Editor's note: This post was edited at 6:50 p.m. to clarify that the power station is taking corrective action on a total of six new violations, and not five as first reported.

Waterford — Millstone Power Station is taking corrective actions on six new violations of federal regulations, the latest in a series of operations, procedure and equipment failures uncovered in Nuclear Regulatory Commission inspections over the last year.

The six violations announced by the NRC Wednesday are all categorized as “green findings” of “very low safety significance,” the lowest in the four-tiered, color-coded severity scale. Five of the violations were found during the NRC’s quarterly safety and compliance inspection that ended Dec. 31, and the sixth was self-reported by the company to the NRC.

“Five is a larger number than we would normally see in a quarterly inspection for any given plant,” said Neil Sheehan, spokesman for the NRC. Typically, he said, quarterly inspections result in one to three findings.

The violations found by the NRC include:

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[naviga:li]Failure to properly assess and manage the risk of work in the switchyard during the Unit 3 refueling outage.[/naviga:li]

[naviga:li]Failure to promptly identify or correct conditions affecting reliability of the chilled water system chiller that helps maintain the stability of the control building, which houses the control room for Unit 3.[/naviga:li]

[naviga:li]Failure to maintain operating restrictions during a temporary order limiting operations of a valve on the auxiliary feedwater pump for Unit 3. Problems with the same pump resulted in the NRC issuing a “white” finding of “low to moderate” safety significance, the second-lowest level, last year. As a result of the white finding, the plant was placed under increased NRC oversight.[/naviga:li]

[naviga:li]Failure to determine if goals or corrective actions for the monitoring plan for the supplementary leak collection and release system should be adjusted after a failure of the ventilation system in an auxiliary building. The system prevents the release of excessive radiation outside the building.[/naviga:li]

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The fifth violation, a “self-revealing finding,” resulted from insufficient estimates of the radiation exposure levels of workers during a Unit 2 refueling outage in spring 2014. During a refueling outage, staff access areas of the plant that are normally off limits. Ken Holt, spokesman for Millstone, said the workers were exposed to levels higher than the company estimated before the work began, but the levels did not endanger the health of the workers.

Sheehan said dosage levels are estimated before work begins so that workers are equipped with the right protective clothing or respirators, or are limited in the time they spend in certain areas.

The company had estimated a radiation dose of 75 person-rem (roentgen equivalent in man) would occur for the entire workforce involved in the refueling work, but the actual dose was 102.225 person-rem, Sheehan said. The number of workers that received a dose of radiation as a result of work activities during the outage was approximately 1,400, he said. About 1,080 Dominion employees work at Millstone, along with about 300 contractors.

NRC regulations limit the radiation exposure dose for a nuclear plant worker to 5 person rem per year.

Holt said the lessons learned in that incident were applied to a Unit 3 outage later in the year.

“We came in way under the estimates for that outage,” he said.

The sixth finding was identified by Dominion and reviewed by the NRC inspectors. It involved degradation of a radiological barrier function caused by human error, according to the NRC report.

The violations reported Wednesday come a day after the NRC notified Millstone that it has determined that a “severity level III” violation occurred during incidents leading up to an unplanned outage of both reactors in May. Severity level III is equivalent to a “white” finding, the second-lowest level.

Sheehan said the NRC found that modifications made to equipment in 2012 worsened the problems that led to the outage, causing both reactors to trip off rather than one. The company should have conducted a complete evaluation of the ramifications before doing the modifications, he said.

Holt said the company has responded to the NRC’s concerns.

“We’ve taken corrective action, and addressed the issues,” he said. “We’ll submit a plan for a permanent resolution by the end of March.” The NRC did not fine Dominion for the violation, but is requiring it to submit a plan by March 31 to ensure this type of outage does not happen again.

j.benson@theday.com

Twitter: @BensonJudy