Skip to main content

1979: Three Mile Island

1979: Three Mile Island

25 years ago

Around 4:00 a.m. on March 28, maintenance workers at the Three Mile Island nuclear-power plant, near Harrisburg, Pennsylvania, accidentally blocked the flow of water into the reactor core. This water acted as a coolant, absorbing the tremendous heat created there; without it, temperatures would build up dangerously, and the core could even melt down. Events like this had been planned for in the reactor’s design, and the staff was trained in dealing with them. The reactor shut down automatically, emergency water pumps were turned on, and control-room workers looked forward to resuming normal operations in a few hours.

What their faulty instruments didn’t show was that a pair of valves in the emergency cooling system were shut, preventing water from reaching the core, while a valve that allowed water to drain from the core remained open. With coolant levels dropping, the core started to overheat dangerously as engineers and technicians struggled, amid a cacophony of alarm horns and a forest of blinking lights, to figure out what was going on. After 16 hours, plant operators finally managed to restore the flow of coolant. The next day a spokesman assured the public that all was well, the situation was routine, and the danger was past.

But it wasn’t. Unanticipated reactions had released hydrogen gas into the reactor vessel, where it accumulated at high pressure and temperature. If it reacted with oxygen, the liberated energy could blow the reactor dome open and spew radioactive material across central Pennsylvania. It took several tense days, during which 140,000 residents left the area, for plant workers to dissolve the hydrogen gas and eliminate the threat.

No one died or was injured at Three Mile Island, and there was no dangerous release of radiation. Yet in the accident’s aftermath, investigators uncovered a widespread disregard for safety throughout the nuclear industry. The government responded with strict and voluminous new regulations.

In retrospect, Three Mile Island was a watershed for nuclear power, though an unusual one. The industry was already in trouble; with costs mounting, orders for new plants had virtually ceased by the late 1970s. On the other hand, despite Three Mile Island, nuclear power generation increased through the 1980s and 1990s as plants ordered earlier were completed; today it supplies about 20 percent of America’s electricity. So Three Mile Island did not kill nuclear power in America, but it did drive a stake through the industry’s heart by greatly boosting both public opposition and the costs of building and running a plant.

We hope you enjoy our work.

Please support this 72-year tradition of trusted historical writing and the volunteers that sustain it with a donation to American Heritage.

Donate

Featured Articles

Famous writers including Emerson, Thoreau, Hawthorne, and the Alcotts turned Sleepy Hollow Cemetery into our country’s first conservation project.

Native American peoples and the lands they possessed loomed large for Washington, from his first trips westward as a surveyor to his years as President.

In his Second Inaugural Address, Abraham Lincoln embodied leading in a time of polarization, political disagreement, and differing understandings of reality.

A hundred years ago, America was rocked by riots, repression, and racial violence.

During Pres. Washington’s first term, an epidemic killed one tenth of all the inhabitants of Philadelphia, then the capital of the young United States.

Now a popular state park, the unassuming geological feature along the Illinois River has served as the site of centuries of human habitation and discovery.  

The recent discovery of the hull of the battleship Nevada recalls her dramatic action at Pearl Harbor and ultimate revenge on D-Day as the first ship to fire on the Nazis.

Our research reveals that 19 artworks in the U.S. Capitol honor men who were Confederate officers or officials. What many of them said, and did, is truly despicable.

Here is probably the most wide-ranging look at Presidential misbehavior ever published in a magazine.

When Germany unleashed its blitzkreig in 1939, the U.S. Army was only the 17th largest in the world. FDR and Marshall had to build a fighting force able to take on the Nazis, against the wishes of many in Congress.

Roast pig, boiled rockfish, and apple pie were among the dishes George and Martha enjoyed during the holiday in 1797. Here are some actual recipes.

Born during Jim Crow, Belle da Costa Greene perfected the art of "passing" while working for one of the most powerful men in America.