Derecho Damage Results in Early Retirement of Duane Arnold Nuclear Power Plant

The Duane Arnold Energy Center (DAEC, Figure 1)—a 615-MW nuclear power plant located in Palo, Iowa—will reportedly not restart after high winds caused extensive damage to the station’s cooling towers. The plant owner, NextEra Energy Resources, had planned to retire the unit on Oct. 30, but after assessing damage caused by an Aug. 10 derecho, the company decided to accelerate the retirement process.

1. The Duane Arnold Energy Center is located in Palo, Iowa, approximately nine miles northwest of Cedar Rapids. It is bordered by cornfields of neighboring farms and the banks of the Cedar River. The cooling towers are visible on the left of this image. Courtesy: NextEra Energy Resources

“[O]ur evaluation found that replacing those towers before the site’s previously-scheduled decommissioning on Oct. 30, 2020, was not feasible,” NextEra Energy Resources said in a statement published by KGAN, the CBS-affiliated television station based in Cedar Rapids, Iowa.

DAEC’s reactor is licensed with the U.S. Nuclear Regulatory Commission (NRC) to operate until Feb. 21, 2034, but NextEra Energy Resources announced in July 2018 that it had struck a deal to shorten a power purchase agreement the company had with Alliant Energy, which would allow it to close the station by the end of 2020. Prior to the storm, NextEra Energy Resources had been working with employees to begin the transition process, offering early retirements, transfers to other jobs within the company, or the opportunity to stay at the facility to assist with the decommissioning. Those options remain intact, a spokesperson told local reporters.

The National Weather Service defines a derecho as “a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms.” Although a derecho can produce destruction similar to the strength of tornadoes, the damage typically is directed in one direction along a relatively straight swath. By definition, if the wind damage swath extends more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length, then the event may be classified as a derecho.

Wind speeds of 70 mph were prevalent during the August 10 storm, but wind speeds up to 126 mph were recorded in eastern Iowa. More than 95% of residents in Linn County, Iowa, lost power due to infrastructure damage during the derecho. DAEC, which is located in Linn County, declared an “Unusual Event” at 12:58 p.m. central time on August 10 due to a loss of offsite power. The event resulted in an automatic scram, which is an immediate insertion of the control rods to shut down the reactor. The unit was operating at 82% power at the time.

Operators submitted a report to the NRC within an hour of the event, noting damage on site, but stating the reactor building was “intact.” The plant was operating both of its standby diesel generators at the time. No problems that would affect reactor safety were reported.

NextEra Energy Resources plans to decommission the plant using the NRC’s SAFSTOR method. Under that scenario, the facility is placed and maintained in a condition that allows it to be safely stored and subsequently decontaminated (deferred decontamination) to levels that permit release for unrestricted use. The company has up to 60 years to complete the decommissioning process using SAFSTOR.

Aaron Larson is POWER’s executive editor (@AaronL_Power, @POWERmagazine).

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