VIENNA - UN nuclear inspectors have found uranium traces in an Iranian underground site refined to a somewhat higher level than the enrichment work normally carried out there, but still well below potential weapons-grade material, diplomatic sources said on Friday.
Nuclear bombs require uranium enriched to 90 percent, but much of the effort required to get there is already achieved once it reaches 20 percent concentration, shortening the time needed for any nuclear weapons "break-out."
One source said the higher level detected was believed to be within variation of the usual activity at the Fordow facility - where Iran is refining uranium to a fissile concentration of 20 percent - making clear it was not a big difference.
"It is not up there... towards nuclear weapons capability," the diplomat said. It could simply be a "production error" but the UN nuclear watchdog had asked Iran to clarify the issue.
Iran started enriching uranium to 20 percent in 2010 and has since sharply expanded the work, alarming Western powers about its intentions as it brings it closer to potential bomb material of 90 percent refined uranium.
Another diplomatic source said he had also heard of the find but it was unclear whether it would be included in an IAEA report due to be released to member states later on Friday. IAEA regularly inspects Fordow and other Iranian nuclear sites.
"My understanding is that the IAEA had found a particle or had tested a sample that had uranium enriched at a higher rate than had been declared at that facility," the first source said of the find at Fordow.
Enriched uranium can be used to fuel power plants, which is Iran's stated aim, or provide material for bombs, if refined much further, which the West suspects may be Iran's ultimate goal. Iran denies that.