Three Mile Island and the Exaggerated Risk of Nuclear Power

You’ve likely heard of the 1979 Three Mile Island nuclear accident. It’s often cited as an example of the dangers of nuclear power. It’s usually mentioned in the same breath as Chernobyl and Fukushima.

But what exactly happened there? Was it truly an exemplar of the grave dangers posed by nuclear power?

The answer is no. No one died. No one was injured. The other reactor on the site was still in operation until September 20 (yes, September 20 of last year). The Three Mile Island incident is an example of both the recallability trap and the sometimes negative results of being too yielding to the demands of the precautionary principle.

The Psychological Impacts

The main impact of the Three Mile Island accident has been psychological rather than physical. Big events like this one shape public attitudes for decades. People don’t remember the real impact of the event; they remember the feelings of uncertainty and fear that came with it. Those feelings now taint the public image of nuclear power in the United States.

The accident at Three Mile Island Unit 2 occurred at 4 a.m. on March 28, 1979. There was a malfunction in the reactor’s secondary cooling circuit, and the temperature of the reactor’s primary coolant rose, causing an automatic shutdown of the reactor. Control room instruments didn’t alert operators that a relief valve failed to close. Because of this, the reactor did not cool as it should have, and the core was damaged. Later that day, a small amount of gas was released accidentally, but the released gas traveled through air filters, which removed all of the radionuclides save the relatively harmless and short half-lived noble gases.

The event caused no physical harm, but the public perception of the risks of nuclear energy was heightened dramatically.

The accident created public fear but posed no real threat to the public. According to the Nuclear Regulatory Commission (NRC), the two million people in the area around TMI-2 at the time of the accident received an estimated dose of only 1 millirem above the usual background

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