Three Mile Island

The thriller China Syndrome, which warned that a nuclear power plant meltdown would blow a hole through the earth all the way to China and "render an area the size of Pennsylvania permanently uninhabitable" had been playing for eleven days when, at 4:00 am on March 28, 1979, Reactor #2 at the Three Mile Island (TMI) nuclear power plant suffered a partial meltdown. The plant was just downriver from Harrisburg, Pennsylvania.

Film story, reality, and perception all interplayed to create near national panic. The accident occurred sequentially. A minor problem caused the temperature of the primary coolant to rise. In one second, the reactor shut down but a relief valve that was supposed to close after ten seconds remained open. Plant instrumentation showed operators that a "close valve" signal had been sent. There was no instrumentation to tell them the valve itself was still open. The reactor's primary coolant drained away and the reactor core suffered serious damage. Fuel rods were damaged, leaking radioactive material into the cooling water and a high temperature chemical reaction created bubbles of hydrogen gas. One of these bubbles burned, creating fears that a larger hydrogen bubble would explode, possibly breaching the plant's containment structure. Some gases were purposefully vented into the atmosphere.

It took nearly a full month the bring the reactor into "cold shutdown" status. That said, there was never danger of a massive explosion and hundreds of readings taken by the Pennsylvania Department of Environmental Resources showed almost no iodine, and all readings were far below health limits. There was, however, widespread panic including a unordered mass evacuation. The greatest problem at TMI was a total failure of communication. Internal radioactivity levels, for example, were reported as ambient (outdoor) air readings.

The many health studies following TMI showed no evidence of abnormal cancer rates. For eighteen years, the Pennsylvania Department of Health maintained a registry of 30,000 people who lived within five miles of TMI; it control rod a rod containing substance that absorbs neutrons inserted into a nuclear reactor to control the rate of the reaction

A civil defense worker is using Geiger counter to check radiation level near a school building following the accidental radiation leak from the nearby Three Mile Island nuclear power plant. Schoolchildren are being evacuated via bus. (©Wally McNamee/Corbis. Reproduced by permission.)

found no evidence on unusual health trends. TMI's only health effect was psychological stress related to the accident.

While there were few long-term health effects, there is no doubt that the accident at TMI permanently changed both the nuclear industry and the Nuclear Regulatory Commission (NRC). "Public fear and distrust increased," the NRC notes in a fact sheet on TMI, "Regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully."

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