Duke Energy is still investigating what caused a loss of offsite power Wednesday night that automatically shut down one unit of its Catawba nuclear plant 18 miles south of Charlotte.
Duke declared an “unusual event,” the lowest of four emergency levels and one not experienced at the plant since 2006. Blasts of released steam may be heard near the plant this afternoon as the shut-down reactor continues to cool, the company said.
“We’re going to complete the investigation and take steps to make sure it doesn’t happen again” before restarting Catawba’s Unit 1, Duke spokesman Tim Pettit said. The plant’s second unit was already shut down to refuel.
Electricity from a switchyard feeding the plant lost energy just after 8 p.m. Wednesday, Pettit said, but it’s not clear where the problem occurred.
“Everything worked as designed,” he said. “Unit 1 tripped and all four (backup) diesel generators started” to supply the plant with power.
The event was declared over at 1:38 a.m. Thursday.
Unusual events can be caused by a wide variety of situations. They pose no threat to public safety but trigger a heightened state of emergency response.
Catawba declared its last unusual event in December 2006 because of a lake in a reactor’s coolant system. In May 2006, an unusual event was due to loss of offside power from an electrical relay problem in the switchyard.
The Nuclear Regulatory Commission will follow-up on the cause of Wednesday’s power loss, spokesman Roger Hannah said, but doesn’t plan to send an inspection team to the plant.