Two undeclared facilities, exposed by an exile group
Iran had signed the Non-Proliferation Treaty and insisted its program was civilian. Then an exiled opposition group announced the existence of an enrichment plant at Natanz and a heavy-water plant at Arak, neither declared to the IAEA. Satellite imagery confirmed construction at both. The crisis that followed has never closed.
How the D workedMore than a decade of clandestine work preceded the exposure. The denial held exactly as long as it was sustainable, and not a day longer.
Chapter 4. IAEA Board report GOV/2003/40; Arms Control Association, Timeline of Nuclear Diplomacy With Iran.