Smithsonian - National Museum of American History, Behring Center
Three Mile Island
Unit 2 nuclear power plant

Three Mile Island: The Inside Story

Five days of crisis

 
Looking east from Goldsboro, on the far side of the Susquehanna River from Three Mile Island.

Click to enlarge imageFigure 4.1. Looking east from Goldsboro, on the far side of the Susquehanna River from Three Mile Island.

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Wednesday, March 28

Although a general emergency has been declared before breakfast, it will be days before any general emergency is felt. By evening the condition of the reactor seems to be improving and radiation levels in the TMI-2 buildings seem to be falling. Now begins the oddly long, slow process of accepting that major damage to the reactor’s core has in fact occurred in the early morning hours.


Thursday, March 29

A day of relative calm—until evening, by which time nuclear engineers and public health officials are beginning to confront the fact of major damage to the reactor. And major damage implies the possibility of large quantities of radioactivity escaping from TMI.


Friday, March 30

Nuclear Regulatory Commission (NRC) officials in Washington, after 48 hours of underestimating the seriousness of the accident, now overestimate the danger. Unsubstantiated reports of dangerous releases of radioactivity lead Pennsylvania Governor Richard Thornburgh, on the NRC’s advice, to recommended that pregnant women and young children leave the area.

Late that night Food and Drug Administration officials rouse chemical manufacturers from bed with urgent requests for a quarter-million bottles of potassium iodide solution. A few drops of this taken in time will block the uptake in the thyroid gland of cancer-causing radioactive iodine, perhaps the most immediately dangerous of the radioactive substances to which reactor fuel is converted by nuclear fission.

Two-ounce (50 ml) bottle of potassium iodide solution prepared and labeled in haste for shipment to Harrisburg, PA.

Click to enlarge imageFigure 4.2. Two-ounce (50 ml) bottle of potassium iodide solution prepared and labeled in haste for shipment to Harrisburg, PA.

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There are, in fact, no releases of radioactivity that constitute a danger to public health. Alarm about reported releases of radioactive gases soon after the accident arose from misunderstandings. And later concern about the possibility of dangerous releases arose from a mistaken conclusion that hydrogen gas accumulated in the reactor vessel could explode.

Saturday, March 31

It is accepted that early on Wednesday morning much of the reactor’s core had stood above the water level. Consequently, it was certain that the zirconium tubes forming the cladding around the intensely hot fuel pellets would react chemically with the hot steam, pulling the oxygen out of H2O molecules and releasing hydrogen. This scenario is supported by the fact, not at first explicable, that at midday on Wednesday there had been a sudden rise in the pressure in the containment building of almost two atmospheres. Almost certainly, this resulted from the rapid burning of hydrogen that had escaped through the PORV from the reactor vessel and cooling system into the reactor containment building. Moreover it is known that some oxygen (and some more hydrogen) is continually being produced in the once-again-water-covered reactor core by the action of radiation on water molecules, breaking them apart into hydrogen and oxygen.

Is there then, or will there soon be, enough oxygen inside the reactor vessel and cooling system for the large amount of hydrogen it holds to burn explosively? Again NRC officials—albeit supported by the opinions and calculations of many experts—unnecessarily heighten fears by telling reporters that an evacuation out to 10 or 20 miles (15 to 30 km) might become necessary.


President Jimmy Carter and Mrs. Carter in the control room of the TMI-2 reactor.

Click to enlarge imageFigure 4.3. President Jimmy Carter and Mrs. Carter in the control room of the TMI-2 reactor.

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Sunday, April 1

Assured that any explosion is at least a couple days away, President and Mrs. Jimmy Carter tour the TMI facility early in the afternoon. In the hours following their visit, the expert consensus swings around to the opposite view—that a hydrogen explosion is simply not possible. The crisis is over—although no one says that loud and clear.

 


For a detailed, documented, and fascinating account of these days of crisis, as well as of the nuclear regulatory background and aftermath, see ref. 32.