plant operations on Friday, with Southern Co (SO.N) , opens new tab taking one of its Georgia nuclear reactors offline and Duke Energy halting output from two coal-fired generating units.

Helene, which left more than 3.5 million homes and businesses without power as it weakened to a tropical storm and moved north, downed power lines and battered other parts of the region's electrical grid.

Southern Company also reduced output from another nuclear reactor at its Edwin I. Hatch Nuclear Power Plant in Georgia after the storm damaged the area's broader power system, the company told Reuters on Friday.

The nuclear plant, which is jointly owned by Southern Co subsidiary Georgia Power, Oglethorpe Power Corporation, Municipal Electric Authority of Georgia and Dalton Utilities, was not significantly harmed by the hurricane, the company said.

"However, the power grid experienced significant damage from the storm and, to maintain grid stability, we adjusted operations at Plant Hatch," Georgia Power spokesperson John Kraft said.

Unit 1 was taken offline and Unit 2 is running at reduced power, Kraft said, adding that the company's larger generation fleet would be able to meet its customers' power demand. The company did not disclose a timeline for restoring full operations.

Duke Energy (DUK.N) , opens new tab, meanwhile, took two coal-fired power units offline at its Crystal River energy complex in Florida in preparation for Helene, the company told Reuters on Friday.

"This will help prevent equipment damage to ensure the units are available to operate for our customers after the storm," company spokesperson Jennifer Garber said.

Tens of thousands of utility workers have been mobilized to assess damage and make repairs to the southeast electrical system, which was beset with high winds and flooding.

Duke Energy (DUK.N) , opens new tab, which primarily supplies power in the Carolinas, has said it has been aggressively moving water through the Catawba-Wateree River Basin in North and South Carolina earlier this week in anticipation of Helene's arrival.

Even with these preparations, Duke warned that lake levels are expected to rise sharply and may not be able to store excess water from the expected rain and increased inflows from upstream, possibly leading to historic flooding in several areas.

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https://www.reuters.com/business/energy/southern-co-shuts-georgia-nuclear-reactor-wake-hurricane-2024-09-27/