Critical mass is ~50kg.

US tests have confirmed it is 89.4% enriched, usable in a nuclear warhead... They thought they were selling their 18g sample to a representative of an Islamist group as a precursor to a bigger consignment. But the buyer was an undercover police officer.

It is the third time in seven years HEU has been intercepted in Georgia. There have been 21 seizures or attempted thefts of weapons-grade material, uranium or plutonium, in the region since the Soviet Union collapsed. In every case the material seized had not been missed and mostly the theft was by an insider...

"Most likely, the materials were stolen in the mid- or early 1990s when a big amount of material disappeared. It's hidden somewhere and from time to time, someone is trying to find new buyers," said Archil Pavlenishvili, head of Georgia's radioactive materials investigation team. "We think that the game is not over. There will be more attempts."

Is the problem of that "big amount of material" being allocated at least as much talent as Stuxnet was?