Waterford - As Dominion repowered the Unit 3 reactor at Millstone Power Station Wednesday, the company continued to investigate the cause of its Dec. 19 shutdown.An electrical fault forced an automatic trip 18 days ago, shutting the plant in the middle of a winter storm.

An electrical fault forced an automatic trip 18 days ago, shutting the plant in the middle of a winter storm.Early Wednesday, the Nuclear Regulatory Commission reported the reactor to be at 15 percent power on its Web site. Dominion spokesman Richard Zuercher said the unit would return to full power "over the next couple of days."

Early Wednesday, the Nuclear Regulatory Commission reported the reactor to be at 15 percent power on its Web site. Dominion spokesman Richard Zuercher said the unit would return to full power "over the next couple of days."The NRC's resident inspectors, who work at the site, monitored the repairs and the restart, said NRC spokesman Neil Sheehan in an e-mail. The Unit 2 reactor has remained at full power throughout the shutdown.

The NRC's resident inspectors, who work at the site, monitored the repairs and the restart, said NRC spokesman Neil Sheehan in an e-mail. The Unit 2 reactor has remained at full power throughout the shutdown.The company replaced a damaged circuit breaker before bringing the reactor back on line, and inspected other circuit breakers as well.

The company replaced a damaged circuit breaker before bringing the reactor back on line, and inspected other circuit breakers as well."The breaker was destroyed so we had to acquire another one," said Zuercher. "The root cause is still inconclusive and we have a team of experts investigating it."

"The breaker was destroyed so we had to acquire another one," said Zuercher. "The root cause is still inconclusive and we have a team of experts investigating it."Factors that may have contributed to the destruction of the circuit breaker included evidence of water intruding into the breaker's "shroud," a protective, normally waterproof metal covering. The breakers are located outside of the building that houses the turbine used to generate electricity, Zuercher said.

Factors that may have contributed to the destruction of the circuit breaker included evidence of water intruding into the breaker's "shroud," a protective, normally waterproof metal covering. The breakers are located outside of the building that houses the turbine used to generate electricity, Zuercher said.One of the breaker's pressure release valves also failed and "may have exacerbated the damage," he said.

One of the breaker's pressure release valves also failed and "may have exacerbated the damage," he said. For competitive purposes, the company does not announce exactly when the reactor is expected to return to service.

For competitive purposes, the company does not announce exactly when the reactor is expected to return to service.