NextEra Energy's 647-MW Duane Arnold nuclear unit in Palo, Iowa, remains shut because of storms that damaged the cooling towers at the plant, NextEra spokesman Peter Robbins said Aug. 11.
The unit experienced an automatic shutdown, or scram, due to a loss of off-site power caused by high winds at 12:58 pm CT Aug. 10, NextEra said in an event report filed to the US Nuclear Regulatory Commission that day. The report did not say whether off-site power had been restored.
Robbins said mid-afternoon Aug. 11, "My understanding is that [the off-site power] is being restored now," meaning Duane Arnold was without off-site power "for approximately 24 hours."
Due to the power loss, the company declared an unusual event, the lowest of four classifications of power reactor emergencies used by NRC.
Duane Arnold was operating at 82% of capacity before it shut, the report added.
The cooling towers that were damaged "are used as part of electricity production to cool steam after it exits the turbine," but "are not required to cool critical nuclear components, including the reactor," Robbins said.
"There was some additional damage to the exterior of some buildings," but safety systems were not impacted, he said.
Duane Arnold is scheduled to permanently cease operations at the end of October.
NextEra began a gradual reduction in output in May. Previously, that power reduction was scheduled to "progress as the shutdown date approaches," NextEra has said.
However, Robbins declined to say Aug. 11 whether the unit is expected to return to service before its permanent shutdown.
NRC Region III spokeswoman Victoria Mitlyng said Aug. 11, "NRC's focus is on making sure the site continues to meet our safety and security requirements, whether it remains offline or returns to power operation. We will continue to provide safety and security oversight as the plant permanently ceases operation."
