The US government’s only facility for handling, processing and storing weapons-grade uranium has been temporarily shut after anti-nuclear activists, including an 82-year-old nun, breached security fences.
Officials said the facility at Oak Ridge, Tennessee, was shut down on Wednesday at least until next week after three activists cut through perimeter fences to reach the outer wall of a building where highly enriched uranium, a key nuclear bomb component, is stored.
WSI Oak Ridge, the contractor responsible for protecting the site, is owned by the international security firm G4S, which was at the centre of a dispute over security at the Olympic Games in London.
The activists painted slogans and threw what they said was human blood on the wall of the facility, one of numerous buildings in the facility known by the code name Y-12 that it was given during the second World War, officials said.
While moving between the perimeter fences, the activists triggered sensors that alerted security personnel. But officials conceded the intruders were still able to reach the building's walls before security personnel got to them.
Ellen Barfield, a spokeswoman for the activists who called themselves Transform Now Plowshares, said three were arrested and charged with vandalism and criminal trespass.
She said the three, identified as Megan Rice (82), Michael Walli (63) and Greg Boertje-Obed (57), were being held in custody and appeared for a hearing before a US magistrate judge in Knoxville, Tennessee.
The date for their trial has been set as October 9th.
Ms Barfield forwarded a statement from the group in which it said the activists had passed through four fences and walked for "over two hours" before reaching the uranium storage building, on which they hung banners and strung crime-scene tape.
Ralph Hutchinson, coordinator for the Oak Ridge Environmental Peace Alliance, said the group's intention was not to demonstrate the lack of security at the plant, but to take a stance against the making of nuclear weapons.
"It wasn't so they could show how easy it was to bust into this bomb plant, it was because the production of nuclear weapons violates everything that is moral and good," Mr Hutchinson said. "It is a war crime."
Officials said that the storage building itself, which was built after the September 11th attacks on New York and Washington, was designed with modern security features and that its contents were not compromised.
A spokeswoman for G4S declined to comment and referred inquiries to government spokespeople.
The security failure was an embarrassment both for the security firm and for the National Nuclear Security Administration, or NNSA, the Energy Department branch that operates US nuclear weapons plants. "It was obviously a pretty serious incident," NNSA spokesman Joshua McConaha said.
NNSA officials said the activists cut through two chain-link fences surrounding the sprawling facility and a third fence surrounding the ultra-secure enriched uranium stockpile building, known as the Highly Enriched Uranium Materials Facility.
The building served as the US government's only "warehouse" for storing highly enriched uranium used in nuclear weapons.
Highly enriched uranium is a radioactive material used in the core of bombs to produce a nuclear detonation. The Oak Ridge plant is one of the most important government installations involved in the maintenance and production of the US nuclear arsenal.