On This Day: Three Mile Island Suffers 'Severe Core Meltdown'


It seemed like a small thing at the beginning.

"Either a mechanical or electrical failure prevented the main feedwater pumps from sending water to the steam generators that remove heat from the reactor core," the U.S. Nuclear Regulatory Commission said.

But the dry language betrayed the severity of the issue, or more accurately, simply required a lot more dry language to run down the cascading emergencies until it got to the heart of the issue: eventually, one of the reactors suffered a "severe core meltdown, the most dangerous kind of nuclear power accident."


It was on this day in 1979 that the Three Mile Island (TMI) nuclear facility near Middletown, Penn. saw the "most serious accident in U.S. commercial nuclear power plant operating history."

But it could've been much worse. The NRC said that unlike Chernobyl in Ukraine and Fukushima in Japan, the building containing the reactor that melted down at TMI remained intact, keeping "almost all of the accident's radioactive material" inside. Though there were some "small radioactive releases," as the NRC put it, the public was spared.

Still, the Associated Press reported that for a week citizens within 20 miles of the facility "lived with the specter of unknown power out of control."

READ: AP Was There: Three Mile Island Nuclear Power Plant Accident

Moreover, U.S. officials and regulators were afraid -- a fear that prompted a rash of new regulations and training procedures.

In the end, officials blamed the disaster on "a combination of equipment malfunctions, design-related problems and worker errors."

Primary Source: NRC Backgrounder on the Three Mile Island Accident

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