I was wrong. It was Pakistan, not Iran. The enrichment program was certainly covert though.
In September 1981, a powerful earthquake measuring 6.1 on the Richter scale shook Islamabad and the surrounding area. Pakistani scientists at Kahuta were on a lunch break when the earth shook, forcing them to run to work stations only to hear the sounds of explosions. Some four thousand centrifuges operating in the Khan Research Laboratory had crashed. The earthquake had unbalanced the rotors, operating in a vacuum at some 64,000 revolutions per minute (RPMs); they hit their casings and turned to powder, making sounds like hand grenades exploding.