Waterford - Suppose a Humvee crashes through the outer security fence at the Millstone Power Station.

Two men wearing Millstone cleaning staff uniforms run out of the vehicle, firing AK-47s as they head towards the fence around Unit 2 reactor. Both are carrying briefcases.

A few minutes later, a suspicious package is found inside one of the containment buildings. It explodes, resulting in limited damage to the building, but no injuries. A radical group contacts the local media and claims responsibility. It alleges that the bomb contained radioactive materials.

That fictitious scenario, described in a Federal Emergency Management Agency training document, is the type of episode FEMA and the Nuclear Regulatory Management Agency are requiring Millstone and local and state emergency response officials to rehearse for the first time this year. Called a "Hostile Action-based Emergency Exercise," its purpose is to test the ability of the plant and local and state officials to respond to actions involving violent force on the plant that might come from land, air or water, Neil Sheehan, spokesman for the NRC, said Friday.

"Post 9/11, the plants need to be able to test for an attack, and incorporate that into their emergency planning," he said.

The first of these drills took place last year at the Three Mile Island Nuclear Generating Station in Pennsylvania, he said. Millstone and several other plants across the country are being required to conduct the exercise this year, and once every eight years after that. It will take place Sept. 8, with a rehearsal scheduled for August, said Ken Holt, Millstone spokesman.

Holt said there was a "hostile action" drill involving a hostage scenario five or six years ago, but that was initiated and evaluated internally by Dominion, the company that owns the plant. The exercise this year is unique because it will be evaluated by the NRC and FEMA.

No U.S. nuclear power plant has ever been the subject of an sabotage attempt, Sheehan said, "and we want to keep it that way." The possibility of a terrorist attack, he said, cannot be discounted.

"The concern is that they could wreak havoc with plant safety systems or try to secure nuclear material," Sheehan said. "Our primary concern is that the plant safety systems remain protected."

He describes a typical scenario: a plane crashes at a power plant. Plant security and local emergency responders must quickly determine whether the crash was deliberate, whether safety equipment was damaged, and how to respond and communicate with local and state officials and the public. The Hostile-Action based Exercise, Sheehan said, is "more focused on external aspects of emergency preparedness rather than testing the on-site facility security personnel."

Holt said local and state emergency preparedness officials have been contacted about the exercise. The exact scenario that will be played out is being created internally, but neither the plant security personnel nor state and local emergency preparedness teams will know what it is until the drill begins.

More typical emergency exercises at Millstone involve response to an equipment failure or a severe storm compromising operations, rather than a deliberate attempt to destroy important systems, take hostages or intimidate plant operators, Sheehan said.

"Even though the potential radiological consequences would be the same whether caused by a hostile action or a safety event," he said, "hostile actions would likely pose unique challenges to emergency responders."

Waterford Police Chief Murray Pendleton, the town's emergency management director, said that in preparation for the drill, he recently attended a meeting in Washington, D.C., where the NRC presented the findings of drills last year at six other plants around the country to learn "what worked well and what didn't." He said southeastern Connecticut is at a big advantage over some other areas with nuclear plants because its local, state and plant officials have been working well together on all types of drills "since the 1970s." It will be unique from other types of exercises at Millstone that focus more on a radiation release from an accident or equipment breakdown than an external threat.

"In this drill," he said, "law enforcement will be the primary player."

In addition to evaluating the response to the attack itself, the drill will also test communications between the plant, emergency responders and the public, and decisions made by local and state officials in the aftermath, Holt said. These include whether local residents are told to take their potassium pills to protect themselves against radiological releases; whether people are told to shelter at home or evacuate; whether farmers are advised to feed livestock only stored grain protected from exposure to radioactive releases; and whether produce in the 10-mile Emergency Planning Zone around Millstone can be sold.

Both Units 2 and 3 will continue producing power during the exercise, Holt said.

"We'll use the simulator control rooms as a stand-in for the actual plants, so the operations won't be affected," he said.

j.benson@theday.com