Security is being stepped up at nuclear power plants in the US amid fears of new terrorist attacks.
The move comes as the International Atomic Energy Agency warns a nuclear attack by terrorists is more likely now than it was before the September 11th attacks.
Experts from around the world are meeting at the IAEA in Vienna to discuss nuclear terrorism and call for a review of nuclear safety at facilities worldwide.
The Federal Aviation Administration in the US has temporarily banned small private airplanes from flying near the 103 nuclear power plants around the US.
Mr Ed Lyman, scientific director for the Nuclear Control Institute, told the BBC nuclear power plants in the US would be vulnerable to the kind of attacks on the World Trade Centre and the Pentagon.
"They were not designed with this kind of attack in mind, and it is foolish to make statements, like some in the industry have, that plants could withstand that," Mr Lyman said.
"The kind of missile generated by the engine of a large aircraft could penetrate several feet of steel-reinforced concrete."
AP