Waterford — Unit 3 at the Millstone Power Station is one of more than a dozen nuclear reactors in the country currently under additional Nuclear Regulatory Commission oversight, due to a violation found last year related to operation of a backup feedwater pump.

Millstone owner Dominion Resources was informed this week of the status of Units 2 and 3 in the NRC’s annual assessment letter. Performance at Unit 2 has met NRC objectives for the past year, placing it in the highest of the five-category system the NRC uses to rate plants.

“We’re pleased Unit 2 is in the Licensee Response Column (the highest level), and we’re working to ensure all corrective actions are in place so that we can return to that same level of performance at Millstone Unit 3,” said Ken Holt, spokesman for Millstone.

Of the nation’s 100 nuclear power plants, 75 including Millstone Unit 2 met all safety and security performance objectives, the NRC said in a statement Friday about the assessment letters. Nineteen plants including Millstone Unit 3 were rated as needing to resolve one or two items of low safety significance, the NRC said. That includes additional inspections and follow-up reviews of corrective actions taken.

Nationwide, three reactors are in “degraded” level of performance, which prompts more NRC inspections, additional oversight and involvement from senior NRC managers, the NRC said. These plants are: Monticello in Minnesota; Pilgrim in Massachusetts; and Point Beach I in Wisconsin. In addition, the Arkansas Nuclear 1 and 2 reactors are in the “multiple degraded cornerstones” category with safety issues of high significance. No plants are currently in the “unacceptable” category, in which they are in danger of being shut down.

Sheehan said that while Dominion was previously informed about the additional oversight of Unit 3, the assessment letter “gives people a high level of overview about how a plant is doing.” The assessments cover Jan. 1, 2014 through Dec. 31, 2014.

“It’s a snapshot in time, where we step back once a year and give a report card for the plants,” he said.

In addition to the Unit 3 “white” finding — the second-lowest of four tiers of violation severity rankings — the NRC informed Dominion in January that it is considering issuing another finding of “greater than green” — the lowest level — for a security-related violation. Once the enforcement action is finalized, the NRC could place Millstone under additional oversight for security, Sheehan said.

Holt said the decision is expected sometime this month.

The assessment letter also informs Dominion of the NRC’s plan for inspections through May 2016, listing 27 areas that will be covered.

j.benson@theday.com

Twitter: @BensonJudy