For only the second time in its history, the US Navy is beginning the slow, tricky process of taking apart a nuclear-powered aircraft carrier

• In April, the Navy published a notice announcing the beginning of planning to scrap the USS Nimitz.
• USS Nimitz entered service in 1975 and has spent nearly 50 years operating all over the world.
• But Nimitz will be only the second nuclear-powered carrier to go through deactivation and defueling.

For the US Navy, the tiny atom has been a big friend. Nuclear power allows the Navy's aircraft carriers and submarines to stay at sea for extended periods, limited only by the endurance of their crews.

But there's a downside to nuclear-powered vessels: How do you dispose of them when they're no longer needed? While most ships eventually end up in the scrapyard, breaking up a radioactive power plant is a different matter — specially when it's in a giant aircraft carrier.