HERSHEY — Federal officials say it will cost more than $900 million to decommission a closed nuclear reactor and related structures at Three Mile Island, the central Pennsylvania plant that was the site of what is considered the worst commercial nuclear power plant accident in U.S. history almost three and a half decades ago.

Dismantling Three Mile Island’s Unit 2 and returning the property to a pre-plant state would cost about $918 million in 2012 dollars, John Buckley of the U.S. Nuclear Regulatory Commission said at a meeting Wednesday evening in Hershey.

Current plans call for reactor owner First Energy to begin dismantling the reactor sometime after 2034, commission officials said, and they expressed confidence about having enough money for the process.

A trust fund set aside by the company contained more than $665 million and the firm will rely on earnings from that amount to funnel additional money into the fund, commission spokesman Neil Sheehan said.

“If there is a deficit, the NRC will go back to the company and ensure that it addresses any shortfalls,” Sheehan said.

Eric Epstein of TMI Alert, a group that favors alternatives to nuclear power and monitors Three Mile Island and two other nuclear plants in Pennsylvania, questioned FirstEnergy’s ability to fund the decommission.

“Let’s be honest, you don’t have the money,” he said. “You don’t have the technology. ... The reality is that the plant will never be decommissioned.”