KNOXVILLE, Tenn. — An 84-year-old nun was sentenced Tuesday to nearly three years in prison for breaking into a nuclear weapons complex and defacing a bunker holding bomb-grade uranium, a demonstration that exposed serious security flaws at the Tennessee plant.

Two other peace activists who broke into the facility with Megan Rice were sentenced to more than five years in prison, in part because they had much longer criminal histories of mostly non-violent civil disobedience.

Although officials said there was never any danger of the protesters reaching materials that could be detonated or made into a dirty bomb, the break-in raised questions about safekeeping at the Y-12 National Security Complex in Oak Ridge. The facility holds the nation’s primary supply of bomb-grade uranium and was known as the “Fort Knox of uranium.”

After the break-in, the complex had to be shut down, security forces were re-trained and contractors were replaced.

In her closing statement, Rice asked the judge to sentence her to life in prison, even though sentencing guidelines called for about six years.

“Please have no leniency with me,” she said. “To remain in prison for the rest of my life would be the greatest gift you could give me.”