Three Mile Island Nuclear Generating Station along Route 441 in Middletown Monday, July 6, 2020.

An early Sunday fire near the now-inactive Three Mile Island nuclear power plant damaged a large transformer at a nearby substation but did not threaten radioactive facilities.

That’s according to Three Mile Island stakeholders, who said the fire was across the street from the island, specifically near a former power plant training center off of Route 441.

At least one resident reported hearing what sounded like an explosion -- a troubling sound in the community closest to the plant, where a 1979 partial reactor meltdown remains the worst commercial nuclear accident in U.S. history.

“A transformer did fail, and it caused a fire,” FirstEnergy spokesman Todd Meyers said Tuesday before explaining that a transformer failure can sometimes be accompanied by loud bangs and flashing lights.

“It probably put on a light show,” Meyers said, later elaborating. “The bang people may have heard was likely caused by large circuit breakers that immediately opened to isolate the damage and protect other adjacent electrical equipment.”

The transformer, Meyers said, is part of a substation owned and operated by FirstEnergy, where electricity generated by the nuclear plant previously was moved into the commercial power grid.

The plant's two reactors -- owned separately by Exelon and EnergySolutions -- no longer produce electricity, but Meyers said FirstEnergy has kept the substation online, accepting energy from other sources and distributing it elsewhere throughout the grid.

“If you think about the electrical transmission grid as an interconnected road system, a substation would be the exit ramp from an interstate highway to smaller secondary roads,” he said.

The larger transformer, which Meyers compared to the size of a “downtown building” on its side, is part of that process, he said. It also was nearing the end of its lifespan, he said.

“We knew from routine inspections that the transformer was showing signs of wear and had planned to make intermediate repairs in the short term with an eye on replacing it in the not-too-distant future,” Meyers said.

But about 2:13 a.m. Sunday, the 500,000-volt transformer caught fire, and emergency responders were called to the area near the island, which is located just above Conoy Township on the Dauphin-Lancaster counties line.

Firefighters in Londonderry Township, Dauphin County were among the responders. They posted about the incident on the Londonderry Volunteer Fire Company Facebook page alongside images of the transformer covered in orange flames and spewing black smoke.

The transformer was taken offline, and firefighters used foam to extinguish the flames, a process that wasn’t completely wrapped up until Sunday afternoon, according to the Facebook post. The Londonderry fire chief couldn’t immediately be reached for additional details, including whether anyone was injured by the blaze.

However, Meyers said damages were contained only to the transformer.

“Our substation crew ascertained that the transformer was irreparably damaged,” he said.

That means the transformer will have to be replaced, Meyers said, explaining a replacement may need to be specially manufactured for the site -- a process that could mean installation won’t be completed for a year or more.

Because backup equipment exists at the substation, it can remain in use even without the damaged transformer, Meyers said, calling the site an “integral part of our regional electrical transmission grid." Those backups also kept local customers from losing power during the fire, he said.

“Loss of the transformer will not cause any power outages,” he said.

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