The Disaster at Three Mile Island

Contributor: Roxann Penny. Lesson ID: 12704

Have you ever seen an atom? Probably not just one, but you've seen collections of them that make up everything. Tiny atoms are powerful and can be dangerous. Learn what happens when things go wrong!


United States

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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Something important is taking place in this picture.

  • What do you think it is?

President Carter leaving Three Mile Island

Image courtesy of Wikimedia Commons

In the United States and all around the world, nuclear power is used to generate electricity that is distributed to millions of consumers.

This energy source is generally considered a safe form of energy; however, if it is not carefully checked, it can be very dangerous. As such, it is no surprise that fear and panic arose on the morning of March 28, 1979, when residents near the Three Mile Island nuclear facility in Pennslyvania noticed something very different about two of the plant's cooling towers.

Find out what occurred on the morning of March 8 below.

What is nuclear power?

Nuclear power is used to produce electricity. Nuclear energy is formed in the nucleus, or core, of atoms. Atoms may be described as tiny particles that make up every object in the universe. They are the building blocks of matter. For example, your computer, desk, and chair are all made up of atoms.

This picture shows the interior of a nuclear reactor:

nuclear reactor

Where is the Three Mile Island nuclear power plant located?

This nuclear power plant is located on Three Mile Island, near the Susquehanna River, Pennslyvania. Nuclear power plants require lots of water to keep their reactors cool. Therefore, it is quite common to find most of these plants located near a river or lake.

Take a look at the following image showing the inside of the Three Mile Island power plant in 1979:

inside Three Mile Island

Image courtesy of Curtis Bathurst

What occurred in March 1979?

Nuclear power plants use lots of water to prevent overheating and to ensure that the reactor (a specially-designed structure used to control a nuclear reaction) operates safely and efficiently. Plant operators have to undergo intense training to know how to operate the plant safely.

However, on the morning of March 28, 1979, a valve used to control the flow of water in the reactor became stuck and was not detected by the plant's instrumentation. The operators of the plant did not detect the problem, and the reactor continued to lose its ability to cool down.

What happened to the reactor?

The reactor (the structure containing the nuclear reaction) failed. As a result, the reactor had to be shut down, but not before it underwent a partial meltdown. Meltdown is used to describe the damage that occurred to the reactor due to overheating.

What did the residents on Three Mile Island observe on the day the accident occurred?

  • So, what did the residents of Three Mile Island observe about the nuclear plant?

The most visible sign that something was wrong was a lack of steam emerging from the two cooling towers. In a nuclear plant, cooling towers are used as vents to release the tremendous amounts of steam generated from the water used to cool the reactor.

Next, take a look at the following images. They show parts of the nuclear facility at Three Mile Island Nuclear Power Plant.

  • What do you observe in the pictures?

Image - Video

Since the partial meltdown of the reactor at Three Mile Island, there has not been another nuclear disaster on American soil.

In fact, stricter regulations and restrictions were implemented as a result of the incident at Three Mile Island. However, despite the new regulations set in place, there still remains a certain amount of fear and uncertainty about nuclear-generated power.

This fear was further amplified by the catastrophic events that took place at the Fukushima Daiichi nuclear power plant in Japan on March 11, 2011. After a devastating earthquake, the three reactors at this plant were badly damaged and over 100,000 people had to be evacuated from their homes.

Nevertheless, nuclear power remains a reliable source of energy for the United States.

Continue exploring this topic by completing a summary interactive in the Got It? section.

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