Three Mile Island – 1979

For an event that fascinated the world and sent a frisson of fear scorching through the USA, the nuclear accident at Three Mile Island was in fact the disaster that never (but nearly) was. The accident could have developed into a ‘China Syndrome’, that hypothetical catastrophe where the core of a nuclear reactor melts down and spews out lethal radioactivity. But it didn’t actually happen. So what did?

The Metropolitan Edison Company operated two pressurized water reactors on an island in Pennsylvania’s Susquehanna River. Unit One (TMI-1) came on line in 1974 and Unit Two (TMI-2) in 1978. The following year, in the early hours of the morning of March 29, a minor cooling system failure in TMI-2 initiated an unfortunate series of events.

Reactor temperature rose, causing automatic shut down. A relief valve failed to close, draining coolant from the reactor core. Inadequate instrumentation meant that control-room staff assumed the valve had closed, so they mistakenly reduced the flow of replacement cooling water. The reactor’s core then overheated and started to melt, contaminating the remaining coolant. This subsequently released radioactive gases into the atmosphere on March 30 and 31.

Once the operators realized what was happening, they plugged the leak and initiated cool-down. After an anxious month, reactor shutdown was finally achieved on April 27. The containment building did its job and – despite acute public apprehension resulting from poor communication – there were no further radioactive leaks.

In 1996, a class action lawsuit claiming damages for ill-health effects was dismissed for lack of hard evidence. Some studies suggested that leukaemia and lung cancer rates increased significantly in the population exposed to radioactive krypton gas and iodine-131, but the official line remains that there were no adverse medical consequences of Three Mile Island. Meanwhile, TMI-1 remains one of the most productive nuclear energy plants in the USA.

When: March 28 1979

Where: Londonderry Township, Dauphin County, Pennsylvania, USA

Toll: None – or at least no proven consequences

You should know: in a rare example of life imitating art, a near-disaster movie entitled The China Syndrome (starring Jane Fonda, Jack Lemmon and Michael Douglas) was released just 12 days before Three Mile island hit the headlines, featuring safety cover-ups at a nuclear plant. Events at Three Mile island ensured that the film became an instant international blockbuster.