Waterford - Dominion violated federal requirements five times over the past three months while operating Millstone Power Station, according to a quarterly inspection report from the Nuclear Regulatory Commission.

While the issues typically did not have "potential safety consequences," willful aspects, or an impact on the NRC's ability to regulate the plants, the handling of these procedural problems and equipment malfunctions should have been foreseen, corrected and prevented, the inspection report states.

In the jargon of the industry, the incidents are considered to be "of low safety significance but more than minor" because they could have been avoided. In each case, plant operators failed to rely on "conservative assumptions" and "err on the side of caution" in decision-making, according to the report and NRC Spokesman Neil Sheehan.

Since two of these cases involved unplanned plant shutdowns, or trips, Millstone's two reactors are closer to triggering additional oversight from the NRC, Sheehan said.

Performance indicators, which are not a part of this inspection process, but run parallel to it, track a "rolling average" of the number of unplanned shutdowns per previous 7,000 hours of operation. So far, the performance indicators are labeled "green," meaning they are minor. An average of more than three per reactor would take the performance indicators from "green" to "white," Sheehan said.

"Because of the shutdowns they've experienced, both of the plants are very close to the point where, if they have a shutdown anytime soon, they could go from 'green' to 'white' and get more oversight from us," Sheehan said.

The Unit 2 reactor is at 2.9 and the Unit 3 reactor is at 2.8, according to documents provided by Sheehan.

"At Millstone, we're focused on safe, reliable operations," Dominion Spokesman Ken Holt said. "We're not satisfied with our performance. We have taken steps to prevent (events like these) from happening again. We've done thorough reviews ... to see if there are any common threads, and we're pursuing action to prevent those things from happening again."

The five violations, for which Dominion is taking or already has taken corrective action, include:

Between May 27 and June 1, operators at Unit 3 took five days instead of eight hours to report the malfunction of exhaust dampers, or vents, to the NRC, even though immediate steps were taken to correct the situation. The vents would not close, creating a breach in the backup system used to vent air from buildings next to the containment area, where the reactor core is located, the report states. The situation didn't result in any unusual radioactive release of any kind, Sheehan said.

"We believe it's essential that they report these kinds of discoveries to us within the required time period," Sheehan said.

On May 17, despite having previously identified problems dating back to 2002 with control of Unit 3 feedwater regulating bypass valves, the valves were oscillating, leading steam generator water levels to fluctuate. The plant tripped as a result.

"The cause was reasonably within Dominion's ability to foresee and correct, and should have been prevented," the inspection report states.

On May 1, Unit 3 operators neglected to service pumps used in the reactor cooling system in a way that would keep the system cool, Sheehan said. One of the pumps began to overheat and vibrate and was almost damaged as a result. Other pumps were still operating, but the work process "was insufficiently robust to ensure" proper cooling was being supplied to other critical equipment, the report states.

On March 17, operators thought they had figured out what caused a 10-second surge in one of several Unit 2 emergency diesel generators, Sheehan said, but it happened again on May 12, rendering that particular emergency diesel generator inoperable. Operators could have identified the problem on March 17, "but didn't," Sheehan said.

On Feb. 26, while the reactor was still operating, Unit 2 operators tried to clean debris from screens in a bay through which water used to cool steam is taken from Long Island Sound. This is the first time the procedure was not done during an outage, and a second bay ended up getting clogged with the debris, causing an automatic shutdown.