Incident Chronology at TMI from NRC: 1979 - 2021

March 28, 1979, 4:00 a.m. - Beginning of the Three Mile Island (TMI) Unit-2 loss-of-coolant, core melt accident. The plant came within 30 minutes of a full meltdown. The reactor vessel was destroyed, and large amounts of unmonitored radiation was released directly into the community.