VIENNA (Reuters) - U.N. nuclear inspectors have found uranium traces in an Iranian underground site refined to a somewhat higher level than the enrichment work normally done there, but still well below the weapons-grade threshold, diplomatic sources said on Friday. One source said the higher level detected at the Fordow site - where Iran has declared it is refining uranium to a fissile concentration of 20 percent only - was believed to be between 20 and 30 percent, making clear this was not a big difference. "It is not up there ... towards nuclear weapons capability," the diplomat said. ...