U.S. dismantles last of powerful nuclear bombs

(Reuters) - The United States dismantled the oldest nuclear bomb in its Cold War arsenal -- and one of the most powerful it ever built -- on Tuesday as part of President Barack Obama's nuclear security policy.

The magaton-class nuclear bomb the size of a minivan and weighing about 10,000 pounds was dismantled at a nuclear weapons storage facility outside Amarillo, Texas.

"This was one of the largest bombs in the American arsenal," said Joshua McConaha, Public Affairs Director for the Department of Energy's National Nuclear Security Administration.

He said the exact strength of the bomb -- known as the B53 -- remains classified, but it is believed to have been many hundreds of times more powerful than the atomic bomb that destroyed Hiroshima in 1945.

Built at the height of the Cold War in the 1962, the bomb was designed to be dropped onto a target by a massive B-52 Stratofortress strategic bomber. McConaha says it contained about 300 pounds of high explosive surrounding the uranium, referred to as 'the pit.'

"The world is a safer place with this dismantlement," said Thomas D'Agostino, Under Secretary of Energy and Administrator of the National Nuclear Security Administration.

"The B53 was a weapon developed in another time for a different world. Today, we are moving beyond the Cold War nuclear weapons complex that built this type of weapons," he said.

The process of eliminating the massive nuclear weapons, known as "the last of the big dogs," began 14 years ago.

"It started with retiring a weapon from active or inactive service," McConaha said. "In this case, President Clinton did that back in the nineties, in 1997."

Many B53s were retired before that, but a "significant number" had remained in the U.S. arsenal, McConaha said.

In addition to challenges related to the bomb's massive size and awesome explosive punch, the dismantlement process was made more difficult by the weapon's use of older technology developed by engineers who have since died.

The explosive is carefully separated from the nuclear materials, McConaha explained. Some materials will be reused, while most of the bomb will be shredded and disposed of.

The number of B53s that were once in service, and the number that have been disassembled, remains classified, but McConaha confirmed that Tuesday's bomb was the final one.

(Editing by Jerry Norton and Anthony Boadle)