At the dawn of the civilian nuclear age in the 1950s, one of the pressing questions was how to find enough fuel for reactors and bombs.
The government and the private sector seized on a man-made substitute for natural uranium, producing about 3,400 pounds of an exotic and expensive material called uranium 233. Today, the problem is how to safely get rid of it.
"We do consider this to be waste," said David G Huizenga, senior administrator for environmental management at the energy department.
"There's no further need for it."
Uranium 233 looked attractive because it could be made in a reactor from thorium. But in the end, ordinary uranium was cheaper, and 233 was not needed.
Now, wary of the security risks posed by the stockpiles, the department is making plans to dispose of them at a cost of $473 million. It faces other disposal challenges, including how to handle thousands of tons of spent fuel from civilian reactors.
Also, uranium 233 is different, as in the proper form it could easily be used to make a bomb.