History's A Disaster

Meltdown at Three Mile Island

• Andrew

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A stuck valve. A wall of alarms. A company line that insisted everything was “fine.” We walk through the morning when Three Mile Island went from a routine shutdown to America’s most defining nuclear scare—and why the fallout was as much about trust as technology.


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Special thank you to Lunarfall Audio for producing and doing all the heavy lifting on audio editing since April 13, 2025, the Murder of Christopher Meyer episode https://lunarfallaudio.com/


SPEAKER_00:

On March 28, 1979, a meltdown in the number two reactor at the Three Mile Island Nuclear Generating Station led to the worst nuclear accident to occur in America. While no injuries or deaths would occur from the accident, cover-ups would ensue, and the nation's trust in nuclear power would rapidly diminish. So, what happened? I'm Andrew, and this is History's A Disaster. Tonight we are diving into the radioactive waters around Three Mile Island, near Harrisburg, Pennsylvania, and taking a look into the accident and cover-up surrounding the nuclear power station. And tonight's episode is brought to you by Sensitive Steve's Steam Bats. Now open 24 hours in Pennsylvania, Puerto Rico, and Guam. Three Mile Island Nuclear Generating Station was a pressurized water reactor operated by Metropolitan Edison Company, located on the Susquehanna River in London Berry Township. Construction on the reactor was started in 1968. By 1974, reactor 1 was brought online. Reactor 2 would come online in 1978. The community welcomed the power plant. Nuclear power was new and cheap, and it meant more good-paying jobs in an area that desperately needed it. It was promoted as safe and no one thought of things like radioactivity or any possible downsides. Now, before we get into the accident, we're going to do a real quick idiot's guide to how a nuclear reactor works. The whole process starts in the nuclear reactor core with fuel rods containing uranium oxide pellets. These fuel rods are submerged in water and hit with neutrons. When the neutrons hit the uranium atoms, fission occurs and the atom is split, which creates a lot of heat and more neutrons which go on to strike more atoms, kicking off a chain reaction and generating a shit ton of heat. The heat is then absorbed by the water and in a pressurized water reactor like Three Mile Island, the water is kept under pressure and pumped out of the core through a heat exchanger which superheats a separate water system. This separate system generates pressurized steam which spins a turbine. The rapidly spinning blades of the turbine are connected to a generator which takes the mechanical energy from the turbine and converts it to electricity. After going through the turbine, the steam goes through a condenser where it meets up with cold water, which condenses and cools the steam, turning it back to water and is pumped back to the steam generator to start the process all over again. In a pressurized water reactor, the irradiated water is kept in a closed loop so it never leaves the reactor. Now with that out of the way, shortly after 4 a.m. on March 28, 1979, a water pump failed, causing the turbine and reactor to shut down automatically as it was designed to do. Under normal circumstances, this would have been a routine shutdown requiring minimal intervention. However, the situation rapidly went to shit due to a ton of equipment failures and human errors. The emergency feedwater pumps, which should have been activated to maintain cooling, were isolated due to maintenance work performed two days earlier. Control room operators, unaware of this critical oversight, watched helplessly as pressure began building in the primary cooling system. As pressure mounted, a relief valve opened to vent steam, but then failed to close properly, a malfunction that no one would notice for hours. This stuck valve allowed thousands of gallons of radioactive water to drain from the reactor core, creating a dangerous situation that the plant's designers had never fully anticipated. The control room erupted in confusion and chaos as alarms sounded and indicator lights flashed. Operators trained for routine situations, but unprepared for an emergency of this size made a series of critical errors. Most significantly, they misinterpreted the readings and believed the reactor had too much water when, in reality, it was extremely low. The two indicator lights that showed there was no water running through the system had been missed. One was covered over with an old maintenance tag, and the second one, well, no one knows, or at least no one claims to know, why it was missed. Acting on this false assumption, they reduced the flow of emergency cooling water, inadvertently accelerating the crisis. By 6 a.m., one-third of the reactor core had been uncovered by coolant. Without adequate cooling, the nuclear fuel began to overheat dramatically. Temperatures inside the core soared to over 4,000 degrees Fahrenheit, hot enough to start melting the fuel rods of uranium fuel pellets. This partial meltdown released radioactive gases and created a potentially explosive hydrogen bubble within the reactor vessel. The plant's operators, still struggling to understand the true nature of the emergency, continued to make decisions based on incomplete and misleading information. The control room's instrumentation, designed for normal operations, provided confusing and contradictory readings during the emergency. Critical indicators showed the reactor vessel was full of water when it was actually now half empty, leading operators to believe their actions were appropriate when they were actually fucking it up even more. As the morning went on, radiation levels within the containment building skyrocketed. Radioactive gases began venting from the plant, though, initially in small quantities, the reactor core continued to deteriorate, with fuel pellets melting and forming a molten mass at the bottom of the reactor vessel. For several hours, plant officials feared that this molten fuel might burn through the reactor vessel and containment structure. Meded's initial response was confused, poorly communicated, and they seriously downplayed just how bad things actually were. Company officials, either poorly informed by plant operators or reluctant to acknowledge the scope of the problem, issued reassuring statements to local authorities and the media that proved to be wildly inaccurate. They told the media, it's fine, everything is fine, nothing to see here. At 7 a.m., MedEd notified the Pennsylvania Emergency Management Agency that a quote-unquote unusual event had occurred at 3 Mile Island. An unusual event is the lowest level of nuclear emergency classification, which was a serious understatement. Part of the reactor core had already melted and radioactive materials were being released, but it was just an unusual event. It hasn't blown up yet, so it'll be fine. Local emergency officials, relying on information from MedEd, initially saw no cause for alarm. The company's public relations team, either uninformed about the true situation or deliberately downplaying the crisis, assured reporters that the plant was operating safely and that there was no threat to public health. These early statements would later prove not only false, but dangerously misleading, contributing to public confusion and undermining the trust in both the company and nuclear authorities. Meanwhile, inside the plant, workers were beginning to grasp the true magnitude of the disaster. Radiation monitors throughout the facility showed readings far exceeding normal levels. Plant personnel evacuated non-essential workers from the reactor building, and those who remained worked in rotating shifts to minimize radiation exposure. As the hours passed, it became increasingly clear that MedEd officials were either unaware of the true severity of the accident or were deliberately attempting to minimize its significance. This information management, whether born of ignorance or intent, constituted a cover-up that would have serious consequences for public safety and trust. Company executives, briefed by plant officials who themselves may not have fully understood the situation, continued to issue statements that contradicted the growing evidence of a serious accident. When pressed by reporters about radiation releases, MedEd spokesmen acknowledged only minor, acceptable levels of radioactivity, failing to mention that significant quantities of radioactive gases had been vented from the plant. No one's grown a third arm yet, so obviously there is no need to worry. Company documents later showed that MedEd officials were aware much earlier than they publicly admitted to that substantial fuel damage had occurred. However, this information was not shared with state and federal authorities, hampering emergency response efforts and leaving the locals in the dark about potential risks to their health and safety. The company's reluctance to fully disclose the severity extended to its interactions with the Nuclear Regulatory Commission. NRC officials depended on information provided by MedEd. They initially accepted the company's assessment that the situation was under control. It wasn't until NRC investigators arrived on site and conducted their own analysis that they realized how fucked up things actually were. By the afternoon of March 28th, independent radiation monitoring by state authorities began to paint a different picture than the one presented by MedEd. Pennsylvania's Department of Environmental Resources detected radiation levels significantly higher than those reported by the company, creating the first major discrepancy between official accounts and independent measurements. Dr. Thomas Garuski, director of Pennsylvania's Bureau of Radiation Protection, became increasingly concerned as his team's readings contradicted MedEd's assessments. Garuski's office detected radiation plumes extending several miles from the plant, indicating that more substantial releases had occurred than the company had admitted to. Federal authorities also began to express concern. The NRC, initially believing MedEd's bullshit idea that it was just a minor incident, started sending additional personnel to the site as conflicting reports emerged. NRC officials, trained to be skeptical of utility company assessments during emergencies, began conducting their own independent evaluation of the situation. Media coverage, initially limited and largely based on med-ed press releases, began to intensify as reporters recognized inconsistencies in the official account. Television news crews arrived at the plant, broadcasting images of the facility and interviewing local residents who were beginning to express concerns about their safety. The visual impact of the cooling towers, surrounded by steam and emergency vehicles, painted a completely different picture from what MedEd was saying. Local residents, many of which lived within sight of the plant's cooling towers, started questioning the official accounts as emergency vehicles multiplied around the facility and rumors of evacuated plant workers spread throughout the town. Phone calls to state authorities increased dramatically, with citizens demanding answers about radiation levels and potential health risks. On March 30th, two days after the initial accident, the crisis took on a new and potentially catastrophic dimension with the discovery of a large hydrogen bubble inside the reactor vessel. This changed the situation from extremely serious into what could be considered an uncontrolled disaster. Hydrogen gas had been generated during the accident when superheated steam reacted with the zirconium cladding of the fuel rods, a process that occurs at extremely high temperatures. This hydrogen had gathered in the upper portion of the reactor vessel, creating a bubble that posed multiple dangers. If the hydrogen concentration reached critical levels and encountered an ignition source, it could explode with enough force to breach the reactor vessel and potentially contaminate the structure itself. The discovery of the hydrogen bubble marked a turning point in both the technical management of the accident and its public perception. NRC officials, now fully engaged in managing the crisis, struggled to determine whether the bubble posed an immediate explosion risk? Initial calculations suggested that the hydrogen concentration might be approaching dangerous levels, leading to urgent discussions about worst-case scenarios. Dr. Harold Denton, the NRC's Director of Nuclear Reactor Regulations, was sent to Three Mile Island to take direct control of the federal response. With Denton there, MedEgg could no longer try to control the narrative. More accurate information about the true nature of the emergency was being directly released to the media. And the hydrogen bubble crisis continued to ramp things up. It needed to be taken care of as quickly as possible. Engineers worked frantically to develop methods for safely removing the hydrogen without triggering an explosion. Various options were considered, including venting the gas to the atmosphere, which would release additional radiation, or attempting to consume the hydrogen through controlled reactions. Each choice was incredibly dangerous, but they were quickly running out of time. The morning of March 30th, Pennsylvania Governor Richard Thurnberg recommended the evacuation of pregnant women and preschool children within a 5-mile radius of the plant. This advisory carefully worded to avoid panic while acknowledging the danger, affecting roughly 3,400 people in the area surrounding 3 Mile Island. The governor's recommendation represented the first official acknowledgement that the accident posed a genuine threat to public health. Schools within the evacuation zone closed, and many families with young children left the area voluntarily. Hotels and motels throughout central Pennsylvania filled up quickly with evacuees. The impact of this recommendation extended far beyond the 3,400 people which were directly affected, as locals throughout the area questioned their own safety. Dornberg's decision was made more difficult by the absence of clear federal guidelines for nuclear emergencies. Unlike natural disasters for which established evacuation procedures existed, nuclear accidents presented unique challenges that emergency management systems were not designed to handle. The governor was in essence forced to make shit up as he went along. Despite Governor Thurnberg's limited evacuation recommendation, a much larger exodus began as news of the hydrogen bubble spread. Over 144,000 people, nearly 40% of the population within a 15-mile radius of the plant, left the area, creating one of the largest peacetime evacuations in American history. Distrust of official statements after days of contradictory information, fear of invisible radiation, and graphic media coverage that emphasized worst-case scenarios led to the mass evacuation. Television reports showed families loading their shit into cars and fleeing the area. Images that reinforced the sense of impending disaster and encouraged others to leave. Highways leading away from Three Mile Island became backed up with people fleeing. No one knew where to go or when they'd be able to come back. Their fear was pushing them to get out and get out now. Gas stations reported long lines and fuel shortages as residents filled their tanks for uncertain journeys. Hotels throughout Pennsylvania, New York, and neighboring states experienced unprecedented demand as Three Mile Island evacuees sought temporary shelter. Businesses within the affected area closed or operated with skeleton crews. While schools throughout the region shut down as teachers and students left the area, farmers worried about radiation contamination of crops and livestock while also having to deal with labor shortages caused by worker evacuations. Local hospitals, already stretched in by staff departures, prepared for potential wounded while also trying to figure out how to treat radiation exposure, something which most hospitals were unprepared for. Medical personnel worked to obtain potassium iodide tablets, which could help protect against thyroid cancer caused by radioactive iodine exposure. Supplies of this were limited and distribution plans were quickly thrown together. As the crisis continued, federal authorities launched an investigation into both the causes of the accident and MetEd's handling of the emergency. The NRC, the EPA, and Department of Health and Human Services sent out experts to assess the situation and prepare for potential long-term health and environmental consequences. NRC investigators, led by Harold Denton, began conducting detailed analysis of the accident while also working to stabilize the reactor. Their preliminary findings painted a disturbing picture of multiple system failures, inadequate operator training, and design deficiencies that had contributed to the severity of the accident. The investigation revealed that the accident was not the result of a single catastrophic failure, but rather a shitload of smaller problems that overwhelmed the plant safety systems and the ability of the operators to respond effectively. Critical safety equipment had been unavailable due to maintenance. Instruments provided misleading information during the emergency, and operators lacked training for the type of complex accident they faced. Federal health officials began monitoring radiation exposure levels among plant workers and nearby residents. While initial assessments suggested that radiation releases had been relatively limited, the long-term health implications remained uncertain. The absence of comprehensive radiation monitoring systems in the area hampered efforts to accurately assess exposure levels and potential health risks. Environmental monitoring expanded to include air, water, soil, and food samples from throughout the region. Agricultural products, particularly milk from dairy cows that might have consumed contaminated grass, received special attention. These monitoring efforts would continue for years following the accident, creating a database of environmental impact that would help with future nuclear safety regulations. As investigators gained access to plant records and began interviewing personnel, a more complete picture of the accident emerged. The investigation revealed not just technical failures but also problems with emergency procedures, communication protocol, and corporate oversight. Investigators discovered that critical safety information that had not been communicated up the chain of command within MedEd, plant operators struggling with an unheard of emergency had not clearly conveyed the severity of the situation to company executives, who in turn had provided an overly optimistic view to government officials and the public. The investigation also showed that similar incidents at other nuclear facilities had not been adequately analyzed or communicated to the industry. A nearly identical accident had occurred 18 months earlier at the Davis Best Nuclear Power Station in Ohio, but that information had not been shared to anyone at Three Mile Island. Shitty training became apparent as investigators interviewed workers at the reactor. Operators had been trained primarily for basic routine operations and simple emergencies, but not for anything too complex. It's a nuclear reactor, after all. What could possibly go wrong? Simulator training, which might have helped prepare for more adverse conditions, was seriously lacking. The investigation into MetEd's handling of the accident showed they were more concerned with public relations and not so much concerned about public safety. Internal company documents obtained through federal subpoenas showed that executives were aware of the accident's severity earlier than they claimed to. Company officials had received detailed briefings about core damage and radiation releases hours before acknowledging these facts to government authorities. This delay in accurate reporting not only slowed down emergency response efforts, but also violated federal regulations. Criminal investigations were initiated to determine whether company officials had violated federal laws by providing false information to government authorities or failing to report required safety information. In 1983, Meded would end up being indicted on 11 counts of falsifying safety test results prior to the accident. They would end up pleading guilty and having to pay out an$11 million settlement along with a$45,000 fine. In the wake of the accident, President Jimmy Carter appointed a special commission led by Dartmouth College President Josh Kemene to conduct a comprehensive investigation of the Three Mile Island accident. The Kemene Commission was the most thorough examination of a nuclear accident in American history. The investigation went beyond the technical aspects of the accident to examine the broader institutional failures that had contributed to the crisis. Over six months, hundreds of witnesses were interviewed, thousands of documents reviewed, and detailed analysis of everything from reactor design to emergency communications were conducted. And their findings were not good. The report concluded that the accident was preventable and resulted from a combination of human error, equipment failure, and institutional inadequacies. More significantly, the commission found that the nuclear industry and its regulators had become complacent about safety, relying too heavily on engineered safety systems while neglecting human factors and emergency preparedness. The Commission identified fundamental problems with the regulatory approach to nuclear safety. The NRC, the report found, had focused too narrowly on technical compliance with regulations while failing to ensure that utilities were actually prepared to operate nuclear facilities safely. The regulatory system had become bureaucratic and inflexible, unable to adapt quickly to new safety information or changing circumstances. The commission called for major changes in reactor design, operator training, emergency preparedness, and regulatory oversight. The report emphasized that nuclear safety required a comprehensive approach that addressed not just technical systems, but also human factors, organizational culture, and emergency response capabilities. These recommendations would lead to a massive overhaul of nuclear regulation. The NRC underwent major reorganization with new emphasis on safety culture, the emergency preparedness and human factor in nuclear plant design and operations. New regulations required enhanced operator training, including more extensive simulator-based education that exposed personnel to complex accident scenarios. Control room design standards were revised to improve the presentation of critical safety information and reduce the potential for operator confusion during emergencies. Emergency planning requirements were substantially strengthened. Nuclear utility companies were required to develop detailed evacuation plans in coordination with local authorities, and regular emergency exercises became mandatory. FEMA was given expanded responsibilities for coordinated nuclear emergency response. The regulatory approach to nuclear safety shifted. Companies were now required to demonstrate not just that their equipment met technical specifications, but that their organizations were capable of safely operating nuclear facilities under both normal and emergency conditions. The Unit 2 reactor, damaged beyond repair, was permanently shut down. The nuclear industry as a whole faced immediate financial impacts as orders for new plants were cancelled or delayed. Public opposition to nuclear power, already growing before the accident, intensified dramatically. Utility companies reconsidered their nuclear expansion plans, leading to the cancellation of dozens of planned reactors. Construction costs for nuclear plants increased significantly as new safety requirements were implemented. Enhanced training programs, improved control room designs, and strengthened emergency preparedness systems all added to the expense of nuclear power development. These costs, combined with growing public acquisition, made nuclear power less economically attractive compared to alternative energy sources. The cleanup of Three Mile Island's damaged Unit 2 reactor became one of the most complex and expensive decontamination projects in industrial history. The process, which would take nearly 12 years and cost over$1 billion, presented technical challenges and raised difficult questions about nuclear waste management. They had to first remove the radioactive water that had gathered in the reactor building. There was over 700,000 gallons of contaminated water that had to be processed to remove radioactive waste before it could be safely disposed of. This process would require the development of new filtration and decontamination technologies. Even worse than this was removing the damaged fuel rods. The partial meltdown had created a mix of melted fuel, structural materials, and debris that had never been encountered before. They had to make special tools and techniques to safely remove this highly radioactive material without exposing workers to dangerous radiation levels. The cleanup process proved invaluable in providing insights into accident recovery procedures that helped emergency planning at other nuclear facilities. Techniques developed for remote handling of radioactive materials, decontamination of contaminated surfaces, and protection of cleanup workers became standard practice for nuclear maintenance operations. Environmental monitoring continued throughout the cleanup process with regular testing of air, water, and soil samples to ensure that radioactive materials were not being released into the air. These monitoring programs provided extensive data on the environmental fate of radioactive materials released during a nuclear accident. While immediate radiation releases were determined to be minor, concerns about potential cancer. Cancer risk and other health effects persisted among residents. Multiple studies were conducted to check the health of people living near Thirma Island. These studies were ran by both federal, state, and independent researchers and continued on for decades afterwards, attempting to identify any excess cancer rates or other health problems that might be attributed to the radiation exposure, while radiation exposure was relatively low, making it difficult to detect health effects above background levels. Initial studies suggested that radiation exposures were below levels typically associated with increased cancer risk, but these findings were met with skepticism by the locals. Some of them reported increased rates of cancer and other health problems. Trying to figure out whether or not it was caused by the accident or not proved to be pretty challenging. This uncertainty would become a source of controversy among the residents. They felt that the government and industry assurances about safety were not credible given the pattern of lies during the accident. They refused to be fooled again. They took a fool me once type attitude. Because of all these concerns and the growing opposition to nuclear power, it would put a stop to the rapid nuclear power expansions. No new nuclear plants were ordered in the United States for more than 30 years, and many existing orders for plants were canceled. The combination of increased safety requirements, public opposition, and economic uncertainty made nuclear power development politically and financially difficult. This, despite the accident leading to improvements in nuclear safety that made existing plants safer and more reliable. And that was the nuclear accident at Three Mile Island. Thanks for listening, and if you liked the show, please consider leaving a rating or review on your Apple Choice. And you can reach out to the show at history as a disaster at gmail.com with questions, comments, or suggestions. As well as following the show on social media like Facebook, Instagram, a few others, TikTok, YouTube, whatever. And share the episode. Your friends will love it. Take care of yourself out there. Chase that dream. Live for today, because tomorrow is never guaranteed. Thanks and goodbye.