On March 28, 1979, the worst nuclear accident in United States history occurred in central Pennsylvania. The incident was rated a five out of seven on an International Nuclear Event scale and led to a sharp increase in anti-nuclear sentiment throughout the nation. Here’s the story of the disaster at Three Mile Island in Pennsylvania.

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Three Mile Island, the facility where the partial nuclear meltdown took place, is located near Middletown, Pennsylvania. A series of mechanical failures in the second reactor's cooling system led to the disaster.
Todd MacDonald/ Flickr
At 4 a.m., the accident occurred. The reactor shut down without warning, causing a relief valve to open. It should have shut 10 seconds later, but remained open; the instrumentation indicated otherwise, which misled the power plant's operators. Over the course of the next few days, radioactive gasses leaked from the plant to the surrounding areas. Luckily, the radioactive content of these gasses was not enough to cause radiation sickness in any inhabitants of the area.

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There were no sicknesses or deaths as a result of the Three Mile Island incident, although the incident caused considerable panic in the area. Confusion in the media led to a minor evacuation. The second nuclear reactor, the core of which melted, was completely destroyed. Clean-up took 12 years and cost $973 million.
Franklin & Marshall College/ Flickr
Though no one suffered injury or death as a result of the Three Mile Island accident, it led to a sharp increase in anti-nuclear sentiment in the country. The Pennsylvania Department of Health kept records on 30,000 people who lived within five miles of Three Mile Island until 1997, when it was determined that there were no long-term health effects from the incident.
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This incident led to increased safety precautions in nuclear facilities and today is remembered as one of the most devastating events in Pennsylvania history.

Do you have any stories from the disaster at Three Mile Island in Pennsylvania? Do you remember this day? Share your experience in the comments! Then learn more about The Darr Mine Disaster, the worst mining disaster in Pennsylvania’s history.

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Three Mile Island in Pennsylvania

Beth Price-Williams | January 25, 2021

What is Pennsylvania known for?

We have such a rich history in Pennsylvania that it seems like we’re always learning something new. Did you know, for example, that Pennsylvania is the birthplace of quite a few inventions? The Ferris Wheel, for example, was invented by George Ferris in 1892. He invented it in Pittsburgh while it debuted at the Chicago’s World Fair. The first emoticon – a smiley face – was created by Scott Fahlman at Carnegie Mellon University, and the first slinky was invented and went on sale in Philadelphia in 1943. In addition to its inventions, Pennsylvania is also known for its fierce rivalries – Steelers versus Eagles. Phillies versus Pirates. Wawa versus Sheetz.

Is Pennsylvania a great place to live?

The rich history of Pennsylvania is just one of the many reasons it’s a simply amazing place to live. Did you know that Pennsylvania’s also home to 121 state parks, including Ricketts Glen State Park? Ricketts Glen boasts 21 waterfalls, which you can see on one epic trail (Falls Trail). It’s also home to 19 national parks. PA also offers a little bit of everything – big cities like Pittsburgh and Philly; small towns like Lititz and New Hope, and enchanting villages like Eagles Mere. You’ll also find professional sports teams in football, baseball, basketball, and hockey.

What are the most well-known parks in Pennsylvania?

History buffs will quickly discover that Pennsylvania is kind of like paradise. One of the most well-known and historic parks in the state is, of course, Valley Forge National Historic Park. Sprawled across 3,000 acres, the national park features hiking trails, with historical markers, monuments, and a Visitor Center. The park also hosts events throughout the year. Gettysburg National Military Park is, arguably, another of the most well-known parks in Pennsylvania. (Even if you can’t make it there, you can explore it virtually.) If you’re also a fan of the paranormal, you’ll love the park, notably Devil’s Den, which is said to be particularly haunted.

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Three Mile Island, Londonderry Township, PA, USA