According to computer simulations, the Missouri River could reach 45.5 feet sometime Sunday. At that level, the plant must be shut down.

Becker said workers were adding sandbags to the levee that protects the nuclear station and other key facilities from the Missouri River.

When the river reaches 42.5 feet, which is forecast to be Friday, the utility is required to issue a Notice of Unusual Event to the Nuclear Regulatory Commission and state and local officials.

That simply means that conditions are not ordinary, and Cooper still would be able to continue generating power.

If the river rises a foot higher, to 43.5 feet, workers will start barricading internal doorways and taking other precautions.

During the historic summerlong flood of 2011, Cooper reached the level of an unusual event notice, and sandbagged and barricaded internal doorways, but the plant was able to continue functioning.

Cooper accounts for about 35 percent of NPPD’s power.

If the plant is shut down, NPPD will be able to get power elsewhere through its own facilities or through a power-sharing network that it belongs to.