Emergency generators powered the plant until an off-site power supply was connected Sunday afternoon, according to OPPD.

Details do count, even if I agree that the story is about underestimated risks. The latest is that the AquaDam berth was damaged not by the flood but human interference:

Added flood protection at Nebraska nuclear plant fails | Iowa Independent

Workers with Omaha Public Power District, owners and operators of Calhoun, had placed a massive AquaDam around the structure and its other flood protection systems. The AquaDam, a tube structure filled with water that was eight-feet tall and 16-feet wide, was punctured early Sunday morning during onsite work.

"Some mechanical equipment tore the side of the dam," Victor Dricks, Region 4 spokesman for the Nuclear Regulatory Commission, told The Iowa Independent Monday by phone. "As a result, the plant switched to emergency power for a period of a about 12 hours."

NRC inspectors were onsite when the incident occurred, and flood waters rushed auxiliary and other buildings at the site. The power supply was cut because water infiltrated the plant's main electrical transformers. Power has since been switched away from emergency generators and to an off-site power supply.

Keeping power at the plant is critical since the reactor core has been refueled and spent fuel remains in a cooling pool. Dricks said the failure of the dam did not adversely impact either the core or the cooling pool. Dry cask storage of spent fuel has long been exposed to the flood waters and, as Dricks told The Iowa Independent last week, poses no risk.

Other, more solid berms were located inside the area also being protected by the AquaDam. Those protections are holding with minor seepage and, of course, additional rainfall being pumped away from the structure and back into the river.