Three Mile Island’s invisible threat

This 1972 photo shows the Three Mile Island plant during construction of the cooling towers for TMI Unit 2 (right). This unit would be the site of a partial meltdown and shut down in 1978, while TMI Unit 1 (left) reopened in 1985 and will remain operational through 2019. (Associated Press)

A Nuclear Regulatory Commission helicopter flies past the cooling towers of the Three Mile Island nuclear power plant, checking radiation levels just hours after technical malfunctions were first reported. (Associated Press)

President Jimmy Carter (center, front) tours the control room of the Three Mile Island plant April 1, 1979, one week after the accident occurred. Pennsylvania Governor Dick Thornburgh (center, rear) and Dr. Harold Denton, Director of the U.S. Nuclear Agency, joined Carter and several unidentified plant employees. (Associated Press)

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.

Chris Becker, a dairy farmer who lived only a mile from the disabled Three Mile Island nuclear power plant, is scanned for radiation during a test in Middletown, Pa. (Associated Press)

Holly Garnish, 32, of Middletown, Pa., holds detectors placed in her shrubs by the Nuclear Regulatory Commission. Garnish’s home was the closest of all area residents to the Three Mile Island plant. (Associated Press)

The final container of radioactive waste is transported from the Three Mile Island plant April 3, 1979, headed for the U.S. Department of Energy facility in Richland, Wash. (Associated Press)

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.”

An employee of the Three Mile Island plant wears a containment mask as he leaves the facility. This photo was taken two days after the accident, soon after the reactor’s coolant leak was officially identified. (Associated Press)

A Three Mile Island employee enters the facility wearing one of the metal decontamination suits personnel had to wear when working near the crippled reactor. (Associated Press)

Evacuees from the area surrounding Three Mile Island watch news updates at the Hershey Sports Arena. (Associated Press)

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.

This diagram shows artist Jay Critchley’s plan for a park to be built in the uncontaminated section of Three Mile Island. The park would have included a shopping plaza, which Critchley named the “Meltdown Mall,” and a museum about nuclear power. (Associated Press)

An anti-Three Mile Island protestor blocking the front gate of the plant is carried away by state police and arrested near Middletown, Pa. Demonstrators were protesting the Nuclear Regulatory Commission’s 1985 decision to restart the undamaged TMI Unit 1 reactor. (Associated Press)

Two protestors wear gas masks while attending a 1989 anti-Three Mile Island rally on the 10th anniversary of the accident. In the background, steam rises from the undamaged, restarted Unit 1 facility. (Associated Press)

“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.

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