Forty years ago today, the United States experienced the most serious nuclear accident in its history.

The partial meltdown at the Three Mile Island nuclear power plant near Harrisburg in 1979 sparked a major anti-nuclear backlash — halting the industry’s growth in the U.S. for decades. Now, amid climate concerns, there’s a big push to keep nuclear plants open.

Nuclear plants provide about 20 percent of the nation’s electricity, but many in the U.S. are old and unprofitable, including Three Mile Island. The plant is scheduled to close this fall — 15 years before its operating license expires.

StateImpact Pennsylvania’s latest documentary, Three Mile Island: The New Nuclear Dilemma explores the plant’s fraught history and the new fight to keep it open:

The show airs on PBS member stations across Pennsylvania and will be preceded by a 30-minute program called Meltdown at Three Mile Island: 40 Years Later, which focuses on what happened during the 1979 accident.