At 9:30 Tuesday morning, Michael O’Connor, director of emergency operations at the Millstone Power Station, summed up the scenario for the roomful of plant staff gathered at the temporary command center at Camp Niantic in East Lyme.

“Twelve adversaries gained access to the protected area, and we still have two at large,” he said. “During the event, one plant employee was killed and one security officer was killed, and one other person was injured. There are additional explosives on site we need to be mindful of.”

O’Connor’s report, given two hours into a “hostile action event” drill for Waterford power plant staff and state and local emergency responders, came as power plant crews pored over computer screens and facility reference manuals to determine how to repair damage to Unit 3 caused by explosives set by fictitious plant intruders. They also simulated a shutdown of Units 2 and 3, the two operating plants at the power station and monitored imaginary radioactive releases that could have occurred if it were a real emergency. Just after 10 a.m., Paul Malzahn, assistant director of technical support at the plant, announced that repairs had been made that stopped radiation leaking from Unit 3.

Ken Holt, spokesman for Millstone, said the plant is required by the Nuclear Regulatory Commission to be assessed on specific types of emergency drills once every two years. The Federal Emergency Management Agency will assess the performance of state and local emergency officials on this drill, he added.

While other recent drills at Millstone have simulated unplanned equipment failures or accidents, this is the first time the drill has involved a terrorist action at the plant since 2006, Holt said. This type of drill was introduced into NRC requirements for nuclear power plants after the Sept. 11, 2001, terrorist attacks, he said.

Scott Devico, spokesman for the state Department of Emergency Services and Police Protection, said the drill involved state police, the National Guard, the Coast Guard, the state departments of Emergency Management and Homeland Security, Transportation, Agriculture, Energy and Environmental Protection and the Red Cross, among others. Representatives of the various groups gathered at the state Armory in Hartford for the drill.

“It was a successful drill,” Devico said. “It was another great example of communication and coordination by all levels of government to respond to an emergency.”

Local emergency command centers were set up at the emergency communications buildings in Waterford and East Lyme. Waterford Police Chief Murray Pendleton, who is the town’s emergency management director, also said local emergency responders performed well to the drill scenario.

At 1 p.m. Friday at the Waterford Public Library, municipal officials will hear a report on the drill from FEMA representatives. At 3 p.m., the public is invited to hear the FEMA report.

j.benson@theday.com

Twitter: @BensonJudy