Note: Middletown Public Library is an archive for materials related to the Three Mile Island accident. The materials are available to view during our normal hours of operation.

Three Mile Island Nuclear Generating Station, otherwise known as TMI, is infamous for the catastrophic partial nuclear meltdown that occurred on March 28th, 1979. The plant, located in Londonderry Township on a small piece of land on the Susquehanna River, powered many homes throughout multiple counties including Dauphin County. The accident was caused due to a sizable amount of both human and mechanical errors, ultimately going down in history as the worst commercial nuclear plant accident in America.

The nuclear plant’s construction first began in the late 1960s. Unit 1 of the power plant (also called TMI-1) began construction on May 18, 1968 and began operation on September 2, 1974. It cost around $400 million. Unit 2 (also called TMI-2) began construction on November 1, 1969 and began operation on December 30, 1978.   

In March 16, 1979, a film called “the China Syndrome” premiered around the country. The thriller raised disturbing questions for viewers about the safety of nuclear power plants. The movie focused on a reporter who accidentally witnessed a nuclear meltdown that the plant tried to covered up. The film grossed $51.7 million and received four Oscar nominations. Twelve days after the film premiered, TMI had its accident. While some credit the accident’s timing in helping to sell tickets, the studio attempted to avoid appearing as if they were exploiting the accident, and pulled the film from some theaters.

On March 28, at TMI-2, the accident that caused the partial meltdown began. The accident was due to many mechanical malfunctions paired with human errors. At around 4 am the unit which had been operating at 97% power one second, suddenly shut down the next second. The unit shut down because a pump that cooled the unit with water suddenly stopped functioning, ultimately serving as a catalyst for the next series of events. Since the pump stopped operating, temperature and pressure within Unit 2 began to rapidly increase, causing a relief valve to pop open. The valve began to cool the unit by allowing steam and water to exit into a tank that was in the basement of the reactor building (causing the water levels within that tank to rise). To fix this problem, the operators on shift attempted to reduce the flow of the water to the tank. Since system levels were supposed to be stabilizing, the relief valve that was open should have closed, but it did not. This valve was unknowingly open for more than two hours, which allowed for too much water to drain out while leaving little to cool the fuel core. The operators used instruments in the TMI control room to figure out why the heat was increasing, but the tools used indicated that the relief valve was shut. In reality, the valve was still open and continuously leaking water. The workers were unaware of this and did not replace the cooling water that leaked from the valve. Without any coolant available, more steam was produced and leaked through the relief valve into the tank. The catastrophic mixture of steam and water caused the reactor’s cooling pumps to aggressively rattle. The operators shut down the manual cooling of the reactor since they were worried that the pumps would rupture from the shaking. Because they shut down the pumps, a large bubble of steam formed inside the reactor vessel that prohibited any coolant from reaching the core; the intensely hot core melted through the cladding for the uranium fuel and leaked radioactive materials into the water.  

By 6 am, they closed a block valve that was between the relief valve and the tank, halting any further water loss. While that was fixed, they still needed to fix the giant steam bubble that was blocking any coolant from entering. There was a threat of a potentially explosive hydrogen gas bubble when the core was unsealed, but it was determined that there was not enough oxygen to make that possible. So, the operators continuously put high-pressure water into the cooling system to minimize or destroy the steam bubble until 7:50 am when they finally succeeded and restored cooling to the core.

However, though cooling was restored the damage was catastrophic. TMI-2 was unusable, half the core had melted, and the cladding around 90% of the fuel rods had failed. 700,000 gallons of radioactive cooling water had been released in the basement of the reactor and tank, effectively contaminating them. In efforts to clean the building, on March 29th and 30th, the operators used multiple pipes and compressors to move the spill, but some of the compressors leaked and released some radioactive gases into the environment. Though initially startling, the World Nuclear Association gave an explanation on the reality of how dangerous the gas was when it was released: “These went through high-efficiency particulate air (HEPA) filters and charcoal filters which removed most of the radionuclides, except for the noble gases. With short half-life and being biologically inert, these did not pose a health hazard.” Another study showed, “The average radiation dose to people living within ten miles of the plant was eight millirem, and no more than 100 millirem to any single individual. Eight millirem is about equal to a chest X-ray, and 100 millirem is about a third of the average background level of radiation received by US residents in a year.” Taking further precaution, an impressive number of epidemiological studies were completed throughout the span of around 10 years that all proved TMI’s radiation leak had little to no affect on the public besides increasing psychological stress levels.

The aftermath of the accident left the world stunned. There were misleading reports on the amount of radiation leaked where some claimed none was released while others said only a small amount was. The mayor of Middletown at the time, Robert G. Reid, was the first to hear about the partial meltdown and confusing claims. He met with the owner of the Army Navy Store to analyze the radiation reading from a Geiger counter. The miscommunication only got worse when the news of a hydrogen bubble that could explode got out, causing mass panic. Governor Dick Thornburgh, called for pregnant women and preschoolers to evacuate the area within a 10-mile radius. Mayor Reid wanted the radius to be extended further to protect the people of his town, but the evacuation plan remained the same. A large portion of the town had evacuated on their own due to the uncertainly of TMI. The mayor even set a curfew to protect the town from looters. March 30th and 31st were the most hectic days after the partial meltdown because of the mass confusion which unintentionally created panic. The situation was so uncertain and scary that the President of the United States came to Middletown. President Jimmy Carter and his wife Rosalynn talked to the community to help settle and calm residents who were filled with fear. He was able to dismiss the wild claims about explosions and massive radiation poisoning, allowing the community to slowly feel more at ease. After a week of emotional recovery, Middletown slowly returned to normal.

TMI continued operating after the meltdown, but it was met with many struggles. To start, the cleanup effort took around 12 years and cost roughly $973 million. The hefty price was necessary to ensure no workers or citizens were at risk. The Unit 2 reactor was cut off from the rest of TMI and placed in long-term storage, with no plans of being used again. The unit had to be defueled, which took much planning and caution. Aspects of the retired plant still had to be monitored. The ventilation and rainwater systems are consistently monitored, along with the equipment that keeps Unit 2 in retirement.

TMI-1 was able to stay open for another 40 years. The company learned many things from the accident and promoted safety and proper training thereafter. TMI and Middletown held a strong bond after the accident due to the company and its workers living in the community and contributing to the town’s economy.

However, on a national level the fear and mistrust towards nuclear power plants did not disappear. A number of plants that were already under construction prior to TMI’s accident began operation, but plans for 39 others were canceled in the wake of the catastrophe. More recently, only one new nuclear power plant has come online in the United States since 2010, the Watts Bar Unit 2 in Tennessee. Two more reactors are currently under construction in Georgia. Six reactors at five plants have been mothballed since 2013, and several others are slated to close in the next few years if they do not receive new financial support.

As for TMI itself, AmerGen (British Energy and PECO Energy) purchased TMI-1 in 1999. In 2003, the plant was sold and bought by Exelon, PECO’s successor. TMI’s ending finally arrived when TMI-1 was shut down in September 2019.

The story of TMI and its partial meltdown is one that is not only remembered in American history, but also personally to all of Middletown. It was one of the town’s scariest incidents. Though they officially shut down in 2019, the cooling towers will be seen for many years to come, a reminder of our history.

Story prepared by: Alexis Jefferson


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Doukopil, Tony. “Three Mile Island Worker on How He Survived Nuclear …” The Daily Beast, 13 July 2017, Editors. “Three Mile Island.”, A&E Television Networks, 18 Dec. 2009,

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Middletown Area Historical Society. “TMI-2 Accident.” 34th Annual Middletown Colonial Arts & Crafts Fair: Times of Trials in Middletown, Pennsylvania, edited by Middletown Area Historical Society, vol. 34th, Triangle Press, 2009, pp. 25–33.

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