"Instances of the loss of nuclear materials have been recorded, but what the quantity is is another question," Yuri Vishnyevsky, head of Gosatomnadzor, said Thursday. "Of those situations that we can talk about in actuality, they involve either grams of weapons-grade or kilograms of the usual uranium used in atomic power plants."
"Most often, these instances are connected with factories preparing fuel: Elektrostal in the Moscow region and Novosibirsk" in Siberia, Vishnyevsky said.
He did not give further details on when the losses were discovered or how the material might have gone missing.
The International Atomic Energy Agency lists two known thefts of uranium from Elektrostal, in 1994 and 1995. In both cases, the uranium was seized by Russian police.
The agency also lists the 1994 seizure in Germany of 400 grams of plutonium brought in from Moscow.
A few grams of Uranium-235, the most common weapons-grade nuclear material, would not be sufficient to make a bomb. But reactor-grade uranium can be enriched to weapons-grade through a complicated process believed to be possessed by some countries trying to develop nuclear weapons, such as Iraq.
Russia's nuclear security has been a high concern in the decade since the Soviet Union's collapse brought financial troubles that reduced funding for state facilities and induced poverty that could motivate nuclear workers to sell atomic materials.
Worries have risen in the wake of increasing terrorism, including last month's attack on a Moscow theater by Chechen gunmen who held hundreds of hostages to press their demand that Russia withdraw troops from Chechnya.
"After Sept. 11 of last year, the situation with regard to security at all Russian nuclear facilities changed for the better, but it still has not reached perfection," Vishnyevsky said.
He estimated that bringing security to its ideal level at Russian nuclear operations would require about 6 billion rubles, or $200 million.
Vishnyevsky made his statements while criticizing a proposed law on technological regulation now being considered by the Duma, the lower house of parliament.
He presented a letter to the Duma from a number of prominent scientists criticizing the proposed law for calling for "the minimal necessary demands for security at the same time that in the whole world and in our country the demands for security in using atomic energy should be the maximum."
It also was reported Friday that a Russian scientific expedition located a Soviet nuclear submarine and 237 containers of radioactive waste in the northern Kara Sea.
The K-27 submarine was dumped in the Kara Sea in 1981, 13 years after one of its reactors released radiation and it was taken out of service, according to the Norway-based environmental group Bellona.
Expedition members also examined what is believed to be the burial site of the reactor section of another nuclear submarine — the K-254, Russian Deputy Emergency Situations Minister Mikhail Faleyev told the Interfax-Military news agency.
Preliminary tests of water, sediment and sea life found that radiation levels are "stable" at both sites, Faleyev said.
Environmental groups say the Soviet Union routinely dumped radioactive waste and nuclear reactors from decommissioned submarines into Arctic waters off the Novaya Zemlya archipelago, a former nuclear testing site.
By Jim Heintz