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Three Mile Island accident -

On March 28, 1979, the Unit 2 reactor (TMI-2) of the Three Mile Island nuclear power station partially melted down after a cooling malfunction.

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A mechanical or electrical failure -

Either a mechanical or electrical failure prevented the main feedwater pumps from sending water to the steam generators. These generators remove heat from the reactor core. Pictured is the plant's other reactor, Unit 1.

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Countdown to near-disaster -

This sequence of events prompted the plant's turbine-generator and then the reactor itself to automatically shut down. Immediately, the pressure in the primary system (the nuclear piping portion of the plant) began to increase.

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Pressure builds -

In order to control that pressure, a relief valve automatically opened. The valve should have closed when the pressure fell to proper levels, but it became stuck open.

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Unaware of the risks -

Instruments in the plant's control room, however, indicated to technicians that the valve was closed.

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The situation becomes worse -

As a result, control room staff were unaware that cooling water in the form of steam was pouring out of the stuck-open valve.

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Alarming incident -

Suddenly alarm bells began ringing and warning lights started flashing. Something was seriously wrong. What operators didn't realize was that the plant was experiencing a loss-of-coolant accident.

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Partial meltdown -

In the confusion, unaware of the stuck-open relief valve and unable to tell if the core was covered with cooling water, plant staff inadvertently took a series of actions that actually uncovered the core. This led to the water level in the pressure vessel dropping further, resulting in the core overheating.

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The cleanup begins -

A combination of equipment and instrument malfunctions, human errors in operating procedures, and mistaken decisions in the ensuing hours caused the accident, according to the United States Nuclear Regulatory Commission (USNRC). Cleanup at the TMI-2 started in August 1979 and officially ended in December 1993.

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Checking radiation levels -

In the months following the accident, concerns were raised about possible adverse effects from radiation on human, animal, and plant life in the area. Superheated steam had formed a large accumulation of hydrogen gas, some of which escaped from the core into the containment vessel of the reactor building. Fortunately, very little of this and other radioactive gases actually escaped into the atmosphere. However, precautions were taken.

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Evacuation procedure -

A Site Area Emergency was declared. On advice from the USNRC, pregnant women and pre-school age children within a five-mile (eight-km) radius of the facility were evacuated. The evacuation zone was later extended to a 20-mile (32-km) radius. Within days, 140,000 people had left the vicinity.

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Environmental concerns -

Farmers, meanwhile, were told to keep their animals under cover and on stored feed.

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Effects on health -

In the wake of the near-meltdown, environmental samples of air, water, milk, vegetation, soil, and foodstuffs were collected by various government agencies monitoring the area. Ultimately, the USNRC concluded that the release of gases had negligible effects on the physical health of individuals or the environment.

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Presidential visit -

US President Jimmy Carter visited Three Mile Island and was briefed on the situation by experts from the USNRC. Though negligible in its health consequences, the accident had sent the nation into panic. It also had widespread and profound effects on the American nuclear power industry.

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'The China Syndrome' (1979) -

Ironically, 12 days before the accident, the movie 'The China Syndrome' had premiered. The film, starring Jane Fonda, Jack Lemmon, and Michael Douglas, follows a reporting team who witness an accident at a nuclear power plant. The Three Mile Island incident gave the picture's subject matter an unexpected prescience.

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Art imitating life -

'The China Syndrome' was attacked by the nuclear industry as irresponsible, claiming it to be "sheer fiction." But the film eerily foreshadowed events that were to take place less than two weeks later and sparked nationwide protests against nuclear power.

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Celebrity protest -

Fonda, together with her political activist husband Tom Hayden, became the celebrity face of the anti-nuclear movement. She's pictured with Hayden speaking to reporters outside the Three Mile Island nuclear plant on September 24, 1979.

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Grassroots demonstration -

Nowhere was the protest against the industry more vocal and impassioned than in Harrisburg and Middletown, where most of the evacuees lived, many within the shadow of the plant's four giant cooling towers.

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Unit 2 closed down -

Three Mile Island remains America's worst nuclear accident. The unharmed Unit 1 reactor at the facility did not resume operation until 1985. TMI-2, however, was damaged beyond repair. Pictured in 2016 is fuel and structural core materials from TMI-2 being shipped by rail from the site to the Department of Energy's Idaho National Engineering Laboratory for research and eventual disposal.

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Effect on the nuclear industry -

Three Mile Island continued to operate. However, the nuclear industry, floundering as a result of economic, regulatory, and public pressures, halted plans for further expansion.

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Challenging times -

Across the United States, nuclear plants were having trouble staying competitive in an era of cheap natural gas, a product of the shale boom.

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The Fukushima disaster -

The Fukushima nuclear disaster in Japan in March 2011 further fueled public concern over the safety of nuclear power plants.

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More public concern -

Back in Middletown, Pennsylvania, demonstrators gathered for their annual vigil in remembrance of the accident at Three Mile Island, only this time they dedicated their candlelit protest to the victims of the earthquake and tsunami in Japan.

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Three Mile Island decommissioned -

In 2019, Unit 1 was shut down. Exelon, the plant's owners, decided to retire the facility, and Three Mile Island was effectively mothballed.

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Prospect of recommissioning -

Then in 2024, American energy company Constellation Energy began exploring the possibility of recommissioning Three Mile Island's dormant Unit 1 reactor, a process that would take several years.

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Back online? -

The move marked a new impetus by tech companies, manufacturers, and energy regulators to find enough zero emissions electricity to keep up with surging demand, reported The Washington Post. The owner of the mothballed Palisades nuclear plant in Michigan (pictured in 1974) is also considering recommissioning the facility.

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Keep reactors running -

In fact, in March 2024, Jennifer Granholm, US energy secretary, visited the Holtec Palisades Training Center after the Biden administration announced a conditional loan commitment of up to US$1.52 billion for a loan guarantee to help restart the shuttered nuclear plant. It was seen as a move to keep reactors running as a major source of zero-carbon power and high-paying jobs.

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The search for net zero -

And the energy company NextEra is also mulling whether to restart a nuclear plant in Iowa.

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AI and the nuclear power industry -

Fueling this renewed interest in nuclear power is artificial intelligence energy demands. According to the Electrical Power Research Institute (EPRI), owners of a third of the US' nuclear plants are reportedly in talks with tech companies to help power data centers.

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AI's demand for energy -

EPRI forecasts suggest that data centers that nourish artificial-intelligence innovation and other tech are forecast to eat up as much as 9% of America's power supply by 2030. The burgeoning electrical vehicle market is driving additional demand.

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More energy required -

AI is being implemented across all industries, from healthcare to financial to retail, and the need for storage and security requires powerful and robust infrastructure. It also requires an awful lot of energy, a load growth the US electrical grid is currently unprepared for.

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Will AI run Three Mile Island? -

And what if artificial intelligence ended up actually running a facility like Three Mile Island, with many of the critical operations given over to an AI system? Nuclear safety advocates fear that the hype and money-saving zeal surrounding AI may produce a human error of judgment about how much AI can handle. And that's an accident waiting to happen.

Sources: (Forbes) (The Washington Post) (Fast Company) (The Post) (Energy Central) (USNRC) (History) (The New York Times Magazine) 

See also: Nuclear threat—Earth's most radioactive locations

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