The Three Mile Island Nuclear Reactor Disaster

What went wrong - and how much worse it could have been

Research Paper (undergraduate), 2018
12 Pages, Grade: 4.0 (=1 in den USA)

Free online reading



The Setting

Disaster Unfolds


Relief and First Response Efforts

Aftermath and Investigation into the Disaster

Lessons Learned and Policy Impact

Implications for Modern Emergency Management




Three Mile Island was the worst commercial nuclear accident at the time although no deaths happened as a result of the partial nuclear meltdown. The event, which happened in Londonderry Township, Pennsylvania, did raise awareness to the potential of a commercial nuclear disaster and to the possibility of many deaths from a possible explosion, fallout, and secondary radiation in later years. Because of the almost major disaster at Three Mile Island, laws and regulations have been passed to ensure that an accident does not happen and threaten the lives of thousands of Americans.

The potential for nuclear disaster had previously been established with a lesser known incident, SL-1, with an Army reactor that had a meltdown killing all three personnel on site actually pinning one of the personnel to the ceiling of the building with one the control rods. The small reactor had a devastating effect. Much larger nuclear reactors, like Three Mile Island, pose an even greater threat to society which was proven just seven years later when Chernobyl had a meltdown. The effects of Chernobyl are still being felt today which is 32 years later at the time of this analysis.

Fortunately for Three Mile Island and the future of Nuclear Power on American Soil, the disaster did not kill anyone initially, and the radioactivity that was released did not rise above normal radiation levels to cause radiation sickness, cancer, or death in years to come.


Three Mile Island is located in Londonderry, PA just south of Hattiesburg on an island in the Susquehanna River according to Google Maps. The position of the nuclear power plant is crucial because it uses the cool water of the river to help cool the plant. The plant’s positioning is followed by many when deciding where to build a nuclear power plant.

The plant consisted of two pressurized water reactors. One was a TMI-1 (Three Mile Island-1) with 800 MWe and entered service in 1974 while the other, TMI-2, was relatively new with 906 MWe (WNA, 2012). TMI-1 was built in 1974 and is one of the best performing reactors to this day, and TMI-2 was built in February of 1978 and began operation in December of the same year (WNA, 2012).

Just after operation of TMI-2, a movie called "The China Syndrome" released in theaters on March 16th of 1979. The movie dealt with a fictional nuclear reactor meltdown in Los Angeles and is classified as a drama/mystery and suspense (Rotten Tomatoes, n.d.). According to the History Channel, experts at the time of the release called nuclear reactor disasters a "black swan" event saying they were almost impossible (, 2008).

The Setting

Built in 1979 and operationalized in the same year, TMI-2 was fully operational at the time of the accident. Although it was not the first of nuclear reactor, it was one of the many that spawned in just a few years. "The size of nuclear plants increased so rapidly in the early 1970s that designers and operators outran their experience base" (Gilinsky, 1980, p. 19).

The plant was operating appropriately at the time of the accident. A stuck pilot relief valve was what caused the issue along with the subsequent steps followed by the personnel. Even though they followed protocol as to how they were trained and did what they believe to be correct, the steps caused further damage.

Disaster Unfolds

On March 28, 1979, it was just another typical morning. At 4 am, there was a minor incident with the secondary cooling circuit of TMI-2 which caused the plant to shut down immediately as designed (WNA, 2012). At this point even though the shutdown was unexpected, the plant reacted as planned and shut down accordingly. The problems began at this point. The pilot operated relief valve (PORV) opened for ten seconds as designed but failed to close (USNRC, 2014).

All the instrumentation available to the workers indicated that the relief valve had been closed and required no further action. The truth of the matter was that the valve was stuck open spewing coolant water and steam into the primary building. Reactors produce extreme heat thus requiring to be covered by coolant water. Since coolant water was escaping by way of the relief valve, the reactor was beginning to be uncovered. The operators did not have instrumentation to determine the level of coverage by coolant water, so they assumed that as long as pressure remained high that the reactor was covered (USNRC, 2014). Operators then shut off emergency coolant pumps because the pressure was increasing and in doing so, caused the reactor to be starved up necessary coolant water.

Once the operators realized what was happening inside the Primary Reactor Building, they began to operate correctly. They finally got coolant water back on the reactor and began to slowly cool the core (WNA, 2012). The operators then began to direct the steam through series of pipes to a decay tank, but some of the radioactivity escaped and was filtered through high-efficiency particulate air (HEPA) filters which removed everything but noble gases (WNA, 2012). These noble gases by nature are inert and pose no detrimental effects to humans.


Although TMI was the greatest nuclear disaster on American soil, no one died. No one got radiation sickness. No one developed cancer as a result of exposure. The reason it is considered the greatest nuclear disaster on American soil is because it opened the door to the POSSIBILITY of a full blown nuclear disaster with nuclear fallout.

One major impact that the TMI disaster did have is that is halted nuclear plant building for about thirty years (Amadeo, 2017). No nuclear plants started after 1974 were completed (, 2008). Support for nuclear energy fell from 69% to 46% in just two years from 1977 to 1979. (, 2008).

The disaster brought into focus long ignored reactor safety problems because machines and men failed, and regulatory review of the reactor was not controlled (Gilinsky, 1980). Gilinsky (1980) also noted that "control room instruments were inadequate. Operators made mistakes. Meters to measure the radioactivity leaving the reactor went off scale. Communications links failed to function, in part because phones where jammed, in part because individuals did not seem to understand what they were supposed to report" (p. 20).

At the time of the disaster, the Cold War was underway. Because of the arms race that was transpiring, anti-nuclear groups were forming that opposed the route that the United States was taking and also with the speed at which technology progressing as far as nuclear is concerned. The disaster at Three Mile Island only fueled these types of groups with one protest garnering 200,000 people is opposition of nuclear power (, 2008).

Containing the Disaster

The cleanup effort lasted 14 years and cost an estimated 1 billion dollars. The damaged reactor was permanently closed and entombed in concrete after the accident. Radioactive fuel and water were removed, and workers eventually shipped 15 tons of radioactive waste to a nuclear waste storage facility in Idaho (, 2008).

According to the United States Nuclear Regulatory Commission, “the TMI-2 reactor is permanently shut down and all its fuel had been removed. The reactor coolant system is fully drained and the radioactive water decontaminated and evaporated. The accident's radioactive waste was shipped off-site to an appropriate disposal area, and the reactor fuel and core debris was shipped to the Department of Energy's Idaho National Laboratory” (USNRC, 2014).

Relief and First Response Efforts

The disaster is a unique one because no died from it, and no health effects were discovered in the multiple studies that were conducted after. First responders did show up such as police, but they were mainly used to keep reporters at bay.

Aftermath and Investigation into the Disaster

President Jimmy Carter created a commission to investigate Three Mile Island and to determine what happened, why it happened, and where to go from here. The President's Commission on the accident at Three Mile Island found many discrepancies and regulations that were questionable at best. The commission released the report after a six-month investigation in to Three Mile Island (TMI) and started with disclaimer: "We do not claim that our proposed recommendations are sufficient to assure the safety of nuclear power" (President's Commission, 1979). Commission personnel found that the "fundamental problems are people-related problems and not equipment problems"

Gilinsky (1980) stated that "reactor systems that were not reviewed will be reviewed. New control room instruments are being required" and also that stricter "operator training and qualification is underway" (p. 20). He also mentions instruments should accurately measure radiation levels outside of facility and emergency planning should required within a certain distance of the facility (Gilinsky, 1980).

Lessons Learned and Policy Impact

Communication is key in any disaster and the same applies here. Whether the communication is from people or indicators from machinery, understanding what is going on is crucial when a disaster is unfolding. The operators also failed to report as they should have once they realized something was amiss. Although the disaster was contained, the results could have been much worse with their failure to report. Proper communication is key in a disaster. News networks will run with anything they believe or think to be correct, so agencies need to communicate proper and correct details of an event to widespread panic.

We also learned that machinery can fail which can cause disasters of untold power. Backup machinery and gages should be installed to provided adequate readings in case something does fail. Since this happened because of a pilot valve malfunction and subsequent improper readings, there should be secondary gear to prevent such an event from occurring or at least provide accurate readings of what is happening inside the nuclear power plant.

The subsequent events after the opening of the pilot valve by the operators was not done in malice or out of being uneducated. They did as they were trained to do. Because of this, extensive training was established to provide operators with possible accident scenarios, so they would know how to respond to an event to prevent another Three Mile Island.

Control rooms were revamped to provide more adequate controls and readings which allows operators to have more control and a better understand of what is happening inside the concrete walls of the plant.

Because of the event of Three Mile Island, sweeping policy changes took effect. These effects now have dropped significant reactor events to an average of almost zero and radiation of operators has steadily decreased since 1985 (Dalton, 2009).

Implications for Modern Emergency Management

Radiation is different than a fire, flood, tornado, or hurricane because it can not be seen. It can only be detected through special equipment. It is also depending on the type of radiation very devastating to the body. The effects that radiation has on the body depends on the type and the amount. Here is a chart from the Mayo Clinic that provides some brief details:

illustration not visible in this excerpt

(Mayo Clinic Staff, 2015)

With the wide range of side effects, triage will have to be set up to see who is the most afflicted and to get them help.

As with any disaster, they are not planned for and can happen at any time. With this disaster, it took some time to unfold and luckily the reactor did not suffer more damage that what it did and possibly cause more radioactive exposure with higher intensity. Emergency managers that have a nuclear reactor in their area should prepare for a disaster regardless of how far technology has come to prevent them.

Emergency managers should also have in place emergency routes to escape the area in case there is a disaster at a nuclear facility. This will lessen the cluster of people trying to leave blocking highways.

Also, with the escape route in mind, the emergency manager needs to have multiple escape routes. The reason being for this is because wind plays a crucial role in which way the nuclear fallout will go and how far it will make it. Depending on the damage of the reactor, release of radioactive material, and which way the wind is blowing, it will determine how far people need to go in order to avoid the nuclear fallout from the reactor as well as which direction.

Following up on the last point, communication will be crucial. News outlets need to be aware of the problem immediately, so they can get the word out to the public to help them understand the severity of the situation. Weather experts need to be contacted to see what the weather will be doing to determine the wind pattern and radioactivity travels. Multiple cities that surround the reactor may need to be advised to be prepared to evacuate.

illustration not visible in this excerpt

Image 1.2 Evacuation Routes for Three Mile Island Area


Victor Gilinsky said it best "Can we live with nuclear power? The answer is... yes. But only if we are willing to pay the price of living with dangerous high technologies. That price is extraordinary car, discipline, and superior craftsmanship" (Gilinsky, 1980, p. 20). Although the disaster was the greatest in American Nuclear history, it is ironic that there were no deaths or associated medical issues from the event given the title. The event happened due to mechanical failure but was exaggerated by the events that followed by the personnel on sight. Due to lack of proper training and evaluation as well as proper mechanical signals, the disaster unfolded and put a halt on nuclear production for a few decades. The event also changed the hearts and minds of the population on their view of nuclear power and the country’s need for it.

Even though Three Mile Island was a major disaster for the United States, it compares very little to major disasters such Chernobyl or Fukushima. Those disasters claimed lives and caused massive damage. Chernobyl is still uninhabited and poses a significant radiological affect. Concrete barriers were erected to seal the reactor that is still highly radioactive. Disasters of this nature can be man-made or natural. Chernobyl was a man-made disaster, whereas Fukushima was the result of was the secondary result of a tsunami. Anywhere there is a nuclear reactor, there is a threat of a nuclear disaster just lurking below the surface.


Gilinsky, V. (1980). The Impact of Three Mile Island. Bulletin of Atomic Scientists, 36(1), 18-20 (2008). Three Mile Island. Retrieved from

Janson, Donald (1979 March 29). Radiation is released in accident at Nuclear Plant in Pennsylvania. The New York Times. Retrieved from

Lanouette, William J. (1980). The Kemeny Commission Report. Bulletin of Atomic Scientists, 36(1), 20-24

President's Commission. (1979). The Accident at Three Mile Island. Washinton: U.S. Government.

Rotten Tomatoes. (n.d.). The China Syndrome. Retrieved from Rotten Tomatoes:

Slagle, Alton. (1979 March 29). Three Mile Island nuclear plant has partial meltdown in 1979. New York Daily News. Retrieved from

The Accident at Three Mile Island. (1980). Bulletin of Atomic Scientists, 36(1), 24-31

United States Nuclear Regulatory Commission. (2014). Backgrounder on the Three Mile Island accident. Retrieved from

World Nuclear Association. (2012). Three Mile Island accident. Retrieved from

12 of 12 pages


The Three Mile Island Nuclear Reactor Disaster
What went wrong - and how much worse it could have been
The University of Southern Mississippi
CJ 610
4.0 (=1 in den USA)
Catalog Number
ISBN (Book)
File size
1448 KB
three, mile, island, disaster
Quote paper
Wesley Hendrix (Author), 2018, The Three Mile Island Nuclear Reactor Disaster, Munich, GRIN Verlag,


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