The top-secret operation began before dawn at an old Soviet reactor outside the eastern European capital of Riga, Latvia. Inside an unmarked truck was some of the most dangerous material in the world: highly enriched uranium -- the basic ingredient for a nuclear bomb and a prime target for terrorists.
Under a full moon and guarded by police cars and a Latvian SWAT team, the truck headed toward Riga International Airport. Dr. Igor Bolshinsky of the U.S. Department of Energy's National Nuclear Security Administration is charged with ensuring that the nuclear material is put where terrorists can't steal it.
"When there is a danger of these materials to get in the hands of terrorists, it makes sense just to eliminate this material -- to eliminate highly enriched uranium," Bolshinsky said.
A Ukrainian-born scientist who now is a U.S. citizen, Bolshinsky has become a one-man wrecking crew for potential weapons of mass destruction. His goal: to remove material that can be used for a nuclear or dirty bombs from vulnerable research reactors in the former Soviet Union.
Once the highly enriched uranium is removed, Bolshinsky sends it to a secure facility in Russia, where it is processed -- or down-blended -- into a less-dangerous fuel.
"I think we are smart enough to realize bad things may happen -- and we are smart enough to prevent it," he said.
Since 2002, Bolshinsky has almost single-handedly removed 269 pounds of fresh, highly enriched uranium from seven countries -- enough to make about five nuclear bombs. And he's just getting started. By 2010, his goal is to remove 2 tons of highly enriched uranium from 14 countries, including his homeland. That's enough for about 80 nuclear bombs.
Ambassador Linton Brooks, head of the National Nuclear Security Administration, which oversees the Energy Department's effort to secure nuclear material around the world, said the task is huge. "This is an effort which is a thousand small victories rather than one galactic one," Brooks said.
A report released this year by Harvard University's John F. Kennedy School of Government says that there is enough material in the former Soviet Union to build 80,000 nuclear weapons -- and only half of it is secured.
"There's certainly a huge amount of material," Brooks said. "The Cold War produced in both sides exceptionally large quantities of material."
At the height of the Cold War, the Soviet Union sent nuclear material to 17 Soviet republics and allies, including a reactor in Latvia.
But with the collapse of the Soviet Union, there was neither the money nor the political will to support these reactors. Today, the Latvia reactor's control room is covered with dust -- it was shut down seven years ago. But the nuclear fuel remained, protected by only a rickety gate, a few guards and some dogs.
Other sites in Russia were protected by simple locks or just wax and some string -- the same technology used to seal official letters hundreds of years ago. The Energy Department says the United States has upgraded security in about half of the sites in the former Soviet Union. But the only failsafe protection is to remove the material and take it to a secure location.
That's where Bolshinsky comes in.
For two days in May, ABC News had exclusive access as Bolshinsky and the U.S. team, along with Russian scientists and the International Atomic Energy Commission, painstakingly measured and recorded every ounce of fresh, weapons-grade, highly enriched uranium from the Latvia reactor.
"You can pick it up with your bare hands," Bolshinsky said. "I use gloves just to protect my hands, but yeah, it can be handled with just your bare hands. That's why it's so attractive to terrorists and other bad guys."
Each fuel rod was carefully wrapped in paper and cloth, labeled, then placed into two specially built metal casks supplied by Russia.
"After we remove this material, this country going be free of fresh HEU," Bolshinsky said, using the acronym for highly enriched uranium. "So we, we cleanse the country. We remove all fresh HEU which was stored here."
Ultimately, only about 6.5 pounds -- a fraction of what is needed to build a nuclear bomb -- was removed from Latvia. At a cost of $340,000 for the operation, that's about $51,500 a pound. In the next five years, the United States expects to spend more than $500 million to reduce the nuclear threat worldwide, including in the former Soviet Union.
But critics say that's nowhere near enough, and that hundreds of millions more are needed. Brooks disagrees.
"Our problems are not primarily money," he said. "Our problems are access in the Russian Federation. Our problems are convincing other countries that they need to take the threat as seriously as we are, and we keep working through that. The greatest incentive in the world is to understand that we're all in the cross hairs, and therefore we want to take away the bullets."
Brooks added that the process will not be quick, despite the urgency that is noted by critics. "It's a cooperative effort," he said. "It involves other countries. And so, if they think other countries should have greater urgency, don't tell me, tell them. And secondly, some of this just simply takes time."
But critics say we don't have time and point to 18 confirmed incidents of nuclear smuggling in the last decade.
Nuclear physicist Peter Zimmerman said not enough is being done to protect America. "All of our recovery efforts are fragmented," he said. "They're under-funded. The United States can afford to spend the money to recover this material ... a lot more than it can afford to replace a city."
He stressed that the threat is serious. "You seen the pictures of Hiroshima and Nagasaki lately?" Zimmerman said. "It's that serious."
It is in part the fear of failure that keeps Bolshinsky going. Before he left Latvia, he went to a former Nazi concentration camp not far from the reactor. Tens of thousands of Jews were murdered there during World War II, including 7,000 children.
"When we trying to prevent proliferation of nuclear weapons, we actually trying to prevent another nuclear war," he said. "And you see how many people was killed, how many people died, during the Second World War. And you realize that the third World War can be much bigger than that. Much more people will die. And it's what keeps you running."
ABC News' Cynthia McFadden reported this story for Nightline.