EXPLAINER | Three Mile Island
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Three Mile Island

On March 28th, 1979 one of the reactors at the The Three Mile Island nuclear power plant near Harrisburg partially melted down. It marked the most serious accident in U.S. commercial nuclear power plant operating history.

The aftermath brought about “sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations,” writes the Nuclear Regulatory Commission. “A combination of equipment malfunctions, design-related problems and worker errors led to TMI-2’s partial meltdown and very small off-site releases of radioactivity.”

The plant’s still operational Unit 1 reactor is now owned by Exelon, while the mothballed Unit 2 reactor is owned by FirstEnergy.

In May 2017, Exelon announced it would prematurely shut down the plant in September 2019—15 years before its license expires. The nuclear power industry has had a hard time competing economically amid slowing demand for electricity and a glut of cheap natural gas.

Both New York and Illinois recently agreed to give billions in subsidies to the nuclear industry by essentially broadening the definition of clean power. The states created so-called zero emission credits for their nuclear plants. There’s been a lobbying push to do something similar in Pennsylvania, but it has yet to gain traction.

Latest stories


This is the control room for the Unit 1 reactor at Exelon Corporation Three Mile Island nuclear generating station in Londonderry Township, Dauphin County. 
May 22, 2017.

What will become of Three Mile Island’s nuclear waste if the plant closes?

In the absence of a long-term solution, the country’s nuclear power plants are left with one option: indefinite on-site storage.

By Wallace McKelvey, PennLive

Chris Achenbach-Kimmel stands for a portrait at Elizabethtown College where she works.

Thyroid cancer study re-ignites debate over Three Mile Island accident’s health effects

The 2017 Penn State College of Medicine study found a certain type of thyroid cancer to be common to those who were near the nuclear plant during the accident.

By Brett Sholtis

Pennsylvania Governor Dick Thornburgh, left, announces the closing of schools in the area around the Three Mile Island PWR, on March 30, 1979, in Harrisburg, Pa., after an accident at the nuclear power plant led to the release of radioactive gas from the reactor into the atmosphere. The governor advised the evacuation of small children and pregnant women. Standing at right is Lt. Gov. William Scranton.

Watch: Gov. Thornburgh speaks two days after Three Mile Island partial meltdown

“We’re getting conflicting reports too,” Gov. Dick Thornburgh said in response to a reporter’s question at a press conference March 30, 1979.

By Lisa Wardle

Three Mile Island power plant.

Red Whittaker stands beside an early prototype of RadPiper, a pipe-crawling robot that will help decommission uranium enrichment facilities in Ohio and Kentucky. Whittaker has worked in robotics for four decades at Carnegie Mellon University, and he developed several robots in the 1980s that helped clean up after the Three Mile Island Incident.

After TMI accident in ’79, this Carnegie Mellon team pitched a novel idea for cleanup: Use robots. It was just the beginning.

“We had a dream and a few pieces of paper and convinced them that we could solve the problem,” one team member recalled.

By Amy Sisk

Rep. Thomas Mehaffie (R- Dauphin) unveils a bill aimed a preventing the early closure of two of Pennsylvania's five nuclear power plants.

Rep. Mehaffie talks up his nuclear bailout bill; opponents line up to trash it

Dauphin County Republican puts the price tag of his nuclear bailout at $500 million annually, arguing that’s cheaper than doing nothing.

By Marie Cusick

Dauphin County's Three Mile Island

Cooling towers at the Three Mile Island nuclear power plant in Middletown.

Unsolicited, PUC commissioner sends legislators a breakdown of nuclear bailout options

In Andrew Place's analysis, Three Mile Island would close under most scenarios
By Marie Cusick

Walter Creitz, right, president of Metropolitan Edison Company, turns away as company Vice President John Herbein answers questions at a news conference in Hershey, Pa., on March 29, 1979. The conference was held because of an accident that occured at the company's Three Mile Island nuclear power plant near Harrisburg, Pa., that caused radiation leakage into the atmosphere.

Watch: MetEd press conference the day after the Three Mile Island accident

Plant owner Metropolitan Edison did not have a communications team to address the situation. Instead, Vice President Jack Herbein and President Walter Creitz spoke directly to reporters in Middletown.

By Lisa Wardle

Three Mile Island Documentary Preview Screening

Register for a screening of two documentaries — one looking at the partial meltdown, and one looking at the future for TMI and the nuclear industry.

By Lisa Wardle
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