‘Unusual event’ keeps reactor down at North Anna

One of the two nuclear reactors at Dominion Virginia Power’s North Anna power station remained shut down Monday because of what the U.S. Nuclear Regulatory Commission called “an unusual event.”
Control-room operators manually shut down Unit 1 late last Friday afternoon after two leaks were detected in water pipes at the reactor in Louisa County.
While the leaks were classified by the NRC as unusual, the federal agency and Dominion also said they were not considered an emergency.

“There was no threat to station employees or the public as a result of this incident,” Dominion spokesman Richard Zuercher said Monday.
Zuercher said a pinhole leak was detected in a weld in the reactor purification system shortly after 4:30 p.m. Friday.
“The leak was very small and could be compared to more of a vapor mist than dripping water,” he said.
The original plan was to divert water from the reactor purification system and repair the weld in less than 60 minutes, a window that would have allowed the utility to keep Unit 1 running without interruption, Zuercher said.
But when operators began diverting water from the reactor purification system into a backup heat exchanger pipe, a 15-gallon-per-minute leak was detected in the pipe, Zuercher said. The pipe leaked for four minutes before it was shut off, he said.

By Monday afternoon, the weld had been repaired and the utility was close to completing repairs to the heat exchanger piping, which helps remove heat from the reactor’s water system.
Zuercher said the utility hoped to have Unit 1 back on line soon. Unit 2 remained at full power.