March 28, 2023

The Three Mile Island Nuclear Accident

The Three Mile Island Nuclear Accident

March 28, 1979. The worst nuclear accident in American history begins when Pennsylvania's Three Mile Island power plant experiences a partial meltdown.


Cold Open

It’s March 28th, 1979 at the Three Mile Island nuclear power station near Harrisburg, Pennsylvania.

It’s a few minutes before 4 AM, and the shift foreman, Frederick Scheimann, is attending to some paperwork in his office. In the basement below, two other men, Donald Miller, and Harold Farst, are taking care of some routine maintenance. And as the clock nears 4 am on the dot, Frederick decides to check in on their progress.

On arriving, Frederick finds Donald and Harold cleaning out the pipes that feed and purify cooling water into one of the plant’s reactors. Donald beckons Frederick over and explains that there’s a slight plumbing problem: one of the pipes that carries away impurities is blocked. He goes on to explain they have been trying for the best part of an hour to flush away the blockage, but it is yet to budge.

Frederick frowns because this is unusual. He peers into a glass window on one of the pipes to try and figure out what the issue might be. But as he inspects the machinery closer, he hears a sudden, loud crashing noise… and then the buildings' loudspeakers blare an alarm that there has been ‘a turbine trip, a reactor trip’.

Frederick rushes to the control room where he finds workers in a frenzy. No one is sure what to do because most, Frederick included, received little training to work at the plant, let alone handle any kind of meltdown. But as they argue over what to do first, the crashing sound stops.

Frederick looks at the clock. It's 37 seconds past 4 AM, and the reactor has shut down. Immediately, the automatic emergency cooling system begins. But when Frederick and his team check the water readings, they determine that there is too much cooling water in the reactor.

So, they shut off the emergency system.

But, in reality, the generator is boiling dry. And it is only getting worse. Unbeknownst to the workers in the control room, a valve intended to release pressure has malfunctioned and remained open allowing coolant to rapidly drain away from the reactor and leave its temperature rising. Frederick and his colleagues think that they have averted disaster, but America’s greatest nuclear accident has just begun.

By the late 1970s, what once was a small nuclear power industry has grown rapidly. With more demand than ever, power plants are often managed by underqualified and undertrained workers. And outside Harrisburg, Pennsylvania, a combination of equipment failures and operational errors will result in a partial reactor meltdown that will draw international attention and heighten concerns over the risks of nuclear energy after the accident at Three Mile Island becomes the worst nuclear disaster in American history on March 28th, 1979.


From Noiser and Airship, I’m Lindsay Graham and this is History Daily.

History is made every day. On this podcast—every day—we tell the true stories of the people and events that shaped our world. 

Today is March 28th, 1979:The Three Mile Island Nuclear Accident.

Act One: Evacuation?

It’s around 6 AM on March 28th, 1979 near Pittsburgh, Pennsylvania.

While the accident at Three Mile Island is still ongoing, Pennsylvania’s governor, Dick Thornburgh, is asleep in bed. Thornburgh has only recently been elected governor, holding office for a mere 71 days. But he’s about to be thrust into the center of an unprecedented public health disaster. 

Two hours ago, a nuclear reactor on Three Mile Island started to experience a partial meltdown. While workers struggled to recognize the issue, contaminated and radioactive cooling water leaked into the building surrounding the reactor, releasing radioactive gases throughout the plant. The open pressure valve that originally caused the reactor to overheat has only just been discovered. And given the severity of the accident, it’s now time for the government to get involved.

So rather than being awoken by his alarm clock, Thornburgh’s telephone is jolted awake by his telephone. Bleary-eyed, he rolls from his bed and picks up the phone. The information he receives is clear and direct: there's a problem at Three Mile Island and he needs to be there — now.

Thornburgh is shaken. His knowledge of nuclear energy is limited. In his short tenure as governor, he has only received one undetailed briefing and never anticipated an accident of the scale of the one presently brewing at Three Mile Island. He's undereducated and ill-prepared but he's got no time to catch up; he has little choice but to go in blind.

Thornburgh is out of the house in a matter of minutes. And when he arrives at Three Mile Island, a state of emergency has already been declared and the media are swarming the site. At the power plant, Thornburgh is fed mixed information. Rumors of evacuation plans are circling, as are stories of dead animals killed by radioactivity. Thornburgh finds himself thrown into an unfamiliar level of crisis management — not only does he need to solve the accident itself, but he must control the building public panic.

His task is complicated by the fact that he simply does not have the facts. The Federal Emergency Management Agency has a plan for evacuation in place but Thornburgh stalls on making the announcement. He doesn’t want to issue an evacuation until he knows the full extent of the radioactive leak. Any unnecessary moves or overreactions might only cause more panic, and the frenzied retreat of 200,000 people living near the power plant could potentially be more destructive than the accident itself.

Instead, Thornburgh builds a team he calls the ‘ad-hocracy’ — a band of trusted advisors and colleagues who, along with the Nuclear Regulatory Commission, help him gain the fullest picture of the events at Three Mile Island. They assert that the radiation levels detected would only have a minimal impact on the public. And though this is good news, Thornburgh decides to keep this information private. At least, for now, he fears any mention of radiation will create unnecessary fear. But Thornburgh does cancel any plans for evacuation having been assured the public is safe.

But not long after Thornburgh makes that decision, Metropolitan Edison, the utility company who runs the plant, releases a statement to the press revealing that there has been a release of radioactivity into the area around Three Mile Island. The result is exactly what Thornburgh intended to avoid - a mass panic.

As the day wears on, efforts are made to solve the immediate issues at the plant. Emergency water pumps are turned back on and the temperature of the reactor is gradually lowered. Thornburgh receives reports that the core of the reactor had soared to 4,000 degrees Celsius and was just an hour away from total meltdown. But now, it’s reported that while the core is damaged, no serious radiation has leaked or been detected outside the plant.

But this information contradicts the earlier reports from the Metropolitan Edison. Not knowing who to trust, some members of the public decide to take no chances, pack their cars, and flee the area. But, despite the panic, Thornburgh remains calm. He reassures residents that the accident is under control and further cooling plans would bring a swift end to the entire incident.

The governor’s composed demeanor will settle the nerves of many, but as contradictory messages continue to spread, protestors will begin to target Three Mile Island, adding more pressure and panic. As the day draws to a close, there’s still one hidden problem lurking at the power plant. Its discovery will have not just Three Mile Island, but the whole of America stricken with fear. 

Act Two: Evacuation!

It’s 10:30 AM on February 29th, 1979, at the Three Mile Island nuclear power plant.

Outside its gates, members of Governor Dick Thornburgh’s ‘ad-hocracy’ team are speaking to a vast number of journalists itching for any new piece of information.

People want answers to what’s unfolding at the reactor. And the confusing messages of the previous day have led journalists, and members of the public, to wonder if the government may be withholding crucial details from them. As a result, anti-nuclear groups have started to gather momentum and now line the streets of Pennsylvania. While Thornburgh may think all is under control at the plant, he now has to contend with the palpable anxiety spreading across his state and the nation. So, Thornburgh’s team has come to Three Mile Island to address those fears and clear up the confusion.

They reveal that a plane equipped for detecting radiation has picked up traces around the plant, but they are minimal and of little concern. Thornburgh and his team remain clear that an evacuation is still not necessary, but people should shut their windows and remain indoors until the issue is fully resolved. For the remainder of the day, work to cool the reactor continues, and it seems that for now, the accident is moving toward a safe conclusion. But then, a new discovery changes everything overnight: as a result of complications in cooling the reactor, a dangerous bubble of hydrogen gas has formed inside the core; if this hydrogen were to ignite and explode, vast amounts of lethal radioactive gas will be released.

The morning after learning about this complication, Thornburgh calls another press conference in nearby Middletown. Backstage, he peers out of a small window looking out to the packed conference room full of journalists and camera operators. The air is filled with nervous chatter as members of the press worry over the severity of the accident and whether this conference will herald good, or bad, news.

As the governor walks into the room, questions from reporters fly toward him. He declines to answer until he sits and raises a hand to silence the crowd. Then, after a sharp intake of breath, Thornburgh reveals that teams working at the plant have found a volatile and potentially dangerous hydrogen gas at the Three Mile Island power plant. He explains that if this hydrogen were to explode, the structural integrity of the reactor could be compromised, and radioactivity could be released into the open air.

The press conference immediately erupts in uproar, hands flail in the air as questions are barked with a new ferocity. But Thornburgh remains calmly poised and raises his hand again for silence. He purses his lips before stating that it is vitally important that pregnant women and children evacuate the area immediately, reversing his previous position. And then, Thornburgh makes his exit leaving the stunned journalists behind.

Backstage, the cacophony of angry, unsatisfied, and panicked reporters fades away, and the governor lets out a long sigh. He turns into a side room to gather himself for a moment. But his attention is quickly grabbed by a television set on the wall. The news shows images and video from areas near Three Mile Island depicting parents already running with their children, cars racing down the streets, and the audible cries of panic. Thornburgh’s heart drops as he feels the full weight of what is at stake. A feeling of powerlessness sweeps over him as he realizes that all he can do is hope that the hydrogen can be contained.

After the governor’s press conference, all schools within five miles of the stricken reactor close their doors. Over 100,000 people decide to evacuate. Full-scale panic sets in as rumors circulate about what's really going on at the power plant. People begin to question how long the hydrogen bubble has been kept from their knowledge, and what else is yet to be revealed. The mixed messages and perceived lack of transparency builds a sense of distrust in the nuclear energy industry, government, and in leaders like Thornburgh.

So over the next 24 hours, the governor will lead an effort to both calm and shelter those directly affected by the accident at Three Mile Island. Meanwhile, inside the plant, workers will risk their lives to attend to the hydrogen bubble and prevent any further radiation leak. Through their perseverance, they will manage to eliminate the threat of explosion. And to many, this will feel like a lucky escape. But Governor Thornburgh will still have his work cut out for him as he grapples with the accident’s lingering repercussions and tries to form a plan to quell the public’s panic.

Act Three: Un-evacuation

It’s April 1st, 1979, four days after the accident at Three Mile Island began.

Pennsylvania Governor Dick Thornburgh sits aboard a bus heading toward the island. Alongside him is his ‘ad-hocracy team’ and a band of photographers, their lenses aimed at the bus’s most distinguished passenger: President Jimmy Carter — the man Thornburgh believes is the key to managing the fallout from the Three Mile Island accident.

After the discovery and reduction of the hydrogen bubble, Thornburgh arranged for President Carter to visit Three Mile Island’s power plant. The president has a unique background in nuclear energy. He has trained as a nuclear engineer and even worked on dismantling a broken nuclear reactor during his time in the US Navy. He seems like the perfect figure to assure the public that Three Mile Island is safe and to quell public's persisting distrust.

But when the bus arrives, the appearance of President Carter does little to deter the anti-nuclear protestors swarming the island and soon surrounding the bus, waving signs high in the air. There’s an unmistakable anger in the crowd who either disbelieve the government’s narrative about the nuclear crisis or are against the idea of nuclear energy itself.

As Thornburgh guides President Carter up to the plant’s gates, the protestors whistle and cry derisively. But the men ignore the yells as they travel into the heart of the power station. Inside the control room, photographers capture the two politicians watching the clean-up operation already underway. Both men know that this is going to be a very expensive accident, financially and politically. But being here, in the control room, where radiation had earlier been detected, seems like a good first step in getting out the message that Three Mile Island is now safe.

And indeed, after President Carter visits the power plant, 98% of the hundreds of thousands of evacuees will return back to their homes. Dick Thornburgh’s response to the nuclear disaster is soon regarded by many as exemplary crisis management. But concerns about the health consequences of the Three Mile Island Accident persist.

While the island will be deemed safe for the public, suspicion remains over the many workers who were exposed to dangerous levels of radiation during the accident’s initial stages. And in the coming years, debate will continue over the effects the accident’s radiation will have on public health. Authorities will maintain that the health effects of the low level of exposure are negligible. But, across the country, protestors will use Three Mile Island `as a reason to continue to campaign against the use of nuclear energy, citing a lack of trained workers and a prioritization of profit over public health.

And at least in part, the protestors’ message will be heard. In the wake of the events at Three Mile Island, new care will be shown toward training power station staff. The US government’s Nuclear Regulatory Commission will strengthen its oversight. And in an effort to enhance safety at all nuclear plants, sweeping changes will come to emergency response planning, operator training, radiation protection, and many other aspects of nuclear operations.

The value of these updates, and the danger still present, will become even more evident after another crisis shakes the world. Yet again, faulty equipment and inadequately trained personnel cause the world’s worst nuclear disaster at Chernobyl in the Soviet Union, just seven years after similar problems sparked the Three Mile Island Accident on March 28th, 1979.


Next on History Daily. March 29th, 1865. During the American Civil War, Union General Ulysses S. Grant launches the Appomattox Campaign, ultimately forcing the Confederates to surrender.

From Noiser and Airship, this is History Daily, hosted, edited, and executive produced by me, Lindsay Graham.

Audio editing by Muhammad Shahzaib.

Sound design by Mischa Stanton.

Music by Lindsay Graham.

This episode is written and researched by Luke Lonergan.

Produced by Alexandra Currie-Buckner.

Executive Producers are Steven Walters for Airship, and Pascal Hughes for Noiser.