North Anna reactor shut down because of leaks

One of the two nuclear reactors at Dominion Virginia Power's North Anna Power Station remained shut down yesterday 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 about 45 miles northwest of Richmond.

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 yesterday.

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-perminute leak was detected in the pipe, Zuercher said. The pipe leaked for four minutes before it was shut off, he said.

The heat exchanger pipe did not leak onto the reactor floor, Zuercher said, but "into a pipe designed to move [the flow] into a water storage tank."

The utility began ramping down Unit 1 from service at 5:18 p.m. Friday.

By yesterday 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 online in the near future.

Unit 2 at the North Anna station, which is located in Louisa County on Lake Anna, remained operating at full power.

The Unit 1 malfunction means two of Dominion's four commercial nuclear reactors in Virginia are either shut down or operating at less than full capacity. One of the two units at the utility's Surry Power Station along the James River is being ramped down for a planned refueling.

Contact Joe Macenka at (804) 649-6804 or .