RICHMOND, SEPT. 1 -- The U.S. Nuclear Regulatory Commission today cited Virginia Power for three minor safety violations after an investigation into the July 15 rupture of a steam generator tube at the North Anna nuclear power plant.

In a related development, a senior Virginia Power executive announced that the utility will spend at least $6.5 million in repairs and safety improvements at North Anna; the company's earlier estimate was $1 million. Unless state utility regulators rule otherwise, those costs almost certainly will be factored into the rates Virginia Power customers pay for electricity.

William L. Stewart, a vice president who oversees the utility's nuclear operations, said extensive testing on the ruptured tube indicates that the break was caused by metal fatigue -- wear and tear associated with constant vibration -- rather than by corrosion.

Stewart characterized the violations cited by the NRC as "not particularly significant." Still, he said they were serious enough to warrant an aggressive new pipe inspection program at North Anna's disabled Unit 1 reactor and its sister plant, Unit 2, both about 90 miles southwest of Washington.

"We don't get 'Atta boys' for having a tube rupture," Stewart told reporters at a briefing at Virginia Power headquarters here. "We had the problem. We wish to hell we didn't."

While no one was injured in the North Anna incident, in which small amounts of radioactivity were released into the atmosphere, that episode and the nonnuclear accident that killed four workers at Virginia Power's Surry nuclear power plant in December renewed troubling questions about safety in the nation's aging nuclear facilities.

This year, the NRC blamed faulty maintenance for the failure of a steam valve at the Surry plant, which triggered the rupture of a pipe that sprayed six workers with scalding water and steam. However, the NRC did not impose a fine with the single safety violation.

Nor did federal regulators impose a fine today in releasing a 41-page inspection report on the North Anna incident, an analysis that described Virginia Power's handling of the tube rupture as "outstanding."

"The operator tripped the plant, isolated the leak and brought the plant to cold shutdown in seven hours," said the NRC report, which was issued from the agency's regional office in Atlanta. "This contributed to a negligible release {of radiation} to the environment," the report added.

The three violations, which Stewart said were in no way related to the cause of the rupture, included the utility's failure to establish safety guidelines for operating a steam generator with a certain kind of plug for leaks, the failure of plant workers to notify a health team when they received a radiation alarm shortly after the rupture, and the failure to perform "adequate" performance checks on radiation monitors.

Also, the NRC listed nine "weaknesses" that it said "need to be resolved," including tardy and inaccurate communications among some plant workers and some emergency procedures that need to be refined.

Stewart said Virginia Power will correct "all problem areas noted by the NRC," none of which requires "fundamental, significant" changes to company policy, he added.

Stewart said the company has launched a $1 million program to correct the stress and vibrations that apparently caused the tube to rupture at North Anna, and he said the remaining costs of the incident -- the time, salaries, materials and research needed to upgrade some of the reactor components -- will be an additional $5.5 million.

The utility, which serves 1.4 million residential and commercial customers in the state, says it plans to restart North Anna Unit 1 at the end of this month and Unit 2 in late October.