Unit 2 at the Millstone Power Station in Waterford is among 75 of the nation’s highest-performing reactors, having met all safety and security performance objectives of the Nuclear Regulatory Commission for the first half of this year.

The NRC said Thursday that overall, 96 of the nation’s 99 operating nuclear power plants were in the two highest performance categories for the first half of 2015.

Unit 3 at Millstone was among 21 plants that are charged with resolving one or two areas of low safety significance, the NRC said in a news release.

Regulatory oversight of these plants includes additional inspections and requirements for corrective actions.

There were no reactors in the third-highest performance category, but three reactors are in the fourth lowest and require the highest level of regulatory oversight, the NRC said.

Arkansas Nuclear 1 and 2 in Russellville, Ark., is in this category because of two safety findings of substantial significance, and Pilgrim in Plymouth, Mass., was in this category because of “longstanding performance issues of low-to-moderate safety significance,” the NRC said.