The Duane Arnold Energy Center will dredge a section of the Cedar River this summer to ensure access to water from the drought-shrunken river, but won’t draw down water from nearby Pleasant Creek Reservoir.
The state’s only nuclear power plant in Palo is one of the largest water users along the Cedar River, drawing 6,000 gallons a minute. The water is used to cool steam after it has been used to generate electricity in the plant’s turbines.
Low Cedar River levels were a concern envisioned when the plant was built more than 40 years ago, because the plant can’t operate without large quantities of water. A 410-acre reservoir was constructed on nearby Pleasant Creek, so water could be discharged into the Cedar River above the plant to increase the flow rate in an emergency.
At the Cedar Rapids gauge downstream from the plant, the river level has dropped below three feet. The water discharge rate was only 21 percent of its typical August rate.
Renee Nelson, communications and public affairs manager, said the plant — which was acquired six years ago by NextEra Energy from Alliant Energy — does not now include a Pleasant Creek Reservoir drawdown in its contingency planning for drought.
“We wouldn’t do so now,” she said. “We would conservatively shut the plant down.”
Nelson said the plant requested water release from Pleasant Creek Reservoir only once, during a 1988 drought. The reservoir is a popular public recreation area managed by the Iowa Department of Natural Resources.
Nelson said the power plant has operated near capacity all summer, except when it reduced output by 5 percent for several hours at the height of last month’s heat wave. That was because of water temperatures in the river, Nelson said.
Water temperatures above 95 degrees would require a plant shutdown, Nelson said.
The plant has taken steps to protect water levels at its Cedar River intake. In 2005, the plant arranged for installation of wing dams on the river to increase water flow, so sedimentation would not fill in the river channel around the water intake.
Nelson said the record flood of June 2008 damaged the wing dams, but they were reconstructed last year.
The plant uses a recirculating cooling water system to condense steam in its turbine. Nelson said the river water is used only to replace the water that evaporates as steam from the plant’s cooling tower and isn’t used in the plant’s turbine itself.
The plant has a separate cooling system for the storage system that holds spent fuel rods. That system does not use river water.
Duane Arnold Energy Center supplies power to Alliant Energy and to members of the Central Iowa Power Cooperative and the Corn Belt Power Cooperative. The latter two are minority owners of the plant.