A special inspection at Duke Energy’s Oconee Nuclear Station will begin Tuesday by the Nuclear Regulatory Commission to assess the degradation of power cables on startup transformers for two of the plant’s three units.
A plant operator making routine inspections on Dec. 7 discovered a disconnected cable that should have been connected to the Unit 3 startup transformer, the NRC said. Further inspection determined that other cables linked to the Unit 1 startup transformer were in a degraded condition.
Duke spokesman Andrew J. Beckner said one of three backup transformers was not properly connected. The cable was repaired and the backup transformer was restored to standby mode.
Beckner said in addition to transformers that operate continuously to supply electricity from each of Duke’s three electrical generation units, backup transformers are also connected to each, remaining in standby mode at all times. They supply electricity to the plant in the event the unit is taken out of service and cannot provide its own electricity.
The backup transformers are part of the multiple redundancies established as part of the nuclear station’s design, Beckner said in an email. At no time was the health and safety of the public or employees impacted, he said.
“Part of our focus on safe operation is ensuring our employees regularly inspect, with a critical eye, all equipment at Oconee Nuclear Station to ensure it is reliable and operating safely, including all backup systems,” he said.
Leonard Wert, acting NRC Region II administrator, said there was not an event when the transformers were needed. “We felt a special inspection was warranted to gather more information about Duke’s response and also determine if there are generic issues that may apply to other plants,” he said.
The senior resident inspector from the Oconee plant and an inspector from the NRC’s region office in Atlanta will conduct the inspection. Another expert from Atlanta will assist in reviewing the data gathered. The team will review the circumstances surrounding the degradation and failure of the cables and the utility’s action after the conditions were identified. It will develop a timeline and review Duke’s testing and maintenance practices.
The onsite inspection will take several days. A written report should be issued within 45 days of its completion.
