ON THIS DAY: March 28, 1979, Three Mile Island nuclear plant leaks radiation

DAUPHIN COUNTY, Pa. — Three Mile Island Nuclear Generating Station, just south of Harrisburg, is infamous for the partial meltdown that became the worst commercial nuclear accident in U.S. history.

Construction on the plant began in 1968, with both of its nuclear reactors coming online in late 1978. Just a few months later, on March 28, 1979, Unit 2 suffered a cooling system malfunction, which resulted in overheating of the reactor core.

Staff at the plant made additional errors, shutting off the emergency cooling system, which led to a partial meltdown. The core melted through its container and caused a geyser of steam to leave the plant, exposing approximately 2 million people to radiation.

Many Dauphin County residents evacuated and concerns for a full meltdown persisted for several days. The plant suffered no further damage, but Unit 2 was never repaired or reactivated.

Adding to the tension, a movie called “The China Syndrome” was released just 12 days before the accident. Initially dismissed as far-fetched, the film starring Jane Fonda, Jack Lemmon and Michael Douglas, depicted a fictional nuclear meltdown outside Los Angeles that contaminates an area “the size of Pennsylvania.”

The accident turned the movie into a blockbuster and started a public debate over the safety of nuclear power. Public fears eroded support and federal regulations and emergency response planning became significantly more complicated, effectively halting the construction of any new nuclear plants for over 30 years afterward.

40 years later, Three Mile Island nuclear accident still haunts some who lived near it

It’s been four decades since the country’s worst nuclear accident in Three Mile Island, Pennsylvania. NBC's Andrea Mitchell, who covered the emergency in 1979, returns to speak with residents and others about the accident and its impact.

Posted by NBC Nightly News with Lester Holt on Thursday, March 28, 2019

The cleanup from the accident took 14 years and is estimated to have cost $1 billion. Unit 2 was entombed in concrete and the waste shipped to a storage facility in Idaho.

Unit 1 was brought back online in 1985 and continued to operate until Sept. 20, 2019.

Exelon Generation, which owns the plant, estimates that it could take 60 years and $1.2 billion to completely decommission the site.

Despite widespread health concerns for the community around the plant, medical studies have found no direct connection linking cancer to the residents.