Three Mile Island accident history explained amid reports of Unit 1 resumption of operations

It’s been half a decade since Three Mile Island provided power to Pennsylvania, but one of the nuclear plant’s idle reactors may be able to restart in the future.

According to a recent Reuters report, Three Mile Island’s owner, Constellation Energy Corporation, is in talks with Governor Josh Shapiro’s office and state lawmakers to potentially bring the plant’s reactor unit 1 back online. This reactor is not the same as the infamous reactor unit 2, which suffered a meltdown in 1979 and has been shut down ever since.

Anonymous sources told Reuters the talks were “more than preliminary,” but neither the governor’s office nor Constellation Energy have publicly confirmed that a restart is imminent.

Constellation Energy, which operates more than a dozen nuclear plants nationwide (including two more in Pennsylvania), has “not yet made a decision” but has concluded that a restart is “technically feasible,” a company spokesman told Reuters. Shapiro’s office, meanwhile, told Susquehanna Valley station Fox 43 that it “recognizes the role Pennsylvania’s nuclear plants play in providing safe, reliable, carbon-free electricity” but did not confirm the talks.

Rumors of a possible restart at Three Mile Island come amid renewed interest in nuclear energy nationally and in Harrisburg. Earlier this month, lawmakers announced the reinstatement of a bipartisan Nuclear Energy Caucus to work to strengthen the state’s nuclear industry. And earlier this year, the Energy Department announced a $1.5 billion loan to reopen a nuclear power plant in Michigan that was scheduled to shut down in 2022.

However, as Reuters reported, any restart would likely face obstacles due to safety and environmental concerns, as well as economic and logistical issues. After all, Three Mile Island was the site of what is believed to be the worst nuclear accident in U.S. history, caused by a nuclear meltdown over 40 years ago. Here’s what you need to know:

When did the meltdown on Three Mile Island occur?

Three Mile Island’s Unit 2 reactor is located on the Susquehanna River, about 10 miles outside of Harrisburg. It came online in December 1978, four years after Unit 1 began generating electricity. Three months later, on March 28, 1979, Unit 2 began a partial meltdown after a “malfunction … resulted in a slight release of radiation into the atmosphere,” according to an Inquirer report at the time.

That disruption led to the shutdown of the plant, which was evacuated. State authorities learned of the incident hours later and declared a “general emergency” – the first ever at a nuclear reactor, the Inquirer reported.

Lieutenant Governor William Scranton immediately afterward called the incident “minor,” but later told reporters that the situation was more complex than representatives of the plant’s then-operator, Metropolitan Edison, had led officials to believe. Officials later reported that people living within five to ten miles of the plant may have been exposed to about ten times the amount of radiation that Met Ed officials estimated.

Officials said at the time that a total meltdown was unlikely and there was no “imminent danger” of a public health threat, the Daily News reported. However, the formation of a “hydrogen bubble” raised the possibility of a total meltdown – which was avoided after the bubble began to shrink.

According to Popular Mechanics, no deaths or injuries were reported, but over 140,000 people temporarily evacuated the area.

What happened during the cleanup on Three Mile Island?

After the meltdown, Bechtel Corporation initiated a multi-billion dollar cleanup effort at reactor unit 2. However, Richard Parks, a senior engineer at the start-up company, became a whistleblower, claiming that the company and the power plant operator were cutting corners on safety.

Parks subsequently worked with the Government Accountability Project and filed a 56-page affidavit with the U.S. Department of Labor detailing the alleged safety problems. At the heart of the case, according to The Inquirer in 1983, was Parks’ concerns about a device at the top of the reactor that was to be used in the cleanup. The problem, Parks said, was that the device had been damaged during the accident and needed to be repaired and tested to ensure its safety – and that he had been harassed by the company and relieved of a number of duties because of his concerns.

In November 1983, a federal grand jury charged Met Ed with falsifying tests to determine whether excessive water was leaking from the cooling system and systematically destroying records of those tests. Ultimately, Met Ed pleaded guilty to falsifying records and was fined $45,000 and ordered to establish a $1 million fund to assist with the cleanup of the plant.

In 2019, EnergySolutions Inc. announced that it would acquire Block 2 for decommissioning and dismantling, a process that is still ongoing. TMI-2 Solutions, a subsidiary of the company, estimates that the process will be completed by 2038.

What happened to Block 1 of Three Mile Island?

Unit 1 was not taken offline when Unit 2 melted down in 1979. In fact, it remained in operation for decades and supplied around 830,000 households with electricity during its lifetime.

But this run ended on September 20, 2019, when Unit 1 was finally disconnected from the power grid after 45 years of operation. The closure came as no surprise – the then owner of the power plant, Exelon, had already announced in 2017 that it would shut down the reactor.

At the time, the company said a shutdown was imminent unless Pennsylvania lawmakers rescued the state’s nuclear industry, which was struggling to compete as electricity prices fell as new natural gas reserves came into play. In the five years before the announcement of the impending shutdown, Unit 1 had lost more than $300 million, according to Exelon, despite being one of the company’s most efficient units.

“We’re not going to be able to cut costs and get out of the situation we’re in,” David Fein, vice president of state government affairs at Exelon Corp., told the Inquirer in 2017. “There are going to have to be some policy changes to address the market deficiencies and market challenges that we’re seeing.”

However, this change never happened.

Decommissioning of Unit 1 is still underway. If the reactor is not restarted, the effort is expected to cost $1.2 billion. And decommissioning would not be completed for about 60 years, with an expected completion date sometime in 2079, the Inquirer reported.