Citing last month's Japanese nuclear disaster, the AP1000 Oversight Group petitioned the NRC to delay consideration of the Westinghouse reactor until lessons from the Fukushima Daiichi power plant are further investigated.
"There is no cause to rush the design certification for the AP1000," said John Runkle, the group's attorney.
The AP1000 is the reactor chosen for power plants proposed for construction across the southeast by Duke Energy, Southern Company, Florida Power & Light, Progress Energy, Tennessee Valley Authority and SCANA.
Only the commission can postpone the certification and licensing processes, the group's petition stated.
In early March, NRC Chairman Greg Jaczko said the commission may take final action on the AP1000 reactors "as early as this summer."
The oversight group, made up of 12 southeastern environmental organizations, said industry pressure evidently caused the NRC to bypass testing of key aspects of the reactor's design despite dissent by one of the agency's longest serving experts, John Ma.
Ma, the lead structural engineer in the NRC's evaluation of the building that shields the reactor, filed a formal dissent against approval of the structure's design in November.
The oversight group's petition also alleged problems with the AP1000's storage density for spent fuel pools, loss of off-site power and a containment structure weaker than those at most U.S. reactors.
"Well before the emergency in Japan, serious shortcomings with the Westinghouse model had been identified," the petition stated. "The events at Fukushima redouble the need for a careful and transparent review of the AP1000 relating to both safety and cost."
The AP1000 was designed by Pittsburgh-based Westinghouse Electric Company, which is majority owned Toshiba and Shaw Group of Baton Rouge, Louisiana.
A Westinghouse spokesman had no comment on the petition but said the AP1000 is "extremely safe."
It "can shut down and cool itself without human intervention for three days," spokesman Vaughn Gilbert told Reuters.