Russia seizes radioactive sodium headed for Iran

Updated at 8:18 a.m. Eastern.

MOSCOW - Russia's customs agency says it has seized radioactive metal from the luggage of a passenger bound for Tehran.

The Federal Customs Service said in a statement that its agents found 18 pieces of metal at Moscow's Sheremetyevo airport after a radiation alert went on. It says the gauges showed that radiation levels were 20 times higher than normal.

Spokeswoman Kseniya Grebenkina told The Associated Press that the luggage had been seized some time ago, but could not specify when. The Iranian hasn't been detained, she said.

The customs agency said prosecutors have launched a probe into the incident.

The pieces contained Sodium-22, Grebenkina said, a radioactive isotope of sodium that could be produced in a particle accelerator. Sodium-22 is a positron-emitting isotope that has medical uses, including in nuclear medicine imaging.

Sergei Novikov, spokesman for the Rosatom nuclear agency, told the AP that the pieces are highly unlikely to have come from Rosatom and said the isotope is produced by particle accelerators, not by nuclear reactors.

In Russia, universities, research institutes and big medical centers can have the technology to produce it, he said.

"There is an extremely slim chance that it could have come from Rosatom," Novikov said.

Novikov said that Rosatom has never sold Sodium-22 to Iran, but it has supplied it with other types of medical isotopes.

Nuclear expert John Large told CBS News that Sodium-22 is not used in nuclear weapons production, and would not likely be used in any attempts to construct a radioactive improvised explosive device, or a so-called "dirty bomb".

A second nuclear expert, Malcolm Grimston of the London-based thinktank Chatham House, also said Sodium-22 is not used in nuclear weapons, but that it is used for medical purposes.

Large said the material must have come from a Russian state-sponsored reactor, as there are no privately-owned reactors that can cope with such a product.

A blanket of international sanctions greatly restricts the import or export of any radioactive materials - and any other materials which could be used in a nuclear program - to or from Iran.

The sanctions make smuggling the best way for the Iranians to acquire radioactive materials to run their working reactors, said Large. He says the size of the luggage would need to be large, as it would need to shield the material, but he adds that it cannot have been that well shielded to have set off the radioactive sensors in the airport.

The United Nations nuclear watchdog agency, the IAEA, says of radioactive sodium:

"Sodium and sodium-potassium eutectic (NaK) have been used as coolants in several research reactors as well as in a small group of prototype and commercial nuclear reactors with fast neutrons. Some of the reactors are still in operation; however, most of them have been already shut down either for their age or for economic reasons. Sophisticated sodium cooled reactors with fast neutrons are considered as a prime candidate for the next generation of future reactors with advanced fuel cycles maximizing resource utilization and minimizing waste production."