U.S. Defense Department proposal to use a nuclear micro-reactor as a power backup for the planned missile defense system in Guam is now being considered by Congress.

But a local watchdog group is sounding the alarm over the danger of the largely untested technology.

Leland Bettis of the local think tank and research group, pacific center for island security has been tracking the missile defense system plans for Guam and the potential for a nuclear micro-reactor.

"That’s not been disclosed by the MDA yet, but we’ve sort of been tracking this," said Bettis. "I think what really drew our attention was over the weekend the Senate Armed Services Committee’s executive summary, their NDAA language includes this piece which asks for a briefing for the Senate about the possibility of placing microreactors in Guam."

Bettis acknowledges that nuclear power has proven to be safe and can provide huge cost savings even for private commercial use.

But he believes a red line is crossed if they become targets in a combat situation.

"Just imagine if these reactors are a principal source of power for some of the measures, and counter-measures that the military is operating they’re certainly going to be a target," he said. "That means that the environmental impact is not just about how does the nuclear reactor perform in producing power but how might a micro nuclear reactor perform if it's targeted and hit."

An article last year in the "Military Times" mentions Guam as a potential site for the mobile nuclear equipment.

It describes a 40-ton reactor that can fit into three to four 20-foot containers and can provide up to 5 megawatts of power.

The Army has been considering the use of mobile nuclear power for years in a program called project Pele, ironically named after the Hawaiian goddess of fire and volcanoes.

The benefits as a power source in remote, austere locations is clear, but there are drawbacks in battle situations.

"If, however, that reactor is struck during conflict all the troops that are around that will be affected," he said. "So, I think the concerns that they had about the use of these particular power devices for military people is magnified ten-fold when you think about the possibility that these might be placed in proximity to a civilian community."

And the military has confirmed that the planned 360-degree missile defense system could have as many as twenty different sites scattered across the island.

Bettis says we need to know now more than ever, what’s going into each of these sites.

"The people that I’ve talked to talk about a micro nuclear reactor and say if it hits you need a set-aside that’s at least a mile. That’s gonna be a very different sort of thing then if you had command and control module in your neighborhood, so I think as a community we need better transparency  about what is being planned at all these locations," he said.