"Highly enriched uranium that's vulnerable is an unacceptable threat to me, and to American citizens everywhere," said professor Graham T. Allison of the Belfer Center for Science and International Affairs at Harvard University. "We're as vulnerable as the weakest link in the chain," he said. Allison advised ABC News on the project, as he had done on two previous ABC News investigative reports dealing with nuclear security.
Nuclear safety experts say there is significant threat of sabotage, even at the facilities using low-enriched uranium.
In the case of sabotage, a facility could, in effect, be turned into a so-called dirty bomb. A dirty bomb uses conventional explosives, such as dynamite, to spread radioactive material. The greater the amount of radioactive material dispersed, the greater the potential danger to the surrounding community.
"Explosive material plus radioactive material equals dirty bomb," Allison said.
Most of the college reactors were built during the Cold War in an effort to demonstrate the peaceful uses of nuclear power. While smaller and less powerful than commercial nuclear power plants, the college reactors are considered a risk, given their radioactive material and location on crowded campuses, often in suburban or urban areas.
"Research reactors aren't required to be protected against sabotage in the same kinds of ways that power reactors are," said Matthew Bunn of Harvard University, former adviser to the White House Office of Science and Technology Policy. "Security costs money and if you actually imposed serious security requirements on them, many of them would probably end up shutting down."
At Florida, Wisconsin, Purdue and Ohio State, Carnegie Fellows were able to gain access to high-security areas with no background checks, carrying large tote bags that were not inspected before they entered the reactor area. School officials said they doubted their reactors posed any risk to the nearby community due to their small size and low amount of radioactive material.
Citing the structural design and shielding of the reactor facilities as well as safety and security measures in place, Roy Zimmerman of the NRC wrote in a letter to ABC News that even if a sabotage attack were attempted against one of the university reactors, "the potential for significant radiation-related health effects to the public is highly unlikely."
At University of Florida, Carnegie Fellows showed up unannounced and were taken through three locked doors and given a full tour of the reactor and the control room by the reactor director. Their bags, which were not searched, were left in an office connected to the reactor room.
"He became our key. And we were able to get into all these rooms through him," said Tamika Thompson, a Carnegie Fellow who recently received her master's degree in journalism from the USC Annenberg School for Communication. "If we were terrorists, we wouldn't need to have him let down his guard, he would be doing the same thing at the end of a gun barrel."
Nuclear safety advocates consider the surprisingly easy access to control rooms and reactor pools a concern.
"A terrorist with a little bit of explosives in a backpack like your students, would be able to release a vast amount of radioactivity in a very populated area," said Dan Hirsch, the head of a nuclear watchdog group called Committee to Bridge the Gap. "Bin Laden would love to do something like that."