The United States could be facing a shortage of lithium, an element vital to the operation of many of the country's nuclear reactors, a study says.

The study from the Government Accountability Office said only China and Russia still produce significant amounts of lithium and the supply may be drying up, The New York Times reported Wednesday.

The possible shortage of lithium -- critical to the operation of 65 out of 100 American nuclear reactors -- "places their ability to continue to provide electricity at some risk," the GAO report said.

The material in question is lithium-7, a byproduct of the production of tritium, the fuel that powers hydrogen bombs.

The United States stopped production of lithium-7 in 1963 when it had a large surplus, now mostly used up. With the U.S. nuclear weapons inventory shrinking, there has been little need to create tritium.

China and Russia apparently still have production capability, but because it is related to their weapons program outsiders do not know how much capacity they might have, experts said.

Per Peterson, the chairman of the nuclear engineering department at the University of California, Berkeley, told The Times it would be "pragmatic" for the United States to re-establish production of lithium-6 from lithium-7, something the GAO report said would take five years and $10 million to $12 million.