GWEN IFILL: Since the end of the Cold War, the U.S. has been working with Russia to make sure its nuclear weapons don't fall into the wrong hands. But how is that program working? We have a report from special correspondent Simon Marks in Moscow.
SIMON MARKS, Correspondent: These are images you would not have been able to see just 15 years ago, not because they didn't exist, but because they were reserved for a handful of select eyes only. The nuclear reactor at the Kurchatov Institute in the northwest of Moscow was once the pride of the Soviet Union.
When it opened in 1943, this facility was called simply "laboratory number two" and had one goal: The creation of a Soviet nuclear bomb. Today its one of eleven nuclear reactors believed operational in the Russian capital.
ROBERT BERLS, Nuclear Threat Initiative: Of the facilities the U.S. government has been working on, only about 22 percent have received full security upgrades.
SIMON MARKS: Robert Berls worries about the Kurchatov Institute. He directs the Moscow office of the Nuclear Threat Initiative, a nongovernmental organization jointly founded by businessman Ted Turner and former Democratic Sen. Sam Nunn of Georgia.
ROBERT BERLS: It's an institute where the U.S. Department of Energy first began doing upgrades of nuclear facilities, but they have several facilities at the Kurchatov Institute.
But it's a relatively open facility, and a group of terrorists could I think very easily break into that facility if they tried hard enough. And, God forbid, if they were ever to get into those research reactors what damage they could do and the horror that could be unleashed on Moscow.
SIMON MARKS: In a bid to allay those fears, the Russians have been displaying some of the security measures they now deploy at the Kurchatov facility, including special troop carriers that have been converted to monitor levels of radioactive contamination in the event of any incident and emergency ministry troops who are kept on site around-the-clock. A corporate video has also been produced, designed to set minds at rest.
SPOKESPERSON (Translated): This is the sound of the protection system being activated in an emergency. Fortunately, it's only a simulation. But we never know.
SIMON MARKS: But what we do know with certainty is that terrorists have at least considered launching an attack against the Kurchatov Institute. In October 2002, Russian troops stormed the Dubrovka Theater in the center of Moscow, ending a siege by fighters from the breakaway Russian region of Chechnya.
For three days, 900 theatergoers and performers were held hostage inside the building. The Russians pumped a still unidentified narcotic gas into the theater in a bid to end the siege. The move killed the Chechen hostage-takers, but also 129 of their captives.
And while that very public military operation was playing out live on Russian television, over at the Kurchatov Institute, the Russians were quietly busy, according to Russian defense analyst Pavel Felgenhauer.
PAVEL FELGENHAUER, Defense Analyst: A friend of mine, a person who I know rather well, who worked in Kurchatov, he was called in immediately to the facility as the tragedy in the theater was evolving, to close down the biggest reactor.
So they acted immediately. They closed down that reactor and they removed a lot of radioactive material; 100,000 cures is a lot of radioactivity.
And the Russian authorities, when the Kremlin sees the real danger of nuclear facilities being captured several miles from the Kremlin, they act. They act, OK, because the threat is serious.
SIMON MARKS: A series of incidents, including last year's school siege in Beslan in southern Russia, also underscored the risk of an attack on a nuclear facility.
The Russian authorities concluded that if fighters from Chechnya or others pursuing a cause were sufficiently desperate to lay siege to a school, they may not hesitate to attack, raid or besiege a nuclear site.
ALEXANDER PIKAYEV, Institute of World Economy: I would say that it's a matter of luck, simply a matter of luck, because, especially in mid-1990s, the situation was so poor that one should be surprised that the worst-case scenario wasn't realized.
SIMON MARKS: Alexander Pikayev has written extensively on the problems securing and safeguarding Russia's nuclear stockpile.
ALEXANDER PIKAYEV: You cannot say, "Well, 50 percent is OK; A situation in 99 percent of facilities is OK," because even if in one facility, which contains probably less than 1 percent of the dangerous nuclear materials, the situation is bad, the amount of that nuclear materials might be enough to make nuclear bomb. So this is still, still dangerous.
SIMON MARKS: Both the U.S. And Russian governments have widely publicized the dismantling of elements of their nuclear stockpile. Missiles are broken apart, the fissile material recovered, and then their parts melted down for scrap.
A U.S. congressional initiative, the Nunn-Lugar Cooperative Threat Reduction Program, succeeded in deactivating 312 Russian nuclear warheads last year alone. But there is an enormous amount of work ahead.
Comprehensive security upgrades have not been completed on more than half of Russia's potentially vulnerable nuclear material. And defense analyst Pavel Felgenhauer says decommissioning warheads can create a raft of new problems to resolve.
PAVEL FELGENHAUER: Decommissioning means that they're dismantled. But the material that they were composed of didn't disappear much. That means it's stored somewhere, most likely stored in much less secure conditions than it was when it was a nuclear warhead.
So dismantling nuclear weapons is good, but that means that the material is less secure as a result. It's not an easy situation, and it's made worse by a mutual lack of trust, by ambiguity over the direction in which U.S.-Russian relations develop.
SIMON MARKS: And U.S.-Russian relations, rocky in general over U.S. concerns about Vladimir Putin's rollback of democratic reforms, are tense on the nuclear issue. The Russians won't allow U.S. inspectors to visit some of their most sensitive sites, a response, they say, to Washington's refusal to cooperate with Russian inspections in the U.S.A.
SERGEI LAVROV, Russian Foreign Minister: If we get facts, which would indicate that we need to do more, we would certainly respond. When we are told that we have general concerns, so why don't you take us here and there for us to see, well, on a reciprocal basis, this is possible.
And we managed to send our experts sometime ago to the States on the invitation to see a site, and eventually they didn't get there. So if those concerns are substantiated, I can assure you we would be the first one to wish to get these things right.
SIMON MARKS: Last month Secretary of State Condoleezza Rice discussed the nuclear issue with President Putin and senior members of his government. In an appearance on a Russian radio station, she was asked whether the U.S. is infringing Russian sovereignty by seeking access to the country's nuclear sites.
CONDOLEEZZA RICE, U.S. Secretary of State: We do not consider, in any way, the inspections that need to take place, issues of sovereignty. These are issues of cooperation, because we all need to be concerned about what happens as we dismantle the old nuclear weapons arsenals.
SIMON MARKS: It isn't only disagreement over how to implement accords on nuclear security that are keeping Russia's so-called "loose nukes" in the headlines.
Those seeking a higher priority for the nuclear issue on the U.S.-Russian bilateral agenda point to strategic realities that they say are contributing to the delay in bringing Russia's potentially deadly materials under control.
The U.S. And Russia military remain on hair-trigger alert, capable of mounting a nuclear attack on each other at a moment's notice. That means that here in Moscow, enormous resources are devoted to maintaining an operational nuclear arsenal.
Resources that are not being spent on threat containment. It's a threat posture rooted in the Soviet era.
And despite the enormous geopolitical changes since then, the Russian government maintains an operational nuclear arsenal scattered across a dozen time zones, and is estimated to produce up to a thousand new nuclear bombs every year to replace active warheads that have reached the end of their operational lives.
PAVEL FELGENHAUER: That's a problem that can be resolved only on a kind of level of heads of state. I mean this is strategic stuff; it can't be done just by confidence-building measures.
A lot of Russian military would want to keep their present holdings, because it's much easier to keep their present structure than to develop a new one. They actively resist any ideas that, not to sort of downgrade the United States' threat.
Because if you begin to talk about America not being a threat, you will be almost immediately branded an American spy. And I know the United States also don't want to change their posture.
SIMON MARKS: So on the 60th anniversary of the Allies' victory in Europe at the end of World War II, it will fall to President Bush and President Putin to try and advance the modern nuclear agenda during their meetings in Moscow.