Floodwaters surrounded several buildings at the Fort Calhoun Nuclear Station early Sunday morning after a water-filled wall collapsed.
The plant, about 19 miles north of Omaha, remains safe, Omaha Public Power District officials said Sunday afternoon.
The U.S. Nuclear Regulatory Commission is monitoring the Missouri River at the plant, which has been shut down since early April for refueling.
The 2,000-foot berm collapsed about 1:25 a.m. Sunday due to “onsite activities,” OPPD officials said. The Aqua Dam provided supplemental flood protection and was not required under NRC regulations.
“We put up the aqua-berm as additional protection,” said OPD spokesman Mike Jones. “(The plant) is in the same situation it would have been in if the berm had not been added. We're still within NRC regulations.”
According to the NRC, the berm was eight-feet tall and 16-feet wide at the base. It was designed to provide protection for the plant's "powerblock" for up to six feet of water. Crews will look at whether it can be patched, OPPD officials said.
On Sunday, floodwater surrounded the nuclear plant's main electrical transformers, and power was transferred to emergency diesel generators.
OPPD officials said the transfer was precautionary because of water leaking around the concrete berm surrounding the main transformers.
Efforts were underway to reconnect to offsite power once all safety checks have been completed.