It took a jury about 2 ½ hours to find the three protesters guilty of a charge of sabotaging the plant and second charge of damaging federal property in July the Y-12 National Security Complex in Oak Ridge in July.
Defense attorneys said in closing arguments that federal prosecutors had overreached in the charges because of the embarrassment caused by the break-in.
"The shortcomings in security at one of the most dangerous places on the planet have embarrassed a lot of people," said Francis Lloyd, who represented Sister Megan Rice of Washington, D.C. "You're looking at three scapegoats behind me."
Prosecutor Jeff Theodore was dismissive of claims that the protesters' actions were beneficial to security at the plant that has had a hand in making, maintaining or dismantling parts of every nuclear weapon in the country's arsenal.
"Right after 9/11, did you notice how much better security got at airports and public buildings?" Theodore said. "Does that mean 9/11 was a good thing? Of course not."
Theodore said the protesters' intent was made clear by the fact that they carried the materials with them to deface the building.
He also noted that their fate could have been far worse because they had entered an area where guards were allowed to use deadly force.
"They're lucky — and thank goodness they're alive — because they went into the lethal zone," he said.
The defense asked for a mistrial over the Sept. 11 comparison, but the judge denied the motion.
In Washington on Wednesday, Neile Miller, acting administrator of the National Nuclear Security Administration, told a Senate subcommittee that officials have taken "decisive action" since the July 28 intrusion at the Y-12, including a new management team and a new defense security chief to oversee all of the agency's sites.
"The severity of the failure of leadership at Y-12 has demanded swift, strong and decisive action by the department," she said. "Since the Y-12 incursion, major actions have taken place to improve security immediately, and for the long term."
Earlier Wednesday, Rice, Michael Walli and Greg Boertje-Obed testified on their own behalf, saying they have no remorse for their actions and were pleased to reach one of the most secure parts of the facility.
The defendants spent two hours inside Y-12. They cut through security fences, hung banners, strung crime-scene tape and hammered off a small chunk of the fortress-like Highly Enriched Uranium Materials Facility, or HEUMF, inside the most secure part of complex.
Rice said during cross examination that she wished she hadn't waited so long to stage a protest inside the plant.
"My regret was I waited 70 years," she said. "It is manufacturing that which can only cause death."
Boertje-Obed, a house painter from Duluth, Minn., explained why they sprayed baby bottles full of human blood on the exterior of the facility.
"The reason for the baby bottles was to represent that the blood of children is spilled by these weapons," he said.
All three defendants said they felt guided by divine forces in finding their way through the darkness from the perimeter of the complex to the enriched uranium plant without being detected.
"I believe it was clearly a miracle," Boertje-Obed said. "There is no other way to explain it."
Walli, who most recently lived in Washington, D.C., agreed.
"It was an answer to prayer," he said.
The protesters' attorneys noted that once they refused to plead guilty to trespassing, prosecutors substituted that charge with a sabotage count that carried a maximum prison term of 20 years. The other charge has a maximum sentence of 10 years. The defense argued during the trial that the more serious charge should be dismissed.
Prosecutors argued the act was a serious security breach that continues to disrupt operations at the facility. The intrusion caused the plant to shut down for two weeks as security forces were re-trained and contractors were replaced.
Federal officials have said there was never any danger of the protesters reaching materials that could be detonated on site or used to assemble a dirty bomb, a position stressed by defense attorneys.
The plant first built as part of the Manhattan Project during World War II that provided enriched uranium for the atomic bomb dropped on Hiroshima, Japan. It makes uranium parts for nuclear warheads, dismantles old weapons and is the nation's primary storehouse for bomb-grade uranium. The facility enjoys high levels of support in the region, and Oak Ridge has always taken pride in its role in building the atomic bomb, viewing it as crucial to the end of the war.
For decades, protesters have rallied at the gates of Y-12 around the anniversary of the bombing of Hiroshima.
An overflow crowd of supporters sang religious songs in the courtroom after the verdict was read.
"Justice was done at Y-12 on July 28," Jack Cohen-Joppa, a supporter of the protesters from Tucson, Ariz., said outside the courthouse after the verdict. "But we're still waiting for it here."
Associated Pres writer Matt Daly in Washington contributed to this report.