Sept. 11. NRC Urges Increased Sercurity

This Article says that the U.S NRC (Nuclear Regulatory Committee) as a precaution that all nuclear plants, non-power reactors, nuclear fuel facilities and gaseous diffusion plants go to the highest level of security. The reason why they have done this is classified. Even though there were no threats of attacking these places they were still concerned that they could be targeted for the highly flammable contents they have. The recommendation was consider prudent because the attacks were on New York and in Washington DC.

I believe that this was a smart precaution, we don't know what they would attack or what they could attack, some of the Power Plants and such could be a good target because they would make a massive explosion. At the time nobody knew what else would be hit so anything that could be targeted should be on alert.