The Three Mile Island (TMI) nuclear incident is the closest the United States ever came to a Chernobyl or Fukushima-level nuclear disaster. In March 1979, a series of human and mechanical 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 atmosphere of the Pennsylvania countryside.
Metropolitan Edison built the Three Mile Island nuclear power plant in the early 1970’s, in south-central Pennsylvania. It sits on a 3 mile long, skinny island in the middle of the Susquehanna River, just 10 miles to the north is the state capital of Harrisburg. You can see its 4 tall cooling towers from the city’s bridges and roof tops.
Ironically a movie thriller, The China Syndrome starring Michael Douglas, opened in theaters that very same month. It was about a fictional Los Angeles power plant, and a near nuclear meltdown caused by human negligence. The nuclear industry scoffed at The China Syndrome, calling it “Hollywood fiction.” When a reactor meltdown gets uncontrollably hot, it causes a gas explosion and breach in its containment structure. This is exactly what would happen to Ukraine’s Chernobyl seven years later.
Three Mile Island had two uranium reactors. TMI-1 started up in 1974 and TMI-2 which was brand new in 1979. At 4:00 AM on Wednesday, March 28, the cooling circulation system in TMI-2 malfunctions, allowing coolant surrounding the hot reactor core to overheat. A relief valve on 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 begin to blare across the plant. Control rods are automatically inserted into the hot core, shutting the reaction down.
Unknown to the night crew, the relief valve was still stuck in the OPEN position.
With the rods in, the now boiling coolant level begins to drop. Water pumps rush new coolant into the reactor. The plant engineers in the control room, unaware of the open/stuck value, think there is plenty of coolant and turn OFF the water flow. This was a terrible human error. Although the reaction is stopped, the core is still VERY hot. The night operators have no clue of the seriousness of what’s happening. The remaining coolant surrounding the core boils away as steam. The exposed fuel rods quickly overheat again, this time melting though their metal container.
It’s not until after 6:00 AM, over 2 hours later, that a new shift of shocked plant engineers realized the pilot-operated relief valve (PORV) is in fact OPEN. They quickly close a manual back-up. Another hour passes before they realize the relief valve’s been open since 4 AM and the reactor is running dangerously low of coolant. At 7:20 a.m. they finally turn on pumps to add water back into the reactor chamber. They sigh as the core is finally submerged again.
However, the water can’t penetrate the melted fuel rods, which continue to heat up.
By 8 in the morning there are at now 20 sweating and very worried operators and their supervisors hunched over consoles in the control room. Radiation levels in the reactor building are so high that regulations require the declaration of a General Public Emergency. Metropolitan Edison station manager Gary Miller gets on the phone with both federal officials and the Pennsylvania governor. He informs them of the elevated radiation levels within TMI-2, and an unknown amount leaked into the air.
No one yet realizes the core had been partially melted down. Some 20 tons of molten fuel and metal lay on the bottom of the reactor vessel. While the walls are 5 in. (13 cm) thick steel, even that will only hold for a few hours against such intense heat. The gas pressure will eventually cause an explosion and rupture of the containment structure. This is what would happen at Chernobyl in 1986.
Luckily, by 9:00 am, 5 hours after the incident started, the reactor vessel gradually begins to cool and the walls hold. The initial danger is past, without anyone yet knowing how dangerous it had been. However, the melting fuel created a large hydrogen bubble inside the reactor unit that might still cause an explosion. This would release even larger amounts of radiation into the Pennsylvania countryside.
Governor Richard Thornburgh was told a geyser of steam released from the plant that night, dumped 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 Jimmy Carter is briefed on the accident at the White House that afternoon. By evening, the reactor condition appears to improve as radiation levels in TMI-2 fall a bit. The control room operators still do not know that major damage to the reactor’s core has occurred.
The message to the public downplayed any real danger.
It wasn’t until the next day, March 29, that two nuclear engineers entered the reactor building and determined that major damage had occurred. AND that possibly large quantities of radioactive xenon gas had escaped into the local atmosphere. Two different federal agencies, including the NRC, relay conflicting information as to whether an evacuation of Harrisburg should happen or not. After waffling, the Dept. of Energy (DoE) finally advised everyone within 10 miles of TMI to just stay inside. Pregnant women and small children within 5 miles should leave the area.
Meanwhile, the large hydrogen bubble in the reactor still threatened to trigger an explosion. Officials finally faced facts: They might need to evacuate everyone within a 20-mile radius, over 600,000 people reaching the Harrisburg suburbs. But what residents and the press soon realize is that there were NO Evacuation Plans in existence, None. The DOE had never considered a breach.
By Friday, March 30, after 2 days of underestimating the accident, DoE officials in Washington DC now overestimate the danger. Governor Thornburgh gives the recommendation that pregnant women and young children within a 10 mile radius should evacuate. Hearing this on the TV and radio, the public began to panic. Rumors quickly spread neighbor-to-neighbor by telephone. There was no internet in 1979.
WHAT TO DO? Grab the kids and leave? Stay indoors, and pray for the best?
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. Hospitals began to admit only emergency cases in preparation for the worst case scenario. The American Red Cross began to prepare for a mass exodus of south-central Pennsylvania.
By Saturday, the Metropolitan Edison plant managers at TMI-2 accept the fact that half of reactor’s core had melted down. So fears now turn to the large hydrogen gas bubble that could still explode. Again, federal officials heighten fears by telling reporters that a general evacuation out to 10, or even 20 miles (15 to 30 km) might be needed. The press picks up on this and reporters begins to fuel panic via TV and radio news.
For bank tellers in Harrisburg, chaos erupts as cars and customers pile up outside, desperately trying to withdraw all their cash. The response by local, state and national officials is both contradictory and confusing. The public doesn’t know what to think or do. Hunker down in the basement or pack up the car and evacuate?
Was the area on the verge of a Chernobyl-level catastrophe? The poor government response to the Three Mile Island ‘Incident‘ is considered a textbook example of what not to do during a 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 clogged traffic. Governor Thornburgh came under fire for supposedly hesitating to evacuate pregnant women and children in the closet zone to TMI. He’d been pleading with Washington, to no avail, for a single point person. What he got was a dozen agency ‘experts’ with conflicting opinions.
On Sunday, April 1, President Jimmy Carter flies in and tours the control room of the TMI facility personally. Within minutes, the press swings around to the view that the danger must be over. It still takes a week though, until April 9, for the Evacuation Order to be lifted. Nevertheless, an estimated 2 million people were exposed to small amounts of radiation in the air. Fear of potential cancers and birth defects were raised by families and the press.
Three Mile Island galvanized the U.S. 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. Congress imposes a moratorium on new reactors which lasts for 30 years. The power national industry switches back to building CO2 producing 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 was entombed in thick concrete. The accident led to sweeping changes in the way the U.S. regulates its remaining nuclear plants.
TMI-1 is today owned by Exelon Corporation and generated electricity in TMI-1 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, until at least 2029. TMI-2 reactor core will remain in its concrete sarcophagus for the foreseeable future.
In the years since, several federal agencies conducted health studies of the people in the area. No adverse effects could be linked to the Three Mile Island Incident. There are no proven health impacts in the nearby population, including cancers caused by radiation exposure. The amount released was determined to not be enough to harm people, animals, or crops.
As for the people who still live in the area, the disaster hasn’t been forgotten and is still debated. Lawsuits claimed there were above-average cancer and birth defect rates in Dauphin County. 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 impact was nowhere near the next 2 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.
The United States should consider itself lucky, in that respect.
Horrible situation. How can engineers build nuclear power stations on rivers and on fault lines next to the ocean in California. I have never believed the fact that Three-Mile Island didn’t cause more cancer and birth defects that we were led to believe. Bad for business after all. The waste products have never been addressed properly.