Floodwaters surround nuke plant after breach

An aerial view of the Fort Calhoun Nuclear Power Plant in eastern Nebraska, surrounded by Missouri River flood waters June 24, 2011.

WASHINGTON (Reuters) - A tear on Sunday in a temporary berm allowed Missouri River flood waters to surround containment buildings and other vital areas of a Nebraska nuclear plant, but reactor systems were not affected.

The Nuclear Regulatory Commission (NRC) said the breach in the 2,000-foot inflatable berm around the Fort Calhoun station occurred around 1:25 a.m. local time.

More than 2 feet of water rushed in around containment buildings and electrical transformers at the 478-megawatt facility located 20 miles north of Omaha.

Reactor shutdown cooling and spent-fuel pool cooling were unaffected, the NRC said.

The plant, operated by the Omaha Public Power District, has been off line since April for refueling.

Crews activated emergency diesel generators after the breach, but restored normal electrical power by Sunday afternoon, the NRC said.

Buildings at the Fort Calhoun plant are watertight, the agency said. It noted that the cause of the berm breach is under investigation.

NRC Chairman Gregory Jaczko and other officials planned to visit the site on Monday.

Jaczko will also visit the Cooper Nuclear Station near Brownville, Nebraska, another facility that has been watched closely with Missouri River waters rising from heavy rains and snow melt.

But water levels in that area 80 miles south of Omaha are receding, relieving worries that water will rise around the Brownville plant.

(Reporting by Lucia Mutikani, John Crawley and Michael Avok)