The Three Mile Island (TMI) nuclear power plant accident is the closest the United States ever came to a Chernobyl or Fukushima-level nuclear disaster. In March 1979, a series of mechanical and human errors caused the worst nuclear accident in U.S. history. It resulted in a partial meltdown of the reactor core, and a release of dangerous radioactive gases into the Pennsylvania atmosphere.
The Metropolitan Edison company built the TMI nuclear power plant in the early 1970’s, in central Pennsylvania. It sits on a 3 mile long, skinny island in the middle of the Susquehanna River, just 10 miles south of the state capital, Harrisburg. You can still see its 4 tall cooling towers from the city’s bridges.
Ironically a movie thriller, The China Syndrome, starring Michael Douglas opened in theaters that same year. The film was about a fictional power plant outside of Los Angeles, and a near nuclear meltdown caused by human negligence. The nuclear industry scoffed at The China Syndrome, calling it “Hollywood fiction.” Experts said a ‘meltdown’—where a nuclear reactor overheats, causing radioactive fuel to melt, resulting in an explosion and breach in containment —was nearly impossible. The superheated uranium core could ‘theoretically’ burn its way through the earth, all the way to China.
TMI had two uranium reactors. TMI-1 started up in 1974 and operated until 2019, and TMI-2 which was brand new in 1979. At 4:00 AM on Wednesday, March 28, 1979, the cooling system in TMI-2 malfunctions, allowing coolant surrounding the hot reactor core to overheat. A release valve on the top of the chamber opens, allowing coolant to escape as steam. But heat continues to rise due to the lack of coolant circulation. Within 10 seconds, alarms go off and control rods are automatically inserted into the hot core, shutting the reaction down.
But unknown to the night crew, the release valve was stuck in the OPEN position.
The now boiling coolant level begins to drop. Water pumps rush new coolant into the reactor, but the plant engineers, unaware of the stuck value, think there is plenty of coolant and turn OFF the flow. This was a terrible human error. Although the reaction is stopped, the core is still VERY hot. The night operators fail to grasp the seriousness of what’s happening. The remaining coolant surrounding the core boils away as steam. The exposed fuel rods quickly overheat, melting though their metal container.
It’s not until after 6:00 AM, over 2 hours later, that plant engineers determine the relief valve is in fact open and quickly close a manual back-up. Another hour passes before they realize the relief valve’s been open all along and the reactor is running dangerously short of coolant. At 7:20 a.m. they finally turn on pumps to add water back into the reactor chamber. The core is finally submerged again, but the water can’t penetrate the hot melted fuel rods, which continue to heat up.
By now there are at least 20 sweating and very worried operators and their supervisors hunched over consoles in the central control room. Radiation levels in the reactor building are so high that regulations require the declaration of a General Public Emergency. The plant director gets on the phone and informs federal and state officials, including the governor, of elevated radiation levels.
However, no one yet realizes the core had been partially melted down. Some 20 tons of molten fuel and metal have sunk to the bottom of the reactor vessel. Now while the walls are 5 in. (13 cm) thick steel, even that will only hold for a few hours against such intense heat, causing an eventual rupture and explosion – the “China Syndrome.”
Luckily, by 9:00 am, 5 hours after the incident started, the reactor vessel gradually begins to cool and the walls holds firm. The initial danger is past, without anyone knowing how great it had been. However, the melting fuel creates a large hydrogen bubble inside the unit that might still cause an explosion, releasing even larger amounts of radiation into the Pennsylvania countryside.
Regardless, a geyser of steam had been released from the top of the plant that night, dumping radioactive contamination into the surrounding counties. Although a general emergency is declared by breakfast, it will be days before any true emergency is felt. President Carter is briefed on the accident at the White House. By evening, the condition of the reactor appears to improve as radiation levels in TMI-2 seem to be falling. The operators still do not believe that any major damage to the reactor’s core has occurred.
The message to the public was to downplay any real danger.
It wasn’t until the next day that nuclear engineers and officials begin to face the fact that major damage occurred to the reactor and that possibly large quantities of radioactivity escaped from TMI-2 into the atmosphere. Different federal agencies relay conflicting information as to whether an evacuation should happen or not. After waffling, the Dept. of Energy (DoE) advised everyone within 10 miles of the power plant to just stay inside. Pregnant women and small children within 5 miles should leave.
Meanwhile, the hydrogen bubble created in the reactor during the meltdown still threatens to trigger an explosion. Officials finally faced facts: They might need to evacuate everyone within a 20-mile radius, over 600,000 people in the Harrisburg suburbs. But what residents didn’t realize was that there were NO ready Evacuation Plans in existence, none. The DOE had never considered it.
By Friday, March 30, after 2 days of underestimating the accident, DoE officials in Washington DC now overestimate the danger. Pennsylvania Governor Richard Thornburgh gives the recommendation that pregnant women and young children within a 5 mile radius should evacuate. Hearing this on the TV and radio, the public was in a nervous quandary. The rumor mill was spread neighbor to neighbor by telephone.
What to do? Grab the kids, lock up your home, and leave? Stay indoors, shut the windows and pray for the best?
Area Catholic priests stoked fears by granting “General Absolution”—a blanket Forgiveness of Sins, usually reserved for wartime. The Federal Reserve sent armored cars to help local banks keep up with the cash demands of evacuating people pulling their money out. Hospitals began to admit only emergency cases in preparation for the worst. The American Red Cross began to prepare for a mass exodus of south-central Pennsylvania.
By Saturday, it’s generally accepted by the Metropolitan Edison plant managers at TMI-2 that half of reactor’s core had melted down. So fears now turn to the hydrogen bubble that could explode. Again, Washington DC officials heighten fears by telling reporters that an evacuation out to 10 or even 20 miles (15 to 30 km) might be needed. The press pick up on this and it begins to fuel panic in the TV and radio news. There was no internet or cell phones in 1979.
For tellers at Harrisburg area banks, chaos erupts as cars and customers pile up, desperately trying to withdraw all their cash, even if they were not under evacuation orders. The response by local, state and national officials is contradictory and confusing—the public doesn’t know what to think or do. Hunker down or evacuate the family?
Was the area on the verge of a China Syndrome-style catastrophe? Or was it OK to just stay home and shut your windows? The poor government response to the TMI ‘Incident’ is considered a textbook example of what NOT to do during an serious state-level emergency. But before 1979, nobody had made adequate plans as to how to respond to an accident at ANY nuclear power plant anywhere in the world.
Some of the local residents simply were not going to risk it.
40% of people who lived within 15 miles of TMI self-evacuate, order or no order. Interstate 81 and the Pennsylvania Turnpike become jammed with bumper to bumper traffic. Governor Thornburgh came under fire for supposedly hesitating to evacuate pregnant women and children in the closet zone to TMI. In fact, he had been asking the DoE for a single point person rather than a dozen Washington experts with conflicting opinions.
On Sunday April 1, President Jimmy Carter flies in and tours the TMI facility personally. Within hours, the press swings around to the view that the danger must be over. It still takes until April 9 for the Evacuation Order to be lifted. Nevertheless, an estimated 2 million people were exposed to albeit small amounts of radiation in the air. Fear of cancers and birth defects were raised by families and the press.
TMI galvanized the US anti-nuclear movement. Public support for nuclear energy plummets nationwide. High profile protests take place around the country, including one in New York City involving 200,000 people. A moratorium on the licensing of new reactors is imposed by Congress and lasts for 30 years. The power industry switches back to building coal and natural gas burning plants
The cleanup effort lasts 14 years and costs almost a billion dollars.
Workers removed radioactive fuel and water, shipping 100 tons to an Idaho National Laboratory storage facility. The damaged TMI-2 reactor is permanently closed and currently entombed in thick concrete. The accident led to sweeping changes in the way the US regulates nuclear plants.
In the years since, several agencies conducted health studies in the area, but no adverse effects could be linked to the TMI Incident. There are no proven health impacts. The amount released was determined to not be enough to harm food, animals, or people.
TMI-1 is today owned and operated by Exelon Corporation and generated electricity for the next 40 YEARs. Exelon finally shut down and closed the aging plant in September, 2019. Dismantling the remaining reactor could take up to 10 years though. TMI-2 will remain in its concrete sarcophagus.
As for the people who still live in the area, the disaster hasn’t been forgotten and is still debated today. Lawsuits claimed there were above-average cancer and birth defect rates in the surrounding Dauphin County area. Hundreds of lawsuits were settled out-of-court. Millions of dollars compensated parents of children born with birth defects.
As frightening at the U.S. Three Mile Island Incident was, the cost and impact was nowhere near other global nuclear power plant disasters. The 1986 Chernobyl Nuclear Disaster in Ukraine cost several hundred billion to contain. It led to the permanent evacuation of 300,000, and caused 4,000 projected deaths. The 2011 Fukushima Daiichi nuclear disaster in Japan was caused by an offshore earthquake’s tsunami. It caused the death of 19,700 and the evacuation of 150,000 people. One can assume the U.S. should consider itself lucky in that respect.
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