The network's "Primetime" news magazine aired its report Thursday night with results of a four-month investigation that reportedly found "gaping security holes" at many of the research reactors operated on 25 college campuses.

"Late at night at the University of Utah, students were unchallenged as they approached the building housing the reactor," according to the ABC report.

"Primetime" quoted one of its undercover interns, who was assigned to gain access to the reactors: "We were expecting, of course, that all the doors would be locked, and we tried to find a door, and the door was open. It was 12:30 a.m., and we walked in, and that was pretty scary."

But the notion that someone could enter the Merrill Engineering Building at night didn't come as a surprise to U. police - who call the reactor a security priority - or Melinda Krahenbuhl, the reactor administrator and director of the school's nuclear engineering program.

The building is often open to accommodate the comings and goings of graduate students and researchers, Krahenbuhl said. But unauthorized people cannot enter the secure reactor facility.

"The reactor safety and security were never compromised," she said.

Further, Krahenbuhl explained, the small amount of "low enriched" uranium that powers the 100 kilowatt reactor is not enough to make a bomb - even if someone were skilled enough to remove it.

"You'd need a lot more fuel," she said. "This reactor is 1,000 times smaller than any [nuclear] power plant in the country."

Nonetheless, the ABC report has at least some members of Congress agitated.

Rep. Edward Markey, D-Mass, a senior member of the House Energy and Commerce Committee that oversees the Nuclear Regulatory Commission, said he wants assurances that all of the research facilities are secured from potential terrorist attacks.

"The security problems exposed here offer yet more evidence that, four years after 9/11, the NRC has not done nearly enough to secure our nation's nuclear facilities," he told ABC.

In a Salt Lake Tribune interview, Markey's spokesman, David Moulton, said ABC's undercover students were able to tour university reactors carrying backpacks and other bags. A suicide bomber could blow up such a facility creating a dirty bomb, he said.

"A dirty bomb, by its nature, doesn't need a lot of radioactivity to exact its purpose," he said. "Such an explosion in an urban area would be sufficient to create panic, if not death."

Moulton said Markey and others will be pressing the NRC about the agency's ability to join the post 9/11 world of security. "Does the NRC enforce its own regulations on campuses?" he asked. "We suspect, no."

Krahenbuhl said the U. forbids visitors from carrying backpacks when touring the reactor facility. Even if they could, she added, a backpack full of explosives could not set off even a small nuclear reaction.

"With the amount of explosives they could carry in a backpack, they could probably kill themselves," she said. "But the amount of water in the reactor would make the explosion ineffectual. It could not disperse the fuel."

An NRC spokesman said that after discussing the report with ABC News for the past two months, agency officials found nothing that posed a security risk.

"Even if there were a malicious act at one of these small research reactors, the possibility of radiological consequences is very, very small," Scott Burnell said. "But if anything ABC provides shows that anyone has not lived up to NRC regulations, we will take action."

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Tribune reporters Greg Lavine and Shinika Sykes contributed to this report.