To that end, the U.S. and Russia signed an agreement Tuesday to dispose of 68 metric tons of excess, weapons-grade plutonium beginning in 2018 - enough to build 17,000 nuclear weapons. CBS News correspondent David Martin reports the Russians are also shutting a facility that's been churning out plutonium for more than half a century.
It was once a secret city lost in Siberia. Krasnoyarsk-26 did not even appear on the map. Until George Crile of CBS News went there 12 years ago, American television cameras had never been allowed to see what went on there deep inside a mountain - the making of enough plutonium for 100 nuclear weapons a year.
Now Krasnoyarsk-26 is going out of business. The reactor that produced the plutonium - the last one in Russia - is shutting down.
"It's a very, very important step for Russia to have taken," said Sig Hecker, the former director of America's own secret nuclear city at Los Alamos, N.M.
But, says Hecker, stopping production still leaves Russia with 150 tons of plutonium.
"They have so much material that the concern of Russian nuclear materials getting out of the proper facilities and out of the proper hands remains very high on my own agenda," he said.
Hecker visited Russia's secret cities in the chaotic years following the fall of the Soviet Union.
"When I saw their practice of how they did the protection, the control and the accounting of their nuclear material, I was terribly concerned," he said.
Hecker says the controls have gotten better, but Krasnoyarsk-26 was the last of 13 reactors that once turned out weapons-grade plutonium for the Soviet Union. The nightmare scenario of a terrorist group like al Qaeda getting its hands on a 20-pound chunk and turning it into a weapon still remains.
"I would say that's a very difficult process but not one that's impossible for a terrorist group," Hecker said.
As for the United States, it has not produced any weapons grade plutonium in 20 years, but still has a stockpile of 100 tons.