By Beyond Nuclear staff

The disaster at Unit 2 of the Three Mile Island (TMI) nuclear power plant near Harrisburg, Pennsylvania, began on March 28, 1979. Today, 39 years later, the reality, of what really happened, and how many people it harmed, remains cloaked in mystery and misinformation. Unlike the popular catchphrase, TMI is a story of too little information.

What happened?

The two unit Three Mile Island nuclear power plant sits on an island in the middle of the Susquehanna River, just ten miles southeast of Harrisburg, Pennsylvania. TMI Unit 2 was running at full power, but had been commercially operational for just 88 days when, at 4 A.M. on Wednesday, March 28, 1979, it experienced either a mechanical or electrical failure that caused the turbine-generator and the nuclear reactor to automatically shut down.

The pressure and temperature in the reactor began to increase, but when a relief valve…