Three Mile Island’s invisible threat

Just hours after learning about a technical malfunction at the Three Mile Island Nuclear Generating Center, Middletown Mayor Robert Reid described citizens as unconcerned.

“I went into a local diner where everyone congregates, and nobody was talking about it,” Reid told The Pittsburgh Press on March 28, 1979.

That silence wouldn’t last long. Within three days, one-quarter of the area’s 950,000 residents had voluntarily evacuated their homes, fleeing the invisible threat of leaked radiation and taking refuge at a relief center in Hershey Arena.

The Three Mile Island plant’s current owner has recently announced it will cease operations in 2019, so we dug into our archives to revisit the largest nuclear power accident in the country’s history, 38 years later.

Around 4:30 a.m. on March 28, operators were struggling to clear a blocked filter in one of the plant’s two reactors when misdirected water triggered an emergency shutdown of the reactor’s coolant pumps.

This set off a series of mechanical failures that culminated with the automatic shutdown of all heat removal systems, and rising temperatures left the reactor’s core partially disintegrated.

Human error dramatically escalated the situation when operators misunderstood how and when to activate the reactor’s manually operated relief valve. Radioactive coolant began to leak from the valve, which had become stuck open, but that did not become clear to employees for nearly three hours after the initial problem began.

The Three Mile Island incident ultimately resulted in very little radioactive exposure to local residents. On average, people in the area were exposed to roughly 1.5 millirems (mrems), a measure estimating the biological effects of radiation exposure. 

In comparison, a chest X-ray exposes patients to about 3.2 mrem. However, officials had an incomplete understanding of the danger posed and badly mismanaged the escalating media barrage.

Then-Pennsylvania Gov. Dick Thornburgh held a press conference two days after the accident to advise pregnant women and preschool children that they should evacuate Middletown. Everybody else was told to remain indoors as much as possible. To this day, there are disagreements over whether those announcements created unnecessary panic and conflicting accusations over who recommended particular courses of action.

“I’m very frightened,” said evacuee Judith Ebersol of Falmouth, Pa. the Saturday following the accident, according to The Pittsburgh Press. “I’m wondering if what happened is really worse than what they’ve been saying. I feel we’ve been lied to and I don’t trust the reports.”

Despite the government’s bungled response, however, some citizens remained unfazed by the accident.

“I don’t think it’s very serious, and I think they should repair the plant and put it back into operating order,” one unnamed Harrisburg resident told The Pittsburgh Press three days after the accident. “This country can’t exist without nuclear power.”

Only one of the plant’s reactors was damaged during the meltdown, and then-owners Metropolitan Edison decided to reactivate the functional reactor in 1985. That decision drew massive backlash from lawmakers and the public, inspiring the protesters seen here and many others around the world. Some activists even called for the plant to be converted into a park.



“We all live in Pennsylvania,” German protesters chanted when the accident occurred, according to the Associated Press. Those chants were renewed upon the plant’s reopening.

A family fishes on the Susquehanna River near Middletown, Pa. in March 1984, the fifth anniversary of the Three Mile Island accident. (Associated Press)

The accident would prove to be a turning point for the country’s energy policies. Prior to 1979, nuclear energy was hailed as the gateway to a clean energy future. But that growth stopped almost immediately following the Three Mile Island debacle. The number of reactors under construction in the U.S. declined every year from 1980 through 1998, and authorizations to build new nuclear plants halted completely until 2012.

Though the ultimate fate of the Three Mile Island facility is unknown, the crisis that consumed it remains a defining moment of the 1970s and the nation’s fight over how best to harness the atom.

— Matt Moret

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