The security contractor at a Tennessee plant that stores America’s supply of weapons-grade uranium has replaced its general manager almost two weeks after three protesters, including an 82-year-old nun, got into a high-security area.

Security firm WSI Oak Ridge confirmed to The Knoxville News Sentinel today that Steven C Hafner was taking over the position from Lee Brooks.

Protesters on July 28 were found hanging banners in the dark, singing and offering to break bread with the security guards at Y-12 Oak Ridge National Security Complex in Knoxville. An affidavit said that before security guards apprehended them, they spray-painted the building with protest slogans and threw blood on it. They were arrested and officials say all nuclear materials are safe.

Afterward, security contractor WSI said it was looking at its procedures and it removed Brooks and Y-12 Protective Force director Gary Brandon from their posts. WSI named John Garrity to replace Brandon. Brooks and Brandon are awaiting reassignments by G4S Government Solutions, the parent company of WSI.

The newspaper reported that a halt to nuclear operations at the plant was still in effect. The plant originally said the stand-down was expected to be lifted by this week and that security personnel would undergo training and refresher instruction.

A spokeswoman for Y-12 did not immediately return a phone call to The Associated Press seeking comment.

The Y-12 plant also makes nuclear warhead parts and provides nuclear fuel for the Navy and research reactors worldwide. The National Nuclear Security Administration's Production Office is responsible for oversight of the security contractors. Last month, WSI-Oak Ridge said it planned to cut as many as 51 jobs, including about 34 security police officer positions at the complex.

The plant produced the material used in the first atomic bomb dropped on Hiroshima, Japan, on August 6, 1945. At annual protests tied to the anniversary, a few protesters have staged deliberate acts of civil disobedience to provoke their arrests including blocking the road into the plant or defying trespassing signs by deliberately crossing a blue line that marks the beginning of federal property.

But on July 28, three protesters went much farther, officials said. An affidavit was filed in federal court this week by the Department of Energy's inspector general. The News Sentinel reported that the affidavit alleges that Megan Rice, a Roman Catholic nun, Michael Walli, 63, and Greg Boertje-Obed, 57, climbed a ridge before dawn, set off alarms as they used bolt cutters to get through three wire fences and made it to the exterior of the Highly Enriched Uranium Materials Facility.

They have been charged with federal charges of trespassing, a misdemeanour, and wilful and malicious destruction of property, a felony.

Federal energy officials and the two US senators from Tennessee called the latest breach troublesome.

At previous protests, arrests peaked in 1989, when 29 people were charged with trespassing at the plant gates. Ten more were arrested in 1990. Then the arrests stopped, because the local district attorney declined to press state charges.

Arrests resumed in 1998 and over the next 10 years, fewer than two dozen were taken in annually and charged in state court with trespassing. The harshest punishments were fines or jail sentences of up to 10 days.

On New Year's Day 2002, a few months after the 9/11 attacks, a dozen protesters made it onto the property carrying 14-foot flags and lighted candles. The activists told The Associated Press that they stopped three times for prayers and spent about a half-hour on the grounds before they were noticed and detained.

Department of Energy officials said the group in 2002 wasn't a serious threat because they never reached sensitive areas.

The complex upgraded security, adding guards, building concrete barriers and adding intrusion detectors to meet standards described as three times tougher than before 9/11.

In 2002, authorities for the first time charged four protesters who crossed the blue line with federal trespassing, still a misdemeanour. They were convicted and sentenced to two months in prison.

At the largest rally ever at the plant, on the 60th anniversary of the bombing in 2005, more than 1100 turned out and 15 were arrested on state charges. Arrests have dwindled since then.

- AP