What Happened At The Three Mile Island Nuclear Power Plant? Everything To Know About The Accident

This article features Government Accountability Project’s whistleblower client, Rick Parks, and was originally published here.

Netflix’s newest four-part docuseries, Meltdown: Three Mile Island, hits screens today. The series details the terrifying partial meltdown of a nuclear power plant in central Pennsylvania in 1979. The documentary features testimonials from the plant’s chief engineer and whistleblower, Richard Parks, and people from the surrounding community.

The fallout from the incident, and the attempt to downplay just how bad it was, are all covered in the documentary, along with some frightening footage of emergency crews driving through the streets, telling residents to close all their doors and windows.

If you’ve never heard of Three Mile Island, you probably have some questions. And even if the name rings a bell, the details about what actually happened on that fateful day in 1979 might still be a bit fuzzy. So, here’s everything you need to know about the incident:

So what actually happened at Three Mile Island?

On March 28, 1979, the Three Mile Island nuclear power plant experienced a partial meltdown of its nuclear reactor core (the place where the nuclear reaction takes place), according to History.comresulting in the “worst accident in the history of the U.S. nuclear power industry.”

The power plant had been built just five years earlier on a sandbar on the Susquehanna River in Pennsylvania.

It all started with a broken pressure valve that let cooling water drain out, History.com explains. The valve had been opened in response to a minor malfunction in one of the reactors’ cooling circuits, but workers in the control room failed to notice that the valve did not close as it was supposed to, per the U.S. Nuclear Regulatory Commission. Without the necessary amount of coolant present, the power plant’s core heated up to 4,000 degrees. If it had hit 5,000 degrees, the plant could have seen a total meltdown.

And if such a core meltdown had occurred, the radiation emanating from the plant would likely have caused some local fatalities. Luckily, the core’s protective shell never broke, and there were no major radiation leaks, History.com reports.

While it seemed as though operators had finally gotten things under control, later that afternoon they discovered that a bubble of hydrogen gas had formed in the reactor building—the result of a chemical reaction that occurred when the core was uncovered during the initial accident, per The World Nuclear Association.

Staff was able to diffuse the hydrogen bubble by periodically opening a vent valve on the reactor cooling system pressurizer, The World Nuclear Association said. Crisis (mostly) averted.

Did anyone die?

Thankfully, no. Local residents were urged to stay inside because experts initially weren’t certain whether the hydrogen bubble would cause a further meltdown or an explosion. Pennsylvania’s governor urged pregnant women and young children to leave the area if they lived within a five-mile radius, and panic ensued. More than 100,000 people fled, according to History.com.

Metropolitan Edison, the company that owned the plant at the time, initially said that no radiation had escaped, but inspectors later determined that there were increased levels of radiation and a contaminated water leak, per Fox 43. Despite this finding, later investigations found that the impact on people was “negligible,” according to the U.S. Nuclear Regulatory Commission.

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The state health department kept tabs on cancer rates in the area for 18 years, and documented no unusual findings, according to The World Nuclear Association. In contrast, when the Chernobyl nuclear plant exploded in 1986, 28 people died and 7,000 cases of childhood thyroid cancer were linked to the event.

How much did it cost to clean up?

A lot. The damaged nuclear reactor system took nearly 12 years and about $973 million to clean up, according to the American Nuclear Society. That included decontaminating plant surfaces, processing water that was used and stored during the cleanup, and the removal of 100 tons of damaged uranium fuel.

More than 1,000 technicians were needed to aid in cleanup efforts.

Richard Parks, a whistleblower, will play a prominent role in the film.

Richard Parks, who was an engineer at the plant, noticed that cleanup efforts were being rushed and regulations that had been put in place by the Nuclear Regulator Commission were being ignored during the cleanup process, according to the Government Accountability Project.

Parks alerted the authorities and was relocated, only to be fired later on.

What is the status of the plant now?

The plant is no longer in operation—it was officially decommissioned in 2019, per Fox 43.