Waterford — Dominion Energy officials are warning area residents not to be alarmed as personnel begin a monthlong, routine maintenance operation on Unit 3 at Millstone.

Officials said they had increased activity at the station over the past several weeks in preparation for the operation. They planned to take Unit 3 offline Thursday for a regularly scheduled refueling.

According to Dominion, more than 900 supplemental staffers will assist the plant’s 1,100 full-time personnel to perform maintenance and prepare the unit for its next 18 months of operation.

Officials reminded residents that taking a unit offline can be a noisy process, as it requires the venting of steam. They expect the maintenance will take about a month.

Anyone with questions can contact Ken Holt, manager of Millstone’s nuclear communications, at (860) 440-0132.