Three Mile Island

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Three Mile Island in Middletown, Pennsylvania on March 28, 1979 was the closest that America ever came to a nuclear power plant disaster. It brought about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations [1].

The accident began at 4 AM in the secondary cooling system of the second unit at TMI. The turbine stopped because approximately a cup of water leaked out through a faulty seal. Moisture got into the air system that drives the instruments and they stopped. This caused the flow to be interrupted because the pumps were off. The turbines then turn off automatically. The turbine does not allow the heat at the core to be released, so the emergency feed water pump kicks on. This did not work because the valve pipes were closed! This was a maintenance issue and did not allow any cooling water to enter into the system, causing a partial meltdown.


[edit] Whose Fault is This?

Operators?

  • they remembered closing the valves
  • with hundreds of valves, they are bound to miss a few and it's not unusual to find some in wrong positions
  • 2 indicator lights showed that the valves were closed
 - 1 was covered with a repair tag hanging on the switch above it
 - The other one was missed and it took 8 minutes to find it.

No cooling water?

  • Steam generator boiled dry
  • No heat was removed, so graphite rods had to be dropped in to stop reactions. *The reactions that still occur produce enough heat to power 180,000 homes.


[edit] Interwiki links