UPDATE 1-"Troubling ineptitude" in security at US nuclear bomb plant
* Activists broke through fences in July; included nun aged 82
* Should be one of the best-protected buildings in U.S.-analyst
* Security firm owned by company at center of Olympics storm
WASHINGTON, Aug 31 (Reuters) - Guards at a U.S. government plant for storing weapons-grade uranium failed to spot activists, including an 82-year-old nun, who cut through its fences until they walked up to an officer's car and surrendered, an official report said on Friday.
The report from the Energy Department's inspector general, Gregory Friedman, criticized multiple failures of sophisticated security systems and "troubling displays of ineptitude" at the Y-12 facility in Oak Ridge, Tennessee in July.
Three anti-nuclear activists, including an 82-year-old nun, were not initially spotted or detained as they cut through three perimeter fences on July 28.
They painted slogans and threw what they said was human blood on the outer wall of a building where highly enriched uranium, a key component of nuclear bombs, is stored.
The building they vandalized was built after the Sept. 11, 2001 al Qaeda attacks on New York and Washington and had been previously touted as "the Fort Knox of uranium" by a senior government official because of its security features.
The facility holds the largest inventories of nuclear material in the world, said Robert Alvarez of the Institute for Policy studies, who was a senior Energy Department official in the 1990s and is an expert on the U.S. nuclear weapons program.
"It should be one of the most well-protected facilities in the United States for that reason," said Alvarez, who said the breach in security was unprecedented.
"This is the kind of lapse that one would expect heads to roll," he said, noting that more rigorous government oversight of contractors is needed.
The United States has been at the forefront of international efforts to stem the proliferation of nuclear weapons to countries like Iran and U.S. President Barack Obama has called nuclear terrorism the "single biggest threat" to U.S. security, given al Qaeda's stated desire to obtain such weapons.
Top nuclear officials from the Energy Department will face scrutiny over the security breach from lawmakers on the House of Representatives' Energy and Commerce Committee on Sept. 12.
TRESPASSERS ALLOWED TO "ROAM ABOUT"
The Y-12 facility is run by Babcock & Wilcox Co which is responsible for security provided by contractor WSI Oak Ridge, owned by international security firm G4S.
G4S was at the center of a political and media storm in Britain over outsourcing of security after it failed to provide enough guards for this year's London Olympics.
Friedman's report said the U.S. government had budgeted about $150 million in taxpayer funds for security at the Y-12 plant for fiscal 2012, yet the officer responding to the alarm did not notice the trespassers until they walked up to his car and "surrendered."
The officer did not draw his weapon nor secure the area, instead letting the trespassers "roam about and retrieve various items from backpacks," the report said.
Another officer hearing alarms did not look outside the building as he was supposed to, and also missed an image of the trespassers on a camera. A third officer turned off the alarm.
Others heard the activists hammering on the building's outside wall, but assumed the sound was from maintenance workers.
"The actions of these officers were inconsistent with the gravity of the situation and existing protocols," Friedman said in the report.
One camera that would have shown the break-in had been broken for about six months, and there was a backlog of repairs needed for security systems at the facility, the report said.
"We found this to be troubling," Friedman said.
A spokesperson for Babcock & Wilcox said the contractors were not commenting on the Inspector General's report, and were deferring to a written response included in the report from the top Energy Department official in charge of the National Nuclear Security Administration (NNSA).
Thomas D'Agostino, the administrator of the NNSA, said changes were underway after the incident.
D'Agostino said staff involved with the incident had been removed, cameras have been fixed, and patrols and training stepped up.
"These steps are just the beginning of the structural and cultural changes that we intend to make," D'Agostino said in his response.
The NNSA was also assessing security at all of its facilities, he said, and notified Babcock & Wilcox earlier this month that its contract could be terminated. The company has 30 days to respond to the "show cause" letter.